基于时频变换的激波风洞天平信号分析与处理

在激波风洞中开展测力试验时,测力系统在风洞流场起动瞬间会受到冲击激励,从而对天平的输出信号产生惯性干扰.天平输出信号中叠加有动态气动力信号和惯性振动信号,有可能无法直接分辨出气动力信号的规律性,信号处理结果与真实气动力之间会产生较大的误差,导致处理结果不可靠.由于模型测力天平系统结构的复杂性,在极短的有效试验时间(毫秒...     

飞行器变后掠过程非定常气动特性形成机理

可变体飞行器变后掠过程中的时变气动力与力矩特性对于飞行安全具有重要意义,是亟待深入研究的基础问题.通过风洞实验对其开展了研究,揭示了可变体飞行器变后掠引起的气动特性动态迟滞现象及滞回环大小与方向的影响因素.基于风洞实验结果和力学中一些重要概念,提出了3种物理效应:流场迟滞效应、附加运动效应、固壁牵连效应,以此定性与定量论证了可变体飞行器变后掠过程中非定常气动特性的形成机理.除了能解释实验现象,这一机理研究亦可用于后续可变体飞行器变后掠过程中的气动特性建模.     

Large eddy simulation on the unsteady aerodynamic response of a road vehicle in transient crosswinds

A large eddy simulation method based on a fully unstructured finite volume method was developed, and the unsteady aerodynamic response of a road vehicle subjected to transient crosswinds was investigated. First, the method was validated for a 1/20-scale wind-tunnel model in a static aerodynamic condition; this showed that the surface pressure distributions as well as the aerodynamic forces and moments were in good agreement with wind-tunnel data. Second, the method was applied to two transient crosswind situations: a sinusoidal perturbation representing the typical length scale of atmospheric turbulence and a stepwise crosswind velocity corresponding to wind gusts. Typical transient responses of the aerodynamic forces and moments such as phase shifting and undershooting or overshooting were observed, and their dependence on the frequency and amplitude of the input perturbation is discussed. Thus, the utility and validity of the large eddy simulation was demonstrated in the context that such transient aerodynamic forces are difficult to measure using a conventional wind tunnel.     

Design of a pulse-type strain gauge balance for a long-test-duration hypersonic shock tunnel

When the measurement of aerodynamic forces is conducted in a hypersonic shock tunnel, the inertial forces lead to low-frequency vibrations of the model, and its motion cannot be addressed through digital filtering because a sufficient number of cycles cannot be obtained during a tunnel run. This finding implies restrictions on the model size and mass as the natural frequencies are inversely proportional to the length scale of the model. Therefore, the force measurement still has many problems, particularly for large and heavy models. Different structures of a strain gauge balance (SGB) are proposed and designed, and the measurement element is further optimized to overcome the difficulties encountered during the measurement of aerodynamic forces in a shock tunnel. The motivation for this study is to assess the structural performance of the SGB used in a long-test-duration JF12 hypersonic shock tunnel, which has more than 100 ms of test time. Force tests were conducted for a large-scale cone with a \(10^{\circ }\) semivertex angle and a length of 0.75 m in the JF12 long-test-duration shock tunnel. The finite element method was used for the analysis of the vibrational characteristics of the Model-Balance-Sting System (MBSS) to ensure a sufficient number of cycles, particularly for the axial force signal during a shock tunnel run. The higher-stiffness SGB used in the test shows good performance, wherein the frequency of the MBSS increases because of the stiff construction of the balance. The experimental results are compared with the data obtained in another wind tunnel and exhibit good agreement at \(M = 7\) and \(\alpha =5^\circ \).     

Application of pressure-sensitive paint for determination of the pressure field and calculation of the forces and moments of models in a wind tunnel

The visualization and measurements of aerodynamic effects on a 3D aircraft model were conducted using an optical pressure measurement system, based on the pressure-sensitive paint (PSP) technique. PSP technology provides a good understanding of the flow around the wind tunnel model. The PSP technique can be used to carry out absolute pressure measurements on a surface of the model and to determine additional aerodynamic data using scientific-grade cameras and image processing techniques. Surface pressures from the top, bottom, left, and right viewing directions were obtained using the DLR-PSP system on the entire surface, which can be observed by eight CCD cameras. Finally, the measured pressures can be integrated to calculate the forces and moments of the complete model, or parts thereof.     

Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel

A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2) of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and pitching moment components.      

结构振动对大型激波风洞气动力测量的干扰

激波风洞起动过程形成冲击载荷激励测力系统的结构振动,气动力测量过程中振动尚未衰减,测力过程可以看作是一个动态的过程,激波风洞中天平输出信号包含了振动干扰的输出信号,现有的解决方法缺乏理论支撑,精度受限. 本文应用振动理论方法,得到了自由振动、强迫振动特性的基本解析结果. 自由振动特性研究中考查了单个振型对测力的干扰及其影响规律以及干扰量幅值随测力截面相对位置的变化规律. 强迫振动特性研究了不同载荷强迫振动下各阶振型对测力的干扰. 研究表明,由于干扰量幅值与加速度幅值的“零点位置” 不重合,传统加速度惯性补偿存在理论上的缺陷. 实验中确定干扰量主要来源需要综合考虑截面位置、载荷作用位置、载荷类型的影响.      

高速列车受电弓风洞试验研究

为了研究高速列车受电弓在较高速度下的整体气动特性、弓网接触压力以及受电弓对支持绝缘子的作用力等综合性能,在FD-09低速风洞中进行了测力试验。试验采用测力天平和力传感器进行测量。通过在FD-09风洞试验段内安装收缩地板的方式首次将受电弓试验风速提高到了380km/h,可以满足高速列车受电弓高速性能研究的需求。研究结果表明：受电弓相对列车运行方向对受电弓升力特性有显著的影响,对弓网接触压力也有较大的影响;通过调节导风板的角度可以有效控制弓网接触压力;受电弓对支持绝缘子的作用力表现为前面拉力后面压力。     

横摆角下汽车尾部湍流特征量的PIV试验分析

汽车尾部湍流场是汽车压差阻力的主要来源,在HD-2汽车模型风洞中,首先使用测力天平和测压系统,对横摆角工况下汽车模型的气动六分力和纵对称截面48个测点的表面压力进行了测量,然后利用PIV测量技术对模型在横摆角分别为0°、15°的尾部湍流场进行了测量,获得该模型尾流场的速度场、涡量场和雷诺应力流场信息,通过计算得出尾流场区域空间相关系数和湍流积分尺度。结果表明:在横摆角工况下,汽车模型尾部涡流的结构呈现向上发展的趋势;尾流场拖拽涡的范围和强度的增大导致了模型气动力出现较大的增加;湍流积分尺度的变化表明,尾部涡流区的分离噪声与涡流分离位置有关,在汽车尾部造型设计中,要尽量推迟尾部涡流的分离。     

高层建筑标准模型风洞测压和测力试验研究

CAARC高层建筑标准模型是国际上通用的风工程标准模型之一,用来检验各个模拟自然风的风洞试验结果,以确保风洞试验测量数据的可信度。本研究使用缩尺比为1：300的CAARC模型,在同济大学TJ-2建筑风洞中进行了B类和D类地面粗糙度风场下的刚性测压试验和高频动态天平试验。在刚性测压试验中测量了建筑模型表面在不同风速和风向角下的平均风压系数,并与国外风洞机构的试验数据进行了对比分析。在高频动态天平试验中,不同风向角下的结构气动力系数和顶点位移被给出,并同样与国外风洞机构进行了对比。风洞试验结果表明：TJ-2风洞能较好地模拟大气边界层风场,且风场品质较好;试验技术可靠,所测得的试验数据具有较高的精度。     

Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight

The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to reduction in the thrust value and increases the lift component. The aerodynamic and performance parameters were nondimensionalized. Appropriate models were introduced which show its aerodynamic performance and may be used in the design process and also optimization of the flapping wing.     

