Numerical Simulation For Ventilated Supercavitation On Underwater Bodies In Drag-reducing Solution

Cavitating means when the local pressure in the flow reduces to the saturatedvapor pressure, the vapor or gas cavities will appear, develop and collapse. when theunderwater bodies sail at a high-speed, the naturally cavitating will occur at the headof the bodies, the local cavities will be formed; at the same time, the gas will bepassed into the local cavities through the breather devices and the pressure in thelocal cavities will be increased; then the cavities grow up and the fully developedcavitating flow will be formed. The gas can surround the whole bodies expect thehead, the ventilated supercavities are formed. In this case, only the head of thebodies is in contact with water; most of the bodies are wrapped by the gas; therebythe resistance will be greatly reduced, it can be widely used in the military fields.When we put little turbulent drag-reducing additives into the water, the surfacetension and turbulent drag will be both reduced while the occurrence of boilingphenomenon will be enhanced, which all may play positive roles in the cavitating.The paper studied the ventilated supercavitating flow on underwater bodiesinfluenced by turbulent drag-reducing additives numerically.Firstly, the models to simulate the ventilated supercavitating flow have beenfounded based on unsteady Reynolds averaged Navier-Stokes scheme. Thetwo-phase ventilated supercavitating flow around the cavitator in water has beennumerically simulated based on different turbulence models; compared the resultswith the existing correlations, we find the results based on Realizable k-ε model arein best agreements with the existing correlations. At the same time, compared thevalues calculated by the Cross viscosity equation and the experimental values of thePAM and CTAC solution viscosity in different concentrations, we find the values ofthe viscosity calculated by the Cross viscosity equation in good agreements with theexperimental values; in other words, the Cross viscosity equation can be used tocalculate the viscosity of the drag-reducing solution.Secondly, the ventilated supercavitating flow on underwater bodies in the waterand drag-reducing solution has been numerically simulated. The flow resistance,constituent characteristics and development processes of the ventilated supercavitiesare all discussed. Numerical results show that the drag-reducing solution mainlyinfluence the viscous drag when the supercavities are not fully formed. Themaximum viscous drag reduction ratio can reach to49.66%in the two-phase flowwhile it can reach to58.13%in the three-phase flow. In the three-phase flow, it alsohas some influence on the pressure drag. The distributions of the constituents in water and drag-reducing solution are almost unanimous in the two-phase flow whilethey are different in the three-phase flow. The vapor bubbles caused by naturallycavitating are bigger and can remain longer in the drag-reducing solution; in otherwords, the drag-reducing solution is conducive to the generation and maintaining ofnatural cavitation.Lastly, a new method has been pointed out to achieve the ventilatedsupercavities, known as the ventilated supercavitaties influenced by drag-reducingsolution passed into; it is means that both the drag-reducing solution and gas arepassed into the water at the same time. The ventilated supercavitating flowinfluenced by drag-reducing solution passed into on underwater bodies in the waterhas been numerically simulated. The flow resistance, constituent characteristics anddevelopment processes of the ventilated supercavities influenced by drag-reducingsolution passed into are all discussed. Numerical results show that with thedrag-reducing solution passed into, the directions of liquid flow have been changed;further it can have influence on the distribution of vortex structures and pressurefield. For the drag reduction, when the drag-reducing solution was passed into, thepressure drags and viscous drags are both changed; the whole drags are all smallerthan only passing into air in the water or solution; in other words, the ventilatedsupercavitaties influenced by drag-reducing solution passed into has the better dragreduction.