Design of Multi-hole Orifice for Sudden Expansion Flow and Numerical Simulation on the Development of Wake in Porous Orifice Plate

To investigate the rectification effect of perforated plates in the inlet system of a compressor test rig with sudden expansion flow, four sets of perforated plates were designed. Effects of the porosity in the core region of sudden expansion flow (referred to as central region) and pore distribution on the mixing process between the wake flow of multi-hole orifices and main flow were studied using numerical simulation method. Results show that increasing the porosity of central region leads to insufficient flow distribution at the periphery of plates. When the opening rate of the central region increases to 1.46 times of upstream and downstream cross-sectional area ratio of the sudden expansion, the proportion of flow distribution in the central region reaches 1.88 times of its area ratio. Consequently, the wake vortices near the wall and corner of plenum chamber merge and elongate, whose length reaches 17 to 24 times of the pore spacing. To suppress the increase and elongation of wake vortices near the wall and corner, it is advisable to select the opening ratio in the central area equivalent to the upstream and downstream cross-sectional area ratio of the sudden expansion. Reducing the pore spacing is the most effective method to shorten the length of wake vortices behind the central region.