Hydrodynamic Vortex Structures in a Diffusion Jet Flame

The chapter presents the results of an experimental study of hydrodynamics and diffusion combustion of jets flowing out of long tubes in the Reynolds number range 200–13,500 into air. The methods used in the experiments are visualization in the ultraviolet region, PIV, and hot-wire anemometry. The amplitude-phase structure of optical filters in systems of the Hilbert diagnostics of phase optical density fields in gaseous and condensed systems was used in this work. A possibility of visualization of disturbances in phase optical density fields with arbitrary amplitudes is demonstrated. Two geometries are studied: jet combustion in a stationary atmosphere and in a cross flow. Propane and hydrogen in a mixture with an inert diluent (CO2) were used as fuels. In the isothermal jet stream, propane-butane mixture and Freon-22 are used. The main attention in the problem is paid to the mechanism of pipe and jet instability interaction, resulting in the vortex motion in several spatial regions. For critical Reynolds numbers in a pipe, the characteristic is the mechanism of two-stage instability caused by turbulent spot (puff) formation inside the pipe and vortex structure generation in the jet-mixing layer. These vortex structures (puff) exert a strong influence both on the isothermal jet and on the flame

Laser Doppler Visualization of 2D Velocity Fields with Minimization Dependence from Multi–Particle Scattering

The method of laser Doppler visualization and measurement of 2D velocity vector field in flows with minimization of influence of a multi–particle scattering is discussed. The investigated section in the flow is illuminated with a laser sheet. Our approach is based on reception of a pair wise difference of normalized frequency–demodulated images of a laser sheet in light beams scattered in various directions. The 2D velocities field is formed from linear combinations of images of the laser sheet in frequency–demodulated light scattered in directions orthogonal to it

Laser Doppler visualisation of the velocity field by excluding the influence of multiparticle scattering

The method of laser Doppler visualisation and measurement of the velocity feld in gas and liquid fows by suppressing the infuence of multiparticle scattering is discussed. The cross section of the fow under study is illuminated by a laser beam transformed by an anamorphic optical system into a laser plane. The effect of multiparticle scattering is eliminated by obtaining differential combinations of frequency-demodulated images of the laser plane in different regions of the angular spectrum of scattered light