Transient Grating Spectroscopy in a Hot Turbulent Compressible Free Jet

Schlamp, Stefan; Rösgen, Thomas; Kozlov,; Rakut, Christian; Kasal, Peter; Wolfersdorf, J. Von

doi:10.2514/1.13794

Cited by 14 publications

(7 citation statements)

References 25 publications

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“…Therefore, the measurements in hot turbulent and chemically reacting free jets were analyzed by determining the time between the signal peaks. Similar to the measurements conducted by Schlamp et al ., a frequency shift occurs at the end of the signal lifetime. Therefore, only the first oscillations were taken into account.…”

Section: Methodsmentioning

confidence: 99%

“…At ITLR, a first feasibility study was conducted by Schlamp et al . Owing to environmental perturbations and weak signal intensity caused by the used interrogation laser, measurements at static temperatures higher than T = 540 K were not possible. Nevertheless, the general applicability was verified.…”

Section: Introductionmentioning

confidence: 99%

“…Successively, the LITA setup was modified and adapted to the requirements at the supersonic combustion test facility. These include, amongst others, the use of a pulsed interrogation beam in order to increase the signal intensity and the protection of the setup against environmental perturbations. Here, we present LITA measurements in laminar, premixed flames and hot, turbulent, supersonic free jets as validation cases for LITA measurements in supersonic, chemically reacting free jets.…”

Section: Introductionmentioning

confidence: 99%

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Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

Hell

Förster

2016

J Raman Spectroscopy

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The scramjet engine is a promising propulsion concept for future space transportation systems. To enhance the engine efficiency, a strong understanding of combustion mechanisms is essential. Laser‐induced thermal acoustics (LITA) – a seedless, non‐intrusive measurement technique – is an auspicious technique for the investigation of supersonic combustion. Here, we present two validation cases and first LITA measurements in a chemically reacting hydrogen/air free jet. The first validation case is the investigation of premixed methane/air and hydrogen/air flames, produced with a commercially available flat flame burner. The comparison with coherent anti‐Stokes Raman spectroscopy measurements resulted in a deviation between the two measurement techniques smaller than the uncertainty of the techniques. The second validation case is the investigation of hot, supersonic air/air free jets at total temperatures of Tt = 1050 K and Tt = 1300 K. The comparison with computational fluid dynamics predictions shows a reasonable agreement with a maximum deviation of 13.9% for the free jet with a temperature of Tt = 1300 K and a good agreement with a maximum deviation of 4.4% for the free jet with a temperature of Tt = 1050 K. The LITA measurements in a chemically reacting hydrogen/air free jet showed a good reproduction of the flame position determined from an OH∗ image. For the presented investigations, we used a homodyne, resonant LITA setup with a pulsed interrogation beam. Copyright © 2016 John Wiley & Sons, Ltd.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

Hell

Förster

2016

J Raman Spectroscopy

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“…As a side effect, inserting flush-mounted windows results in a smaller pump beam intersection angle Θ which entails an increased fringe spacing constant Λ. However, this proves advantageous due to longer signal lifetimes, resulting from an increased number of signal oscillations, i.e., induced sound wave periods, effectively increasing measurement accuracy, particularly when frequency-domain DFT is used for signal processing [37].…”

Section: Laser Optical Set-upmentioning

confidence: 99%

“…A background subtraction routine is used for both techniques to minimize stray light noise influence. With a relevant laser pulse length of ~ 10 ns, turbulence and convection effects on the opto-acoustic grating (of sub-microsecond duration ~ 100 ns) are not considered relevant and hence are not treated separately in the data analysis [27,37].…”

Section: Calibration Proceduresmentioning

confidence: 99%

In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

2021

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Experimental determination of test gas caloric quantities in high-enthalpy ground testing is impeded by excessive pressure and temperature levels as well as minimum test timescales of short-duration facilities. Yet, accurate knowledge of test gas conditions and stagnation enthalpy prior to nozzle expansion is crucial for a valid comparison of experimental data with numerical results. To contribute to a more accurate quantification of nozzle inlet conditions, an experimental study on non-intrusive in situ measurements of the post-reflected shock wave stagnation temperature in a large-scale free-piston reflected shock tunnel is carried out. A series of 20 single-shot temperature measurements by resonant homodyne laser-induced grating spectroscopy (LIGS) is presented for three low-/medium-enthalpy conditions (1.2–2.1 MJ/kg) at stagnation temperatures 1100–1900 K behind the reflected shock wave. Prior limiting factors resulting from impulse facility recoil and restricted optical access to the high-pressure nozzle reservoir are solved, and advancement of the optical set-up is detailed. Measurements in air agree with theoretical calculations to within 1–15%, by trend reflecting greater temperatures than full thermo-chemical equilibrium and lesser temperatures than predicted by ideal gas shock jump relations. For stagnation pressures in the range 9–22 MPa, limited influence due to finite-rate vibrational excitation is conceivable. LIGS is demonstrated to facilitate in situ measurements of stagnation temperature within full-range ground test facilities by superior robustness under high-pressure conditions and to be a useful complement of established optical diagnostics for hypersonic flows.

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LIGS measurements in the nozzle reservoir of a free-piston shock tunnel

et al. 2018

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Transient Grating Spectroscopy in a Hot Turbulent Compressible Free Jet

Cited by 14 publications

References 25 publications

Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

LIGS measurements in the nozzle reservoir of a free-piston shock tunnel

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Transient Grating Spectroscopy in a Hot Turbulent Compressible Free Jet

Cited by 14 publications

References 25 publications

Validation of laser‐induced thermal acoustics for chemically reacting H2/air free jets

Validation of laser‐induced thermal acoustics for chemically reacting H2/air free jets

In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

LIGS measurements in the nozzle reservoir of a free-piston shock tunnel

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Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets