Fabian Zander

Measurements of Air Plasma/Ablator Interactions in an Inductively Coupled Plasma Torch

Studies of the ultraviolet and visible emission from an atmospheric pressure air plasma and its interaction with two carbon-based ablative materials were performed in an inductively coupled plasma torch. These experiments were conducted at a plate power of 40 kW, which produced an air plasma in local thermodynamic equilibrium with a maximum temperature of approximately 6200 K, corresponding to a specific enthalpy of 16.4  MJ/kg. Three techniques were developed to measure the ablator surface temperature. Recession rates and product species profiles were measured for two different materials (ASTERM™ and carbon-bonded carbon fiber) at a plasma velocity of approximately 20  m/s. Measured surface temperatures were in the range of 2100 to 2300 K, and corresponding hot-wall heat fluxes were approximately 1.4  MW/m2. Spatially resolved profiles of the main species detected in the boundary layer were recorded, and they showed evidence of strong coupling between the ablated material and the freestream.

Ablation radiation coupling investigation in earth re-entry using plasma wind tunnel experiments

An overview of a comprehensive experimental study to investigate ablative materials in a high enthalpy air plasma flows including radiation effects is given. Through the application of surface thermometry, in-situ recession measurements with photogrammetry, optical emission spectroscopy from vacuum-ultraviolet (120 nm) to near infrared wavelengths (950 nm), pyrometry and thermography, a complete set of data for the investigation of ablation radiation coupling has been acquired. The paper presents the background of this project, the suite of experimental setups and first results for a carbon preform sample and a cooled copper sample. All systems acquired data and first comparisons to chemical equilibrium calculations have been assessed.

Experimental setup for vacuum ultraviolet spectroscopy for earth re-entry testing

This paper presents the experimental system which has been designed to measure vacuum ultraviolet (VUV) optical emission spectra. It has been tested at the plasma wind tunnel PWK1 at the Institute of Space Systems. The setup, its calibration and qualification are reported. Wind tunnel experiments have been conducted with a local mass-specific enthalpy of 68.4MJ/kg and a stagnation pressure of 24.4 hPa. The radiation is collected through a magnesium fluoride window mounted close to the stagnation point of a sample. The received light is redirected to the spectrometer with a series of mirrors in an evacuated light path. The spectral range between 116-197 nm was investigated. The lower limit is due to the transmission of the window material. Measurements with a cooled copper and a carbon preform material sample are presented. The measured VUV spectra feature atomic nitrogen and oxygen lines for both the copper and the material sample. Atomic carbon lines are present in the case of the material sample.

Aerothermodynamic investigation of inductively heated CO2 plasma flows for Mars entry testing

This paper presents the characterization of an inductively coupled CO2 plasma relevant for Mars entry. Key plasma parameters are measured using Two Photon Absorption LaserInduced Fluorescence (TALIF), Optical Emission Spectroscopy (OES) and a High-Speed Camera (HSC) as non-intrusive diagnostic methods. In addition heat flux, enthalpy and total pressure are intrusively probed to supplement the characterization. TALIF provides data about translational temperature, velocity and the density of ground state atomic oxygen. From OES rotational and vibrational temperatures for identified molecular species and excitation temperatures for atomic species are derived. Preliminary HSC results show the pulsing behaviour of the generator and, in combination with bandwidth filters, atomic emission distributions. The diversity of the applied measurement techniques offers an extensive characterization of the flow, hence enabling the identification of suitable test conditions for the early stages of Martian entries.

Vacuum Ultraviolet Emission Spectroscopy System for Superorbital Re-entries

The following paper outlines the importance of vacuum ultraviolet (VUV) aerothermodynamic heating during re-entry, the current level of uncertainty in the models used to predict radiative heating load, and the challenges associated with reducing this uncertainty. A method has been developed at The Centre for Hypersonics that allows the capture of VUV emission spectra from across and through the surface of a blunt model. Two superorbital conditions were generated to match high-speed points on a re-entry trajectory and validated computationally and experimentally. The proposed system has been constructed and a calibration procedure developed. There have now been over one hundred experiments at superorbital velocities conducted with this system and some sample uncalibrated spectral images are presented.

