Masahito Mizuno

Spectroscopic Flow Evaluation in Inductively Coupled Plasma Wind Tunnel

Radiation spectroscopy of high-enthalpy flows in a 110-kW-class inductively coupled plasma wind tunnel is conducted to improve the accuracy of the radiation code and to measure the flow properties in the test section of the wind tunnel in detail. Imaging spectroscopy is done to obtain radial profiles of emission spectra at a single moment, from which the radial distribution of the emission intensity is determined by the inverse Abel conversion. The molecular temperature and the chemical species concentration are determined by the spectrum fitting method through the use of the radiation code, SPRADIAN2. To accomplish better agreement between the numerical predictions and experiments, the theoretical model and the spectroscopic data for the radiation code are replaced with more accurate data to reflect the recent experimental and theoretical results. As a result, the radial distributions of the temperature, the concentration of the impurities as well as the major chemical components, and the flow enthalpy are accurately determined for nitrogen and air flows in the test section of the wind tunnel.

Arc Heated Wind Tunnel Flow Diagnostics using Laser- Induced Fluorescence of Atomic Species

Two-photon Laser induced fluorescence diagnostics system for atomic oxygen has been installed at the 750kW arc heated wind tunnel in JAXA in order to obtain velocity, translational temperature, and number density of atomic oxygen simultaneously. It was observed that the center of excitation wavelength is shifted in the shock layer. The Doppler shift due to the free stream velocity has a same order effect on the excitation wavelength. The translational temperature distribution was deduced from spectral broadening and the absolute atomic number density was obtained with a calibration technique by a reference xenon gas cell. Nomenclature a = effective branching ratio of the observed fluorescence transition Ap = cross sectional area of laser beam c = velocity of light, m/s Ep = laser pulse energy, J F(t) = normalized temporal profile of laser pulse h = Planck’s constant, Jxs I

Laser induced fluorescence of nitric oxide and atomic oxygen in an arc heated wind tunnel

Laser induced fluorescence diagnosis system for NO and O detection has been introduced in the 750kW arc heated wind tunnel in JAXA. Parameters in the measurement have been optimized and operational wind tunnel conditions for the LIF measurement has been determined. Nitric oxide fluorescence was observed at a total enthalpy no greater than 10 MJ/kg. Whereas atomic oxygen fluorescence was observed at a total enthalpy less than 20 MJ/kg in this wind tunnel. It was observed that the center of excited wavelength is shifted in the shock layer. The Doppler shift due to the free stream velocity has a same order effect on excitation wavelength. The translational temperature was reduced from the measurement using spectral broadening of atomic oxygen excitation spectrum.

Comprehensive Flow Characterization in a 110-Kilowatt Inductively-Coupled-Plasma Heater

E LECTRICALLY heated wind tunnels are widely used as one of the ground-test facilities to evaluate the performance of thermal protection system (TPS) materials for atmospheric reentry vehicles. Recent interests in TPS development may be focused on accurate assessment of heat generation due to chemical reactions on the gas– surface interface, such as catalytic recombination on the surface, and oxidation and nitridation of the TPS material. To accurately assess the contributions of such processes to the net heat transfer rate, it is necessary to obtain detailed information about the flow properties such as temperature and concentration of the atomic species when TPS materials are tested. In the past studies [1,2], in an attempt to measure the thermochemical properties of the testflow in a 110-kWinductively-coupledplasma (ICP) heater at the Aerospace Research Center, Japan Aerospace Exploration Agency [3], emission spectroscopy associated with the line-by-line spectrum analysis was conducted by using the radiation code SPRADIAN2 [2]. The temperature and the chemical composition in the test flow were successfully determined under the representative operating conditions. More recently, the nitridation rate coefficient for the carbon surfacewasmeasured in the nitrogen test flow using the ICP heater [4,5]. In this experiment, to eliminate atomic oxygen remaining in the test section as an impurity, the ambient gas in the test section was replaced with pure nitrogen before ignition of the ICP heater. The experimental results indicated successful reduction of atomic oxygen by the gas replacement; however, its effectiveness has not been quantitatively assessed yet. In this study, following the preceding studies, comprehensiveflow characterization in a wide range of the operating conditions is conducted for future use in thermal protection materials testing and evaluation. A new imaging optical system is introduced to obtain emission spectra with less optical aberration in a wider wavelength range than before. The presence and source of impurities in the test flow are discussed more elaborately. Finally, effectiveness of the gas replacement on reduction of impurities is quantitatively assessed by obtaining the radial distribution of the impurities in the core flow of the test section.

