Analysis of the Immediate Boundary Conditions of an Axial Flow Impeller

The design and analysis of impellers for mixing applications such as stirred tank reactors (STR) have significant application in many engineering processes. In particular, the evaluation of the turbulent flow boundary conditions immediately around a model impeller has been examined using flow visualization, laser Doppler anemometry (LDA) and particle image velocimetry (PIV). Mean and fluctuating velocities are presented for all three velocity components. Good agreement between LDA and PIV measurements was obtained once an optimized PIV arrangement was defined. Turbulence parameters such as kinetic energy, dissipation, and length scales are estimated from the measurements. Several approaches to evaluating dissipation were used. Triggered PIV measurements were used to evaluate the variation in radial and tangential velocities in the entire planes above and below the impeller at constant axial distances. The size and orientation of the vortices shed from the impeller blade tips and the corresponding regions of high kinetic energy and dissipation indicate the importance of these structures in mixing.