Numerical Study of Cavitating Structure Near Wake of a Circular Cylinder
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A study of the existing literature on flow past circular cylinder reveals that less work has been reported in the upper sub-critical flow regime which corresponds to Reynolds number (ReD) in the range 2x104 < ReD < 2x105. Hence, this work brings out the flow features in the near wake of a cylinder for a sub-critical flow regime under non-cavitating as well as under different cavitating conditions. A three-dimensional numerical study of flow around a circular cylinder was carried out at ReD=6.4x104 for a wide range of cavitation number (1.06 ≥ σ/σi ≥ 0.5). Unsteady Reynolds averaged Navier-Stokes (URANS) approach coupled with Schnerr-Sauer cavitation model available in ANSYS-Fluent was used for this purpose. With the help of fine mesh around the cylinder and choice of suitable time step size, this study identifies factors influencing the occurrence of cavitation and portrays dynamics of cavities downstream of the cylinder. As a part of the validation of the numerical approach, variations of mean pressure coefficient around the cylinder as well as mean and fluctuating coefficients of base pressure have been compared with experimental data available in literature and a good agreement between the two have been observed. With a reduction in cavitation number, cavitation activity extends downstream. Based on the fast Fourier transformation (FFT) of pressure and vapor fraction data, it can be concluded that vortex shedding is suppressed due to the formation of extended cavities in the wake. Another interesting observation is the interplay between flow turbulence and cavitation structures. Simulations indicate that with increasing downstream distance from x/d=0.3 (near the cylinder) to x/d=3 (away from the cylinder), pressure recovers and turbulent kinetic energy decreases in case of non-cavitating flow. However, in case of cavitating flow, turbulent kinetic energy is higher at the region of collapse of vapor pockets than that at near the cylinder which is lower than that corresponding to the non-cavitating case at the same location.