On the Numerical Difficulties in Calculating Laminar Separation Bubbles

Abstract

Behaviour of laminar separation bubbles on the surfaces of compressor and turbine blades has increasingly attracted the attention of researchers and designers of turbomachinery in the last years. For the numerical investigation of laminar separation bubbles transition models are implemented into Navier-Stokes flow solvers to predict their location, extent and behaviour accurately. Several researchers conducted comparative studies to investigate the applicability of different transition models for separated-flow transition. In this work a comprehensive numerical study is carried out to investigate not only the influence of the transition model, but of the solution method in general on laminar separation bubble prediction. The flow around a NACA 0012 airfoil at different angles of attack where laminar separation bubbles were observed in experiments is chosen as test case. Different flow solvers (Osher and Roe scheme), different turbulence models as well as different solution procedures were applied together with transition models. The results show that besides the transition model other parameters like the discretisation scheme of the turbulence model or the flow solver have a comparably large influence on the computational result.