The TTP Transonic wind tunnel Mach number uniformity analysis

The distribution of the Mach number in the test section of the Brazilian Pilot Transonic Wind Tunnel was evaluated for the subsonic, transonic and low supersonic regimes. A convergent–divergent nozzle was designed and manufactured to increase the TTP envelope up to Mach number 1.3. Static and total pressures of the airflow are input quantities for the isentropic equation used for Mach number estimation. Static pressure measurements at the test section stations are accomplished by a centreline pressure probe and by distributing pressure taps along the upper and lower walls. Data reduction includes the evaluation of the uncertainties associated with the measured quantities, as well as their propagation to the output quantity, by employing the Monte Carlo method. Least squares fitting is applied to the experimental data in order to supply Mach number calibration curves. Sources of error causing non-uniform flow for Mach number equal to 1.3 are pointed out.     

基于PLC的LT风洞内三维高精度探针定位系统

机翼模型受力试验是飞机翼型设计必不可少的关键环节,风洞是进行空气动力学试验的必备装置。该文介绍了基于LT(低湍流)风洞的探针三维高精度位移测控系统的组成,详细分析了LT风洞现场实验条件及应满足的控制要求,在此基础上,论述了系统的总体设计方案,硬件结构和触摸屏的组态过程,重点论述了PLC的硬件配置及控制软件的设计。运行实践证明,该系统满足设计要求,运行可靠。有效地解决了翼型实验研究中探针在风洞中准确定位控制的难题。     

Development of radially movable multichannel Reynolds stress probe system for a cylindrical laboratory plasma

A new radially movable multichannel azimuthal probe system has been developed for measuring azimuthal and radial profiles of electrostatic Reynolds stress (RS) per mass density of microscale fluctuations for a cylindrical laboratory plasma. The system is composed of 16 probe units arranged azimuthally. Each probe unit has six electrodes to simultaneously measure azimuthal and radial electric fields for obtaining RS. The advantage of the system is that each probe unit is radially movable to measure azimuthal RS profiles at arbitrary radial locations as well as two-dimensional structures of fluctuations. The first result from temporal observation of fluctuation azimuthal profile presents that a low-frequency fluctuation (1-2 kHz) synchronizes oscillating Reynolds stress. In addition, radial scanning of the probe system simultaneously demonstrates two-dimensional patterns of mode structure and nonlinear forces with frequency f = 1.5 kHz and azimuthal mode number m = 1.     

Pressure measurement in a blow-down wind tunnel

An automatic system for steady pressure measurement in a small hand-controlled supersonic wind tunnel is described. The ratio of model surface pressure to tunnel blowing pressure was measured using a Scanivalve controlled by a small digital computer. The software contained provision for the rejection of samples which were not sufficiently steady, and a transducer calibration routine was included to enable a variety of transducers to be used with the system. Typically, 18 pressure tappings could be sampled in a 50 s run (including start-up time) with an error of ±2% in the pressure ratio. The system should be applicable to any situation where run times are limited and difficulty is experienced in maintaining precise control over blowing pressure.     

直流低速风洞流场特性研究

对一直流低速风洞的试验段流场品质进行实验研究,利用IFA300热膜风速仪测量了风洞试验段的流场,获得试验段两截面中心线上速度和湍流度分布,结果表明,该风洞具有较好的流场均匀性和稳定性,具备了开展横流中的紊动射流实验研究的基本条件。     

风洞模型强迫振动装置的动力学仿真研究

为了验证风洞模型强迫振动装置的结构参数取值的合理性,建立了强迫振动装置的动力学方程及相对应的模型,并用MATLAB／SIMULINK软件进行仿真分析;装置中部分构件之间存在摩擦,并且具有一定的刚度,由于风洞模型强迫振动装置是一种精度要求很高的系统,为保证计算结果的准确性,在建立强迫振动装置的动力学方程时必须考虑这些因素;当高度调节机构处于极限工况时,计算结果表明：伺服电机的最大驱动力矩为8．2N·m,小于伺服电机的额定驱动力矩9．23N·m,强迫振动装置的结构参数取值是合理的,并且有优化的空间。     

Measuring probe alignment errors on cylindrical coordinate measuring machines

This note describes a method for measuring probe alignment errors on precision cylindrical coordinate measuring machines. Specifically, this method is used to determine the minimum distance between the line of travel of the center of a spherical probe tip and the axis of rotation of a rotary axis. Within the Timken facility, we refer to this error as intersection error [Bryan JB. Private communication; 7 June 1992]. In addition to intersection error, this method determines the position along the probe line of travel at which the center of the probe tip passes nearest to the axis of rotation. This position is commonly referred to as probe offset error. It is used to adjust the probe location such that its radial position is zero where it intersects (or nearly intersects) the axis of rotation. In this way, the probe tip location is datumed to the axis of rotation.     

