The spatial structure of the velocity field in a stirred vessel with water has been measured and analyzed using the laser Doppler velocimeter technique, with the immersing depth and agitation speed of the impeller re-...The spatial structure of the velocity field in a stirred vessel with water has been measured and analyzed using the laser Doppler velocimeter technique, with the immersing depth and agitation speed of the impeller re-maining approximately constant. The experimental results were provided such as the mean velocity field, fluctuat-ing velocities, turbulent kinetic energy, Reynolds shear stress and time series of the velocity in the stirred tank. These results probably provided the valuable basis to further optimize and enlarge the stirred tank in the industrial process.展开更多
Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The...Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al＇s （2004） relationship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity to the maximum velocity, ranges from 0.2 to 0.6. Kang et al＇s （2004） relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al＇s relationship.展开更多
Oceanic turbulence measurements made by an acoustic Doppler velocimeter(ADV)suffer from noise that potentially affects the estimates of turbulence statistics.This study examines the abilities of Kalman filtering and a...Oceanic turbulence measurements made by an acoustic Doppler velocimeter(ADV)suffer from noise that potentially affects the estimates of turbulence statistics.This study examines the abilities of Kalman filtering and autoregressive moving average models to eliminate noise in ADV velocity datasets of laboratory experiments and offshore observations.Results show that the two methods have similar performance in ADV de-noising,and both effectively reduce noise in ADV velocities,even in cases of high noise.They eliminate the noise floor at high frequencies of the velocity spectra,leading to a longer range that effectively fits the Kolmogorov-5/3 slope at midrange frequencies.After de-noising adopting the two methods,the values of the mean velocity are almost unchanged,while the root-mean-square horizontal velocities and thus turbulent kinetic energy decrease appreciably in these experiments.The Reynolds stress is also affected by high noise levels,and de-noising thus reduces uncertainties in estimating the Reynolds stress.展开更多
A water track laser Doppler velocimeter(LDV)is developed with advantages of high update rate,high real-time performance,high concealment,light weight,and small dimensions.The water track LDV measures the advance veloc...A water track laser Doppler velocimeter(LDV)is developed with advantages of high update rate,high real-time performance,high concealment,light weight,and small dimensions.The water track LDV measures the advance velocity of the underwater vehicle with respect to the surrounding water.The experimental results show that the water track LDV has an accuracy of 96.4%when the moving velocity of the vehicle with respect to the ground exceeds 0.25 m/s.Thus,the water track LDV is promising in the application of underwater navigation to aid the strapdown inertial navigation system.展开更多
The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alte...The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alternating current source.The coil is located at a fixed height in such a way that its plane is perpendicular to the gravity vector,which in turn is parallel to the axis of the cylinder.The position of the cylinder can vary in height with respect to the coil.The forced flow of the considered electrically conductive liquid is generated due to the action of the localized electromagnetic force.It is assumed that under the action of the alternating magnetic field,the liquid is heated uniformly,and the resulting heat is quickly absorbed by the forced flow,so that liquid free convection can be neglected.The experiment is carried out using an ultrasonic Doppler anemometer.One transducer is installed in the axially located cylinder sluice and the other transducer is placed in the near-wall region.According to the results,a velocity profile,corresponding to a two-tori flow pattern can be hardly obtained in the low frequency range of the power supply.However,this is possible in the high frequency range.The average velocity profiles depend essentially on the location of the coil relative to the cell.The spectral analysis of velocity signals shows that the amplitude of the velocity pulsations is comparable to the average value of the flow velocity.Such experimental results and their verification through comparison with numerical calculations are intended to support the development of new methods for reducing the intensity of vortex flows during the electromagnetic separation of impurities through an electromagnetic induction mechanism(able to produce an electromotive force that displaces particles).展开更多
