Studies on Cooling Air Ejected Over a Corrugated Wall: Its Aerodynamic Behavior and Film Effectiveness

Abstract

This paper describes experimental studies on aerodynamic behaviors of the air ejected from several discrete hole rows on a corrugated wall and the resultant film effectiveness over the wall. The corrugated wall is a model of an air-cooled liner surface for aero-engine augmentors. Measurements on the aerodynamic aspects are conducted by use of a pneumatic five-hole probe in order to clarify the features of the ejected air over the corrugated wall. The temperature field is examined by traversing a thermocouple, which also reveals the behavior of the ejected air. Film effectiveness associated with the air-ejection is then determined from the extrapolation of the measured temperature profile. It is accordingly found that the air jets near the ejection holes behave like those from the holes on a flat-plate, being accompanied by upward and downward secondary flows around the jets. Close inspections on the behavior of the jets also reveal that the jet cores tend to diminish much faster than those in the flat-plate case, which is probably due to a mixing of the high-momentum jet and low-momentum air on the ‘valley’ of the corrugated wall. Such characteristics of the jets result in transversely uniform distribution of the temperature which is favorable to the liner surface protection from the extremely hot gas.