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

本方案的目的是研究可压缩湍流边界层中用于减阻的微吹概念。这似乎是合理的，因为最近对不可压缩流动中均匀吹气的研究表明，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，阻力效益也是不可预测的，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，因此必须非常仔细地处理才能获得可靠的参考数据。因此，目前的所有研究都将通过在高性能计算机系统上进行直接数值模拟(DNS)来进行，该计算机系统提供不受可能不适当的湍流模型影响的有洞察力的数据。这将使我们能够获得具有重大基础和实用价值的新的定性和定量信息。前兆项目的头两年半已经表明，我们的数值系统能够为可压缩零压力梯度湍流边界层的一般情况提供突出的结果，这在可靠性和科学意义上是独一无二的。这项建议的第二个目的是通过提供可压缩逆压梯度湍流边界层的可比参考数据来继续这项基本工作，这对于后续的均匀吹气研究是必要的。由于数值设置已经在亚音速马赫数的低马赫数逆压梯度情况下得到验证，这些结果有望提供与零压梯度湍流边界层相同的精度，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底流，将研究和改进使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获得用于验证可压缩问题的大涡模拟和湍流模型的DNS数据，包括研究不同的吹气温度和马赫数的影响。还将执行与解析表达式的比较。相关的研究在许多方面都是开创性的，将为可压缩湍流边界层控制领域的流动物理提供新的和重要的基础见解，这将导致减阻以节省燃料和最大限度地减少环境污染。

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.