Numerical Investigation of Surface Roughness Effects on Heat Transfer in a Turbine Cascade

Turbine entry temperature has seen a steady increase over the years as it is directly linked to the overall efficiency of a gas turbine engine, thus determining fuel consumption and ultimately CO2 emissions. An accurate estimation of the heat loads is of paramount importance to design the cooling system and determine the life-span of the component, therefore it is mandatory to assess the capability of CFD to predict the involved phenomena. Surface roughness plays a key role in determining the heat transfer and becomes relevant especially in case of in-service degradation and additive-manufactured components. It is seen that for a turbine blade in service for about a thousand hours, the surface roughness has similar effects as turbulence on the heat transfer. This paper is focused on the study of the influence of roughness, turbulence and Reynolds number on the aerodynamics and heat transfer by using commercial code ANSYS Fluent. Transition was accounted exploiting the Transition-SST model, whereas roughness was modeled with an equivalent sand grain approach. Numerical results have been compared against experimental data from the literature.