An Experimental Investigation into the Influence of Ramp-Mounted Vortex Generators on the Performance of a Flush Waterjet Inlet

Abstract

The use of ramp-mounted vortex generators for reduction of pump face flow distortion within a generic flush type waterjet inlet has been investigated experimentally. Tests were performed in a cavitation tunnel with the model inlet fitted to the ceiling of the test section and an upstream boundary layer artificially thickened to 30° of the inlet duct diameter. A group of four delta-shaped vortex generators on the inlet ramp mounted symmetrically about the vertical center plane were tested at six streamwise locations and at two incidences. The vortex generators were oriented each side of the centerplane to produce corotating vortex pairs opposing the effects of the dominant secondary flow within the curved duct. The model inlet was fitted with a range of instrumentation to investigate the ramp pressure distribution, lip incidence, and pump face flow properties. Lip cavitation inception, and vortex generator cavitation inception and occurrence were also investigated. Pump face flow distortion within the bare duct flow, which was dominated by a total pressure/velocity deficit at the top of the disc, was significantly reduced by the addition of the vortex generators. Circumferential distortion improvements were assessed using a distortion parameter, harmonics of the velocity variation, and considerations of rotor blade incidence variation. The vortex generators were found to have little effect on local lip pressures and consequently lip cavitation inception; they also had a negligible effect on the duct pressure recovery. Cavitation occurrence on the vortex generators was found to present potential performance limitations at low cavitation numbers.