scholarly journals Effects of Anisotropic Turbulence on Propagation Characteristics of Partially Coherent Beams with Spatially Varying Coherence

2018 ◽  
Vol 8 (11) ◽  
pp. 2025 ◽  
Author(s):  
Wentao Dao ◽  
Chunhao Liang ◽  
Fei Wang ◽  
Yangjian Cai ◽  
Bernhard J. Hoenders
Keyword(s):  
Turbulent Medium ◽  
Average Intensity ◽  
Weak Turbulence ◽  
Anisotropic Turbulence ◽  
Turbulence Regime ◽  
Coherence Parameter ◽  
Coherent Beams ◽  
Local Intensity ◽  
Spatially Varying ◽  
Analytical Expressions

Based on the extended Huygens-Fresnel (eHF) principle, approximate analytical expressions for the spectral density of nonuniformly correlated (NUC) beams are derived with the help of discrete model decompositions. The beams are propagating along horizontal paths through an anisotropic turbulent medium. Based on the derived formula, the influence of the anisotropic turbulence (anisotropy factors, structure parameters) on the evolution of the average intensity, the shift of the intensity maxima and the power-in-the-bucket (PIB) are investigated in detail through numerical examples. It is found that the lateral shifting of the intensity maxima is closely related to the anisotropy factors and the strength of turbulence. Our results also reveal that, in the case of weak turbulence, the beam profile can retain the feature of local intensity sharpness, but this feature degenerates quickly if the strength of the turbulence increases. The value of PIB of the NUC beams can be even higher than that of Gaussian beams by appropriately controlling the coherence parameter in the weak turbulence regime. This feature makes the NUC beams useful for free-space communication.

ANALYTICAL REPRESENTATIONS FOR THE TRUNCATED SPECTRAL CHARACTERISTICS OF THE FOUR-POINT COHERENCE FUNCTION OF A LASER BEAM IN A TURBULENT MEDIUM

2021 ◽  
Vol 88 (6) ◽  
pp. 872-880
Author(s):  
N. N. Rogovtsov ◽  
V. Ya. Anissimov
Keyword(s):  
Functional Equation ◽  
Refractive Index ◽  
Laser Beam ◽  
Spectral Characteristic ◽  
Spectral Characteristics ◽  
Coherence Function ◽  
Turbulent Medium ◽  
Analytical Expressions

New analytical representations for the truncated spectral characteristics of the four-point coherence function of a laser beam propagating in a turbulent medium are obtained. These representations are valid for any level of fluctuations of the refractive index in air. For two particular cases they turn into exact analytical representations previously derived by the authors with using of an integro-functional equation for truncated spectral characteristic of the four-point coherence function. A constructive procedure for obtaining approximate analytical expressions of the four-point coherence function of a laser beam propagating in a turbulent medium is proposed.

Resonant oscillations of a gas in an open-ended tube in a weak turbulence regime

1998 ◽  
Vol 39 (3) ◽  
pp. 404-410
Author(s):  
R. G. Galiullin ◽  
É. R. Galiullina ◽  
E. I. Permyakov
Keyword(s):  
Weak Turbulence ◽  
Turbulence Regime

scholarly journals RANS canopy constants from weak turbulence regime

2011 ◽  
Vol 318 (7) ◽  
pp. 072020
Author(s):  
J Viana Lopes ◽  
J M L M Palma ◽  
A Silva Lopes
Keyword(s):  
Weak Turbulence ◽  
Turbulence Regime

Turbulence Regimes and Turbulence Intermittency in the Stable Boundary Layer during CASES-99

2012 ◽  
Vol 69 (1) ◽  
pp. 338-351 ◽  
Author(s):  
Jielun Sun ◽  
Larry Mahrt ◽  
Robert M. Banta ◽  
Yelena L. Pichugina
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Threshold Value ◽  
Weak Turbulence ◽  
Intermittent Turbulence ◽  
Surface Exchange ◽  
Turbulence Intermittency ◽  
Turbulence Regime ◽  
Local Shear ◽  
Turbulence Generation

Abstract An investigation of nocturnal intermittent turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three turbulence regimes at each observation height: 1) regime 1, a weak turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate turbulence regime when top-down turbulence sporadically bursts into the otherwise weak turbulence regime. For regime 1, the strength of small turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the turbulence strength increases systematically with wind speed as a result of turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the boundary layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluctuations. The preference of the turbulence regimes during CASES-99 is closely related to the existence and the strength of low-level jets. Because of the different roles of the bulk and local shear with regard to turbulence generation under different wind conditions, the relationship between turbulence strength and the local gradient Richardson number varies for the different turbulence regimes. Turbulence intermittency at any observation height was categorized in three ways: turbulence magnitude oscillations between regimes 1 and 2 as wind speed varies back and forth across its threshold value, episodic turbulence enhancements within regime 1 as a result of local instability, and downbursts of turbulence in regime 3.

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