To promote high-speed boundary layer transition,this paper proposes an active self-sustaining dual jets(SDJ)actuator utilizing the energy of supersonic mainflow.Employing the nanoparticle-based planar laser scattering...To promote high-speed boundary layer transition,this paper proposes an active self-sustaining dual jets(SDJ)actuator utilizing the energy of supersonic mainflow.Employing the nanoparticle-based planar laser scattering(NPLS),supersonic flat-plate boundary layer transition induced by SDJ is experimentally investigated in an Ma-2.95 low-turbulence wind tunnel.Streamwise and spanwise NPLS images are obtained to analyze fine flow structures of the whole transition process.The results reveal the transition control mechanisms that on the one hand,the jet-induced shear layer produces unstable Kelvin–Helmholtz instabilities in the wake flow,on the other hand,the jets also generates an adverse pressure gradient in the boundary layer and induce unstable streak structures,which gradually break down into turbulence downstream.The paper provides a new method for transition control of high-speed boundary layer,and have prospect both in theory and engineering application.展开更多
The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a...The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.展开更多
Large Eddy Simulation(LES)is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators(PSJAs)on a hemisphere in supersonic inflow,and analyze the effect of e...Large Eddy Simulation(LES)is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators(PSJAs)on a hemisphere in supersonic inflow,and analyze the effect of energy allocation and array angle on the drag reduction performance of opposing Plasma Synthetic Jet(PSJ)in this paper.Numerical simulation results have been compared with experimental data,confirming the validity of the simulation method.The results show that different energy allocations have a significant effect on the drag of the hemisphere.However,the effect of the change in array angle on the drag of the hemisphere is not as noticeable as the effect caused by energy allocation.Interference regions between the two PSJAs occur,which undermine the effectiveness of drag reduction.High Turbulent Kinetic Energy(TKE)regions primarily concentrate on the core region of the jet and downstream of the bow shock.The influence of the array angle on TKE is most evident in the downstream region of the exits of the PSJs on both sides.Temporal evolution of the coherent structures reveals that as the PSJ intensity decreases,the largescale vortices progressively break up into smaller-scale vortices,and energy is also transferred from large-scale structures to small-scale structures.展开更多
To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actua...To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders.Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated.Then,flight tests were carried out to verify the control abilities,providing a novel technology for the design of a future rudderless FWA.Results show that synthetic jets could narrow the dead zone area,improve the flow velocity near the trailing edge,and then move the trailing-edge separation point and the leading-edge stagnation point downwards,which make the effective Attack of Angle(AOA)increase,thereby enhancing the pressure envelope area.Circulation control based on synthetic jets could improve the lift,drag and nose-down moment.The variations of lift and nosedown moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency.Finally,synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA,which could realize the roll and pitch control without deflections of rudders during the cruise stage,and the maximum roll and pitch angular velocity are 12.64(°)/s and 8.51(°)/s,respectively.展开更多
To effectively reduce the loss of strong shock wave at the trailing edge of the supersonic cascade under high backpressure,a shock wave control method based on self-sustaining synthetic jet was proposed.The self-susta...To effectively reduce the loss of strong shock wave at the trailing edge of the supersonic cascade under high backpressure,a shock wave control method based on self-sustaining synthetic jet was proposed.The self-sustaining synthetic jet was applied on the pressure side of the blade with the blow slot and the bleed slot arranged upstream and downstream of the trailing-edge shock,respectively.The flow control mechanism and effects of parameters were investigated by numerical simulation.The results show that the self-sustaining synthetic jet forms an oblique shock wave in the cascade passage which slows down and pressurizes the airflow,and the expansion wave downstream of the blow slot weakens the shock strength which can effectively change the Mach reflection to regular reflection and thus weaken the shock loss.And the suction effect can reduce loss near blade surface.Compared with the baseline cascade,the self-sustaining jet actuator can reduce flow losses by 6.73%with proper location design and vibration of diaphragm.展开更多
For achieving the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a novel yaw effector based on Reverse Dual Synthetic Jets(RDSJ)was proposed without the movement of rudders.Eff...For achieving the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a novel yaw effector based on Reverse Dual Synthetic Jets(RDSJ)was proposed without the movement of rudders.Effects on aerodynamic characteristics of a small-sweep FWA and control mechanism were investigated by numerical simulations.Finally,reverse dual synthetic jet actuators were integrated into a real FWA and flight tests were firstly carried out.Numerical results show that RDSJ could make drag coefficient increase and weaken lift coefficient,which generate a yawing moment and a rolling moment in the same direction,realizing control of heading attitudes,but strong coupling with the pitching moment occurs at large angles of attack.For control mechanism,RDSJ could produce two reverse synthetic jets out of phases,improve the reverse pressure gradient and hence form alternate recirculation zones or even early large-area separation,which cause the rise of pressures before exits and the dip of pressures behind exits,achieving improvement of drag and the yawing moment.The results of flight tests support that RDSJ could realize control of heading attitudes without deflections of rudders during the cruise stage and achieve the maximal yaw angular velocity of 10.12(°)/s,verifying the feasibility of this novel yaw effector.展开更多
