Licentiate seminar
Computational studies of passive vortex generators for flow control
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| Defendant |
Main Advisor |
Extra Advisor |
Date |
| Florian von Stillfried |
Arne Johansson |
Stefan Wallin |
2009-12-16 |
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| Opponent |
| Sinisa Krajnovic, Chalmers tekniska högskolan
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| Evaluation committee |
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AbstractMany flow cases in fluid dynamics face undesirable flow separation due to rising static pressure on wall boundaries. This occurs e.g. due to geometry as in a highly curved turbine inlet duct or e.g. on flow control surfaces such as wing trailing edge flaps within a certain angle of attack range. Here, flow control devices are often used in order to enhance the flow and delay or even totally eliminate flow separation. Flow control can e.g. be achieved by using passive or active vortex generators (VG) that enable momentum mixing in such flows. This thesis focusses on passive VGs, represented by VG vanes that are mounted upright on the surface in wall-bounded flows. They typically have an angle of incidence to the mean flow and, by that, generate vortex structures that in turn allow for the desired momentum mixing in order to prevent flow separation. A statistical VG model approach, developed by KTH Stockholm and FOI, the Swedish Defence Research Agency, has been evaluated computationally. Such a statistical VG model approach removes the need to build fully resolved three-dimensional geometries of VGs in a computational fluid dynamics mesh. Usually, the generation of these fully resolved geometries is rather costly in terms of preprocessing and computations. By applying this VG model, the costs reduce to computations without VG effects included. Nevertheless, the VG model needs to be set up in order to define the modelled VG geometry in an easy and fast preprocessing step. The presented model has shown sensitivity for parameter variations such as the modelled VG geometry and the VG model location in wall-bounded zero pressure gradient and adverse pressure gradient flows on a flat plate, in a diffuser, and on an airfoil with its high-lift system extracted. It could be proven that the VG model qualitatively describes correct trends and tendencies for these different applications.
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