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Large eddy simulation of shock boundary layer interaction control using micro-vortex generators.

机译：利用微涡发生器对冲击边界层相互作用控制的大涡模拟。

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摘要

The performance of supersonic engine inlets and external aerodynamic surfaces can be critically affected by shock wave/boundary layer interactions (SBLIs), whose severe adverse pressure gradients can cause boundary layer separation. Currently such problems are avoided primarily through the use of boundary layer bleed/suction which can be a source of significant performance degradation. This study investigates a novel type of flow control device called micro-vortex generators (muVGs) which may offer similar control benefits without the bleed penalties. muVGs have the ability to alter the near-wall structure of compressible turbulent boundary layers to provide increased mixing of high speed fluid which improves the boundary layer health when subjected to flow disturbance. Due to their small size, muVGs are embedded in the boundary layer which provide reduced drag compared to the traditional vortex generators while they are cost-effective, physically robust and do not require a power source.;To examine the potential of muVGs, a detailed experimental and computational study of micro-ramps in a supersonic boundary layer at Mach 3 subjected to an oblique shock was undertaken. The experiments employed a flat plate boundary layer with an impinging oblique shock with downstream total pressure measurements. The moderate Reynolds number of 3,800 based on displacement thickness allowed the computations to use Large Eddy Simulations without the subgrid stress model (LES-nSGS). The LES predictions indicated that the shock changes the structure of the turbulent eddies and the primary vortices generated from the micro-ramp. Furthermore, they generally reproduced the experimentally obtained mean velocity profiles, unlike similarly-resolved RANS computations. The experiments and the LES results indicate that the micro-ramps, whose height is h≈0.5delta, can significantly reduce boundary layer thickness and improve downstream boundary layer health as measured by the incompressible shape factor, H. Regions directly behind the ramp centerline tended to have increased boundary layer thickness indicating the significant three-dimensionality of the flow field. Compared to baseline sizes, smaller micro-ramps yielded improved total pressure recovery. Moving the smaller ramps closer to the shock interaction also reduced the displacement thickness and the separated area. This effect is attributed to decreased wave drag and the closer proximity of the vortex pairs to the wall.;In the second part of the study, various types of muVGs are investigated including micro-ramps and micro-vanes. The results showed that vortices generated from muVGs can partially eliminate shock induced flow separation and can continue to entrain high momentum flux for boundary layer recovery downstream. The micro-ramps resulted in thinner downstream displacement thickness in comparison to the micro-vanes. However, the strength of the streamwise vorticity for the micro-ramps decayed faster due to dissipation especially after the shock interaction. In addition, the close spanwise distance between each vortex for the ramp geometry causes the vortex cores to move upwards from the wall due to induced upwash effects. Micro-vanes, on the other hand, yielded an increased spanwise spacing of the streamwise vortices at the point of formation. This resulted in streamwise vortices staying closer to the wall with less circulation decay, and the reduction in overall flow separation is attributed to these effects. Two hybrid concepts, named "thick-vane" and "split-ramp", were also studied where the former is a vane with side supports and the latter has a uniform spacing along the centerline of the baseline ramp. These geometries behaved similar to the micro-vanes in terms of the streamwise vorticity and the ability to reduce flow separation, but