Validation of Turbine Airfoil Leading Edge Pressure and Skin Friction Modeling and Measurement

Abstract

New pressure and skin friction measurements on a cylinder were made and compared with analytical and computational modeling. The measurements were made in what we call the stagnation region, such as exists on the leading edge of a turbine airfoil. The new skin friction measurements were made with an oil film interferometry technique that has been used in earlier turbine cascade studies, and the accuracy of the technique is demonstrated by comparisons with the analytical and computational modeling. The analytical model is an exact solution for laminar stagnation point or Hiemenz flow, and it is based solely on a reference velocity and a length scale, both which describe the free stream acceleration and pressure gradient in the stagnation region. Comparisons were made between the analytical model and measurements of preasure and skin friction from other cylinder studies in the open literature. These comparisons were used to demonstrate that the analytical model accounts for variations in the free stream pressure gradient and acceleration of the flow due to blockage, separation location, and compressibility. The simplicity of the analytical model allows one to quickly characterize stagnation region aerodynamics based only on a pressure profile, which can be used, for example, to assess the computational grid density in the stagnation region of a turbine airfoil. This basic cylinder experiment along with the analytical modeling are shown to be particularly effective for the validation of skin friction techniques, and this study serves to validate the OFI method used in earlier cascade studies.