In this paper, the finite element method (FEM) and particle image velocimetry (PIV) techniques are utilized to obtained the flow field along the inlet passage, chamber, metering port, and outlet passage of a spool valve at several different geometrical dimensions. For numerical simulation, the stream function &psi and vorticity &omega forms of continuity and Navier-Stokes equations are employed, and the finite element method is applied to discretize the equations. Selfdeveloped simulation codes are executed to compute the values of the stream function and vorticity at each node in the flow domain. Then, according to the correlation between the stream function and velocity components, the velocity vectors of the entire field are calculated. For particle image velocimetry experiments, a pulse Nd: YAG laser is exploited to generate a laser beam. Convex and concave lenses are combined with each other to produce a 1.5-2 mm thickness laser sheet to illuminate the desired plane. Polystyrene spherical particles with a diameter of 30-50 µm are seeded into the fluid as tracing particles. A Kodak ES1.0 CCD camera is employed to capture the images of interest. The images are processed by FFT cross-correlation algorithm, and the processing results are displayed in the form of velocity vector plots. Numerical simulation results and PIV experiments both show that there are three main areas in the spool valve where vortices are formed. Numerical results also indicate that the valve opening and the chamber dimensions have some effects on the flow structure of the valve. The investigation is helpful for qualitatively analyzing the energy loss, noise generation, and steady state flow forces. It can even help in designing the geometrical structure and flow passage.

Keywords: flow field, spool valve, finite element method (FEM), particle image velocimetry (PIV)