Abstract
The simulation of fully turbulent, three-dimensional, cavitating flow over Delft twisted foil is conducted by an implicit large eddy simulation (LES) approach in both smooth and tripped conditions, the latter by including leading-edge roughness. The analysis investigates the importance of representing the roughness elements on the flow structures in the cavitation prediction. The results include detailed comparisons of cavitation pattern, vorticity distribution, and force predictions with the experimental measurements. It is noted that the presence of roughness generates very small cavitating vortical structures which interact with the main sheet cavity developing over the foil to later form a cloud cavity. Very similar to the experimental observation, these interactions create a streaky sheet cavity interface which cannot be captured in the smooth condition, influencing both the richness of structures in the detached cloudy cavitation as well as the extent and transport of vapour. It is further found to have a direct impact on the pressure distribution, especially in the mid-chord region where the shed cloud cavity collapses.
Highlights
It is generally accepted that an efficient propeller needs to operate in cavitating conditions while still preventing the negative effects of cavitation including noise, vibrations and erosion, which are the results of high-frequency pressure fluctuations induced by the cavity collapse [1,2]
In region (I), the measured pressure is close to the saturation pressure, which indicates a dominant sheet cavitation over this region
Effects of the leading-edge roughness on the flow vortices development and cloud cavitation formation are investigated by the numerical modelling of turbulent cavitating flows around the Delft Twist11 foil
Summary
It is generally accepted that an efficient propeller needs to operate in cavitating conditions while still preventing the negative effects of cavitation including noise, vibrations and erosion, which are the results of high-frequency pressure fluctuations induced by the cavity collapse [1,2]. The numerical simulation of cavitation, involves very complex flow physics modelling, such as mass transfer, compressibility, and the simultaneous presence of various temporal and spatial flow scales, making it a challenging fluid dynamic concept. Twisted foils have been used experimentally as the flow, which by design can resemble some structures of three-dimensional propeller cavitating flows, such as interaction of the cavity with vortical structures, cavity collapses, vibration and erosion risk, with the possibility of being tested in a more controlled condition. The cavitation regime of a twisted foil, is highly affected by a possible laminar boundary layer forming on the leading edge. An attached leading-edge sheet cavity does not develop when the boundary layer is laminar, and remains attached to the surface even if the pressure falls below the saturation pressure.
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