To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure di...To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure distribution on stator blades is measured under the conditions of different axial spacing between the rotor and the stator, different rotating speeds and an extensive range of the mass flow. Amplitudes and frequencies of aerodynamic forces are analyzed by the Fourier transform. Experimental results show that under the effect of the rotor wake, the dominant frequencies of pressure fluctuations on stator blades are the rotor blade passing frequency （BPF） and its harmonics. The higher harmonics of the rotor BPF in the fore part of the suction side are more prominent than that in the other parts of the stator blade. Otherwise, fluctuations of the pressure and the aerodynamic force on stator blades vary with the mass flow, the rotating speed and the axial spacing between the rotor and the stator.展开更多
The turbine in an LH2/LOX rocket engine is designed as a two-stage supersonic partialadmission turbine. Three-dimensional steady and unsteady simulations were conducted to analyze turbine performance and aerodynamic f...The turbine in an LH2/LOX rocket engine is designed as a two-stage supersonic partialadmission turbine. Three-dimensional steady and unsteady simulations were conducted to analyze turbine performance and aerodynamic forces on rotor blades. Different configurations were employed to investigate the effects of the axial gap and nozzle distribution on the predicted performance and aerodynamic forces. Rotor blades experience unsteady aerodynamic forces because of the partial admission. Aerodynamic forces show periodicity in the admission region, and are close to zero after leaving the admission region. The unsteady forces in frequency domain indicate that components exist in a wide frequency region, and the admission passing frequency is dominant.Those multiples of the rotational frequency which are multiples of the nozzle number in a fulladmission turbine are notable components. Results show that the turbine efficiency decreases as the axial gap between nozzles and the 1 st stage rotor（rotor 1） increases. Fluctuation of the circumferential aerodynamic force on rotor 1 blades decreases with the axial gap increasing. The turbine efficiency decreases as the circumferential spacing between nozzles increases. Fluctuations of the circumferential and axial aerodynamic forces increase as the circumferential spacing increases. As for the non-equidistant nozzle distribution, it produces similar turbine performance and amplitudefrequency characteristics of forces to those of the normal configuration, when the mean spacing is equal to that of the normal case.展开更多
Effects of unsteady deformation of a＇flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flappi...Effects of unsteady deformation of a＇flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flapping wing are not much affected by considerable twist, but affected by camber deformation. The effect of combined camber and twist deformation is similar to that of camber deformation. With a deformation of 6% camber and 20% twist （typical values observed for wings of many insects）, lift is increased by 10% - 20% and lift-to-drag ratio by around 10% compared with the case of a rigid fiat-plate wing. As a result, the deformation can increase the maximum lift coefficient of an insect, and reduce its power requirement for flight. For example, for a hovering bumblebee with dynamically deforming wings （6% camber and 20% twist）, aerodynamic power required is reduced by about 16% compared with the case of rigid wings.展开更多
An aerodynamic force and moment measurement was conducted in JF12 long-testduration detonation-driven shock tunnel of Institute of Mechanics,Chinese Academy of Sciences.The test duration of JF12 is 100–130 ms.The nom...An aerodynamic force and moment measurement was conducted in JF12 long-testduration detonation-driven shock tunnel of Institute of Mechanics,Chinese Academy of Sciences.The test duration of JF12 is 100–130 ms.The nominal Mach number is 7.0 and the exit diameter of the contoured nozzle is 2.5 m.The total enthalpy is 2.5 MJ/kg which duplicates the hypersonic flight conditions of Mach number 7.0 at 35 km altitude.The test model is the standard aerodynamic force model of 10° half-angle sharp cone.The length of the test model is 1500 mm and the weight is 57 kg.The aerodynamic forces were measured with a six-component strain balance.The angles of attack were set to be à5°,0°,5°,10° and 14°,respectively.The experimental results show that in the 100–130 ms test duration,the signals of strain balance have 3–4 complete vibration cycles.So,the aerodynamic forces and moments can be obtained directly by averaging the signals of balance without acceleration compensation.The force measurement error of repeatability of JF12 is less than 2%.The aerodynamic force coefficients of JF12 are in good agreement with those of conventional hypersonic wind tunnels.For this test model at Mach number 7.0 and total enthalpy of 2.5 MJ/kg,the real-gas effects on aerodynamic force characteristics are not very evident.展开更多
Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, un...Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, under the combined action of aerodynamic load and piezoelectric excitation, is introduced. Two-degree of freedom(DOF)nonlinear dynamic models for the time-varying coefficients describing the transverse vibration of the deploying laminate under the combined actions of a first-order aerodynamic force and piezoelectric excitation were obtained by selecting a suitable time-dependent modal function satisfying the displacement boundary conditions and applying second-order discretization using the Galerkin method. Using a numerical method, the time history curves of the deploying laminate were obtained, and its nonlinear dynamic characteristics,including extension speed and different piezoelectric excitations, were studied. The results suggest that the piezoelectric excitation has a clear effect on the change of the nonlinear dynamic characteristics of such piezoelectric laminated composite plates. The nonlinear vibration of the deploying cantilevered laminate can be effectively suppressed by choosing a suitable voltage and polarity.展开更多
As a basic principle in classical mechanics,the Galilean invariance states that the force is the same in all inertial frames of reference.But this principle has not been properly addressed by most unsteady aerodynamic...As a basic principle in classical mechanics,the Galilean invariance states that the force is the same in all inertial frames of reference.But this principle has not been properly addressed by most unsteady aerodynamic force theories,if the partial force contributed by a local flow structure is to be evaluated.In this note,we discuss the Galilean-invariance conditions of the partial force for several typical theories and numerically test what would happen if these conditions do not hold.展开更多
Based on Reynolds average Navier-Storkes equations of viscous incompressible fluid and k-ε two equations turbulent model, the aerodynamic forces of high-speed magnetically-levitated （maglev） trains in transverse an...Based on Reynolds average Navier-Storkes equations of viscous incompressible fluid and k-ε two equations turbulent model, the aerodynamic forces of high-speed magnetically-levitated （maglev） trains in transverse and longitudinal wind are investigated by finite volume method. Near 80 calculation cases for 2D transverse wind fields and 20 cases for 3D longitudinal wind fields are analyzed. The aerodynamic side force, yawing, drag, lift and pitching moment for different types of maglev trains and a wheel/rail train are compared under the different wind speeds. The types of maglev train models for 2D transverse wind analysis included electromagnetic suspension （EMS） type train, electrodynamic suspension （EDS） type train, EMS type train with shelter wind wall in one side or two sides of guideway and the walls, which are in different height or/and different distances from train body. The situation of maglev train running on viaduct is also analyzed. For 3D longitudinal wind field analysis, the model with different sizes of air clearances beneath maglev train is examined for the different speeds. Calculation result shows that： ① Different transverse effects are shown in different types of maglev trains. ② The shelter wind wall can fairly decrease the transverse effect on the maglev trains. ③ When the shelter wall height is 2 m, there is minimum side force on the train. When the shelter wall height is 2.5 m, there is minimum yawing moment on the train. ④ When the distance between inside surfaces of the walls and center of guideway is 4.0 m, there is minimum transverse influence on the train. ⑤ The size of air clearance beneath train body has a small influence on aerodynamic drag of the train, but has a fairly large effect on aerodynamic lift and pitching moment of the train. ⑥ The calculating lift and pitching moment for maglev train models are minus values.展开更多
An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge w...An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667.展开更多
Physical monotonicity is a pervasive phenomenon in the aerodynamic characteristics of aircraft,where the aerodynamic lift consistently increases with the angle of attack within the stalling range.Existing machine lear...Physical monotonicity is a pervasive phenomenon in the aerodynamic characteristics of aircraft,where the aerodynamic lift consistently increases with the angle of attack within the stalling range.Existing machine learning models for aerodynamic predic-tions often overlook this monotonicity,resulting in poor interpretability and credibility.To address this issue,we introduce a monotonic model,the Deep Lattice Network,which integrates the monotonicity constraint of the lift coefficient into machine learn-ing based aerodynamic prediction framework.In this paper,we propose a novel deep learning model,Deep Lattice Cross Network,which aims to rapidly predict aerody-namic forces with high precision while ensuring monotonic constraints.Multi-Task Learning method is utilized to simultaneously predict both lift and drag coefficients,thereby enhancing the efficiency of the model.To optimize the training process and minimize costs,we adopt a unique two-phase deep network training strategy.Based on computational fluid dynamics simulation datasets of a morphing aircraft,the model is trained,and the efficacy of the model is tested by two interpolation and two extrapolation datasets.The results show a remarkable alignment with com-putational fluid dynamics outcomes across all test scenarios.Extended testing across a wider range of attack angles further highlights the superiority of the Deep Lat-tice Cross Network in upholding monotonicity.Incorporating monotonicity constraints not only improves predictive accuracy of the model but also greatly enhances its physi-cal interpretability,which is crucial for advancing the development of more depend-able aerodynamic prediction models.展开更多
