Yury A. Litvinenko

Visualization of conventional and combusting subsonic jet instabilities

Results of experimental studies of round and plane propane micro jet combustion in a transverse acoustic field at small Reynolds numbers are presented in this paper. Features of flame evolution under the given conditions are shown. Based on the new information obtained on free micro jet evolution, new phenomena in flame evolution in a transverse acoustic field with round and plane propane micro jet combustion are discovered and explained.

Plane Jets Affected by Initial Conditions and Acoustic Perturbations

In this chapter, results of experimental studies on the influence of initial conditions at the nozzle exit and acoustic perturbations on a plane jet structure and characteristics of its evolution and stability are considered. Basic features of the laminar and turbulent plane jets at one and the same Reynolds number are demonstrated. It is found that the jets are subjected to sinusoidal oscillations suppressing the varicose mode of instability.

BREAKDOWN OF A STREAK VIA DEVELOPMENT OF VARICOSE SECONDARY MODE ON THE STRAIGHT WING WITH PRESSURE GRADIENT

In the present experimental work, which utilizes a hot-wire visualization method, an influence of external pressure gradient on the development of secondary instabilities in the straight wing boundary layers has been demonstrated for the first time. The comparison of experimental data and direct numerical simulation results of this process has been given.

Diffusion Combustion of a Hydrogen Microjet at Variations of its Velocity Profile and Orientation of the Nozzle in the Field of Gravitation

ABSTRACT Experimental data on diffusion combustion of round hydrogen microjets with a parabolic and a “top-hat” mean velocity profiles at the nozzle exit at different spatial orientation of the microjets are reported. Most of all, we are interested in the behavior of the so-called «bottleneck flame region» of the jet and its contribution to the diffusion combustion. As is found, in the cases of the jet velocity opposite and orthogonal to the direction of the gravitational force, the main features of combustion are practically the same. Otherwise, at the velocity vector matching the direction of the gravitational force, the combustion characteristics become much different. Combustion in the «bottleneck flame region» is found to be more stable at the parabolic profile while the stability of combustion is reduced at the top-hat velocity distribution at the nozzle exit. Then, the flame detachment occurs in the absence of the «bottleneck flame region» and the microjet combustion is terminated at a much higher velocity. An inversion of the dependence l/d = f(U0) is observed at the transition from the parabolic to the top-hat velocity profile of the jet. The ratio of the «bottleneck flame region» size (l) to the nozzle exit diameter (d) is l/d. The nozzle heating is shown to have a profound effect on the microjet combustion.

Evolution and Breakdown of a Subsonic Round Jet

We begin with the dynamics of a round jet emphasizing the contribution of longitudinal disturbances to the perturbed flow pattern. Important issues are generation, spatial development, and interaction of the three-dimensional structures with the ring vortices.

Round Jet Instability Affected by Initial Conditions

Obviously, evolution of a jet depends on the initial conditions at the nozzle exit. In particular, varying the nozzle geometry and, hence, the velocity distribution near its exit, it is possible to modify instability of the jet and its dynamics.

Stability of Subsonic Macro- and Microjets and Combustion

In this chapter, results of experimental studies on stability and combustion of round and plane propane macro- and microjets at low Reynolds numbers in transverse acoustic field are considered. Some features of flame evolution are shown.

Origination and Evolution of Coherent Structures in Laminar and Turbulent Round Jets

In this chapter, dynamics of laminar and turbulent round jets is under further consideration. Experimental data testify to similarities of the generation and development of coherent structures in both cases. Also, almost one and the same response of the jets to external acoustic oscillations is demonstrated.

Instability of Free and Wall Plane Jets

In this chapter we proceed with plane jets focusing, again, on the formation and development of longitudinal structures of laminar flow disturbances and their interaction with the Kelvin–Helmholtz vortices. Some visualization results on a free jet are presented and, then, a perturbed wall jet is considered in more detail.