On Active Control of Film-Cooling Flows

Abstract

A technical assessment of the potential improvements resulting from the application of active control of film cooling is discussed in this paper. Two methods of film-cooling jet excitation are theoretically evaluated. Film-cooling control through pulsation of the coolant stream mass flow rate is further examined on the basis of existing experimental and preliminary computational results. A potentially optimal range of coolant pulsation parameters are identified through theoretical and mechanistic arguments based on understanding of basic physical phenomena occurring in pulsed film-cooling flow, i.e. that of a pulsed jet in cross-flow. Guidelines for the choice of potentially optimum frequency and duty cycle windows of the controlling flow pulsations are identified, as well as the related mean and peak-to-peak blowing ratios. Evidence from existing experimental data and computations are invoked to validate these guidelines. Because of the limited experimental/computational data on this subject further work is necessary in order to fully verify the aforementioned flow-pulsing parameter ranges.