用平均速度剖面法测量壁湍流摩擦阻力

用IFA300恒温热线风速仪精细测量风洞中不同雷诺数流动条件下的平板湍流边界层近壁区域对数律平均速度剖面．利用平板湍流边界层近壁区域的对数律平均速度剖面与壁面摩擦速度、流体黏性系数等内尺度物理量的关系和壁面摩擦速度与壁面摩擦切应力的关系,在准确测量平板湍流边界层近壁区域对数律平均速度剖面的基础上,测量平板湍流边界层的壁面摩擦阻力．实现了平板湍流边界层壁面摩擦阻力的无干扰或微小干扰测量．该种方法操作简便,不需要在流场中安装测力天平、传感器等复杂的测量装置,不需要对湍流边界层的壁面进行破坏,不会影响湍流边界层壁面附近区域原有的流场条件,是一种切实可行的测量平板湍流边界层壁面摩擦阻力的简便方法．     

Aerodynamic experimentation with ducted models as applied to hypersonic air-breathing vehicles

 A methodology of experimentation in high supersonic wind tunnels for studying aerodynamic characteristics of hypersonic flying vehicles powered by air-breathing engines is discussed. Investigations of such total aerodynamic forces as drag, lift and pitching moment at testing the models are implicit when the air flow through the model ducts is accomplished so that to provide the simulation of the external flow around the airplane and flow over the inlets, but the operating engines and, hence, the exhaust jets are not modeled. The methods used for testing such models are based on the measurement of duct stream parameters alongside with the balance measurement of aerodynamic forces acting on the models. In the tests, aerometric tools are used such as narrow metering nozzles (plugs), pitot and static pressure probes, stagnation temperature probes and pressure orifices in walls of the model duct. The aerometric data serve to determine the flow rate and momentum of the stream at the duct exit. The internal non-simulated forces of the model ducts are also determined using the conservation equations for energy, mass flow and momentum, and these forces are eliminated from the aerodynamic test results. The techniques of the said model testing have been well developed as applied to supersonic aircraft, however their application for hypersonic vehicles whose models are tested at high supersonic speeds, Mach number M _∞>4, implies some specific features. In the present paper, the results of experimental and theoretical study of these features are discussed. Some experimental data on aerodynamics of hypersonic aircraft models received in methodological tests are also presented. The tunnel experiments have been carried out in the Mach number range M _∞=2–6. Received: 25 July 1996/ Accepted: 14 December 1998     

Upwind sail aerodynamics: A RANS numerical investigation validated with wind tunnel pressure measurements

The aerodynamics of a sailing yacht with different sail trims are presented, derived from simulations performed using computational fluid dynamics. A Reynolds-averaged Navier–Stokes approach was used to model sixteen sail trims first tested in a wind tunnel, where the pressure distributions on the sails were measured. An original approach was employed by using two successive simulations: the first one on a large domain to model the blockage due to the wind tunnel walls and the sails model, and a second one on a smaller domain to model the flow around the sails model. A verification and validation of the computed aerodynamic forces and pressure distributions was performed. The computed pressure distribution is shown to agree well with the measured pressures. The sail surface pressure was correlated with the increase of turbulent viscosity in the laminar separation bubble, the flow reattachment and the trailing edge separation. The drive force distribution on both sails showed that the fore part of the genoa (fore sail) provides the majority of the drive force and that the effect of the aft sail is mostly to produce an upwash effect on the genoa. An aerodynamic model based on potential flow theory and a viscous correction is proposed. This model, with one free parameter to be determined, is shown to fit the results better than the usual form drag and induced drag only, even if no friction drag is explicitly considered.     

某飞机部件测力风洞试验天平研制与应用

为满足某飞机部件高速风洞测力试验的需要,研制了四台部件测力天平,用来同时测量飞机机翼不同部件(全翼、外翼、翼尖弹、弹架组合)所受的气动载荷。由于是全模试验,天平的设计载荷不匹配,安装空间极度受限。设计时,全翼天平采用了机身中部安装方案、外翼天平与机翼加工成一体并且采用了新型多柱梁结构;翼尖弹天平和弹架组合天平采用了杆式天平方案。上述措施不仅满足了天平的测量需要,也确保了天平在模型中的安装位置以及测力的有效性。该部件测力试验已经在中国空气动力研究与发展中心FL-26风洞完成。试验结果表明,天平测力结果准确可靠,精准度高,达到了预期的目标。     

EXPERIMENTAL DETERMINATION OF THE AERODYNAMIC ADMITTANCE OF A BRIDGE DECK SEGMENT

The gust loading on bridge decks is described by the dynamic forces on a chord-wise strip and by the spatial distribution of these forces across the span. An experimental method to evaluate the aerodynamic admittance of a segment of a bridge deck that includes a combination of the cross-sectional admittance and the spatial distribution of the forces is presented in this paper. The method is based on wind tunnel tests in turbulent flow on a motionless section model of the deck. The approach has been validated experimentally on a closed-box girder bridge deck but can be applied to bridge decks of any cross-section.     

