EFFECT OF DENSITY RATIO ON FILM-COOLING EFFECTIVENESS DISTRIBUTION AND ITS UNIFORMITY FOR SEVERAL HOLE GEOMETRIES ON A FLAT PLATE

摘要

Film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by Pressure Sensitive Paint (PSP) under different density ratios. Several hole geometries are studied, including a streamwise cylindrical hole, a compound-angled cylindrical hole, a streamwise fan-shape hole, a compound-angled fan-shape hole, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (0) of 35°.The compound angle (β) is 45°. The fan-shape hole has a 10° expansion in the spanwise direction. In order to have a fair comparison, the pitches are kept as Ad for the cylindrical and the fan-shape holes, and 8d for the double-jet film-cooling holes. The investigated uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. Effects of density ratios (DR=1.0, 1.5 and 2.5) on film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M=0.5, 1.0, 1.5, and 2.0) are also considered. Results show that at higher density ratios, the lateral spread for discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, and the DJFC holes is more advantageous, and the high effectiveness region near the downstream hole exit is larger. Mostly, increased lateral-uniformity is obtained at DR=2.5 due to better coolant coverage and enhanced lateral spread, but the effects of density ratios on lateral-uniformity are not monotonic in some cases. Utilizing compound angle configuration leads to increased lateral-uniformity due to stronger spanwise motion of the jet. Generally, with higher blowing ratio, the lateral-uniformity for the discrete-hole geometries decreases due to narrower traces, while it for the DJFC holes increases due to stronger spanwise movement.