Velocity field imaging in supersonic reacting flows near atmospheric pressure

Allen, Mark G.; Davis, Steven J.; Kessler, William J.; Legner, Hartmut H.; McManus, Keith; Mulhall, Phillip A.; Parker, Terry; Sonnenfroh, David M.

doi:10.2514/3.12159

Cited by 23 publications

(10 citation statements)

References 19 publications

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“…These methods are more accurate at higher velocities, as the Doppler shift is larger and more easily measured, but they often yield only average flow velocities owing to a lack of signal strength. Many of these Doppler-based molecular velocity methods are based on laser-induced fluorescence of molecules (or atoms) that are added to the flows such as copper, 5 hydroxyl, 6,7 nitric oxide, 8 sodium, 9 and iodine. 10 The addition of such species is often impractical in test facilities.…”

Section: Introductionmentioning

confidence: 99%

Hydroxyl tagging velocimetry in a supersonic flow over a cavity

Pitz¹,

Lahr²,

Douglas³

et al. 2005

Appl. Opt.

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Hydroxyl tagging velocimetry (HTV) measurements of velocity were made in a Mach 2 (M 2) flow with a wall cavity. In the HTV method, ArF excimer laser (193 nm) beams pass through a humid gas and dissociate H2O into H + OH to form a tagging grid of OH molecules. In this study, a 7 x 7 grid of hydroxyl (OH) molecules is tracked by planar laser-induced fluorescence. The grid motion over a fixed time delay yields about 50 velocity vectors of the two-dimensional flow in the plane of the laser sheets. Velocity precision is limited by the error in finding the crossing location of the OH lines written by the excimer tag laser. With a signal-to-noise ratio of about 10 for the OH lines, the determination of the crossing location is expected to be accurate within +/- 0.1 pixels. Velocity precision within the freestream, where the turbulence is low, is consistent with this error. Instantaneous, single-shot measurements of two-dimensional flow patterns were made in the nonreacting M 2 flow with a wall cavity under low- and high-pressure conditions. The single-shot profiles were analyzed to yield mean and rms velocity profiles in the M 2 nonreacting flow.

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Section: Introductionmentioning

confidence: 99%

Hydroxyl tagging velocimetry in a supersonic flow over a cavity

Pitz¹,

Lahr²,

Douglas³

et al. 2005

Appl. Opt.

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show abstract

“…In Doppler-shift methods that measure local velocity, the Doppler shift of radiation scattered from molecules (or atoms) is measured and related to velocity. In laser-induced fluorescence (LIF) methods, one records the Doppler shift of the LIF emission from gases, such as copper [10], hydroxyl [11,12], nitric oxide [13], sodium [14], and iodine [15]. Doppler-shift LIF methods are well suited to high-speed flows where the Doppler shift is much larger and more easily measured.…”

Section: Introductionmentioning

confidence: 99%

Hydroxyl-Tagging-Velocimetry Measurements of a Supersonic Flow over a Cavity

Lahr

Pitz

Douglas

et al. 2010

Journal of Propulsion and Power

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Hydroxyl-tagging-velocimetry measurements were made throughout the compressible flowfield of a Mach 2 air flow over a cavity. The supersonic flowfield simulates the pilot region of scramjet combustion under nonreacting conditions. In the hydroxyl-tagging-velocimetry method, ArF excimer laser (193 nm) beams pass through a humid gas flow, dissociating water to form a tagging grid of hydroxyl molecules. The hydroxyl-tagging-velocimetry grid density has been increased to 11 11 to yield up to 120 velocity vectors of the two-dimensional flow over a fixed time delay of 2-3 s. Instantaneous single-shot measurements of two-dimensional flow patterns were made in the nonreacting Mach 2 flow over a wall cavity under low-and high-backpressure conditions. Single-shot profiles were analyzed to yield mean and rms deviation velocity profiles in the Mach 2 nonreacting flow. Compressibility greatly reduces the growth rate of the supersonic shear layer formed at the edge of the cavity. A set of velocity data (spanning the entire length of the cavity) for an open wall cavity in a supersonic flow under low-and high-backpressure conditions was compiled for validation of computational fluid dynamics models.

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“…In the resonantly excited Doppler shift methods, the fluorescent emission is measured with respect to the laser excitation wavelength to monitor the Doppler frequency shift. For example, Doppler shifts of sodium [4], iodine [5], copper [6], nitric oxide [7] and hydroxyl [8,9] have been used to measure the gas flow velocity. The Doppler shift of Rayleigh-scattered laser light has been measured with Fabry-Pérot interferometers and molecular filters to give the velocity field [10,11].…”

Section: Introductionmentioning

confidence: 99%

N2O molecular tagging velocimetry

Elbaz

Pitz

2012

Appl. Phys. B

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A new seeded velocity measurement technique, N 2 O molecular tagging velocimetry (MTV), is developed to measure velocity in wind tunnels by photochemically creating an NO tag line. Nitrous oxide "laughing gas" is seeded into the air flow. A 193 nm ArF excimer laser dissociates the N 2 O to O( 1 D) that subsequently reacts with N 2 O to form NO. O 2 fluorescence induced by the ArF laser "writes" the original position of the NO line. After a time delay, the shifted NO line is "read" by a 226-nm laser sheet and the velocity is determined by time-of-flight. At standard atmospheric conditions with 4% N 2 O in air, ∼1000 ppm of NO is photochemically created in an air jet based on experiment and simulation. Chemical kinetic simulations predict 800-1200 ppm of NO for 190-750 K at 1 atm and 850-1000 ppm of NO for 0.25-1 atm at 190 K. Decreasing the gas pressure (or increasing the temperature) increases the NO ppm level. The presence of humid air has no significant effect on NO formation. The very short NO formation time (<10 ns) makes the N 2 O MTV method amenable to low-and highspeed air flow measurements. The N 2 O MTV technique is demonstrated in air jet to measure its velocity profile. The N 2 O MTV method should work in other gas flows as well (e.g., helium) since the NO tag line is created by chemical reaction of N 2 O with O( 1 D) from N 2 O photodissociation and thus does not depend on the bulk gas composition.

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Velocity field imaging in supersonic reacting flows near atmospheric pressure

Cited by 23 publications

References 19 publications

Hydroxyl tagging velocimetry in a supersonic flow over a cavity

Hydroxyl tagging velocimetry in a supersonic flow over a cavity

Hydroxyl-Tagging-Velocimetry Measurements of a Supersonic Flow over a Cavity

N2O molecular tagging velocimetry

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