Horizontal Velocity Components Research Articles

Predicting mean velocity profiles inside urban canyons

Knowledge of mean wind profiles is important for applications in wind engineering and air quality modeling. Yet despite advances in our ability to simulate winds on street scales, existing theoretical predictions do not apply to the important limit of tall, closely packed buildings or generalize to realistic geometries. We present an alternative strategy based on the existence of intense layers of vorticity at solid boundaries and the roof level. Following the approach in vortex dynamics, wherein the velocity field is modelled by approximating the vorticity field, spatially and temporally averaged vertical profiles of the horizontal velocity components are derived from the numerical Green's functions for the three-dimensional Poisson equation and vortex sheets located at the top and bottom of an urban canyon; mean profiles of the spanwise velocity along the canyon axis are obtained similarly. The method is applied to skimming flow for idealised and realistic canyons and tested against building-resolving simulations. Good agreement is obtained for a wide range of external wind directions, including winds that are parallel to the canyon axis. For a unit-aspect-ratio street canyon, the relative error in the streamwise velocity is 30−50% over the entire canyon, but 10−20% when the top and bottom boundary layers are excluded; the errors in the spanwise velocity are smaller. It is shown that the model can be successfully calibrated from single-point measurements taken above the urban canopy.

Primitive Equations with half horizontal viscosity

We consider the $3D$ primitive equations and show, that one does need less than horizontal viscosity to obtain a well-posedness result in Sobolev spaces. Furthermore, we will also investigate the primitive equations with horizontal viscosity and show that these equations are well-posed without imposing any boundary condition for the horizontal velocity components on the vertical boundary.

An approach for multi-dimensional land subsidence velocity estimation using time-series Sentinel-1 SAR datasets by applying persistent scatterer interferometry technique

The time-series interferometric synthetic aperture radar (InSAR) techniques has the potential of estimating the land subsidence at a high accuracy of nearly in millimeter scale. The major limitation of the present InSAR methods like persistent scatterer interferometry (PSI) is that they measure land deformation velocities only in the direction of the radar line of sight (LOS). Hence, the real prospects of the deformation velocity, i.e. the horizontal and vertical components of velocity remain uncertain. This study is focusing on retrieving PSI based multi-dimensional land deformation velocity along horizontal and vertical directions in an urban region by using ascending and descending pass Sentinel-1 datasets. The area for this study is Lucknow city in Uttar Pradesh state of India. The estimated LOS velocity vectors from ascending and descending pass time-series datasets are utilized for retrieving multidimensional subsidence velocity. Further, the retrieved time-series land subsidence is correlated to the groundwater level variation during the considered time span.

A Model for the Spectrum of the Lateral Velocity Component from Mesoscale to Microscale and Its Application to Wind-Direction Variation

A model for the spectrum of the lateral velocity component $$S_v(f)$$ is developed for a frequency range from about 0.2 $$\hbox {day}^{-1}$$ to the turbulence inertial subrange, with the intent of improving the calculation of flow meandering over areas the size of offshore wind farms and clusters. These sizes can correspond to a temporal scale of several hours, much larger than the validity limit of typical boundary-layer models, such as the Kaimal model, or the Mikkelsen–Tchen model. The development of the model is based on observations from one site and verified with observations from another site up to a height of 241 m. The model describes three ranges: (1) the mesoscale from $$0.2\ \hbox {day}^{-1}$$ to about $$10^{-3}\ \hbox {Hz}$$ where a mesoscale spectral model from Larsen et al. (2013: QJR Meteorol Soc 139: 685–700) is used; (2) the spectral gap where the normalized v spectrum, $$fS_v(f)$$ , can be approximated to be a constant; (3) the high-frequency range where a boundary-layer model is used. In order to demonstrate a general applicability of the lateral velocity spectrum model to reproduce the statistics of wind-direction variability, models for both horizontal velocity components, u and v, are used through an inverse Fourier transform technique to produce time series of both components, which in theory could have been the ensemble for calculating the corresponding spectra. The ensemble is then used to calculate directional statistics, which in turn are compared with corresponding statistics from the measured time series. We demonstrate the relevance of the constructed spectral models for calculating meandering effects for large wind farms and wind-farm clusters.

