Reducing flow separation in jet pumps

Abstract

Introduction Jet pumps are static components that can be used in closed-loop, traveling wave thermoacoustic devices to suppress a time-averaged mass flux (Gedeon streaming) that can exist [2]. The minimization of convective heat transport caused by this mass flux is of vital importance due to the detrimental effect it has on the device’s efficiency. Jet pumps have an asymmetric shape, resulting in asymmetric minor losses. This causes a time-averaged pressure drop that suppresses Gedeon streaming when the minor losses are tuned correctly [1]. Current jet pump designs are mainly based on a quasi-steady approximation using minor loss coefficients [1]. A recent numerical study on conventional jet pump designs has shown that the quasi-steady approximation is only accurate in a small range of operating conditions [4]. It is shown that, above certain wave amplitudes, flow separation occurs during the half-cycle where the bulk flow is moving in the diverging direction of the jet pump. The flow separation originates from the small jet pump opening as a result of the local adverse pressure gradient. Due to the flow separation the asymmetry in minor losses diminishes, resulting in a severe downgrade of the jet pump performance compared with the quasi-steady approximation. The current work will investigate the flow separation behavior by varying the geometry of the jet pump. The goal is to minimize the flow separation and shift it to higher wave amplitudes, therewith increasing the effectiveness and robustness of jet pumps.