Shockwave effects on supersonic combustion using hypermixer struts

Abstract

This study describes combustion features due to streamwise vorticity when using hypermixer struts at Mach numbers of 2.5 and 3.5. Two types of struts are used with hydrogen fuel (at an equivalence ratio of 0.4) injected at sonic speed from the trailing edges of the struts. To study the effects of shockwaves on streamwise vorticity formation and supersonic combustion for an alternating-wedge strut, the intersection point at which the shockwaves cross the central axis is varied by changing the length of the strut. When the incident shock is near the trailing edge of the strut, boundary-layer separation occurs on the ramp of the strut due to pressure increase near the strut and subsonic combustion occurs on the basis of this separation. Conversely, when the incident shock is far from the trailing edge of the strut, a streamwise vortex is generated by the strut and supersonic combustion caused by this vortex makes it effective at entraining fuel into itself. Each flame structure obtained here unquestionably differs in its combustion mode. For a separation-resistant strut, the results show that a streamwise vortex with the required circulation can be induced behind the strut without separation. Moreover, the combustion depends strongly on the incident shockwaves in that the combustion efficiency is not subject to the mixing efficiency because the moderate combustion originates near the point at which the formed streamwise vortex interacts with the shockwaves. Therefore, because an ignition point with moderate combustion can detach from its trailing edge, with a separation-resistant strut, it is possible to control the combustion and avoid an excessive heat load.

Streamwise vortex breakdown due to the interaction with crossed shock waves

“…2011; Fureby et al. 2015; Hiejima & Oda 2020). Further, the advantages of strut-type injections with streamwise vortices on supersonic mixing and transition were summarised (Hwang & Min 2022).…”

“…ramps, pylons, struts and lobed mixers) is a promising approach for enhancing the mixing of fuel and air in a supersonic flow because the vortices can mitigate compressibility effects (Sandham & Reynolds 1991;Morkovin 1992;Lele 1994;Naughton, Cattafesta & Settles 1997;Hiejima 2013Hiejima , 2019. Among these devices, the hypermixer struts mounted in the centre of a channel or combustor, which can generate supersonic streamwise vortices, have excellent mixing and combustion capabilities in supersonic flows (Settles 1991;Waitz et al 1997;Gerlinger et al 2008;Burns et al 2011;Fureby et al 2015;Hiejima & Oda 2020). Further, the advantages of strut-type injections with streamwise vortices on supersonic mixing and transition were summarised (Hwang & Min 2022).…”

“…Based on this concept, Hiejima (2018) indicated the conditions for the occurrence of vortex breakdown in supersonic flows without shocks and found that the breakdown occurs without a stagnation point and subsonic region. Further, vortex breakdown is due to instability in helicity under strong swirl conditions (Hiejima 2020). Therefore, as a difference exists between incompressible and compressible vortex breakdowns without shock interactions, bubble structures in shock-induced vortex breakdowns may differ from those in incompressible breakdowns.…”

Numerical investigation of the effect of strut geometries on the flow characteristics in a model combustor

“…However, large pressure loss is inevitable for large ramp angles. Hiejima and Oda (2020) conducted numerical studies of a strut-based combustor that falls into the category of hypermixers inducing streamwise vorticity in the primary flow stream. The proposed hypermixer strut referred to as separation-resistant strut induces a streamwise vortex that interacts with the compression waves where the combustion is initiated.…”

Two-stage growth mode for lift-off mechanism in oblique shock-wave/jet interaction

“…However, a normal injection of gaseous fuel may lose its effect at relatively high inflow Mach number as Ma> 3 due to the unaffordable injection pressure, which indicates that a liquid-fuel injection is preferred 17 . Thus, producing streamwise vortex other than normal injection to enhance gaseous mixing at hypervelocity is desired 18 . Utilizing the potential shock structures embedded in supersonic flows, the so-called shock-enhanced mixing mechanism with fuel jet, which creates strong axial vortices that stretches the fuel-air interface 2 .…”