Improvements of film cooling effectiveness by using Barchan dune shaped ramps

Abstract

In the present study, an experimental investigation was conducted to explore a novel film cooling design with Barchan-dune-shaped-ramp (BDSR) concept to augment the effectiveness of film cooling injection from discrete holes. Inspired by the unique shape of Barchan dunes commonly seen in deserts to prevent sand particles on the ground from being blown away by the oncoming airflow, the BDSR concept was proposed to enable the coolant streams exhausted from coolant injection holes to stay more firmly on the surface of interest for improved film cooling performance. During the experiments, while coolant streams were injected from discrete circular holes on a flat test plate at an injection angle of 35°, a row of BDSRs were mounted on the test plate at either downstream or upstream of the coolant injection holes for improved film cooling effectiveness. While a high-resolution Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the dynamic mixing process between the coolant jet streams and the mainstream flows over the test plate, a Pressure Sensitive Paint (PSP) technique was used to map the corresponding adiabatic film cooling effectiveness on the surface of interest based on a mass-flux analog to traditional temperature-based cooling effectiveness measurements. The cooling effectiveness data of the BDSR design were compared quantitatively against those of a conventional film cooling design without BDSR (i.e., baseline case) under the same test conditions in order to evaluate the effects of the BDSRs on the film cooling effectiveness over the surface of interest. The effects of the locations and height of the BDSRs in relation to the coolant injection holes on the film cooling effectiveness at different blowing ratios (i.e., the coolant-to-mainstream mass flux ratios) were examined quantitatively based on the PIV and PSP measurements. The detailed flow field measurements were correlated with the measured film cooling effectiveness distributions to elucidate the underlying physics in order to explore/optimize design paradigms for better film cooling protection of turbine blades from harsh environments.