Abstract
In this paper, the turbulent attached cavitating flows around two different twisted hydrofoils, named as NACA0009 and Clark-y, are studied numerically, with emphasis on cavity shedding dynamic behavior and the turbulence flow structures. The computational method of large eddy simulation (LES) coupled with a homogeneous cavitation model is applied and assessed by previous experimental data. It was found that the predicted results were in good agreement with that of the experiment. The unsteady cavity morphology of the two hydrofoils undergoes a similar quasi-periodic process, but has different shedding dynamic behavior. The scale of the U-type shedding structures forming on the suction surface of NACA0009 is larger than that of Clark-y. This phenomenon is also present in the iso-surface distributions of Q-criterion. Otherwise, the time-averaged cavity morphology is dramatically different for the two hydrofoils, and it is found that the attached location of the cavity is closely related to the hydrofoil geometry. The time fluctuation of the lift force coefficients is affected significantly by the cavity shedding dynamics. Compared with NACA0009, the lift force of Clark-y shows more fluctuation, due to its complicated shedding behavior. Further analysis of the turbulent structure indicates that the more violent shedding behaviors can induce higher levels of turbulence velocity fluctuations.
Highlights
Cavitation is a very important flow phenomenon that influences the design and operation of hydraulic machines [1,2,3,4], such as pumps, ship propellers, and turbomachinery
Ganesh et al [14] conducted a series of experiments and found that the formation and propagation of a bubbly shock wave could cause large-scale shedding of an attached cavity at a small enough cavitation number
Wang [15] indicated that a bubbly shock wave can cause void fraction discontinuity in sheet/cloud cavitating flows in a convergent–divergent channel
Summary
Cavitation is a very important flow phenomenon that influences the design and operation of hydraulic machines [1,2,3,4], such as pumps, ship propellers, and turbomachinery. Energies 2018, 11, 2768 three-dimensional (3D) hydrofoils; Luo et al [11] observed the unsteady cavity behaviors around a mini hydrofoil, and studied the Reynolds number effect on cavitation scale; and Wang et al [12]. Studied unsteady cavitating flow around an axisymmetric projectile, and discussed the effect of free surface on the cavity. These transient cavitating flows present different flow structures, the mechanism of their unsteadiness and shedding dynamics are similar. Wang [15] indicated that a bubbly shock wave can cause void fraction discontinuity in sheet/cloud cavitating flows in a convergent–divergent channel
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