Influence of turbulence integral length scale on aerostatic coefficients of bridge sections

2020 ◽  
pp. 136943322097943
Author(s):  
Cheng Pei ◽  
Cunming Ma ◽  
Junxin Wang ◽  
Xin Chen ◽  
Fan Chen
Keyword(s):  
Active Control ◽  
Simulation Method ◽  
Uniform Flow ◽  
Integral Length Scale ◽  
Length Scale ◽  
Wind Fields ◽  
Control Grid ◽  
Integral Scale ◽  
Box Girder ◽  
Integral Scales

This study investigates the influence of turbulence on the aerostatic coefficients of typical bridges by obtaining force measurements via the simulation of turbulence in wind tunnels. The traditional simulation method for turbulence based on spires and grilles cannot be employed for the accurate simulation of the large integral scale of turbulence in an actual wind field. Thus, in this study, the turbulence integral length scale was effectively increased using an active control grid. The wind fields of different turbulence integral scales were generated by controlling the vibration frequency of the active control grid. The aerostatic coefficients of five typical bridge sections (single-box girder, twin-box girder, truss girder, edge girder, and edge-box girder) were measured under turbulent and uniform flow. The test results were compared and analyzed, which revealed that the drag coefficients increased in accordance with a decrease in the reduced turbulence integral length scale, and they were lower under turbulent flow than under uniform flow.

Span-wise coherence of fluctuating forces on twin bridge decks and the turbulence effect

2019 ◽  
Vol 22 (15) ◽  
pp. 3207-3221 ◽  
Author(s):  
Jinlin Xia ◽  
Ke Li ◽  
Yaojun Ge
Keyword(s):  
Turbulence Intensity ◽  
Low Frequency ◽  
Correlation Coefficients ◽  
Linear Functions ◽  
Frequency Curve ◽  
Integral Scale ◽  
Box Girder ◽  
Pressure Testing ◽  
Integral Scales ◽  
Turbulence Effect

Unlike the adequate researches on a single-box girder, the understanding of span-wise force correlation on twin decks is limited. A sectional model pressure testing of a widely slotted twin-box girder has been carried out in the background of a 5000-m-long bridge. Three grid configurations separated the effect of turbulence intensity and integral scale. Seven test sections were set on the model with totally 532 pressure taps. After the correction of pressure distortion, the correlation coefficients and integral scales of forces were compared on the leeward and the windward decks. Root coherence of lift was analyzed in detail at several separation distances. Pressure signals were used to explain why force coherence is stronger than flow and why “low frequency curve” phenomenon occurs. Considering the shortage of existing expressions, a simple but efficient form was proposed which can fit the coherence on the leeward, the windward, and the whole decks. The parameters in different flows can be reconstructed by linear functions which benefits new model’s application. In the final, the influences of turbulence intensity and integral scale on force coherence were illustrated.

Thermo-mechanical coupling particle simulation of three-dimensional large-scale non-isothermal problems

2017 ◽  
Vol 34 (5) ◽  
pp. 1551-1571 ◽  
Author(s):  
Ming Xia
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Simulation Method ◽  
Particle Simulation ◽  
Similarity Criteria ◽  
Particle Model ◽  
Length Scale ◽  
Content Type ◽  
Mechanical Coupling ◽  
Particle Simulation Method

Purpose The main purpose of this paper is to present a comprehensive upscale theory of the thermo-mechanical coupling particle simulation for three-dimensional (3D) large-scale non-isothermal problems, so that a small 3D length-scale particle model can exactly reproduce the same mechanical and thermal results with that of a large 3D length-scale one. Design/methodology/approach The objective is achieved by following the scaling methodology proposed by Feng and Owen (2014). Findings After four basic physical quantities and their similarity-ratios are chosen, the derived quantities and its similarity-ratios can be derived from its dimensions. As the proposed comprehensive 3D upscale theory contains five similarity criteria, it reveals the intrinsic relationship between the particle-simulation solution obtained from a small 3D length-scale (e.g. a laboratory length-scale) model and that obtained from a large 3D length-scale (e.g. a geological length-scale) one. The scale invariance of the 3D interaction law in the thermo-mechanical coupled particle model is examined. The proposed 3D upscale theory is tested through two typical examples. Finally, a practical application example of 3D transient heat flow in a solid with constant heat flux is given to illustrate the performance of the proposed 3D upscale theory in the thermo-mechanical coupling particle simulation of 3D large-scale non-isothermal problems. Both the benchmark tests and application example are provided to demonstrate the correctness and usefulness of the proposed 3D upscale theory for simulating 3D non-isothermal problems using the particle simulation method. Originality/value The paper provides some important theoretical guidance to modeling 3D large-scale non-isothermal problems at both the engineering length-scale (i.e. the meter-scale) and the geological length-scale (i.e. the kilometer-scale) using the particle simulation method directly.

