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Eighth International Symposium on Turbulence and Shear Flow Phenomena
August, 28-30, 2013, Poitiers, Futuroscope, France

DOI: 10.1615/TSFP8

HIGH-SPEED IMAGING AND PIV MEASUREMENTS IN TURBULENT CAVITATING FLOWS AROUND 2D HYDROFOILS

pages 1-6
DOI: 10.1615/TSFP8.1570
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SINOPSIS

The paper reports on high-speed imaging and PIV study of cavitating flows around a flat plate with semicircular leading edge and a NACA0015 hydrofoil. Both foils were investigated at a series of attack angles ranging from 0 to 9° with varying cavitation number. Several known types of cavitation common to both foils, but also some different patterns, were registered. At small angles of incidence (less than 3°), cavitation on the plate begins in form of a streak array (bubble-band) whereas on the hydrofoil as travelling bubbles. For the regimes with developed cavitation on the NACA0015 hydrofoil, the scattered and discontinuous bubble streaks branch and grow but subsequently merge into bubble clouds forming a remarkably regular lattice pattern. Once the incidence angle increased to 9°, the cavitation on the hydrofoil changed to a streaky pattern like that on the plate at zero attack angle, whereas the regime on the plate showed no significant changes. The time-averaged velocity and turbulence moments show that the incipience of cavitation is governed by the development of the carrier-fluid flow around the foil leading edges, but the subsequent flow pattern depends strongly on the cavitation regime displaying markedly different distributions compared to the noncavitating case. The influence of the test object scale and the foil surface roughness on the cavitation pattern as well as on the mean velocity and turbulence intensity was analyzed. Thus, surface roughness leads to faster turbulization of the boundary layer and, consequently, to growth of the transversal dimension of the turbulent wake. Turbulent wake past the foil was shown to be wider for the larger hydrofoil due to the flow acceleration as a result of greater flow blockage.

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