A dual-frequency laser Doppler velocimeter implemented by a dual-polarization fiber grating laser is proposed, with the two laser frequencies produced by the two orthogonally polarized laser outputs of the fiber grati...A dual-frequency laser Doppler velocimeter implemented by a dual-polarization fiber grating laser is proposed, with the two laser frequencies produced by the two orthogonally polarized laser outputs of the fiber grating laser. The reflected laser outputs from a moving target experience the Doppler frequency shift, which is shown to be linearly related to the velocity and the beat note frequency difference between the laser outputs and the reflected light. With a digital frequency demodulation scheme, a high sensitivity of 0.64 MHz/（m/s） and a velocity resolution of less than 0.5% of the velocity for velocity measurement are demonstrated, which shows that the proposed laser Doppler velocimeter is capable of measurement of wide range of velocity.展开更多
Particle descent velocities in an annular stripper were measured by a laser Doppler velocimetry(LDV)system.In the radial direction,particle descent velocity was relatively constant in the mid-region of the stripper an...Particle descent velocities in an annular stripper were measured by a laser Doppler velocimetry(LDV)system.In the radial direction,particle descent velocity was relatively constant in the mid-region of the stripper and increased towards the walls on both sides,exhibiting an anti-U-shaped distribution.Particle descent velocity in the radial mid-region increased with the increase of superficial gas velocity,and the maximum in the outer wall region increased significantly with the increase of solid mass flux.Superficial stripping gas velocity had stronger effect on particle velocity distributions near the stripper gas distributor,and such effect weakened with the increase of the distance from the distributor.Local particle velocity and its radial profiles could be adjusted by changing the superficial stripping gas velocity.Empirical formulas were established to describe the relationships between the local particle velocity and cross-sectional averaged velocity based on the effects of operating conditions and measuring positions.The result showed that the predicted data was in good agreement with the experimental value.展开更多
The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air class...The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier＇s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated trader different operating conditions by laser Doppler velocimeter（LDV）, and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage＇s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage＇s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage＇s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage＇s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.展开更多
Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity...Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) x 104 Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090ms for the two-phase flow formed inside the LJ and less than 0.5ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocirneter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.展开更多
A turbulent separation-rcattachment flow in a two-dimensional asymmetrical curved-wall diffuser is studied by a two-dimensional laser doppler velocimeter.The turbulent boundary layer separates on the lower curved wall...A turbulent separation-rcattachment flow in a two-dimensional asymmetrical curved-wall diffuser is studied by a two-dimensional laser doppler velocimeter.The turbulent boundary layer separates on the lower curved wall under strong pressure gradient and then reattaches on a parallel channel.At the inlet of the diffuser,Reynolds number based on the diffuser height is 1.2×10~5 and the velocity is 25.2m/s.The re- sults of experiments are presented and analyzed in new defined streamline-aligned coordinates.The experiment shows that after Transitory Detachment Reynolds shear stress is negative in the near-wall backflow region. Their characteristics are approximately the same as in simple turbulent shear layers near the maximum Reynolds shear stress.A scale is formed using the maximum Reynolds shear stresses.It is found that a Reynolds shear stress similarity exists from separation to reattachment and the Schofield-Perry velocity law ex- ists in the forward shear flow.Both profiles are used in the experimental work that leads to the design of a new eddy-viscosity model.The length scale is taken from that developed by Schofield and Perry.The composite velocity scale is formed by the maximum Reynolds shear stress and the Schofield Perry velocity scale as well as the edge velocity of the boundary layer.The results of these experiments are presented in this paper展开更多
