Bow and Stern Control Surface’s Effectiveness and Influence on Supercavity

The numerical model of supercavitating flow field was established based on multiphase model, cavitation model, and turbulence model. The model was employed to simulate the supercavitation flow for the supercavitating vehicle with two types of control surfaces: bow rudder and stern rudder. The influence of both control surfaces on the supercavity shape and rudder effectiveness is compared under the different rudder angles (0-12°), and the effectiveness and the influences on supercavities of bow rudder and stern rudder were explored according to the numerical research results. From the research results, the following conclusions can be drawn: (1) the bow rudders have stable rudder effectiveness and available rudder angle, and the bow rudders also have significant influence on supercavities’ shape. (2) By contrast with the bow rudder, stern rudders’ effectiveness is difficult to predict accurately, and the phenomenon of stalling will occur when stern rudders’ rudder angle exceeds 6°; however, there is almost no influence of stern rudders on supercavities. (3) The bow and stern rudders joint control mode must take the influence on supercavities’ shape and the accuracy of control force’s forecasting into account at the same time. The research is helpful to the optimizing of superhigh-speed vehicles and the design of control modes.

Raising the Speed Limit of Axial Piston Pumps by Optimizing the Suction Duct

The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps. However, increasing the speed beyond the limit always accompanies cavitation, leading to the decrease of the volumetric efficiency. The pressure loss in the suction duct is considered a significant reason for the cavitation. Therefore, this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit. At first, a computational fluid dynamics (CFD) model based on the full cavitation model (FCM) is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model. Then the topology optimization is conducted for obtaining the minimum pressure loss in the suction duct. Comparing the original suction duct with the optimized one in the simulation model, the pressure loss in the suction duct gets considerable reduction, which eases the cavitation intensity a lot. The simulation results prove that the speed limit can increase under several different inlet pressures.

Numerical study of cavitating flow over hydrofoil in the presence of air

Purpose The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are performed with the assumption of different models. The Singhal cavitation model and the models which resolve the non-condensable gas including 2phases and 3phases are implemented in the numerical model. The calculations are performed with the uRANS model with assumption of the constant temperature of the mixture. The two-phase flow is simulated with a mixture model. The dynamics and structures of cavities are compared with literature data and experimental results. Design/methodology/approach The cavitation regime can be observed in some working conditions of turbomachines. The phase transition, which appears on the blades, is the source of high dynamic forces, noise and also can lead to the intensive erosion of the blade surfaces. The need to control this process and to prevent or reduce the undesirable effects can be fulfilled by the application of non-condensable gases to the liquid. Findings The results show that the Singhal cavitation model predicts the cavity structure and related characteristics differently with 2phases and 3phases models at low cavitation number where the cavitating flow is highly dynamic. On the other hand, the impact of dissolved air on the cloud structure and dynamic characteristic of cavitating flow is gently observable. Originality/value The originality of this paper is the evaluation of different numerical cavitation models for the prediction of dynamic characteristics of cavitating flow in the presence of air.