The effect of baffle on flow structures and dynamics stirred by pitch blade turbine

Abstract

•In order for a better understanding of how baffle impacts on the flow field stirred by pitched blade turbine (PBT), the Particle Image Velocimetry (PIV) experiment was conducted in baffled and unbaffled tank, with time-averaged method, phase-resolved method and Proper Orthogonal Decomposition (POD) method applied to analyze the turbulent characteristics. The POD quadruple decomposition method was adopted to decompose the flow structures of different scales. As indicated by the experimental results, in the measured area, an independent circulation area develops under the impeller, thus forming a pattern of double circulation flow in the unbaffled tank. There is a relatively concentrated distribution of incoherent flow structures in the stirred flow field, and these small-scale flow structures hinder transfer to the whole stirred tank, which makes it easy for the difference in local concentration to arise. With the addition of baffle, the axial discharge of fluid is enhanced, and the independent circulation area under the turbine shows change, and the large-scale convection of main body develops. The stirring-induced incoherent flow structure shows a wider range of distribution, while the small-scale structure under the stirring tank creates a more favorable condition for the diffusion into the whole stirred tank.