Numerical Simulations and Pressure Measurements of the Flow of an Oily Control Valve for Decreasing its Operating Noise.

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The valve noise due to cavitation has frequently been serious problems with the increase of an operating pressure. This study contributes to the optimistic design of velve and to the decrease of cavitation noise by studying the internal flow of the calve in the transient process of closing and opening. First, at Reynolds number of about 10 ^3, for poppet valves with different configurations, we have carried out noise tests and numerically simulated oil-flows under an assumption of noncavitating conditions by a finite difference method. In addition, we have performed the measurements of pressure at two locations in a valve chamber, the flow visualization and noise tests. By comparison of the measured and computed results, good correspondences between the flow pattern and noise measurements were obtained. It is confirmed that the noise is mainly generated from cavitation and strongly depends on the valve configuration of the poppets and the sleeves. A large valve chamber is effective to … More suppress cavitation due to the formation of a stationary large circulating flow, and the second stage restrictors is effective to reduce the pressure fluctuation by suppressing the generation of periodic vortiodic vortices. On the other hand in the case of expansion valve, simulation were made for both laminar and turbulent (kappa-epsilon turbulence model) flows. For laminar flow, strong vortex street was observed to shed along the axis of chamber downstream the poppet and pressure fluctuation also increases, while for turbulent flow by kappa-epsilon turbulence model, the jet flow separated from the poppet gets reattached over chamber walls, resulting in the formation of recirculation region just behind the poppet and the decrease of pressure fluctuation. These results agree well with visualization. Second, for spool valve, nomerical simulations were conducted for various valve configuration. The static characteristics at various valve open/close ratios and dynamic characteristics in the transient process of opening and closing operation, such as flow patterns, axial forces and angles of jet were computed. For static characteristics, fluid forces change, greatly corresponding with the flow direction through the valve and the associated recirculation region. For dynamic characteristics, unsteady flow patterns, force fluctuations in the transient process of closing and opening operations were numerically simulated. Correspondence between the vortices formed from valve shoulder and the fluctuating component of fluid forces with high frequency was certified. In experiments, both actual valves and valve-models with half size of actual one were employed. Axial forces at various valve open/cose ratios were measured using a load cell. The measured results agree well with those of simulations. In addition, flow-patterns visualized with the half size model were found to agree quantiatively well with those of simulations. With the assumption of laminar, axial symmetric flow, t Less