Composite scramjet combustor

An investigation is undertaken into the potential use of carbon-carbon materials for Scramjet combustors and configurations utilising regenerative and radiative cooling are considered. The analysis uses the ANSYS package to couple a CFD analysis of the fuel cooling with a structural thermal analysis. One sample result is also compared with numerical analysis. One of the variations investigated was the value of the thermal conductivity of the carbon-carbon as the values for this found in the literature vary greatly. Examples using high and low thermal conductivity are computed showing the resulting difference in temperatures. The results show that for a representative Mach 8 Scramjet flight a thermal equilibrium is achievable whilst keeping the maximum temperatures within the limits of the material. Copyright

Hot Wall Testing Methodology for Impulse Facilities

The design of hypersonic flight systems requires extensive ground testing to understand the flow characteristics that are important for the flight vehicle. The work presented within this paper demonstrates a new model pre-heating technique that allows models to be tested in hypersonic impulse facilities with wall temperatures in excess of 2000 K. Utilising carbon fibre models and resistive heating, this technique enables a new range of testing opportunities in these facilities. Preliminary testing has been conducted demonstrating increased surface chemistry rates with an elevated wall temperature model representative of a blunt body atmospheric entry vehicle. This methodology has enabled a range of new testing to be proposed including blunt body models investigating the effect of hot walls, ablating surfaces and surface reactions on the flow field. Additional testing targeting boundary layer physics and scramjet flow phenomena have also been proposed including investigations into transition, boundary layer development, shock interactions, boundary layer combustion, mixing and ignition lengths and radical farming. The effect of the increased wall temperature on these phenomena is of great interest for the understanding of the hypersonic flow fields.

Probing the use of spectroscopy to determine the meteoritic analogues of meteors

Context. Determining the source regions of meteorites is one of the major goals of current research in planetary science. Whereas asteroid observations are currently unable to pinpoint the source regions of most meteorite classes, observations of meteors with camera networks and the subsequent recovery of the meteorite may help make progress on this question. The main caveat of such an approach, however, is that the recovery rate of meteorite falls is low (<20%), implying that the meteoritic analogues of at least 80% of the observed falls remain unknown. Aims. Spectroscopic observations of incoming bolides may have the potential to mitigate this problem by classifying the incoming meteoritic material. Methods. To probe the use of spectroscopy to determine the meteoritic analogues of incoming bolides, we collected emission spectra in the visible range (320–880 nm) of five meteorite types (H, L, LL, CM, and eucrite) acquired in atmospheric entry-like conditions in a plasma wind tunnel at the Institute of Space Systems (IRS) at the University of Stuttgart (Germany). A detailed spectral analysis including a systematic line identification and mass ratio determinations (Mg/Fe, Na/Fe) was subsequently performed on all spectra. Results. It appears that spectroscopy, via a simple line identification, allows us to distinguish the three main meteorite classes (chondrites, achondrites and irons) but it does not have the potential to distinguish for example an H chondrite from a CM chondrite. Conclusions. The source location within the main belt of the different meteorite classes (H, L, LL, CM, CI, etc.) should continue to be investigated via fireball observation networks. Spectroscopy of incoming bolides only marginally helps precisely classify the incoming material (iron meteorites only). To reach a statistically significant sample of recovered meteorites along with accurate orbits (>100) within a reasonable time frame (10–20 years), the optimal solution may be the spatial extension of existing fireball observation networks.

Shock standoff on hemi-spherical bodies in hypervelocity flows

Computational modelling of hypervelocity flows is critical in the design of re-entry vehicles and validated simulation codes are required to meet this need. Bertin and Cummings [1] and Gnoffo et al. [2] discuss the requirements and importance of the validation of computational codes with experimental data.

Emission Spectroscopy of a Mach Disk at Titan Atmospheric Entry Conditions

The prediction of heat transfer is important for atmospheric entry applications, as it guides the design of a spacecraft thermal protection system (TPS). The radiative heat transfer processes encountered by a spacecraft upon atmospheric entry are more complex in nature than the convective heat transfer and therefore more challenging to predict accurately, resulting in the use of large safety factors.