scholarly journals Models results Comparison of different approaches to turbulence for flow past a heated flat plate

2021 ◽  
Vol 264 ◽  
pp. 01008
Author(s):  
Zafar Malikov ◽  
Dilshod Navruzov ◽  
Xikmatulla Djumayev
Keyword(s):  
Experimental Data ◽  
Flat Plate ◽  
Fluid Model ◽  
Fundamental Difference ◽  
Rans Models ◽  
Two Fluid Model ◽  
Almost All ◽  
Substance Transfer ◽  
Two Fluid ◽  
Good Agreement

This paper compares the results of the well-known Spalart-Allmares (SA) model and the two-fluid model for the flow around a heated flat plate. These models represent different approaches to the problem of turbulence. The SA model is a one-parameter model and a representative of the RANS models. This model is currently the most popular and is used to solve many practical problems. The advantage of this model is that its accuracy is quite good and simple for numerical implementation. Therefore, the SA model is included in almost all the codes of the software package. The two-fluid model used in this work has been developed recently [15]. In the pioneering works, it is shown that the basis for constructing this model is the possibility of representing a turbulent flow in the form of a heterogeneous mixture of two liquids. Therefore, this model is derived from the dynamics of two liquids. In these works, it is also shown that the developed two-fluid model is able to adequately describe complex anisotropic turbulences. The fundamental difference between these two models is that the SA model uses the substance transfer equation, while the two-fluid model uses the dynamics equation. To compare the two models, we compare their numerical results with the known experimental data. It is shown that the results of both models are close to each other and are in good agreement with the experimental data.

Initiation and Statistical Evolution of Horizontal Slug Flow With a Two-Fluid Model

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
A. O. Nieckele ◽  
J. N. E. Carneiro ◽  
R. C. Chucuya ◽  
J. H. P. Azevedo
Keyword(s):  
Experimental Data ◽  
Slug Flow ◽  
Fluid Model ◽  
Subsequent Development ◽  
Complex Flow ◽  
Horizontal Pipes ◽  
Dimensional Version ◽  
Two Fluid Model ◽  
Log Normal ◽  
Two Fluid

In the present work, the onset and subsequent development of slug flow in horizontal pipes is investigated by solving the transient one-dimensional version of the two-fluid model in a high resolution mesh using a finite volume technique. The methodology (named slug-capturing) was proposed before in the literature and the present work represents a confirmation of its applicability in predicting this very complex flow regime. Further, different configurations are analyzed here and comparisons are performed against different sets of experimental data. Predictions for mean slug variables were in good agreement with experimental data. Additionally, focus is given to the statistical properties of slug flows such as shapes of probability density functions of slug lengths (which were represented by gamma and log-normal distributions) as well as the evolution of the first statistical moments, which were shown to be well reproduced by the methodology.

scholarly journals Numerical Study of Shear Banding in Flows of Fluids Governed by the Rolie-Poly Two-Fluid Model via Stabilized Finite Volume Methods

Processes ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 810
Author(s):  
Jade Gesare Abuga ◽  
Tiri Chinyoka
Keyword(s):  
Finite Volume ◽  
Numerical Algorithm ◽  
Numerical Study ◽  
Fluid Model ◽  
Shear Banding ◽  
Numerical Algorithms ◽  
Viscoelastic Fluids ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Good Agreement

The flow of viscoelastic fluids may, under certain conditions, exhibit shear-banding characteristics that result from their susceptibility to unusual flow instabilities. In this work, we explore both the existing shear banding mechanisms in the literature, namely; constitutive instabilities and flow-induced inhomogeneities. Shear banding due to constitutive instabilities is modelled via either the Johnson–Segalman or the Giesekus constitutive models. Shear banding due to flow-induced inhomogeneities is modelled via the Rolie–Poly constitutive model. The Rolie–Poly constitutive equation is especially chosen because it expresses, precisely, the shear rheometry of polymer solutions for a large number of strain rates. For the Rolie–Poly approach, we use the two-fluid model wherein the stress dynamics are coupled with concentration equations. We follow a computational analysis approach via an efficient and versatile numerical algorithm. The numerical algorithm is based on the Finite Volume Method (FVM) and it is implemented in the open-source software package, OpenFOAM. The efficiency of our numerical algorithms is enhanced via two possible stabilization techniques, namely; the Log-Conformation Reformulation (LCR) and the Discrete Elastic Viscous Stress Splitting (DEVSS) methodologies. We demonstrate that our stabilized numerical algorithms accurately simulate these complex (shear banded) flows of complex (viscoelastic) fluids. Verification of the shear-banding results via both the Giesekus and Johnson-Segalman models show good agreement with existing literature using the DEVSS technique. A comparison of the Rolie–Poly two-fluid model results with existing literature for the concentration and velocity profiles is also in good agreement.

