Bubble Burst Control Using Smart Structure Sensor Actuators for Stall Suppression

摘要

AFTER the laminar boundary layer separates from the airfoilnsurface, the flow can reattach to the surface as a turbulent shearnlayer. The region between the laminar separation and thenreattachment is called a laminar separation bubble [1]. Dependingnon the chordwise extent of the laminar separation bubble, it can benclassified as a short bubble or a long bubble. Once the short bubblenfails to reattach on the airfoil surface, which is commonly known asnshort-bubble burst, this causes the airfoil to stall abruptly. Methodsndo exist to predict the short bubble [2]. Active flow control methodsnsuch as oscillatory blowing [3], plasma [4], and piezoelectric [5]nactuators are useful methods for flow separation delay. Previousnstudies conducted by Rinoie et al. [6], the control of the short-bubblenburst was proposed. Their work considered the control of thenseparated shear layer development artificially and their experimentalnresults confirmed that the use of a thin plate placed on a NACA 0012nairfoil was effective for suppression of laminar separation-bubblenburst formed on the leading edge of the airfoil and increased both thenstall angle and the maximum lift coefficient (approximately 10%nincrement, as compared with the clean airfoil) at a chord Reynoldsnnumber of 1:3 u0001 105n. The particle image velocimetry data alsonrevealed that the vortical structures originated from Kelvin–nHelmholtz instability inside the separated shear layer are enhancednby those formed at the trailing edge of the plate, and this forces thenseparated shear layer to reattach downstream of the plate. Morenrecently, the effectiveness of both the thin and rectangular plates wasnexamined [7] on a NACA 631-012 airfoil at a chord Reynoldsnnumber of 1:3 u0001 105n. Themaximumlift coefficient of the airfoilwithnplate attachment (obtained from the total force measurements) wasnapproximately 17% higher than the value of the clean airfoil (i.e.,