Experimental and Computational Study of Mixing Mechanisms in an Axisymmetric Lobed Mixer

摘要

The mixing mechanisms downstream of an axisymmetric 12-lobed mixer are studied through a combined experimental and computational investigation. A series of simulations based on the unsteady Navier-Stokes equations are used to identify the relative roles of large-scale, instability-driven transient flow structures and smaller-scale turbulence on the flow development within and downstream of the lobed mixer. Medium- and large-scale unsteady motions are captured by the fine spatial and temporal resolution of the unsteady Reynolds-averaged Navier-Stokes simulations, and small-scale turbulence is captured using shear-stress transport and scale-adaptive shear-stress transport turbulence models. The simulations are validated against four-wire thermal anemometry measurements in a scaled lobed-mixer wind-tunnel model with turbulent, axial inflow conditions. Favorable agreement between the measured and simulated flowfields demonstrates the predictive capability of the simulations. The simulation results illustrate the creation of streamwise vorticity in the lobes and its subsequent interaction with the spanwise vorticity shed from the trailing edge of the lobed mixer. The extent of this interaction is shown to strongly affect the mixing of the flow downstream of the lobed-mixer discharge plane. The results also illustrate that the large-scale transient flow structures are significantly weakened by smaller-scale turbulence present in the flow, establishing the role of smaller-scale turbulence in mixing the flow downstream of the lobed mixer.