Experimental Investigation for The Influences of Bio-Inspired Tubercles Length on Aerodynamic Performance of Highly Cambered Airfoils in Low-Re Transient-Flow Regime

Abstract

Tubercles, that are bioinspired from the pectoral flippers of the acrobatic humpback whale, are among the highly superior flow control techniques. Many studies showed the highly promising aerodynamic gain that can be obtained from using these leading-edge perturbations. The attained efficiency depends mainly on the design aspects for blade/wing and its tubercles which have to be optimally set according to the selected airfoil and the specific operational flow regime. The spanwise length of perturbations, one of their geometrical aspects, is postulated to be of a great effect; however, it is little considered in research works. The objective of the present work is to investigate the effects of changing the tubercled length of the leading edge on the aerodynamic performance for highly cambered models at a low-Re transient flow regime which is considered to be the optimum design range for these highly applicable airfoils. An experimental approach was employed to test three models of the high lift S1223 airfoil with different waviness ratios (the waved length/total one) (20.83%, 50%, and 100% of the total span), and compare them with their smooth-leading edge counterpart. The tests were conducted in a subsonic wind tunnel at $\text{Re}=100,000$ under an infinite-span (quasi-2D) basis over an attack-angle range from the zero-lift angle up to 30 degrees. The results revealed the great influence of the tubercled length on the aerodynamic performance as the fully modified model attained earlier stall but with highly soft characteristics while the least-tubercled one delayed the abrupt stall behavior of the baseline model by 22% without a penalty on the maximum lift coefficient.