Mario Carbonaro

Thermodynamic and Transport Properties for Inductive Plasma Modeling

A review is given of models for the thermodynamic and transport properties of inductive plasmas under conditions of local thermodynamic equilibrium. The thermodynamic properties of individual species are computed using a statistical mechanics formulation based upon the rigid rotator and harmonic oscillator model. Complex cut-off criteria for the electronic levels and anharmonicity corrections are not needed for practical equilibrium calculations. An efficient iterative technique is proposed for the calculation of the equilibrium mixture thermodynamics properties. Through a Schur-complement approach the number of unknowns in the nonlinear system, which determines the equilibrium chemical composition, may be reduced to the number of basic elements. The method is demonstrated for equilibrium air computations. The plasma transport properties are computed with the method of Chapman and Enskog. Accurate formulas for the heavy particle and electron transport properties are discussed. Through a straightforward argument the result of Butler and Brokaw for the reactive thermal conductivity is shown to be valid for ionized equilibrium mixtures. Computed results for the thermodynamic and transport properties of air are compared with numerical and experimental results of other researchers.

Disturbance Level Characterization of a Hypersonic Blowdown Facility

Free-stream disturbances have a dominant role on boundary layer stability and transition, especially in high speed ows. The assessment of the ow quality in a wind tunnel is therefore a key issue especially in transition to turbulence studies. With this purpose a detailed characterization of the free-stream disturbance level of the VKI H3 Mach 6 Wind Tunnel at di erent Reynolds number is carried out by means of classical intrusive measurements techniques (hot-wire anemometry and Pitot pressure probes). Issues concerning the aerodynamic heating of the probes are investigated and a special calibration technique is developed in order to compensate for these e ects. Statistical and spectral analyses are compared with the data available in the literature for other hypersonic wind tunnels, working at similar ranges of Mach and Reynolds numbers. A combined data reduction technique is also developed which allows to extract all ow quantities uctuations from those directly measurable through the above-mentioned instrumentations. By means of this technique, the validity of some physical hypotheses on the ow can be veri ed. Moreover, a Kovasznay modal analysis allows to characterize the origin of the disturbances.

Experimental and computational determination of the VKI Plasmatron operating envelope

The present paper deals with the experimental determination of the operating envelope of the Plasmatron facility, designed and built at the von K&m&n Institute for Fluid Dynamics as the test bench of the European Space Agency to perform testing of TPS materials before their use in flight. As such the prime requisite of the facility is its capacity to reach specified values of stagnation pressure and catalytic cold wall stagnation point heat flux. These two variables are measured using a water-cooled Pitot probe and a steady-state heat flux probe. The paper contains the description of these probes and details about their use, as well as an analysis of experimental uncertainty. The results of the envelope exploration are presented and it is shown that the facility reaches and outdoes its basic requirements. The experimental results are also compared to the values predicted by a quasi-one-dimensional nozzle code of a plasma flow in chemical equilibrium. It is shown that the experimental values agree well with the predicted values. Results of measurements at various positions of the plasma jet are also reported. The decrease of heat flux and dynamic pressure with axial distance from the torch is essentially linear. The onedimensional model was shown to fail to predict the effect of mass flow rate, due to strong twodimensional effects in the jet. Perspectives of supersonic operation are examined in view of the pumping capacity. A brief description of the facility is also part of the report.

Experimental investigation of the flowfield about an unswept afterbody

In general, the flowfield about the aft portion of an aircraft fuselage employing an upswept afterbody is complex and can have a detailed vortex structure. Directional pressure probe measurements show that the afterbody wake evolution is weakly dependent on the Reynolds number. Pressure taps are used to investigate the effect of base slant on the base pressure distribution. The base pressure distribution is found to increase along the upswept ramp in the freestream direction. Using oil flow visualizations general conclusions are drawn about the surface flow topology. Two distinct regions of flow separation are identified. An analytical model of the crossflow wake structure is developed from the experimental data. This model allows for conclusions to be drawn about the crossflow vortex structure and provides simple analytical expressions for the vorticity and swirl velocity distributions in the crossflow plane.

Aerodynamic Force Measurements in the VKI Longshot Hypersonic Facility

Measurements of aerodynamic forces and moments on reentry bodies are performed in the VKI Longshot hypersonic facility, using a sting-mounted strain gauge balance. Inertial corrections are applied to compensate the effect of inevitable model vibrations. This involves the measurement of model accelerations, using miniature sensors. Inertial corrections are optimized, taking into account accelerometers transverse sensitivity effects, time lags, signal filtering or smoothing, and tuning for the inertia of the vibrating masses.

THERMODYNAMIC AND TRANSPORT PROPERTIES FOR INDUCTION PLASMA MODELING

The development at the von Karman Institute of an inductively heated plasma wind tunnel has brought a need for theoretical and numerical investigation of high-temperat ure gases (plasmas) of different types. The thermodynamic properties of individual species are computed using statistical thermodynamics formulations based on the rigid rotator and harmonic oscillator model. A discussion is made about cut-off criteria for the electronic levels, low-temperature corrections to the partition function and anharmonicity considerations. It is shown that sufficient accuracy is obtained for practical applications of chemical equilibrium without complex cut-off criteria and anharmonicity corrections. The mixture thermodynamic properties are computed at chemical equilibrium using the equilibrium reactions approach. An efficient formulation has been obtained for mole fraction or mass fraction computation which allows the reduction of the system of unknowns to a size equal to the number of basic nuclei types. The method is illustrated by 3-species argon and 13-species air plasma computations. Finally, transport properties are computed from kinetic theory of gases. The underlying mixture rules and the collisional data used as input are discussed and results are shown for a 13-species air plasma. Be c e f

CHARACTERIZATION OF A "MINI-PLASMATRON" FACILITY BY PITOT PROBE MEASUREMENTS

The VKI Minitorch is used as a facility to test and to develop measurement techniques for plasma flows, to be applied to the VKI Plasmatron. The behavior of a cooled Pitot probe in the Minitorch plasma jet is briefly examined. The influence of the geometrical configuration of the gas injection in the Minitorch and of the peripheral and central mass flow rates on the plasma flow are determined, by comparison of the dynamic pressure profiles of the plasma jet measured in each condition.

Enhanced Mixing in Co-Flowing Laminar Streams

In chemical lasers a mixture of F, F2, He and DF in a thermochemical equilibrium state at a total temperature between 1000 and 2000°K and a total pressure between 3 and 5 bars is expanded rapidly through a bank of small supersonic nozzles into the laser cavity. The fluorine-carrying gas exits at a Mach number of about 5 and with a static pressure of about 2000 Pa. Due to the extremely small dimensions of the nozzles and the low density of the gases, the Reynolds numbers based on nozzle width is of the order of 1000 and the flow is commonly laminar.