A numerical investigation on the effect of the inflow conditions on the self-similar region of a round jet

1998 ◽  
Vol 10 (4) ◽  
pp. 899-909 ◽  
Author(s):  
B. J. Boersma ◽  
G. Brethouwer ◽  
F. T. M. Nieuwstadt
Keyword(s):  
Numerical Investigation ◽  
The Self ◽  
Round Jet ◽  
Similar Region ◽  
Self Similar ◽  
Inflow Conditions

Coherent Structures and Correlation Fields in the Mixing Transition of a Turbulent Round Free Jet

2018 ◽  
Author(s):  
Benedikt Krohn ◽  
Sunming Qin ◽  
Victor Petrov ◽  
Annalisa Manera
Keyword(s):  
Coherent Structures ◽  
High Speed ◽  
Near Field ◽  
The Self ◽  
Turbulent Shear ◽  
Past Century ◽  
Self Similarity ◽  
Free Jet ◽  
Similar Region ◽  
Self Similar

Turbulent free jets attracted the focus of many scientists within the past century regarding the understanding of mass- and momentum transport in the turbulent shear field, especially in the near-field and the self-similar region. Recent investigations attempt to understand the intermediate fields, called the mixing transition or ‘the route to self-similarity’. An apparent gap is recognized in light of this mixing transition, with two main conjectures being put forth. Firstly the flow will always asymptotically reach a fully self-similar state if boundary conditions permit. The second proposes partial and local self-similarity within the mixing transition. We address the later with an experimental investigation of the intermediate field turbulence dynamics in a non-confined free jet with a nozzle diameter of 12.7 mm and an outer scale Reynolds number of 15,000. High speed Particle Image Velocimetry (PIV) is used to record the velocity fields with a final spatial resolution of 194 × 194 μm2. The analysis focuses on higher order moments and two-point correlations of velocity variances in space and time. We observed local self-similarity in the measured correlation fields. Coherent structures are present within the near-field where the turbulent energy spectrum cascades along a dissipative slope. Towards the transition region, the spectrum smoothly transforms to a viscous cascade, as it is commonly observed in the self-similar region.

Characteristics of Turbulent Three-Dimensional Wall Jets

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
M. Agelin-Chaab ◽  
M. F. Tachie
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Orthogonal Decomposition ◽  
The Self ◽  
Shear Stresses ◽  
Spread Rate ◽  
Similar Region ◽  
Self Similar ◽  
Proper Orthogonal

Three-dimensional turbulent wall jet was investigated using a particle image velocimetry technique. Three Reynolds numbers based on the jet exit velocity and diameter of 5000, 10,000, and 20,000 were studied. Profiles of the mean velocities, turbulence intensities, and Reynolds shear stresses as well as two-point velocity correlations and proper orthogonal decomposition analyses were used to document the salient features of the wall jets. The decay and spread rates are independent of Reynolds numbers in the self-similar region. The estimated values of 1.15, 0.054, and 0.255 for the decay rate, wall-normal spread rate, and lateral spread rate, respectively, are within the range of values reported in the literature. The two-point correlation analysis showed that the inclination of the streamwise velocity correlation contours in the inner layer is 11±3 deg in the wall region, which is similar to those of canonical turbulent boundary layers. The results from the proper orthogonal decomposition indicate that low-order modes contribute more to the turbulence statistics in the self-similar region than in the developing region. The Reynolds shear stresses are the biggest benefactors of the low-order mode contribution while the wall-normal turbulence intensities are the least.

Instantaneous three-dimensional concentration measurements in the self-similar region of a round high-Schmidt-number jet

1994 ◽  
Vol 279 ◽  
pp. 313-350 ◽  
Author(s):  
M. Yoda ◽  
L. Hesselink ◽  
M. G. Mungal
Keyword(s):  
Concentration Gradient ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Concentration Field ◽  
The Self ◽  
Gradient Field ◽  
Geometrical Parameters ◽  
Similar Region ◽  
Self Similar ◽  
Local Topology

The virtually instantaneous three-dimensional concentration fields in the self-similar region of natural or unexcited, circularly excited and weakly buoyant round jets of Reynolds number based on nozzle diameter of 1000 to 4000 are measured experimentally at a spatial resolution of the order of the Kolmogorov length scale. Isoconcentration surfaces are extracted from the concentration field. These surfaces along with their geometrical parameters are used to deduce the structure and modal composition of the jet. The concentration gradient field is calculated, and its local topology is classified using critical-point concepts.Large-scale structure is evident in the form of ‘clumps’ of higher-concentration jet fluid. The structure, which has a downstream extent of about the local jet diameter, is roughly axisymmetric with a conical downstream end. This structure appears to be present only in fully turbulent jets. The antisymmetric two-dimensional images previously thought to be axial slices of an expanding spiral turn out in our data to instead be slices of a simple sinusoid in three dimensions. This result suggests that the helical mode, when present, is in the form of a pair of counter-rotating spirals, or that the +1 and −1 modes are simultaneously present in the flow, with their relative phase set by initial conditions.In terms of local structure, regions with a large magnitude in concentration gradient are shown to have a local topology which is roughly axisymmetric and compressed along the axis of symmetry. Such regions, which would be locally planar and sheet-like, may correspond to the superposition of several of the layer-like structures which are the basic structure of the fine-scale passive scalar field (Buch & Dahm 1991; Ruetsch & Maxey 1991).