The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation...The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation technology was used to measure the dynamic deformation of the wing.The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects.The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility.The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell.The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution.The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces.In addition,the total forces,i.e.,the sum of the CFD result and inertial result,are compared with the experimental results,and an overall good agreement is obtained.展开更多
The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing ...The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing loads are studied in the longitudinal and lateral maneuver states. The flight loads of the wing fixed at the root are calculated at different angles of attack. The aileron efficiency with respect to the dynamic pressures and aileron deflections are also studied. The results indicate that the flight loads of the wings vary nonlinearly with the angle of attack and dynamic pressure. Due to the high-lift aerofoil, elastic components are a large portion of the wing loads, especially for small angles of attack and high dynamic pressure condi-tions. The aileron efficiency is significantly affected by aileron deflections, dynamic pressures and angles of attack when the nonlinear experimental aerodynamic forces are used for calculation. In states with high dynamic pressures and large aileron deflections, aileron reversal can occur. The aileron deflection and angle of attack have a nonlinear effect on the aileron efficiency. An efficient method for analyzing the flight loads and structural design of high-aspect-ratio wings is derived in this study, and the analysis can provide insight into the distribution of flight loads for high-aspect-ratio wings.展开更多
Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The ...Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element(FE) model through surface effect elements prior to conducting forced response calculations.Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases,time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant.Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation(FFT).Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.展开更多
An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to bla...An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and ParaInetric Polynomial Method. After getting the solution of the unsteady flow field, the work done by the unsteay aerody natnic force acting on the blade can be obtained. The negative or positive work is the criterion of the aeroelastic stability Numerical results indicate that there are instabilities of the torsional vibration in some boency bands.展开更多
A simplified theoretical method based on the quasi-steady wing theory wasproposed to study the unsteady aerodynamic forces acting on an airfoil flying in non-uniform flow.Comparison between the theoretical results and...A simplified theoretical method based on the quasi-steady wing theory wasproposed to study the unsteady aerodynamic forces acting on an airfoil flying in non-uniform flow.Comparison between the theoretical results and the numerical results based on nonlinear theory wasmade. It shows that the simplified theory is a good approximation for the investigation of theaerodynamic characteristics of an airfoil flying above sea-waves. From on the simplified theory itis also found that an airfoil can get thrust from a wave-disturbed airflow and thus the total dragis reduced. And the relationship among the thrust, the flying altitude, the flying speed and thewave parameters was worked out and discussed.展开更多