Turbulent Fluxes of the Dust Aerosol on the Desertified Area

Vertical turbulent dust aerosol fluxes are determined on the basis of measurements of fluctuations of the content of aerosol particles and the vertical component of the wind velocity for a desertified territory of Astrakhan oblast. The normalized flux or the uplift velocity of the dust aerosol reached 5 cm/s. It is found that the vertical turbulent aerosol flux is significantly affected by convective-related variations in the horizontal and vertical components of the wind velocity. It is shown that the daily variability of the uplift velocity of the aerosol agrees with that of the turbulent heat flux and that the mass dust aerosol flux is correlated with a maximum particle size of ~1.5 µm.

Spectral Observation Theory and Beam Debroadening Algorithm for Atmospheric Radar

In order to measure the variance of wind velocity, which is contributed from turbulence, via radar observations, it is necessary to remove the unwanted contribution from strong horizontal velocity components through the finite beamwidth of the radar. This effect is referred to as beam broadening. Although the amount of beam broadening has thus far been calculated based on the approximating assumption that the pattern of the beam is rotationally symmetric and has very low sidelobes, we need to take a more theoretical approach to radar—one that does not have a simple beam pattern like the Antarctic Program of the Antarctic Syowa Station (PANSY) radar (69S, 39E). In this article, we clarify the theoretical relationship in a very simple form between the turbulence spectrum, which is directly associated with the variance of turbulence, two-way beam patterns, and the observed spectrum, using autocorrelation functions (ACFs). The theory is thoroughly universal and applicable to any type of atmospheric radar, such that we can quantitatively analyze radar observation systems. Furthermore, we propose a “debroadening” algorithm based directly on this theory and from calculations of the general maximum likelihood (ML). We performed numerical simulations that validate our theory and the algorithm.

Experimental study of thermal plumes generated by a cluster of high-rise compact buildings under moderate background wind conditions

When background wind is moderate, urban environment may face great challenges as removal ability of airborne pollutants, anthropogenic heat and moisture reduces. Under this condition, buoyancy-driven flow can break the dominant role of the background wind and affect the urban environment greatly. Knowledge of buoyant flow dynamics is essential for understanding urban wind/thermal environment and related pollutant transport.As one important buoyant flow, thermal plumes generated by a cluster of high-rise compact buildings are modelled using a laboratory water channel in this study. Flow similarity, when the buoyancy is prominent, is well satisfied. Mean flows, turbulent statistics, and rising features under different Froude (Fr) numbers are systematically explored by two-dimensional particle image velocimetry (PIV) technique.Overall, the transition of buoyancy-dominated and wind-dominated flow dynamics is observed when Fr number varies. For horizontal and vertical velocity components, peak magnitude and position are quantitatively determined on four building poles. Fr number obviously changes the relative magnitude of v-peak among four poles. Turbulence statistics, including velocity variance, turbulence kinetic energy, power spectral density, turbulent momentum flux, and turbulence production, are systematically analyzed, which show consistent results. As Fr number decreases, the plume mixing is enhanced. When particularly aiming at the plume region, smaller Fr numbers usually make the maximum velocities occur more in the plume central part rather than the boundaries. A quantitative rational function is given to describe the relation between Fr number and the rising angle, as a = 8.76/(Frq + 0.097).

Development of unsteady convection in a rectangular cavity with sudden heating of a vertical wall

Unsteady thermal gravitational-capillary convection in a rectangular cavity with sudden heating of one of the vertical walls by electric current was experimentally investigated. The development in time of the spatial form of ethyl alcohol flows with the Prandtl number Pr = 16 at 20°C was studied. The development of the hydrodynamic boundary layer on the heated wall and the flow along the free surface of a liquid layer was examined. The profiles of the vertical and horizontal velocity components were measured during the development of boundary layers and flow in a volume of liquid. Evolution of temperature fields on the free surface of a liquid layer was studied using a thermal imager.

