Hydrodynamic equations well describe averaged parameters of
turbulent steady flows, at least in pipes where boundary conditions
can be estimated. The equations might outline the parameters
fluctuations as well, if entry conditions at current boundaries
were known. This raises, in addition, the more comprehensive
problem of the primary perturbation nature, noted by H.A. Lorentz,
which still remains unsolved. Generally, any flow steadiness should
be supported by pressure waves emitted by some external source,
e.g. a piston or a receiver. The wave plane front in channels
quickly takes convex configuration owing to Rayleigh's law of
diffraction divergence. The Schlieren technique and pressure wave
registration were employed to investigate the wave interaction with
boundary layer, while reflecting from the channel wall. The
reflection induces boundary-layer local separation and following
pressure rapid increase within the perturbation zone. It propagates
as an acoustic wave packet of spherical shape, bearing oscillations
of hydrodynamic parameters. Superposition of such packets forms a
spatio-temporal field of oscillations fading as 1/r. This implies a
mechanism of the turbulence. Vorticity existing in the boundary
layer does not penetrate in itself into potential main stream. But
the wave leaving the boundary layer carries away some part of fluid
along with frozen-in vorticity. The vorticity eddies form another
field of oscillations fading as 1/r2. This implies a second
mechanism of turbulence. Thereupon the oscillation spatio-temporal
field and its randomization development are easy computed. Also,
normal burning transition into detonation is explained, and the
turbulence inverse problem is set and solved as applied to plasma
channels created by laser Besselian beams.
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