An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to th...An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to the interface between the vegetation and the non-vegetation lanes, and a lateral momentum exchange occurs between the slow- moving water in the former lane and the fast-moving water in the latter lane. Under a uniform flow condition, the three-dimensional with different discharges and water depths are （3D） instantaneous velocities of two cases measured with a 16 MHz acoustic Doppler velocimeter （micro ADV）. The longitudinal variation of the streamwise velocity and the vertical variation of the Reynolds stress are analyzed. A quadrant analysis is carried out to investigate the outward and inward interaction, ejection, and sweep phenomenon caused by the vegetation variation across the channel. The results show that the flow characteristics in the vegetation lane are similar to those in an open channel fully covered with submerged vegetation, and the flow characteristics in the smooth non-vegetation lane are similar to those in a free open channel. For the cases studied here, the width of the mixing region is about 10~ of the channel width, and the mixing region is mainly on the non-vegetation half.展开更多
Experimental campaigns were carried out to extract results from the flow in an open cylindrical channel under precession. The bore or the hydraulic jump is the main concentration. The experimental results are varied;t...Experimental campaigns were carried out to extract results from the flow in an open cylindrical channel under precession. The bore or the hydraulic jump is the main concentration. The experimental results are varied;this includes velocity results and geometrical ones related to the depths, phases, and lengths. For the geometrical ones a Coupled-Charged Device Camera (CCD) is used to extract pictures, those enable us to get quantitative and qualitative results. For the velocity results, Acoustic Doppler Velocimeter (ADV) is used to extract the velocity signals under the bore surface, after analyzing them it turned out that they have Cnoidal form, thus a new BBM model is derived, which is exactly as the one derived by Peregrine (1966), the only difference is the forcing gravity term, this model is solved analytically after omitting this gravity term as it is considered small, and the solution is compared with the real signals with good match. Finally, a new relationship that connects between the conjugate depths after and before the bore is derived which has time-space dependency due to the Centrifugal effect, it was also used and compared with some experimental results.展开更多
This study presents results from a vegetation-induced flow experimental study which investigates 3-D turbulence structure profiles,including Reynolds stress,turbulence intensity and bursting analysis of open channel f...This study presents results from a vegetation-induced flow experimental study which investigates 3-D turbulence structure profiles,including Reynolds stress,turbulence intensity and bursting analysis of open channel flow.Different vegetation densities have been built between the adjacent vegetations,and the flow measurements are taken using acoustic Doppler velocimeter(ADV)at the locations within and downstream of the vegetation panel.Three different tests are conducted,where the first test has compact vegetations,while the second and the third tests have open spaces created by one and two empty vegetation slots within the vegetated field.Observation reveals that over 10%of eddies size is generated within the vegetated zone of compact vegetations as compared with the fewer vegetations.Significant turbulence structures variation is also observed at the points in the non-vegetated row.The findings from burst-cycle analysis show that the sweep and outward interaction events are dominant,where they further increase away from the bed.The effect of vegetation on the turbulent burst cycle is mostly obvious up to approximately two-third of vegetation height where this phenomenon is also observed for most other turbulent structure.展开更多
Laser Doppler vibrometer （LDV） has a potential application prospect in remote sensing. Based on the correlation theories of heterodyne detection, a LDV system with a configuration of all fiber and heterodyne techniq...Laser Doppler vibrometer （LDV） has a potential application prospect in remote sensing. Based on the correlation theories of heterodyne detection, a LDV system with a configuration of all fiber and heterodyne techniques is developed to detect the sound signal through the vibration of glass. Experimental results show that the LDV system has an ability to acquire the real-time speech signal 25 m away through glass. While, the system signal-to-noise ratio （SNR） value decreases with the increase of the glass thickness and the detection distance.展开更多
In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exer...In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exerted on the shear plates by the bottom shear stress in the wave boundary layer. Under immobile bed condition, grains of sand were glued uniformly and tightly onto the shear plate, being prevented from motion with the fluid flow and generation of sand ripples. The distribution of the bottom mean shear stress varying with time was measured by examining the interaction between the shear plate and shear transducers. The relation between the force measured by the shear transducers and its voltage is a linear one. Simultaneous measurements of the bottom velocity were carried out by an Acoustic Doppler Velocimeter （ADV）, while the whole process was completely controlled by computers, bottom shear stress and velocity were synchronously measured. Based on the experimental results, it can be concluded that （1） the friction coefficient groews considerably with the increase of the Reynolds number, （2） the shear stress is a function varying with time and linearly proportional to the velocity. Compared with theoretical results and previous experimental data, it is shown that the experimental method is feasible and effective, A further study on the bed shear stress under regular or irregular waves can be carried out. And applicability to the laboratory studies on the initiation of sediments and the measurement of the shear stress after sediment imigration.展开更多
Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind ...Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind tunnel. The present results clearly indicate thatthe logarithmic velocity profile over the riblets surface is shifted upward with a 30. 9% increasein the thickness of the viscous sublayer. Also a change in the log-law region is found. And themaximum value of streamwise velocity fluctuations is reduced by approximately 17%. The skewness andflatness factors do not show any change besides those in the region of y^+ 【 0. 6 . It is evidentthat the Reynolds shear stress over the riblets is reduced. Further more, in log-law region, theReynolds shear stress has a larger reduction of up to 18%.展开更多
To address the challenges of non-cooperative and remote acoustic detection, an all-fiber laser Doppler vibrometer(LDV) is established. The all-fiber LDV system can offer the advantages of smaller size, lightweight des...To address the challenges of non-cooperative and remote acoustic detection, an all-fiber laser Doppler vibrometer(LDV) is established. The all-fiber LDV system can offer the advantages of smaller size, lightweight design and robust structure, hence it is a better fit for remote speech detection. In order to improve the performance and the efficiency of LDV for long-range hearing, the speech enhancement technology based on optimally modified log-spectral amplitude(OM-LSA) algorithm is used. The experimental results show that the comprehensible speech signals within the range of 150 m can be obtained by the proposed LDV. The signal-to-noise ratio(SNR) and mean opinion score(MOS) of the LDV speech signal can be increased by 100% and 27%, respectively, by using the speech enhancement technology. This all-fiber LDV, which combines the speech enhancement technology, can meet the practical demand in engineering.展开更多
In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm...In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm,8mm and 10mm,respectively.For each diameter of glass rods,four typical cases are considered with various densities and arrangements of glass rods.The flow velocities in the four cases are measured by the 3-D laser Doppler velocimeter(LDV).The water surface slope,the flow velocity,the water head loss,the vegetation drag force and the hydraulic slope are calculated,analyzed and discussed.The horizontal,vertical and total vegetation densities in the vegetation area are defined and the relationship between these physical parameters and the water surface slope are studied.The head loss and the hydraulic slope in the vegetation area are also calculated,compared and analyzed.It is indicated that the water surface slope and velocity,the head loss and the hydraulic slope in the vegetation area have a close relationship with the arrangement,the density,and the plant diameter of the vegetation.展开更多
A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenome...A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenomenon was verified simultaneously in this paper by laser Doppler velocimeter measurement and numerical analyses with volume of fluid approach coupled with a large eddy simulation turbulent model.The general agreement of mean velocities between numerical predictions and experimental results in self-similar region is good for two cases:Reynolds numbers 2090 and 2970,which correspond to the stable impinging jet and flapping jet.Results show that the flapping jet is a new flow pattern for submerged turbulent plane jets with characteristic flapping frequency,and that the decay of the mean velocity along the jet centerline is considerably faster than that of the stable impinging state.展开更多
The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the lamina...The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the laminar case where the Reynolds number ReA is much smaller than the transition value. The theoretical analysis of the Stokes layer in oscillating flow over a narrow channel was made first. Then Laser Doppler Velocimeter （LDV） was employed to measure the Stokes boundary layer above an oscillating flat plate and inside the oscillating narrow channel at various ReH numbers. At the same time, the phase angle difference along the vertical direction in both analysis and experiment were provided. The good agreements are shown between the measured results and the theoretical solution.展开更多
基金Supported by the Natural Science Foundation of Inner Mongolia (No.200408020715).
