This paper deals with time dependent performance characteristics of cavitating hydrofoils, the flow around which has been simulated using pressure-based finite volume method. A bubble dynamics cavitation model was use...This paper deals with time dependent performance characteristics of cavitating hydrofoils, the flow around which has been simulated using pressure-based finite volume method. A bubble dynamics cavitation model was used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. For choosing the turbulence model and mesh size a non cavitating study was conducted. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence （SST） κ-ω model, Re-Normalization Group （RNG） κ-ε model with enhanced wall treatment are used to capture the turbulent boundary layer along the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ = 0.8 and σ = 0.4. Moreover, this study is focused on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers.展开更多
A hydroelectric power generator, which is able to extract the water flow energy from the hydroelastic response of an elastically supported rectangular wing, is experimentally investigated. An electric motor is used to...A hydroelectric power generator, which is able to extract the water flow energy from the hydroelastic response of an elastically supported rectangular wing, is experimentally investigated. An electric motor is used to excite pitching oscillations of the wing. Both the wing and the electric motor are supported by leaf springs which are designed to work both as a linear guide for the sway oscillations and as elastic elements. The wing mass in sway direction necessary to achieve a hydroelastic response is obtained by utilizing a mechanical snubber mechanism. The appropriate load to generate electricity is provided by magnetic dampers. In the previous paper, the generating power rate and the efficiency were examined through the experiments with a single wing model, and the feasibility of the flapping wing hydroelectric power generator was verified. In this paper, the influence of the neighboring wings is examined by using two experimental apparatuses, with the intention of achieving a practical cascade wing generator. Tests revealed that the cascade moving in-phase with the neighboring wings at narrower intervals has a higher rate of electric power generation.展开更多
In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow stru...In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry （PIV） technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscillatory behavior of the whole sheet cavitation is obtained, with large length fluctuations and vapor cloud shedding, and also the cavitation structure depends on the interaction of the water-vapor mixture and the periodic vortex shedding. The main purpose of this experimental study is to offer information for validating computational models, and shed light on the unsteady multiphase transport process of cavitating flows. Furthermore, with an emphasis on the dynamics of the attached turbulent cavitating flows, a filter-based model （FBM） is derived from the k-6 two-equation model, a conditional averaging method aimed at improving unsteady simulation is applied to computation. In comparison to the standard k-ε model, overall, the filter-based model is shown to improve the predictive capability considerably.展开更多
文摘This paper deals with time dependent performance characteristics of cavitating hydrofoils, the flow around which has been simulated using pressure-based finite volume method. A bubble dynamics cavitation model was used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. For choosing the turbulence model and mesh size a non cavitating study was conducted. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence （SST） κ-ω model, Re-Normalization Group （RNG） κ-ε model with enhanced wall treatment are used to capture the turbulent boundary layer along the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ = 0.8 and σ = 0.4. Moreover, this study is focused on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers.
文摘A hydroelectric power generator, which is able to extract the water flow energy from the hydroelastic response of an elastically supported rectangular wing, is experimentally investigated. An electric motor is used to excite pitching oscillations of the wing. Both the wing and the electric motor are supported by leaf springs which are designed to work both as a linear guide for the sway oscillations and as elastic elements. The wing mass in sway direction necessary to achieve a hydroelastic response is obtained by utilizing a mechanical snubber mechanism. The appropriate load to generate electricity is provided by magnetic dampers. In the previous paper, the generating power rate and the efficiency were examined through the experiments with a single wing model, and the feasibility of the flapping wing hydroelectric power generator was verified. In this paper, the influence of the neighboring wings is examined by using two experimental apparatuses, with the intention of achieving a practical cascade wing generator. Tests revealed that the cascade moving in-phase with the neighboring wings at narrower intervals has a higher rate of electric power generation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50679001 and 50979004)
文摘In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry （PIV） technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscillatory behavior of the whole sheet cavitation is obtained, with large length fluctuations and vapor cloud shedding, and also the cavitation structure depends on the interaction of the water-vapor mixture and the periodic vortex shedding. The main purpose of this experimental study is to offer information for validating computational models, and shed light on the unsteady multiphase transport process of cavitating flows. Furthermore, with an emphasis on the dynamics of the attached turbulent cavitating flows, a filter-based model （FBM） is derived from the k-6 two-equation model, a conditional averaging method aimed at improving unsteady simulation is applied to computation. In comparison to the standard k-ε model, overall, the filter-based model is shown to improve the predictive capability considerably.
