A Phenomenological Turbulence Model and its Application to Heat Transport in Infinite Rod Arrays With Axial Turbulent Flow

1975 ◽  
Vol 97 (2) ◽  
pp. 231-237 ◽  
Author(s):  
H. Ramm ◽  
K. Johannsen
Keyword(s):  
Turbulent Flow ◽  
Turbulence Model ◽  
Energy Transport ◽  
Internal Flow ◽  
Wide Range ◽  
Line Flow ◽  
Plain Tube ◽  
Prandtl Numbers ◽  
Good Agreement ◽  
Model Approach

The “turbulence-model” approach has been applied to solve the Reynolds equations of momentum and energy for an incompressible, steady-state, one-directional, hydrodynamically fully developed, turbulent internal flow. To close the turbulence equations, a phenomenological model of turbulent motion and energy transport has been developed which includes anisotropy effects. Predictions made for the turbulent diffusivities of heat in turbulent flow in a plain tube are found to be in good agreement with the experimental data over a wide range of Reynolds and Prandtl numbers. Corresponding results for infinite rod arrays with in-line flow also compare favorably with the few reliable data available.

scholarly journals Direct Numerical Simulation of separated turbulent flow in axisymmetric diffuser

2021 ◽  
Vol 2103 (1) ◽  
pp. 012214
Author(s):  
A S Stabnikov ◽  
D K Kolmogorov ◽  
A V Garbaruk ◽  
F R Menter
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Model Improvement ◽  
Good Agreement

Abstract Direct numerical simulation (DNS) of the separated flow in axisymmetric CS0 diffuser is conducted. The obtained results are in a good agreement with experimental data of Driver and substantially supplement them. Along with other data, eddy viscosity extracted from performed DNS could be used for RANS turbulence model improvement.

Flow Between Contrarotating Disks

1995 ◽  
Vol 117 (2) ◽  
pp. 298-305 ◽  
Author(s):  
X. Gan ◽  
M. Kilic ◽  
J. M. Owen
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Boundary Layers ◽  
Turbulence Model ◽  
Computational Study ◽  
Reynolds Numbers ◽  
The Core ◽  
Wide Range ◽  
Type Flow ◽  
Radial Outflow

The paper describes a combined experimental and computational study of laminar and turbulent flow between contrarotating disks. Laminar computations produce Batchelor-type flow: Radial outflow occurs in boundary layers on the disks and inflow is confined to a thin shear layer in the midplane; between the boundary layers and the shear layer, two contrarotating cores of fluid are formed. Turbulent computations (using a low-Reynolds-number k–ε turbulence model) and LDA measurements provide no evidence for Batchelor-type flow, even for rotational Reynolds numbers as low as 2.2 × 104. While separate boundary layers are formed on the disks, radial inflow occurs in a single interior core that extends between the two boundary layers; in the core, rotational effects are weak. Although the flow in the core was always found to be turbulent, the flow in the boundary layers could remain laminar for rotational Reynolds numbers up to 1.2 × 105. For the case of a superposed outflow, there is a source region in which the radial component of velocity is everywhere positive; radially outward of this region, the flow is similar to that described above. Although the turbulence model exhibited premature transition from laminar to turbulent flow in the boundary layers, agreement between the computed and measured radial and tangential components of velocity was mainly good over a wide range of nondimensional flow rates and rotational Reynolds numbers.

Flow Between Contra-Rotating Discs

1993 ◽  
Author(s):  
Xiaopeng Gan ◽  
Muhsin Kilic ◽  
J. Michael Owen
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Boundary Layers ◽  
Turbulence Model ◽  
Reynolds Numbers ◽  
The Core ◽  
Rotating Discs ◽  
Wide Range ◽  
Type Flow ◽  
Radial Outflow

The paper describes a combined experimental and computational study of laminar and turbulent flow between contra-rotating discs. Laminar computations produce Batchelor-type flow: radial outflow occurs in boundary layers on the discs and inflow is confined to a thin shear layer in the mid-plane; between the boundary layers and the shear layer, two contra-rotating cores of fluid are formed. Turbulent computations (using a low-Reynolds-number k-ε turbulence model) and LDA measurements provide no evidence for Batchelor-type flow, even for rotational Reynolds numbers as low as 2.2 × 104. Whilst separate boundary layers are formed on the discs, radial inflow occurs in a single interior core that extends between the two boundary layers; in the core, rotational effects are weak. Although the flow in the core was always found to be turbulent, the flow in the boundary layers could remain laminar for rotational Reynolds numbers up to 1.2 × 105. For the case of a superposed outflow, there is a source region in which the radial component of velocity is everywhere positive; radially outward of this region, the flow is similar to that described above. Although the turbulence model exhibited premature transition from laminar to turbulent flow in the boundary layers, agreement between the computed and measured radial and tangential components of velocity was mainly good over a wide range of nondimensional flow rates and rotational Reynolds numbers.

