Analysis of Turbulent Structure of Particle-laden Flow on Riblet Wall
The effect of riblet wall on the turbulent coherent structure of clean water and particle-laden two-phase flow in turbulent boundary layer was studied with particle image velocimetry(PIV).The streamwise-normal two-dimensional velocity field information of liquid phase was investigated in single phase flow and particle-laden flow with polystyrene particles of 155μm respectively.The two-dimensional spatial topologies such as streamwise velocity,the streamwise fluctuation velocity,Reynolds shear stress and spanwise vorticity in ejection and sweep events under four working conditions were extracted with quadrant splitting method.The riblet wall increases the streamwise velocity and spanwise vorticity of eject events in both clear water and particle-laden two-phase flow,reduces the spanwise fluctuation velocity and Reynolds stress,and weakens the momentum exchange in the boundary layer.For the sweep event,the riblet wall has no obvious effect on the clean water.In the particle-laden two-phase flow,all the first-and second-order turbulent statistics,such as the streamwise velocity,stremwise fluctuation velocity,Reynolds stress and spanwise vorticity,present to be enhanced by the riblet.In the particle-laden two-phase flow,the riblet wall can significantly promote the burst frequency of eject events in the coherent structure,so that the number of eject events is more than that of sweep events.The ejection event of coherent structure plays a predominant role in the momentum exchange in the boundary layer.In turbulent flow with particles,the riblet significantly increases the frequency of ejection events and the transport efficiency of particles near the wall to the high-speed fluid region,indicating that the riblet has a positive effect on particle transport.
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