Experimental flow field investigations of a film cooling hole featuring an orifice

• Anti-CRVP effect of a film cooling hole featuring orifice is examined.
• CRVP strength is greatly decreased due to double-decker vortices canceling out.
• Kidney-shaped jet merges to a round jet providing better surface coverage.
• CRVP might not have obvious impact on jet lift-off.

This paper presents the flow field downstream of a film cooling hole geometry featuring orifice, referred to as nozzle hole, on a flat plate using PIV. The experiments were performed with blowing ratios from 0.5 to 2.0, density ratio of 1.0 and mainstream Reynolds number of 115,000. Velocity fields and vorticity fields of nozzle hole jet are compared with that of cylindrical hole jet. The results indicate that nozzle hole jet features double-decker vortices structure, resulting in vortices canceling out and significant reduction in CRVP strength. The streamwise vorticity of nozzle hole jet averages a drop of 55% at low blowing ratio 0.5 in comparison to cylindrical case. At high blowing ratio from 1.0, 1.5 and 2.0, the average drop is 30%–40%. A round jet bulk is observed to merge from the two legs of a typical kidney-shaped jet and the merged jet brings better coverage over the surface. In addition, it is found that CRVP strength might not have strong impact on jet lift-off but influences jet-mainstream mix characteristics.