Experimental Study of Flow in a High Aspect Ratio 90 Deg Curved Diffuser

Measurements for developing turbulent flow in a high aspect ratio (AS = 6), small area ratio (AR = 2), 90 deg curved diffuser have been made. Mean velocities, static and total pressures, and turbulence intensities were measured using a three-hole pressure probe and a hot-wire probe. Flow visualization studies were also made using a tuft probe. Experiments show that, except for a very small zone near the exit, there is no flow reversal in any part of the diffuser. Streamwise bulk flow is seen to shift toward the concave wall side in the downstream half of the diffuser, under the influence of centrifugal force. One pair of counter-rotating vortical motion was identified at 30 deg turn, which break into more pairs (at least two) of counter-rotating vortices in the downstream. The z-plane velocity profiles show a nearly 2-D flow in the initial part of the diffuser but subsequently the flow becomes increasingly 3-D. A static pressure recovery coefficient of 51 percent was achieved.