Secondary flows and inlet skew in axial flow turbine cascades

Abstract

This thesis presents a detailed experimental investigation of the effects of inlet skew on the secondary flows and losses in a linear cascade of high turning turbine rotor blades. The blade that was used was modified from its original design to give aerodynamic similarity in the cascade flow conditions. Three levels of inlet skew were investigated using pressure probe instrumentation and the surface oil flow technique of flow visualisation. The results have shown that inlet skew has a profound effect on the secondary flows and on the magnitude of the secondary losses. The flowfield of the cascade was modelled using several computer models. Although reasonable results were obtained with a fully viscous three-dimensional code the other models were unable to predict accurately the magnitude of the losses or even the relative effect of inlet skew on the losses. This thesis also presents measurements of the turbulent flowfield of a similar linear cascade. It was found that regions of high turbulent kinetic energy were associated with regions of high total pressure loss. It was also found that the mass averaged total pressure loss and turbulent kinetic energy followed similar distributions in the cascade.