Measurements and Prediction of Laminar Turbulent Transition at High Free-Stream Turbulence in Boundary Layers with Pressure Gradients

University essay from Chalmers tekniska högskola/Institutionen för tillämpad mekanik

Abstract: The laminar-turbulent transition has significant influence on determining the aerodynamic characteristics of immersed bodies such as evolution of losses, the appearance of separation and stall. Also, the transition behavior has a dominant effect on the distributions of wall shear stress and surface heat transfer. To predict and manage the turbulence in different flow cases is beneficial for optimum advantage, namely, to reduce it when it is harmful (e.g. to decrease the skin friction or heat transfer) and to increase it when it is desirable (to avoid flow separation). The prediction of transition at high free-stream turbulence is of particular importance in turbomachinery where the boundary layer state defines the blade heat transfer and the flow separation margins.This project report presents a study on measurements and prediction of laminar-turbulent transition at high free-stream turbulence in boundary layers of the airfoil-like geometries with presence of the external pressure gradient changeover. The experiments are performed for a number of flow cases with different flow Reynolds number, turbulence intensity and pressure gradient distributions. The results were then compared to numerical calculations for same geometries and flow conditions. The experiments and computations are performed for the flow parameters which are typical for turbomachinery applications and the major idea of current study is the validation of the turbulence model which can be used for such engineering applications.