Numerical comparisons of the performance of a hydraulic coupling with different pump rotational speeds

Abstract

Abstract.A hydraulic coupling is a hydrodynamic device for transmitting rotating mechanical power. It is widely used in the machinery industry because of its advantages of high energy transmission efficiency, shock absorption and good adaptability, etc. In this paper, SIMPLEC algorithm and SST k-ω turbulence model were employed to simulate the steady state flows at operating conditions of two different rotational speeds (3000r/min and 7500 r/min) of the pump of a specified hydraulic coupling model. The results indicate the existence of similarity in the distributions of the flow fields between the two speeds, but the efficiency at the optimum condition is larger with higher rotational speed. It is concluded that the similarity principle of the efficiency of the hydraulic couplings does not apply in this case due to the relatively high rotating speed and small geometric specifications. It is also shown that the radially stratified pressure distribution on the torus section becomes more obvious with larger speed ratios, since the centrifugal movement plays more dominant roles over the circulating movement in these situations. When the speed ratio is small, with the completion of the circulating flow, the pressure distribution presents in a more circular pattern around the neutral zone of the torus section. IntroductionEnergy transmission by the utilization of the hydraulic coupling is one of the energy-saving technologies [1] . A hydraulic coupling can realize flexible connection by using fluid kinetic energy to transmitting power, which has some advantages in engineering applications, e.g., good adaptability and shock absorption, etc. Due to the complexity of the three-dimensional incompressible viscous flows, and the gas-liquid two-phase distribution variations at different working conditions in a partially filled hydraulic coupling, precise theoretical analysis of the flows and the hydraulic losses remains difficult.The design of the hydraulic coupling has been evolved from the traditional one-dimensional beam method, to the optimization design based on three-dimensional CFD analysis [2] . CFD analysis of the flows in the hydraulic coupling has gain prevalence over the years, since it provides not only the external characteristic (e.g., transmitted torque, etc.), but also internal flow details, which are helpful in analysing the flow mechanism within the hydraulic coupling [3]

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