文摘The spatial structure of the velocity field in a stirred vessel with water has been measured and analyzed using the laser Doppler velocimeter technique, with the immersing depth and agitation speed of the impeller re-maining approximately constant. The experimental results were provided such as the mean velocity field, fluctuat-ing velocities, turbulent kinetic energy, Reynolds shear stress and time series of the velocity in the stirred tank. These results probably provided the valuable basis to further optimize and enlarge the stirred tank in the industrial process.
基金the National Natural Science Foundation of China (50221903, 50309007)
文摘Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al＇s （2004） relationship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity to the maximum velocity, ranges from 0.2 to 0.6. Kang et al＇s （2004） relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al＇s relationship.
基金The National Key Research and Development Program of China under contract No.2017YFC1404000the Basic Scientific Fund for National Public Research Institutes of China under contract No.2018S03the National Natural Science Foundation of China under contract Nos 41776038 and 41821004
文摘Oceanic turbulence measurements made by an acoustic Doppler velocimeter(ADV)suffer from noise that potentially affects the estimates of turbulence statistics.This study examines the abilities of Kalman filtering and autoregressive moving average models to eliminate noise in ADV velocity datasets of laboratory experiments and offshore observations.Results show that the two methods have similar performance in ADV de-noising,and both effectively reduce noise in ADV velocities,even in cases of high noise.They eliminate the noise floor at high frequencies of the velocity spectra,leading to a longer range that effectively fits the Kolmogorov-5/3 slope at midrange frequencies.After de-noising adopting the two methods,the values of the mean velocity are almost unchanged,while the root-mean-square horizontal velocities and thus turbulent kinetic energy decrease appreciably in these experiments.The Reynolds stress is also affected by high noise levels,and de-noising thus reduces uncertainties in estimating the Reynolds stress.
基金supported by the Major Basic Autonomous Research Project of College of Advanced Interdisciplinary Studies,National University of Defense Technology,China(No.ZDJC19-12)the Natural Science Foundation of Hunan Province,China(No.2021JJ30782)。
文摘A water track laser Doppler velocimeter(LDV)is developed with advantages of high update rate,high real-time performance,high concealment,light weight,and small dimensions.The water track LDV measures the advance velocity of the underwater vehicle with respect to the surrounding water.The experimental results show that the water track LDV has an accuracy of 96.4%when the moving velocity of the vehicle with respect to the ground exceeds 0.25 m/s.Thus,the water track LDV is promising in the application of underwater navigation to aid the strapdown inertial navigation system.
基金supported by Russian Science Foundation Grant RSF-22-19-20106。
文摘The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alternating current source.The coil is located at a fixed height in such a way that its plane is perpendicular to the gravity vector,which in turn is parallel to the axis of the cylinder.The position of the cylinder can vary in height with respect to the coil.The forced flow of the considered electrically conductive liquid is generated due to the action of the localized electromagnetic force.It is assumed that under the action of the alternating magnetic field,the liquid is heated uniformly,and the resulting heat is quickly absorbed by the forced flow,so that liquid free convection can be neglected.The experiment is carried out using an ultrasonic Doppler anemometer.One transducer is installed in the axially located cylinder sluice and the other transducer is placed in the near-wall region.According to the results,a velocity profile,corresponding to a two-tori flow pattern can be hardly obtained in the low frequency range of the power supply.However,this is possible in the high frequency range.The average velocity profiles depend essentially on the location of the coil relative to the cell.The spectral analysis of velocity signals shows that the amplitude of the velocity pulsations is comparable to the average value of the flow velocity.Such experimental results and their verification through comparison with numerical calculations are intended to support the development of new methods for reducing the intensity of vortex flows during the electromagnetic separation of impurities through an electromagnetic induction mechanism(able to produce an electromotive force that displaces particles).