Pressure-sensitive paint(PSP) technique was employed to experimentally investigate the aerodynamic force effect of vacuum plume in this study. The characterization and comparison for two types of PSP were firstly cond...Pressure-sensitive paint(PSP) technique was employed to experimentally investigate the aerodynamic force effect of vacuum plume in this study. The characterization and comparison for two types of PSP were firstly conducted in an air pressure range from0.05 to 5000 Pa. The PSPs were prepared using PtTFPP as the active dye and different binders, i.e., polymer-ceramic(PC) and poly(1-trimethylsilyl-1-propyne) [poly(TMSP)]. The static calibrations showed that PtTFPP/poly(TMSP) had a higher pressure sensitivity and a lower temperature dependency compared to PtTFPP/PC in this pressure range. The pressure distributions of a single and two interacting plumes impinging onto a flat plate model were measured using PSP technique. The experimental data were compared to numerical solutions that combined both the computed fluid dynamics(CFD) and direct simulation Monte Carlo(DSMC) methods. Remarkable agreements were achieved, demonstrating the feasibility and accuracy of the numerical approach.Finally, the aerodynamic force effect of interacting plumes at different separation distances was investigated numerically.展开更多
Metal foil strain gauges remain the state-of-the-art transducers for wind tunnel balances.While strain gauge technology is very mature,piezoresistive semiconductor sensors offer alternatives that are worth exploring t...Metal foil strain gauges remain the state-of-the-art transducers for wind tunnel balances.While strain gauge technology is very mature,piezoresistive semiconductor sensors offer alternatives that are worth exploring to assess their unique benefits,such as better strain resolution and accuracy,which would enable balances to be designed with higher factors to safety and hence longer fatigue lifetimes.A new three-component balance,based on temperature compensated semiconductor strain gauges,is designed,calibrated and tested in a hypersonic low density wind tunnel.The static accuracy of the semiconductor balance is calibrated better than 0.3%FS,and the dynamic accuracy of the balance is established using a HB-2 standard model in a Mach 12 hypersonic flow.Good experimental repeatability is confirmed to be better than 2.5%FS,and the effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with computational fluid dynamics simulations,as well as reference wind tunnel results under similar conditions.展开更多
The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trains...The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trainspeed in the tunnel is extremely important.In this study,this problem is investigated numerically in the frameworkof the standard k-εtwo-equation turbulence model.In particular,an eight-car urban rail train passingthrough a tunnel at different speeds(140,160,180 and 200 km/h)is considered.The results show that the maximumaerodynamic drag of the head and tail cars is most affected by the running speed.The pressure at selectedmeasuring points on the windward side of the head car is very high,and the negative pressure at the side windowof the driver’s cab of the tail car is also very large.From the head car to the tail car,the pressure at the same heightgradually decreases.The positive pressure peak at the head car and the negative pressure peak at the tail car aregreatly affected by the speed.展开更多
Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard,...Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard, the aerodynamic uplift forces of pantographs with baffles are numerically investigated, and an optimization method to determine the baffle angle is proposed. First, the error between the aerodynamic resistances of the pantograph obtained by numerical simulation and wind tunnel test is less than 5%, which indicates the accuracy of the numerical simulation method. Second, the original pantograph and pantographs equipped with three different baffles are numerically simulated to obtain the aerodynamic forces and moments of the pantograph components.Three different angles for the baffles are-17°, 0° and 17°.Then the multibody simulation is used to calculate the aerodynamic uplift force of the pantograph, and the optimal range for the baffle angle is determined. Results show that the lift force of the baffle increases with the increment of the angle in the knuckle-downstream condition, whereas the lift force of the baffle decreases with the increment of the angle in the knuckle-upstream condition. According to the results of the aerodynamic uplift force, the optimal angle of the baffle is determined to be 4.75° when the running speed is 350 km/h, and pantograph–catenary contact forces are 128.89 N and 129.15 N under the knuckledownstream and knuckle-upstream operating conditions,respectively, which are almost equal and both meet the requirements of the standard EN50367:2012.展开更多
文摘To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure distribution on stator blades is measured under the conditions of different axial spacing between the rotor and the stator, different rotating speeds and an extensive range of the mass flow. Amplitudes and frequencies of aerodynamic forces are analyzed by the Fourier transform. Experimental results show that under the effect of the rotor wake, the dominant frequencies of pressure fluctuations on stator blades are the rotor blade passing frequency （BPF） and its harmonics. The higher harmonics of the rotor BPF in the fore part of the suction side are more prominent than that in the other parts of the stator blade. Otherwise, fluctuations of the pressure and the aerodynamic force on stator blades vary with the mass flow, the rotating speed and the axial spacing between the rotor and the stator.
