Question

When the hydrofoil shown was tested, the minimum pressure on the surface of the foil was found to be 75 kPa absolute when the foil was submerged 1.8 m and towed at a speed of 6 m/s. At the same depth, at what speed will cavitation first occur? Assume irrotational flow for both cases and T = 10 °C.

Answer 1

Sol Given data: minimum pressure on the surface of the foil = 75 kpa , foil submeged 6-8 m (Pran Speed Cro] = 6 m/s Temperature (t) = loc a) Absolute value of the minimum pressure nshen cavitation OCCUYS Pear Pot1.88 - 101325 +1.8 x 9810 = 118983 pa = 118-983 kpa : Pear 118.883 kepa b) pressure coefficient when cavitation occurs pressure coefficient - Ccp2 Pmin - Pear (svor]/2 (75-118.983.]x103 (1000x6)/2 (:-S= 1000 kg/m3] = -2.4435 . pressure coefficient c 'Cep] = = -2.4435 velocity at which cavitation nill occur vapour press core at loc vp = V min = 1230 pa

.: pressure coefficient ccp) Prin - Po [Svor] 12 -2.4495 12.30- 118983 (1000x V63/ 96.3806 ó. V = 796.3806 i v 9.817 mls pressure coefficient ccp) = 9.817 m/s