scholarly journals Visualization of Two Counter-rotating Supersonic Vortices

2020 ◽  
pp. 40-46
Author(s):  
Vitaly Borisov ◽  
Alexander Davydov ◽  
Tatiana Konstantinovskaya ◽  
Alexander Lutsky
Keyword(s):  
Parallel Algorithm ◽  
Turbulent Flows ◽  
Numerical Data

In this work, a visualization of supersonic counter-rotating vortices pair is performed using the methods of maximum vorticity and the λ2-criterion. Numerical data were obtained on the supercomputer system K-60 at the KIAM RAS using a parallel algorithm for modeling of turbulent flows.

Numerical Simulation of Turbulent Flows in Ribbed Pipes

2005 ◽  
Author(s):  
Sowjanya Vijiapurapu ◽  
Jie Cui
Keyword(s):  
Turbulent Flows ◽  
Turbulence Models ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Friction Resistance ◽  
Circular Pipes ◽  
Computational Fluid Dynamics Cfd ◽  
Stress Models ◽  
Type Intermediate

The Reynolds averaged Navier-Stokes (RANS) equations were solved along with three turbulence models, namely κ-ε, κ-ω, and Reynolds stress models (RSM), to study the fully developed turbulent flows in circular pipes roughened by repeated square ribs. The spacing between the ribs was varied to form three representative types of surface roughness; d–type, intermediate, and k–type. Solutions of these flows at two Reynolds numbers were obtained using the commercial computational fluid dynamics (CFD) software Fluent. The numerical results were validated against experimental measurements and other numerical data published in literature. Extensive investigation of effects of rib spacing and Reynolds number on the pressure and friction resistance, flow and turbulence distribution was presented. The performance of three turbulence models was also compared and discussed.

Numerical Simulation of Channel Flows by a One-Equation Turbulence Model

1997 ◽  
Vol 119 (4) ◽  
pp. 885-892 ◽  
Author(s):  
V. I. Vasiliev ◽  
D. V. Volkov ◽  
S. A. Zaitsev ◽  
D. A. Lyubimov
Keyword(s):  
Numerical Simulation ◽  
Turbulent Flows ◽  
Turbine Blade ◽  
Turbulence Model ◽  
Turbulent Viscosity ◽  
Numerical Data ◽  
Equation Model ◽  
Channel Flows ◽  
Parabolic Flows

A one-equation model for turbulent viscosity, previously developed and tested for parabolic flows, is implemented in elliptic cases. The incompressible 2-D and axisymmetric flows in channel with back step as well as the incompressible and compressible 2-D flows in turbine blade cascades are calculated. The CFD procedures, developed for both incompressible and compressible turbulent flows simulation, are described. The results of calculations are compared with known experimental and numerical data.

scholarly journals Boundedness of the velocity derivative skewness in various turbulent flows

2015 ◽  
Vol 781 ◽  
pp. 727-744 ◽  
Author(s):  
R. A. Antonia ◽  
S. L. Tang ◽  
L. Djenidi ◽  
L. Danaila
Keyword(s):  
Turbulent Flows ◽  
Nauk Sssr ◽  
Numerical Data ◽  
Universal Constant ◽  
Energy Dissipation Rate ◽  
Small Scale ◽  
Grid Turbulence ◽  
Similarity Hypothesis ◽  
Velocity Derivative ◽  
Scale Turbulence

The variation of $S$, the velocity derivative skewness, with the Taylor microscale Reynolds number $\mathit{Re}_{{\it\lambda}}$ is examined for different turbulent flows by considering the locally isotropic form of the transport equation for the mean energy dissipation rate $\overline{{\it\epsilon}}_{iso}$. In each flow, the equation can be expressed in the form $S+2G/\mathit{Re}_{{\it\lambda}}=C/\mathit{Re}_{{\it\lambda}}$, where $G$ is a non-dimensional rate of destruction of $\overline{{\it\epsilon}}_{iso}$ and $C$ is a flow-dependent constant. Since $2G/\mathit{Re}_{{\it\lambda}}$ is found to be very nearly constant for $\mathit{Re}_{{\it\lambda}}\geqslant 70$, $S$ should approach a universal constant when $\mathit{Re}_{{\it\lambda}}$ is sufficiently large, but the way this constant is approached is flow dependent. For example, the approach is slow in grid turbulence and rapid along the axis of a round jet. For all the flows considered, the approach is reasonably well supported by experimental and numerical data. The constancy of $S$ at large $\mathit{Re}_{{\it\lambda}}$ has obvious ramifications for small-scale turbulence research since it violates the modified similarity hypothesis introduced by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82–85) but is consistent with the original similarity hypothesis (Kolmogorov, Dokl. Akad. Nauk SSSR, vol. 30, 1941, pp. 299–303).

