Unsteady Wall Interference Effect of Dynamic Stall

This study leverages computational fluid dynamics to quantify unsteady wall interference mechanisms pertinent to dynamic stall by using a sinusoidally pitching NACA0012 airfoil. The similarity and nonsimilarity evolutions of dynamic stall caused by unsteady wall interference are depicted in detail. In the similarity evolution process, the unsteady wall interference is primarily manifested as lift effect and stall excitation effect, with Cl multiple peaks in this process following a consistent exponential influence rate. In the nonsimilarity evolution stage, the mechanism of the difference between the Cl and Cm double-peak time delays is revealed as the effect of different vortices. As the tunnel wall height decreases, the compressive effect on the vortex structure amplifies, with the critical wall height threshold experimentally verified at H∕c = 5. Two mechanisms are revealed for the difference in the position of dynamic stall vortex in the nonsimilarity evolution stage. In the first type of mechanism, where g₁ (time-dependent term in the mechanism of positional discrepancy of the dynamic stall vortex) is predominant, it is a combination of the flow acceleration effect and the time-cumulative effect. In the second type of mechanism, where g₂ (time-independent term) is predominant, it is a combination of the stall excitation effect and the flow acceleration effect.