文摘The turbine in an LH2/LOX rocket engine is designed as a two-stage supersonic partialadmission turbine. Three-dimensional steady and unsteady simulations were conducted to analyze turbine performance and aerodynamic forces on rotor blades. Different configurations were employed to investigate the effects of the axial gap and nozzle distribution on the predicted performance and aerodynamic forces. Rotor blades experience unsteady aerodynamic forces because of the partial admission. Aerodynamic forces show periodicity in the admission region, and are close to zero after leaving the admission region. The unsteady forces in frequency domain indicate that components exist in a wide frequency region, and the admission passing frequency is dominant.Those multiples of the rotational frequency which are multiples of the nozzle number in a fulladmission turbine are notable components. Results show that the turbine efficiency decreases as the axial gap between nozzles and the 1 st stage rotor（rotor 1） increases. Fluctuation of the circumferential aerodynamic force on rotor 1 blades decreases with the axial gap increasing. The turbine efficiency decreases as the circumferential spacing between nozzles increases. Fluctuations of the circumferential and axial aerodynamic forces increase as the circumferential spacing increases. As for the non-equidistant nozzle distribution, it produces similar turbine performance and amplitudefrequency characteristics of forces to those of the normal configuration, when the mean spacing is equal to that of the normal case.
基金Project supported by the"Fan Zhou"Youth Science Fund of Beijing University of Aeronautics and Astronautics (No.20070404)
文摘Effects of unsteady deformation of a＇flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flapping wing are not much affected by considerable twist, but affected by camber deformation. The effect of combined camber and twist deformation is similar to that of camber deformation. With a deformation of 6% camber and 20% twist （typical values observed for wings of many insects）, lift is increased by 10% - 20% and lift-to-drag ratio by around 10% compared with the case of a rigid fiat-plate wing. As a result, the deformation can increase the maximum lift coefficient of an insect, and reduce its power requirement for flight. For example, for a hovering bumblebee with dynamically deforming wings （6% camber and 20% twist）, aerodynamic power required is reduced by about 16% compared with the case of rigid wings.
基金supported by the National Natural Science Foundation of China(Nos.11672312,11532014)
文摘An aerodynamic force and moment measurement was conducted in JF12 long-testduration detonation-driven shock tunnel of Institute of Mechanics,Chinese Academy of Sciences.The test duration of JF12 is 100–130 ms.The nominal Mach number is 7.0 and the exit diameter of the contoured nozzle is 2.5 m.The total enthalpy is 2.5 MJ/kg which duplicates the hypersonic flight conditions of Mach number 7.0 at 35 km altitude.The test model is the standard aerodynamic force model of 10° half-angle sharp cone.The length of the test model is 1500 mm and the weight is 57 kg.The aerodynamic forces were measured with a six-component strain balance.The angles of attack were set to be à5°,0°,5°,10° and 14°,respectively.The experimental results show that in the 100–130 ms test duration,the signals of strain balance have 3–4 complete vibration cycles.So,the aerodynamic forces and moments can be obtained directly by averaging the signals of balance without acceleration compensation.The force measurement error of repeatability of JF12 is less than 2%.The aerodynamic force coefficients of JF12 are in good agreement with those of conventional hypersonic wind tunnels.For this test model at Mach number 7.0 and total enthalpy of 2.5 MJ/kg,the real-gas effects on aerodynamic force characteristics are not very evident.
