Experimental analysis of tip vortex cavitation mitigation by controlled surface roughness
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Experimental analysis of tip vortex cavitation mitigation by controlled surface roughness * Urban Svennberg1, Abolfazl Asnaghi2, Robert Gustafsson1, Rickard E. Bensow2 1. Kongsberg Hydrodynamic Research Centre, Kongsberg Maritime AB, Kristinehamn, Sweden 2. Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg, Sweden (Received May 28, 2020, Revised August 19, 2020, Accepted September 3, 2020, Published online December 2, 2020) ©China Ship Scientific Research Center 2020 Abstract: This study presents results of experiments where roughness applications are evaluated in delaying the tip vortex cavitation inception of an elliptical foil. High-speed video recordings and laser doppler velocimetry (LDV) measurements are employed to provide further details on the cavitation behavior and tip vortex flow properties in different roughness pattern configurations. The angular momentum measurements of the vortex core region at one chord length downstream of the tip indicate that roughness leads to a lower angular momentum compared with the smooth foil condition while the vortex core radius remains similar in the smooth and roughened conditions. The observations show that the cavitation number for tip vortex cavitation inception is reduced by 33% in the optimized roughness pattern compared with the smooth foil condition where the drag force increase is observed to be around 2%. During the tests, no obvious differences in the cavitation inception properties of uniform and non-uniform roughness distributions are observed. However, the drag force is found to be higher with a non-uniform roughness distribution. Key words: Roughness, tip vortex, mitigation, cavitation, suppression
Introduction The physics of tip vortex cavitation (TVC), involves simultaneous presence of small flow structures and phase change. Since controlling TVC is vital for low-noise propellers[1-3], intensive efforts have been conducted both experimentally and numerically to understand the physics of this flow. The marine industry generally seeks only to increase the tip vortex core pressure to alleviate cavitation, and to do so, a few approaches are proposed and tested. These approaches generally can be classified into two groups. In the first group, which is called active control, the tip vortex flow is changed by injection of a solution, e.g., air, polymer, or water. In the second group so called passive control, either the propeller geometry is modified or its surface properties, e.g., roughness. In the injection method, interaction between the injected solution and the original tip vortex defines the mitigation. Consequently, the location of injection, the type and amount of injected solution are decisive * Biography: Urban Svennberg (1967-), Male, Ph. D., E-mail: [email protected] Corresponding author: Rickard E. Bensow, E-mail: [email protected]
parameters[4-5]. As an example, Chahine et al.[4] observed up to 35% delay in TVC inception (TVCI) by injecting some combinations of polymer soluti
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