Numerical Prediction of Wind Flow Around Irregular Models

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
D. Y. Wang ◽  
Y. Zhou ◽  
Y. Zhu ◽  
Tim K. T. Tse
Keyword(s):  
Bluff Body ◽  
Numerical Models ◽  
Vortex Motion ◽  
Velocity Profiles ◽  
Wind Flow ◽  
Lateral Velocity ◽  
Fluctuating Pressure ◽  
Pressure Coefficients ◽  
Numerical Predictions ◽  
Building Models

This paper presents numerical predictions of flow around irregular-plan buildings (S-, R-, L- and U-shaped models) in high Reynolds number. The adopted computational approach and numerical models are described firstly. Then comparative analysis with the numerical and experimental data has been conducted to verify the reliability of the numerical predictions. Finally, characteristics of mean and fluctuating pressure distributions and vertical and lateral velocity profiles of the flow around the four models have been investigated and assessed thoroughly. The study shows that satisfactory results can be obtained by large eddy simulation (LES), especially when fluctuating wind velocity is considered in the inflow boundary. Distribution of mean pressure coefficients on front faces is relatively regular. Large fluctuating pressure coefficients are induced by strong vortex motion. Velocity profiles of wind flow are disturbed obviously among the four building models, especially in weak flow. The disturbed intensity decreases with increasing of the distance away from bluff body. The suggested MDS (Maximum Disturbance Scopes) away from bluff body are generally 0.25H in inflow zones, 0.4H in roof zones, 0.5H in both side zones and 3H in weak zones.

4D Investigation of Vortex Fluid Motion Inside the Eyeball

2021 ◽  
pp. 73-88
Author(s):  
S.A. Skladchikov ◽  
N.P. Savenkova ◽  
P.I. Vysikaylo ◽  
S.E. Avetisov ◽  
D.V. Lipatov ◽  
...  
Keyword(s):  
Numerical Models ◽  
Fluid Motion ◽  
Vortex Motion ◽  
Dissipative System ◽  
Fluid Flows ◽  
Vitreous Cavity ◽  
Posterior Chamber ◽  
Medicinal Substance ◽  
Fluid Transfer ◽  
And Diffusion

The eye is a complex system of boundaries and fluids with different viscosities within the boundaries. At present, there are no experimental possibilities to thoroughly observe the dynamic 4D processes after one or another method of eye treatment is applied. The complexity of cumulative, i.e., focusing, and dissipative, i.e., scattering, convective and diffusion 4D fluxes of fluids in the eye requires 4D analytical and numerical models of fluid transfer in the human eyeball to be developed. The purpose of the study was to develop and then verify a numerical model of 4D cumulative-dissipative processes of fluid transfer in the eyeball. The study was the first to numerically evaluate the values of the characteristic time of the drug substance in the vitreous cavity until it is completely washed out, depending on the injection site; to visualize the paths of the vortex motion of the drug in the vitreous cavity; to determine the main parameters of the 4D fluid flows of the medicinal substance in the vitreous cavity, depending on the presence or absence of vitreous detachment from the wall of the posterior chamber of the eye. The results obtained are verified by the experimental data available to doctors. In the eye, as a partially open cumulative-dissipative system, Euler regions with high rates of cumulative flows and regions with low speeds or stagnant Lagrange flow zones are defined

Innovative Volumetric Solar Receiver Micro-Design Based on Numerical Predictions

2015 ◽  
Author(s):  
Raffaele Capuano ◽  
Thomas Fend ◽  
Bernhard Hoffschmidt ◽  
Robert Pitz-Paal
Keyword(s):  
Solar Radiation ◽  
Energy Demand ◽  
Large Scale ◽  
Solar Power ◽  
Numerical Models ◽  
Numerical Predictions ◽  
Proper Design ◽  
Global Increase ◽  
Solar Power Tower ◽  
Solar Receiver

Due to the continuous global increase in energy demand, Concentrated Solar Power (CSP) represents an excellent alternative, or add-on to existing systems for the production of energy on a large scale. In some of these systems, the Solar Power Tower plants (SPT), the conversion of solar radiation into heat occurs in certain components defined as solar receivers, placed in correspondence of the focus of the reflected sunlight. In a particular type of solar receivers, defined as volumetric, the use of porous materials is foreseen. These receivers are characterized by a porous structure called absorber. The latter, hit by the reflected solar radiation, transfers the heat to the evolving fluid, generally air subject to natural convection. The proper design of these elements is essential in order to achieve high efficiencies, making such structures extremely beneficial for the overall performances of the energy production process. In the following study, a parametric analysis and an optimized characterization of the structure have been performed with the use of self-developed numerical models. The knowledge and results gained through this study have been used to define an optimization path in order to improve the absorber microstructure, starting from the current in-house state-of-the-art technology until obtaining a new advanced geometry.

