Control of turbulent boundary layer flow using near-wall weak volume forcing

• Applicant: Dr.-Ing. Georg Khujadze
• Subject Area: Fluid Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548539340

The primary objective of the project is the control of turbulence and drag reduction in a flat plate boundary layer flow by spanwise reflection symmetry breaking. The main strategy to achieve this is to impose specially designed seed velocity perturbations with specific length scales into the flow. These perturbations draw energy from the flow and undergo transient growth, causing the flow spanwise reflection symmetry breaking and the generation of a spanwise mean flow with the peak near the wall. This changes the interplay between linear transient growth and nonlinear (transverse) cascade processes that, at the specially designed imposed seed velocity perturbations, leading to the substantial reduction of the level of the turbulence. The aim of this investigation is to find the optimal amplitude and design of the imposed seed velocity perturbations which, forming a spanwise mean flow with the peak close to the wall, will lead to a significant reduction of the turbulence level. This strategy was applied to the plane Couette flow and reduction of the turbulence level up to 45% was achieved. The preliminary work in the case of streamwise developing boundary layer flow was also done and promising preliminary results were obtained. In the framework of the proposed project, the introduction of the specially designed seed velocity field is planned to be achieved through a specific near-wall volume forcing located in the viscous sub-layer. While this forcing is theoretical/hypothetical, its simplicity makes it the optimal first step in the developing of the concept of indirect active control of flat plate boundary layer flow turbulence. It helps to gain insight into the design of the seed velocity field that should be generated at the wall of the boundary layer flow through more realistic specific nonuniform blowing and suction or by, also specific, surface roughness, to achieve significant drag and turbulent kinetic energy reduction.

• DFG Programme: Research Grants