Turbulence drag reduction is of great significance for the range increase of hypersonic flight vehicles.The proposed velocity-temperature coupling control method(Liu et al,Phys Rev Fluids 6:044603,2021)is further exte...Turbulence drag reduction is of great significance for the range increase of hypersonic flight vehicles.The proposed velocity-temperature coupling control method(Liu et al,Phys Rev Fluids 6:044603,2021)is further extended to the hypersonic turbulent boundary layer.Direct numerical simulation results of four comparative cases show that the heated wall blowing achieves a drag reduction rate of 10.58%,which is about the sum of wall blowing(5.27%)and wall heating(6.35%).By evaluating the control efficiency,however,it is found that heated wall blowing is not as good as wall blowing and cannot obtain net energy saving rate.The modified FIK decompositions of skin friction coefficient indicate that the cliffy decrease of the mean convection term is the primary contribution for the drag reduction.Effects of the proposed control measure on turbu-lence statistics and coherent structures are also analyzed.Streamwise vortex is found to be away from the wall,thus leading to a lower friction drag.展开更多
Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-mo...Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a twoelectrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial,the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.展开更多
In order to improve the control ability of synthetic jets in compressible boundary layer,a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was pro...In order to improve the control ability of synthetic jets in compressible boundary layer,a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was proposed.As fundamental investigations on the effects of synthetic jet temperature on the jet behavior and flow field characteristics were essentially necessary,preliminary numerical simulations were conducted to study the influence of temperature(200 K and 400 K)on the flow field characteristics of synthetic jets using Large Eddy Simulations(LES)model.Time-averaged flow fields showed that different temperatures led to variable behavior of two strands of jets.For dual synthetic cold jets,a potential-core arose apparently with its height ranging from 0.01 to 0.03 m,while for dual synthetic hot jets,two strands of jets emerged downstream.The modal decomposition of instantaneous flow fields had been done using both Proper Orthogonal Decomposition(POD)and Dynamic Mode Decomposition(DMD).Various modes showed different characteristics of the flow fields.As the POD method focuses on the energy of flow while the DMD method focuses on the frequency,the first two modes had many similarities,but the third and fourth modes demonstrated completely different vortex structures.The current researches play a role of preliminary investigations for further and comprehensive exploration of novel flow control measures in global velocity field.展开更多
The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability o...The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability of DSJA to control the attitudes of UAV during cruising.DSJA is improved into an actuator with two diaphragms and three cavities,which has higher energy levels.Actuators,differentially distributed on both sides of the wings,are installed on the trailing edge close to the wing tips.Flight tests,containing Differential Circulation Control(DCC)using double-side actuators,Positive Circulation Control(PCC)using left-side actuators and Negative Circulation Control(NCC)using right-side actuators,are implemented at cruising speed of 25 m/s.Results show that roll attitude control without rudders could be realized by DSJAs.DCC and NCC can generate the rightward roll and yaw angular velocity,prompting UAV to turn right.The stronger controlling ability can be achieved by DCC,with the maximum roll angular velocity of 15.62(°)/s.PCC can generate a rightward roll moment,but a leftward yaw moment will be produced at the same time.Leftward yaw induces the leftward rolling moment,which weakens the roll control effect,making UAV keep to yaw to the left with a small slope.展开更多
Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet(PSJ)for drag reduction for a hemisphere.Firstly,flow field changes of opposing PSJ are analyzed by comparin...Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet(PSJ)for drag reduction for a hemisphere.Firstly,flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3.As PSJ is a kind of unsteady pulsed jet,the shock standoff distance increases initially and then decreases under the control of PSJ,which corresponds to the change of the strength of PSJ.Accordingly,the amount of drag reduction of the hemisphere increases initially and then decreases.It is found that there is a short period of“drag rise”during the formation of PSJ before the drag reduction,which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator(PSJA).Secondly,the effects of five parameters,including exit diameter,discharge energy of PSJA,Mach number,static pressure of incoming flow and angle of attack,on drag reduction of opposing PSJ were studied in detail by using numerical method.It is found that the Maximum Pressure Ratio(MPR)has a significant impact on the average drag reduction for a configuration-determined PSJA.For the configuration selected in this study,the flow field of opposing PSJ shows typical Short Penetration Mode(SPM)in a control cycle of PSJ when the MPR is less than 0.89.However,the flow field shows typical Long Penetration Mode(LPM)at some time when the MPR is bigger than 0.89.Relatively better drag reduction is achieved in this case.展开更多
