Cavitation in a tip vortex remains a challenging issue in a variety of engineering problems. In this study, we perform large eddy simulation of wetted and cavitating flows around a stationary elliptical hydrofoil with the cross section of NACA (National Advisory Committee for Aeronautics) 16–020. The Schnerr–Sauer cavitation model is adopted for phase transport. The numerical results are verified by comparing with the experimental measurements. Instantaneous vorticity and pressure in both wetted and cavitating flows are studied. It is found that the cavitation promotes the production of vorticity and increases the boundary layer thickness. To further analyze the influence of cavitation on the tip vortices, each term in the transport equation of enstrophy is examined. In the cavitating flow, the dilatation and baroclinic torque terms are promoted to be equally dominant as the vortex stretching term, while in the wetted flow the stretching term is the only dominant one. The axial and azimuthal velocities in the cavity are smaller than those in wetted tip-vortical flow, while the pressure inside is nearly equal to the constant saturation pressure. A tip vortex model with four regions in cavitating flow is built and compared to the wetted flow model. A weakly meandering motion of the tip vortex is observed in the near field. To study the surface wave behaviors of the tip vortex, the space-time velocity correlation analysis is carried out. The surface wave moves at a speed smaller than the incoming flow. A dominating helical mode is found and is consistent with the analytical and experimental results.

This paper presents a multi-objective optimization methodology that applies the Non-dominated Sorting Genetic Algorithm-II(NSGA-II) to propeller design, and realizes Fluid-Structure Interaction (FSI) weak-coupling based on Panel Method (PM) and the Finite Element Method (FEM). The FSI iterative process and the convergent pressure coefficient distribution and pressure fluctuation of HSP (a propeller installed on a Japanese bulk freighter-Seiun-Maru) are numerical calculated. The FSI results turn out to have higher precision than those without FSI. The appropriate optimization parameters are chosen after studying five cases. The Sobol method, a global Sensitivity Analysis (SA) algorithm, is used to quantify the dependence of objectives and constraints on the input parameters. In the multi-objective optimization methodology, efficiency, unsteady force, and mass are chosen as optimum objectives under certain constraints. Effectiveness and robustness of the methodology are validated by running the program starting from four different random values, which all improve the objectives and converge to the similar results. The proposed multi-objective optimization methodology could be a promising tool for propeller design to help improve design efficiency and ability in the future.

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For on-line insulation monitoring of turbine generator it is an important problem to describe the Partial Discharge (PD) pulse propagation process in stator windings. According to the frequency characteristics of PD and winding structure properties, the paper expounds that PD pulse travelling mode in slot and end windings is quasi-TEM mode, so the multi-conductor transmission line model is feasible in analyzing PD propagation characteristics. Based on the simulation and test results, the paper discusses the occurrence of fast and slow components in PD waveform propagation. The coupling effects existing between upper and lower bar in the same slot, and among end windings are the causes of fast component. In this paper the traveling speeds of PD pulses and the relation between the speeds and the parameters of turbine generator are investigated. The test and simulation results are shown taking the effects of laminated core into account.

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