Chapter 4. Influence of initial conditions at the nozzle exit on
the round jet structure
Multimedia files Nos. 4.1 – 4.3
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. Initial conditions effect at the nozzle exit on the round jet
structure // Thermophysics and Aeromechanics, 2008. Vol. 15. No. 1, pp. 59-73
2.
Kozlov V.V., Grek G.R., Kozlov G.V., Litvinenko Yu.A. Physical aspects of subsonic jet flows evolution // The collection of
proceedings «Successes of mechanics of continuum» to the 70-anniversary of academician V.A. Levin, 2009. Dalnauka,
Vladivostok, pp. 331-351, in Russian
1. Experimental set - up
2. Results of hot – wire anemometer measurements
3. Smoke flow visualization with laser sheet
Experimental set - up
Experimental set - up: Vitoshinsky nozzle -1, honeycomb - 2, grids - 3, settling chamber
- 4, lengthening tubes (430,870,1300 and 4000 mm) - 5, fan - 6, inclined tube
micromanometer - 7, smoke generator – 8, video camera – 9, dynamic loudspeaker – 10,
hot – wire probe – 11, hot – wire anemometer – 12, analog to digital converter – 13, PC
– 14, turbulizer – 15.
Scheme of jet flow visualization and hot – wire measurements
1 - Settling chamber, 2 – Grids, 3 - Vitoshinsky nozzle, 4 – Jet core, 5 – Ring vortices, 6
– Streaky structures, 7 – Laser sheets, 8 - Dynamic loudspeaker, 9 - video camera, 10 Hot – wire probe, 11 - Hot – wire anemometer, 12 - Analog to digital converter, 13 – PC.
Free round jet set – up photo for generation of jet with top –
hat mean velocity profile at the nozzle exit
Nozzle
в
г
Distributions of the mean (a) and fluctuation (b) streamwise velocity component in a round
jet cross section at different distances downstream from the nozzle exit (1,2,3 - at x = 2,10,
20 mm, accordingly); smoke visualization patterns of a jet in longitudinal (c) and transverse (d)
sections, U0 = 5 m/s (Re = U0  d / n  6700)
Free round jet with top – hat mean velocity profile at the
nozzle exit, jet cross sections
Double click
here
Video file No. 4.1
Free round jet set – up with lengthening tube of 430 mm
photo (dnozzle = 20 mm)
Round jet with nozzle lengthening up to 430 mm
Top - hat mean velocity
profile at the nozzle exit
gradually comes nearer to
the parabolic shape in case
of classical (short) nozzle
lengthening up to 430 mm.
Region of laminar jet flow without ring vortices
Double click
here
Video file No. 4.2
Free round jet set – up with lengthening tube of 870 mm
photo (dnozzle = 20 mm)
Round jet with nozzle lengthening up to 870 mm
Top - hat mean velocity
profile at the nozzle exit
gradually comes nearer to
the parabolic shape in case
of classical (short) nozzle
lengthening up to 870 mm.
Region of laminar jet flow without ring vortices
Double click
here
Video file No. 4.3
Free round jet set – up with lengthening tube of 4000 mm
photo (dnozzle = 20 mm)
Round jet with nozzle lengthening up to 4000 mm
Top - hat mean velocity
profile at the nozzle exit is
completely transformed into
the parabolic one at nozzle
lengthening up to 4000 mm
Region of laminar jet flow without ring vortices
KEY POINTS:
 The flow structure and evolution of a round jet are strongly affected by the initial
conditions at the jet origin.
 Through a proper modification of the nozzle profile (hence, the radial mean-velocity
distribution) the laminar part of the jet becomes much more extended.
 In the laminar jet the acoustic effect on the flow pattern becomes visible well behind the
nozzle outlet where the ring vortices start to grow.
 Profiling the nozzle combined with forced turbulization of its boundary layer makes it
possible to create a fully turbulent flow immediately at the jet origin.