Aircraft icing has long been a plague to aviation for its serious threat to flight safety.Recently,researches about a newly proposed deicing method based on Plasma Synthetic Jet Actuator(PSJA)have just started.To meet...Aircraft icing has long been a plague to aviation for its serious threat to flight safety.Recently,researches about a newly proposed deicing method based on Plasma Synthetic Jet Actuator(PSJA)have just started.To meet the requirements of in-flight deicing,structure of PSJA needs to be adjusted.This paper completed the detailed design and experimental validation of a novel plasma striker,which was a modified version of PSJA.Influences of mass of the moving part and rod shapes on the ice-breaking performances were also studied.Besides,a“conical-nosed rod configuration”was proposed.Its purpose was to ensure a good ice-breaking performance of the plasma striker on long ice,by generating a splitting failure.Results show that,though mass of the moving part was just several grams,ice-breaking performance was better when the mass was lighter.The rectangular rod could generate an elliptical circumferential crack,whose major axis was parallel to the direction of the long side of the rectangular rod.And the“conical-nosed rod”concept was verified to be able to generate a splitting crack which can spread completely to the far end of long ice,and the crack direction was parallel to edge line of the cone.In general,the plasma striker has the advantages of simple structure,low energy consumption,little harm to the flow field and the aircraft skin.Simulations will be carried out in future works to study in detail the working process of the plasma striker.展开更多
For lessening the weight and volume of flow control system,enlarging the circulation control applying area of angle of attack(AOA),and achieving nice controlling characteristics,a novel lift enhancement method based o...For lessening the weight and volume of flow control system,enlarging the circulation control applying area of angle of attack(AOA),and achieving nice controlling characteristics,a novel lift enhancement method based on dual synthetic jet actuators(DSJAs)and synthetic jet actuator(SJA),and an adaptive proportional integral and differential(PID)algorithm based on radial basis function neural network are introduced.DSJAs are uniformly located along the chord to suppress the separation and trailing-edge SJA is applied to achieve the high circulation.Velocities of actuators are modulated to realize the real speed profile and on–off controlling laws of DSJAs are designed.Numerical simulations show that DSJAs and SJA could suppress the separation completely and move leading-edge stagnation point and trailing-edge separation point downstream even at AOA of 19°,hence achieve the highest lift and nose-down moment augmentation(ΔCl_(max)=0.92,ΔCm_(max)=0.02534),andΔL/D can reach 11.39 at AOA of 18°.Stalling is delayed to more than 19°.Linear lift area and pitch-break angle are both increased to 16°.ΔCl/C_(μ) can reach 76.7,indicating the greatest control efficiency.The results of adaptive PID control,whose controlling effects are proved better than PID,indicate that lift could track the objective with the rise time of 0.0325 s and finally keep steady,suggesting the nice stability and rapidness.展开更多
The excellent vectoring characteristic of Dual Synthetic Jet(DSJ)provides a new control strategy for the active flow control,such as thrust vectoring control,large area cooling,separated flow control and so on.For inc...The excellent vectoring characteristic of Dual Synthetic Jet(DSJ)provides a new control strategy for the active flow control,such as thrust vectoring control,large area cooling,separated flow control and so on.For incompressible flow,the influence relation of source variables,such as structure parameters of actuators,driving parameters and material attributes of piezoelectric vibrating diaphragm,on the vectoring DSJ and a theoretical model are established based on theoretical and regression analysis,which are all verified by numerical simulations.The two synthetic jets can be deemed as a main flow with a higher jet velocity and a disturbing flow with a lower jet velocity.The results indicate that the influence factors contain the low-pressure area formed at the exit of the disturbing flow,which could promote the vectoring deflection,and the impact effect of the disturbing flow and the suppressive effect of the main flow with the effect of restraining the vectoring deflection.The vectoring angle is a complex parameter coupled by all source variables.The detailed theoretical model,whose error is controlled within 3.6 degrees,can be used to quantitatively assess the vectoring feature of DSJ and thus to provide a guidance for designing the control law applied in the active flow control.展开更多
The Dual Synthetic Jet Actuator(DSJA) is used to develop a new type of lift enhancement device based on circulation control, and to control the flow over the two-dimensional(2D)NACA0015 airfoil. The lift enhancement d...The Dual Synthetic Jet Actuator(DSJA) is used to develop a new type of lift enhancement device based on circulation control, and to control the flow over the two-dimensional(2D)NACA0015 airfoil. The lift enhancement device is composed of a DSJA and a rounded trailing edge(Coanda surface). The two outlets of the DSJA eject two jets(Jet 1 and Jet 2). Jet 1 ejects from the upper trailing edge, which increases the circulation of airfoil with the help of the Coanda surface. Jet2 ejects from the lower trailing edge, which acts as a virtual flap. The Reynolds number based on the airfoil chord length and free flow velocity is 250000. The results indicate that the circulation control method based on Dual Synthetic Jet(DSJ) has good performance in lift enhancement, whose control effect is closely related to momentum coefficient and reduced frequency. With the increase of the reduced frequency, the control effect of the lift enhancement is slightly reduced. As the momentum coefficient increases, the control effect becomes better. When the angle of attack is greater than 4°, the increments of lift coefficients under the control of DSJ are larger than those under the control of the steady blowing at a same momentum coefficient. The maximum lift augmentation efficiency can reach 47 when the momentum coefficient is 0.02, which is higher than the value in the case with steady blowing jet circulation control.展开更多
