Effect of scramjet inlet vortices on fuel plume elongation and mixing rate

Abstract

Hypersonic air-breathing propulsion can improve cost and flexibility of Low Earth Orbit (LEO) satellite launch missions. However, at the high flight Mach numbers required for access-to-space, performance margins are extremely tight. Techniques to improve mixing efficiency can push this technology forward. However, these are required to produce a minimal increase in losses and heat loads to be viable. The use of inlet-generated vortices in scramjets for mixing enhancement was previously studied. These vortices interact with the injected fuel plume, stretching it and increasing its effective surface for mixing. Moreover, these vortices are intrinsic to the flowfield. Therefore, contrary to other methods, when using inlet vortices mixing is enhanced without producing additional heat loads or losses. This work studies the vortex-injection interaction through numerical RANS simulations. A non-dimensional variable defining the quality of the plume shape for mixing purposes is proposed. This parameter is used to assess the effect of vortex intensity and injector location on fuel plume shape. The results show the ability of inlet vortices to modify fuel plume shape significantly increasing fuel mixing rate with minimal impact on losses.

Experimental and numerical heat transfer from vortex-injection interaction in scramjet flowfields

“…Halving y + produced a 3% change in heat flux in the region of interest. The meshes used in the current study are equivalent to the ones used in a previous numerical study (16) , which includes a grid dependency study investigating several key parameters for vortex-injection interactions, such as mixing efficiency and penetration. Grids using approximately 3.8 to 4.0 million cells depending on the volume of the domain were found to be adequate.…”

“…Figure 2(b) shows a slice normal to the flow and illustrates how the vortex is generated by the shock-viscous interactions. The resulting vortex is equivalent to those generated in the inlet of non-axisymmetric scramjets (16,17) , where differing compression rates between ramp and sidewalls lead to similar interactions. Figure 3 shows the model used in the experimental campaign.…”

“…For the vortices presented in their work, the distance required to achieve 50% mixing efficiency can be reduced by a factor of two or more, compared to the case of injection in the undisturbed freestream. The largest mixing rate enhancements correspond to injection approximately half way between the vortex core and the separation line created by the SWBLI (16) . In their numerical studies, Llobet et al used a canonical geometry consisting of a flat plate and a compression wall, which can generate vortices representative of 2-D and 3-D shape transitioning inlets (17,18) The aim of the current work is to replicate the geometry of these prior works in experiment, to collect heat transfer data downstream of the vortex-injection interaction, and to benchmark prior numerical studies by providing corresponding experimental data.…”

“…The benefits of exploiting these streamwise vortices and flow structures for mixing rate enhancement in scramjets was first explored, to the authors knowledge, in works by Llobet et al (15,16) which showed promising improvement in mixing.…”

“…Llobet et al (16) studied the vortex-injection interaction using Reynolds Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD). They showed that by injecting into a representative streamwise vortex, typical for inlet-sidewall SWBLI in scramjet engines, the air-fuel mixing rate is improved substantially.…”