液压风洞尾撑系统的设计

在简要分析机械传动式风洞尾撑系统的原理的基础上,介绍了液压风洞尾撑系统的原理及其设计。这对发展我国的液压风洞尾撑具有参考价值     

Investigation of gas particle flow in an erosion wind tunnel

Trajectories of small particles approaching the test specimen in an erosion tunnel are analytically determined. The two-dimensional equations of motion are solved for a spherical particle under the sole influence of aerodynamic drag. The two-dimensional gradients of gas properties in the flow field are determined by a numerical solution of the equations describing a compressible inviscid fluid. At one inlet condition, the trajectories are computed for coal ash particles of various sizes approaching test specimens at several orientations. Trends are identified in the approaching characteristics that may be related to the observed erosion. The results indicate that, for ash particles with diameters less than 10 μm, significant numbers are deflected away from the specimen. These particles would otherwise impact with the specimen if they had more inertia to resist the turning effect of the flow field. Ash particles with diameters less than 30 μm which do impact with the specimen do so over a wide range of incident angles quite different from the angle between the specimen surface and the tunnel axis and at lower velocities than those at the test section inlet. The importance of fluid mechanics in erosion studies is presented in this paper.     

Control of an all-movable foreplane for a three surfaces aircraft wind tunnel model

This article deals with design and realisation of a canard foreplane control system for an aeroelastic demonstrator, suitable for wind tunnel testing. Hardware and software will be described as the methodology adopted to design, implement and realise the software. Specific attention is devoted to PID application, tuning and fuselage vibration control implementation. Results of preliminary test and simulations are presented and show realistic system effectiveness in damping fuselage bending and torsion. This work describes all the activity performed at Politecnico di Milano before wind tunnel testing at VZLU, Prague, as part of Active Aeroelastic Aircraft Structures (3AS) EU project.     

Design optimization of a wind tunnel force balance using stepwise response surface method

A force balance measures the forces being applied to an object in a wind tunnel test. The force balance needs to be optimized to generate an acceptable gauge reading while guaranteeing no structural failure by the wind tunnel loadings. This paper proposes a stepwise response surface method (RSM) for design optimization of a force balance. Three sampling techniques were tried in the RSM study, and finite element simulation was used for functional evaluation. The first trial was based on broad sampling, followed by a second trial based on narrow sampling. The data from these trials was then utilized in a final regression, in which a quadratic model was generated to identify the final optimum point. The final design of the force balance provides satisfactory gauge readings with decreased stress values even though the roll moment is greatly increased.

     

Robust model of a transient wind tunnel for off-design aerothermal testing of turbomachinery

Short duration wind tunnels offer an economical approach to study the aero-thermal operation of propulsion components, while reproducing temperature ratios, Reynolds and Mach numbers of the actual engine conditions. The present paper aims at modeling with high fidelity the von Karman Institute compression tube facility. This wind tunnel was simulated using the EcosimPro suite to characterize the behavior of each subcomponent during the whole test envelope, including the turbine map at off-design. The numerical predictions were then assessed through the comparison with experimental data. The model was proven to be an effective tool to accurately evaluate all the operating regimes that a research turbine experienced during the experimental sequence. Consequently, the present model allows exploiting the complete test run duration to obtain unique experimental data from the turbomachinery operating at far off-design conditions. The capability to experimentally test components at off-design is fundamental to understand the flow physics of any gas turbine engine operating at extreme conditions and to characterize the transient performances of fluid-machinery in high-speed propulsion concepts. However, technical dissemination on these aspects is scarce.     

On the impact of anemometer size on the velocity field in a closed wind tunnel

In the present paper, experimental and numerical investigations of the flow around different types and sizes of anemometers are presented and discussed.The measurements of the flow field at different distances upstream of the anemometer are performed with a laser Doppler Anemometer. The computational results are in good agreement with the experimental ones since the observed deviations are of the same order of magnitude. These results show that anemometers may induce a strong distortion of the velocity field, even far upstream of the anemometer. This distortion has to be taken into account in the anemometer calibration field to yield reliable and consistent measurements.     