A new skill of modulating driving signals of a synthetic jet with low frequency is introduced to enhance the control authority.Based on dynamic mesh technique,the effect of flow control over a NACA0015 airfoil with a ...A new skill of modulating driving signals of a synthetic jet with low frequency is introduced to enhance the control authority.Based on dynamic mesh technique,the effect of flow control over a NACA0015 airfoil with a Synthetic Jet Actuator(SJA)has been investigated.The SJA is located at x/c=10%,and two jet injection angles of 90°and 30°have been considered.Flow structures indicate that modulation with low frequency can reduce the dissipation rate of vortices after they shed off the surface.Thus aerodynamic performance of the airfoil could be improved.For the injection angle of 90°,modulation can increase the control authority of the SJA.Compared to the unmodulated case,increment of lift-to-drag ratio is up to 15%.The modulating frequency corresponding to the largest increment is F_(M)^(+)≈1.For the injection angle of 30°,improvement of aerodynamic forces positively relates to momentum coefficient of the SJA.Due to the decrease of effective momentum,modulation degrades the effect of flow control.The opposite responses to modulation are believed to have a relationship with the variation of primary control mechanism.When jet injection angle varies from 90°to 30°,the primary mechanism changes from the interaction of vortices and waves to the direct momentum addition.The skill of modulation of driving signals is very useful for applications of SJA.展开更多
A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Eule...A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Euler–Lagrange framework is proposed.The model is validated in single particle configurations with varying particle diameters.The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the various physical/chemical sub-models are presented.The combustion time of single aluminum particles predicted by the model are in very good agreement with empirical correlations for particles with diameters larger than 10μm.The prediction error for smaller particles is noticeably reduced when using a heat transfer model that is capable of capturing the transition regime between continuum mechanics and molecular dynamics.The predictive capabilities of the proposed model framework are further evaluated by simulating the aluminum/air Bunsen flames of Mc Gill University for the first time.Results show that the predicted temperature distribution of the flame is consistent with the experimental data and the double-front structure of the Bunsen flame is reproduced well.The burning rates of aluminum in both single particle and particle cloud configurations are calculated and compared with empirical correlations.Results show that the burning rates obtained from the present model are more reasonable,while the correlations,when embedded in the Euler–Lagrange context,tend to underestimate the burning rate in the combustion stage,particularly for the considered fuel-rich flames.展开更多
In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probabili...In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probability density function transport equation by ESF method that considers the interaction mechanism between flame and turbulence with high precision.At the same time,by making use of the advantage of the FGM model,this model is able to incorporate the detailed chemical reaction mechanism(GRI 3.0)with acceptable computational cost.The new model has been implemented in the open source CFD suite-Open FOAM.Validation of the model has been carried out by simulating the Sandia flame series(three turbulent piloted methane jet flames)issued by the National Laboratory of the United States.The accuracy and advancement of the ESF/FGM turbulent combustion model are verified by comparing the LES results of the new model with the rich experimental data as well as the RANS results.The results demonstrate that the model has a strong ability in capturing combustion phenomena such as extinction and re-ignition in turbulent flame,which is essential in the accurate prediction of the combustion process in real combustion devices,for example,aircraft engines.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11602299,11872374,and 51809271)
文摘To promote high-speed boundary layer transition,this paper proposes an active self-sustaining dual jets(SDJ)actuator utilizing the energy of supersonic mainflow.Employing the nanoparticle-based planar laser scattering(NPLS),supersonic flat-plate boundary layer transition induced by SDJ is experimentally investigated in an Ma-2.95 low-turbulence wind tunnel.Streamwise and spanwise NPLS images are obtained to analyze fine flow structures of the whole transition process.The results reveal the transition control mechanisms that on the one hand,the jet-induced shear layer produces unstable Kelvin–Helmholtz instabilities in the wake flow,on the other hand,the jets also generates an adverse pressure gradient in the boundary layer and induce unstable streak structures,which gradually break down into turbulence downstream.The paper provides a new method for transition control of high-speed boundary layer,and have prospect both in theory and engineering application.
