Turbulence Intensity and Turbulent Kinetic Energy Parameters over a Heterogeneous Terrain of Loess Plateau

A deep understanding of turbulence structure is important for investigating the characteristics of the atmospheric boundary layer,especially over heterogeneous terrain.In the present study,turbulence intensity and turbulent kinetic energy（TKE）parameters are analyzed for different conditions with respect to stability,wind direction and wind speed over a valley region of the Loess Plateau of China during December 2003 and January 2004.The purpose of the study is to examine whether the observed turbulence intensity and TKE parameters satisfy Monin–Obukhov similarity theory（MOST）,and analyze the wind shear effect on,and thermal buoyancy function of,the TKE,despite the terrain heterogeneity.The results demonstrate that the normalized intensity of turbulence follows MOST for all stability in the horizontal and vertical directions,as well as the normalized TKE in the horizontal direction.The shear effect of the wind speed in the Loess Plateau region is strong in winter and could enhance turbulence for all stability conditions.During daytime,the buoyancy and shear effect together constitute the generation of TKE under unstable conditions.At night,the contribution of buoyancy to TKE is relatively small,and mechanical shearing is the main production form of turbulence.

Consistency of the directionality of partially coherent beams in turbulence expressed in terms of the angular spread and the far-field average intensity

Under the quadratic approximation of the Rytov＇s phase structure function, this paper derives the general closed-form expressions for the mean-squared width and the angular spread of partially coherent beams in turbulence. It finds that under a certain condition different types of partially coherent beams may have the same directionality as a fully coherent Gaussian beam in free space and also in atmospheric turbulence if the angular spread is chosen as the characteristic parameter of beam directionality. On the other hand, it shows that generally, the directionality of partially coherent beams expressed in terms of the angular spread is not consistent with that in terms of the normalized far-field average intensity distribution in free space, but the consistency can be achieved due to turbulence.

ATMOSPHERIC TURBULENCE INTENSITY AND DIFFUSION PARAMETER OVER COMPLICATED TOPOGRAPHY OF EASTERN GUANGDONG

Based on observations by a dual-theodolite anemometer tracking balanced balloons and an American Gill UVW anemograph for complicated underlying surface in Meizhou, eastern Guangdong, turbulent fluctuations of the Lagrangian and Eulerian systems are determined for the area. Following the Taylor formular in respect to a few reference frames, horizontal and vertical turbulence intensity and atmospheric diffusion parameters σy and σx are then computed and compared with those obtained by the PG method and BNL experiments. It is found that within heights less than 100 m above the ground σy and σx are larger than values of PG and BNL with all conditions of stability and stratification.

Long-and short-term average intensity for multi-Gaussian beam with a common axis in turbulence

With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.

Effect of turbulence intensity on airfoil flow:numerical simulations and experimental measurements

The effect of the turbulence intensity of the oncoming stream on the aerodynamic characteristics of the NACA-0012 airfoil is investigated by a direct numerical simulation. The numerical results are found to be consistent with the experimental measurements. Based on the finite spectral QUICK scheme, the simulation gets the high accuracy results. Both the simulation and the experiment reveal that the airfoil stall does not exist for the low turbulence intensity, however, occurs when the turbulence intensity increases sufficiently. Besides, the turbulence intensity has a significant effect on both the airfoil boundary layer and the separated shear layer.

Numerical Analysis of the Influence of Turbulence Intensity on Iced Conductors Gallop Phenomena

Turbulence is expected to play a relevant role in the so-called conductor gallop phenomena,namely,the high-amplitude,low-frequency oscillation of overhead power lines due to the formation of ice structures and the ensu-ing effect that wind can have on these.In this work,the galloping time history of a wire with distorted(fixed in time)shape due to the formation of ice is analyzed numerically in the frame of afluid-solid coupling method for different wind speeds and levels of turbulence.The results show that the turbulence intensity has a moderate effect on the increase of the conductor’s aerodynamic lift and drag coefficients due to ice accretion;nevertheless,the corresponding changes in the torsion coefficient are very significant and complicated.A high turbulence intensity can affect the torsion coefficient in a certain range of attack angles and increase the torsion angle of the conductor.Through comparison of the galloping phenomena for different wind velocities,it is found that the related amplitude grows significantly with an increase of the wind speed.For a relatively large wind speed,the galloping amplitude is more sensitive to the turbulence intensity.Moreover,the larger the turbulence intensity,the larger the conductor’s vertical and horizontal galloping amplitudes after icing.The torsion angle also increases with an increase in the wind speed and turbulence intensity.

