Question

When the hydrofoil shown was tested, the minimum pressure on the surface of the foil was found to be 80 kPa absolute when the foil was submerged 1.9 m and towed at a speed of 7 m/s. At the same depth, at what speed will cavitation first occur? Assume irrotational flow for both cases and T = 10 °C. Water = 10°C (50°F) (a) What is the absolute pressure of the atmosphere? kPa (b) What is the specific weight of water at this temperature? N/m3 (c) What is the absolute pressure in the water at the depth of the hydrofoil? kPa (d) What is the vapor pressure of water at this temperature? kPa Click if you would like to Show Work for this question: Open Show Work

Answer 1

Solution - Depth do 1.9m Towing speed - 7 m/s Part -1:- The absolute of pressure atmosphere is 101.3 kpa The Specific Specific weight of water at 10°C is 9810 N/m3 1.9 m - The absolute pressure at a depth of - is :- Po - Patm thr 101.3 x 103 + 1.9 x 9810 Po 119.939 kpa of Water at 10°C is The 1230 Pa. vapour pressure Pvapor 1.230 kpa Part-2:- → The difference between the minimum pressure and water at pressure 1.9 m depth is obtained 1:- Pmin - Po 80 - 119.939 Pmin- PO = 39.939 kpa + The is obtained as : dynamic pressure pvz. 1000 x (7)2 24500 Pa - 24.5 kpa 2 2 CS Scanned with CamScanner

The value of pressure Coefficient is obtained on:- Cp = Pmin - po PV2 2 Cp- 39.339 24.5 Cp : -1.63 Part-3 = The absolute Value of minimum pressure when Cavitation OCwrs is equal to the vapor pressure at 10°c. .: Pcay Pvapor Pray = 1.230 kPa remains constant - The value of pressure coefficient Cp = -1.63 at which cavitation will the velocity Now, occar: evaluating Cp = Pray - Po e Vcay 2 2 -1.63 - 1230 119939 1ooo x Vcav? 2 Vcay = V = 12.068 m/s CS Scanned with CamScanner