基金supported by the National Natural Science Foundation of China (Nos. 92271110, 12202488, 12072352 and T2221002)the National Major Science and Technology Project of China (Nos. J2019-II-0016-0037 and J2019-Ⅲ-0010-0054)the Natural Science Program of National University of Defense Technology, China (No. ZK22-30)。
文摘The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.
基金Supported by the National Science and Technology Major Project of China(No.J2019-ΙΙΙ-0010-0054)the National Natural Science Foundation of China(Nos.52075538,12202488,92271110)+1 种基金the Natural Science Foundation of Hunan Province,China(No.2023JJ30622)the Natural Science Program of National University of Defense Technology,China(No.ZK22-30).
文摘Large Eddy Simulation(LES)is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators(PSJAs)on a hemisphere in supersonic inflow,and analyze the effect of energy allocation and array angle on the drag reduction performance of opposing Plasma Synthetic Jet(PSJ)in this paper.Numerical simulation results have been compared with experimental data,confirming the validity of the simulation method.The results show that different energy allocations have a significant effect on the drag of the hemisphere.However,the effect of the change in array angle on the drag of the hemisphere is not as noticeable as the effect caused by energy allocation.Interference regions between the two PSJAs occur,which undermine the effectiveness of drag reduction.High Turbulent Kinetic Energy(TKE)regions primarily concentrate on the core region of the jet and downstream of the bow shock.The influence of the array angle on TKE is most evident in the downstream region of the exits of the PSJs on both sides.Temporal evolution of the coherent structures reveals that as the PSJ intensity decreases,the largescale vortices progressively break up into smaller-scale vortices,and energy is also transferred from large-scale structures to small-scale structures.
基金the National Natural Science Foundation of China(Nos.U2141252,11972369,52075538).
文摘To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders.Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated.Then,flight tests were carried out to verify the control abilities,providing a novel technology for the design of a future rudderless FWA.Results show that synthetic jets could narrow the dead zone area,improve the flow velocity near the trailing edge,and then move the trailing-edge separation point and the leading-edge stagnation point downwards,which make the effective Attack of Angle(AOA)increase,thereby enhancing the pressure envelope area.Circulation control based on synthetic jets could improve the lift,drag and nose-down moment.The variations of lift and nosedown moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency.Finally,synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA,which could realize the roll and pitch control without deflections of rudders during the cruise stage,and the maximum roll and pitch angular velocity are 12.64(°)/s and 8.51(°)/s,respectively.
基金co-supported by the National Natural Science Foundation of China(No.52075538)the National Science and Technology Major Project,China(No.J2019-II-0016-0037)+1 种基金the Natural Science Foundation of Hunan Province,China(No.2020 JJ2030)the Foundation of National University of Defense Technology,China(No.ZK-22-30)。
文摘To effectively reduce the loss of strong shock wave at the trailing edge of the supersonic cascade under high backpressure,a shock wave control method based on self-sustaining synthetic jet was proposed.The self-sustaining synthetic jet was applied on the pressure side of the blade with the blow slot and the bleed slot arranged upstream and downstream of the trailing-edge shock,respectively.The flow control mechanism and effects of parameters were investigated by numerical simulation.The results show that the self-sustaining synthetic jet forms an oblique shock wave in the cascade passage which slows down and pressurizes the airflow,and the expansion wave downstream of the blow slot weakens the shock strength which can effectively change the Mach reflection to regular reflection and thus weaken the shock loss.And the suction effect can reduce loss near blade surface.Compared with the baseline cascade,the self-sustaining jet actuator can reduce flow losses by 6.73%with proper location design and vibration of diaphragm.
基金supported by the National Natural Science Foundation of China(Nos.U2141252,11972369 and 52075538)。
文摘For achieving the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a novel yaw effector based on Reverse Dual Synthetic Jets(RDSJ)was proposed without the movement of rudders.Effects on aerodynamic characteristics of a small-sweep FWA and control mechanism were investigated by numerical simulations.Finally,reverse dual synthetic jet actuators were integrated into a real FWA and flight tests were firstly carried out.Numerical results show that RDSJ could make drag coefficient increase and weaken lift coefficient,which generate a yawing moment and a rolling moment in the same direction,realizing control of heading attitudes,but strong coupling with the pitching moment occurs at large angles of attack.For control mechanism,RDSJ could produce two reverse synthetic jets out of phases,improve the reverse pressure gradient and hence form alternate recirculation zones or even early large-area separation,which cause the rise of pressures before exits and the dip of pressures behind exits,achieving improvement of drag and the yawing moment.The results of flight tests support that RDSJ could realize control of heading attitudes without deflections of rudders during the cruise stage and achieve the maximal yaw angular velocity of 10.12(°)/s,verifying the feasibility of this novel yaw effector.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972369,52075538 and 11872374)the Youth Science and Technology Innovation Award funded project of National University of Defense Technology(Grant No.434517314).