A model for the aerodynamic coefficients of rock-like debris

This study presents a model to determine the aerodynamic forces on an irregularly shaped object for prediction of trajectories of debris. We classify the debris according to shape and use wind tunnel tests to create a database of aerodynamic forces of similarly sized objects. We have then validated the database results against wind tunnel measurements of aerodynamic coefficients of rock-like debris objects. Although the individual errors may be significant, the results show a generally good agreement with our model prediction and a small average error.     

循环神经网络在智能天平研究中的应用

激波风洞地面试验对高超声速飞行器高焓气动特性研究至关重要, 而高精度气动力测量是其中的关键技术. 在脉冲型激波风洞中进行测力试验时, 风洞起动时流场瞬间建立, 对测力系统会产生较大的冲击. 测力系统在瞬时冲击作用下受到激励, 系统的惯性振动信号在短时间内无法快速衰减, 天平的输出信号中会包含惯性振动干扰量, 导致脉冲型风洞测力试验精准度的进一步提高遇到瓶颈. 为了解决短试验时间内激波风洞快速准确测力问题, 发展高精度的动态校准技术是提升受惯性干扰天平性能的关键方法. 因此, 本文采用循环神经网络对天平动态校准数据进行训练和智能处理, 旨在消除输出动态信号中的振动干扰信号. 本文对该方法进行了误差分析, 验证了该方法的可靠性, 并将该方法应用于激波风洞测力试验中, 切实有效降低了惯性振动对天平输出信号的干扰影响. 根据智能模型的样本验证分析, 各分量载荷相对误差比较小, 其中高频轴向力分量处理结果的相对误差约1%. 在风洞试验数据验证中, 也得到了比较理想的结果, 同时与卷积神经网络模型处理的结果进行了对比分析.      

Experimental investigation on non-stationary wind loading effects generated with a multi-blade flow device

Overcoming the spatial constraints of the small-scale wind tunnel at Northeastern University, a multi-blade flow device (MBFD) has been installed within the facility’s test chamber to generate ramps in measured wind velocities by redirecting horizontally driven flows. As a continuation feasibility study, this paper analyzes the aerodynamic loads imparted on a building model from these simulated non-stationary outflows. Base forces are recorded with a high-frequency force balance sensor (HFFB) and compared to digital simulations using a modified quasi-steady aerodynamic load approach. Under certain conditions, the forces obtained from both physical and numerical procedures coincide well with each other, although differences arise due to assumptions and deficiencies in the modeling. Nonetheless, results indicate that altering horizontal flows with this device is suitable for replicating non-stationary aerodynamic loads, within the confines of a small-scale wind, “straight” tunnel.     

A numerical and experimental hybrid approach for the investigation of aerodynamic forces on stay cables suffering from rain-wind induced vibration

The aerodynamic forces on a stay cable under a rain-wind induced vibration (RWIV) are difficult to measure directly in a wind tunnel test. This paper presents a hybrid approach that combines an experiment with computational fluid dynamics (CFD) for the investigation on aerodynamic forces of a stay cable under a RWIV. The stay cable and flow field were considered as two substructures of the system. The oscillation of the stay cable was first measured by using a wind tunnel test of a RWIV under an artificial rainfall condition. The oscillation of the cable was treated as a previously known moving boundary condition and applied to the flow field. Only the flow field with the known moving cable boundary was then numerically simulated by using a CFD method (such as Fluent 6.3). The transient aerodynamic forces of the stay cable with a predetermined cable oscillation were obtained from numerical calculations. The characteristics of the aerodynamic forces in the time domain and frequency domain were then analysed for various cases. To verify the feasibility and accuracy of the proposed hybrid approach, the transient aerodynamic forces were applied to a single-degree-of-freedom model (SDOF) of the stay cable to calculate the RWIV of the cable. A comparison was performed between the oscillation responses of the stay cable obtained from the calculated (SDOF model) and experimental results, and the results indicate that the hybrid approach accurately simulates the transient aerodynamic forces of the stay cable. The equivalent damping ratios induced by the aerodynamic forces were obtained for various wind speeds. Furthermore, a nonlinear model of the aerodynamic force is proposed based on the calculation results, and the coefficients in the model were identified by a nonlinear least-squares technique.