Friction Reduction in Turbulent Journal Bearings by Highpolymers

1980 ◽  
Vol 102 (4) ◽  
pp. 439-444 ◽  
Author(s):  
H. Fukayama ◽  
M. Tanaka ◽  
Y. Hori
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Polymer Solution ◽  
Friction Factor ◽  
Polymer Concentration ◽  
Journal Bearings ◽  
Friction Reduction ◽  
Dilute Polymer Solutions ◽  
Wide Range ◽  
Good Agreement

The friction reduction by dilute polymer solutions is investigated experimentally in turbulent journal bearings. The effects of polymer substances, polymer concentration, bearing clearance, and journal eccentricity on friction reduction are examined over the wide range of Reynolds number in the superlaminar regime. In the experiments, the friction of polymer solution is less than 40 percent of that of Newtonian turbulent flow under the best conditions. The calculated friction factor for the Couette flow is in good agreement with the corresponding measured one. Degradation of highpolymer is also investigated experimentally, and is found to be affected by polymer concentration.

Modeling of mass transfer in biofilms in oscillatory flow conditions using k-ɛ turbulence model

2003 ◽  
Vol 3 (1-2) ◽  
pp. 201-207
Author(s):  
H. Nagaoka ◽  
T. Nakano ◽  
D. Akimoto
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Turbulence Model ◽  
Uptake Rate ◽  
Oscillatory Flow ◽  
Substrate Uptake ◽  
Flow Conditions ◽  
Mass Transfer Mechanism ◽  
Substrate Uptake Rate ◽  
Good Agreement

The objective of this research is to investigate mass transfer mechanism in biofilms under oscillatory flow conditions. Numerical simulation of turbulence near a biofilm was conducted using the low Reynold’s number k-ɛ turbulence model. Substrate transfer in biofilms under oscillatory flow conditions was assumed to be carried out by turbulent diffusion caused by fluid movement and substrate concentration profile in biofilm was calculated. An experiment was carried out to measure velocity profile near a biofilm under oscillatory flow conditions and the influence of the turbulence on substrate uptake rate by the biofilm was also measured. Measured turbulence was in good agreement with the calculated one and the influence of the turbulence on the substrate uptake rate was well explained by the simulation.

scholarly journals Separate Universe calibration of the dependence of halo bias on cosmic web anisotropy

2020 ◽  
Vol 499 (3) ◽  
pp. 4418-4431 ◽  
Author(s):  
Sujatha Ramakrishnan ◽  
Aseem Paranjape
Keyword(s):  
Dark Matter ◽  
High Precision ◽  
Gaussian Distribution ◽  
Initial Perturbation ◽  
Analytical Framework ◽  
Web Environment ◽  
Wide Range ◽  
Galaxy Assembly ◽  
Very High ◽  
Good Agreement

ABSTRACT We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias b1 and b2 on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy α to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work that exploits the near-lognormal shape of the distribution of α and results in very high precision calibrations. We present convenient fitting functions for the dependence of b1 and b2 on α over a wide range of halo mass for redshifts 0 ≤ z ≤ 1. Our calibration of b2(α) is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results that showed that α is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of b1 and b2 on any such secondary property that has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using α as a segregating variable in multitracer analyses.

Evaluation of Trinder's Glucose Oxidase Method for Measuring Glucose in Serum and Urine

1975 ◽  
Vol 21 (12) ◽  
pp. 1754-1760 ◽  
Author(s):  
John A Lott ◽  
Kathie Turner
Keyword(s):  
Glucose Oxidase ◽  
Oxidase Activity ◽  
Color Reaction ◽  
Critical Variable ◽  
Wide Range ◽  
Serum And Urine ◽  
Good Agreement

Abstract Trinder's method for glucose has nearly all the attributes of an ideal automated colorimetric glucose oxidase procedure. The chemicals used in the color reaction with peroxidase are readily available, the solutions are stable and can be prepared by the user, the method is highly specific and largely free of interferences, the sensitivity can be adjusted by the user to cover a wide range of glucose concentrations, and the reagents are not hazardous. We found very good agreement between results by this method and by the hexokinase and Beckman Glucose Analyzer methods. The method has been modified and adapted to the AutoAnalyzer I and SMA 6/60 (Technicon) with manifolds that give very little interaction between specimens. A study of the method by the simplex technique revealed that the glucose oxidase activity in the reagent is the most critical variable.

