A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps

TL;DR

This study uses computational fluid dynamics to analyze vortex formation and flow separation in oscillatory jet pump flows, revealing flow regimes and performance characteristics relevant to thermoacoustic devices.

Contribution

It introduces a detailed CFD model to investigate flow regimes and compares results with quasi-steady approximations, highlighting their limitations.

Findings

Similar minor losses across different geometries when scaled by displacement amplitude

Identification of four distinct flow regimes in oscillatory jet pump flow

Quasi-steady approximation valid only for small displacement amplitudes

Abstract

A two-dimensional computational fluid dynamics model is used to predict the oscillatory flow through a tapered cylindrical tube section (jet pump) placed in a larger outer tube. Due to the shape of the jet pump, there will exist an asymmetry in the hydrodynamic end effects which will cause a time-averaged pressure drop to occur that can be used to cancel Gedeon streaming in a closed-loop thermoacoustic device. The performance of two jet pump geometries with different taper angles is investigated. A specific time-domain impedance boundary condition is implemented in order to simulate traveling acoustic wave conditions. It is shown that by scaling the acoustic displacement amplitude to the jet pump dimensions, similar minor losses are observed independent of the jet pump geometry. Four different flow regimes are distinguished and the observed flow phenomena are related to the jet pump performance. The simulated jet pump performance is compared to an existing quasi-steady approximation which is shown to only be valid for small displacement amplitudes compared to the jet pump length.