Numerical investigations of micro blowing in compressible turbulent boundary layers with zero and adverse pressure gradients in stream-wise direction

本文的目的是研究微吹的概念在可压缩湍流边界层表面摩擦阻力减少。这似乎是合理的，因为最近对不可压缩流中的均匀吹风的研究显示出非常有希望的减阻结果。然而，与不可压缩情况相比，可压缩微吹要复杂得多，阻力效益也难以预测，因为表面摩擦分布也受到吹气温度的很大影响。此外，可压缩情况受到数值设置引起的更多不确定性的影响，因此需要非常仔细地处理以获得可靠的参考数据。因此，目前所有的研究都将通过直接数值模拟（DNS）在高性能计算机系统上进行，该系统提供的有洞察力的数据不会受到可能不适当的湍流模型的影响。这将使获得具有重大基础和实用价值的新的定性和定量信息成为可能。在前两年半的前驱项目中，我们的数值设置能够为可压缩零压力梯度湍流边界层的一般情况提供出色的结果，这在可靠性和科学相关性方面是独一无二的。本提案的第二个目的是通过提供可压缩逆压力梯度湍流边界层的可比参考数据来继续这项基础工作，这是后续均匀吹风研究所需要的。由于数值设置已经在亚音速马赫数下的低马赫数逆压梯度情况下得到了验证，因此这些结果有望提供与零压力梯度湍流边界层相同的精度水平，因此将引起科学界的极大兴趣。利用可压缩的零压和逆压梯度基流，将研究和改进利用微吹的可压缩边界层控制的预测和建模，这可能是世界上第一次，这样将获得用于验证大涡模拟和湍流模型的dns数据，用于可压缩问题，包括研究不同吹气温度和马赫数的影响。还将执行与解析表达式的比较。相关研究在许多方面都具有开创性，并将为可压缩湍流边界层控制领域的流动物理提供新的重要基础见解，从而减少阻力，节省燃料，减少对环境的污染。

The purpose of the present proposal is to investigate the concept of micro-blowing for skin-friction drag reduction in compressible turbulent boundary layers. This appears justified because recent investigations of uniform blowing in incompressible flows have shown very promising drag-reduction results. However, in comparison to the incompressible case, compressible micro-blowing is much more complex and drag benefits are yet unpredictable, since the skin-friction distribution is also massively influenced by the blowing-gas temperature. In addition, the compressible case is subject to much more uncertainties caused by the numerical setup, such that a very careful treatment is necessary to obtain reliable reference data. Therefore, all present investigations will be performed via Direct Numerical Simulations (DNS) on a high-performance computer system that delivers insightful data which is not biased by a possibly inappropriate turbulence model. This will allow obtaining new qualitative and quantitative information of great fundamental and practical value.It has already been shown in the first two and a half years of a precursor project, that our numerical setup is capable of providing outstanding results for the generic case of a compressible zero-pressure-gradient turbulent boundary layer, which are unique in terms of reliability and scientific relevance. A second aim of this proposal is to continue this fundamental work by also providing comparable reference data for the compressible adverse-pressure-gradient turbulent boundary layer, which is needed for the following investigations with uniform blowing. Since the numerical setup already has been validated for low-Mach number adverse-pressure gradient cases at subsonic Mach numbers, these results are expected to provide the same level of accuracy as for the zero-pressure-gradient turbulent boundary layer and will therefore be of great interest for the scientific community.Using the compressible zero- and adverse-pressure gradient base flows, prediction and modeling of compressible boundary-layer control using micro-blowing will be investigated and improved, probably for the first time in the world such that DNS-data for validation of Large Eddy Simulations and turbulence models will be obtained for the compressible problem including investigations of the influence of varying blowing-gas temperature and Mach number. Comparisons with analytical expressions will also be performed. The related investigations are pioneering in many aspects and will provide new and important fundamental insight into the flow physics in the area of compressible turbulent boundary-layer control which will lead to drag reduction for fuel savings and minimizing pollution of the environment.