基于PLC的矿用简易风洞设计

针对部分煤矿没有校准流量计用的标准实验风洞,对现场使用的流量计无法调校,调校困难等问题,该文设计了一种用于煤矿现场流量计调校的简易低速风洞。该实验风洞以西门子S7-1200系列PLC为核心,采用变频器拖动离心风机在实验管段上产生一个可调、均匀、稳定的气流,通过PLC对标准表和被测表参数进行采集和计算,将校准系数写入被测表中,并通过触摸屏进行集中显示和操作,实现了对矿用流量计的自动调校。测试表明:该实验风洞可以产生一个0~19 m/s的稳定气流,可对管径为250 mm及以下的流量计进行调校,该实验风筒实现方法简单易于推广使用,对提高现场流量计测量精度具有重要意义。     

Reproduction of air velocity in the entrance region of the test pipe in a wind tunnel

The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.     

杆式风洞应变天平动态解耦-补偿

采用串行动态解耦-补偿网络实现多维力/力矩传感器的动态解耦-补偿,对已有的设计方法进行了改进。基于单通道加载实验数据,通过系统辨识方法设计网络的各个环节。具体针对六维杆式风洞应变天平,采用负阶跃单元加载法进行动态标定实验。对力矩加载实验数据进行预处理。采用OE模型描述串行动态解耦-补偿网络中的各个环节,通过基于预报误差的系统辨识方法确定其参数。对实验数据处理的结果表明,所设计的杆式风洞应变天平动态解耦-补偿网络能将杆式天平的维间动态耦合误差由高至88.85%降低至6%以内,主通道阶跃响应调节时间缩短至30 ms以内且超调量降低至5%以下,从而大幅度改善了杆式风洞应变天平的动态性能。     

气象低速风洞参数及性能测试

通过对风洞不同风速段进行“频率—速度”参数拟合,校正了气象风洞的实验参数,并对风洞的风场气流均匀性及风速稳定性进行了测试.当风速相对较低时,整个风洞风场属于层流及缓冲层范畴,而在高风速下,风场属于湍流范畴.在0～1 m/s风速段,特别是在风速低于0.5 m/s时,风速变异系数C.V及风速相对偏差δ都达到了较高的水平,外界环境的变化对风洞风场的影响较大;而当风速在1～30m/s范围时,两个指标均相对较低,这说明随着风速的提高,风洞风场对外界环境变化的反映变得不敏感.     

直流式低速风洞壳体有限元分析

根据试验要求所设计的直流式低速风洞为薄壁结构,风洞的风扇位于动力段内。运行过程中,动力电机不可避免地会将振动传到壳体上,诱导其振动,并影响风洞试验段的流场品质。针对此种现象,利用有限元分析方法,对壳体模型进行网格划分,分析风洞全流场和壳体模态,得到了风洞试验段湍流度和风洞壳体模态分析结果。结果表明,直流式低速风洞的壳体结构设计合理,模态频率分布适当,在保证低速风洞试验段流场品质满足实验要求的前提下,壳体发生共振的可能性很小。     

省级检定业务风洞流场特性研究

针对甘肃省气象计量检定站改造后的HDF-500直流低速风洞,对其流场特性进行研究.通过对风洞试验段内气流流速的测量结果计算和分析,表明该风洞的试验段风速与变频器频率呈线性关系,且气流流速范围达到改造的要求.改造后风洞的气流稳定性、均匀性、气流偏角和噪音均符合性能要求,具备开展检定业务的基本条件.     

Vibrational characteristics of sphere model installed in wind tunnel test section

The vibrational characteristics of a sphere model installed in a wind tunnel test section were quantitatively investigated using a noncontact laser vibrometer. The sphere was supported by two fine wires passing perpendicularly through the center of the model in an X-shape. Each end of the wire was fastened firmly to the frame of the test section with a secure turnbuckle. This fixation method was evaluated by laser vibrometry measurement of the vibration of the sphere and by spectral analysis. The maximum displacement of the sphere was found to be less than 30 nm with the characteristic frequency on the order of hundreds of kilohertz. The effects of the vibrational displacement and frequency of the model were negligible considering the model dimensions and the shedding frequency of the sphere wake.