scholarly journals Dissipation-scale fluctuations and mixing transition in turbulent flows

2008 ◽  
Vol 606 ◽  
pp. 325-337 ◽  
Author(s):  
VICTOR YAKHOT
Keyword(s):  
Probability Density ◽  
Turbulent Flows ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Numerical Data ◽  
Reaction Rates ◽  
Diffusion Time ◽  
Necessary Condition ◽  
Scalar Dissipation ◽  
Dissipation Scale

A small separation between reactants, not exceeding 10−8 − 10−7 cm, is the necessary condition for various chemical reactions. It is shown that random advection and stretching by turbulence leads to the formation of scalar-enriched sheets of strongly fluctuating thickness ηc. The molecular-level mixing is achieved by diffusion across these sheets (interfaces) separating the reactigants. Since the diffusion time scale is $\tau_{d}\,{\propto}\,\eta_{c}^{2}$, knowledge of the probability density Q(ηc, Re) is crucial for evaluation of mixing times and chemical reaction rates. According to Kolmogorov–Batchelor phenomenology, the stretching time τeddy ≈ L/urms = O(1) is independent of large-scale Reynolds number Re = urmsL/ν and the diffusion time $\tau_{d}\,{\approx}\,\tau_{\it eddy}/\sqrt{{\it Re}}\,{\ll}\, \tau_{\it eddy}$ is very small. Therefore, in previous studies, molecular diffusion was frequently neglected as being too fast to contribute substantially to the reaction rates. In this paper, taking into account strong intermittent fluctuations of the scalar dissipation scales, this conclusion is re-examined. We derive the probability density Q(ηc, Re, Sc), calculate the mean scalar dissipation scale and predict transition in the reaction rate behaviour from ${\cal R}\,{\propto}\,\sqrt{Re}$ ($Re\,{\leq}\, 10^{3}-10^{4})$ to the high-Re asymptotics ${\cal R}\,{\propto}\, {\it Re}^{0}$. These conclusions are compared with known experimental and numerical data.

scholarly journals Interaction analysis of two streamwise supersonic vortices by visualization methods

2021 ◽  
Author(s):  
Vitaly Evgenyevich Borisov ◽  
Alexandr Alexandrovich Davydov ◽  
Tatiana Vitalievna Kostantinovskaya ◽  
Alexander Evgenievich Lutsky
Keyword(s):  
Turbulent Flows ◽  
High Performance ◽  
Interaction Analysis ◽  
Applied Mathematics ◽  
Numerical Data ◽  
Attack Angle ◽  
Keldysh Institute ◽  
Computing Systems ◽  
Trailing Edges ◽  
Performance Computing

In this paper we present an analysis and comparison of two streamwise supersonic vortices interaction with using the methods of maximum vorticity and the ?2-criterion. Mach number of incoming flow was M? = 3. A pair of vortices was generated by two coaxial straight wings with sharp leading, tip and trailing edges. Two configurations are considered: a pair of counter-rotating vortices and a pair of co-rotating vortices. In the case of counterrotating vortices the wings attack angle was 10 degrees. In the case of co-rotating vortices the attack angle of one of the wings was 10 degrees, the attack angle of other one was -10 degrees. Numerical data were obtained in the domain of 10 wing chords downstream from a wings axis by a computational model based on the URANS equations with SA turbulence model. Numerical simulations were performed on the hybrid supercomputing system K-60 at the Keldysh Institute of Applied Mathematics RAS using the developed software package ARES for 3D turbulent flows modeling on high performance computing systems. The main simulation was performed on 224 cores. The simulations were carried out on unstructured grids with hexagonal cells.

