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

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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.