Atmospheric turbulence chamber for optical transmission experiment: characterization by thermal method

Abstract

A turbulence chamber (0.78 x 0.23 x 2.59 m(3)) consisting of ten small electric heater/blowers with an aluminum foil screen and three screens of 2-mm aluminum wire meshes can generate the nearly homogeneous isotropic turbulence within the 0.5 x 0.05 x 2-m(3) region at the 0.11-m height of optical measurements. The temperature structure constant squared C(2)(T) = 52.9 K(2) m(-?) was obtained from the temperature structure function measurements measured by using a differential microthermocouple system. The refractive-index structure constant squared C(2)n<sub/>at the 632.8-nm wavelength was calculated from C(2)(T):C(2)(n) = 3.00 x 10(-11)m(-?). The average wind velocity and temperature were 0.41 m/sec and 53 degrees C, respectively. From the power spectrum of temperature fluctuations, the inner and outer scales of turbulence are determined: l(o) = 5.0 mm and L(0) = 6.5 cm. The measured temperature structure function and power spectrum of temperature fluctuations satisfy the ? and -5/3 power similarity laws in the inertial subrange, respectively.

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

“…Typical values of C 2 n for the atmosphere are four to five orders of magnitude larger than those obtained by Ndlovu (2013) and compare more favourably to the values determined in our work (Gochelashvili and Shishov, 1974;Gamo, 1978). Previously published values of C 2 n vary drastically from one source to another and are debatable (Gochelashvili and Shishov, 1974;Gamo, 1978).…”

“…Previously published values of C 2 n vary drastically from one source to another and are debatable (Gochelashvili and Shishov, 1974;Gamo, 1978). 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 disturbance.…”

Wind tunnel simulations to detect and quantify the turbulent effects of a propagating He-Ne laser beam in air

“…For this reason, modeling the atmosphere in a laboratory has been the preferred method since specific conditions can be controlled while others are measured. In this way, we have been able to produce highly comparable results, as shown in literature, using relatively cheaper and robust equipment (Gochelashvili and Shishov, 1974;Gamo, 1978;Magee, 1993).…”

<title>Characterization of laboratory-generated turbulence by optical phase measurements</title>

“…Majumdar and Gamo measure the temperature structure function as a primary means of characterizing the generated turbulence [15]. The temperature structure function is defined as the mean square, temperature difference between two temperature probes,…”

“…In the inertial subrange, the temperature structure function is proportional to r2/3: 18) where CT is the temperature structure constant [45]. This 2/3 power relationship is often called the Kolmogorov-Obukhov similarity law [15].…”