MEASUREMENTS OF A SWIRLING TURBULENT BOUNDARY-LAYER DEVELOPING IN A CONICAL DIFFUSER

Measurements were made of the swirling boundary layer developing in a conical diffuser with a 20-degrees included angle and an area ratio of 2.84. The inlet swirl was close to solid-body rotation and was of sufficient magnitude to prevent boundary layer separation but just insufficient to cause recirculation in the core flow. A single hot-wire was traversed from the wall to the centerline to determine the mean velocities. All six Reynolds stresses were measured within the boundary layer using a rotatable X-probe. The discussion concentrates on the complex response of the turbulence to the numerous perturbations imposed by the swirl and the geometry, of which the dominant ones appear to be the axial pressure gradient and the streamline curvature.