Cavitation Inception Observations on Axisymmetric Headforms with Turbulence Stimulators.
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD
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Cavitation inception observations were made in the DTNSRDC 36-inch water tunnel on three axisymmetric headforms with and without various turbulence stimulators installed. Direct measurements of transition, made on two of the headforms with and wothout distributed surface roughness, were found to correlate reasonably well with the computed spatial amplification factors, e to the Nth power with 7 or N or 10. The computed e to the Nth power factors were then used to estimate transition at other test conditions without direct transition measurements. The predicted transition locations on all three smooth headforms occur at position considerably aft of the minimum pressure locations. The three smooth headforms have different types of incipient cavitation--small band, transient spot, traveling bubble, and attached spot. The measured cavitation inception numbers for those cases are all significantly smaller than the computed negative values of the minimum pressure coefficient, -C sub pmin. The predicted transition locations on the three headforms with densely- and loosely-packed 60 micron distributed roughness occur a considerable distance upstream of the minimum pressure locations. Therefore, the flows over all three headforms with distributed roughness are turbulent at the C sub pmin locations for the Reynolds numbers tested. Under this condition, the measured cavitation inception numbers are found to approximate well the values of -C sub pmin. The incipient cavitation is in the form of attached small bubble lines evenly distributed around the minimum pressure locations. Author
- Test Facilities, Equipment and Methods
- Fluid Mechanics