基金supported by the National Natural Science Foundation of China (Grants 11402126, 11502122, and 11290152)the Scientific Research Foundation of the Inner Mongolia University of Technology (Grant ZD201410)
文摘Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, under the combined action of aerodynamic load and piezoelectric excitation, is introduced. Two-degree of freedom(DOF)nonlinear dynamic models for the time-varying coefficients describing the transverse vibration of the deploying laminate under the combined actions of a first-order aerodynamic force and piezoelectric excitation were obtained by selecting a suitable time-dependent modal function satisfying the displacement boundary conditions and applying second-order discretization using the Galerkin method. Using a numerical method, the time history curves of the deploying laminate were obtained, and its nonlinear dynamic characteristics,including extension speed and different piezoelectric excitations, were studied. The results suggest that the piezoelectric excitation has a clear effect on the change of the nonlinear dynamic characteristics of such piezoelectric laminated composite plates. The nonlinear vibration of the deploying cantilevered laminate can be effectively suppressed by choosing a suitable voltage and polarity.
基金This work was supported by the National Natural Science Foundation of China(Grant 11472016).
文摘As a basic principle in classical mechanics,the Galilean invariance states that the force is the same in all inertial frames of reference.But this principle has not been properly addressed by most unsteady aerodynamic force theories,if the partial force contributed by a local flow structure is to be evaluated.In this note,we discuss the Galilean-invariance conditions of the partial force for several typical theories and numerically test what would happen if these conditions do not hold.
基金This project is supported by National Natural Science Foundation of China(No.59975078).
文摘Based on Reynolds average Navier-Storkes equations of viscous incompressible fluid and k-ε two equations turbulent model, the aerodynamic forces of high-speed magnetically-levitated （maglev） trains in transverse and longitudinal wind are investigated by finite volume method. Near 80 calculation cases for 2D transverse wind fields and 20 cases for 3D longitudinal wind fields are analyzed. The aerodynamic side force, yawing, drag, lift and pitching moment for different types of maglev trains and a wheel/rail train are compared under the different wind speeds. The types of maglev train models for 2D transverse wind analysis included electromagnetic suspension （EMS） type train, electrodynamic suspension （EDS） type train, EMS type train with shelter wind wall in one side or two sides of guideway and the walls, which are in different height or/and different distances from train body. The situation of maglev train running on viaduct is also analyzed. For 3D longitudinal wind field analysis, the model with different sizes of air clearances beneath maglev train is examined for the different speeds. Calculation result shows that： ① Different transverse effects are shown in different types of maglev trains. ② The shelter wind wall can fairly decrease the transverse effect on the maglev trains. ③ When the shelter wall height is 2 m, there is minimum side force on the train. When the shelter wall height is 2.5 m, there is minimum yawing moment on the train. ④ When the distance between inside surfaces of the walls and center of guideway is 4.0 m, there is minimum transverse influence on the train. ⑤ The size of air clearance beneath train body has a small influence on aerodynamic drag of the train, but has a fairly large effect on aerodynamic lift and pitching moment of the train. ⑥ The calculating lift and pitching moment for maglev train models are minus values.
基金Projects(51978222,51722805,U2106222) supported by the National Natural Science Foundation of ChinaProject(HIT.BRETIV 201803) supported by the Fundamental Research Funds for the Central Universities,China。
文摘An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667.
基金supported by the National Natural Science Foundation of China(Grants No.12202384 and No.U2241274)the Defense Industrial Technology Development Program(Grants No.JCKY2023205B013 and No.JCKY2021205B003).
