Chapter 6. Influence of initial conditions at the nozzle exit
and acoustics effect on the plane jet flow structure and its
stability
Multimedia files Nos. 6.1 – 6.9
The results of researches presented in presentation are published in the following
main articles:
1. Kozlov G.V., Grek G.R., Sorokin A.M., Litvinenko Yu.A. Influence of the initial conditions at the nozzle exit on a flow structure
and stability of the plane jet // Vestnik NSU. Seria: Physics. 2008, Vol. 3, vip. 3, pp. 25-37 in Russian.
2. Yu. A. Litvinenko, G. R. Grek, V. V. Kozlov, and G. V. Kozlov Subsonic round and plane macrojets and microjets in a
transverse acoustic field // Doklady Physics, 2011, vol. 56, № 1, pp. 26-31.
Scheme of experimental set – up and procedure of the jet study
1 – settling chamber; 2 – Vitoshinsky nozzle; 3 – set of grids; 4 – honeycomb; 5 – punched
plate; 6 – dividing plate; 7 – fan; 8 – smoke generator; 9 – extension channel; 10 – inclined
micro - manometer; 11 – video camera; 12 – dynamic loudspeaker; 13 – hot – wire probe;
14 – hot – wire anemometer; 15 – analog - digital converter (ADC); 16 – PC; 17 – turbulizer
Experimental set – up photo for generation of the plane jet with
parabolic (a) and top – hat (b) mean velocity profile at the nozzle
exit
Laminar plane jet with parabolic mean velocity profile at the
nozzle exit
It is found, that laminar plane jet with parabolic mean velocity profile
at the nozzle exit subjected by sinusoidal mode instability
Smoke visualization patterns of the laminar plane jet streamwise
sections without acoustic effect (1) and at acoustic effect (2, 3, 4,
5– at f = 30, 40, 50, 60 Hz, respectively). It is found, that acoustics
excite the sinusoidal mode instability of a plane jet. The wave
length of disturbances is reduced with frequency growth.
Smoke visualization patterns of the laminar plane jet
streamwise sections
Acoustic field with frequency
of F = 30 Hz
Video file No. 6.1
Natural jet oscillation and
acoustic field with frequency
of F = 30 Hz
Video file No. 6.2
Double click
here
Double click
here
Smoke visualization jet with top – hat mean velocity profile
at the nozzle exit (natural disturbances)
Video file No. 6.3
Double click
here
Plane jet with top – hat mean velocity profile at the nozzle exit involve three
independent of each other instability regions:
1. Two independent of each other narrow regions of strong velocity gradient
near nozzle.
2. Region with parabolic mean velocity profile far downstream from a nozzle
Plane jet with top – hat mean velocity profile at the nozzle exit,
U0 = 3 m/s, without triggering (streamwise section)
Double click
here
Video file No. 6.4
Plane jet with top – hat mean velocity profile at the nozzle exit,
U0 = 3 m/s, F = 30 Hz (streamwise section).
Double click
here
Video file No. 6.5
Plane jet with top – hat mean velocity profile at the nozzle exit,
U0 = 3 m/s, F = 30 Hz (overall view).
Double click
here
Video file No. 6.6
Smoke visualization of the plane jet cross section with top – hat
mean velocity profile at the nozzle exit. (roughness elements
are located on single nozzle side)
Double click
here
Video file No. 6.7
Natural streaky structures interaction with the cylindrical vortices
of a vortex street of the plane jet with parabolic mean velocity
profile at the nozzle exit
Streaky structures interaction with the
left vortices of a sinusoidal vortex street.
Streaky structures interaction with the
right vortices of a sinusoidal vortex street.
Smoke visualization of the streaky structures interaction with
a single cylindrical vortex of a vortex street of the plane jet
with parabolic mean velocity profile at the
nozzle exit (jet cross section)
Double click
here
Video file No. 6.8
Smoke visualization of the plane jet overview with the roughness
elements. Parabolic mean velocity profile at the nozzle exit.
Smoke visualization patterns of the streaky structures interaction
with the cylindrical vortices of a vortex street (streaky structures
are excited by a single roughness element)
Smoke visualization patterns of the streaky structures interaction
with the cylindrical vortices of a vortex street (streaky structures
are excited by the four roughness elements)
Turbulent plane jet
Mean velocity profiles at different
distances from the nozzle
Fluctuation velocity profiles at different
distances from the nozzle
Smoke visualization patterns of the turbulent plane jet streamwise
sections without acoustic effect (1) and at acoustic effect (2, 3, 4,
5– at f = 30, 40, 50, 60 Hz, respectively).
Turbulent plane jet streamwise section smoke
visualization at acoustics excitation.
Double click
here
Video file No. 6.9
KEY POINTS:
 Oscillatory behavior of the laminar plane jet with a parabolic mean velocity and that of the
turbulent plane jet are much similar with large scale anti-symmetric oscillations dominating
the flow pattern.
 Both laminar and turbulent plane jets are receptive to external acoustic excitation so that
the characteristics of their oscillations can be modified at variation of the forcing frequency.
 Longitudinal structures of velocity perturbations generated by surface roughness at one
side of the nozzle modulate the adjacent shear layer of the plane jet with a top-hat mean
velocity profile and the entire flow pattern of the plane parabolic jet.