Oblique water waves scattering by a thick barrier with rectangular cross section in deep water

The problem of oblique scattering of surface waves by a thick partially immersed rectangular barrier or a thick submerged rectangular barrier extending infinitely downwards in deep water is studied here to obtain the reflection and transmission coefficients semi-analytically. Use of Havelock’s expansion of water wave potential function reduces each problem to an integral equation of first kind on the horizontal component of velocity across the gap above or below the barrier. Multi-term Galerkin approximations involving polynomials as basis functions multiplied by appropriate weight functions are used to solve these equations numerically. Evaluated numerical results for the reflection coefficients are plotted graphically for both the barriers. The study reveals that the reflection coefficient depends significantly on the thickness of the barrier. The accuracy of the numerical results is checked by using energy identity and by obtaining results available in the literature as special cases.

Circulation-Enhanced Tank Heating Using Shallow Profile Coil Bundles

Heavy fuel oils require heated tanks to facilitate their transportation and processing. This paper proposes and investigates three- and four-level heating coil bundles. Numerical study revealed that powerful large-scale circulation of the heated fluid enhances heat transfer, delivering 16.7% and 23% improvements to the average heat transfer coefficient for the three- and four-level bundles, respectively. Furthermore, this circulation improves oil mixing and limits the variation in bulk oil temperature to − 0.3 to + 1.3 °C from the average. The study also quantified oil flow velocity near the bottom of the tank. The time-averaged horizontal components of velocity, estimated 25 mm and 50 mm above the bottom of the tank, exceed 2 mm/s and 4 mm/s, respectively. The proposed heating coil bundles feature a compact design that reduces the material and labor costs of construction and that, by occupying only a small portion of the bottom of the tank, improves accessibility, maintenance, and cleaning.

Thermal Radiations and Mass Transfer Analysis of the Three-Dimensional Magnetite Carreau Fluid Flow Past a Horizontal Surface of Paraboloid of Revolution

The dynamics of the 3-dimensional flow of magnetized Carreau fluid past a paraboloid surface of revolution is studied through thermal radiation and mass transfer analysis. The impacts of Brownian motion and chemical reaction rate are considered on the flow dynamics. The system of nonlinear PDEs are converted to coupled ODEs by employing suitable transformation relations. The developed ODEs are solved by applying the standard procedure of homotopy analysis method (HAM). The impacts of various interesting parameters on the state variables of the Carreau fluid (velocity components, temperature, concentration, and shear stress) are explained through various graphs and tables. It is found that the horizontal velocity components augment with the rising magnetic parameter and Grashof number values. The fluid temperature augments with the higher values of the pertinent parameters except Prandtl number. The Nusselet number and fluid concentration enhance with the augmenting Brownian motion parameter. The shear stress augments with the rising Grashof number. The agreement of the obtained and published results validate the accuracy of the employed technique.

Note on global regular solution to the 3D liquid crystal equations

In this paper we provide a sufficient condition for regularity of solutions to the 3D nematic liquid crystal flows. More precisely, we prove that if the horizontal velocity component uh=(u1,u2) satisfies ∇uh∈Lq(0,T;Lp(R3)),3p+2q≤32,2≤p≤∞, then the solution (u,d) is regular.

Melting Phenomenon in a Squeezed Rheology of Reactive Rate Type Fluid

The present study concentrates on squeezed unsteady magneto-hydrodynamic flow of Jeffrey fluid confined between two infinite parallel plates. Description of heat transfer process is disclosed through melting and thermal radiation effects. Features of viscous dissipation are also incorporated. Characteristics of mass transport are explored with chemical reaction. Modulated nonlinear partial differential equations are reduced by implementing appropriate transformations. Approximate convergent solutions are calculated through analytical technique. Characteristics of velocity, concentration and fluid temperature are illustrated graphically and also discussed comprehensively in physical. Skin friction co-efficient and Nusselt number are sketched and discussed through graphs. It is noticed that horizontal velocity component and temperature of Jeffrey liquid are dominant for greater melting parameter. Moreover, temperature field decays for dominant thermal radiation parameter.

