The filling effect of blockages in wide angle diffusers

Filling of the velocity profile at the exit of diffusers caused by a blockage placed at the diffuser exit plane was investigated. Diffusers tested had total included angles of 15 deg, 30 deg, 45 deg and 180 deg and were of area ratios 2 and 3.5. The Reynolds number at the diffuser entry was 6.6 x 10 to the 4th power. Significant filling was measured for diffusers with a total included angle of 30 deg or greater, accompanied by an increase in static pressure recovery. It was shown that the flow behind the blockage had large spanwise pressure gradients which caused divergent flow and filling. It is suggested that heat exchangers within which nonaxial flow of cooling air is possible are likely to be more efficient.