Evacuated tube transportation is an important development direction for the high-speed transportation technology of the future.However,a train running at supersonic speed in a closed tube can create an unstable aeroth...Evacuated tube transportation is an important development direction for the high-speed transportation technology of the future.However,a train running at supersonic speed in a closed tube can create an unstable aerothermal phenomenon,causing the temperature to rise sharply inside the tube and endangering the safe operation of trains and equipment.The blockage ratio is one of the key factors affecting the aerodynamic characteristics in the tube.In this paper,a 2 D axisymmetric model and Delayed Detached Eddy Simulation(DDES)based on the Shear Stress Transport(SST)k-ωturbulence model are used to study the aerothermal environment in the tube.The calculation method used in this paper was verified by a wind tunnel experiment.The aerothermal phenomenon and distribution of the flow field in the tube with different blockage ratios were compared and analysed.The results show that the aerothermal environment is significantly affected by the blockage ratio.A choking limit formed in the flow field will aggravate the aerodynamic phenomenon as the blockage ratio increases,which further deteriorates the aerothermal environment of the tube.Moreover,the existence of the choking limit,shock wave,and Mach disk make the flow field in the tube more complicated.展开更多
At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)...At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)and selected blockage ratio.This paper experimentally investigates the effect of rib blockage ratio(ranges from 0 to 0.3)on pressure loss and heat transfer in a rotating square channel under high rotation number(up to 0.81).The ribs staggered on leading and trailing walls were oriented 90°to the mainstream flow.The Reynolds number and the wall-to-fluid temperature ratio varied from 20000 to 40000 and 0.08 to 0.2,respectively.The results showed that a larger blockage ratio resulted in a better heat transfer but a higher pressure drop.The optimum blockage ratio was 0.1 for the best thermal performance.The rotational effects were weakened in the passage with a higher blockage ratio,where the critical rotation number could not be observed.Moreover,the heat transfer enhancement induced by rotation was more significant when the temperature ratio increased.Finally,the correlations were developed for the pressure drop and the convective heat transfer on the leading and trailing edges.展开更多
The present study focuses on the mitigation of shock wave using novel geometric passages in the flow field.The strategy is to produce multiple shock reflections and diffractions in the passage with minimum flow obstru...The present study focuses on the mitigation of shock wave using novel geometric passages in the flow field.The strategy is to produce multiple shock reflections and diffractions in the passage with minimum flow obstruction,which in turn is expected to reduce the shock wave strength at the target location.In the present study the interaction of a plane shock front(generated from a shock tube)with various geometric designs such as,1)zig-zag geometric passage,2)staggered cylindrical obstructions and 3)zigzag passage with cylindrical obstructions have been investigated using computational technique.It is seen from the numerical simulation that,among the various designs,the maximum shock attenuation is produced by the zig-zag passage with cylindrical obstructions which is then followed by zig-zag passage and staggered cylindrical obstructions.A comprehensive investigation on the shock wave reflection and diffraction phenomena happening in the proposed complex passages have also been carried out.In the new zig-zag design,the initial shock wave undergoes shock wave reflection and diffraction process which swaps alternatively as the shock front moves from one turn to the other turn.This cyclic shock reflection and diffraction process helps in diffusing the shock wave energy with practically no obstruction to the flow field.It is found that by combining the shock attenuation ability of zig-zag passage(using shock reflection and diffraction)with the shock attenuation ability of cylindrical blocks(by flow obstruction),a drastic attenuation in shock strength can be achieved with moderate level of flow blocking.展开更多
The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors f...The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.展开更多
Inverse stochastic resonance(ISR)is a phenomenon in which the firing activity of a neuron is inhibited at a certain noise level.In this paper,the effects of potassium channel blockage on ISR in single Hodgkin-Huxley n...Inverse stochastic resonance(ISR)is a phenomenon in which the firing activity of a neuron is inhibited at a certain noise level.In this paper,the effects of potassium channel blockage on ISR in single Hodgkin-Huxley neurons and in small-world networks were investigated.For the single neuron,the ion channel noise-induced ISR phenomenon can occur only in a certain small range of potassium channel blockage ratio.Bifurcation analysis showed that this small range is the bistable region regulated by the external bias current.For small-world networks,the effect of non-homogeneous network blockage on ISR was investigated.The network blockage ratio was used to represent the proportion of potassium-channel-blocked neurons to total network neurons.It is found that an increase in network blockage ratio at small coupling strengths results in shorter ISR duration.When the coupling strength is increased,the ISR is more significant in the case of a large network blockage ratio.The ISR phenomenon is determined by the network blockage ratio,the coupling strength,and the ion channel noise.Our results will provide new perspectives on the observation of ISR in neuroscience experiments.展开更多