基金supported by the National Natural Science Foundation of China(Grant Nos.12202488 and 12002377)the Natural Science Program of National University of Defense Technology(Grant No.ZK22-30)Independent Cultivation Project for Young Talents in College of Aerospace Science and Engineering.
基金the National Natural Science Foundation of China(Grant Nos.12202488 and 12072306)Natural Science Program of NUDT(ZK22-30)Independent Cultivation Project for Young Talents of the College of Aerospace Science and Engineering.
文摘Turbulence drag reduction is of great significance for the range increase of hypersonic flight vehicles.The proposed velocity-temperature coupling control method(Liu et al,Phys Rev Fluids 6:044603,2021)is further extended to the hypersonic turbulent boundary layer.Direct numerical simulation results of four comparative cases show that the heated wall blowing achieves a drag reduction rate of 10.58%,which is about the sum of wall blowing(5.27%)and wall heating(6.35%).By evaluating the control efficiency,however,it is found that heated wall blowing is not as good as wall blowing and cannot obtain net energy saving rate.The modified FIK decompositions of skin friction coefficient indicate that the cliffy decrease of the mean convection term is the primary contribution for the drag reduction.Effects of the proposed control measure on turbu-lence statistics and coherent structures are also analyzed.Streamwise vortex is found to be away from the wall,thus leading to a lower friction drag.
基金supported by the National Natural Science Foundation of China(Nos.11372349,11502295,and11572349)
文摘Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a twoelectrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial,the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.
基金supported by the National Natural Science Foundation of China(Nos.11602299,11502295,11572349,11872374 and 51809271).
文摘In order to improve the control ability of synthetic jets in compressible boundary layer,a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was proposed.As fundamental investigations on the effects of synthetic jet temperature on the jet behavior and flow field characteristics were essentially necessary,preliminary numerical simulations were conducted to study the influence of temperature(200 K and 400 K)on the flow field characteristics of synthetic jets using Large Eddy Simulations(LES)model.Time-averaged flow fields showed that different temperatures led to variable behavior of two strands of jets.For dual synthetic cold jets,a potential-core arose apparently with its height ranging from 0.01 to 0.03 m,while for dual synthetic hot jets,two strands of jets emerged downstream.The modal decomposition of instantaneous flow fields had been done using both Proper Orthogonal Decomposition(POD)and Dynamic Mode Decomposition(DMD).Various modes showed different characteristics of the flow fields.As the POD method focuses on the energy of flow while the DMD method focuses on the frequency,the first two modes had many similarities,but the third and fourth modes demonstrated completely different vortex structures.The current researches play a role of preliminary investigations for further and comprehensive exploration of novel flow control measures in global velocity field.
基金co-supported by the National Natural Science Foundation of China(Nos.11972369,11872374)the Youth Science and Technology Innovation Award Funded Project of National University of Defense Technology,China(No.434517314)。
文摘The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability of DSJA to control the attitudes of UAV during cruising.DSJA is improved into an actuator with two diaphragms and three cavities,which has higher energy levels.Actuators,differentially distributed on both sides of the wings,are installed on the trailing edge close to the wing tips.Flight tests,containing Differential Circulation Control(DCC)using double-side actuators,Positive Circulation Control(PCC)using left-side actuators and Negative Circulation Control(NCC)using right-side actuators,are implemented at cruising speed of 25 m/s.Results show that roll attitude control without rudders could be realized by DSJAs.DCC and NCC can generate the rightward roll and yaw angular velocity,prompting UAV to turn right.The stronger controlling ability can be achieved by DCC,with the maximum roll angular velocity of 15.62(°)/s.PCC can generate a rightward roll moment,but a leftward yaw moment will be produced at the same time.Leftward yaw induces the leftward rolling moment,which weakens the roll control effect,making UAV keep to yaw to the left with a small slope.
基金co-supported by the National Natural Science Foundation of China(Nos.52075538,12002377,11872374)the Natural Science Foundation of Hunan Province,China(Nos.2020JJ5670,2020JJ2031)+1 种基金the research program of National University of Defense Technology(No.ZK18-03-11)China Postdoctoral Science Foundation(No.2019M652754)。
文摘Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet(PSJ)for drag reduction for a hemisphere.Firstly,flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3.As PSJ is a kind of unsteady pulsed jet,the shock standoff distance increases initially and then decreases under the control of PSJ,which corresponds to the change of the strength of PSJ.Accordingly,the amount of drag reduction of the hemisphere increases initially and then decreases.It is found that there is a short period of“drag rise”during the formation of PSJ before the drag reduction,which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator(PSJA).Secondly,the effects of five parameters,including exit diameter,discharge energy of PSJA,Mach number,static pressure of incoming flow and angle of attack,on drag reduction of opposing PSJ were studied in detail by using numerical method.It is found that the Maximum Pressure Ratio(MPR)has a significant impact on the average drag reduction for a configuration-determined PSJA.For the configuration selected in this study,the flow field of opposing PSJ shows typical Short Penetration Mode(SPM)in a control cycle of PSJ when the MPR is less than 0.89.However,the flow field shows typical Long Penetration Mode(LPM)at some time when the MPR is bigger than 0.89.Relatively better drag reduction is achieved in this case.