文摘Physical monotonicity is a pervasive phenomenon in the aerodynamic characteristics of aircraft,where the aerodynamic lift consistently increases with the angle of attack within the stalling range.Existing machine learning models for aerodynamic predic-tions often overlook this monotonicity,resulting in poor interpretability and credibility.To address this issue,we introduce a monotonic model,the Deep Lattice Network,which integrates the monotonicity constraint of the lift coefficient into machine learn-ing based aerodynamic prediction framework.In this paper,we propose a novel deep learning model,Deep Lattice Cross Network,which aims to rapidly predict aerody-namic forces with high precision while ensuring monotonic constraints.Multi-Task Learning method is utilized to simultaneously predict both lift and drag coefficients,thereby enhancing the efficiency of the model.To optimize the training process and minimize costs,we adopt a unique two-phase deep network training strategy.Based on computational fluid dynamics simulation datasets of a morphing aircraft,the model is trained,and the efficacy of the model is tested by two interpolation and two extrapolation datasets.The results show a remarkable alignment with com-putational fluid dynamics outcomes across all test scenarios.Extended testing across a wider range of attack angles further highlights the superiority of the Deep Lat-tice Cross Network in upholding monotonicity.Incorporating monotonicity constraints not only improves predictive accuracy of the model but also greatly enhances its physi-cal interpretability,which is crucial for advancing the development of more depend-able aerodynamic prediction models.
基金supported by the National Natural Science Foundation of China (No. 11872314)the Key R&D Program in Shaanxi Province of China (No. 2020GY-154)
文摘The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment.To obtain the real deformation pattern of the flapping wing,the digital image correlation technology was used to measure the dynamic deformation of the wing.The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects.The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility.The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell.The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution.The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces.In addition,the total forces,i.e.,the sum of the CFD result and inertial result,are compared with the experimental results,and an overall good agreement is obtained.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60736025, 90716006, 10902006)the Doctoral Pro-gram Foundation of Institutions of Higher Education of China (Grant No. 20091102110015)the Major Programs of China National Space Administration (Grant No. D2120060013)
文摘The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing loads are studied in the longitudinal and lateral maneuver states. The flight loads of the wing fixed at the root are calculated at different angles of attack. The aileron efficiency with respect to the dynamic pressures and aileron deflections are also studied. The results indicate that the flight loads of the wings vary nonlinearly with the angle of attack and dynamic pressure. Due to the high-lift aerofoil, elastic components are a large portion of the wing loads, especially for small angles of attack and high dynamic pressure condi-tions. The aileron efficiency is significantly affected by aileron deflections, dynamic pressures and angles of attack when the nonlinear experimental aerodynamic forces are used for calculation. In states with high dynamic pressures and large aileron deflections, aileron reversal can occur. The aileron deflection and angle of attack have a nonlinear effect on the aileron efficiency. An efficient method for analyzing the flight loads and structural design of high-aspect-ratio wings is derived in this study, and the analysis can provide insight into the distribution of flight loads for high-aspect-ratio wings.
文摘Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element(FE) model through surface effect elements prior to conducting forced response calculations.Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases,time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant.Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation(FFT).Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.
文摘An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and ParaInetric Polynomial Method. After getting the solution of the unsteady flow field, the work done by the unsteay aerody natnic force acting on the blade can be obtained. The negative or positive work is the criterion of the aeroelastic stability Numerical results indicate that there are instabilities of the torsional vibration in some boency bands.
文摘A simplified theoretical method based on the quasi-steady wing theory wasproposed to study the unsteady aerodynamic forces acting on an airfoil flying in non-uniform flow.Comparison between the theoretical results and the numerical results based on nonlinear theory wasmade. It shows that the simplified theory is a good approximation for the investigation of theaerodynamic characteristics of an airfoil flying above sea-waves. From on the simplified theory itis also found that an airfoil can get thrust from a wave-disturbed airflow and thus the total dragis reduced. And the relationship among the thrust, the flying altitude, the flying speed and thewave parameters was worked out and discussed.
