Olof Grundestam

Explicit algebraic subgrid stress models with application to rotating channel flow

New explicit subgrid stress models are proposed involving the strain rate and rotation rate tensor, which can account for rotation in a natural way. The new models are based on the same methodology ...

Techniques for deriving explicit algebraic Reynolds stress models based on incomplete sets of basis tensors and predictions of fully developed rotating pipe flow

Different techniques for deriving explicit algebraic Reynolds stress models (EARSMs) using incomplete sets of basis tensors are discussed. The first is the Galerkin method which has been used by several authors. The second alternative technique, proposed here, is based on the least-squares method. The idea behind the latter method is to minimize the error induced in the implicit relation, i.e., the algebraic Reynolds stress model (ARSM) equation, due to the use of incomplete sets of basis tensors. It is argued that since the system matrix of the ARSM equation is not symmetric and positive definite, the Galerkin method does not give EARSMs that are optimal in the strict classical sense. The possible singular behavior depending on the choice of the basis tensors has also been investigated. It is demonstrated that many of the EARSMs based on incomplete tensor bases, expressed in general three-dimensional mean flows, have singularity problems in some flows, such as general two-dimensional (2D) mean flows or m...

Application of Reynolds Stress Models to High-Lift Aerodynamics Applications

A recently proposed explicit algebraic Reynolds stress model (EARSM) based on a nonlinear pressure strain rate model has been implemented in an industrial CFD code for unstructured grids. The new EARSM was then used to compute the flow around typical three element high-lift devices used on transport aircraft both in 2D and 3D. For 2D mean flow, various angles of attack have been investigated. Two different grids have been used, one coarse grid with 35,000 nodes and fine grid with 340,000 nodes. Furthermore, a 3D take-off configuration including fuselage was computed using a computational grid with about three million grid points. For the 2D case and pre-stall angles of attack, the new EARSM makes fair predictions. For higher angles of attack, the new EARSM and the baseline EARSM show a large sensitivity to the transition point location. The original transition setting leads to a premature stall while an alternative transition setting gives predictions that are in good agreement with experiments. For lower angles of attack, there are indications on minor improvements. One angle of attack close to the maximum lift was computed for the 3D case and compared with previous computations. No significant differences were found with the new EARSM compared with the baseline EARSM. Also the convergence rate and computational effort by using the new EARSM are comparable with the baseline EARSM.