Characteristics of separated flows including cavitation effects

A program of study has been carried out to obtain the characteristics of two-dimensional separated flows including cavitation effects. The effects of wall interference and cavitation on the characteristics of flow past bluff bodies and backward facing steps were examined. Separated flows so generated can be a major source of flow induced vibration and noise.

For non-cavitating flow past sharp-edged bluff bodies, a simplified procedure is developed to determine the effects of wall interference on the drag coefficient. The characteristics related to inception, choking, cavity geometry and cavity pressure field were determined on the basis of experimental results for cavitating flow past bluff bodies. In this context, models based on theoretical considerations were also developed to determine the inception and choking cavitation characteristics. For sharp-edged bluff bodies, the length of vortex formation region was determined, recognising it as a significant parameter which precedes the zone where cavitation damage is most probable. Visual observations of the length of formation region supported the view that cavitation stabilises the vortex against its break-up.

The effects of wall interference and cavitation on the frequency of vortex shedding behind bluff bodies were also determined. The absence of the Karman vortex street was noted for flow past bluff bodies which were subject to very severe wall interference effects.

At very large Reynolds numbers, the reattachment of two-dimensional separated shear layers downstream of backward facing steps were investigated. Two backward facing steps were used to study the influence of expansion ratio on incipient cavitation indices at various Reynolds numbers. The frequency of vortex shedding and pressure distribution downstream of separation were obtained for both cavitating and non-cavitating flow conditions.