Sonic Injection into a Mach 5.0 Freestream Through Diamond Orifices

Abstract

An experimental study to characterize the near-field (x/d < 8.0) flow for sonic air injection through 15-deg half-angle diamond-shaped orifices at four incidence angles (10, 27.5, 45, and 90 deg) and two total pressures (0.10 and 0.46 MPa) into a high Reynolds number (53 × × 10 6 ) Mach 5.0 freestream was performed. A 90-deg circular injector, with the same exit port area and total pressures, was examined for comparative purposes. The experimental methods included surface oil flow visualization, shadowgraph photography, Mie scattering flow visualization, pressure-sensitive paint, and a pitot-cone five-hole pressure probe. Flowfield documentation, jet penetration, and shock-induced total pressure loss were derived from these data. Attachment of the interaction shock wave was found to depend on both incidence angle and injector pressure. Penetration correlations were developed for both the diamond and circular injectors. An approximate analysis indicated that the shock-induced total pressure loss decreased with decreasing incidence angle and injection pressure, and the largest losses were incurred by the 90-deg circular injector. Nomenclature= axial coordinate y = transverse coordinate y p = penetration z = lateral coordinate α = incidence angle relative to x axis, positive counterclockwise = shock standoff distance δ = boundary-layer thickness δ * = boundary-layer displacement thicknessaverage stagnation pressure ratio ρ = dsensity Subscripts c = cone surface eb = effective back j = injector max = maximum shock location n = normal ref = reference pressure, 1.0 atm

Mixing Characteristics of Inclined Fuel Injection via Various Geometries for Upstream-Fuel-Injected Scramjets

“…These high-velocity crossflow conditions have been found to render normal fuel injection impractical due to substantial total pressure penalty in the aforementioned experimental and numerical studies [14,15]. The same tendency has been observed in a recent multiobjective design optimization conducted by the author using evolutionary algorithms for fuel injection through a circular porthole into a crossflow of Mach 5.7 [25].…”

“…Existing literature is rather sparse for transverse injection into high supersonic crossflow, but the comparative experimental and computational studies for circular and diamond injectors conducted by Bowersox et al [14,15] are selected and considered for comparison here. In these studies, flowfields caused by the interactions of a Mach 5 airstream and normal air injection at a sonic speed were investigated experimentally [14] and numerically using high-fidelity models, including the detach-eddy simulation (DES) turbulence model [15]. CFD simulations have been conducted for the corresponding configuration and conditions, applying the same numerical procedure, boundary conditions, mesh topology, and specifications at the finest resolution (χ m 1.5), as described in this section, with the differences being in the flow conditions, injectant properties, and dimensions.…”

“…Higher penetration was observed with the diamond injectors, exceeding the circular ones that initially produced larger penetration in the vicinity of injection. The penetration with the diamond injectors increased with the injection angle, which was attributed to the results from a tradeoff between the reduction in the initial penetration due to larger effective backpressure and the penetration increase from the larger effective jet-to-freestream momentum ratio defined as J eff ≡ J sin α j [14], where J and α j are the jet-to-freestream momentum ratio and injection angle, respectively. An experimental study conducted using helium injected at Mach 1.7 through a 15-deg-inclined injector into a Mach 6 crossflow by Fuller et al revealed a decrease in the core penetration growth rate and the concentration decay rate in an underexpanded case [16], as compared to matched-pressure injection.…”

“…For injection characteristics into higher supersonic crossflows, the flowfields in the presence of sonic air injection through diamond orifices into a faster crossflow of Mach 5 were investigated in experimental and computational studies conducted by Bowersox et al [14] and Srinivasan and Bowersox [15], respectively. The shockinduced total pressure loss with the diamond injector was found to be smaller than that with the circular one for normal direction, and it decreased with decreasing incidence angle and injection pressure (J 0.08-1.73).…”

“…Scramjet intakes with upstream fuel injection are commonly equipped with fuel injectors inclined 45 deg or further on this ground. However, rather scarce knowledge has been available from preceding studies for the mixing characteristics of inclined fuel injection into a hypersonic crossflow of Mach 5 via various injector geometries, apart from circular and diamond shapes [14][15][16]25].…”