DRAG REDUCTION OF PARTICLE-LADEN CHANNEL FLOW BY SPANWISE WALL OSCILLATION: A DIRECT NUMERICAL SIMULATION

Study on drag reduction of turbulent channel flow has its significance in both scientific researches and industry applications. The passive drag reduction technique that has been reported to be effective is to add dispersed materials into the single-phase turbulence. On the other hand, the active drag reduction technique, i.e., spanwise wall oscillation, which can be controlled in advance, has attracted wide attention in recent years. Drag reduction induced by spanwise wall oscillation has been successfully applied to single-phase turbulence, however, there is few attentions is paid to the drag reduction of particle-laden channel flow by the aforementioned active technique. Therefore, the drag reduction of particle-laden channel flow by spanwise wall oscillation is studied in this paper by direct numerical simulations. The major concern is two-folded: the first is the turbulent modulation and mechanism of particle-laden channel flow induced by spanwise wall oscillation, and the second is the coupling effect of laden particles and wall oscillation on drag reduction. Comparing with non-oscillation particle-laden channel flow, the wall drag of particle-laden channel flow is reduced by spanwise wall oscillation. The optimal oscillation period is found to achieve the maximum drag reduction rate, which is similar with the trend of single-phase channel flow. With the same volume fraction, channel flow with small size particle exhibits large drag reduction. Comparing with non-oscillation single-phase turbulence, for small oscillation period scenario the coupling contribution of laden particles and wall oscillation has weak and even negative effect on drag reduction, as the oscillation period increases the coupling contribution becomes significant and the maximum magnitude is around 10% of the overall drag reduction.