Updating empirical results of wind loads on cooling towers for turbulence intensity effects

Variations of wind effects on large cooling towers observed at different turbulence intensities for our previous full-scale measurements might be caused by the inherent uncertainties in our physical experiments.Accordingly,the one-way analysis of variance(ANOVA)technique is employed for analyzing the data measured on the prototype Pengcheng cooling tower.Because ANOVA indicates that the variations of full-scale wind effects are basically the effects of turbulence intensity,the empirical results of wind loads on cooling towers obtained by generalizing physical experimental data without considering the turbulence intensity effects are updated using model test results obtained in multiple flow fields.The empirical fluctuating wind pressure distribution is updated based on the fact that the fluctuating wind pressure coefficient linearly increases with the increase in the turbulence intensity,and the empirical formulae of the spectra and the coherences is updated based on conservative assumptions.Comparisons of the empirical results and full-scale measurement data suggest that the original empirical results are either too conservative or unsafe for use.However,economic efficiency and conservativeness will be balanced if the updated empirical results are employed for the wind engineering design.

Near ground wind characteristics during typhoon Meari:Turbulence intensities, gust factors, and peak factors

Wind data were collected during the 2011 typhoon Meari at heights of 10, 20, 30, and 40 m above the ground using a 40 m high anemometer tower in the coastal area near Shanghai Pudong International Airport. Wind speeds and directions, turbulence intensities, gust factors, and peaks were analyzed using the time records of wind speed. The results show that turbulence intensity components in longitudinal, lateral, and vertical directions decrease with mean wind speed, regardless of elevations, and the turbulence intensities are in a linear relationship with mean wind speeds. The ratios of three turbulence intensity components(i.e. Iu, Iv, Iw) at heights of 10, 20 and 40 m were calculated and equal to be 1:0.88:0.50, 1:0.84:0.57, and 1:0.9:0.49, respectively. In addition, the gust factors in three directions exhibit a reduction with increasing mean wind speed. The peak factors at different heights show a similar trend and slightly decrease with mean wind speed; average peak factors for all 10-min data from Typhoon Meari are 2.43, 2.48, and 2.47, respectively.

Study on concentration and turbulence of solid-liquid FAE in dispersal process

This paper describes numerical simulation on dispersion of the solid-liquid mixed fuel driven by explosion load. A model used in numerical calculation for dispersion of solid-liquid mixed fuel was established in this study. The concentration and turbulent intensity in the multiphase cloud of the solidliquid mixed fuel were obtained by numerical simulation. It was found that the fuel concentration tended to be 0.15 kg/m^3, the turbulence intensity tended to be 7 in 90 ms. The numerical results agree with those measured in the experiment.

ATMOSPHERIC TURBULENCE STRUCTURE AND SPECTRAL CHARACTERISTICS AT NEAR SURFACE LAYER ON TROPICAL COASTS

By use of an observational experiment at the village of Tianwei, Haikou, Hainan province in 1990,characteristic turbulence values such as velocity component spectra and turbulence intensity are studied.The data were mostly obtained in cloudy condition, so that the stability parameter (L) and thermal flux (wt) did not vary diurnally while the turbulent energy and mean-temperature did. The basic characteristics of turbulence spectra are similar to those with fine weather, hems close to local isotropy in the inertial subrange. The velocity spectra agree with the law of "-2/3 th power"in Kolmogrov’s similarity theory. The relationship between turbulent intensity of components δi/U* (i=u,v,w) and stability Z/L is studied follow ins the Monim-Obukhov(M-O) similarity theory. It is shown that the two observe the law of "1/3 th power", though the turbulent intensity and energy are generally larger than those on the flat underlying topography.

