Title: Source term based synthetic turbulence inflow generator for eddy-resolving predictions of an airfoil flow including a laminar separation bubble
Authors: Schmidt, Stephan
Breuer, Michael 
Language: eng
Issue Date: 26-Mar-2017
Publisher: Elsevier
Document Type: Article
Source: Enthalten in: Computers & fluids. - Amsterdam [u.a.] : Elsevier Science, 1973. - Online-Ressource . - Bd. 146.2017, Seite 1-22
Journal / Series / Working Paper (HSU): Computers & fluids : an international journal
Volume: 146
Page Start: 1
Page End: 22
Publisher Place: Amsterdam
© 2016 Elsevier Ltd The present paper addresses the issue of the strong dependency of eddy-resolving simulations for turbulent flows on the employed inflow conditions. Thus, the objective of this study is to analyze the influence of the inflow conditions on the external wall-bounded flow past the SD7003 airfoil and more precisely on the form and size of the laminar separation bubble. Motivated by the typically coarse resolution of the inlet region of the computational domain used for hybrid simulations, the synthetic turbulence is introduced within the flow field by a flexible source term treatment. The generated turbulent fluctuations are taken into account in the momentum equation by source terms and hence allow a shift from the inlet to a finer resolved region, where the damping of small structures due to the grid resolution is negligible. To provide a proper formulation of a synthetic turbulence inflow generator (STIG), the digital filter concept of Klein et al. (J. Comp. Phys. 186, 652–665, 2003) is merged with a large-eddy simulation (LES) as well as a hybrid LES-URANS method. The synthetically generated velocity fluctuations are distributed in an area of influence which is in accordance with the digital filter concept of the STIG. An automatic calculation of the dimension of the influence region is ensured by the employment of the integral scales which are used during the generation of the synthetic turbulence inflow generator inflow. The definition of the required input quantities for the STIG in case of the flow past a SD7003 airfoil at Rec=60,000 and an angle of attack α=4∘ are based on experimental data including a turbulence intensity of TI = 0.28%. Due to separation, transition and subsequent reattachment this is a demanding test case in which the shape and the size of the separation bubble strongly depends on the oncoming turbulence. The reference velocity profiles of the experimental measurements are compared with a wall-resolved LES and hybrid simulations performed on two grids with a coarser resolution. The evaluation of the results of the simulations applying the STIG and without turbulence intensity showed an improved level of agreement between the STIG based simulations and the experiment. Moreover, the turbulence intensity is varied to understand the behavior of the LSB in more detail.
Organization Units (connected with the publication): Strömungsmechanik 
ISSN: 0045-7930
Publisher DOI: 10.1016/j.compfluid.2016.12.023
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