A Two-Region Model for Gradient Modification of Salt-Gradient Solar Ponds by Radial Injection

1996 ◽  
Vol 118 (1) ◽  
pp. 37-44 ◽  
Author(s):  
G. A. Eghneim ◽  
S. J. Kleis
Keyword(s):  
Turbulence Model ◽  
Field Model ◽  
Numerical Study ◽  
Numerical Models ◽  
Domain Boundary ◽  
Near Field ◽  
Solar Ponds ◽  
Numerical Predictions ◽  
Region Model ◽  
Salt Gradient

A combined experimental and numerical study was conducted to support the development of a new gradient maintenance technique for salt-gradient solar ponds. Two numerical models were developed and verified by laboratory experiments. The first is an axisymmetric (near-field) model which determines mixing and entrainment in the near-field of the injecting diffuser by solving the conservation equations of mass, momentum, energy, and salt. The model assumes variable properties and uses a simple turbulence model based on the mixing length hypothesis to account for the turbulence effects. A series of experimental measurements were conducted in the laboratory for the initial adjustment of the turbulence model and verification of the code. The second model is a one-dimensional far-field model which determines the change of the salt distribution in the pond gradient zone as a result of injection by coupling the near-field injection conditions to the pond geometry. This is implemented by distributing the volume fluxes obtained at the domain boundary of the near-field model, to the gradient layers of the same densities. The numerical predictions obtained by the two-region model was found to be in reasonable agreement with the experimental data.

Analysis on Flow-Induced Vibration of Underwater Horizontal Gate

2010 ◽  
Vol 163-167 ◽  
pp. 293-298
Author(s):  
Wei Wei ◽  
Hao Ren
Keyword(s):  
Numerical Models ◽  
Coherence Function ◽  
Hydrodynamic Pressure ◽  
Vibration Response ◽  
Flow Induced Vibration ◽  
Structural Dynamic ◽  
Fluctuating Pressure ◽  
Frequency Components ◽  
Random Vibration Theory ◽  
Different Levels

The best is to read these instructions and follow the outline of this text. The physical and numerical models were combined to analyze flow-induced vibration response of Qingshuihe River underwater horizontal gate in this paper; the pressures acting on the gate were divided into two parts: the fluctuating pressure of flow on the stationary gate and the hydrodynamic pressure caused by the gate vibration, which is additional pressure induced by disturbed flow. The temporal-spatial correlation of fluctuating pressures obtained by model experiments between different nodes was analyzed. In the study the coherence function is defined in frequency domain with consideration of different levels of correlation for different frequency components, and the nodal load of the fluctuating pressure could be obtained. A new distribution of additional mass with considering radial vibration of the gate is adopted as equivalent hydrodynamic pressure. Based on random vibration theory, the flow-induced vibration response of the gate was obtained. The results provide the reliable reference evidence for structural dynamic design of the gate and show that the hydrodynamic stability of the gate can meet the requirement. On the other hand, it is shown that this method is reasonable and feasible.

An analytical theory of distributed axisymmetric barotropic vortices on the β-plane

1994 ◽  
Vol 269 ◽  
pp. 301-321 ◽  
Author(s):  
G. M. Reznik ◽  
W. K. Dewar
Keyword(s):  
Radiation Effects ◽  
Planetary Wave ◽  
Complete Solution ◽  
Asymptotic Series ◽  
Vortex Motion ◽  
Present Theory ◽  
Analytical Theory ◽  
Wave Radiation ◽  
Initial Value ◽  
Numerical Predictions

An analytical theory of barotropic β-plane vortices is presented in the form of an asymptotic series based on the inverse of vortex nonlinearity. In particular, a solution of the initial value problem is given, in which the vortex is idealized as a radially symmetric function of arbitrary structure. Motion of the vortex is initiated by its interaction with the so-called ‘β-gyres’ which, in turn, are generated by the vortex circulation. Comparisons of analytical and numerical predictions for vortex motion are presented and demonstrate the utility of the present theory for times comparable to the ‘wave’ timescale. The latter exceeds the temporal limit derived from formal considerations. The properties of the far-field planetary wave radiation are also computed.This theory differs from previous calculations by considering more general initial vortex profiles and by obtaining a more complete solution for the perturbation fields. Vortex trajectory predictions accrue error systematically by integrating vortex propagation rates which are too strong. This appears to be connected to higher-order planetary wave radiation effects.