基金co-supported by the National Natural Science Foundation of China(No.12002377,52075538,11872374),the Open Fund of the Key Laboratory of IcingAnti/De-Icing(No.1901IADL20190401)+1 种基金the Natural Science Foundation of Hunan Province(No.2020JJ5670,2020JJ2031)China Postdoctoral Science Foundation(No.2019M652754).
文摘Aircraft icing has long been a plague to aviation for its serious threat to flight safety.Recently,researches about a newly proposed deicing method based on Plasma Synthetic Jet Actuator(PSJA)have just started.To meet the requirements of in-flight deicing,structure of PSJA needs to be adjusted.This paper completed the detailed design and experimental validation of a novel plasma striker,which was a modified version of PSJA.Influences of mass of the moving part and rod shapes on the ice-breaking performances were also studied.Besides,a“conical-nosed rod configuration”was proposed.Its purpose was to ensure a good ice-breaking performance of the plasma striker on long ice,by generating a splitting failure.Results show that,though mass of the moving part was just several grams,ice-breaking performance was better when the mass was lighter.The rectangular rod could generate an elliptical circumferential crack,whose major axis was parallel to the direction of the long side of the rectangular rod.And the“conical-nosed rod”concept was verified to be able to generate a splitting crack which can spread completely to the far end of long ice,and the crack direction was parallel to edge line of the cone.In general,the plasma striker has the advantages of simple structure,low energy consumption,little harm to the flow field and the aircraft skin.Simulations will be carried out in future works to study in detail the working process of the plasma striker.
基金This work was supported by the National Natural Science Foundation of China(Grants 11972369,11872374,and 52075538).
文摘For lessening the weight and volume of flow control system,enlarging the circulation control applying area of angle of attack(AOA),and achieving nice controlling characteristics,a novel lift enhancement method based on dual synthetic jet actuators(DSJAs)and synthetic jet actuator(SJA),and an adaptive proportional integral and differential(PID)algorithm based on radial basis function neural network are introduced.DSJAs are uniformly located along the chord to suppress the separation and trailing-edge SJA is applied to achieve the high circulation.Velocities of actuators are modulated to realize the real speed profile and on–off controlling laws of DSJAs are designed.Numerical simulations show that DSJAs and SJA could suppress the separation completely and move leading-edge stagnation point and trailing-edge separation point downstream even at AOA of 19°,hence achieve the highest lift and nose-down moment augmentation(ΔCl_(max)=0.92,ΔCm_(max)=0.02534),andΔL/D can reach 11.39 at AOA of 18°.Stalling is delayed to more than 19°.Linear lift area and pitch-break angle are both increased to 16°.ΔCl/C_(μ) can reach 76.7,indicating the greatest control efficiency.The results of adaptive PID control,whose controlling effects are proved better than PID,indicate that lift could track the objective with the rise time of 0.0325 s and finally keep steady,suggesting the nice stability and rapidness.
基金supported by the National Natural Science Foundation of China(Nos.11972369 and 11872374)。
文摘The excellent vectoring characteristic of Dual Synthetic Jet(DSJ)provides a new control strategy for the active flow control,such as thrust vectoring control,large area cooling,separated flow control and so on.For incompressible flow,the influence relation of source variables,such as structure parameters of actuators,driving parameters and material attributes of piezoelectric vibrating diaphragm,on the vectoring DSJ and a theoretical model are established based on theoretical and regression analysis,which are all verified by numerical simulations.The two synthetic jets can be deemed as a main flow with a higher jet velocity and a disturbing flow with a lower jet velocity.The results indicate that the influence factors contain the low-pressure area formed at the exit of the disturbing flow,which could promote the vectoring deflection,and the impact effect of the disturbing flow and the suppressive effect of the main flow with the effect of restraining the vectoring deflection.The vectoring angle is a complex parameter coupled by all source variables.The detailed theoretical model,whose error is controlled within 3.6 degrees,can be used to quantitatively assess the vectoring feature of DSJ and thus to provide a guidance for designing the control law applied in the active flow control.
