Formation of surface trailing counter-rotating vortex pairs downstream of a sonic jet in a supersonic cross-flow

Abstract

Direct numerical simulations were conducted to uncover physical aspects of a transverse sonic jet injected into a supersonic crossflow at a Mach number of 2.7. Simulations were carried out for two different jet-to-crossflow momentum flux ratios (J ) of 2.3 and 5.5. It is identified that collision shock waves behind the jet induce a herringbone separation bubble in the near-wall jet wake and a reattachment valley is formed and embayed by the herringbone recirculation zone. The recirculating flow in the jet leeward separation bubble forms a primary TCVP (trailing counter-rotating vortex pair) close to the wall surface. Analysis on streamlines passing the separation region shows that the wing of the herringbone separation bubble serves as a micro-ramp vortex generator and streamlines acquire rotating momentum downstream to form a secondary surface TCVP in the reattachment valley. Herringbone separation wings disappear in the farfield due to the cross interaction of lateral supersonic flow and the expansion flow in the reattachment valley, which also leads to the vanishing of the secondary TCVP. A three-dimensional schematic of surface trailing wakes is presented and explains formation mechanism of the surface TCVPs. (a) x/D=3.5 for J =5.5 and x/D=3.5 for J =2.3 (b) x/D=8 for J =5.5 and x/D=5.5 for J =2.3 (c) x/D=12 for J =5.5 and x/D=8 for J =2.3 (d) x/D=18 for J =5.5 and x/D=12 for J =2.3 Figure 11. Contours of the mean flow streamwise velocity and streamlines on cross planes of J =5.5 and J =2.3, isolines of u/U∞=0.0 are superimposed

Turbulence decay in a supersonic boundary layer subjected to a transverse sonic jet

“…Our research work on jet interaction with supersonic cross-flow (JISC) clarified the upper trailing CVP (Sun & Hu, 2018b) and surface lower trailing CVP (Sun & Hu, 2018a).…”

“…The air inflow parameters (shown in Table I) are set in accordance with the Ma=2.7 experiments of Sun et al (2013) with stagnation pressure P 0 = 101,325 Pa and stagnation temperature T 0 =300 K. The bottom wall inflow 99% boundary-layer thickness, which is the same for all simulations, is estimated to be δ i =5.12mm, with the compressible (including density variations) boundary-layer displacement δ i * =1.75mm and momentum thicknesses θ=0.38mm and corresponding Reynolds numbers Re δ* =15,367, Re θ =3,337 respectively. A sketch of the computational domain is shown in the previous papers (Sun & Hu 2018a;Sun & Hu 2018b) and…”

“…Since the turbulent levels originating from the jet orifice in the experiments are not known, a uniform profile across the jet orifice is implemented without any disturbance. It might be argued that turbulence would not be thoroughly resolved in the jet; however, it is believed that the overall behavior of coherent structures in jet and boundary layer will not be affected by this assumption (Sun & Hu 2018a;Sun & Hu 2018b).…”

“…The jet is centred 75mm downstream of the inlet with an orifice diameter of D=2mm. The grid used in the current simulation is kept the same with the setup in our previous work (Sun & Hu 2018a;Sun & Hu 2018b). As analyzed, the grid setup ensures a fine DNS resolution in the near-wall region and a quasi-DNS (QDNS) resolution in the jet and the mainstream due to the unknown information about the smallest scales in the jet plume, as denoted by Sandham, Johnstone & Jacobs (2017).…”

Effect of fluid injection on turbulence and noise reduction of a supersonic jet

“…Figure 3 shows the instantaneous density contours for the four nozzles studied in this work. The additional shock structures due to fluid injection can be characterized by comparison with jets in supersonic cross-flow [36]. Figure 3b shows the instantaneous density contours in the vicinity of fluid injection for the 1FC-1FI jet.…”