Numerical Simulation Of The Flow Field And Research On The Control Of Flow Separation In Hydrodynamic Coupling

The hydrodynamic coupling is one of the important hydrodynamic transmission components , which has the advantage of energy conservation, improvement of transmission quality and so on. It is widely used in industries, such as shipping, metallurgy, power generation, mining, petrochemical, textile, lifting and transportation, etc. Some methods have been used widely during the development and design of new hydrodynamic coupling in companies abroad which have leading technology such as optimization design theory, the finite element method, dynamic simulation, etc. The technology of hydrodynamic coupling had been introduced into our country since 1970s, however, nowadays, most domestic institutes still stagnate at the level of traditional design, which design new hydrodynamic coupling by using similarity-rule according to good design model parameters on the basis of similarity theory, check it by empirical formulas and finally test it by experiment. So the development and research ability of our own is relatively weak.The inner flow in hydrodynamic coupling can be divided into mainstream region and the boundary layer region. Due to the rotation of impellers, the flow in boundary layer region is a extremely complex three-dimensional viscous flow. When the working fluid passes by vanes, the separation of boundary layer, the diffusion of eddy and the dissipation of energy are fairly serious. In addition, it is also accompanied by the generation of secondary flow, separation flow and refluence during the development of three-dimensional boundary layer flow. These irregular flows have great impact on the performance of hydrodynamic coupling. As a result, not only the energy lost of flow increases sharply, but also pressure pulsation caused by this flow phenomenon makes hydrodynamic coupling create mechanical vibration under working situation. Therefore, how to control separatedflow of the inner flow appears particularly important under working situation. The purpose of this paper is to control the flow separation in the inner flow by drilling holes in turbine vane, and simulates the inner flow field before and after drilling holes with the help of Unigraphics and CFD software, then the numerical result of the inner flow field before and after drilling holes can be achieved by solving N-S equation directly.As for the incompressible viscous flow, the continuity equation and momentum equation are called as Navier-Stokes equations, which are short for N-S equations. Reynolds averaging is the most useful method for simulating the turbulence. But in the Reynolds averaging equations, Reynolds stress makes the equations unclosed, because of which the turbulent viscosity method is introduced. Many turbulence models are established to make the equations closed. Among them the k ? e two-equation model is used widely. After the comparison to different methods such as FEM, FDM and FAM, Finite Volume Method is chosen to solve the equation. RNG k ? e two-equation mode is chosen to be turbulence model, Up wind method is the way to accomplish the space discretion. SIMPLE and PISO are two strategies for coupling the pressure between continuity equation and momentum equation. In this paper, the former is more favorable.Actually the inner flow field of hydrodynamic is very complex, so some simplification and basic supposal are made before numerical simulation. First, the three-dimension geometric model and computational mesh model before and after drilling holes are finished. Then the model is computed in CFD software by using unsteady flow method, and the sliding mesh theory is employed to define the interface between the flow passages of pump and turbine, the divided face of flow passage is defined as periodic boundary conditions. Thereafter, the flow characteristics of distribution in different working situation are achieved after numerical simulation, the velocity and pressure distribution of the flow field before and after drilling holes are contrastively analyzed under different working situations. Based on which the primary characteristics are computed. Thenumerical result is proved to be reliable after comparison with experimental data. So the flow separation is controlled effectively and the inner flow field is improved greatly. The flow loss is decreased apparently under the condition that there is no change on diameter of circle of circulation. Torque coefficient is increased differently under most working conditions after drilling holes,The control measure of flow separation, numerical simulation results, algorithm and the definition of boundary condition presented in this paper are fairly valuable for the analysis of three-dimension flow field in hydrodynamic coupling. On the base of this, the inner flow fields of other hydrodynamic couplings and similar hydrodynamic components can be simulated numerically.