1. technology in achieving affordable, on-demand access to the orbital environment. However, problems of high thermomechanical loads and low propulsion efficiencies associated with scramjets must be addressed. Recently, efforts have focused on electromagnetic (EM) flow control to mitigate these issues. Several promising EM concepts have emerged, including the control of shock location for inlet mass-capture, fuel mixing enhancement, boundary layer transition control, and the magnetogasdynamic (MGD) energy bypass method.1-6Previous work by the authors and others has resulted in the development of a fully-coupled solver for the MGD subset of the Navier-Stokes and Maxwell equations.6For the purpose of establishing baseline data, a flight-sized, three-dimensional Mach 10 cruise vehicle has been modelled and performance tested using this solver without the inclusion of MGD effects.7This testing uncovered flow features that kept the inlet compression below the level needed for efficient combustion. Therefore, this paper documents the effort to improve inlet compression through the application of localized MGD effects.
2. with the AJAX program,5Kuranov et al. have focused on a parameter-based quasi-1D analysis (as well as some 2D numerical studies). This analysis utilized the inviscid subset of the Navier-Stokes fluid flow equations (i.e. the Euler equations) coupled to a source term formulation of Maxwell's equations for electromagnetic fields. The latter equations were cast in terms of the applied magnetic flux density, B, the load factor, k, and a scalar electrical conductivity, σ. In addition, the model assumed a calorically perfect gas existed throughout the flow. A final, critical supposition was that the flow sustained a level of ionization sufficient to ensure appreciable MGD interaction. Assuming all of the enthalpy extracted from the flow was made available to the MGD accelerator, AJAX was shown in some cases to produce 5-10% higher specific impulse than a conventional scramjet of the same geometry when approximately 10% of the freestream enthalpy was extracted from the flow.8
3. The conceptual work conducted by Kuranov et al. on the AJAX vehicle was among the first to show the potential for electromagnetic-fluid interactions to improve the performance of scramjet engines, and it has, in turn, spawned an abundance of further MGD flow control research. Inspired in part by AJAX and related efforts, Air Force Research Laboratory (AFRL) researchers extended the capability to analyze MGD flow control applications by developing a CFD code, referred to as FDL3D ICE, to model the fully-coupled, three-dimensional Navier-Stokes and Maxwell's equations for a non-ideal gas.9The code has many features including the ability to take advantage of the strengths and efficiencies of different computational techniques. In the research described here, the electromagnetic source term formulation, as given by Equations 1- 4, is used to take advantage of the fact that practical scramjet flows occur at a low magnetic Reynold's number, Rem,andconductivity. Thismethodhasprovenconducivetoallowingimplicittime-integrationand traditional upwind spatial discretization such as the Roe flux difference scheme that is much less diffusive in capturing flow discontinuities such as shocks.
4. In addition to the electromagnetic terms, both turbulence and thermochemical effects may be considered. Regardingtheformer, atwoequationk-ǫturbulencemodelbasedonliquidmetalflowsisincorporated. Until quite recently, this code did not address chemical kinetics, instead relying on the assumption of a calorically perfect, nonreactive gas. Two options now exist to address this issue. For problems only involving air a fourth order polynomial curve fit for γ valid from 50-3400K is available,11which obviates the computational expense of solving the species conservation equation. This is the approach taken for the inlet flow studied here. However, for detailed thermochemistry modelling (e.g. scramjet combustor problems), a loosely coupled finite rate chemistry algorithm was implemented in 2005.12
5. The control volume (CV) formulation of the governing equations of motion lends itself to the determination of system-level interactions and overall performance determination. These equations can be derived directly from the differential form of the equations by application of Reynold's transport theorem to a fixed control volume.13Furthermore, if the flow properties can be assumed constant across the flow cross-section, then the quasi-1D approach reduces the flow to dependence on a single spatial coordinate. Even though the inlet flow considered here has a complex 3D character, by taking area and volumetric averaging of the grid point flow properties, the quasi-1D approach can provide reasonable, conservative results. Finally, two more assumptions are made to obtain the equations that follow: (1) a single CV average value for the thermochemical properties can be taken (e.g. γ,CV,Cp, etc) and (2) the flow is steady in the sense that the influence of any ∂/∂t terms is negligible with respect to the steady terms. With this in mind, the CV equations for the scramjet inlet are given by Equations 9 - 13.