Evaluating the Euler-Euler approach for predicting a strongly 3D bubble-induced recirculatory flow with OpenFOAM

Abstract

Wastewater treatment plants use bubbly flows to promote grit removal from the plant’s influent. Computational fluid dynamics is an attractive tool to virtually prototype grit-chamber designs. This study assesses a two-phase unsteady Reynolds-averaged Euler-Euler (uRANS-EE) approach to predict bubble induced recirculatory flow in a laboratory tank of similar complexity to that expected in a full-scale grit-chamber. Numerical results are validated against a comprehensive experimental data set consisting of a 3D reconstruction of the flow field using a multi-plane stereoscopic particle image velocimetry technique, void fraction profiles using an optical probe and bubble rise-velocities using high-speed video. Depending on the combination of modeling parameters the predicted volumetric fluid flux returning towards the diffuser varied between 60 and 97% of the experimental flux. Predicted rise velocities exceeded measured values by a factor between 1.15 to 1.75 and near bed velocities were underpredicted by upwards of 25%. The principal 3D flow field features were predicted to a sufficient accuracy to support the use of the uRANS-EE approach for numerical grit-chamber prototyping.