Flow field measurements of leading-edge separation vortex formed on a delta wing with vortex flaps

Wind tunnel tests are carried out using a 70 delta wing model with leading-edge vortex flaps. The structure of the leading-edge separation vortex over the leading-edge vortex flap is measured by use of a 5 holes pitot probe, surface pressure measurement technique and oil flow visualization technique. Separation vortices formed on a plain delta wing, on a vortex flap and inboard the vortex flap hinge line are clearly visualized. Results indicate that the flow around the vortex flaps is classified into several different cross flow patterns. The streamwise flap deflection angle is defined to discuss the vortex flap performance. The optimum lift to drag ratio is attained when the amount of the wing angle of attack is not far different from that of the streamwise flap deflection angle, as long as the vortex flap is deflected modestly.     

A temperature-cancellation method of pressure-sensitive paint on porous anodic alumina using 1-Pyrenesulfonic acid

A temperature-cancellation method of pressure-sensitive paint is introduced. It uses an intermediate wavelength of two luminescent peaks, which are opposite in the temperature dependency. 1-Pyrenesulfonic acid is used as a luminophore to describe this method, which is applied onto a porous anodic alumina using the dipping deposition. The concentration of the luminophore solution is varied from 0.001 to 0.09 mM. It controlled the luminescent peak ratio, temperature cancelled wavelength, and pressure sensitivity. The cancellation wavelength is ranged from 429±13 to 493±23 nm. An optical band-pass filter with the temperature cancellation can be also provided by controlling the concentration.     

Numerical flow visualization of stall suppression of a symmetrical aerofoil by leading-edge moving durface

This paper applies the numerical simulation techniques based on the generalized conservation of circulation (GCC) method to investigate the effects of momentum injection by a leading-edge moving surface on flow past a two-dimensional aerofoil at a Reynolds number of 1000. The stream function and vorticity contours obtained together with the animated flow visualization show that the stall flow region is highly unsteady and consist mainly of large vortices being shed alternately. They are confined to a narrow region near the upper surface of aerofoil asC _u (the ratio of the speed of the moving surface to the free stream velocity) is raised. The proximity of vortices to the upper surface of aerofoil at highC _u is caused by the ability of free stream to negotiate around the leading edge since the leading-edge moving surface suppresses the growth of boundary layer by reducing the relative between the inviscid flow and the wall. As well-formed large scale vortices are associated with low pressure regions, their proximity to the aerofoil leads to increase in lift as speed ratio increases     

前缘曲率对三维边界层内被激发出非定常横流模态的影响研究

三维边界层感受性问题是三维边界层层流向湍流转捩的初始阶段,是实现三维边界层转捩预测与控制的关键环节.在高湍流度的环境下,非定常横流模态的失稳是导致三维边界层流动转捩的主要原因;但是,前缘曲率对三维边界层感受性机制作用的研究也是十分重要的课题之一.因此,本文采用直接数值模拟方法研究在自由来流湍流作用下具有不同椭圆形前缘三维（后掠翼平板）边界层内被激发出非定常横流模态的感受性机制;揭示不同椭圆形前缘曲率对三维边界层内被激发出非定常横流模态的扰动波波包传播速度、传播方向、分布规律、感受性系数以及分别提取获得一组扰动波的幅值、色散关系和增长率等关键因素的影响;建立在不同椭圆形前缘曲率情况下,三维边界层内被激发出非定常横流模态的感受性问题与自由来流湍流的强度和运动方向变化之间的内在联系;详细分析了不同强度各向异性的自由来流湍流在激发三维边界层感受性机制的物理过程中起着何种作用等.通过上述研究将有益于拓展和完善流动稳定性理论,为三维边界层内层流向湍流转捩的预测与控制提供依据.     

Visualizing strake and wing vortices in supersonic flow by a thermographic technique

The Unsteady Computerized Thermographic Technique (UCTT) provides patterns of the Stanton number on a body surface. These patterns are the imprints of the flow field. The UCTT already proved to be a powerful, not intrusive diagnostic tool both for the visualization and the strength evaluation of vortical structures on the lee-side surface of delta wing models. The patterns are obtained by processing, by an “ad hoc” mathematical model, the temperature time evolution of the model surface. The temperature is measured at a distance by a thermocamera. In previous tests on delta wing models, the used thermocamera showed a limitation in the optics and did not provide an appropriate space resolution and, therefore, a detailed visualization of whole vortical structure. In the present paper this limitation has been overcome. The optics improvement has doubled the space resolution of thermocamera. Tests, made at angle of attack of 6-deg. and Mach number of 1.92, verified that this improvement was substantial. In fact, the detection of secondary vortex on delta wing model and strake vortices on a double delta wing model was made possible. Unfortunately, it was not possible to visualize details of vortical structure on a Gothic wing model. Tests showed that vortical patterns were similar to the one on delta wing model.     

Pressure sensitive paint evaluation on a supercritical wing at cruise speed

A comparative wind tunnel test of various Pressure Sensitive Paint (PSP) formulations has been performed at the Institute for Aerospace Research (IAR) 1.5 m×1.5 m Trisonic Blowdown Wind Tunnel. The model under study is a prototype supercritical wing of a half model. The results are presented at the cruise Mach number:M=0.74. The effect of the Reynolds number on the pressure distribution is assessed by varying the stagnation pressure of the flow. The evaluated paints all use the same porphyrin molecule as the luminescent sensor and the differences in sensitivity to pressure and temperature are a result of the PSP binder, which differs for each formulation. Examples of the processed results are given and the accuracy of the different PSP formulations is also discussed.     