Azimuth correction system of an inclinometer

The paper is devoted to azimuth correction system of an inclinometer used for well drilling in high latitude areas. In these areas, ordinary types of navigation equipment (gyroscopic and magnetic sensors) are ineffective because of small horizontal component of the Earth rotation velocity and significant values of magnetic declination. In the paper, an approach to the correction system study is described. The system consisting of two vibrational sources shifted from the wellhead to a certain distance in the direction of projected drilling and spaced to same distance from the specified direction is characterized.Special attention is given to investigation of a motion model of a flexible shaft, which is proposed as the vibrational source of the system. On the basis of experiments and calculations, it is shown in the paper that in a complex mechanical system with a flexible shaft of vibrational source, a consistent multi-resonant effect can be observed when the shaft starts rotating. Moreover, a simulation model and results of estimation of the vibrational source power are presented. A possibility of use a compact “handheld” vibrational source with flexible shaft for azimuth correction system operation is shown

장애물 외관비에 따른 건물협곡에서의 수평대칭흐름에 관한 연구

In this study, the variation in wind velocity of horizontal flow formed inside the building canyon was investigated numerically according to the L(Length)/H(Height) ratios of the building. The variations in positive and negative values of horizontal wind velocity components in x- and y-direction were derived and analyzed with vector fields in x-y sections. In the case of L/H=1.0, symmetry vortex on the L/2 center basis was found to be formed in the building canyon. In the case of L/H=3.0, the horizontal wind flow was separated, and additional vortex was developed. The double-symmetry vortexes were reinforced by the increase of L/H ratios. The horizontal wind flow and symmetry development patterns formed in the building canyon can be also interpreted in conjunction with the reverse changes in horizontal wind velocity components. It is expected that these findings can be utilized for quantitative assessment of fine-scale local airflows and various wind environments in urban areas.

Solution of the system of gas-dynamic equations for the processes of interaction of vibrators with the air

The modern practice of using vibratory machines involving small seeds of low weight faces such an undesirable phenomenon as the effect exerted on the kinematics of vibrational movement of particles of fractions of the seed mixture by the aerodynamic forces and momenta. The periodic movement of air relative to the working planes of a vibratory machine arises due to fluctuations in the packets of these planes, which form flat aerodynamic channels. Consequently, the issues of studying the processes of interaction between the working bodies of vibratory machines and the air environment, aimed to justify their structural improvements, appear relevant. Existing mathematical models, which assess the parameters of air movement relative to the working planes of vibratory machines, produce only a generalized pattern and are flat. This paper proposes a statement, as well as an estimated finite difference scheme, of solving a three-dimensional boundary value problem on calculating the field of velocities and pressures in the region of air, located between two parallel synchronously oscillating planes. The problem employs a system of differential equations to describe the flow of the perfect gas. The finite difference scheme has been solved by a sweep method.Using the sweep method to solve these kinds of problems makes it possible to ensure the convergence and stability of estimation schemes, regardless of the step and other parameters of the grid applied. A variant of the calculation has been given, which demonstrated the feasibility of the proposed method for the assigned boundary conditions and parameters of the vibrational mode of machine operation. It has been established that in the working space enclosed between two oscillating planes there are both vertical (transverse) and horizontal (longitudinal) components of air velocity, which change over time

Cross-contamination effect on turbulence spectra from Doppler beam swinging wind lidar

Abstract. Turbulence velocity spectra are of high importance for the estimation of loads on wind turbines and other built structures, as well as for fitting measured turbulence values to turbulence models. Spectra generated from reconstructed wind vectors of Doppler beam swinging (DBS) wind lidars differ from spectra based on one-point measurements. Profiling wind lidars have several characteristics that cause these deviations, namely cross-contamination between the three velocity components, averaging along the lines of sight and the limited sampling frequency. This study focuses on analyzing the cross-contamination effect. We sample wind data in a computer-generated turbulence box to predict lidar-derived turbulence spectra for three wind directions and four measurement heights. The data are then processed with the conventional method and with the method of squeezing that reduces the longitudinal separation distances between the measurement locations of the different lidar beams by introducing a time lag into the data processing. The results are analyzed and compared to turbulence velocity spectra from field measurements with a Windcube V2 wind lidar and ultrasonic anemometers as reference. We successfully predict lidar-derived spectra for all test cases and found that their shape is dependent on the angle between the wind direction and the lidar beams. With conventional processing, cross-contamination affects all spectra of the horizontal wind velocity components. The method of squeezing improves the spectra to an acceptable level only for the case of the longitudinal wind velocity component and when the wind blows parallel to one of the lines of sight. The analysis of the simulated spectra described here improves our understanding of the limitations of turbulence measurements with DBS profiling wind lidar.