基金co-supported by the National Natural Science Foundation of China(Nos.11972369 and 11872374)the Youth Science and Technology Innovation Award funded project of National University of Defense Technology,China(434517314).
文摘The Dual Synthetic Jet Actuator(DSJA) is used to develop a new type of lift enhancement device based on circulation control, and to control the flow over the two-dimensional(2D)NACA0015 airfoil. The lift enhancement device is composed of a DSJA and a rounded trailing edge(Coanda surface). The two outlets of the DSJA eject two jets(Jet 1 and Jet 2). Jet 1 ejects from the upper trailing edge, which increases the circulation of airfoil with the help of the Coanda surface. Jet2 ejects from the lower trailing edge, which acts as a virtual flap. The Reynolds number based on the airfoil chord length and free flow velocity is 250000. The results indicate that the circulation control method based on Dual Synthetic Jet(DSJ) has good performance in lift enhancement, whose control effect is closely related to momentum coefficient and reduced frequency. With the increase of the reduced frequency, the control effect of the lift enhancement is slightly reduced. As the momentum coefficient increases, the control effect becomes better. When the angle of attack is greater than 4°, the increments of lift coefficients under the control of DSJ are larger than those under the control of the steady blowing at a same momentum coefficient. The maximum lift augmentation efficiency can reach 47 when the momentum coefficient is 0.02, which is higher than the value in the case with steady blowing jet circulation control.
基金supported by the National Natural Science Foundation of China(Nos.:11872374 and 11602299)。
文摘A new skill of modulating driving signals of a synthetic jet with low frequency is introduced to enhance the control authority.Based on dynamic mesh technique,the effect of flow control over a NACA0015 airfoil with a Synthetic Jet Actuator(SJA)has been investigated.The SJA is located at x/c=10%,and two jet injection angles of 90°and 30°have been considered.Flow structures indicate that modulation with low frequency can reduce the dissipation rate of vortices after they shed off the surface.Thus aerodynamic performance of the airfoil could be improved.For the injection angle of 90°,modulation can increase the control authority of the SJA.Compared to the unmodulated case,increment of lift-to-drag ratio is up to 15%.The modulating frequency corresponding to the largest increment is F_(M)^(+)≈1.For the injection angle of 30°,improvement of aerodynamic forces positively relates to momentum coefficient of the SJA.Due to the decrease of effective momentum,modulation degrades the effect of flow control.The opposite responses to modulation are believed to have a relationship with the variation of primary control mechanism.When jet injection angle varies from 90°to 30°,the primary mechanism changes from the interaction of vortices and waves to the direct momentum addition.The skill of modulation of driving signals is very useful for applications of SJA.
基金supported by the National Natural Science Foundation of China(No.51706241)Hunan Provincial Natural Science Foundation of China(Nos.2020JJ4665 and 2021JJ30775)+1 种基金Hunan Provincial Innovation Foundation for Postgraduate,China(No.CX2019-0050)support provided by China Scholarship Council(No.201903170201)。
文摘A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Euler–Lagrange framework is proposed.The model is validated in single particle configurations with varying particle diameters.The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the various physical/chemical sub-models are presented.The combustion time of single aluminum particles predicted by the model are in very good agreement with empirical correlations for particles with diameters larger than 10μm.The prediction error for smaller particles is noticeably reduced when using a heat transfer model that is capable of capturing the transition regime between continuum mechanics and molecular dynamics.The predictive capabilities of the proposed model framework are further evaluated by simulating the aluminum/air Bunsen flames of Mc Gill University for the first time.Results show that the predicted temperature distribution of the flame is consistent with the experimental data and the double-front structure of the Bunsen flame is reproduced well.The burning rates of aluminum in both single particle and particle cloud configurations are calculated and compared with empirical correlations.Results show that the burning rates obtained from the present model are more reasonable,while the correlations,when embedded in the Euler–Lagrange context,tend to underestimate the burning rate in the combustion stage,particularly for the considered fuel-rich flames.
基金supported by the National Natural Science Foundation of China(No.51706241).
文摘In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probability density function transport equation by ESF method that considers the interaction mechanism between flame and turbulence with high precision.At the same time,by making use of the advantage of the FGM model,this model is able to incorporate the detailed chemical reaction mechanism(GRI 3.0)with acceptable computational cost.The new model has been implemented in the open source CFD suite-Open FOAM.Validation of the model has been carried out by simulating the Sandia flame series(three turbulent piloted methane jet flames)issued by the National Laboratory of the United States.The accuracy and advancement of the ESF/FGM turbulent combustion model are verified by comparing the LES results of the new model with the rich experimental data as well as the RANS results.The results demonstrate that the model has a strong ability in capturing combustion phenomena such as extinction and re-ignition in turbulent flame,which is essential in the accurate prediction of the combustion process in real combustion devices,for example,aircraft engines.
