High Enthalpy Nozzle Flow Research Articles

Flow Characterization of a Detonation Gun Facility and First Coating Experiments

A computer-controlled detonation gun based spraying device has been designed and tested to obtain particle velocities over 1200 m/s. The device is able to be operated in two modes based on different flow-physical principles. In one mode, the device functions like a conventional detonation gun in which the powder is accelerated in a blast wave. In the other mode, an extension of the facility with a nozzle uses the detonated gas for an intermittently operated shock tunnel process in which the particles are injected into and accelerated by a quasi-steady high enthalpy nozzle flow with high reservoir conditions. Presented are experimental results of the operation without nozzle in which the device generates moderate to high particle velocities in an intermittent process with a frequency of 5 Hz. A hydrogen/oxygen mixture and Cu and WC-Co (88/12) powders are used in the experiments. Operation performance and tube outflow are characterized by time-resolved Schlieren images and pressure measurements. The particle velocities in the outflow are obtained by laser Doppler anemometry. Different substrate/powder combinations (Al/Cu, Steel/Cu, Al/WC-Co, and Steel/WC-Co) have been investigated by light microscopy and measurements of microhardness.

Particle Acceleration in a High Enthalpy Nozzle Flow with a Modified Detonation Gun

The quality of thermal sprayed coatings depends on many factors which have been investigated and are still in scientific focus. Mostly, the coating material is inserted into the spray device as solid powder. The particle condition during the spray process has a strong effect on coating quality. In some cases, higher particle impact energy leads to improved coating quality. Therefore, a computer-controlled detonation gun based spraying device has been designed and tested to obtain particle velocities over 1200 m/s. The device is able to be operated in two modes based on different flow-physical principles. In one mode, the device functions like a conventional detonation gun in which the powder is accelerated in a blast wave. In the other mode, an extension with a nozzle transforms the detonation gun process into an intermittent shock tunnel process in which the particles are accelerated in a high enthalpy nozzle flow with high reservoir conditions. Presented are experimental results of the operation with nozzle in which the device generates very high particle velocities up to a frequency of 5 Hz. A variable particle injection system allows injection of the powder at any point along the nozzle axis to control particle temperature and velocity. A hydrogen/oxygen mixture is used in the experiments. Operation performance and nozzle outflow are characterized by time resolved pressure measurements. The particle conditions inside the nozzle and in the nozzle exit plane are calculated with a quasi-one-dimensional WENO-code of high order. For the experiments, particle velocity is obtained by particle image velocimetry, and particle concentration is qualitatively determined by a laser extinction method. The powders used are WC-Co(88/12), NiCr(80/20), Al2O3, and Cu. Different substrate/powder combinations for varying particle injection positions have been investigated by light microscopy and measurements of microhardness.

Energy Bin Model for High-Enthalpy Flows Using Prior Recombination Distribution

An energy-bin-based coupling model for recombination is derived for high-enthalpy nozzle flows using oxygen as the test gas. The coupling between vibrational and rotationalmodes is taken into account by the use of energy bins. A prior recombination distribution of molecules, dependent on the total energy available to a recombining system, is obtained using information theory. The low-lying electronically excited states of oxygen are also considered. The energy levels are obtained assuming the oxygen molecules behave as Morse oscillators. The results from a statespecific model are used to compare with the energy-bin approach. The energy-bin approach using only the ground state of the oxygen molecule predicts similar conditions at the nozzle test section as the state-specific model. The inclusion of the excited electronic states in the energy-bin approach calculations produces test section conditionswith significant chemical nonequilibrium and also predicts nontrivial concentrations of the electronically excited states. The effect of energy bias in the initial recombination distribution and the sensitivity of the test section conditions to the interbin rate constants are also investigated.

Vibrational Modeling of CO2 in High-Enthalpy Nozzle Flows

A state-specific vibrational model for CO 2 , CO, O 2 , and O systems is devised by taking into account the first few vibrational states of each species. All vibrational states with energies at or below 1 eV are included in the present work. Of the three modes of vibration in CO 2 , the antisymmetric mode is considered separately from the symmetric stretching mode and the doubly degenerate bending modes. The symmetric and bending modes are grouped together because the energy transfer rates between the two modes are very large due to Fermi resonance. The symmetric and bending modes are assumed to be in equilibrium with the translational and rotational modes. The kinetic rates for the vibrational-translation energy exchange reactions and the intermolecular and intramolecular vibrational-vibrational energy exchange reactions are based on experimental data to the maximum extent possible. Extrapolation methods are employed when necessary. This vibrational model is then coupled with an axisymmetric computational fluid dynamics code to study the expansion of CO 2 in a nozzle.

