Implementation and Analysis of a Semi-Empirical Vortex Generator Model in OpenFOAM

Abstract

Passive vortex generators (VGs) are small plate-devices that are placed on the top of wings, in an array configuration, in order to delay or event prevent stall. Due to their small size, when compared to the wing, a highly refined mesh is required to accurately simulate the flow behaviour downstream the VG location. As a consequence, the computational time required for a high fidelity 3D computational simulations is very large. In recent years, there have been efforts to create models that allow the computation of the VGs effect without grid them. Reducing this way the computational effort. During this thesis a semi-empirical model, the Wendt model, was implemented in OpenFOAM and later analysed and compared with gridded VG simulations. The Wendt model is used to predict the vortex circulation and peak vorticity. These entities are then used to calculate the vortex velocity profile at a certain position downstream the VG location. In this projects besides the predictive capabilities of the model, it was tested the hypothesis that to mimic the flow behaviour of a gridded VG simulation, it is enough to impose a vortex velocity profile at a certain position downstream the VG location. It was seen that the Wendt model is able to predict reasonably well peak vorticity and circulation on the tested parameter range, but for higher values of freestream velocities and lower values of height-to-boundary-layer-thickness-ratio and aspect ratio. Furthermore it was seen that, although the implemented model produce inconsistent flow results, the implementation made can be used for that propose. With the correct vortex circulation, peak vorticity and vortex position inputs, it is possible to mimic the correct vortex development as well as the correct flow behaviour, but only far from the VG location, where the influence of the vanes in the streamwise velocity is no longer relevant.