Estimation of the Thermodynamic Properties of Branched Hydrocarbons

2000 ◽  
Vol 122 (3) ◽  
pp. 147-152 ◽  
Author(s):  
Hui He ◽  
Mohamad Metghalchi ◽  
James C. Keck
Keyword(s):  
Thermodynamic Properties ◽  
Degrees Of Freedom ◽  
Statistical Thermodynamic ◽  
Motion Modes ◽  
Branched Alkanes ◽  
Branched Hydrocarbons ◽  
Wide Range ◽  
On Line ◽  
Kinetic Calculations ◽  
Good Agreement

A simple model has been developed to estimate the sensible thermodynamic properties such as Gibbs free energy, enthalpy, heat capacity, and entropy of hydrocarbons over a wide range of temperatures with special attention to the branched molecules. The model is based on statistical thermodynamic expressions incorporating translational, rotational and vibrational motions of the atoms. A method to determine the number of degrees of freedom for different motion modes (bending and torsion) has been established. Branched rotational groups, such as CH3 and OH, have been considered. A modification of the characteristic temperatures for different motion mode has been made which improves the agreement with the exact values for simple cases. The properties of branched alkanes up to 2,3,4,-trimthylpentane have been calculated and the results are in good agreement with the experimental data. A relatively small number of parameters are needed in this model to estimate the sensible thermodynamic properties of a wide range of species. The model may also be used to estimate the properties of molecules and their isomers, which have not been measured, and is simple enough to be easily programmed as a subroutine for on-line kinetic calculations. [S0195-0738(00)00902-X]

scholarly journals Rate Equation Modelling of Nonlinear Dynamics in Directly Modulated Multiple Quantum Well Laser Diodes

VLSI Design ◽  
1998 ◽  
Vol 8 (1-4) ◽  
pp. 355-360 ◽  
Author(s):  
Stephen Bennett ◽  
Christopher M. Snowden ◽  
Stavros Iezekiel
Keyword(s):  
Nonlinear Dynamics ◽  
Quantum Well ◽  
Multiple Quantum Well ◽  
Period Doubling ◽  
Rate Equations ◽  
Multiple Quantum ◽  
Quantum Well Laser ◽  
Wide Range ◽  
Multiple Quantum Well Laser ◽  
Good Agreement

A theoretical (using rate equations) and experimental study of the nonlinear dynamics of a distributed feedback multiple quantum well laser diode is presented. The analysis is performed under direct modulation. Period doubling and period tripling are identified in both the measurements and simulations. Period doubling is found over a wide range of modulation frequencies in the laser. Computational results using rate equations show good agreement with the experimental results.

scholarly journals DFT calculation and assignment of vibrational spectra of aryl and alkyl chlorophosphates

2014 ◽  
Vol 12 (2) ◽  
pp. 153-163
Author(s):  
Viktor Anishchenko ◽  
Vladimir Rybachenko ◽  
Konstantin Chotiy ◽  
Andrey Redko
Keyword(s):  
Vibrational Spectra ◽  
Basis Sets ◽  
Heavy Atoms ◽  
Wide Range ◽  
Complete Assignment ◽  
Key Factor ◽  
Polarization Functions ◽  
Experimental Values ◽  
Semi Empirical ◽  
Good Agreement

AbstractDFT calculations of vibrational spectra of chlorophosphates using wide range of basis sets and hybrid functionals were performed. Good agreement between calculated and experimental vibrational spectra was reached by the combination of non-empirical functional PBE0 with both middle and large basis sets. The frequencies of the stretching vibrations of the phosphate group calculated using semi-empirical functional B3LYP for all basis sets deviate significantly from the experimental values. The number of polarization functions on heavy atoms was shown to be a key factor for the calculation of vibrational frequencies of organophosphates. The importance of consideration of all the stable rotamers for a complete assignment of fundamental modes was shown.

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