Effects of axial rectangular groove on turbulent Taylor-Couette flow from analysis of experimental data

Abstract

The relationship between a rough or structured surface topology and its hydraulic resistance was analysed in the case of fully turbulent Taylor-Couette flow at fixed radii ratio η = 0.9375 and for Reynolds numbers Re i from 2×10 4 to 13×10 4. Three configurations of inner cylinder having 6, 12 and 24 grooves of a same rectangular shape and regularly distributed were compared to a reference smooth cylinder with only inner cylinder rotating. Such configurations are common in electric motors of high power density where a better understanding of flow pattern and heat transfer is essential to enhance their design and to develop appropriate cooling system. Torque and pointwise velocity measurements were performed. The effects of the flow modulations induced by the grooves on the friction coefficient and the flow features were examined. The results showed significant difference in the flow pattern and an increase of the friction coefficient with increasing the groove number. However, the drag-increasing capacity of each groove was further reduced by increasing the groove number. It was also found that, the local scaling exponent between friction coefficient and Reynolds number was insensitive to the present surface roughness, suggesting that the bulk flow contribution is similar for all the four configurations.