Study on effect of surface roughness on resistance based on results from experiments and simulation with CFD and LBM

Abstract

In this paper, the rotating disk with a diameter of 50mm is selected as a simplified object to study the effect of surface roughness on resistance. The accuracy of different CFD models is studied to reduce the simulation error through rheometer experiment of smooth disk. Then, optimized models are used to calculate the torque of rough disks with different roughness. Compared with results from rheometer experiment, it’s found that smooth disk doesn’t have pressure drag, but rough disk has pressure drag. And the disk surface with roughness of 90μm has the maximum drag reduction rate of 3.26% at speed of 400rpm. There is an uncertain and irregular relationship between drag reduction effect and surface microgroove under different Reynolds number, so, the flow in microgrooves on rough surfaces is simulated for further analysis by LBM. Compared with channel without microgroove, channel with microgroove reduces the velocity gradient on bottom wall and there is vortex in each microgroove. The velocity gradient on bottom wall attains a minimum when the height of microgroove is 90μm, which has the minimum viscous friction, however, the pressure difference between inlet and outlet of channel with microgroove height of 90μm doesn’t reach a minimum. Therefore, when applied to macroscopic objects, the microgrooves, which can reduce the viscous friction, probably increase the total resistance due to the pressure drag.