This paper presents results of a study regarding hydraulic oil flow viscous wall drag effect on flow induced forces inside hydraulic valves using Computational Fluid Dynamics (CFD) computer simulations. Flow induced forces, also often referred to as flow forces, are very important in valve design and optimization. A common way used in CFD simulation to calculate flow forces is to integrate the pressure field, from CFD solutions, over related surface regions on a targeted valve component such as an actuator. However, in some cases, flow induced viscous wall drag forces on valve actuators, caused by oil flow velocity near solid component surfaces due to fluid viscosity, can be very significant. In this article, cases with different common valves used in mobile hydraulics have been studied, which includes spool type valves and poppet valves. Typical procedures of flow force CFD simulations and flow induced force calculations are presented. Oil flow viscous wall drag force and its effects on flow induced forces under different conditions are compared and discussed. Factors affect valve actuator wall drag force as well as how to use this force for better valve control are also explored.
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