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首页> 外文学位 >Development of the spectral difference method and application in the numerical investigation of the separated and transitional flows over a low-Reynolds number airfoil.
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Development of the spectral difference method and application in the numerical investigation of the separated and transitional flows over a low-Reynolds number airfoil.

机译：谱差法的发展及其在低雷诺数翼型分离流和过渡流数值研究中的应用。

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摘要

The development of the high-order accuracy spectral difference (SD) method on hexahedral mesh and its applications in aeroacoustic and aerodynamic problems are carried out in this work. Two absorbing boundary conditions, the absorbing sponge zone and the perfectly matched layer, are developed and implemented for the SD method discretizing the Euler and Navier-Stokes equations on unstructured grids. The performance of both boundary conditions is evaluated and compared with the characteristic boundary condition for a variety of benchmark problems including vortex and acoustic wave propagations. The applications of the perfectly matched layer technique in the numerical simulations of unsteady problems with complex geometries are also presented to demonstrate its capability.;Numerical simulations of the low-Reynolds number (Re = 104 ∼ 105 ) flows over a SD7003 airfoil at moderate incidences (10°) are performed. A low-frequency convective instability is observed to dominate the spectrum near the leading edge and be responsible for the growth of the disturbance in the attached boundary layer. The characteristic frequency, the growth rate and the wave shape are investigated based on the numerical results. The growth of the low-frequency instability is not in agreement with parallel flow stability theory, nor with leading edge receptivity theory. And it has a higher growth rate than the Tollmien-Schlichting (T-S) wave. The effects of the angle-of-attack (AoA), the Reynolds number and the airfoil geometry on the low-frequency instability are investigated and discussed.;The mechanisms in the breakdown process are investigated and discussed. it is observed that the breakdown of the shedding vortices starts at approximately the location with the maximum negative streamwise flow velocity. And the reverse flow in the separation region directly triggers the generation of three dimensional disturbances and the streamwise vorticities. In addition, the secondary instability which initiates the breakdown process differs in cases at different AOAs. The elliptic and hyperbolic instabilities observed in bluff-body wakes are found to occur in the breakdown process of current cases. Furthermore, the sequence of breakdown states at various incidences is found to be similar to that of the bluff-body wakes at various Reynolds numbers.;A numerical investigation of passive LSB control techniques using roughness bumps on a low-Reynolds number wing is conducted as a further study. The previous case at Re = 6x104 and AoA = 4° is used as the baseline (uncontrolled) case. In the controlled cases, roughness bumps are strategically placed near the leading edge of the wing for the purpose of improving aerodynamic performance in terms of the lift to drag ratio. The location, bump size, the number of bumps and the AoA are varied to study the effects. The pressure drag forces in the controlled cases are found to be reduced significantly when the LSB are reduced or avoided, resulting in much improved lift over drag ratio.
机译：这项工作进行了六面体网格上的高阶精度谱差（SD）方法的发展及其在空气声学和空气动力学问题中的应用。为将非结构网格上的Euler和Navier-Stokes方程离散化的SD方法，开发并实现了两个吸收边界条件，即吸收海绵区和完美匹配层。对两种边界条件的性能进行了评估，并将其与特征边界条件进行了比较，以解决各种基准问题，包括涡旋和声波传播。还介绍了完美匹配层技术在复杂几何形状的非定常问题数值模拟中的应用，以证明其功能。低雷诺数（Re = 104〜105）在中等入射角上流过SD7003机翼的数值模拟（<10°）进行。观察到低频对流不稳定性主导了前沿附近的频谱，并导致了所附着边界层中干扰的增加。基于数值结果，研究了特征频率，增长率和波形。低频不稳定性的增长与并行流动稳定性理论不符，也与前沿接受理论不符。而且它的增长率比Tollmien-Schlichting（T-S）浪高。研究并讨论了攻角，雷诺数和机翼几何形状对低频不稳定性的影响。研究了击穿过程中的机理。可以观察到，脱落涡旋的分解大约在最大负向流流速的位置开始。分离区域中的逆流直接触发三维扰动的产生和沿流的涡旋。此外，在不同AOA的情况下，引发故障过程的继发性不稳定性也有所不同。发现在钝体尾流中观察到的椭圆和双曲线不稳定性发生在当前病例的分解过程中。此外，发现在各种入射角下的击穿状态的序列与在各种雷诺数下的钝体尾流的序列相似。;对低雷诺数机翼上使用粗糙度凸块的被动LSB控制技术进行了数值研究，其结果如下：进一步的研究。 Re = 6x104且AoA = 4°的先前情况用作基线（不受控制）情况。在受控情况下，为了提高升力/阻力比的空气动力学性能，可以在机翼的前缘附近策略性地设置凹凸。改变位置，凸块大小，凸块数量和AoA来研究效果。当减少或避免LSB时，在受控情况下的压力阻力被显着减小，从而导致提升的阻力比大大提高。

著录项

  • 作者

    Zhou, Ying.;

  • 作者单位

    Iowa State University.;

  • 授予单位 Iowa State University.;
  • 学科 Engineering Aerospace.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 141 p.
  • 总页数 141
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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