基金supported by the National Natural Science Foundation of China under Grant Nos.11474133,61235005,and 61307100
文摘A dual-frequency laser Doppler velocimeter implemented by a dual-polarization fiber grating laser is proposed, with the two laser frequencies produced by the two orthogonally polarized laser outputs of the fiber grating laser. The reflected laser outputs from a moving target experience the Doppler frequency shift, which is shown to be linearly related to the velocity and the beat note frequency difference between the laser outputs and the reflected light. With a digital frequency demodulation scheme, a high sensitivity of 0.64 MHz/（m/s） and a velocity resolution of less than 0.5% of the velocity for velocity measurement are demonstrated, which shows that the proposed laser Doppler velocimeter is capable of measurement of wide range of velocity.
基金Supported by the National High-Tech R&D Program of China(2011AA05A204)the Fundamental Research Funds for the Central Universities(222201817013).
文摘Particle descent velocities in an annular stripper were measured by a laser Doppler velocimetry(LDV)system.In the radial direction,particle descent velocity was relatively constant in the mid-region of the stripper and increased towards the walls on both sides,exhibiting an anti-U-shaped distribution.Particle descent velocity in the radial mid-region increased with the increase of superficial gas velocity,and the maximum in the outer wall region increased significantly with the increase of solid mass flux.Superficial stripping gas velocity had stronger effect on particle velocity distributions near the stripper gas distributor,and such effect weakened with the increase of the distance from the distributor.Local particle velocity and its radial profiles could be adjusted by changing the superficial stripping gas velocity.Empirical formulas were established to describe the relationships between the local particle velocity and cross-sectional averaged velocity based on the effects of operating conditions and measuring positions.The result showed that the predicted data was in good agreement with the experimental value.
基金supported by National Natural Science Foundation of China (Grant No. 50474035)
文摘The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier＇s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated trader different operating conditions by laser Doppler velocimeter（LDV）, and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage＇s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage＇s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage＇s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage＇s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.
基金Supported by the National Natural Science Foundation of China (No. 29876022) and Grant of State Key Laboratory of High Speed Hydrodynamics (No. 2007).
文摘Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) x 104 Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090ms for the two-phase flow formed inside the LJ and less than 0.5ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocirneter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.
文摘A turbulent separation-rcattachment flow in a two-dimensional asymmetrical curved-wall diffuser is studied by a two-dimensional laser doppler velocimeter.The turbulent boundary layer separates on the lower curved wall under strong pressure gradient and then reattaches on a parallel channel.At the inlet of the diffuser,Reynolds number based on the diffuser height is 1.2×10~5 and the velocity is 25.2m/s.The re- sults of experiments are presented and analyzed in new defined streamline-aligned coordinates.The experiment shows that after Transitory Detachment Reynolds shear stress is negative in the near-wall backflow region. Their characteristics are approximately the same as in simple turbulent shear layers near the maximum Reynolds shear stress.A scale is formed using the maximum Reynolds shear stresses.It is found that a Reynolds shear stress similarity exists from separation to reattachment and the Schofield-Perry velocity law ex- ists in the forward shear flow.Both profiles are used in the experimental work that leads to the design of a new eddy-viscosity model.The length scale is taken from that developed by Schofield and Perry.The composite velocity scale is formed by the maximum Reynolds shear stress and the Schofield Perry velocity scale as well as the edge velocity of the boundary layer.The results of these experiments are presented in this paper
基金supported by the National Natural Science Foundation of China(Nos.51379154,51479145,and 51439007)the Program for New Century Excellent Talents in University of China(No.NCET-11-0393)
文摘An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to the interface between the vegetation and the non-vegetation lanes, and a lateral momentum exchange occurs between the slow- moving water in the former lane and the fast-moving water in the latter lane. Under a uniform flow condition, the three-dimensional with different discharges and water depths are （3D） instantaneous velocities of two cases measured with a 16 MHz acoustic Doppler velocimeter （micro ADV）. The longitudinal variation of the streamwise velocity and the vertical variation of the Reynolds stress are analyzed. A quadrant analysis is carried out to investigate the outward and inward interaction, ejection, and sweep phenomenon caused by the vegetation variation across the channel. The results show that the flow characteristics in the vegetation lane are similar to those in an open channel fully covered with submerged vegetation, and the flow characteristics in the smooth non-vegetation lane are similar to those in a free open channel. For the cases studied here, the width of the mixing region is about 10~ of the channel width, and the mixing region is mainly on the non-vegetation half.
