Inlet free-stream turbulence effects on diffuser performance

The performance of a subsonic two dimensional diffuser was experimentally evaluated as a function of inlet free-stream turbulence parameters. Anisotropic inlet free-stream turbulence with the eddy axis perpendicular to the flow and parallel to the diverging walls of the diffuser appears to be more effective at transmitting energy to the diverging walls of the diffuser, thereby improving diffuser performance, as compared to isotropic turbulence or anisotropic turbulence with the eddy axis perpendicular to the diverging walls of the diffuser. The pressure recovery of the diffuser was found to be strongly dependent upon the inlet free-stream total turbulence intensity, was independent of eddy size for large eddy dimensions, and was dependent upon eddy size for small eddy dimensions. The improvement in the diffuser's static pressure recovery coefficient at a total included divergence angle of 20 deg, compared to the low inlet turbulence case, was found to be as much as 21 times larger than the pressure loss across the turbulence generators.