Numerical Simulation of Effect of Internals on Slugging Fluidization and Analysis of Nonuniformity Index

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiaoling Wang ◽  
Liang Yu ◽  
Jun Wang
Keyword(s):  
Experimental Data ◽  
Granular Flow ◽  
Fluidized Beds ◽  
Fluid Model ◽  
Two Fluid Model ◽  
Reasonable Prediction ◽  
Two Fluid ◽  
Radial Nonuniformity ◽  
Flow Nonuniformity

Abstract The Two-Fluid Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) was applied to simulate 3-D dense fluidized beds with different complex internals. The slugging fluidization was found in the simulated results. When the internals were placed into the reactors, the simulated results showed that the slugs were broken up and bubbling fluidization was formed instead of slugging fluidization. The formation, growth, size, and shape of bubbles were validated to ensure a reasonable prediction. Furthermore, the simulated pressure drop was compared with the corresponding experimental data from the dense fluidized beds with different complex internals, and good agreements were observed. Finally, the flow nonuniformity in the dense fluidized beds was evaluated by a developed method. This method extended Radial Nonuniformity Index (RNI) to Face Nonuniformity Index (FNI) and Volume Nonuniformity Index (VNI). From the calculated FNI and VNI, the fluidization quality of the fluidized beds was quantitatively judged as follows: No.3 > No.1> No.2 > No.4 > Without Internal.

The thermal conductivity of tin at low temperatures

1955 ◽  
Vol 229 (1179) ◽  
pp. 473-492 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Low Temperatures ◽  
Fluid Model ◽  
Accurate Method ◽  
Resistance Thermometers ◽  
Lattice Waves ◽  
Normal States ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Good Agreement

An account is given of an accurate method of measuring the thermal conductivity of metals between 0·2 and 4°K using carbon aquadag resistance thermometers. Experimental curves are shown for tin specimens of different crystal structure and of varying impurity contents in both superconducting and normal states, and they are analyzed on the basis of the two-fluid model of superconductivity. It appears that at low temperatures the conductivity is mainly due to the lattice, since the observed temperature variation for all specimens is consistent with a T 3 law at sufficiently low temperatures. Good agreement is obtained between the effective mean free paths of the lattice waves and the values expected from the rod dimensions and crystal sizes. The electronic contribution to the thermal conduction in the superconducting state falls very rapidly below T c , and, to a first approximation, the ratio of this contribution to that in the normal state is a function of temperature and not of impurity. The effects of magnetic fields on measurements of thermal conductivity are also briefly discussed and it is shown that the results may be complicated by frozen-in flux.

scholarly journals Investigation on Bubble Diameter Distribution in Upward Flow by the Two-Fluid and Multi-Fluid Models

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5776
Author(s):  
Yongzhong Zeng ◽  
Weilin Xu
Keyword(s):  
Experimental Data ◽  
Volume Fraction ◽  
Fluid Model ◽  
Bubble Diameter ◽  
Diameter Distribution ◽  
Bubble Flow ◽  
Calculation Results ◽  
Two Fluid Model ◽  
Gas Volume ◽  
Two Fluid

Bubble flow can be simulated by the two-fluid model and the multi-fluid model based on the Eulerian method. In this paper, the gas phase was further divided into several groups of dispersed phases according to the diameter by using the Eulerian-Eulerian (E-E) multi-fluid model. The diameters of bubbles in each group were considered to be the same, and their distributions were reorganized according to a specific probability density function. The experimental data of two kinds of bubble flow with different characteristics were used to verify the model. With the help of the open-source CFD software, OpenFOAM-7.x (OpenFOAM-7.0, produced by OpenFOAM foundation, Reading, England), the influences of the group number, the probability distribution function, and the parameters of different bubble diameters on the calculation results were studied. Meanwhile, the numerical simulation results were compared with the two-fluid model and the experimental data. The results show that for the bubble flow with the unimodal distribution, both the multi-fluid model and the two-fluid model can obtain the distribution of gas volume fraction along the pipe radius. The calculation results of the multi-fluid model agree with the experimental data, while those of the two-fluid model differ greatly from the experimental data, which verifies the advantage of the multi-fluid model in calculating the distribution of gas volume fraction in the polydisperse bubble flow. Meanwhile, the multi-fluid model can be used to accurately predict the distribution of the parameters of each phase of the bubble flow if the reasonable bubble diameter distribution is provided and the appropriate interphase force calculation model is determined.

Simulation of the Critical Flashing Flow With the Transient 1D Two-Fluid Model

Volume 3 ◽  
2004 ◽  
Author(s):  
Janez Gale ◽  
Iztok Tiselj
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Fluid Model ◽  
Computer Code ◽  
Relaxation Model ◽  
Moby Dick ◽  
Two Fluid Model ◽  
The Mathematical Model ◽  
Two Fluid

The paper presents results of the 1D computer code WAHA, developed for the water hammer simulations, applied for the simulation of the critical flashing flow in the “Super Moby Dick” convergent-divergent nozzle. The mathematical model of the code is briefly introduced with special emphasis on applied dispersed flow homogeneous-relaxation model of inter-phase heat and mass transfer. The results of the simulations of the critical flashing flow are compared to the experimental data.

