Numerical Investigation of the Effect of Roughness and Passing Wakes on LP Turbine Blades Performance

A quasi-three-dimensional, blade-to-blade, time-accurate, viscous solver has been used to study the effects of blade surface roughness elements, and incoming bar wakes on blade loading and losses of modern LP blade cascades at low Reynolds number. The T106 and VKI-T2 cascades, recently tested experimentally at the Von Karman Institute, were selected as test cases. A simplified geometrical model was adopted for the roughness element, in order to incorporate it in quasi-3D analyses using a single grid structure. Good agreement with experimental data in terms of blade loading distributions and losses was found using a low-Reynolds number formulation of Menter's SST, k- model. The blade performance improvements, expected in the presence of roughness elements or incoming wakes, were correctly predicted by the calculations. The basic flow mechanisms leading to such improvements was recognized in the suction side separation reduction, which was satisfactorily reproduced in the numerical analisys.