Vehicles flying through the atmosphere at hypersonic speeds excite the air surrounding them to very high temperatures in the post-shock and boundary layer regions. Various chemical reactions associated with the elevated temperatures of these regions are initiated as a result. These reactions in turn affect the thermodynamic and transport properties of the air, as well as the lift, drag, and surface temperatures experienced by such vehicles. Accurate and efficient numerical solutions of the aerothermochemistry equations are therefore needed to predict these viscous, chemically-reacting flows, and to predict the aerodynamic and thermal loads experienced by such vehicles.

CFDRC has develped fully-coupled finite rate chemistry with an arbitrary number of species models, as well as thermal non-equilibrium models. Those models are designed to handle flows with a calorically perfect gas, or with thermo-chemical non-equilibrium gas. These technologies have been incorporated into the CFD-FASTRAN code. In addition, CFDRC has developed the Unified Flow Solver UFS for rarefied and continuum flow regions. This solver is capable of automatically switching between a deterministic Boltzmann solver and a continuum CFD solver depending on local gradients of gas density, flow velocity, and temperature.

CFDRC engineers used the CFD-FASTRAN code to conduct time-accurate, coupled CFD and rigid body dynamics simulations of the staging event of NASA's X-43-A hypersonic research vehicle. The objectives of the analysis were to assist NASA in evaluating the stability of the vehicle and assess the re-contact risks during the staging event. The X-43A vehicle separates from the Pegasus booster at Mach 7 and an altitude of 95,000 ft. Hydraulic pistons push the flyer forward and away from the booster to initiate the staging, while the tail control surfaces increase their deflection up to 8 degrees to trim the vehicle to the 2-degree angle-of-attack required to activate the vehicle's scramjet.

This computation was made possible by the coupling between the flow and body motion modules (such as 6-DoF and prescribed motion), enabling the simulationi of the full physics of the problem, incorporating the combined effects of the hypersonic flow, with the vehicle interference effects, the forcing of the hydraulic pistons, and the deflection of the tail control surfaces. Full Navier-Stokes computations, with the K-e turbulence model, were used on grids with 2.5 million points. The accompanying images show the Mach number plots at various points in the staging sequence.

This study met its objectives, as our NASA customers gained more confidence in their engineering analysis. Our analysis also helped NASA develop the control surface deflections for the Mach 10 test flight.

CFDRC and Martin Baker engineers developed a static aerodynamic-coefficient database for the Beagle 2 Mars probe. The database covers the probe's entire entry trajectory, over which the speed varied from Mach 1.5 to Mach 28. More than 50 reacting and non-reacting flow cases were computed for the database. An eight-species (CO₂, CO, N₂, O₂, NO, C, N, O), nine-reaction, thermo-chemical non-equilibrium model was used for all cases with Mach numbers of 7 and above. The aerodynamic coefficients were then provided and used to generate a blended aerodynamic database for vehicle EDLS development.

At high altitudes and low ambient pressures, the rocket plumes of missile control jets expand much faster and wider than at sea level. The plume expansion may even interfere with the targeting sensors in the nose of the missile.

In this study, CFDRC engineers used CFD-FASTRAN to compute the interaction of a control jet with the hypersonic flow field around the AIT interceptor missile at an altitude of 110,000 feet and a velocity of 3.5 km/sec (corresponding to a Mach number of 8.2). The jet exit Mach number was 3.5. Reacting and non-reacting simulations of the mixing of the solid propellant exhaust jet with the external flow showed the potential for external afterburning of the plume gases.

CFDRC engineers conducted satellite flow simulations to predict the flow field and critical heat loads on satellite components exposed to the upper atmosphere at an altitude of 90 kilometers and velocities in excess of 2400 m/sec (corresponding to a Mach number of 8.8). The flow was at the limit of the continuum flow regime (with a Knudsen number of 0.01). CFDRC's engineers generated 3-D models of the complex satellite geometry with its various attachments, including solar panels and antennae, and performed the complex flow calculations. The computations revealed highly complex heating patterns due to the shock system that forms around the satellite. This helped our customer gain more confidence in the system deployments as the head loads predicted were below critical loads.

These complex computations were obtained using the CFD-FASTRAN code, which employs finite rate chemistry and thermo chemical non-equilibrium models to handle hypersonic reacting flows.