Template matching for improved accuracy in molecular tagging velocimetry

Ramsey, Marc; Pitz, Robert W.

doi:10.1007/s00348-011-1098-y

Cited by 43 publications

(15 citation statements)

References 15 publications

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“…3 in terms of the SNR averaged over 100 frames. The SNR is calculated as (I signal − I bg )∕(4 bg ) , with I signal and I bg the signal and background intensity, respectively, and bg the background standard deviation, following the definition of Ramsey and Pitz (2011). This definition is quite conservative due to the factor 4 intended to approximate peak-to-peak noise amplitude.…”

Section: Tracer Excitation Spectrum and Wavelength Selectionmentioning

confidence: 99%

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Validation Data Acquisition in HTTF during PCC Events

Bardet

2018

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Hydroxyl tagging velocimetry (HTV) is characterized for the first time at extended pressures (1 and 3 atm) and temperatures (295 K to 673 K) in an attempt to improve measurement precision for low speed flows. While previous investigations have focused on ambient and flame temperatures (>1400 K), the present study investigates between these two extreme conditions, wherein both the local chemistry and thermodynamic state of the gas may hinder or aid the functionality of the technique. Effects of temperature and pressure on the hydroxyl (OH) excitation spectrum are assessed and compared to simulations to determine the optimal laser frequency, and OH species lifetime and tracer line diffusion are examined to determine the relative efficiency of the photo-dissociation process and the quality of the resulting signal. A twofold increase in the photo-dissociation efficiency is observed at elevated temperatures. Tag line spread was found to be dominated by shear rather than molecular diffusion. Velocity measurement precision was characterized for time delays ranging from 5 μs to 3.2 ms and was found to be inversely proportional to the time delay selected, supporting the need for the extended tracer lifetimes observed at higher temperatures when used for lowvelocity applications. Velocity profiles measured in heated jets of nitrogen and air indicate measurement uncertainties as low as 0.1 m s −1 (at 68% confidence level), while comparison with particle image velocimetry (PIV) measurements showed peak deviations in the observed velocity profiles to be less than 2%. The results suggest the high utility of HTV at making measurements in low-velocity flows at moderate temperatures.

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Section: Tracer Excitation Spectrum and Wavelength Selectionmentioning

confidence: 99%

“…As a results, a SNR larger than 4 is considered good and can yield a displacement precision of about 0.1 pixel. Below a SNR of 4, precision is reduced, although a measurement precision of 0.5 pixel can still be achieved for SNR = 1 (Ramsey and Pitz 2011).…”

Section: Tracer Excitation Spectrum and Wavelength Selectionmentioning

confidence: 99%

Validation Data Acquisition in HTTF during PCC Events

Bardet

2018

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“…Even when there are apparent breaks, one can see the tag line at a diminished intensity. In the center of the line, a SNR of 4 or higher is achieved that is sufficient for accurate velocity measurement [43] when the line is displaced about 10 pixels. For the 10 μs time delay (Fig.…”

Section: Velocimetry Applicationmentioning

confidence: 99%

Vibrationally excited hydroxyl tagging velocimetry

Grady

Pitz

2014

Appl. Opt.

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A new molecular-based velocity method is developed for high-temperature flame gases based on the hydroxyl tagging velocimetry (HTV) technique. In vibrationally excited HTV (VE-HTV), two photons from a KrF laser (248 nm) dissociate H₂O into a tag line of vibrationally excited OH (v=1). The excited state OH tag is selectively detected in a background of naturally occurring ground state OH (v=0). In atmospheric pressure laboratory burners, the OH (v=1) tag persists for 5-10 μs, allowing single-shot velocity measurements along a 2 cm line under lean, stoichiometric, and rich flame conditions with temperatures reaching 2300 K. Mean velocity measurements are demonstrated in a lean (ϕ=0.78) premixed H₂/air turbulent flame (Re=26,550) laboratory flame. The VE-HTV method is best suited to measure high-speed velocities in hot combustion environments in the presence of background OH.

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“…The SNRs for undelayed and delayed images are SNR = 7.5 and SNR = 3.5, respectively. For a delayed image with SNR = 3.5, we expect to be able to determine the displacement of a NO tag grid intersection to 0.1-0.2 pixel accuracy using either template matching or cross-correlation methods [38]. In the gas flow of ∼15 m/s with a time delay of 80 µs, the tag line displaces about 1 mm (21 pixel) and one would expect a velocity accuracy of <1%.…”

Section: No Tag Spectral Identification Formation and Lifetimementioning

confidence: 99%

“…The velocity average over the potential core of the jet (±3 mm) is 15.4 m/s which is in agreement with the expected average jet exit velocity of 15 ± 0.5 m/s based on the mass flow meter readings. For future work, we would write grids into the gas flow which would allow us to measure the velocity in two dimensions and one component of vorticity [38].…”

Section: N 2 O Mtv Imaging and Velocity Measurement In An Air Jetmentioning

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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Template matching for improved accuracy in molecular tagging velocimetry

Cited by 43 publications

References 15 publications

Validation Data Acquisition in HTTF during PCC Events

Validation Data Acquisition in HTTF during PCC Events

Vibrationally excited hydroxyl tagging velocimetry

N2O molecular tagging velocimetry

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