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UNSTEADY AERODYNAMIC EFFECTS IN PITCHING AIRFOILS STUDIED THROUGH LARGE-EDDY SIMULATIONS

Prabal S. Negi
Linne FLOW Centre, KTH Mechanics SE-100 44 Stockholm, Sweden

Ricardo Vinuesa
MMAE Department Illinois Institute of Technology Chicago, IL 60616, USA; Linne FLOW Centre, KTH Mechanics SE-100 44 Stockholm, Sweden

Phillipp Schlatter
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden

Ardeshir Hanifi
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden; Swedish Defence Research Agency, FOI, SE-164 90 Stockholm, Sweden

Dan S. Henningson
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden

Sinopsis

Wall-resolved large-eddy simulations (LES) are utilized to investigate the flow-physics of an airfoil undergoing pitch oscillations. A relaxation-term (RT) based filtering procedure is employed to add limited high order dissipation to account for the dissipation from the smallest scales which are not resolved. Validation of the procedure is presented for turbulent channel flows and for flow around a wing section. The procedure is then used for the simulation of small-amplitude pitching airfoil at Rec = 100;000 with a reduced frequency k = 0:5. The investigation of the unsteady phenomenon is done in the context of a natural laminar flow airfoil, the performance of which depends critically on the suction side transition characteristics. The dynamic range of the pitch cycle sees the appearance, destabilization and disappearance of a laminar separation bubble at the leading edge. An abrupt change is seen in the lift coefficient, which is linked to a rapid movement of the transition point over the suction side. Destabilization of the laminar separation bubble is the cause of these rapid transition movements which occur near the end of the pitch-up phase of the cycle.