A Lattice Boltzmann Bluff Body Model for VIV Suppression

2006 ◽  
Author(s):  
Jannette B. Frandsen
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Lattice Boltzmann ◽  
Water Waves ◽  
Bluff Body ◽  
Numerical Models ◽  
Bluff Bodies ◽  
Free Surfaces ◽  
Viv Suppression ◽  
Reynolds Number Flows

In this paper, the suitability of a mesoscopic approach involving a single phase Lattice Boltzmann (LB) model is examined. In contrast, to continuum based numerical models, where only space and time are discrete, the discrete variables of the LB model are space, time and particle velocity. With reference to the Boltzmann equation of classical kinetic theory, the distribution of fluid molecules is represented by particle distribution functions. The LB method simulates fluid flow by tracking particle distributions. It is notable that the formulation avoids the need to include the Poisson equation. An elastic-collision scheme with no-slip walls is prescribed. The central idea behind proposing the present formulation is many fold. One goal is to capture smaller scales naturally, postponing the need of applying empirical turbulence models. Another goal is to get further insight into nonlinearities in steep and breaking free surfaces to improve current continuum mechanics solutions. Although the long term goal is to predict bluff-body high Reynolds number flows and breaking water waves, the present study is limited to laminar flow simulations and continuous free surfaces. The case studies presented include bluff bodies embedded in Reynolds number flows in the order of 100–200. The free surface test cases represent bore propagation past a single and multiple structures. The 2-D uniform grid solutions are compared with findings reported in the literature. Vortex patterns are studied when single or several objects are located in the bluff-body wakes. From a mitigation point of view, the model presents an easy means of re-arranging bluff bodies to study optimum solutions for VIV suppression with/without a free surface.

scholarly journals Distribution of the external pressure coefficients on the elliptic tower: experimental measurement compared with numerical modelling

2020 ◽  
Vol 313 ◽  
pp. 00047
Author(s):  
Michal Franek ◽  
Marek Macák ◽  
Oľga Hubová
Keyword(s):  
Cfd Simulation ◽  
Flow Simulation ◽  
External Pressure ◽  
Wind Pressure ◽  
Wind Flow ◽  
Suitable Model ◽  
Pressure Coefficients ◽  
Building Model ◽  
High Rise ◽  
Experimental Values

The wind flow around the elliptical object was investigated experimentally in the BLWT wind tunnel in Bratislava and subsequently solved by computer wind flow simulation. On a high-rise building model, the external wind pressure coefficients were evaluated for different wind directions and then compared with the numerical CFD simulation in ANSYS, where different models of turbulence and mesh types were used. The aim of the article was to evaluate and compare the obtained values and after analysing the results to choose the most suitable model of turbulence and mesh types, which showed the smallest deviations from the experimental values.

Improved Performance of a Radial Turbine Through the Implementation of Back Swept Blading

2008 ◽  
Author(s):  
Liam Barr ◽  
Stephen W. T. Spence ◽  
Paul Eynon
Keyword(s):  
Numerical Study ◽  
Numerical Models ◽  
Internal Flow ◽  
Turbine Rotor ◽  
Point Of View ◽  
Blade Angle ◽  
Element Analysis ◽  
Numerical Predictions ◽  
Radial Turbine ◽  
Optimum Velocity

This report details the numerical investigation of the performance characteristics and internal flow fields of an 86 mm radial turbine for a turbocharger application. A new blade was subsequently designed for the 86 mm rotor which departed from the conventional radial inlet blade angle to incorporate a 25° inlet blade angle. A comparative analysis between the two geometries is presented. Results show that the 25° back swept blade offers significant increases in efficiency while operating at lower than optimum velocity ratios (U/C). This enhanced efficiency at off-design conditions would significantly improve turbocharger performance where the turbine typically experiences lower than optimum velocity ratios while accelerating during engine transients. A commercial CFD code was used to construct single passage steady state numerical models. The numerical predictions show off-design performance gains of 2% can be achieved, while maintaining design point efficiency. Primary and secondary flow patterns are examined at various planes within the turbine blade passage and reasons for the increase in performance are discussed. A finite element analysis has been conducted to assess the stress implications of introducing a non-radial angle at turbine rotor inlet. A modal analysis was also carried out in order to identify the natural frequencies of the turbine geometry, thus calculating the critical speeds corresponding to the induction of the excitational frequencies from the stator vanes. Although the new blade design has resulted in stress increases in some regions, the numerical study has shown that it is feasible from both an aerodynamic and structural point of view to increase the performance characteristic of a radial turbine through the implementation of back swept blading.

