Experimental Validation of Flow Force Models for Fast Switching Valves

This paper comprises a detailed study of the forces acting on a Fast Switching Valve (FSV) plunger. The objective is to investigate to what extend different models are valid to be used for design purposes. These models depend on the geometry of the moving plunger and the properties of the surrounding medium. A few analytic expressions have been suggested in the literature and these have been supported by CFD simulations, yielding accurate coherence for a large part of the fluid domain. However, when a moving body approaches a stationary body, squeeze film effects will occur if the plunger velocity is non-zero. This is the case in FSVs, where it results in an additional dampening effect, which is of relevance when analyzing contact-impact. Experimental data from different tests cases of a FSV has been gathered, with the plunger moving through a medium of either oil or air. This data is used to compare and validate different models, where an effort is directed towards capturing the fluid squeeze effect just before material on material contact. The test data is compared with simulation data relying solely on analytic formulations. The general dynamics of the plunger is validated for the established models, but an additional investigation of the dampening force is necessary. Therefore, numerical analyses are introduced to enhance the knowledge of the hydrodynamic end dampening. This has a visible effect on the velocity profile at the end-stop. This profile represents the measurements more accurately, but it is not possible to verify the velocity profile at the valve seat end-stop due to measurement uncertainties.