Heat Transfer and Drag Reduction in Flows Over Riblet Mounted Surfaces

2003 ◽  
Author(s):  
Stefan aus der Wiesche
Keyword(s):  
Heat Transfer ◽  
Drag Reduction ◽  
Turbulent Flows ◽  
Numerical Data ◽  
Smooth Wall ◽  
Reynolds Analogy ◽  
Turbulent Drag ◽  
Prandtl Numbers ◽  
Laminar And Turbulent Flows ◽  
Good Agreement

The heat transfer in a channel with its lower wall mounted with streamwise V-shaped riblets is investigated numerically using a LES approach. Both laminar and turbulent flows are considered. At the riblet wall the turbulent drag is reduced by 6% in comparison to the smooth wall, whereas for laminar flow the riblets lead to a significant drag increase. The effect of riblets on heat transfer is investigated explicitly for small Prandtl numbers Pr and an appropriate correlation is derived. This correlation indicates that the Reynolds analogy is not violated in case of Pr = 1 despite the extraordinary turbulent drag reducing mechanism. The numerical results for drag reduction are in good agreement with available experimental and numerical data, and the results are faced with corresponding heat transfer results found in the literature.

On the motion of gas bubbles in homogeneous isotropic turbulence

1997 ◽  
Vol 336 ◽  
pp. 221-244 ◽  
Author(s):  
P. D. M. SPELT ◽  
A. BIESHEUVEL
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Gas Bubbles ◽  
Numerical Data ◽  
Equation Of Motion ◽  
Equivalent Diameter ◽  
Approximate Analysis ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Velocity ◽  
The Mean

This paper is concerned with the motion of small gas bubbles, equivalent diameter about 1.0 mm, in isotropic turbulent flows. Data on the mean velocity of rise and the dispersion of the bubbles have been obtained numerically by simulating the turbulence as a sum of Fourier modes with random phases and amplitudes determined by the Kraichnan and the von Kármán–Pao energy-spectrum functions, and by calculating the bubble trajectories from a reasonably well-established equation of motion. The data cover the range β[les ]1, where β is the ratio between the turbulence intensity and the velocity of rise of the bubbles in still fluid. An approximate analysis based on the assumption that β is small yields results that compare favourably with the numerical data, and clarifies the important role played by the lift forces exerted by the fluid.

Reduced Order Modeling of Steady Turbulent Convection Flows Using the POD

2005 ◽  
Author(s):  
Jeffrey Rambo ◽  
Yogendra Joshi
Keyword(s):  
Data Processing ◽  
Turbulent Flows ◽  
Design Space ◽  
Dynamic Models ◽  
Numerical Data ◽  
Large Data ◽  
Approximate Solutions ◽  
System Response ◽  
Fluid Systems ◽  
Low Dimensional

In the characterization and design of complex distributed parameter thermo/fluid systems, detailed experimental measurements or fine numerical calculations often produce excessively large data sets, rendering more advance analyses inefficient or impossible. Acquiring the experimental or numerical data is usually a time consuming task, severely restricting the number and range of parameters and ultimately limiting the portion of the design space that can be explored. To develop low dimensional models, it is desirable to decompose the system response into a series of dominant physical modes that describe the system, while incurring a minimal loss of accuracy. The proper orthogonal decomposition (POD) has been successful in creating low dimensional dynamic models of turbulent flows and here its utility is extended to produce approximate solutions of steady, multi-parameter RANS simulations within predefined limits. The methodology is illustrated through the 2-dimensional analysis of an air-cooled data processing cabinet containing 10 individual servers, each with their own flow rate. The results indicate that a flux matching procedure can reduce the model size by 4 orders of magnitude while adequately describing the airflow transport properties within engineering accuracy. This low dimensional description of the flow inside the data processing cabinet can in turn be used to further explore the design space and efficiently optimize the system.

Simulation of turbulent flows with the entropic multirelaxation time lattice Boltzmann method on body-fitted meshes

2018 ◽  
Vol 849 ◽  
pp. 35-56 ◽  
Author(s):  
G. Di Ilio ◽  
B. Dorschner ◽  
G. Bella ◽  
S. Succi ◽  
I. V. Karlin
Keyword(s):  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Local Refinement ◽  
High Reynolds ◽  
Boltzmann Method ◽  
Dynamics Problems ◽  
Refinement Strategy ◽  
Wall Bounded Turbulence

We propose a body-fitted mesh approach based on a semi-Lagrangian streaming step combined with an entropy-based collision model. After determining the order of convergence of the method, we analyse the flow past a circular cylinder in the lower subcritical regime, at a Reynolds number$Re=3900$, in order to assess the numerical performances for wall-bounded turbulence. The results are compared to experimental and numerical data available in the literature. Overall, the agreement is satisfactory. By adopting an efficient local refinement strategy together with the enhanced stability features of the entropic model, this method extends the range of applicability of the lattice Boltzmann approach to the solution of realistic fluid dynamics problems, at high Reynolds numbers, involving complex geometries.

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