Development of inclined non-parallel planar starting jets in an adverse-pressure-gradient crossflow

In this article, we address the influence of an adverse pressure gradient (APG) on high-aspect ratio pulsed jets interacting with a steady crossflow. The APG magnitude is varied by adjusting the opening angle in a one-sided diffuser test section. Representing typical boundary conditions found in active separation control, jets are operated at a velocity ratio r = ujet/Uinf ≈ 2.5 and an inclination angle α = 30°. Phase-locked velocity field measurements indicate that the qualitative flow appearance is not affected by the APG. Pulsed jets propagate along the wall, characterized by a leading vortex half ring for all configurations. From a quantitative perspective, however, the APG does affect the jet properties, inasmuch as it contributes to a more distinct velocity decay. This results in a smaller induced circulation and a decreased propagation speed associated with the jets. It is also shown that the streamwise distance up to which the flow field can be affected is influenced by the amount of fluid ejected per pulsed jet. Only jets with a relatively long pulse duration are effective over the entire diffuser ramp. The results presented in this paper can thus enable a deeper understanding of some important actuation parameters in active separation control.