The analysis of a jet structure inside a reverse chamber

The paper presents experimental results for an axisymmetrical jet flow impinging with outflow through a reverse chamber. The test results include the average distributions and fluctuations of pressures on the impinged wall and the side wall of the chamber. The presented results cover further the mean velocities and the velocity fluctuations in the reverse chamber in relation to two velocity components: axial and radial. The purpose of the paper is to indicate the differences between different flow situations: the axisymmetrical free jet, the impinging jet hitting a flat surface, and a flow geometrically alike, however, restricted in outflow through a reverse annular chamber.

Diffusive turbulence in a confined jet experiment

An experimental analysis of the turbulence in an axisymmetrical jet within a closed tube is presented. At some distance from the nozzle, a turbulent region develops, where the kinetic energy of the mean flow almost vanishes. In this region, the turbulence is transported by turbulent diffusion and its energy decreases with the distance from the inlet. A complete description of the flow field has been achieved using laser Doppler anemometry. Some unusual features are highlighted: the statistical moments of the velocity decay exponentially, the integral length scales remain constant, the radial profiles are self-similar and the Reynolds stress tensor is isotropic and homogeneous in the radial direction. These results highlight the roles of pressure fluctuations and any mean residual motion in the return to isotropy.

Nonlinear spatial evolution of helical disturbances to an axial jet

We investigate the weakly nonlinear spatial evolution of helical disturbances of an axisymmetrical jet which are the analogue of three-dimensional disturbances, such as a single oblique wave (the wave vector is directed at an angle to the main flow velocity) in plane-parallel flows. It is shown that when a supercriticality is large enough, the perturbation amplitude A grows in the streamwise direction (along z) explosively: A ∼ (z0 — z)−5/2, though more slowly than in the case of essentially three-dimensional disturbances in the form of a pair of oblique waves (A ∼ (z0 — z)−3; Goldstein & Choi 1989). The nonlinearity needed for such a growth, is due equally to the cylindricity of shear layer and to the spatial character of the evolution (in the temporal problem the ‘evolution’ contribution is absent). At a smaller supercriticality, the evolution equation has a non-local (integral in z) nonlinearity, unusual for the regime of a viscous critical layer. Scenarios of disturbance development for different levels of supercriticality are studied, with proper account taken of viscous broadening of the flow.

Vortex evolution in a round jet

A study has been made of the varicose instability of an axisymmetrical jet with a velocity distribution radially uniform at the nozzle mouth except for a laminar boundary layer at the wall. The evolutionary phenomena of instability, such as the rolling up of the cylindrical vortex layer into ring vortices, the coalescence of ring vortex pairs, and the eventual disintegration into turbulent eddies, have been investigated as a function of the Reynolds number using smoke photography, stroboscopic observation, and the light-scatter technique.Emphasis has been placed on the wavelength with maximum growth rate. The jet is highly sensitive to sound and the effects of several types of acoustic excitation, including pure tones, have been determined.