Description of Transitional Flow Modeling

Kurzfassung

This report has been made during the European project HiAer - High Level Modeling of High Lift Aerodynamics. Within the project, the report was published as deliverable D1.1-1. The report consists of two parts. The first part, Navier-Stokes Airfoil Computations with e* Transition Prediction Including Transitional Flow Regions, contains the theoretical background for the work done in Task 1.1, that is dedicated to the implementation of new infrastructure into the flow solvers. The second one, Modeling of Transitional Flow and its Application on a High Lift Multi-element Airfoil Configuration, describes the implementation of the theory into a Navier-Stokes code and its applications and contains test case results. The flow around laminar airfoils can be computed using a Navier-Stokes method coupled to a transition prediction method based on the e* approach. Applying point transition at the predicted transition location produces a strong viscous/inviscid interaction region which prevents the coupled system to converge, whereas the introduction of transitional flow regions resolves that problem. A conventional model is proposed, which is applicable in flow regions where transition is predicted well upstream of laminar separation, together with a special transitional length model for flows where the boundary-layer stays laminar up to separation. The implementation of the model into a Navier-Stokes code is described and the strategy of determing the transition locations is outlined. The model is tested at a 2-dimensional high lift configuration consisting of the three elements. Computational results for two different versions of the transitional length are shown and compared. The second part of the report focuses on the background of the implementation work and the testing of the functionalities of the algorithms. Details of the implementation, which are consequences of the transition prediction strategy, are outlined. The testing is described and documented by a large number of commented plots of the computed flow fields and the results of the approximate transition prediction procedure and the transition length models. The main objective of this task is to supply a reliably working infrastructure in a RANS code to perform the desired approximate transition prediction. This report is documenting that the work has successfully been done.