Follow-up proposal: Direct numerical simulation of a turbulent wall boundary layer at high Reynolds number

• Applicant: Dr.-Ing. Christoph Wenzel
• Subject Area: Fluid Mechanics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458524799

In this follow-up application, the DFG project ‘Direct numerical simulation of a turbulent wall boundary layer at high Reynolds number’ is suggested to be extended for an additional 21 months. In the first funding period, the research group at IAG has successfully advanced the state of the in-house DNS solver NS3D and its auxiliary tools such that the first ever M=2 compressible turbulent boundary layer DNS reaching a Reynolds number (Re) of Re_\theta=8200, Re_\tau=1400 from a low transitional Re_\theta=300 has been started, and to date has completed about 95% of its planned timesteps. A 2022 publication by Ceci et al. has confirmed that the inlet method used, namely the application of synthetic turbulence at very low Re followed by an uninterrupted and fully resolved transit space, can be effectively considered the only method which delivers highly reliable DNS results across all metrics. The present DNS, which will be completed early in the following funding period, will therefore deliver the first highly reliable compressible high Re turbulent boundary layer dataset. Whereas the primary motivation behind the calculation of the DNS is the investigation of turbulence physics, the primary challenges during realization of the calculation have been those related to high performance computing (HPC) at full machine scale, which has required direct cooperation with HPC experts. Several aspects of the NS3D solver, its I/O system and its postprocessing platform have been upgraded for the specific purpose of being able to run and handle data at extreme scale for the fulfillment of the current project. Thus, the applicants consider the successful implementation of the DNS confirmation that the objectives of the first funding period have been successfully met. Initial results clearly show the onset of the targeted high Re behavior, namely the spectral separation of dominant turbulent scales. Thus, the research focus in the second funding period is the physical investigation of high Re flow. The DNS data will be thoroughly published, accompanied by a data catalog made publicly available to the turbulence research community. Physical aspects to be investigated include the properties of the large turbulence structures which, unique to the present DNS, can be followed from very low Re to very high Re over a continuous range.

• DFG Programme: Research Grants