A Numerical and Experimental Performance Comparison of an 86 MM Radial and Back Swept Turbine

2009 ◽  
Author(s):  
Liam Barr ◽  
Stephen Spence ◽  
David Thornhill ◽  
Paul Eynon
Keyword(s):  
Numerical Models ◽  
Performance Comparison ◽  
Point Of View ◽  
Blade Angle ◽  
Experimental Performance ◽  
Numerical Predictions ◽  
Radial Turbine ◽  
Optimum Velocity ◽  
Performance Results ◽  
Performance Gains

This report details the numerical and experimental investigation of the performance characteristics of a conventional radial turbine compared with a new back swept design for the same application. The blade geometry of an existing turbine from a turbocharger was used as a baseline. A new back swept blade was subsequently designed for the rotor, which departed from the conventional radial inlet blade angle to incorporate a 25° inlet blade angle. A comparative numerical analysis between the two geometries is presented. Results show that the 25° back swept blade offers significant increases in efficiency while operating at lower than optimum velocity ratios (U/C). Improvements in efficiency at off-design conditions could significantly improve turbocharger performance since the turbine typically experiences lower than optimum velocity ratios while accelerating during engine transients. A commercial CFD code was used to construct single passage steady state numerical models. The numerical predictions show off-design performance gains of 2% can be achieved, while maintaining design point efficiency. A finite element stress analysis was conducted to show that the nonradial inlet blade angle could be implemented without exceeding the acceptable stress levels for the rotor. A modal analysis was also carried out in order to identify the natural blade frequencies, showing that these were not significantly changed by the implementation of backswept blading. A prototype backswept rotor was produced and tested in a direct comparison with the baseline rotor geometry. Experimental performance results showed strong correlations with those obtained numerically, and verified the predicted performance gains at off-deign velocity ratios. This numerical and experimental study has shown that it is feasible from both an aerodynamic and structural point of view to improve the performance characteristic of a radial turbine at lower than optimum velocity ratios through the implementation of back swept blading.

Wind Flow Over a Complex Terrain in Nygårdsfjell, Norway

2015 ◽  
Author(s):  
Muhammad Bilal ◽  
Narendran Sridhar ◽  
Guillermo Araya ◽  
Sivapathas Parameswaran ◽  
Yngve Birkelund
Keyword(s):  
Wind Energy ◽  
Wind Turbine ◽  
Complex Terrain ◽  
Wind Farm ◽  
Turbulence Models ◽  
Future Research ◽  
Wind Flow ◽  
Governing Equations ◽  
The North ◽  
Numerical Predictions

The understanding of atmospheric flows is crucial in the analysis of dispersion of a contaminant or pollutant, wind energy and air-quality assessment to name a few. Additionally, the effects of complex terrain and associated orographic forcing are crucial in wind energy production. Furthermore, the use of the Reynolds-averaged Navier-Stokes (RANS) equations in the analysis of complex terrain is still considered the “workhorse” since millions of mesh points are required to accurately capture the details of the surface. On the other hand, solving the same problem by means of the instantaneous governing equations of the flow (i.e., in a suite of DNS or LES) would imply almost prohibitive computational resources. In this study, numerical predictions of atmospheric boundary layers are performed over a complex topography located in Nygårdsfjell, Norway. The Nygårdsfjell wind farm is located in a valley at approximately 420 meters above sea level surrounded by mountains in the north and south near the Swedish border. Majority of the winds are believed to be originated from Torneträsk lake in the east which is covered with ice during the winter time. The air closest to the surface on surrounding mountains gets colder and denser. The air then slides down the hill and accumulates over the lake. Later, the air spills out westward towards Ofotfjord through the broader channel that directs and transforms it into highly accelerated winds. Consequently, one of the objectives of the present article is to study the influence of local terrain on shaping these winds over the wind farm. It is worth mentioning that we are not considering any wind turbine model in the present investigation, being the main purpose to understand the influence of the local surface topography and roughness on the wind flow. Nevertheless, future research will include modeling the presence of a wind turbine and will be published elsewhere. The governing equations of the flow are solved by using a RANS approach and by considering three different two-equation turbulence models: k-omega (k–ω), k-epsilon (k–ε) and shear stress transport (SST). Furthermore, the real topographical characteristics of the terrain have been modeled by extracting the required area from the larger digital elevation model (DEM) spanning over 100 km square. The geometry is then extruded using Rhino and meshed in ANSYS Fluent. The terrain dimensions are approximately 2000×1000 meter square.

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