Bubble induced turbulence model improved by direct numerical simulation of bubbly flow

Abstract

Direct numerical simulations (DNS) provide a description of turbulent flow fields at every point in space and time. Since every statistical quantity can be computed, this data should be useful for the development of closure models. In this paper, models for bubbly turbulent flows, in a two-fluid framework, are investigated using DNS data. A front tracking method is employed to simulate turbulent flow with deformable bubbles in a vertical channel. Quantities such as void fraction, average velocities, velocity fluctuations, and turbulence statistics are computed and presented. After processing the DNS data, the turbulence kinetic energy and dissipation equations, based on the k-ε model and explicit algebraic stress model (EASM), are analyzed. The model for bubble-induced turbulence, represented by source terms in the k and ε equations, is re-evaluated using coefficients derived from the DNS results. This work is a first step to show what can be done by using the DNS data to evaluate turbulence closure models. More simulations should be conducted in future works to further improve such models.