Infrared diode laser absorption measurements in the HEG free stream flow

Mohamed, Ajmal Khan; Henry, D.; Bize, D.; Beck, Walter

doi:10.2514/6.1998-2870

Cited by 9 publications

(5 citation statements)

References 7 publications

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“…In addition to the many NO transitions successfully measured, H 2 O and CO absorption was also observed. Though the presence of measurable quantities of these species was unexpected, it is not unprecedented in hypersonic facility freestream flows [24]. The integrated absorbance from the stronger of two resolvable CO transitions (visible in Fig.…”

Section: Resultsmentioning

confidence: 97%

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Measurements of Reflected Shock Tunnel Freestream Nitric Oxide Temperatures and Partial Pressure

Girard¹,

Finch²,

Strand³

et al. 2021

AIAA Journal

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This paper reports on measurements of freestream nitric oxide (NO) rotational and vibrational temperatures and partial pressures, collected in the Caltech T5 reflected shock tunnel. Quantum cascade lasers, emitting mid-infrared light resonant with fundamental rovibrational NO transitions, were directed through the supersonic (Mach ∼5) freestream flow. Tunable diode laser absorption spectroscopy (TDLAS) was used to measure the path-averaged rotational and vibrational temperatures of NO in the flow, in addition to the NO partial pressure. The temperature measurements demonstrate strong evidence of NO rotational and vibrational equilibrium during the 1 ms test period. Agreement between vibrational and rotational temperatures was observed in all experiments, including one h 0;∞ ≈ 8 MJ∕kg and four h 0;∞ 18 MJ∕kg experiments, during and after the nominal test time. Absorption from CO and H 2 O was also observed in the TDLAS measurements, though their concentrations cannot be accurately estimated. The goal of these and future experiments is to develop and demonstrate TDLAS experimental strategies for high-enthalpy impulse facilities and to help to inform improvements of existing models and solvers used for prediction of freestream conditions.

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Section: Resultsmentioning

confidence: 97%

“…Lee et al [22] and McMillin et al [23] used PLIF of NO to study transverse fuel injection and combustion in supersonic flows in shock tube experiments at Stanford. Mohamed et al used tunable infrared diode lasers for absorption measurements to probe NO concentrations, temperature, and velocity at the ONERA F4 wind tunnel [24].…”

mentioning

confidence: 99%

Measurements of Reflected Shock Tunnel Freestream Nitric Oxide Temperatures and Partial Pressure

Girard¹,

Finch²,

Strand³

et al. 2021

AIAA Journal

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“…Nitric oxide densities are often measured in shock tubes using line-of-sight absorption of a rapidly-scanning narrow-frequency laser (see for example, Chang et al 4 and Mohamed et al 5 ). While these methods are generally robust and reliable, they have two important limitations.…”

Section: Introductionmentioning

confidence: 99%

Measurement of NO density in a free-piston shock tunnel using PLIF

Danehy¹,

O’Byrne²

1999

37th Aerospace Sciences Meeting and Exhibit

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We investigate the feasibility of using a combined absorption-planar laser-induced fluorescence (PLIF) method for measuring nitric oxide (NO) number density in the freestream of a free-piston shock tunnel. The absorption coefficient is determined from the exponential decay in PLIF intensity through a uniform region of flow. The NO density is determined from the measured absorption coefficient, assuming a known pressure and temperature, determined independently. The measured NO density is insensitive to the pressure and temperature, however. The current measurements are contaminated by the variation of the spectral profile of the laser as it propagates through the flowresulting in a large systematic error. We show that this systematic error could be nearly eliminated by using a spectrally narrower laser.

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“…Some famous examples of interferometry are the Michelson Morley experiment [96] and LIGO [97]. In 1887, Michelson and Morley conducted an experiment to show the existence of the aether, a substance thought, at the time, to provide a medium for light and gravity to travel through.…”

Section: Interferometrymentioning

confidence: 99%

“…It was predicted that the motion of the Earth through the aether would cause the reading on the detector to shift by 0.4 fringes. The average detected fringe shift was only 0.01, which became a major milestone of disproving the aether theory [96,98]. More recently, the LIGO detector was successfully used to detect gravitational waves moving through space.…”

Section: Interferometrymentioning

confidence: 99%

Spectral analysis of atomic argon radiation in an expanding hypersonic flow

Kelly¹

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Entering the atmosphere of a planet is one of the key phases of many space missions, being significant for both interplanetary travel and for returning home to Earth, and remains one of the major challenges of interplanetary missions. Convective and radiative heat loads pose a significant threat to equipment and personnel during this process. Thermal protection systems are employed to mitigate the thermal loads, but are expensive in both cost and mass of the vehicle. Knowledge of these thermal heat loads requires accurate understanding of the flow-field that will develop around the vehicle. Experimental measurements are needed due to significant uncertainty in current aerothermodynamic models. Measurements in actual flight tests are difficult, due to the massive cost and the complexity of the flight tests themselves. This makes ground tests, conducted in hypersonic wind tunnel facilities, an essential practical alternative. Aerodynamic data for interplanetary flight can be generated in specialised wind tunnel facilities. Impulse facilities, specifically, have the ability to replicate planetary entry conditions. Due to the hostile nature of hypersonic test flows, sensors on the body of the test model may suffer damage from repeated use. Instrumentation attached to the test model can also influence the flow-field, impacting on the accuracy of measurements. Spectroscopic measurements are a non-intrusive method of extracting properties of the hot gas during testing, by measuring the radiation emitted by the gas, which have the advantage of not interfering with the gas flow during measurement. This thesis reports on the use of spectroscopic techniques to probe a radiating hypersonic flow-field, extracting population densities of excited states, and then determining the thermochemical state of the gas. A simplified two-dimensional wedge geometry was used to generate an oblique shock wave followed by an expansion. The aim of the project was to investigate the potential non-equilibrium flow effects during the expansion, an afterbody effect which remains poorly understood. Argon was chosen for the test gas as it is a monatomic gas with chemistry limited to ionisation and only two thermal modes. Such a simplified gas potentially allows for more direct and quantifiable determination of equilibrium or non-equilibrium of the gas as it expands, serving as a good basis for development of fundamental understanding and model development. Two experimental campaigns were conducted using the X2 expansion tube at The University of Queensland. The first campaign examined a relatively low-density argon flow which was expected to contain thermochemical non-equilibrium regions, due to the low gas density. The second campaign examined a higher density argon flow which was expected to be closer to thermochemical equilibrium. A structured analytical framework was developed to analyse the spectral data, which was coded into the application SELA. The populations of excited electronic energy levels were determined by examining the spectral emi...

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Infrared diode laser absorption measurements in the HEG free stream flow

Cited by 9 publications

References 7 publications

Measurements of Reflected Shock Tunnel Freestream Nitric Oxide Temperatures and Partial Pressure

Measurements of Reflected Shock Tunnel Freestream Nitric Oxide Temperatures and Partial Pressure

Measurement of NO density in a free-piston shock tunnel using PLIF

Spectral analysis of atomic argon radiation in an expanding hypersonic flow

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