Ablation Radiation Coupling Investigation in Earth Re-entry Using Plasma Wind Tunnel Experiments

Loehle, Stefan; Hermann, Tobias; Zander, Fabian; Fulge, Hannes; Marynowski, T.

doi:10.2514/6.2014-2250

Cited by 23 publications

(23 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The results for the stagnation point region are summarized in Table 6. These values are both approximately double of what is expected from equilibrium calculations [39]. Possibly, the thermal boundary layer increases the total number density of the gas due to a lower translational temperature close to the surface.…”

Section: Discussionmentioning

confidence: 60%

See 1 more Smart Citation

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Hermann

Löhle

Zander

et al. 2016

Journal of Thermophysics and Heat Transfer

Self Cite

View full text Add to dashboard Cite

This paper presents the analysis of optical emission spectroscopic measurements from vacuum ultraviolet (120 nm) to near infrared (960 nm) in a high-enthalpy air plasma flow corresponding to superorbital reentry conditions. The vacuum ultraviolet measurements have been realized with a new experimental setup allowing measurements through a bore hole in the sample. Using the commonly applied optical emission spectroscopy from the side, the radiation transport along the line of sight of the vacuum ultraviolet measurements has been assessed. This allowed the determination of the local ground state densities of atomic oxygen and atomic nitrogen from a branching ratio analysis and the blackbody limiting correction of the vacuum ultraviolet radiation. Through the analysis of the absorption in the borehole, the spectra have been corrected, resulting in a stagnation point radiative heat flux in the vacuum ultraviolet of 235 kW∕m 2 .= local mass-specific enthalpy, MJ∕kg I = arc current, A K = proportionality constant for air, W∕MJ∕kg·Pa 0.5 ·m 1.5 k = Boltzmann constant, J∕K k cal = calibration factor, W∕m 2 · nm · sr∕counts∕s L λ = spectral radiance, W∕m 2 · nm · sr L λ;Limit = blackbody limit spectral radiance, W∕m 2 · nm · sr M = magnification _ m = mass flow, g∕s n = number density, m −3 n i = excited state population density, m −3 n 0 = ground state population density, m −3 P = electric power, kW P k = spectral line shape, nm −1 p = pressure, hPa _ q = heat flux, kW∕m 2 R eff = effective nose radius, mm r = radial distance, mm S = raw signal, counts/s s = distance from the probe surface, mm s 0 = distance between object and focusing element, mm= vibrational quantum number x = axial distance from the nozzle, mm y = horizontal distance from the nozzle, mm z = vertical distance from the nozzle, mm α λ = absorption coefficient, m −1 δ = full width at half-maximum of line broadening, nm ε λ = emission coefficient, W∕m 3 · nm · sr ε = spectrally integrated emission coefficient, W∕m 3 · sr λ = wavelength, nm σ λ = absorption cross section, m 2 Subscripts BB = blackbody DL = deuterium lamp exc = electronic excitation IS = integrating sphere l = lower state rot = rotational tot = total trans = translational u = upper state vib = vibrational

show abstract

Section: Discussionmentioning

confidence: 60%

“…The goal of the investigation is the assessment of ablationradiation coupling [39]. Therefore, the focus is on the measurement of the plasma emission incident on the model surface that, in the case of the VUV radiation, is achieved by looking through the sample into the boundary layer.…”

Section: Optical Pathmentioning

confidence: 99%

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Hermann

Löhle

Zander

et al. 2016

Journal of Thermophysics and Heat Transfer

Self Cite

View full text Add to dashboard Cite

show abstract

“…These can be detected with this setup. Several research groups are recently applying emission spectroscopy to analyze the reactive boundary layer forming around ablative heat shield materials 19,22,43,44 . MacDonald et al 22 preformed ablation tests in an inductively coupled plasma.…”

Section: Discussionmentioning

confidence: 99%

“…The facilities in use for material characterization are most commonly arc-heated [17][18][19][20] or induction coupled 21,22 torches, which provide high gas enthalpies with air as test gas, ideal for the simulation of atmospheric reentry. The subsonic 1.2MW Inductively Coupled Plasma (ICP) torch of the Plasmatron facility at the von Karman Institute (VKI) is able to reproduce the aerothermodynamic environment of atmospheric entry in the stagnation point boundary layer of a test object for a wide range of pressures and heat fluxes [23][24][25] .…”

Section: Introductionmentioning

confidence: 99%

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Helber

Chazot

Hubin

et al. 2016

JoVE

View full text Add to dashboard Cite

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions.Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

show abstract

“…The plasma emits radiation in a region of roughly 0.06 m around the symmetry axis. The spectrum contains two significant regions: first, from 300 to 730 nm, containing mostly molecular emissions; and second, from 730 to 955 nm, which is dominated by atomic features from oxygen and nitrogen [10][11][12]. The measured spectra are shown in Figs.…”

Section: Optical Emission Spectra Datamentioning

confidence: 99%

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

Fulge

Löhle

Fasoulas

2016

Journal of Thermophysics and Heat Transfer

View full text Add to dashboard Cite

Based on the spline method for inverse Abel transformation, this paper presents an improved noise-resistant Abeltransformation 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, highenthalpy flows or supersonic nozzle flows), the emission has an offcentered Gaussian-like shape. In this test case, the signal-to-noise ratio is varied to show the noise resistance of the code. In addition, the code is used to Abel transform an emission spectrum acquired in a plasma wind tunnel at the Institute of Space Systems at the University of Stuttgart. The new algorithm shows good results and is used to determine local emissivities along the stagnation line.

show abstract

Ablation Radiation Coupling Investigation in Earth Re-entry Using Plasma Wind Tunnel Experiments

Cited by 23 publications

References 16 publications

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

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

Contact Info

Product

Resources

About