The influence of atomic and molecular metastable states inhigh-enthalpy nozzle expansion nitrogen flows

The role of atomic and molecular electronically excited states onthe whole kinetics of an high-enthalpy nozzle flow has been examined by usinga self-consistent model which couples Euler equations with appropriate masterequations and with the Boltzmann equation for the electron energy distributionfunction (eedf). The results show that in high-enthalpy flows metastableatomic nitrogen can form structures in the eedf through superelasticcollisions, partially smoothed by electron-electron Coulomb collisions.

High enthalpy nozzle flow sensitivity study and effects on heat transfer

The sensitivity of the flow along the nozzle and in the test section of high enthalpy wind tunnels to the thermochemical response of the nozzle expansion process, as well as effects on the pressure and heat transfer distributions over the Electre blunt cone standard test model, are examined in the framework of properly characterizing the test section flow field in such facilities. Particularly sensitive to the thermochemical behaviour of the nozzle flow, in the facilities under consideration, are the static pressure, static temperature and Mach number, whereas stagnation point (pitot) pressure and heat transfer data or freestream velocity are inadequate for the characterization of the thermochemical state of the flow. The Electre and nozzle wall pressure data in the F4 arc jet wind tunnel suggest, in contrast to nonequilibrium computations, that the flow in the F4 nozzle is close to equilibrium. In the HEG and, to some extent, the T5 piston-driven shock tunnels, there are indications that significant heat losses occur in the reservoir. Lastly, simple semi-empirical formulations for stagnation point heating are shown to perform reasonably well in high enthalpy flow conditions.

High enthalpy nozzle flow sensitivity study and effects on heat transfer

High enthalpy nozzle flow sensitivity study and effects on heat transfer

ノズル内における高エンタルピー気流の電離特性に関する実験的考察

A study of ionization characteristics of high enthalpy nozzle flow has been carried out by using the arc-heated wind tunnel with conical nozzle, where argon gas is used for the simplicity of analyzing the phenomenon. In this experiment, the exit pressure is relatively low, so that the non-equilibrium flow can be realized. The electron temperature and electron number density are measured by Langmuir probes at three stations located on the nozzle surface for several stagnation temperatures. The test results are compared with the analysis using the frozen flow which is commonly treated in such a flow. As a result, the nonequilibrium flow with non-frozen flow characteristics were obtained near the nozzle surface. The experimental result of electron number density rapidly decreases toward the downstream unlike the analysis. On the other hand, the electron temperature showed good agreement with each other. Thus, the ionization characteristics were made clear near the nozzle surface.

Determination of stagnation chamber temperature in high-enthalpy nozzle flows

Carslaw, H. S. and Jaeger, J. C., Conduction of Heat in Solids, 2nd ed., Oxford University Press, London, 1959, Chap. 2. Vallerani, E., Technique Solution to a Class of Simple Ablation Problems, Meccanica, Vol. 9, Jan. 1974, pp. 94-101. Zien, T. F., An Integral Approach to Transient HeatConduction Problems with Phase Transition, NSWC/WOL/TR 7537, Naval Surface Weapons Center, White Oak Lab., Silver Spring, Md., March 1975. Also, AIAA Paper 76-171, Wash. D.C., Jan. 1976.

Catalysis of recombination in nonequilibrium nozzle flows

The effects of a chemically active additive were investigated for nonequilibrium expansions of a dissociating gas. Numerical solutions were obtained in order to assess the catalytic influence of free radicals formed by bonding between the additive element and atoms of the dissociating gas. High-enthalpy nozzle flows of hydrogen with small quantities of carbon addition were studied over a range of equilibrium reservoir conditions appropriate to nuclear and electrothermal rocket operation. A chemical kinetic model consisting of eight species and twelve reaction steps evolved from studies of composition histories based on various finite-rate reaction schemes. Through two-body abstraction and association reactions between hydrogen atoms and hydrocarbon species, more of the energy in hydrogen dissociation is released than would kinetically be available in the absence of carbon. In some cases, this effect counterbalances the increased molecular weight so that the specific impulse of the system exceeds that of pure hydrogen in finite-rate nonequilibrium flows.