文摘Experimental campaigns were carried out to extract results from the flow in an open cylindrical channel under precession. The bore or the hydraulic jump is the main concentration. The experimental results are varied;this includes velocity results and geometrical ones related to the depths, phases, and lengths. For the geometrical ones a Coupled-Charged Device Camera (CCD) is used to extract pictures, those enable us to get quantitative and qualitative results. For the velocity results, Acoustic Doppler Velocimeter (ADV) is used to extract the velocity signals under the bore surface, after analyzing them it turned out that they have Cnoidal form, thus a new BBM model is derived, which is exactly as the one derived by Peregrine (1966), the only difference is the forcing gravity term, this model is solved analytically after omitting this gravity term as it is considered small, and the solution is compared with the real signals with good match. Finally, a new relationship that connects between the conjugate depths after and before the bore is derived which has time-space dependency due to the Centrifugal effect, it was also used and compared with some experimental results.
文摘This study presents results from a vegetation-induced flow experimental study which investigates 3-D turbulence structure profiles,including Reynolds stress,turbulence intensity and bursting analysis of open channel flow.Different vegetation densities have been built between the adjacent vegetations,and the flow measurements are taken using acoustic Doppler velocimeter(ADV)at the locations within and downstream of the vegetation panel.Three different tests are conducted,where the first test has compact vegetations,while the second and the third tests have open spaces created by one and two empty vegetation slots within the vegetated field.Observation reveals that over 10%of eddies size is generated within the vegetated zone of compact vegetations as compared with the fewer vegetations.Significant turbulence structures variation is also observed at the points in the non-vegetated row.The findings from burst-cycle analysis show that the sweep and outward interaction events are dominant,where they further increase away from the bed.The effect of vegetation on the turbulent burst cycle is mostly obvious up to approximately two-third of vegetation height where this phenomenon is also observed for most other turbulent structure.
文摘Laser Doppler vibrometer （LDV） has a potential application prospect in remote sensing. Based on the correlation theories of heterodyne detection, a LDV system with a configuration of all fiber and heterodyne techniques is developed to detect the sound signal through the vibration of glass. Experimental results show that the LDV system has an ability to acquire the real-time speech signal 25 m away through glass. While, the system signal-to-noise ratio （SNR） value decreases with the increase of the glass thickness and the detection distance.
基金National Natural Science Foundation for Distinguished Young Scholars of China (Grant No. 40428001).
文摘In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exerted on the shear plates by the bottom shear stress in the wave boundary layer. Under immobile bed condition, grains of sand were glued uniformly and tightly onto the shear plate, being prevented from motion with the fluid flow and generation of sand ripples. The distribution of the bottom mean shear stress varying with time was measured by examining the interaction between the shear plate and shear transducers. The relation between the force measured by the shear transducers and its voltage is a linear one. Simultaneous measurements of the bottom velocity were carried out by an Acoustic Doppler Velocimeter （ADV）, while the whole process was completely controlled by computers, bottom shear stress and velocity were synchronously measured. Based on the experimental results, it can be concluded that （1） the friction coefficient groews considerably with the increase of the Reynolds number, （2） the shear stress is a function varying with time and linearly proportional to the velocity. Compared with theoretical results and previous experimental data, it is shown that the experimental method is feasible and effective, A further study on the bed shear stress under regular or irregular waves can be carried out. And applicability to the laboratory studies on the initiation of sediments and the measurement of the shear stress after sediment imigration.