Properties of multi-Gaussian Schell-model beams carrying an edge dislocation propagating in oceanic turbulence

Based on the theory of coherence, the model of multi-Gaussian Schell-model(MGSM) beams carrying an edge dislocation generated by the MGSM source is introduced. The analytical cross-spectral density of MGSM beams carrying an edge dislocation propagating in oceanic turbulence is derived, and used to study the evolution properties of the MGSM beams carrying an edge dislocation. The results indicate that the MGSM beam carrying an edge dislocation propagating in oceanic turbulence will evolve from the profile with two intensity peaks into a flat-topped beam caused by the MGSM source, and the beam will evolve into the Gaussian-like beam due to the influences of oceanic turbulence in the far field.As the propagation distance increases, the MGSM beam carrying an edge dislocation propagating in oceanic turbulence with the larger rate of dissipation of mean-squared temperature(χT) and ratio of temperature to salinity contribution to the refractive index spectrum(?) or the smaller rate of dissipation of kinetic energy per unit mass of fluid(ε) evolves into the flat-topped beam or a Gaussian beam faster.

Particle modulations to turbulence in two-phase round jets

The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer （PDA）. Laden with very large particles, no significant attenuations of turbulence intensities were measured in the farfields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop- erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.

Non-Gaussian statistics of partially coherent light in atmospheric turbulence

We derive theoretically and verify experimentally a concise general expression for the normalized intensity correlations(IC)of partially coherent light in a weak atmospheric turbulence in the fast detector measurement regime.The derived relation reveals that the medium turbulence acts,in general,as an additional noise source enhancing the IC of partially coherent beams.The maximum of the beam IC is,in general,enhanced,causing the fields to exhibit super-Gaussian statistics.On the other hand,the relation indicates that turbulence-induced noise is negligible for sufficiently low coherence light,which reveals the condition for the turbulence-free correlation imaging.

Statistical Theory of Turbulence by the Late Lamented Dr. Shunichi TsugéCase Study on Flow through a Grid in Wind Tunnel

This paper is concerned with statistical theory of turbulence by the late lamented Dr. Shunichi Tsugé.? The theory has been applied to the primary flow through a grid fixed vertically with respect to the horizontal axis of the wind tunnel.?The first analytical solution has been obtained and explained the well-known “the inverse-linear decay law” of the turbulent intensity.? It is believed that the present result is the first exact solution in the theory of turbulence.

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 1–Turbulence properties and particle chord time and length

This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.

Subcarrier Intensity Modulated Optical Wireless Communications:A Survey from Communication Theory Perspective

Subcarrier intensity modulation with direet detection is a modulatiou/detection technique tbr optical wireless communication systems, where a pre-modulated and properly biased radio frequency signal is modulated on the intensity of the optical carrier. The most important benefits of subcarrier intensity modulation are as follows： 1） it does not provide irreducible error floor like the conventional on-off keying intensity modulation with a fixed detection threshold; 2） it provides improved spectral efficiency and supports higher order modulation schemes; and 3） it has much less implementation complexity compared to coherent optical wireless communications with heterodyne or homodyne detection. In this paper, we present an up-to-date review of subcarrier intensity modulated optical wireless communication systems. We survey the error rate and outage performance of subcarrier intensity modulations in the atmospheric turbulence channels considering different modulation and coding schemes. We also explore different contemporary atmospheric turbulence fading mitigation solutions that can be employed for subcarrier intensity modulation. These solutions include diversity combining, adaptive transmission, relay assisted transmission, multiple-subcarrier intensity modulations, and optical orthogonal frequency division multiplexing. Moreover, we review the performance of subcarrier intensity modulations due to the pointing error and synchronization error.

Turbulent boundary layers and hydrodynamic flow analysis of nanofluids over a plate

A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.

