Effect of periodic passing wakes on the leading edge film cooling effectiveness (studies on 90-degree-inclination cooling holes)

摘要

Detailed studies are conducted on film effectiveness of discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a similar configuration to that of typical turbine blades except for the spanwise inclination angle. Secondary air is heated so that the temperature difference between the primary and secondary air is about 20 K. In this case, the air density ratio of the primary and secondary flows becomes less than unity; therefore the density ratio encountered in an actual aero-engine cannot he simulated in the present study. A spoped-wheel-type wake generator is used in this study. Moreover, three types of turbulence grids are used to elevate the free-stream turbulence intensity. We adopt three blowing ratios of the secondary flow to the primary flow. For each of the blowing ratios, wake-affected adiabatic wall temperature around the test surface is measured with the thermocouples in the test model. The effect of elevated free-stream turbulence on the wake-affected film effectiveness is also investigated. Flow visualization by use of liquid crystal is performed to obtain qualitative information on the film-effectiveness distributions.