文摘Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind tunnel. The present results clearly indicate thatthe logarithmic velocity profile over the riblets surface is shifted upward with a 30. 9% increasein the thickness of the viscous sublayer. Also a change in the log-law region is found. And themaximum value of streamwise velocity fluctuations is reduced by approximately 17%. The skewness andflatness factors do not show any change besides those in the region of y^+ 【 0. 6 . It is evidentthat the Reynolds shear stress over the riblets is reduced. Further more, in log-law region, theReynolds shear stress has a larger reduction of up to 18%.
基金supported by the National Natural Science Foundation of China(No.61205143)
文摘To address the challenges of non-cooperative and remote acoustic detection, an all-fiber laser Doppler vibrometer(LDV) is established. The all-fiber LDV system can offer the advantages of smaller size, lightweight design and robust structure, hence it is a better fit for remote speech detection. In order to improve the performance and the efficiency of LDV for long-range hearing, the speech enhancement technology based on optimally modified log-spectral amplitude(OM-LSA) algorithm is used. The experimental results show that the comprehensible speech signals within the range of 150 m can be obtained by the proposed LDV. The signal-to-noise ratio(SNR) and mean opinion score(MOS) of the LDV speech signal can be increased by 100% and 27%, respectively, by using the speech enhancement technology. This all-fiber LDV, which combines the speech enhancement technology, can meet the practical demand in engineering.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11861003,11761005).
文摘In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm,8mm and 10mm,respectively.For each diameter of glass rods,four typical cases are considered with various densities and arrangements of glass rods.The flow velocities in the four cases are measured by the 3-D laser Doppler velocimeter(LDV).The water surface slope,the flow velocity,the water head loss,the vegetation drag force and the hydraulic slope are calculated,analyzed and discussed.The horizontal,vertical and total vegetation densities in the vegetation area are defined and the relationship between these physical parameters and the water surface slope are studied.The head loss and the hydraulic slope in the vegetation area are also calculated,compared and analyzed.It is indicated that the water surface slope and velocity,the head loss and the hydraulic slope in the vegetation area have a close relationship with the arrangement,the density,and the plant diameter of the vegetation.
基金supported by the National Natural Science Foundation of China(Grant No.10472046)the Priority Academic Program Development of Jiangsu Higher Education Institutions,grants from the Postgraduate Research and Innovation Project of Jiangsu Province(Grant No.CX08B_035Z)PhD Thesis Innovation and Excellence Fund of Nanjing University of Aeronautics&Astronautics(Grant No.BCXJ08-01)
文摘A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenomenon was verified simultaneously in this paper by laser Doppler velocimeter measurement and numerical analyses with volume of fluid approach coupled with a large eddy simulation turbulent model.The general agreement of mean velocities between numerical predictions and experimental results in self-similar region is good for two cases:Reynolds numbers 2090 and 2970,which correspond to the stable impinging jet and flapping jet.Results show that the flapping jet is a new flow pattern for submerged turbulent plane jets with characteristic flapping frequency,and that the decay of the mean velocity along the jet centerline is considerably faster than that of the stable impinging state.
基金Project supported by the Hongkong SAR Government under the RGC (Grant No. 6165/98E)the RIG (Grant No. R195/96.EG15)supported by the HKUST (Grant No. 6254/02E).
文摘The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the laminar case where the Reynolds number ReA is much smaller than the transition value. The theoretical analysis of the Stokes layer in oscillating flow over a narrow channel was made first. Then Laser Doppler Velocimeter （LDV） was employed to measure the Stokes boundary layer above an oscillating flat plate and inside the oscillating narrow channel at various ReH numbers. At the same time, the phase angle difference along the vertical direction in both analysis and experiment were provided. The good agreements are shown between the measured results and the theoretical solution.