scholarly journals The non-equilibrium region of grid-generated decaying turbulence

2014 ◽  
Vol 744 ◽  
pp. 5-37 ◽  
Author(s):  
P. C. Valente ◽  
J. C. Vassilicos
Keyword(s):  
Turbulent Flows ◽  
Integral Scale ◽  
Dissipation Coefficient ◽  
Integral Scales ◽  
Usual Equilibrium ◽  
Decaying Turbulence ◽  
Equilibrium Region ◽  
Non Equilibrium

AbstractThe previously reported non-equilibrium dissipation law is investigated in turbulent flows generated by various regular and fractal square grids. The flows are documented in terms of various turbulent profiles which reveal their differences. In spite of significant inhomogeneity and anisotropy differences, the new non-equilibrium dissipation law is observed in all of these flows. Various transverse and longitudinal integral scales are measured and used to define the dissipation coefficient $C_{\varepsilon }$. It is found that the new non-equilibrium dissipation law is not an artefact of a particular choice of the integral scale and that the usual equilibrium dissipation law can actually coexist with the non-equilibrium law in different regions of the same flow.

scholarly journals Simulation and Analysis of SAR Images of Oceanic Shear-Wave-Generated Eddies

Sensors ◽  
2019 ◽  
Vol 19 (7) ◽  
pp. 1529 ◽  
Author(s):  
Yuhang Wang ◽  
Min Yang ◽  
Jinsong Chong
Keyword(s):  
Shear Wave ◽  
Quantitative Methods ◽  
Surface Current ◽  
Simulation Method ◽  
Surface Pattern ◽  
Wind Fields ◽  
Sar Images ◽  
Qualitative And Quantitative Methods ◽  
Oceanic Eddies ◽  
Simulated Images

Synthetic Aperture Radar (SAR) is widely used in oceanic eddies research. High-resolution SAR images should be useful in revealing eddy features and investigating the eddy imaging mechanism. However, SAR imaging is affected by various radar parameters and environmental factors, which makes it quite difficult to learn directly from SAR eddy images. In order to interpret and evaluate eddy images, developing a proper simulation method is necessary. However, seldom has a SAR simulation method for oceanic eddies, especially for shear-wave-generated eddies, been established. As a step forward, we propose a simulation method for oceanic shear-wave-generated eddies. The Burgers-Rott vortex model is used to specify the surface current field of the simulated eddies. Images are then simulated for a range of different radar frequencies, radar look directions, wind speeds, and wind directions. The results show that the simulated images are consistent with actual SAR images. The effects of different radar parameters and wind fields on SAR eddy imaging are analyzed by qualitative and quantitative methods. Overall, the simulated images produce a surface pattern and brightness variations with characteristics resembling actual SAR images of oceanic eddies.

Results of an attempt to generate a homogeneous turbulent shear flow

1966 ◽  
Vol 25 (1) ◽  
pp. 97-120 ◽  
Author(s):  
W. G. Rose
Keyword(s):  
Shear Flow ◽  
Test Section ◽  
Energy Spectra ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Hot Wire ◽  
Effective Distance ◽  
Integral Scale ◽  
Point Space ◽  
Integral Scales

