CFD Analysis of Mixing Characteristics of Several Fuel Injectors at Hypervelocity Flow Conditions

Abstract

CFD analysis is presented of the mixing characteristics and performance of three fuel injectors at hypervelocity flow conditions. The calculations were carried out using the VULCAN-CFD solver and Reynolds-Averaged Simulations (RAS). The high Mach number flow conditions match those proposed for the planned experiments conducted as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The EIMP aims to investigate scramjet fuel injection and mixing physics, improve the understanding of underlying physical processes, and develop enhancement strategies and functional relationships relevant to flight Mach numbers greater than eight. Because of the high Mach number flow considered, the injectors consist of a fuel placement device, a strut; and a fluidic vortical mixer, a ramp. These devices accomplish the necessary task of distributing and mixing fuel into the supersonic cross-flow albeit via different strategies. Both of these devices were previously studied at lower flight Mach numbers where they exhibited promising performance in terms of mixing efficiency and total pressure recovery. For comparison, a flush-wall injector is also included. This type of injector generally represents the simplest method of introducing fuel into a scramjet combustor, however, at high flight Mach number conditions, the dynamic pressure needed to induce sufficient fuel penetration may be difficult to achieve along with other requirements such as achieving desired levels of fuel-to-air mixing at the required equivalence ratio. The three injectors represent the baseline configurations planned for the experiments. The current work discusses the mixing flow field behavior and differences among the three fuel injectors, mixing performance as described by the mixing efficiency and the total pressure recovery, and performance considerations based on the thrust potential.

Comparison of Several Global Mixing Performance Metrics for High-Speed Fuel Injectors

“…Results of the previously performed CFD simulations of the strut and ramp injector are provided by Drozda et al [10][11][12], however important modeling details are repeated here and selected results are shown for illustrative purposes. Reynolds-averaged simulations were performed using the Viscous Upwind aLgorithm for Complex flow ANalysis (VULCAN-CFD) code [17].…”

“…This typically occurred when the value of the L 2 -norm of the steady-state equation-set residual decreased by about 4-5 orders of magnitude. Grid dependence analyses for the numerical simulations of both the strut and ramp injectors were previously assessed by Drozda et al [10]. The numerical simulations took advantage of the geometric symmetries of the injectors, therefore, only a single injector is simulated with the symmetry boundary conditions used at the midplane between the adjacent injectors.…”

“…Though its overall upward penetration is limited, the helium mass fraction contours do show that the CVP entrains the helium injected through the bottom two fuel ports upwards towards the top of the fuel plume. For further details on the CFD simulations and discussion of their results, the reader is referred to the previous works of Drozda et al [10][11][12].…”

“…The CFD simulations of the mixing flowfields (under both experimental and notional flight conditions) provide detailed flowfield information which cannot be measured in the experiments and allow for the calculation of performance metrics. Thus far, three different types of fuel injectors, a strut, ramp, and flushwall injector, have been investigated both experimentally [8,9] and computationally [10][11][12]. These injectors were chosen as baselines for an initial study and represent the three basic classes of injectors commonly considered for high speed propulsive flowpaths.…”