Wind Tunnel Study on Wind and Turbulence Intensity Profiles in Wind Turbine Wake

In recent years, there has been a rapid development of the wind farms in Japan. It becomes very important to investigate the wind turbine arrangement in wind farm, in order that the wake of one wind turbine does not to interfere with the flow in other wind turbines. In such a case, in order to achieve the highest possible efficiency from the wind, and to install as many as possible wind turbines within a limited area, it becomes a necessity to study the mutual interference of the wake developed by wind turbines. However, there is no report related to the effect of the turbulence intensity of the external flow on the wake behind a wind turbine generated in the wind tunnel. In this paper, the measurement results of the averaged wind profile and turbulence intensity profile in the wake in the wind tunnel are shown when the turbulence intensity of the external wind was changed. The wind tunnel experiment is performed with 500mm-diameter two-bladed horizontal axis wind turbine and the wind velocity in wake is measured by an I-type hot wire probe. As a result, it is clarified that high turbulence intensities enable to the entrainment of the main flow and the wake and to recover quickly the velocity in the wake.

Large Eddy Simulation Study on the Turbulence and Flame Characteristics under Analogical Integral Scale and Turbulence Intensity of Turbulent Premixed Flames

Bunsen burner is a typical geometry for investigating the turbulence-flame interaction.In most experimental studies,only turbulence intensity u′and integral scale l0 are used to characterize the turbulent flow field,regardless of the perforation geometry of perforated plates.However,since the geometry influences the developing process and vortex broken,the plate geometry has to be considered when discussing the flame-turbulence interaction.In order to investigate conditions at the same l0 and u′using different geometries,large eddy simulation of CH_(4)/air flames with dynamic TF combustion model was performed.The model validation shows good agreement between Large Eddy Simulation(LES)and experimental results.In the non-reacting flows,the Vortex Stretching of circular-perforated plate condition is always larger than that of slot-perforated plate condition,which comes from the stresses in the flow fields to stretch the vorticity vector.In reacting flows,at the root of the flame,the Vortex Stretching plays a major role,and the total vorticity here of circular-perforated plate condition is still larger(53.8%and 300%larger than that of the slot-perforated plate at x/D=0 and x/D=2.5,respectively).More small-scale vortex in circular-perforated plate condition can affect and wrinkle the flame front to increase the Probability Density Function(PDF)at large curvatures.The 3D curvature distributions of both cases bias to negative values.The negative trend of curvatures at the instant flame front results from the Dilatation term.Also,the value of the Vortex Stretching and the Dilatation at the flame front of circular-perforated plate condition is obviously larger.

Influence of Collective Boulder Array on the Surrounding Time-averaged and Turbulent Flow Fields

Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their importance in the quantification of the bedload rate,the collective influence of a boulder array on the approach timeaveraged and turbulent flow field has to date been overlooked.The overarching objective is,thus,to assess the collective effects of a boulder array on the time-averaged and turbulent flow fields surrounding an individual boulder within the array,placing particular emphasis on highlighting the bed shear stress spatial variability.The objective of this study is pursued by resolving and comparing the timeaveraged and turbulent flow fields developing around a boulder,with and without an array of isolated boulders being present.The results show that the effects of an individual boulder on the time-averaged streamwise velocity and turbulence intensity were limited to the boulder's immediate vicinity in the streamwise(x/d c < 2-3) and vertical(z/d c < 1) directions.Outside of the boulder's immediate vicinity,the time-averaged streamwise velocity was found to be globally decelerated.This global deceleration was attributed to the form drag generated collectively by the boulder array.More importantly,the boulder array reduced the applied shear stress exerted on theindividual boulders found within the array,by absorbing a portion of the total applied shear.Furthermore,the array was found to have a "homogenizing" effect on the near-bed turbulence thus significantly reducing the turbulence intensity in the near-bed region.The findings of this study suggest that the collective boulder array bears a portion of the total applied bed shear stress as form drag,hence reducing the available bed shear stress for transporting incoming mobile sediment.Thus,the effects of the boulder array should not be ignored in sediment transport predictions.These effects are encapsulated in this study by Equation(6).