Accession Number : ADA296662

Title :   A Study of Tip Vortices and Cavitation on a Propeller in a Non-uniform Flow Field.

Descriptive Note : Doctoral thesis 1992-1994,

Corporate Author : CALIFORNIA INST OF TECH PASADENA

Personal Author(s) : McKenney, Elizabeth A.

PDF Url : ADA296662

Report Date : 23 MAY 1995

Pagination or Media Count : 165

Abstract : Unsteady lifting surface flows are important subjects for study, both for the purposes of improving propulsive or lifting efficiency and also for mitigating the destructive effects and noise caused by cavitation. Some progress may be made by selecting a simple type of unsteadiness for closer study. In the present work, this tactic was implemented in two ways: the operation of a propeller at an angle of yaw to the freestream and the pitching oscillation of a finite-span hydrofoil. A new facility was designed and constructed to set a propeller at an angle of yaw to the freestream, creating a fairly simple non-uniformity in the propeller inflow. Tip vortex cavitation inception measurements were made for a range of yaw angles and freestream velocities, and photographs of the cavitation were taken to illustrate the effects of the yaw angle. The unsteady tip vortex flow field was measured on an oscillating finite aspect ratio hydrofoil using Particle Image Velocimeter (PIV), reveal in how the circulation varied during a typical oscillation cycle. The results were compared with unsteady infinite-span theory, and also with recent measurements using LDV techniques on the same foil. The hydrofoil was also the focus of a study of surface cavitation. High-speed motion pictures of the cavitation cycle helped to separate the process into its component stages, and variations with cavitation number and reduced frequency of oscillation were observed. The acoustic signals generated by the cavity collapse were correlated with the motion pictures, providing insights into the correspondence between the flow structures involved in the cavity collapse process and the sound generated gy them. The results from these studies provide valuable insights into the effects of unsteadiness in lifting surface flows. (AN)

Descriptors :   *VORTICES, *FLOW FIELDS, *MARINE PROPELLERS, *NONUNIFORM FLOW, *CAVITATION, VELOCITY, HIGH FREQUENCY, PITCH(MOTION), YAW, TWO DIMENSIONAL, SHOCK WAVES, SHIP MOTION, EFFICIENCY, TURBULENCE, ANGLE OF ATTACK, WAKE, DATA ACQUISITION, ACOUSTIC SIGNALS, UNSTEADY FLOW, FLOW NOISE, OSCILLATION, FREE STREAM, CIRCULATION, SHIP HULLS, ASPECT RATIO, BOUNDARY LAYER FLOW, LASER VELOCIMETERS, HIGH SPEED PHOTOGRAPHY, HYDROFOILS, LIFTING SURFACES, BLADE TIPS, MOTION PICTURE PHOTOGRAPHY.

Subject Categories : Marine Engineering
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE