Wake/shear layer interaction for low-Reynolds-number flow over multi-element airfoil

Abstract: Time-resolved particle image velocimetry (TR-PIV) and hydrogen bubble visualization are employed to study the effects of Reynolds number on the wake/shear layer interactions over multi-element airfoil (30P30N). The Reynolds number based on the stowed chord length (Re _c ) ranges from 9.3 × 10 ³ to 3.05 × 10 ⁴ . According to the variation of dominated flow structures, a critical Re _c interval from 1.27 × 10 ⁴ to 1.38 × 10 ⁴ is found, which is novel for the low-Reynolds-number flow over multi-element airfoil. The slat wakes can be divided into two types by this critical interval. When Re _c is smaller than this critical interval, no roll-up occurs to the shear layer of slat cusp. Görtler vortices generated by a virtual curved wall dominate the slat wake. When Re _c is larger than this critical interval, roll-ups occur to the shear layer of slat cusp, which is similar to the cases at high Reynolds number (Re _c ~ 10 ⁶ ). These roll-ups and their evolution result in the co-existence of spanwise vortices and streamwise vortices in the slat wake. Different kinds of slat wake result in different kinds of wake/shear layer interactions above the main element. The flow physics behind these complex interactions, especially the novel flow structures and their evolution, is analyzed in detail to contribute to the fundamental research of wake/shear layer interactions. When Görtler vortices dominate the slat wake, they could trigger streaky structures within the leading-edge separated shear layer of the main element. When spanwise vortices and streamwise vortices co-exist in the slat wake, novel spanwise “double secondary vortices” are triggered above the main element by the spanwise vortices of slat cusp shear layer. Graphical abstract: [Figure not available: see fulltext.].