Fluidic-based Virtual Aerosurface Shaping

Recent work on a novel approach to the control of the aerodynamic performance of lifting surfaces by fluidic modification of their apparent aerodynamic shape, or virtual aerosurface shaping is reviewed. This flow control approach emphasizes fluidic modification of the “apparent” aerodynamic shape of the surface with the objective of altering or prescribing the streamwise pressure gradient. Control is effected by the interactions of arrays of synthetic jet actuators with the cross flow that displace the local streamlines near the surface and thereby induces an ‘apparent’ modification of the flow boundary. The operating frequency of the control jets is high enough so that the actuation period is at least an order of magnitude lower than the relevant characteristic time scale of the flow. Therefore, the interaction domains between the control jets and the cross flow are quasi-steady and hence the induced aerodynamic forces are virtually time-invariant. These effects are investigated at two practical domains of the flight envelope. The first is at post stall angles of attack where the ability to suppress separation implies robust control over large changes in circulation and accumulation and shedding of vorticity. An important element of this approach is the evolution and coherence of the vertical structures within the controlled wake with the objective of mitigating unsteady aerodynamic forces. The second domain is that of small angles of attack when the baseline flow is typically fully attached and therefore less amenable to flow control approaches that require separation.