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Article

Statistical modeling of the influence of turbulent flow separation control devices

Authors: von Stillfried, , Lögdberg, O., Wallin, S.W., Johansson, A.V.J.
Document Type: Article
Pubstate: Published
Journal: 47th AIAA Aerospace Sciences Meeting, Orlando, FL
Volume: AIAA-2009-1501  
Year: 2009

Abstract

Modeling arrays of passive vortex generators (VGs) pairs, mounted in the fully turbulent boundary layer of a flat plate and generating streamwise counterrotating vortex structures is the object of this investigation. Usually, a sound computational fluid dynamics (CFD) investigation requires an adequate grid with a corresponding large number of grid points around such VGs in order to obtain an accurate solution of this flow case. This, in turn, leads to a time-demanding grid generation which often comes along with lots of practical challenges during the creation. An effective way to get around this time-consuming process is to introduce a way to model these flow separation devices statistically and, by that, to add their statistical physical effects to the governing equations rather than resolving their geometries in the computational grid. KTH, the Royal Institute of Technology Stockholm, and FOI, the Swedish Defence Research Agency, have developed a computational tool for statistical VG modeling that makes it possible to simulate and add the additional statistical effects of passive VGs in wall-bounded flows, whereas the need for a local mesh refinement is no longer required. This approach for the modeling of passive VGs turbulent flow separation devices is presented using a two dimensional Navier-Stokes flow solver. Computational results for fully three dimensional resolved VGs as well as experimental results are evaluated and compared to this statistical VG model approach. It is shown that the VG model approach gives very promising results that compare well to results from CFD and experiments. Nevertheless, the influence of the vortex structures on the flow and on the turbulent stresses decays quicker than it is observed in experiments. Furthermore, the statistical VG model is evaluated for asymmetric diffuser flow and compared to experimental data with as well as without VGs. It is shown that the VG model is capable of predicting the influence of the VGs on decreased and vanished separation of this highly sensitive flow case, giving a better pressure recovery at the diffuser’s outlet.