Quantitative visualization of micro-tube flow using micro-PIV

This paper describes PIV measurements ofthe flow field in a micro round tube with an internal diameter of 100 μm in order to examine micro-scale effects. Since the refractive index of the micro tube almost corresponds to that of water, the inner flow in the tube can be observed clearly. The micro PIV system has been developed using a microscope, a high sensitive CCD camera, a double pulsed Nd:YAG laser and optics. Applying the micro PIV technique to the flow, the velocity distributions with spatial resolution of 1.8 × 1.8 μm were measured even near the wall in the center plane of the round tube. It was found that the velocities near the tube wall were smaller than the theoretical values calculated by using Poiseuille’s law. It is believed that this disparity is due to micro-scale effects such as interference between particles and the wall, friction at the wall, surface tension and so on.     

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd:YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd:YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.     

Quantitative visualization of the change of turbulence structure caused by a normal shock wave

Journal of Visualization - A speckle photographic technique is used for visualizing the planar distribution of the refractive deflection angles of light transmitted through the compressible...     

Quantitative visualization of the three-dimensional flow structures of a sweeping jet

Journal of Visualization - The flow characteristics of a sweeping jet ejecting from a typical feedback channel fluidic oscillator were investigated using time-resolved particle image velocimetry....     

PIV and LDA velocity measurements near walls and in the wake of a delta wing

Velocity measurements in flow regions with high turbulent intensities can be performed with high accuracy by means of optical methods. Despite the validity ranges of these methods, great care must be used in taking measurements near solid walls, where high noise levels are present due to the scattering of the light on the wall, and in flows with high vorticity regions like the ones in the wake of a finite wing. In this paper, Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) velocity measurement techniques are used in these two experimental situations and their results compared. This comparison shows that good measurements can be obtained from both techniques and that the resulting data sets do not provide alternative but rather complementary information.     

机翼变形的双激光器实时测量原理

在飞机机身的上下位置分别安装一个激光器,提出了一种实时测量在飞行过程中机翼弹性变形量的方法。以激光器与安装反射镜的机翼顶端之间的测量距离数据为依据,得到机翼或机身上任意点的实时变形量。机翼或机身上任意点的实时变形量是从机翼变形数据库中提取的数据量计算得到。根据弹性薄板理论,利用理想二维梁为例说明了该方法的实现过程,并且进行仿真说明。该方法对实时测量机翼弹性变形量具有普遍意义和实际应用价值。     

Numerical flow visualization of first cycle and cyclic motion of a rigid fling-clapping wing

A flow visualization of the two-dimensional rigid fling-clap motions of the flat-plate wing is performed to get the knowledge of fling-clapping mechanism that might be employed by insects during flight. In this numerical visualization, the time-dependent Navier-Stokes equations are solved for two types of wing motion; ‘fling followed by clap and pause motion’ and ‘cyclic fling-clapping motion’. The result is observed regarding the main flow features such as the sequential development of the two families of separation vortex pairs and their movement. For the ‘fling followed by clap and pause motion’, a strong separation vortex pair of counterrotation develops in the opening between the wings in the fling phase and they then move out from the opening in the following clap phase. For ‘the cyclic fling-clapping motion’, the separation vortex pair developed in the outside space in the clap phase move into the opening in the following fling phase. The separation vortex pair in the opening developed in the fling phase of the cyclic motion is observed to be stronger than those of the ‘fling followed by clap and pause motion’. Regarding the strong fling separation vortex and the weak clap separation vortex above it in the opening, the flow pattern of the fling phase of the cyclic fling and clap motion is different to that of the fling phase of the first cycle. The flow pattern of the third cycle of the cyclic fling-clapping motion is observed to be almost same as that of the second cycle. Therefore, a periodicity of the flow pattern is established after the second cycle.     

Quantitative visualization of high-speed 3D turbulent flow structures using holographic interferometric tomography

Using holographic interferometry the three-dimensional structure of unsteady and large-scale motions within subsonic and transonic turbulent jet flows has been studied. The instantaneous 3D flow structure is obtained by tomographic reconstruction techniques from quantitative phase maps recorded using a rapid-switching, double reference beam, double pulse laser system. The reconstruction of the jets studied here reveal a three-dimensional nature of the flow. In particular an increasing complexity can be seen in the turbulence as the flow progresses from the jet nozzle. Furthermore, a coherent three-dimensional, possibly rotating, structure can be seen to exist within these jets. The type of flow features illustrated here are not just of fundamental importance for understanding the behavior of free jet flows, but are also common to a number of industrial applications, ranging from the combustion flow within an IC engine to the transonic flow through the stages of a gas turbine.     

The impact of the pitching motion on the structure of the vortical flow over a slender delta wing under sideslip angle

The primary purpose of this investigation is to observe the effect of the pitching motion on the vortical flow structure and bursting of leading-edge vortices over a delta wing under the sideslip angle, β using a dye visualization technique. In the current work, a delta wing with a sweep angle of Λ = 70° was oscillated in upstroke and downstroke direction to be able to discover the influence of pitching motion on the flow characteristics of the delta wing. The values of mean angles of attack were selected as α_m = 25° and α_m = 35°, and the sideslip angle was altered from β = 0 to 16°. The delta wing oscillated with the various periods of T_e = 5 s, 20 s, and 60 s, respectively. Amplitude of motion was adjusted as α_o =  ± 5°. It is found that the pitching motion of the delta wing under the sideslip angle β varies the location of the vortex bursting and vortical flow structure substantially.