Time-Frequency Analysis and Transitional Boundary Layer Investigation over a Pitching Airfoil

Abstract

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2.7×10 5) is experimentally investigated through the space-frequency and time-frequency analyses of hot-film signals. Boundary layer events are visualized based on the spacefrequency and time-frequency plots. The precursor phenomena for turbulent as well as fully separated flows are presented based on the time-frequency analysis. A new technique based on the time-frequency analysis of hot-film signals is presented to measure the transition onset as well as the relaminarization locations. This technique is based on the analysis of highfrequency disturbances of the measured data. Special attention is focused on the spatial/temporal progression of the transition onset and the relaminarization points, compared to the static values, for different oscillation frequencies and amplitudes. Investigations are performed prior to, within and beyond the static stall angle of attack conditions. The results obtained by the new technique will be discussed and compared with the observations from the previous investigators.

Investigation of the aerodynamic effects of bio-inspired modifications on airfoil at low Reynolds number

“…Nowadays, passive control techniques have garnered preference over their active counterparts due to their inherent energy efficiency [4]. A selection of these controllers can be organized such as vortex generators [5][6][7][8], employing roughness material [9,10], using flexibility [11][12][13][14][15][16][17][18][19][20], utilizing the dimple [21], riblet [22,23], considering the bio-inspired tubercles [24][25][26][27][28][29] and performing bio-inspired applications [30][31][32].…”