Numerical Simulation Of Vehicle Water-exit Course With Cavitation Under Wave Effect

As the development and utilization of marine resources has been paid more andmore attention, the underwater vehicle technology research and application are alsostrengthened day by day. When the vehicle moves at high speed underwater, there areair bubbles in the shoulder and tail. Due to the density of air much smaller than water,the movement characteristics of the vehicle can get certain effect. When the vehicle ismoving from the water into the air, it will be very complex on the surface load becauseof the influence of the wave force and the bubble collapse. To ensure the vehicle has asmooth underwater movement process and move out of water at correct direction until itreaches the expected location, it’s very nessary to launch the research on wavephenomenon, cavitation mechanism and their coupling effect of the dynamiccharacteristics of the vehicle when it moves from the water into the air.Based on CFD technology, numerical silmulations on water-exit course of thevehicle with cavity bubbles influenced by wave force was performed, in order to obtainthe cavitation time-varying characteristics and the time-space distribution data of forceand surface pressure loading when the vehicle were moving from the water into the aircoupled with wave and cavitation. Establishing under different wave phase the rule ofthe vehicle influenced by wave force and cavitation collapse on the water-exit course,the optimal wave phase for water-exit course was founded through a detailed analysis ofthe data acquired. On the situation of vehicle moving from the water into the air underthe optimal wave phase, further research and analysis were taken on the hydrodynamiccharacteristics of the vehicle influenced by wave and cavitation when the vehicle movedat2°、6°、10°angle of attack with or against the wave from the water into the air andat the angle of45°with or against the wave from the water into the air, respectively.The results of the study show that, the vehicle has the biggest impact load causedby cavitation asymmetric collapse when the water-exit course is being on the wave crest,followed the wave trough. When water-exit course is being on the middlephase(θ=90°,θ=270°), the vehicle gets better symmetry bubble geometry characteristicand mechanical load characteristic, and it is also easier to control the direction of thevehicle. Especially on the phase θ=270°, the water-exit course performs the best, so it isthe optimal wave phase in the research.On the optimal wave phase, the angle of attack of the vehicle has great influenceon the hydrodynamic characteristics for the water-exit course, and the greater the angleof attack, the bigger of the force load and the torque load. At the same angle of attack,the load characters of the vehicle being with or against the wave are almost the same,while the distribution of the bubbles on vehicle are different between positive side andnegative side. With the wave, bubbles mainly cover on negative side, while against the wave, bubbles mainly cover on positive side.On the optimal wave phase, the vehicle with the wave or against the wave hassome effect on the hydrodynamic characteristics for the water-exit course at the angle of45°. With the wave, bubbles on positive side get lager geometry length and thicknessthan that on negative side, while against the wave, bubbles on negative side get lagergeometry length and thickness than that on positive side. But there is little difference onforce load for the vehicle between the situation with the wave and the situation againstthe wave. Only when the cavitation collapses, the situation with the wave shows aslightly bigger impact on the vehicle than that against the wave.