110 kW New High Enthalpy Wind Tunnel heated by Inductively-Coupled-Plasma

New inductively coupled plasma-heated wind tunnel was completed and some performance evaluations have been conducted to simulate atmospheric reentry environment and to study catalytic effect and so on. Maximum power of this wind tunnel is 110 kW, and maximum total enthalpy is presently about 20 MJ/kg. The electronic excitation temperature was evaluated in the torch, and it was about 10000 K. This result was compared with real gas CFD analysis coupled with electromagnetic field. At the test section, maximum heat flux was about 1 MW/m 2 , and the obtained temperature of C/C-SiC samples was about 1500 degree C, which was same condition of actual flight. This new wind tunnel can operate more numbers of runs to obtain experimental data effectively than the existing arc-heated wind tunnel because of easiness of maintenance. This wind tunnel still has some problems, which are instability of the flow at low mass flow rate and effect of rotational flow. The modification of gas supply system might be needed as one of the idea to solve this problem.

Evaluation of Surface Catalytic Effect on TPS in 110kW ICP-heated wind tunnel

New 110kW inductively coupled plasma (ICP)-heated wind tunnel in JAXA-ISTA was constructed and some performance evaluations have been conducted to simulate atmospheric reentry environment. Using this wind tunnel, initial heating tests for catalytic effect research were carried out, and new materials were tested to evaluate its characteristics including catalysis, emissivity, and so on. SiC coating samples showed comparatively low temperature, but high catalytic coating showed higher temperature. The difference was about 100 ~ 200 C, and it corresponded to 0.3 ~ 0.4MW/m 2 of heat flux. The difference of heat flux due to effect of catalytic effect was reasonable to compare with former CFD results for arc-heated wind tunnel tests. Ultra high temperature ceramic (UHTC) material was also tested, and its characteristics changed from low catalytic region to high catalytic region as the temperature increased. It was caused by changing catalytic effect and emmisivity due to oxidization.

Experimental and Numerical Study of Thermal Response of Ablator in an Arc-Jet Facility

To study the surface catalysis of the ablating materials, the efficiency of catalytic recombination of atomic oxygen is evaluated for graphite and carbon-carbon composite experimentally. In the experiment, the catalytic efficiency is determined by measuring the spatial variation of atomic oxygen concentration by actinometry. By using the computational tool with the catalytic efficiency value obtained in this study, the thermal response of ablative test piece under arc-jet flow condition is analyzed for one operating condition. Calculated surface temperature is in between the results for the cases of the noncatalytic and fully catalytic conditions, and well reproduce the measured one. It is suggested from the study that even the small catalytic efficiency of materials increases considerable amount of heat flux resulting in the increase in surface temperature.

Nonequilibrium plasma flow properties in arc-heated wind tunnels

Turbulent plasma flows in arc heaters such as JAXA 750 kW, NASA 20 MW and Kyushu University 20 kW facilities were investigated and the distributions of flow-field properties were successfully obtained. For this purpose, an integrated analysis model to simulate various-scale arc-heated flows with high accuracy was developed. The turbulent flow field was described by the Navier-Stokes equations with a multitemperature model, which was tightly coupled with electric-field and radiation-field calculations. An accurate and low-cost radiation model and a low-Reynolds number two-equation turbulence model were introduced into the flow-field simulation. Arc discharge in constrictor section and expansion processes in nozzle section play key roles for forming an arc-heated flow. Thus, it is important to correctly model those phenomena for predicting the high-enthalpy flow properties accurately. To validate the present numerical model, the computed results were compared with the corresponding experimental data for the mass-averaged enthalpy, temperatures and number density. Through the comparison of the predicted results with detailed experimental data obtained by spectroscopic and laser-induced fluorescence techniques, the present integrated analysis model was validated. In addition, the mechanisms of energy input by discharge and energy loss were discussed with distributions of the temperature and heat flux derived from the arc column. Although it was indicated that more detailed discharge model is possibly required in order to describe arc discharge with higher accuracy, the present flow-field model was found to give generally good agreement for various operating conditions of the facilities.

Numerical Calculation of Rarefied Oxygen Flow for Surface Catalysis Evaluation

†† Direct simulation Monte Carlo code is developed to study a catalytic process of atomic oxygen on thermal protection material surface. The present method employs the phenomenological electronic excitation model and the heterogeneous catalytic model. Numerical method is applied to simulate the flowfield around a test piece put into the rarefied dissociating oxygen test flow. The calculated number density ratio of oxygen to argon is compared with the measured emission intensity ratio of oxygen line to argon line. The sensitivity analysis is made by varying Eley-Rideal reaction cross section under the several conditions of collisional desorption cross section, sticking coefficient, and total number of surface site. It is found from the study that the probability value of Eley-Rideal reaction for the test piece made of a sintered silicon carbide is about 0.035, while the value of about 0.1 is deduced for the test piece made of copper.

Study of Nitrogen Recombination Coefficient for SiC Material Surfaces

The catalytic efficiency of atomic nitrogen recombination is estimated in the surface temperature range from 300 to 1360 K at the total pressure of 14.7 Pa for silicon carbide experimentally. For this purpose, the spatial variation of atomic nitrogen concentration is measured by actinometry. The inductively coupled plasma of molecular nitrogen with argon is employed. In the present paper, the obtained catalytic efficiency values are shown, and the problems in evaluating the catalytic efficiency as well as the necessity of the numerical simulation inside the quartz tube in order to obtain the accurate catalytic efficiency are described.