Development and Verification Models of Vertical Stratification, Dryout and Slug Boiling of Superheated Sodium for LMFBR Safety Analyses

2014 ◽  
Author(s):  
Nikolay A. Pribaturin ◽  
Eduard V. Usov ◽  
Ivan G. Kudashov ◽  
Marina E. Kuznetsova ◽  
Anton A. Butov ◽  
...  
Keyword(s):  
Experimental Data ◽  
Fluid Model ◽  
Vertical Stratification ◽  
Theoretical Studies ◽  
Pressure Gradients ◽  
Vapor Quality ◽  
Simulated Experiment ◽  
Two Fluid Model ◽  
Experimental And Theoretical Studies ◽  
Two Fluid

A new model which describes the dynamics of a vertically stratified flow correctly within the limits of a single-pressure two-fluid model has been developed. The model is based on the modification of finite-differences of convective terms and pressure gradients taking into account a distinct interface. We propose to use the vapor quality as a criterion for the onset of dryout. The choice of the criterion is based on the analysis of experimental and theoretical studies. To determine the boundary vapor quality we used the correlation xcr = 1.26·G0.2, which was found from experimental data fit. A review of articles has shown that for today it is impossible to predict correct superheat value. Therefore the superheat value was determined as a parameter of the model from the experimental data of a particular simulated experiment. Thus a boiling up regime was selected. The model described in this paper allows us to calculate the boiling up of sodium under the superheat conditions as well as problems of the evolution of the vapor volume. The verification of the models was done by using the SOCRAT-BN code [1]. SOCRAT-BN is a coupled code which consists of modules for calculation of damage and melting of a reactor’s core, thermohydraulic processes and neutron physics. The models of vertical stratification, dryout and slug boiling of superheated sodium are described in details in this paper. Also we present the results of verification for the models within analytic tests and experimental data.

A Two-Fluid Model for Reacting Turbulent Two-Phase Flows

1994 ◽  
Vol 116 (2) ◽  
pp. 427-435 ◽  
Author(s):  
S. H. Chan ◽  
M. M. M. Abou-Ellail
Keyword(s):  
Experimental Data ◽  
Fluid Transport ◽  
Fluid Model ◽  
Mixture Fraction ◽  
Beta Function ◽  
Reacting Flows ◽  
Transport Equations ◽  
Two Phase ◽  
Two Fluid Model ◽  
Two Fluid

A reacting two-fluid model, based on the solution of separate transport equations for reacting gas-liquid two-phase flow, is presented. New time-mean transport equations for two-phase mixture fraction f and its variance g are derived. The new two-fluid transport equations for f and g are useful for two-phase reacting flows in which phases strongly interact. They are applicable to both submerged and nonsubmerged combustion. A pdf approach to the reaction process is adopted. The mixture fraction pdf assumes the shape of a beta function while the instantaneous thermochemical properties are computed from an equilibrium model. The proposed two-fluid model is verified by predicting turbulent flow structures of an n-pentane spray flame and a nonreacting bubbly jet flow for which experimental data exist. Good agreement is found between the predictions and the corresponding experimental data.

Numerical Solution of Wavy-Stratified Fluid-Fluid Flow With the One-Dimensional Two-Fluid Model: Stability, Boundedness, Convergence and Chaos

2014 ◽  
Author(s):  
William D. Fullmer ◽  
Alejandro Clausse ◽  
Avinash Vaidheeswaran ◽  
Martin A. Lopez de Bertodano
Keyword(s):  
Experimental Data ◽  
Fluid Flow ◽  
Chaotic Behavior ◽  
Fluid Model ◽  
Linear Instability ◽  
Energy Transfer Mechanism ◽  
One Dimensional ◽  
Two Fluid Model ◽  
The One ◽  
Two Fluid

In this paper the one-dimensional two-fluid model is used to dynamically simulate slightly inclined fluid-fluid flow in a rectangular channel. By that, it is specifically meant that the solutions exhibit a wavy pattern arising from the inherent instability of the model. The conditions and experimental data of Thorpe (1969) are used for comparison. The linear instability of the model is regularized, i.e., made well-posed, with surface tension and axial turbulent stress with a simple turbulent viscosity model. Nonlinear analysis in an infinite domain demonstrates for the first time one-dimensional two-fluid model chaotic behavior in addition to limit cycle behavior and asymptotic stability. The chaotic behavior is a consequence of the linear instability (the long wavelength energy source) the nonlinearity (the energy transfer mechanism) and the viscous dissipation (the short wavelength energy sink). Since the model is chaotic, solutions exhibit sensitive dependence on initial conditions which results in non-convergence of particular solutions with grid refinement. However, even chaotic problems have invariants and the ensemble averaged water void fraction amplitude spectrum is used to demonstrate convergence and make comparisons to the experimental data.

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