Vortex dynamics for flow around the slat cove at low Reynolds numbers

Time-resolved particle image velocimetry (TR-PIV) is employed to investigate the vortex dynamics around the slat cove of a 30P30N multi-element airfoil at a fixed geometric angle of attack of 4A ° within the stowed chord Reynolds number range of 9.3A ×A A ≤A RecA ≤A 5.2A ×A 10. The results link the frequency properties to the vortex shedding patterns of the slat cusp shear layer. With increasing Rec, three types of vortex dynamics are identified: (i) no vortex shedding from the slat cusp shear layer and the absence of hydrodynamic feedback in the slat cove (9.3A ×A A ≤A RecA ≤A 1.27A ×A 10); (ii) impingement of shed vortices on the underside of the slat trailing edge at a steady location (1.38A ×A ≤A RecA ≤A 1.83A ×A 10); (iii) impingement of shed vortices on the underside of the slat trailing edge at unsteady locations (2.41A ×A ≤A RecA ≤A 5.2A ×A 10). The fluctuations generated by shed vortices link the slat cusp and trailing edge by the hydrodynamic feedback in the slat cove. Besides the fundamental frequency and its harmonics, subharmonics and fractional harmonics occur to the slat cusp shear layer in the Rec range of 2.41A ×A 10-5.2A ×A 10. Subharmonics make the impingement locations of shed vortices unsteady. Fractional harmonics trigger the secondary instability of the braid region between two consecutive vortices to generate more shed vortices. The vortex dynamics in this Rec range is found to persist to RecA A 10.