Control of flow separation using adaptive airfoils

Abstract

A novel way of controlling compressible flow separation, using a dynamically deforming leading edge airfoil whose nose curvature can be changed by 400 percent to keep the flow attached at post-stall angles of attack is reported. The strong fluid acceleration around the airfoil nose and the resulting steep adverse pressure gradient were reduced by progressively rounding the airfoil leading edge. Steady flow studies at M = 0.3 showed that the flow separating at about 14 deg angle of attack over a NACA 0012 airfoil could be kept attached up to about 18 deg by increasing the nose radius. Also, a fully separated flow at high angles could be made to reattach by rounding the leading edge. Interestingly, the flow over an airfoil having a nearly semicircular nose was separated even at low angles. The research showed that a 'window' of angles of attack and airfoil profiles exists in which it appears possible to keep the flow attached through a maneuver. The shape change also modified the multiple shocks that form over the NACA 0012 airfoil at M = 0.45. Significant effects of shape change were observed on the vorticity flux in the flow. AbstractA novel way of controlling compressible flow separation, using a dynamically deforming leading edge airfoil whose nose curvature can be changed by 400% to keep the flow attached at post-stall angles of attack is reported. The strong fluid acceleration around the airfoil nose and the resulting steep adverse pressure gradient were reduced by progressively rounding the airfoil leading edge. Steady flow studies at M -0.3 showed that the flow separating at about 14 degrees angle of attack over a NAG A 0012 airfoil could be kept attached up to about 18 degrees by increasing the nose radius. Also, a fully separated flow at high angles could be made to reattach by rounding the leading edge. Interestingly, the flow over an airfoil having a nearly semicircular nose was separated even at low angles. The research showed that a "window" of angles of attack and airfoil profiles exists in which it appears possible to keep the flow attached through a maneuver. The shape change also modified the multiple shocks that form over the NAG A 0012 airfoil at M =; 0.45. Significant effects of shape change were observed on the vorticity flux in the flow.

Mimicking the humpback whale: An aerodynamic perspective

“…Incorporating the concept of DDLE, experiments were performed by Chandrasekhara et al [46,47]. The inclusion of DDLE helped in improving the stall characteristics.…”

Transitioning active flow control to applications

“…6 In recent years, a limited number of active flow control applications are being tested in the laboratory. These applications include dynamic stall control using a deformable leading edge, 7 separation control for takeoff and landing flight conditions using piezo devices, 8 pulsed vortex generators, 9 and zero-net-mass oscillations, 10,11 duct-flow separation control and fore-body vortex control using zero-net-mass suction and blowing, and thrust vectoring with zero-net-mass oscillatory actuation. 12 Although the continued demonstration of active flow control in the laboratory will continue for many years, other research areas such as power management and electronics for tens to hundreds of self-adaptive controller systems, the life-cycle and/or degradation of the active devices with operation, impact of the embedded devices on the structural integrity of the vehicle, and control management for local and distributed failure modes require a mature level of understanding and predictability prior to bringing the flow control from the laboratory to real applications.…”

Lift characteristics of pitching NACA0015 airfoil due to unsteady forced surface inflation

“…Then, the conditions of maximum thrust generation were obtained. In recent investigations by Chandrasekhara et al [14], it has been confirmed experimentally and numerically that the curve near the leading edge has much influence on the development of dynamic stall. Further, the local dynamic deformation of leading edge (That leads to local expansion of leading edge) is very impressive on the flow characteristics.…”