Bubble Bursting and Stall Hysteresis on Single-Slotted Flap High-Lift Configuration
Slotted multi-element cone gurations are widely used because they are very effective in increasing themaximum lift of airfoils during takeoff and landing. However, when stall occurs in the leading-edge region of one of the elements,theoutcomeisa suddenanddangerousdropinperformanceofthewholecone guration.Theresultsofthe experimental verie cation of a computer-designed single-slotted e ap are presented. Many realistic cone gurations, including the computed optimum, were tested and compared to the numerical predictions. For a number of these cone gurations, sudden leading-edgestall due to thebursting of a laminarbubblewasdetected on the e ap, followed byseverestallhysteresis.Presentnumericaldesigncodesdo nothelpthedesignermuchinpredictingthisimportant phenomenon, and wind-tunnel testing remains necessary. Therefore, there is a need for better bubble bursting prediction methods. A possible direction for improvement is discussed, focusing on the unsteadiness of the e ow. Nomenclature Cd = drag coefe cient Cl = lift coefe cient Clmax = maximum lift coefe cient Cp = pressure coefe cient c = aerodynamic chord with e ap nested Rk = ree nement ratio Tu = freestream turbulence level, p u 02 =V U = uncertainty V = velocity x; y = coordinates ® = angle of attack ± = displacement thickness µ = momentum thickness