Optimization of the regulation needle structure based on the flow regulation characteristic and flow loss mechanism

Abstract

The regulation needle is a key component of the variable ejector to guarantee the quality of flow control and improve ejector performance. However, the studies related to the variable ejector lack regulation needle structure optimization. In this paper, for both linear and arc-shaped nozzles, three different profiles of regulation needles: linear, elliptical, and parabolic types are optimized based on the flow regulation characteristic (FRC) and local flow loss mechanism. The calculation method of the variable nozzle FRC is established. The results show that for the arc-shaped nozzles when the bottom radius R_s of the regulation needle is 0.75 times throat radius R_t, a linear regulation needle with half-top angle α_s being 32° is recommended, which makes the FRC ideal, minimizes the entropy production and maximizes the pressure recovery ratio (PRR). For the linear nozzles equipped with the elliptical regulation needle, as the ratio of the height to the bottom radius of the regulation needle head (RHR) increases, the FRCs get closer to the ideal parabolic type, however, the entropy production increases and the PRR decreases. Therefore, the RHR is advised to be 3 for linear nozzles. The findings can serve as important guidance for optimizing variable ejector design.