The paper aimed to study the flow structure at the wake of the bluff body with altered blockage ratio(BR)keeping the fixed aspect ratio(AR).The study was conducted by a finite volume technique using commercial softwar...The paper aimed to study the flow structure at the wake of the bluff body with altered blockage ratio(BR)keeping the fixed aspect ratio(AR).The study was conducted by a finite volume technique using commercial software Ansys-Fluent.The CFD analysis of the bluff body is mainly subjected to the lower subcritical Reynolds number range(5000 to 15,000)along with blockage ratio as an important factor.The flow parameters such as drag coefficient,pressure,and kinetic energy variations are analyzed here for the Reynolds number(Re)and BR.It was observed that at fixed Re,t he drag coefficient(C_(D))increases with an increase in the BR while decrease with increasing Re for a fixed value of BR.展开更多
In this paper,the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0,the total temperature at 700 K and the total pressure at 520 k Pa(simulated flight Mach numb...In this paper,the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0,the total temperature at 700 K and the total pressure at 520 k Pa(simulated flight Mach number at 3.5)were studied by using the flame stabilizing method of cavity and strut from three aspects such as blockage ratios,kerosene equivalence ratios,location and quantity of injection holes.The results showed that:(A)The combustor with the strut realized the independent and stable combustion of kerosene.The combustion-induced back pressure in the block test with blockage ratio of 20%and 10%destroyed the inlet flow conditions;while the blockage ratio was 7.3%and 5%,the incoming flow conditions when kerosene was burned stably were not destroyed.(B)The kerosene Equivalence Ratio(ER)was more likely to be disturbed upstream than the induced back pressure when it rose,and an excessively high-ER would reduce the combustion efficiency;when the equivalence ratio was constant,the combustion efficiency of the blockage ratio of 7.3%was higher than the blockage ratio of 5%.The combustion efficiencies were 0.86(ER=0.13)and 0.78(ER=0.19)when the blockage ratio was 5%,respectively;the combustion efficiencies were 0.89(ER=0.16)and 0.82(ER=0.19)when the blockage ratio was 7.3%,respectively;the combustion efficiencies were 0.51(ER=0.25),0.81(ER=0.3),0.65(ER=0.34)and0.62(ER=0.42)when the blockage ratio was 20%,respectively.(C)The porous injection provided behind the strut was beneficial to the atomization of kerosene and improved the combustion efficiency of kerosene;the second injection after the cavity would reduce the combustion efficiency due to insufficient oxygen and combustion space.This study expanded the working range of ramjet and provided a reference fuel injection scheme for Turbine-Based Combined Cycle(TBCC)engine.展开更多
基金supported by the National Natural Science Foundation of China(51805453 and 51978575)the Fundamental Research Funds for the Central Universities(2682018CX14)+1 种基金Project funded by China Postdoctoral Science Foundation(2019M663551)Doctoral Innovation Fund Program of Southwest Jiaotong University。
文摘Evacuated tube transportation is an important development direction for the high-speed transportation technology of the future.However,a train running at supersonic speed in a closed tube can create an unstable aerothermal phenomenon,causing the temperature to rise sharply inside the tube and endangering the safe operation of trains and equipment.The blockage ratio is one of the key factors affecting the aerodynamic characteristics in the tube.In this paper,a 2 D axisymmetric model and Delayed Detached Eddy Simulation(DDES)based on the Shear Stress Transport(SST)k-ωturbulence model are used to study the aerothermal environment in the tube.The calculation method used in this paper was verified by a wind tunnel experiment.The aerothermal phenomenon and distribution of the flow field in the tube with different blockage ratios were compared and analysed.The results show that the aerothermal environment is significantly affected by the blockage ratio.A choking limit formed in the flow field will aggravate the aerodynamic phenomenon as the blockage ratio increases,which further deteriorates the aerothermal environment of the tube.Moreover,the existence of the choking limit,shock wave,and Mach disk make the flow field in the tube more complicated.
文摘At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)and selected blockage ratio.This paper experimentally investigates the effect of rib blockage ratio(ranges from 0 to 0.3)on pressure loss and heat transfer in a rotating square channel under high rotation number(up to 0.81).The ribs staggered on leading and trailing walls were oriented 90°to the mainstream flow.The Reynolds number and the wall-to-fluid temperature ratio varied from 20000 to 40000 and 0.08 to 0.2,respectively.The results showed that a larger blockage ratio resulted in a better heat transfer but a higher pressure drop.The optimum blockage ratio was 0.1 for the best thermal performance.The rotational effects were weakened in the passage with a higher blockage ratio,where the critical rotation number could not be observed.Moreover,the heat transfer enhancement induced by rotation was more significant when the temperature ratio increased.Finally,the correlations were developed for the pressure drop and the convective heat transfer on the leading and trailing edges.
