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COMPUTATIONAL ANALYSIS OF LOCALLY FORCED FLOW OVER A WALL-MOUNTED HUMP AT HIGH-RE NUMBER

Sanjin Saric
Technische Universität Darmstadt, Department of Mechanical Engineering, Chair of Fluid Mechanics and Aerodynamics, Darmstadt, Germany,

Suad Jakirlic
Department of Mechanical Engineering Institute of Fluid Mechanics and Aerodynamics (SLA) / Center of Smart Interfaces (CSI) Technische Universitat Darmstadt Petersenstrasse 17, D-64287 Darmstadt, Germany

Cameron Tropea
Technische Universität Darmstadt, Institute of Fluid Mechanics and Aerodynamics, Center of Smart Interfaces, International Research Training Group Darmstadt-Tokyo on Mathematical Fluid Dynamics, Germany

Abstrakt

An incompressible, high-Reynolds number flow (slightly less then 1 Mio. per chord) over a smoothly contoured wall-mounted hump was studied computationally by using the LES (Large Eddy Simulation) and DES (Detached Eddy Simulation) methods. In addition the Spalart−Allmaras model within the RANS (Reynolds-Averaged Navier-Stokes) framework was tested. The focus of the investigation was on the effects of the local perturbation of the hump boundary layer introduced by the spatially uniform (in the spanwise direction) steady suction and oscillatory suction/blowing through a narrow opening (4mm) situated at the hump crest immediately upstream of the natural separation point. Reference experiments have shown that both flow control mechanisms cause a shortening of the recirculation bubble relative to the baseline configuration (no flow control). The LES method, despite the coarse mesh (with a total of 4 Mio. cells) for this high Reynolds number, wall-bounded flow, was capable of capturing important effects of the flow control qualitatively and quantitatively, whereas DES failed to do so, inspite of superior results in the baseline case. A sensitivity study of the RANS-LES interface position within the DES approach shows that a RANS region chosen too thin (with the interface situated at the very beginning of the logarithmic layer) can lead to a strong reduction of the turbulent viscosity causing a low turbulence level within the shear layer region aligned with the recirculation zone, which in turn leads to a larger separation bubble.