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Recent developments in the study of very high energy non-equilibrium fluid flows are reviewed. These are flows of molecular gases which exhibit substantial degrees of mode disequilibrium, specifically high energy in molecular vibrational and electronic modes, and high electron energies when the gases are weakly ionized. In contrast, the modes of molecular translation and rotation remain at lower energies. Attention is focused on high density, collision-dominated gases. Studies in two systems are presented: A small wind tunnel where an M = 5 steady air flow over small models is produced, and a flowing carbon monoxide gas laser, exhibiting very high energy loading of the vibrational quantum states. The development of non-intrusive optical diagnostics to measure vibrational and electronic state populations and rotational/translational mode temperatures in the flows, with high spatial and temporal resolution, is presented. Kinetic modeling and experimental validation studies in these environments are also discussed., To be published in Progress in Aerospace Sciences, 2014.

PRINCIPAL OBJECTIVE: "Develop experimentally validated kinetic mechanisms and modeling codes capable of predicting the impact of nonequilibrium plasmas on reactive processes, particularly on ignition,chemical energy release, and flameholding in combustors of flight vehicle engines." PRIMARY DELIVERABLES: * Extensive new experimental data sets of non-equilibrium plasma chemical energy conversion kinetics over a wide range of initial temperatures and pressures, in a variety of complementary new test facilities, specifically designed and fabricated for this program. * Detailed non-equilibrium plasma chemical energy conversion kinetic mechanisms, validated over a wide range of conditions, using data from multiple facilities. * Extensive experimental data sets on ignition delay, flameholding and laminar flame speed augmentation by nonequilibrium discharges, including nsec pulsed, DC/RF, and microwave. * High fidelity multi-dimensional plasma combustion modeling codes, validated in a series of model flows, with emphasis on the high subsonic to supersonic flow regimes., Prepared in cooperation with Princeton University; Drexel University ;Pennsylvania State University; and Georgia Institute of Technology. Document consists entirely of briefing charts. U.S. Government or Federal Rights License. The original document contains color images.

Ignition and flameholding in nonequilibrium plasma cavity flows. Objectives: * Further studies of cavity ignition and flameholding by repetitive nsec pulse plasmas in fuel injection flows (hydrogen and hydrocarbons) * High frame rate (10-20 kHz) NO and OH PLIF imaging of ignition process using burst mode laser * Increasing flow velocity beyond 100 m/sec, operating at low global equivalence ratios * Comparison with kinetic modeling calculations using reduced plasma chemical ignition mechanism. Plasma flameholding mechanism after ignition -- thermal or not? Outcome: Demonstration of true predictive capability of the model., Document consists entirely of briefing charts. U.S. Government or Federal Rights License. The original document contains color images.

The report presents results of cold MHD flow deceleration experiments using repetitively pulsed, short pulse duration, high voltage discharge to produce ionization in M=3-4 nitrogen and air flows in the presence of transverse DC electric field and transverse magnetic field. MHD effect on the flow is detected from the flow static pressure measurements. Retarding Lorentz force applied to the flow produces a static pressure increase of up to 20%, while accelerating force of the same magnitude results in static pressure increase of up to 10%. The measured static pressure changes are compared with modeling calculations using quasi-one-dimensional MHD flow equations and with predictions of a 3-D Navier-Stokes / MHD flow code, showing good agreement. Comparison of the experimental results with the modeling calculations shows that the retarding Lorentz force increases the static pressure rise produced by Joule heating of the flow, while the accelerating Lorentz force reduces the pressure rise. The effect is produced for two possible combinations of the magnetic field and transverse current directions producing the same Lorentz force direction (both for accelerating and retarding force).

The Nonequilibrium Thermodynamics Laboratories (NETL) at the Ohio State University are conducting this research program into the physics of high energy air flows. The particular environments being studied are gas flows in which large amounts of energy are stored internally in the flow molecules, although the gas temperatures remain relatively cold. Such environments occur in hypervelocity aerospace vehicle flow fields, notably behind the bow shock wave in front of the vehicle, and in the after-body expansion and the rocket exhaust expansion flows behind the vehicle.

The effects of weak ionization on the strength of shock waves in supersonic gas flows were studied in an experimental program. Claims that weak ionization can substantially reduce shock wave strength, independently of any plasma heating effects, were evaluated. Experiments were conducted in both shock tubes and in supersonic, steady flow, plasma wind- tunnels. Temperatures and ionization levels in the flows were measured. It was demonstrated that shocks can be weakened by creating an electric discharge in the flow, but this effect is purely a consequence of the Joule heating of the plasma. Without heating, ionization alone does not weaken the shock., The original document contains color images. All DTIC reproductions will be in black and white.

The present report incorporates the results of experimental and analytical research into kinetic mechanisms and rates of collisional and radiative energy transfer processes in nonequilibrium gas and plasma flows, such as exist in high-altitude rocket plumes, supersonic nozzles, and behind shock waves. The kinetic processes under consideration include vibrational relaxation and molecular dissociation of air species (N2 and 02), as well as of key combustion products (such as CO and NO), which are primarily responsible for persistent visible and ultraviolet radiation in low-density plumes. Associative ionization in collisions of vibrationally excited molecules, as well as strong coupling between plasma electrons and vibrationally excited species are also studied in detail. Finally, the report incorporates the results of kinetic modeling of nonequilibrium, reacting, ionized flows in supersonic nozzles, MHD channels, and behind the shock waves.