PSI - Issue 27

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Muhammad Yusvika et al. / Procedia Structural Integrity 27 (2020) 109–116 Yusvika et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. The cavitation patterns of the biased propeller (a1, a2,a3) and balanced propeller (b1,b2,b3) (Feng and Lu, 2019).

Under the same operating conditions, the balanced propeller produces a smaller water-vapor volume fraction than a biased propeller. At the propeller rotates to 150° and 240° , the water vapor volume fraction of the balanced propeller is 2.56% and 9.36%. It can be concluded that the balanced propeller is a better design based on the performance under the cavitation condition. 4. Cavitation profile under behind-hull operations To improve the accuracy of the prediction of the phenomenon of cavitation on propellers, researchers also consider various aspects that may allow as the factors that are underlying the cavitation inception. Behind the hull condition, the direction of fluid flow can have many differences depending on the surface contour of the hull. It can be allowed that the cavitation pattern and the hull pressure fluctuation behind hull conditions have differences compared to open flow conditions. So, cavitation flow behind the hull condition is essential to be considered to understand the cavitation behavior and the pressure fluctuation. Paik et al. have performed unsteady Reynolds-Averaged Navier-Stokes (RANS) equations to simulate cavitation flow and hull pressure fluctuation for a marine propeller operating behind hull conditions (Paik et al., 2013). The simulations are performed using ANSYS Fluent, a commercial CFD software. The simulations are validated by the experiment that has been carried out in Samsung Cavitation Tunnel (SCAT). The simulation results, which, compared to the experimental results, show good agreement for the cavitation pattern and the hull pressure fluctuation induced by the propeller. Schneer and Sauer's cavitation model was applied to the numerical setup using Multiple Reference Frame (MRF) approaches. The results for simulation under cavitating flow compared with the experimental results were started for the wakefield without the propeller. Fig. 2 shows the comparison of the velocity contour of the experimental research compared with simulation results at the propeller plane. The wake velocity contour and vector are very similar. Then, cavitation patterns at iso-surface α = 0.1 are presented and also have an agreement results with experimental observation. a b

Fig. 2. (a) Velocity contours and cavitation pattern, respectively. (a) Experimental observation; (b) Simulation results (Paik et al. 2013).

The hull pressure fluctuations at design draught conditions are compared with experimental data. For the simulations that have been conducted by Paik et al., the pressure fluctuations are performed for two types of propeller cavitation conditions, there are design ballast condition and ballast draught condition (Paik et al., 2013). From Fig. 3, it can be known that the first blade frequency has similar results between the experimental results and simulation results. Several points to note the position of pressure transducers are installed on the model experimental and numerical setup. The amplitudes of the first blade frequency are higher by 10% than the experimental results. In contrast, for the second blade frequency, the pressure amplitudes are significantly lower than the experiments because the effect of the axial velocity gradient may be diminished because the larger cavity extends in the ballast draught conditions.