are more physically robust than the thin vanes.;Next, Mach number effect on flow past the micro-ramps (h∼0.5delta) are examined in a supersonic boundary layer at M=1.4, 2.2 and 3.0, but with no shock waves present. The LES results indicate that micro-ramps have a greater impact at lower Mach number near the device but its influence decays faster than that for the higher Mach number cases. This may be due to the additional dissipation caused by the primary vortices with smaller effective diameter at the lower Mach number such that their coherency is easily lost causing the streamwise vorticity and the turbulent kinetic energy to decay quickly. The normal distance between the vortex core and the wall had similar growth indicating weak correlation with the Mach number; however, the spanwise distance between the two counter-rotating cores further increases with lower Mach number.;Finally, various muVGs which include micro-ramp, split-ramp and a new hybrid concept "ramped-vane" are investigated under normal shock conditions at Mach number of 1.3. In particular, the ramped-vane was studied extensively by varying its size, interior spacing of the device and streamwise position respect to the shock. The ramped-vane provided increased vorticity compared to the micro-ramp and the split-ramp. This significantly reduced the separation length downstream of the device centerline where a larger ramped-vane with increased trailing edge gap yielded a fully attached flow at the centerline of separation region. The results from coarse-resolution LES studies show that the larger ramped-vane provided the most reductions in the turbulent kinetic energy and pressure fluctuation compared to other devices downstream of the shock. Additional benefits include negligible drag while the reductions in displacement thickness and shape factor were seen compared to other devices. Increased wall shear stress and pressure recovery were found with the larger ramped-vane in the baseline resolution LES studies which also gave decreased amplitudes of the pressure fluctuations downstream of the shock.
机译：超声波/发动机进气口和外部空气动力学表面的性能可能会受到冲击波/边界层相互作用（SBLI）的严重影响，其严重的不利压力梯度会导致边界层分离。当前，主要通过使用边界层渗出/抽吸来避免此类问题，边界层渗出/抽吸可以是显着的性能下降的来源。这项研究研究了一种新型的流量控制装置，称为微涡流发生器（muVGs），它可以提供类似的控制益处而不会造成流失。 muVG具有改变可压缩湍流边界层的近壁结构的能力，以提供增加的高速流体混合，从而在受到流动扰动时改善边界层的健康状况。由于muVG的体积小，因此它们被嵌入边界层中，与传统的涡流发生器相比，它们具有更低的阻力，同时它们具有成本效益，物理坚固性并且不需要电源。进行了斜向冲击在3马赫超音速边界层中的微坡道的实验和计算研究。实验采用了带有冲击斜向冲击的平板边界层，并进行了下游总压力测量。基于位移厚度的3,800的中等雷诺数允许计算使用不带子网格应力模型（LES-nSGS）的大涡模拟。 LES的预测表明，冲击改变了微斜坡产生的涡流和初级涡旋的结构。此外，与类似解析的RANS计算不同，他们通常复制了实验获得的平均速度曲线。实验和LES结果表明，高度为h＆ap; 0.5delta的微坡道可以显着减小边界层的厚度并改善下游边界层的健康状况（以不可压缩的形状因子H表示）。边界层厚度增加，表明流场具有明显的三维性。与基准尺寸相比，较小的微坡道可改善总压力。将较小的斜坡移至更靠近冲击相互作用的位置，也可以减小位移的厚度和分离的区域。这种影响归因于波浪阻力的减小和涡流对与壁的更近距离。；在研究的第二部分，研究了各种类型的muVG，包括微型斜坡和微型叶片。结果表明，muVGs产生的涡流可以部分消除激波引起的流分离，并且可以继续夹带高动量通量以用于下游的边界层恢复。与微型叶片相比，微型斜坡使下游位移厚度更薄。但是，由于耗散，特别是在冲击相互作用之后，微斜坡的沿流涡旋强度下降得更快。另外，由于引起的上冲作用，对于斜面几何形状，每个涡旋之间的接近的翼展方向上的距离导致涡旋芯从壁向上移动。另一方面，微叶片在形成点产生了沿流方向的涡流的沿展向方向的增大的间距。这导致沿流方向的涡流保持更靠近壁，循环衰减较小，并且总体流分离的减少归因于这些作用。还研究了两个混合概念，分别称为“厚叶片”和“分体斜面”，其中前者是带有侧支撑的叶片，而后者沿基线坡道的中心线具有均匀的间距。这些几何形状在流向涡流和减少流分离的能力方面与微型叶片相似，但比薄型叶片在物理上更坚固。接下来，马赫数对通过微型斜坡的流动有影响（h〜0.5在超音速边界层中以M = 1.4、2.2和3.0检查δ），但不存在冲击波。 LES结果表明，微斜坡对设备附近的较低马赫数具有更大的影响，但其影响的衰减速度要比较高马赫数情况下的衰减更快。这可能是由于在较低的马赫数下具有较小有效直径的初级涡流引起的附加耗散，从而使它们的相干性容易丧失，从而导致沿流方向的涡流和湍动能迅速衰减。涡流核心与壁之间的法线距离具有相似的增长，表明与马赫数的相关性较弱；然而，随着马赫数的降低，两个反向旋转的铁心之间的跨距进一步增大。最后，在正常冲击条件下，研究了包括微型匝道，分裂匝道和新型混合概念“斜叶”在内的各种muVG。马赫数为1.3。特别是，通过改变叶片的尺寸对其进行了广泛的研究，设备的内部间距和相对于冲击的流向位置。与微型斜坡和分离斜坡相比，倾斜叶片提供了更高的涡度。这显着减小了设备中心线下游的分离长度，其中较大的倾斜叶片和后缘间隙增大，从而在分离区域的中心线处产生了完全附着的流动。粗分辨率LES研究的结果表明，与冲击下游的其他设备相比，较大的斜叶可以最大程度地减少湍动能和压力波动。其他好处包括可忽略不计的阻力，同时与其他设备相比，位移厚度和形状因数减小了。在基线分辨率LES研究中，较大的斜叶片发现壁剪切应力和压力恢复增加，这也使冲击下游的压力波动幅度减小。

著录项

  • 作者

    Lee, Sang.;

  • 作者单位

    University of Illinois at Urbana-Champaign.;

  • 授予单位 University of Illinois at Urbana-Champaign.;
  • 学科 Engineering Aerospace.;Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 202 p.
  • 总页数 202
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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