Markus Fertig

Recombination Coefficients and Spectral Emissivity of Silicon Carbide-Based Thermal Protection Materials

The method for determining the recombination coefficients for ceramic materials in air plasma and pure oxygen plasma is described. Additionally, a new method lor the in situ determination of the spectral emissivity of high-temperature ceramic materials is presented. Values of the recombination coefficients for considered materials, resulting from the described methodology, are given at temperatures between 1483 and 1851 K and pressures between 356 and 950 Pa and compared with literature. Values of the spectral emissivities of the investigated materials are presented in a temperature range from about 1200 to 1820 K and compared with values obtained by other authors. Obtained results will be used for the development of catalytic sensors in the frame of the European reentry program EXPERT.

Oxidation Behavior of Siliconcarbide-Based Materials by Using New Probe Techniques

Hysteresis of passive to active and active to passive transition of SiC oxidation behavior has been investigated theoretically, numerically, and experimentally. Theoretical and experimental investigations show a strong interaction between transition and catalysis. Dependence on plasma composition is shown.Arecently developed reaction model has been implemented in the advanced nonequilibrium Navier–Stokes code URANUS. Results are presented for the highly dissociated flow around the MIRKA capsule. In this case, radiation adiabatic surface temperatures have been found to be 120Khigher for active oxidation conditions as compared to passive oxidation conditions. To investigate transition behavior in detail, various new probe measurement techniques have been developed. Important additional observations have been made in chemical nonequilibrium.Within plasma wind-tunnel testing, a sudden temperature increase of up to 400 K was found with the transition from passive to active oxidation. Theoretical and numerical predictions show good qualitative and quantitative agreement with experimental results.

Upwind Relaxation Algorithm for Re-entry Nonequilibrium Flows

The development of the Navier-Stokes solver URANUS (Upwind Relaxation Algorithm for Nonequilibrium Flows of the University of Stuttgart) will be described.

Hybrid Code Development for the Numerical Simulation of Instationary Magnetoplasmadynamic Thrusters

This paper describes the numerical modeling of rarefied plasma flows under conditions where continuum assumptions fail. We numerically solve the Boltzmann equation for rarefied, non-continuum plasma flows, making use of well known approaches as PIC (Particle in Cell) and as DSMC (Direct Simulation Monte Carlo). The mathematical and numerical modeling is explained in some detail and the required computational resources are investigated.

SiO2 Catalysis Modeling for CFD Calculations

In this paper, the elementary reaction steps adsorption/desorption of atoms as well as Eley-Rideal and Langmuir-Hinshelwood reaction mechanisms will be explained. Analytical solutions for recombination probabilities will be given for adsorption, desorption and Eley-Rideal chemistry as well as for adsorption, desorption and Langmuir-Hinshelwood chemistry. The main focus of the paper will be on the calibration of the catalysis model in comparison to models and experimental results of other authors. Finally, CFD results will be presented for the Shuttle equivalent hyperboloid. The results will be compared with published CFD results and experimental data.

Influence of Chemical Accommodation on Re-entry Heating and Plasma Wind Tunnel Experiments

The influence of chemical accommodation coefficients on the forebody heating of the ballistic MIRKA re-entry capsule was investigated numerically with the nonequilibrium Navier-Stokes code URANUS. Chemical accommodation coefficients have been modeled physically consistent for all possible catalytic recombination mechanisms at the surface, i.e. direct recombination, the Eley-Rideal reaction type as well as the Langmuir-Hinshelwood reaction type. The difference in surface temperature was below 6 K when comparing the thermal nonequilibrium simulations, taking into account chemical accommodation coefficients below unity, with the thermal equilibrium simulations. In a second step, typical plasma wind tunnel conditions with stagnation pressures of 800 Pa and a total specific enthalpy of 20 MJ kg used to determine recombination coefficients in the plasma wind tunnel at IRS have been addressed. Given the chemical accommodation coefficient, only little uncertainty in determining recombination coefficients has been found.

