Mixing and Diffusion in Regular/Fractal Grid Turbulence

Sakai, Yasuhiko; Nagata, Koji; Suzuki, Hiroki

doi:10.1007/978-3-319-33310-6_2

Cited by 7 publications

(9 citation statements)

References 62 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It appears very clearly that the longitudinal integral scale L x increases with the distance downstream of the grid for the two types of grids. On the other hand, L x increases with increasing U ∞ , which is consistent with previous results of [3,9]. On the other hand, L x is greater for the turbulence generated by the FSG than for the turbulence generated by the SFSG.…”

Section: Resultssupporting

confidence: 91%

See 1 more Smart Citation

The Decay of Turbulence Generated by Square Grid and Spaced Square Grid

Mahjoub¹,

Ouadoud²,

Redondo³

2022

Topical Problems of Fluid Mechanics 2022

View full text Add to dashboard Cite

Fractal grids generate multi-scale turbulent flows which interact with each other and form new multi-scales with different properties compared with those generated by classical grids. The goal of this work was to study the influence of geometry multiscale fractal on the generation and decay of turbulence by comparing the turbulence produced by a traditional fractal square grid FSG for short to that produced by a spaced fractal square grid SFSG for short with similar physical properties. The velocity measurements were performed in an open circuit suction type wind tunnel using a constant temperature hot wire anemometer at various positions in the x direction along the tunnel’s center line and for three different Reynolds numbers ReL0 based on the inlet velocity U? and the length of the largest grid bar L0. It was found that the turbulence intensity decays with distance from the grid for SFSG. Whereas, for FSG at low Reynolds numbers the turbulence intensity shows the same behaviour as for SFSG but for higher Reynolds numbers the turbulence intensity increases to reach a peak at a distance xpeak from the grid and then decays. In the inhomogeneous region, for both types of grids, a scaling range spans over a decade with an exponent near, but not exactly, k?5/3. In contrast, the length of the scaling range larger for FSG than for SFSG.

show abstract

Section: Resultssupporting

confidence: 91%

“…The longitudinal Taylor scale λ decreases with the distance downstream of the two types of grids for U ∞ = 1.5m/s and U ∞ = 2.5m/s. However, λ increases with the distance downstream of the two types of grids for U ∞ = 5m/s, which is consistent with previous results [3,9].…”

Section: Discussionsupporting

confidence: 92%

The Decay of Turbulence Generated by Square Grid and Spaced Square Grid

Mahjoub¹,

Ouadoud²,

Redondo³

2022

Topical Problems of Fluid Mechanics 2022

View full text Add to dashboard Cite

show abstract

“…Turbulence in a free circular jet was investigated by [13] to study the necessary conditions for self-preservation of free turbulent flow with a virtual excitation source. Jet technique applications related to mixing and diffusion in grid-generated turbulence are given in extensive study [14]. Interesting results on turbulence behaviour in a free jet were obtained using direct calculations of three-dimensional NavierStokes equations.…”

Section: Main Bodymentioning

confidence: 99%

Using small-scale turbulence for forming a solid fluid jet

Сидоренко¹,

Толкачов²

2018

ХНУПС

View full text Add to dashboard Cite

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...

show abstract

“…Several modern developments, which apply the latest technical methods of research and theoretical concepts, can be useful for the search for a new idea of jet preservation. Extensive publication [6] considers a number of such methods. In particular, it considers positions of the jet technique that relate to mixing and diffusion in a turbulent flow created by lattices.…”

Section: Literature Review and Problem Statementmentioning

confidence: 99%