scholarly journals Theoretical and Observational Implications of a Super-Horizon-Scale Inhomogeneous Cosmological Model

1999 ◽  
Vol 183 ◽  
pp. 270-270
Author(s):  
K. Tomita
Keyword(s):  
Cosmological Model ◽  
Gravitational Theory ◽  
The Self ◽  
Homogeneous Region ◽  
Low Density ◽  
Similar Region ◽  
Inhomogeneous Cosmological Model ◽  
Observational Fact ◽  
Self Similar ◽  
Inner Region

We discuss the theoretical and observational implications of an inhomogeneous cosmological model consisting of three regions: the inner low-density homogeneous region, the self-similar (or partially similar) inhomogeneous region and the outer nearly flat homogeneous region. When we assume Einstein's gravitational theory without cosmological constant, the standard inflation theory, and the observational fact of local low density around us, this model is found to be reasonable. The boundary between the inner region and the self-similar region is assumed to be in a spherical shell corresponding to the epoch of redshift z = 1.5–2.0, when the numbers of QSOs and Ly α clouds changed rapidly.

Velocity and Scalar Fields of a Turbulent Buoyant Jet in the Self-Similar Region

2019 ◽  
Vol 206 (2) ◽  
pp. 307-321
Author(s):  
Sunming Qin ◽  
Benedikt Krohn ◽  
Victor Petrov ◽  
Annalisa Manera
Keyword(s):  
Scalar Fields ◽  
The Self ◽  
Buoyant Jet ◽  
Similar Region ◽  
Self Similar

A Study of Near-Field Entrainment in Gas Jets and Sprays Under Diesel Conditions

1999 ◽  
Vol 122 (2) ◽  
pp. 385-395 ◽  
Author(s):  
Scott Post ◽  
Venkatraman Iyer ◽  
John Abraham
Keyword(s):  
Rate Constant ◽  
Computational Study ◽  
Near Field ◽  
The Self ◽  
Experimental Results ◽  
Entrainment Rate ◽  
Gas Jets ◽  
Similar Region ◽  
Mass Entrainment ◽  
Self Similar

This paper presents a computational study of entrainment characteristics in the near-field of gas jets under atmospheric and Diesel conditions and sprays under Diesel conditions. Computed flowfield information is used to estimate the rate of mass entrainment in the jet and derive the entrainment rate constant. The value of the entrainment rate constant is compared to experimental results in the literature. It is found that the computed values of the constant in the near-field are less than the values in the self-similar region of the jet with the values increasing monotonically from the orifice to the self-similar region. These results are consistent with experimental results. In the case of sprays, it is found that it is difficult to arrive at firm conclusions because the results are sensitive to several parameters that are not well known and to the numerics. The computed results for sprays are also discussed relative to measurements in sprays quoted in the literature. [S0098-2202(00)00802-6]

scholarly journals Hausdorff measure and Assouad dimension of generic self-conformal IFS on the line

2020 ◽  
pp. 1-31
Author(s):  
Balázs Bárány ◽  
Károly Simon ◽  
István Kolossváry ◽  
Michał Rams
Keyword(s):  
Hausdorff Measure ◽  
Similar Case ◽  
Iterated Function Systems ◽  
The Self ◽  
Dimensional Hausdorff Measure ◽  
Assouad Dimension ◽  
Iterated Function ◽  
Self Similar ◽  
Weak Separation ◽  
Topological Sense

This paper considers self-conformal iterated function systems (IFSs) on the real line whose first level cylinders overlap. In the space of self-conformal IFSs, we show that generically (in topological sense) if the attractor of such a system has Hausdorff dimension less than 1 then it has zero appropriate dimensional Hausdorff measure and its Assouad dimension is equal to 1. Our main contribution is in showing that if the cylinders intersect then the IFS generically does not satisfy the weak separation property and hence, we may apply a recent result of Angelevska, Käenmäki and Troscheit. This phenomenon holds for transversal families (in particular for the translation family) typically, in the self-similar case, in both topological and in measure theoretical sense, and in the more general self-conformal case in the topological sense.

scholarly journals Onset of the Mach Reflection of Zel’dovich–von Neumann–Döring Detonations

Entropy ◽  
2021 ◽  
Vol 23 (3) ◽  
pp. 314
Author(s):  
Tianyu Jing ◽  
Huilan Ren ◽  
Jian Li
Keyword(s):  
Hot Spot ◽  
Mach Reflection ◽  
Near Field ◽  
The Self ◽  
Small Scale ◽  
Mach Stem ◽  
Self Similarity ◽  
Von Neumann ◽  
Similarity Problem ◽  
Self Similar

The present study investigates the similarity problem associated with the onset of the Mach reflection of Zel’dovich–von Neumann–Döring (ZND) detonations in the near field. The results reveal that the self-similarity in the frozen-limit regime is strictly valid only within a small scale, i.e., of the order of the induction length. The Mach reflection becomes non-self-similar during the transition of the Mach stem from “frozen” to “reactive” by coupling with the reaction zone. The triple-point trajectory first rises from the self-similar result due to compressive waves generated by the “hot spot”, and then decays after establishment of the reactive Mach stem. It is also found, by removing the restriction, that the frozen limit can be extended to a much larger distance than expected. The obtained results elucidate the physical origin of the onset of Mach reflection with chemical reactions, which has previously been observed in both experiments and numerical simulations.

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