Hannes Fulge

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.

Improved Abel Inversion Method for Analysis of Spectral and Photo-Optical Data of Magnetic Influenced Plasma Flows

This paper presents the derivation of an alternative method called spline method to perform inverse Abel transformation of measured data sets. At first the general approach of Abel transformation is shown. The following section shows the principle of operation of the existing methods. Then the new spline method is derived, which is a combination of the known Fourier method and f-Interpolation method with polynomials with an analytical solution of the forward Abel transform. All methods are tested on three test cases: an off centered Gaussian function, a cubic function and photo-optical data of a plasma flow in front of a spherical probe head. The results of the different methods are compared, limitations are shown and their advantages are pointed out. The new method is advantageous for noisy data and due to its spline based approach no assumptions about the local distribution are needed.

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.

Noise-Resistant Abel-Transformation Algorithm Tested on Optical Emission Spectroscopy

Based on the spline method for inverse Abel transformation, this paper presents an improved noise-resistant Abel-transformation algorithm that is particularly useful for the Abel transformation of noisy measurement data. The algorithm is applied to three numerical test cases. The results are compared with the results of a Radon transformation. Due to the known local distribution, the results of the Abel transformation can easily be interpreted and evaluated. A cubic spline is chosen as a test case to show that the code is implemented correctly, since the algorithm is based on such a spline. A Gauss profile is used for testing due to the fact that a line-of-sight integration of a Gaussian profile can be performed analytically. Random noise is added to the signal with a signal-to-noise ratio of 20. An offcentered Gaussian profile and its symmetric are chosen because, in many practical applications (for example, high-enthalpy flows or supersonic nozzle flows), the emission has an offcentered Gaussian-like sh...

A New Inductively Driven Plasma Generator (IPG6)—Setup and Initial Experiments

As part of the partnership between the Center for Astrophysics, Space Physics and Engineering Research (CASPER) at Baylor University and the Institute of Space Systems (IRS) at the University of Stuttgart, a new design for a modular inductively driven plasma generator (IPG) is being developed and tested within CASPER and the IRS. The current IPG design is built on a well-established heritage of modular IPGs designed and operated at IRS. This latest IPG source enables the electrodeless generation of high-enthalpy plasmas and will provide CASPER researchers with the ability to operate with various gases at plasma powers of approximately 15 kW. It will also provide minimized field losses and operation over a wide scope of parameters not possible using existing designs requiring flow-controlled stabilization.

Analysis of Wavelength Modulation Spectroscopy for Water Vapour Measurements in Supersonic Combustion

In this paper measurements of temperature and mole fraction of water vapour by wavelength modulation spectroscopy (WMS) are presented. This work is focused on hypersonic combustion diagnostics using tunable diode laser absorption spectroscopy (TDLAS) at 1995 nm. The experiments are performed with a vertical cavity surface emitting laser diode (VCSEL) which is tunable by current and temperature. Water vapour temperature and mole fraction are determined by matching the second harmonic (2f) peak height normalized by its first harmonic (1f) value to a database of simulated signals based on the characteristics of the laser. The measurements have been performed on flat flames for proof of concept. Two different flame conditions are investigated and the results are compared with direct absorption measurements using the same equipment and the application of a calibration free WMS method to the acquired data as presented by Rieker et al. The investigated flames have been extensively analysed using coherent anti-stokes Raman scattering (CARS) measurements and equilibrium calculations by Prucker et al. The results using direct absorption agree fairly well with the published CARS data. The applied WMS methods agree well with each other, however, there is a significant discrepancy to the direct absorption measurements at the high temperature condition. Since the resulting values for the two different flame conditions with a nominally large temperature difference are close to each other, independent from the applied WMS method, it is concluded that further research of the WMS technology is required with respect to the applied transitions and its sensitivity to the investigated flows.