Measurement of the structure coefficient of refractive index fluctuations in a turbulent premixed butane-air flame by means of a laser-based interferometer technique

Nyobe, Elisabeth Ngo; Pemha, Elkana; Hona, Jacques; Bilong, Jean; Lamara, Maurice

doi:10.1016/j.optlaseng.2014.02.009

Cited by 4 publications

(2 citation statements)

References 23 publications

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“…The higher values of C 2 n , as described by Ngo Nyobe et al (2014), describe a highly turbulent atmosphere and predict a high level of visual blurring such as the wavy lines one may encounter when looking at a hot C 2 n (m -2/3 ) range Reference 1.1 × 10 -12 -2.6 × 10 -12 This work 1.0 × 10 -9 -1.8 × 10 -7 Wright and Schutz, 1967 6.0 × 10 -16 -3.0 × 10 -15 Weichel, 19905.7 × 10 -12 -4.2 × 10 -10 Magee, 1993 Tunick et al, 2005 2.5 × 10 -19 -1.1 × 10 -17 Ndlovu, 2013 (3.3 ± 0.15) × 10 -18 Ngo Nyobe et al, 2014 6. Determination of C 2 n From Eq.…”

Section: Comparison Of C 2 N Data From Various Publicationsmentioning

confidence: 71%

Experimental verification of the turbulent effects on laser beam propagation in space

Augustine¹,

Chetty²

2014

Atmósfera

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RESUMEN óíntegramente los efectos térmicos de un rayo láser que se propaga en el aire. Las mejoras incorporadas al diseño previo incluyeron un láser más potente, un sistema de formación de turbulencias de alta precisión, un sensor de presión integrado, y una plataforma para ajustar la altura entre el rayo láser y el modelo de turbulencia. Este diseño no sólo puede reproducir resultados previos con exactitud, sino que además permitió la medición exitosa de nuevos datos sobre la intensidad de la turbulencia C 2 n , la varianza de Rytov (cintilación) y el diámetro de coherencia (parámetro de Fried). Los interferogramas resultantes se analizaron utilizando transformadas rápidas de Fouse incrementan en relación con la temperatura. La región turbulenta mostró perturbaciones muy intensas, en el rango de 1.1 × 10 -12 m -2/3 a 2.7 × 10 -12 m -2/3 . A pesar de la intensidad de la turbulencia, con relación a la cintilación se demostró algo diferente, ya que la condición para un entorno de turbulencia débil se determinó en el laboratorio y se esperaba un bajo índice de cintilación. Esto es resultado de las distancias de propagación relativamente cortas obtenidas en el laboratorio. En la atmósfera abierta las trayectorias cubren grandes distancias y, para determinar los efectos de la turbulencia, el modelo debe generar turbulencias de mayor efectos térmicos de la turbulencia en un rayo láser en propagación. ABSTRACT beam propagating in air. Improvements made to the setup include a new, more powerful laser, a precision designed turbulence delivery system, an imbedded pressure sensor, and a platform for height adjustability between the laser beam and the turbulence model. The setup was not only able to reproduce previous results exactly but also allowed new data for the turbulence strength C 2 n , the Rytov variance (scintillation) and the coherence diameter (Fried's parameter) to be successfully measured. Analysis of the produced interferograms disturbances, in the range of 1.1 × 10 -12 m -2/3 to 2.7 × 10 -12 m -2/3 . In spite of the strong turbulence strength, scintillation proved otherwise, since the condition for a weak turbulence environment was determined in the laboratory and a low scintillation index was to be expected. This is as a result of the relatively short propagation distances achieved in the laboratory. In the open atmosphere, path lengths extend over vast distances and in order for turbulent effects to be realized, the turbulence model must generate stronger turbulence. The model was, therefore, able to demonstrate its ability to fully quantify and determine the thermal turbulence effects on a propagating laser beam.

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Section: Comparison Of C 2 N Data From Various Publicationsmentioning

confidence: 71%

Experimental verification of the turbulent effects on laser beam propagation in space

Augustine¹,

Chetty²

2014

Atmósfera

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“…For a strong indoor turbulence, Consortini et al [13] have obtained: C 2 n = 2.96 × 10 −11 m −2/3 . In our previous paper [14], we have obtained the following value: C 2 n = 3.27× 10 −8 m −2/3 for a turbulent premixed butane -air flame by means of a laser based interferometer technique. For the measured temperature structure coefficient C 2 T = 3.75×10 2 K 2 m −2/3 , we have computed the probabilities P n=nmax l,m of the positions of the laser beam impact on the photocell plane.…”

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confidence: 96%

Engineering Laser-Based Diagnostic in a Hot Wind Tunnel Jet: Measurement of the Temperature Structure Coefficient by Using an Optimization Technique

Lamara¹,

Nyobe²,

Pemha³

2018

PIER M

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This paper is devoted to an engineering laser-based diagnostic technique which is able to extract the value of the temperature structure coefficient in a hot turbulent wind tunnel jet, by using a thin laser beam which is sent into the jet. Some experimental investigations are carried out to characterize the jet under study and the probabilities of the positions of the laser beam impact on a photocell are measured. The theoretical values of the same probabilities are computed by assuming that the laser beam direction is a Markov random process. By means of an optimization technique with constraints, based on the Golden Section algorithm, the temperature structure coefficient of the jet is determined. The validity of the result obtained is proved by a good agreement which is observed in the comparison between another parameter computed from that result and the previously published data.

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Laser beam propagation through a turbid heated medium: analysis of the positional impacts of the heat source

et al. 2020

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Measurement of the structure coefficient of refractive index fluctuations in a turbulent premixed butane-air flame by means of a laser-based interferometer technique

Cited by 4 publications

References 23 publications

Experimental verification of the turbulent effects on laser beam propagation in space

Experimental verification of the turbulent effects on laser beam propagation in space

Engineering Laser-Based Diagnostic in a Hot Wind Tunnel Jet: Measurement of the Temperature Structure Coefficient by Using an Optimization Technique

Laser beam propagation through a turbid heated medium: analysis of the positional impacts of the heat source

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