文摘The present study focuses on the mitigation of shock wave using novel geometric passages in the flow field.The strategy is to produce multiple shock reflections and diffractions in the passage with minimum flow obstruction,which in turn is expected to reduce the shock wave strength at the target location.In the present study the interaction of a plane shock front(generated from a shock tube)with various geometric designs such as,1)zig-zag geometric passage,2)staggered cylindrical obstructions and 3)zigzag passage with cylindrical obstructions have been investigated using computational technique.It is seen from the numerical simulation that,among the various designs,the maximum shock attenuation is produced by the zig-zag passage with cylindrical obstructions which is then followed by zig-zag passage and staggered cylindrical obstructions.A comprehensive investigation on the shock wave reflection and diffraction phenomena happening in the proposed complex passages have also been carried out.In the new zig-zag design,the initial shock wave undergoes shock wave reflection and diffraction process which swaps alternatively as the shock front moves from one turn to the other turn.This cyclic shock reflection and diffraction process helps in diffusing the shock wave energy with practically no obstruction to the flow field.It is found that by combining the shock attenuation ability of zig-zag passage(using shock reflection and diffraction)with the shock attenuation ability of cylindrical blocks(by flow obstruction),a drastic attenuation in shock strength can be achieved with moderate level of flow blocking.
基金supported by Sichuan Science and Technology Program(No.2019YJ0227)China Postdoctoral Science Foundation(No.2019M663550)+1 种基金China Postdoctoral Science Foundation(No.2019M663550)Science and Technology Program of China Railway Group Limited(No.2018-S-02).
文摘The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.
基金the National Natural Science Foundation of China(No.12175080)the Fundamental Research Funds for the Central Universities(No.CCNU22JC009),China.
文摘Inverse stochastic resonance(ISR)is a phenomenon in which the firing activity of a neuron is inhibited at a certain noise level.In this paper,the effects of potassium channel blockage on ISR in single Hodgkin-Huxley neurons and in small-world networks were investigated.For the single neuron,the ion channel noise-induced ISR phenomenon can occur only in a certain small range of potassium channel blockage ratio.Bifurcation analysis showed that this small range is the bistable region regulated by the external bias current.For small-world networks,the effect of non-homogeneous network blockage on ISR was investigated.The network blockage ratio was used to represent the proportion of potassium-channel-blocked neurons to total network neurons.It is found that an increase in network blockage ratio at small coupling strengths results in shorter ISR duration.When the coupling strength is increased,the ISR is more significant in the case of a large network blockage ratio.The ISR phenomenon is determined by the network blockage ratio,the coupling strength,and the ion channel noise.Our results will provide new perspectives on the observation of ISR in neuroscience experiments.
文摘The paper aimed to study the flow structure at the wake of the bluff body with altered blockage ratio(BR)keeping the fixed aspect ratio(AR).The study was conducted by a finite volume technique using commercial software Ansys-Fluent.The CFD analysis of the bluff body is mainly subjected to the lower subcritical Reynolds number range(5000 to 15,000)along with blockage ratio as an important factor.The flow parameters such as drag coefficient,pressure,and kinetic energy variations are analyzed here for the Reynolds number(Re)and BR.It was observed that at fixed Re,t he drag coefficient(C_(D))increases with an increase in the BR while decrease with increasing Re for a fixed value of BR.
基金Sponsored by the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University,China(No.CX2020132)。
文摘In this paper,the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0,the total temperature at 700 K and the total pressure at 520 k Pa(simulated flight Mach number at 3.5)were studied by using the flame stabilizing method of cavity and strut from three aspects such as blockage ratios,kerosene equivalence ratios,location and quantity of injection holes.The results showed that:(A)The combustor with the strut realized the independent and stable combustion of kerosene.The combustion-induced back pressure in the block test with blockage ratio of 20%and 10%destroyed the inlet flow conditions;while the blockage ratio was 7.3%and 5%,the incoming flow conditions when kerosene was burned stably were not destroyed.(B)The kerosene Equivalence Ratio(ER)was more likely to be disturbed upstream than the induced back pressure when it rose,and an excessively high-ER would reduce the combustion efficiency;when the equivalence ratio was constant,the combustion efficiency of the blockage ratio of 7.3%was higher than the blockage ratio of 5%.The combustion efficiencies were 0.86(ER=0.13)and 0.78(ER=0.19)when the blockage ratio was 5%,respectively;the combustion efficiencies were 0.89(ER=0.16)and 0.82(ER=0.19)when the blockage ratio was 7.3%,respectively;the combustion efficiencies were 0.51(ER=0.25),0.81(ER=0.3),0.65(ER=0.34)and0.62(ER=0.42)when the blockage ratio was 20%,respectively.(C)The porous injection provided behind the strut was beneficial to the atomization of kerosene and improved the combustion efficiency of kerosene;the second injection after the cavity would reduce the combustion efficiency due to insufficient oxygen and combustion space.This study expanded the working range of ramjet and provided a reference fuel injection scheme for Turbine-Based Combined Cycle(TBCC)engine.