文摘Pressure-sensitive paint(PSP) technique was employed to experimentally investigate the aerodynamic force effect of vacuum plume in this study. The characterization and comparison for two types of PSP were firstly conducted in an air pressure range from0.05 to 5000 Pa. The PSPs were prepared using PtTFPP as the active dye and different binders, i.e., polymer-ceramic(PC) and poly(1-trimethylsilyl-1-propyne) [poly(TMSP)]. The static calibrations showed that PtTFPP/poly(TMSP) had a higher pressure sensitivity and a lower temperature dependency compared to PtTFPP/PC in this pressure range. The pressure distributions of a single and two interacting plumes impinging onto a flat plate model were measured using PSP technique. The experimental data were compared to numerical solutions that combined both the computed fluid dynamics(CFD) and direct simulation Monte Carlo(DSMC) methods. Remarkable agreements were achieved, demonstrating the feasibility and accuracy of the numerical approach.Finally, the aerodynamic force effect of interacting plumes at different separation distances was investigated numerically.
文摘Metal foil strain gauges remain the state-of-the-art transducers for wind tunnel balances.While strain gauge technology is very mature,piezoresistive semiconductor sensors offer alternatives that are worth exploring to assess their unique benefits,such as better strain resolution and accuracy,which would enable balances to be designed with higher factors to safety and hence longer fatigue lifetimes.A new three-component balance,based on temperature compensated semiconductor strain gauges,is designed,calibrated and tested in a hypersonic low density wind tunnel.The static accuracy of the semiconductor balance is calibrated better than 0.3%FS,and the dynamic accuracy of the balance is established using a HB-2 standard model in a Mach 12 hypersonic flow.Good experimental repeatability is confirmed to be better than 2.5%FS,and the effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with computational fluid dynamics simulations,as well as reference wind tunnel results under similar conditions.
基金supported by the Beijing Postdoctoral Research Foundation(No.2023-ZZ-133)Scientific Research Foundation of Beijing Infrastructure Investment Co.,Ltd.(No.2023-ZB-03)Fundamental Research Funds for the Central Universities(No.2682023ZTPY036).
文摘The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trainspeed in the tunnel is extremely important.In this study,this problem is investigated numerically in the frameworkof the standard k-εtwo-equation turbulence model.In particular,an eight-car urban rail train passingthrough a tunnel at different speeds(140,160,180 and 200 km/h)is considered.The results show that the maximumaerodynamic drag of the head and tail cars is most affected by the running speed.The pressure at selectedmeasuring points on the windward side of the head car is very high,and the negative pressure at the side windowof the driver’s cab of the tail car is also very large.From the head car to the tail car,the pressure at the same heightgradually decreases.The positive pressure peak at the head car and the negative pressure peak at the tail car aregreatly affected by the speed.
基金supported by National Key Research and Development Program of China (No. 2020YFA0710902)National Natural Science Foundation of China (No. 52072319)+1 种基金National Natural Science Foundation of China (Nos. 52072319 and 12172308)State Key Laboratory of Traction Power (2019TPL_T02)。
文摘Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard, the aerodynamic uplift forces of pantographs with baffles are numerically investigated, and an optimization method to determine the baffle angle is proposed. First, the error between the aerodynamic resistances of the pantograph obtained by numerical simulation and wind tunnel test is less than 5%, which indicates the accuracy of the numerical simulation method. Second, the original pantograph and pantographs equipped with three different baffles are numerically simulated to obtain the aerodynamic forces and moments of the pantograph components.Three different angles for the baffles are-17°, 0° and 17°.Then the multibody simulation is used to calculate the aerodynamic uplift force of the pantograph, and the optimal range for the baffle angle is determined. Results show that the lift force of the baffle increases with the increment of the angle in the knuckle-downstream condition, whereas the lift force of the baffle decreases with the increment of the angle in the knuckle-upstream condition. According to the results of the aerodynamic uplift force, the optimal angle of the baffle is determined to be 4.75° when the running speed is 350 km/h, and pantograph–catenary contact forces are 128.89 N and 129.15 N under the knuckledownstream and knuckle-upstream operating conditions,respectively, which are almost equal and both meet the requirements of the standard EN50367:2012.
