EVOLUTION OF VORTICAL STRUCTURE OVER DELTA-WING WITH TRANSIENT ALONG-CORE BLOWING

Over delta-wing with a 75-deg sweep angle and 40-deg of the angle of a ttack, the vortex core subject to transient along-core blowing is inve stigated experimentally. In response to the transient along-core blowi ng, the vortex core, before breakdown, serves as a transmitting vessel that steadily delivers the supplied momentum to overcome the strong a dverse along-core pressure gradient, especially near the onset locatio n of the vortex breakdown. The central region of the vortex core is fo und to be more sensitive to the external perturbation than the outer r egion. This key characteristic of the vortex core is the reason for tr ansformation of the along-core velocity distribution from the velocity excess (or jet-like) profile to the velocity deficit (or wake-like) p rofile as the onset of vortex breakdown is encountered. The magnitude of suction peak coefficient measured on the wing surface along the vor tex core direction increases in response to the transient along-core b lowing. Then it recovers to the unperturbed value as the vortex breakd own recovers to its long-time averaged location. Variation of pressure gradient along the vortex center differs from the gradient of the suc tion peak coefficient measured on the wing surface along tile vortex c ore direction. The latter is primarily due to the integrated induction from the conical vortex structure above the wing surface. However, th e former reflects only the local behavior near the central region of t he vortex core.