Mode conversion and damping of MHD waves in stratified viscous solar atmosphere

We study the mode conversion and damping of MHD waves in a gravitationally stratified low-$\beta $ to high-$\beta $ isothermal atmosphere of the Sun permeated by a uniform vertical magnetic field. We solve the MHD equations by MacCormack method to examine the effect of viscosity on amplitudes of physical quantities such as velocity, mass density, gas pressure and magnetic field before and after the $\beta \approx 1$ layer. It is found that mode conversion occurs at the point $z \approx -1.8$ in $\beta \approx 1$ layer and viscosity does not influence the mode conversion phenomenon. In the presence of viscosity, the amplitudes of vertical and horizontal velocity components, horizontal and vertical magnetic field components, gas pressure and mass density decrease and decay of amplitude is stronger for higher values of viscosity. In the low $\beta $ plasma, damping length decreases with the increase in viscosity but remains almost unchanged in the high $\beta $ plasma. When the driving frequency increases, conversion from slow to fast mode decreases.

Finite-difference modeling of the inflow profile in an isolated homogeneous isotropic partially opened reservoir

The article is devoted to the study of tributary profiles arising from the selection of hydrocarbons from partially opened reservoirs. The calculations were performed based on the finite-difference program for calculating the pressure and velocity fields in the formation, based on the solution of the problem of the pressure field in an isolated isotropic homogeneous formation, localized in the range from H 1 to − H 2 and perforated in the range − H < z < H , which is completely contained in the interval of the reservoir. Graphical dependencies are constructed for the pressure field, the vertical and horizontal components, and the velocity modulus of the fluid filtered from the periphery to the well. Level lines for the indicated fields are presented and, based on their analysis, important regularities of the flow are revealed. A computational experiment showed that there are no vertical flows at the hole in the perforated part of the formation, and when they are removed from the well, they are non-zero. It was shown that interlayer flows exist even in homogeneous partially opened formations. At the same time, the inflow from an imperfectly opened homogeneous isotropic reservoir producing in a given depression mode is not uniform, and the maximum modulus of the horizontal velocity component in all curves is reached at the boundaries of the perforation interval. It is shown that in the center of a symmetrically perforated and imperfectly opened formation a minimum specific inflow is observed.

Wind Profiling in the Lower Atmosphere from Wind-Induced Perturbations to Multirotor UAS.

We present a model-based approach to estimate the vertical profile of horizontal wind velocity components using motion perturbations of a multirotor unmanned aircraft system (UAS) in both hovering and steady ascending flight. The state estimation framework employed for wind estimation was adapted to a set of closed-loop rigid body models identified for an off-the-shelf quadrotor. The quadrotor models used for wind estimation were characterized for hovering and steady ascending flight conditions ranging between 0 and 2 m/s. The closed-loop models were obtained using system identification algorithms to determine model structures and estimate model parameters. The wind measurement method was validated experimentally above the Virginia Tech Kentland Experimental Aircraft Systems Laboratory by comparing quadrotor and independent sensor measurements from a sonic anemometer and two SoDAR instruments. Comparison results demonstrated quadrotor wind estimation in close agreement with the independent wind velocity measurements. However, horizontal wind velocity profiles were difficult to validate using time-synchronized SoDAR measurements. Analysis of the noise intensity and signal-to-noise ratio of the SoDARs proved that close-proximity quadrotor operations can corrupt wind measurement from SoDARs, which has not previously been reported.