An approximately homogeneous turbulent shear flow is generated in an open-return wind tunnel test-section by a plane parallel-rod grid of uniform rod diameter and non-uniform rod spacing. The grid design is based upon an analysis by Owen & Zienkiewicz (1957). Hot-wire measurements taken in this flow include mean velocities, component turbulence intensities, shear and two-point space correlations, and energy spectra. In addition, microscales, obtained both from instantaneous time derivatives of the hot-wire signal and from two-point space correlations, and integral scales, calculated both from correlations and energy spectra, are reported.Based upon these results, it is concluded that, far enough away from the grid and the test-section wall boundary layers:The turbulence intensities are maintained at uniform values by the nearly constant mean shear.The turbulent shear stress approaches an asymptotic value.Measured two-point space correlation coefficients and one-dimensional energy spectra attain self-preserving forms.When distance downstream of the grid is measured in terms of the number of ‘local’ grid rod spacings, (see discussion of microscales obtained from time derivatives), the Taylor microscale defined by the correlation coefficientRuu(rX, 0, 0) grows linearly with this ‘effective’ distance over most of the region measured.The limited number of integral scale determinations and experimental uncertainty allow only the statements that the magnitude of the longitudinal scale is roughly one-eighth the lateral dimension of the square test-section and tends to increase slightly with ‘effective’ distance from the grid.The lateral integral scales are approximately one-half the longitudinal scales and also increases with distance from the grid.The integral scale which characterizes the size of the eddy primarily responsible for momentum transfer is roughly one-tenth the test-section lateral dimension (measured at one point only).

Study of Energy Spectra of Turbulence by the Vortex Method

2004 ◽  
Author(s):  
Yoshifumi Ogami
Keyword(s):  
Shear Layer ◽  
Wave Length ◽  
Vortex Method ◽  
Energy Spectra ◽  
Integral Scale ◽  
Velocity Fluctuations ◽  
Integral Scales ◽  
The Given

The energy spectra produced by the vortex method are studied. The strengths of the vortices are determined so that the energy spectra correspond to the given target spectra for two different integral scales. Velocity fluctuations produced by the simulation of vortex shear layer are obtained and energy spectra of these fluctuations are examined. It is found that in the case of the larger integral scale, the spectra almost agree with the target in the range up to the cut-off wave length, and that in the case of the smaller scale, the deviation of the spectra from the target is quite large.

Lateral dispersion in random cylinder arrays at high Reynolds number

2008 ◽  
Vol 600 ◽  
pp. 339-371 ◽  
Author(s):  
YUKIE TANINO ◽  
HEIDI M. NEPF
Keyword(s):  
Turbulence Intensity ◽  
Turbulent Diffusion ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Laboratory Data ◽  
Integral Length Scale ◽  
Length Scale ◽  
Linear Superposition ◽  
Cylinder Diameter ◽  
The Mean

Laser-induced fluorescence was used to measure the lateral dispersion of passive solute in random arrays of rigid, emergent cylinders of solid volume fraction φ=0.010–0.35. Such densities correspond to those observed in aquatic plant canopies and complement those in packed beds of spheres, where φ≥0.5. This paper focuses on pore Reynolds numbers greater than Res=250, for which our laboratory experiments demonstrate that the spatially averaged turbulence intensity and Kyy/(Upd), the lateral dispersion coefficient normalized by the mean velocity in the fluid volume, Up, and the cylinder diameter, d, are independent of Res. First, Kyy/(Upd) increases rapidly with φ from φ =0 to φ=0.031. Then, Kyy/(Upd) decreases from φ=0.031 to φ=0.20. Finally, Kyy/(Upd) increases again, more gradually, from φ=0.20 to φ=0.35. These observations are accurately described by the linear superposition of the proposed model of turbulent diffusion and existing models of dispersion due to the spatially heterogeneous velocity field that arises from the presence of the cylinders. The contribution from turbulent diffusion scales with the mean turbulence intensity, the characteristic length scale of turbulent mixing and the effective porosity. From a balance between the production of turbulent kinetic energy by the cylinder wakes and its viscous dissipation, the mean turbulence intensity for a given cylinder diameter and cylinder density is predicted to be a function of the form drag coefficient and the integral length scale lt. We propose and experimentally verify that lt=min{d, 〈sn〉A}, where 〈sn〉A is the average surface-to-surface distance between a cylinder in the array and its nearest neighbour. We farther propose that only turbulent eddies with mixing length scale greater than d contribute significantly to net lateral dispersion, and that neighbouring cylinder centres must be farther than r* from each other for the pore space between them to contain such eddies. If the integral length scale and the length scale for mixing are equal, then r*=2d. Our laboratory data agree well with predictions based on this definition of r*.

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