Improved CFD Predictions for High Lift Flows in the European Project EUROLIFT II

Abstract

In the framework of the European High Lift Programme EUROLIFT II the numerical and experimental validation of high lift configurations initiated in EUROLIFT are being pursued. This present contribution describes a summary of the CFD improvements carried out in this project. The improvements cover turbulence modeling and grid generation. More sophisticated turbulence models beyond the eddy viscosity concept are evaluated as well as unsteady effects and efficiency enhancement through wall function approaches. Different techniques to reduce the number of nodes in unstructured grids have been implemented in partners grid generators, mainly through the stretching of elements and introduction of hexahedral elements. The overlapping grid technique for high lift flows are demonstrated as well. Efficiency enhancement through wall functions show that the cost can be reduced to about 50% or more. The computed results agree well with results from near wall resolved grids in the linear range but the maximum lift is over-predicted. Explicit algebraic Reynolds stress models as well as full differential Reynolds stress models improve the predictions in the maximum lift region compared to standard eddy viscosity models. Introducing stretching of unstructured grids along leading and trailing edges as well as introducing hexahedral elements can substantially reduce the number of grid nodes while maintaining the solution accuracy. Overlapping grid techniques for high lift flows show good results but some grid dependencies are observed.