Using small-scale turbulence for forming a solid fluid jet

Abstract

ВступProblem statement. Increasing the range and kinetic energy of a submerged fluid jet is a topical problem in fluid jet technologies, in particular, power waterjet guns. The main deterrent to its solving is the unavoidable jet breakup process. There is no common approach to control this phenomenon. Hence, for each process, a technique is chosen to enable using the jet before it breaks up. An effective technique is fluid discharge in an elastic or plastic container. However, each discharge preparation procedure restricts using the technique. Recently, unique fountains have appeared with a solid translucent jet several meters long. Visually, these jets are considered laminar ones; however, as will be shown below, such a view is erroneous. At the same time, the flow in these fountains has interesting features that deserve closer attention.Jet breakup is caused by interaction of external and internal destructive factors. Fluid turbulence originates as early as in the channel. In the jet, it develops into strong turbulence and creates conditions for jet dispersion and aeration under the effect of the force of gravity and air resistance.It is impossible to avoid turbulence in a highvelocity flow. However, existing conceptions and prospects enable passing artificially to turbulent flow, which has passed the active phase and does not create large turbulent eddies. Such properties belong to small-scale turbulence (SST) formed within the decaying turbulence. It must be propelled to a jet to delay its destruction.Analysis of the latest researchers and publications. The basis for choosing SST as a means against eddy formation stems from the energy spectrum of fully developed turbulence at high Reynolds numbers. It was represented by Kolmogorov's phenomenological theory [1], whose statements are a basis for studying all turbulent flows [2][3]. According to them, the kinetic energy of turbulence is cascaded without loss from large to small scales according to the Richardson-Kolmogorov cascade. Energy dissipation occurs at the end of the sequence under the effect of viscosity, with virtually all SST properties being determined by the dissipation rate [4]. According to Kolmogorov [1], SST wave numbers belong to the inertial energy interval, which has no dissipation and local interaction. Such turbulence depends weakly on the mean flow velocity. Hence, a conditional flow with SST will be resistant to influences to a certain degree.The actual composition and local characteristics of developed turbulence [4] differ from the simplified model presented. In particular, there exists a nonequilibrium turbulence with an appropriate law of nonequilibrium dissipation [5], which co-exists with the common law of equilibrium dissipation in different areas of the same flow. Hence, the complexity of developed turbulence only drives more the need for an experimental search of conditions that produce an intensive SST and its localisation in a flow at high Reynolds numbers.Purpose of the article. The main purpose of the article is to demonstra...

The concept of creating a pulse water gun with a large action range

“…However, based of modern concepts of the nature of turbulence, it is possible to prevent development of strong turbulence by means of artificially created small-scale (SS) turbulence. Paper [9] considers its importance for provision of stabilization of a jet.…”

“…For example, a pure laminar jet should not scatter illumination light like a lightguide, and the observed luminescence of jets indicates light scattering on small-scale turbulent fluctuations. A work [9] considers a more complex demonstration light effect, which is also caused by SS turbulence.…”