Numerical Simulation For Supercavitation In Drag-Reducing Solution

The potential drag reduction associated with supercavitation has led to interest in supercavitation flow. When the speed of an underwater vehicle reaches a certain value, water pressure near the cavitator placed at the nose will be lower than the saturated vapor pressure, cavitation happens, with cavities generating in the head position; when the speed is larger than the critical value, the body will be completely enshrouded in a gaseous cavity, that emanates downstream of a cavitator, which is called supercavitation. Now supercavitation is a revolutionary method to make drag reduce up to 80% on an underwater vehicle. Supercavitating flow is a conundrum which includes many complex flow phenomena such as unsteady flow, phase transition, and turbulence in hydrodynamics. So it's still a challenge to simulate the supercavitating flow numerically on both physical and numerical aspects. The simulation of cavitating flows is of great importance for the efficient design and performance of many engineering devices. The surface tension suppresses the expansion process of a vacuole and accelerates its shrinkage process. Adding a minute amount of surfactant additive or polymers into water, the surface tension of water can be decreased dramatically. Furthermore, the surfactant molecules can transform into network microstructures so as to impart viscoelasticity into surfactant solution and then inhibit turbulence, i.e., drag reduction.Natural supercavitation in water and drag-reducing solution, respectively, had been numerically simulated based on unsteady Reynolds Averaged Navier-Stonkes (URANS) scheme, and Mixture-multiphase model was used. The Cross viscosity equation was adopted to represent the flow characteristics of drag-reducing solution. The configuration and resistance characteristics of natural supercavitation were discussed. The numerical simulation results indicated that at the same cavitation number, the size of supercavity in drag-reducing solution is larger than that in water, and the drag coefficient is smaller than that in water. The surface tension plays an important part in cavity generation and maintaining. There exists a critical cavitation number for drag-reducing solution. Furthermore, the numerical simulation results are in good agreement with the available experiments.The comparisons of configuration and resistance characteristics of ventilated supercavitation in water and in drag-reducing solutions are made. At the same cavitation number and the same ventilation rate, the resistance is smaller in drag-reducing solutions than that in water.