Numerical Simulation and IRS Instrumentation Design for EXPERT

ur Raumfahrtsysteme will contribute three ∞ight instrumentations to the European re-entry vehicle EXPERT. PYREX is a pyrometric entry experiment which measures TPS rear side temperature distribution in the nose cone, PHLUX is a catalysis based sensor system which determines the local dissociation degree of the air plasma and RESPECT is a miniaturizied spectrometer to be used for gaining spectral data in the postshock regime around EXPERT during its entry into Earth’s atmosphere. In this paper, axisymmetric numerical calculations using the URANUS nonequilibrium Navier-Stokes code are presented. In the course of designing PHLUX, measurements of total emissivity for difierent materials in the temperature regime 750 K - 1750 K were conducted using a newly developed method. Calibration measurements with a laboratory model of RESPECT are presented.

Determination of Recombination Coefficients and Spectral Emissivity of Thermal Protection Materials

*† ‡ § This paper describes the method for the determination of the recombination coefficients for ceramic materials in air plasma and pure oxygen plasma. Additional a new method for the in situ determination of the spectral emissivity of the high temperature ceramic materials is presented. Values of the recombination coefficients for some materials, resulting from the described methodology, are given and compared with literature. Values of the spectral emissivities of the investigated materials are presented and compared with values obtained by other authors. Obtained results will be used for the development of catalytic sensors in the frame of the European re-entry program EXPERT.

Experimental and Numerical Analysis of the Impact of a Strong Permanent Magnet on Argon Plasma Flow

The interaction between a probe body and argon plasma flow is investigated to examine to what extent the thermal loads on a vehicle during the re-entry into the Earth’s atmosphere can be reduced by applying a magnetic field. The experiments are performed using a strong permanent magnet installed inside a probe body of the so called European standard. An insert of high magnetic permeability was used to increase the magnetic field strength in front of the probe, which then was measured to be 0.12 T. Former investigations showed only weak influence on the bow shock geometry but definite impact on the temperature as well as on the boundary layer. In order to obtain a stronger interaction, several aspects of the setup have been revised. In contrast to earlier experiments, a spherical probe head is used in this investigation. Also, the plasma generator has been changed in order to achieve higher enthalpies und thus stronger magnetic interaction. The argon plasma condition had to be defined and first characterization measurements have been made. All experiments performed were steady state and the test duration was about 5 minutes. Pictures of the experiments were analyzed and showed a definite impact of the magnetic field on the bow shock geometry. Due to the magnet, the bow shock distance increased by roughly 13% whereas the recorded light intensity of the bow shock region increased by a factor of 2.7. The analysis of the center line intensity of each test case indicates that the magnetic field is affecting the argon plasma flow upstream, beyond the bow shock.

The In- Flight Sensor Systems PYREX, PHLUX and RESPECT for the Capsule EXPERT

*† ‡ § ** †† ‡‡ §§ Miniaturized flight experiments being developed at IRS for the European capsule program EXPERT are presented. PYREX, a pyrometric entry experiment, measures rear side temperatures and heat fluxes on ceramic TPS. It has already been flown (EXPRESS, MIRKA). PYREX-KAT38 is a fully qualified six-channel measurement system and was intended to be operated aboard the X-38. A similar design is being further developed for temperature and heat flux measurements in the nose structure of the EXPERT capsule. PHLUX (Sensor system for catalytic experiments) is a pyrometric catalysis based sensor system being developed for the EXPERT capsule. A breadboard with two sensors opposite each other has already been developed for ground tests by means of plasma wind tunnel experiments to qualify the sensor functionally and to investigate the plasma composition. The flight experiment aims to estimate the dissociation degree during the entry using measured heat fluxes on different catalytic surfaces. RESPECT is a spectrometer to be used to gain spectral data in the flow field around EXPERT during its entry. The main goal is to obtain more detailed information about the plasma state in the post shock regime by measuring the spectrally resolved radiation onto the surface. The data will be used for the comparison with results of numerical simulations to validate of aerothermodynamic models.