Abstract-In the view of measuring directional fluctuations of a thin laser beam sent through a heated turbulent jet, an optical method using interference and diffraction with the out coming beam is proposed. The experimental set-up is described. A new technique for separating directional fluctuations of the laser beam is explained. From the measurement of the interference pattern perturbations, are deduced the Rms of the laser beam deflection angle, the spectrum of directional fluctuations of the laser beam, and the value of a scattering coefficient characterizing the heated turbulent jet. The measured spectrum reveals a −8/3 power law and the value obtained for that coefficient is nearly equal to that found in previous works. This agreement enables to conclude that the experimental technique used is efficient and satisfactory.

Abstract-Using the geometrical optics approximation, a theoretical prediction of the deflection angle correlation of a laser beam propagating in a hot turbulent jet is found as a functional form of the turbulent spectrum of the refractive index fluctuations. By applying the modified Von Karman model and Tatarskii model, the structure coefficient of the refractive index and the deflection angle correlation of the laser beam are then computed by means of a numerical procedure. Experiments to measure the structure coefficient are performed. A good agreement between the experimental results obtained and the theoretical predictions demonstrates the validity of the theoretical approach.

In this paper, the axisymmetric flow of a viscous fluid through a porous annular tube with walls kept at different temperatures is studied theoretically. The physical properties of the fluid remain constant, notably its specific mass, its dynamic viscosity and its thermal diffusivity. The nondimensional parameters which the solutions of the problem depend on are defined. A numerical integration using the shooting method is applied for solving the Navier–Stokes equations and the energy equation. Bifurcation diagrams are presented and enable to highlight significant properties of the flow. Some thermal behaviors corresponding to specific values of the parameters are performed. Asymmetric solutions of the steady flow are described and some results about velocity components are also analyzed.

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