Applied Mechanics and Materials Vols. 444-445

Abstract: A numerical simulation method on noise prediction, which incorporates aerodynamics and sound wave equations based on acoustic analogy, is presented in the paper. Near-field unsteady aerodynamic characteristic can be obtain by large eddy simulation (LES), and far-field propagation of sound waves and spatial sound-field can be obtain by solving the time-domain integral equations of Ffowcs Williams and Hawings (FW-H). Based on the method, a numerical simulation was done on a two-dimension cylinder and a three-dimension flat plate with blunt leading edge. The agreement of numerical results with experiment data validated the Feasibility of the method. The results also indicate that LES can describe vortex generation and shedding in the flow-fields, and FW-H formulation, which has taken time-lag between sound emission and reception times into account, can simulate time-effect of sound propagation toward far-fields.

Abstract: The static-state error is existed in the pressure valve, coupled with the characteristics of high vaporization pressure, low viscosity, and small compressibility, so that the fluid dynamics and friction force of hydraulic pressure valve are increased. The pressure valve will easily come up with produce cavitation erosion and wire drawing. Those appearances would seriously affect the performance of the pressure valve and its life cycle. A new type of static water pressure reducing valve is designed in this paper. It has a special structure which can complete the internal dynamic pressure feedback of the valve. The static mathematical model of value is established. And the static characteristic is analysed by using MATLAB simulation, which provides the static pressure characteristic curve, static pressure flow curve. It comes up with a result that this valve has good static pressure, and high precision pressure regulator.

Abstract: If deviating from the optimal operation conditions, flow separation will occur on the blade of the runner in a low specific speed turbine. At this time, the turbulent flow of flow field in the blade duct will be in a strong non-equilibrium state, and thus the blade duct vortexes will be generated. To further study the mechanism of blade duct vortexes and to control the generation of these vortexes, Spalart-Allmaras (S-A) model was used to numerically simulate and calculate the internal flow in the low specific speed turbine runner under low load conditions. The blade duct vortexes in the turbine runner were accurately predicted. The effect of short blade in eliminating and reducing the vortexes in the low specific speed turbine runner was analyzed and compared.

Abstract: Numerical simulation of unsteady flow and flow-induced sound of an airfoil and a wing/plate junction are performed in the paper by large eddy simulation (LES) and FW-H acoustic analogy. The vortical flows around a NACA0015 airfoil at two angles of attack (0°and 8°) are simulated and analyzed by vortex identification. Simultaneously, the wall pressure fluctuations of the airfoil are computed. At two angles of attack, the flow induced sound of the airfoil is predicted. The computed power spectra agree well with experimental measurements. So the capability of large eddy simulation in predicting unsteady flow and flow induced sound is validated. Subsequently, the horse-shoe vortex around a wing/plate junction in water is computed. Furthermore, the calculations of wall pressure fluctuations and flow induced sound of the junction model at three velocities are accomplished. The predicted results are compared favorably with measured data in large circulation water channel. So the numerical approach for flow induced sound of wing/plate junction in water is validated. It shows that the numerical simulation method in the paper is credible.

Abstract: To make the submersible axial flow pump have better performance, it is very significant to know about the flowing distributions. Based on N-S equations and Standard turbulence model and SIMPLE algorithm, a CFD analysis was made of the full flow passage in this type of pump. The study result shows the flow rule and will provide a guide for the designing and the producing practice.

Abstract: This paper is concerned with propagating features of pressure waves induced by water hammer in a long liquid-conveyed pipe subjected to hyper high water head. Effects of dynamically weak compressibility of the water in pipe and pipe wall elasticity on the propagating physics were investigated by comparing in-site measurements and theoretical analyses. The pressure wave form and propagating speed were significantly effected due to weak compressibility of the water and the interactions of the waves. The wave performs a strong unsteadiness while it propagates along the pipe. This study tries to explain an event with consideration of both the dynamically weak compressibility of the water in pipe and the closing features of the valves controlled actively.

Abstract: This paper is concerned with an analytical solution of transient flow on the four-equation model in fluid-structure interaction (FSI) for a reservoir-pipe-vane system subjected to a sudden closure of hydro turbine vane. The analytical solution is derived corresponding to the junction coupling based on a vane motion. The result obtained from the analytical solution is used to analyze the coupling features between pipe transient flow and hydro turbine vane motion.

Abstract: Life lies in movement, Football is now the most popular sport in the world. Fluent12.1 software is employed in this thesis to model the numerical simulation of the pressure which the ball with different angular velocity and different velocity bears. Simulation results show that the pressure difference on the surface of the ball with a certain speed will increase if the angular velocity increases. The pressure difference on the surface of the ball with a certain angular velocity will increase if the velocity increases. The radian of ball will become more bigger.

Abstract: Based on two phase homogeneous mixture model, numerical simulation of the cavitating flow was performed on a centrifugal pump. Cavity shapes and performance of the pump in variable cavitation numbers were obtained. Numerical results show that the numerical method can be used to predict the cavitation performance of centrifugal pump; the incipient cavitation number is predicted, and the cavity shape is similar with the experiment; cavitation usually appears in the suction surface of the blade and locates in the inlet side, and becomes longer to the outlet direction with lower cavitation number; when the cavitation number is relatively higher, cavitating region locates in the inlet area of the blade and is relatively stable, while develops and separates when cavitation number becomes lower; when the cavitation number equals to the incipient cavitation number, performance of the centrifugal pump has no change almost, only when cavitation number reduces to some extent, the head decreases abruptly and also the efficiency, which means the pump operates in a bad condition and this condition should be avoided in the practical operation.

Abstract: Pressure distribution of supercritical airfoil at flight Reynolds number could not be fully simulated except in cryogenic wind tunnel such as NTF (National Transonic Facility) and ETW (European Transonic Wind tunnel), which is costly and time resuming. This paper aimed to explore an engineering extrapolation to flight Reynolds number from low Reynolds number wind tunnel data for supercritical airfoil pressure distribution. However, the extrapolation method requiring plenty of data was investigated based on the CFD results for the reason of low cost and short period. Flows over a typical supercritical airfoil were numerically simulated by solving the two dimensional Navier-Stokes equations, with applications of ROE scheme spatial discretization and LU-SGS time march. Influence of computational grids convergence and turbulent models were investigated during the process of simulation. The supercritical airfoil pressure distribution were obtained with Reynolds numbers varied from 3.0×10⁶ to 30×10⁶ per airfoil chord, angles of attack from 0 degree to 6 degree and Mach numbers from 0.74 to 0.8. Simulated results indicated that weak shock existed on the upper surface of supercritical airfoil at cruise condition, that the shock location, shock strength and trailing edge pressure were dependent of Reynolds number, attack angles and Mach numbers. A similar parameter describing the Reynolds number effects factors was obtained by analyzing the relationship of shock wave location, shock front pressure and trailing edge pressure. Based on the similar parameter, airfoil pressure distribution at Reynolds number 30×10⁶ was obtained by extrapolation. It was shown that extrapolated result compared well with simulated result at Reynolds number 30×10⁶, implying that the engineering method was at least promising applying to the extrapolation of low Reynolds number wind tunnel data.