The Effectiveness of Film Cooling with Injection of Pulsating Air Flow (Review)

Abstract

An analytical review is presented of scientific publications with the results of physical and numerical simulation of the effect of the pulsating cooling air flow on the effectiveness of thermal cooling η, specifically on the airfoil part of turbine blades. The tests carried out under nearly full-scale conditions have revealed positive, variable, or negative effects of pulsations on the effectiveness of the film cooling. It has been found that a positive or negative effect of pulsations superimposed on the injected air flow is determined by the transport mechanisms in the film-cooling system, which are observed without pulsations. At the same time, fan-shaped holes give a higher local effectiveness of the film cooling compared to classical cylindrical holes not only in the steady-state case without changing the coolant flowrate but also in the case with pulsating flow injection. In the steady-state case, this occurs at a blowing ratio of m = 1.0, and that with the pulsating flow injection is at m = 1.5 and 2.0. This is caused by the more uniform coverage by the gas-air mixture of the cooled surface downstream of the section with pulsating air flow injection. Moreover, at m = 1.5 for holes of both shapes, the pulsating coolant flow with m = 1.5 offers a higher spanwise averaged effectiveness of film cooling, \(\bar {\eta },\) than the injected steady flow does. The examined methods for predicting the effect of pulsating flow injection on \(\eta \) require only knowledge of the steady flow behavior and enable us to assess when pulsing would be beneficial or detrimental for the effectiveness of film cooling.