Cavitation on two-dimensional hydrofoils with swept leading edges always displays some 3-dimensional effects. It is well known that the cavity closure on such hydrofoil is not perpendicular to the ...channel walls, but is curved in a distinctive pattern. The cavitation pocket is longer in the region where the hydrofoil is the shortest. Also the dynamics of cavitation is very distinctive. In the region where the hydrofoil is the longest attached and steady cavitation with no cloud separation exists. On the other side, where the hydrofoil is the shortest, cavitation cloud separations occur.
Different explanations for this pattern were proposed in the past but they have not jet been clearly confirmed neither experimentally nor by numerical simulation.
In the present paper a clear explanation supported by the numerical simulation and also by experimental measurements, is given.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The steady and unsteady cavitation phenomena on a 2D NACA0015 hydrofoil predicted by the multiphase RANS code FLUENT are studied in this paper. Besides a numerical sensitivity study of the ...non-cavitating condition, the present investigation focuses on two cavitation numbers: σ=16 (steady cavitating flow) σ=1.0 (with dynamic shedding). With a modified SST K – ω turbulence model, a periodic shedding is revealed: the main sheet cavity breaks up by the re-entrant jet and a cloudy cavity forms and is convected with the downstream flow. Finally, the experience with FLUENT has been used to discuss the general ability of multiphase RANS codes to predict the cavitation erosion risk.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPCLJ, UPUK, VKSCE, ZAGLJ
A transport equation-based cavitation model was developed according to the homogeneous assumption in this paper. The mechanism of evaporation and condensation was considered in the model. The ...non-condensable gas was also taken into account in cavity formation and development. The RNG turbulence model was employed with a modified turbulent viscosity according to the mixed density.The proposed model was implemented to simulate the steady cavitating flow around a NACA66 airfoil. The pressure coefficient distributions on the suction side of the foil agreed well with the experiment results. Furthermore, the effects of non-condensable gas, inlet turbulent kinetic energy and turbulence dissipation rate on the cavity length were evaluated. The proper values of non-condensable gas, inlet turbulent kinetic energy and turbulence dissipation were selected. Then, the proposed model was applied to an unsteady cavitating flow. The numerical results clearly reflected the whole process of the cavitation cloud generation, grow
Based on the Reynolds time-ave raged N-S equations, the unsteady cavitating flow around ys930 hydrofoil was simulated by the RNG k- epsilon turbulence model and the mixture two-phase caviatation ...model. The characteristics of unsteady cavitating flow and the cavity evolution process around the hydrofoil at a 10 deg attack angle at three cavitation numbers 1.0, 0.8 and 0.5 were obtained. The results show that there are two parts in a cavity, the front part is attached to the suction surface of the hydrofoil and full of water vapor. The rear part is the periodic, unsteady, collapsible two-phase flow zone. The attaching point of the front part is basically stable, the length of the cavity initially is increased, subsequently decreased. The length is decided by cavitation number and strength of re-entrant jet simultaneously. The thickness of the cavity firstly rises, and then is reduced. The smaller the cavitation number, the closer to the trailing edge of the hydrofoil the maximum thickness location. The strength
The paper presents the re-entrant jet analysis of cavitating turbulent flow on a hydrofoil. Analysis was performed by OpenFOAM code. A mixture assumption and a finite rate mass transfer model were ...introduced. The finite volume method is used to solve the governing equations of the mixture model and the pressure-velocity coupling is handled via a Pressure Implicit with Splitting of Operators (PISO) procedure. The result of numerical simulation clearly explained the mechanism of re-entrant jet and quasi-periodic law of cavitating flow on a hydrofoil.
Numerical simulations of cavitating flows on 2D NACA0015 hydrofoils with and without obstacle are performed. Cavitation model is based on a transfer equation for a void mass fraction and an improved ...RNG k-ɛ model is adopted to study the turbulent cavitating flows around the foils. Different arrangements and geometric parameters of the obstacles are investigated. Computational results show that cloud cavitation can be reduced effectively by an obstacle placed on the foil surface; also the performance of the hydrofoil is changed by the obstacle simultaneously.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPCLJ, UPUK, VKSCE, ZAGLJ
Ventilated cavities are characterized by the cavity shape, size, inception mechanism, cavity pressure with drag reduction, re-entrant jet and bubble breakoff from the cavity tip. All these ...characteristics are dependent upon each other. The aim of the present work is to study these aspects in an integrated way. Ventilated cavity formation was studied in a transparent acrylic channel by sparging gas behind straight blades. Clinging, partial, full and large cavity shapes were observed. Cavity transitions are correlated with the Froude and aeration numbers. Other cavities such as slug, and emulsion cavity were also observed. Bubble breakoff from the cavities is found to be dependent on the cavity type. Typically, large bubbles breakoff from slug cavities while smaller bubble sizes are observed breaking off from emulsion cavities. Other cavity shapes show a mixed breakoff pattern of varying proportion of large and small bubbles. Change in drag force on the blade is found to be dependent on the cavity shape and size. The cavity pressure is correlated with the liquid velocity over the blade and the superficial gas velocity. Negative and positive cavity pressure is found to be associated with the presence and absence of re-entrant jet.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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