Experimental Flow Field Investigations Downstream a Film Cooling Scheme Over a Flat Plate Using the PIV Technique

This paper presents experimental investigations of the flow field characteristics downstream a Scaled-Up Micro-Tangential Jet (SUMTJ) film cooling scheme using the Particle Image Velocimetry (PINT) technique over a flat plate. The SUMTJ scheme is a shaped scheme designed so that the secondary jet is supplied tangentially to the surface. The scheme combines the thermal benefits of tangential injection and the enhanced material strength of discrete holes schemes, compared with continuous slot schemes. The flow field characteristics downstream one row of holes were investigated at three blowing ratios, 0.5, 1.0 and 1.5, calculated based on the scheme exit area. A density ratio of unity, a Reynolds Number of 1.16E+5 and an average turbulence intensity of 8%, were used throughout the investigations. The performance of the SUMTJ scheme was compared to that of the circular hole scheme, based line case, at the same test conditions and blowing ratios. From the investigations, it was noticeable that the SUMTJ scheme jet stays attached to the surface for long downstream distances at all investigated blowing ratios. Moreover, the lateral expansion angles of the scheme help perform a continuous film from adjacent jets close to the schemes exits; however, they have bad impact on the uniformity of the film thickness in the lateral direction. The vorticity strength downstream the SUMTJ scheme in the y-z plane was much less than the vorticity strength downstream the circular scheme at all blowing ratios. However, the vorticity behavior in the shear layer between the secondary SUMTJ scheme jet and the mainstream was changing dramatically with blowing ratio. The latter is expected to have a significant impact on the film cooling performance enhancement with blowing ratio increase.