A Theory for Cavitation Inception in a Flow Having Laminar Separation.
Abstract
An approximate theory is developed to predict onset of cavitation on hemispherical head forms for Reynolds numbers at which laminar separation is known to occur. Fairly good agreement is obtained between cavitation inception (or desinence) trends recently measured and the present theory which is based upon first principles as far as possible. Moreover, the observed occurrence of a lowest speed for 'bubble-ring' cavitation, which is the only cavitation form considered, and the range of 'cutoff' speeds predicted by the present asymptotic theory show very encouraging agreement. Like the experiments, this theory suggests that the cutoff speed and its accompanying cutoff cavitation number can also depend on water temperature, provided that the initial size attributed to a 'typical' spherical free-stream air bubble nucleus also varies with temperature. At 80 F (26.6 C) it is found that the typical nucleus from which bubble-ring cavitation orginates has a radius of about seven microns. At higher temperatures the nucleus radius decreases from this value while at lower temperatures the initial radius exceeds the value noted. It is also found that: the onset cavitation number should be less than the magnitude of the pressure coefficient at the laminar separation point; and that the cavitation number increases with free-stream velocity. As long as there is an appreciable concentration of dissolved air in the water, it is also found that in agreement with experiment, the onset of bubble-ring cavitation is practically independent of air content.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 19, 1979
- Accession Number
- ADA082851
Entities
People
- B. R. Parkin
Organizations
- Pennsylvania State University