The Influence of Roughness on a High Pressure Steam Turbine Stage: An Experimental and Numerical Study

Abstract

This work deals with the influence of roughness on highpressure steam turbine stages. It is divided in three parts. In the first one, an experimental campaign on a linear cascade is described, in which blade losses are measured for different values of surface roughness and in a range of Reynolds numbers of practical interest. The second part is devoted to the basic aspects of the numerical approach and consists of a detailed discussion of the roughness models used for computations. The fidelity of such models is then tested against measurements, thus allowing their finetuning and proving their reliability. Finally, comprehensive computational fluid dynamics (CFD) analysis is carried out on a highpressure stage, in order to investigate the influence of roughness on the losses over the entire stage operating envelope. Unsteady effects that may affect the influence of the roughness, such as the upcoming wakes on the rotor blade, are taken into account, and the impact of transitionrelated aspects on the losses is discussed.