Investigation of Flow Topology and Aerodynamic Bifurcation for Aircraft with Vented Strakes

Three wind tunnel experiments were conducted to investigate flow topology changes associated with several vented strake aircraft configurations. Abrupt changes in the force and moment data for the vents-open configurations indicated that a flow bifurcation occurred at angles of attack between approximately 15 and 20 degrees. In order to characterize the flow topologies of the vents-open and vents-closed configurations, balance, oil flow, and laser sheet flow visualization data were gathered and analyzed. A key off-body flow topology change due to opening the strake vents is that the flow through the vents moves the powerful strake vortex up off the wing and creates a secondary vortical structure that diverts inboard the strake vortex trajectory. An important on-body flow topology change that accompanies the bifurcation for the vents-open configurations is the migration of reverse flow from the midboard section of the wing onto the outer wing. This region of reverse flow stems from the flow through the open strake vents and the resulting trajectory change of the strake vortices. Furthermore, at angles of attack consistent with the aerodynamic bifurcation reverse flow from the midboard portion of the wing interacts with a vortex on the outer wing that creates a large degree of unsteadiness and an abrupt loss of lift on the outer wing. These topological changes result in flow asymmetries consistent with wing drop observed in early developmental flight tests for a vents-open pre-production Super Hornet configuration.