Wind Tower Design Research Articles

CFD Analysis of an Innovative Wind Tower Design with Wind-Inducing Natural Ventilation Technique for Arid Climatic Conditions

CFD Analysis of an Innovative Wind Tower Design with Wind-Inducing Natural Ventilation Technique for Arid Climatic Conditions

Evaluating commercial feasibility of a new tall wind tower design concept using a stochastic levelized cost of energy model

Abstract Wind power generation has seen a dramatic increase in the 21st century and the Department of Energy (DOE) envisions that wind energy will become a much larger part of overall power generation in the U.S. by 2050. Wind turbines have continued to grow in size during the last few decades with towers commonly built at a height of 80 m for typical utility-scale turbines in the Unites States, and this is accompanied by certain transportation and logistics challenges. The newly proposed tall tower technology has been designed to be cost-effective in assembling towers as high as 140 m from precast concrete module components that are capable of transport on the U.S. road system. This paper presents an alternative wind tower design with potential for reducing the overall levelized cost of energy (LCOE); it evaluates a hexagonal precast concrete wind tower solution that facilitates use of a taller wind turbine generator for harvesting stronger, steadier, and more frequent wind resources to increase wind energy production and lower the overall LCOE. An integrated team of industry experts was consulted to support development of a stochastic life cycle cost model using a parametric estimate of the cost and fabrication and assembly schedules of this new wind tower design concept as well as forecasting the projected revenue to be created by the new technology. The study concludes that this new design concept is a commercially viable solution, with an estimated LCOE savings ranging from 2% to 4% compared with the typical 80 m turbine deployed in the United States, and it also provides wind power potential to previously untapped regions in the country. This paper helps to inform energy developers, manufacturers, and policy makers, both regionally and nationally, of a possible economically feasible wind tower design solution.

Stability analysis of newly developed polygonal cross-sections for lattice wind towers

The pursuit for cheaper energy is leading the current wind tower design to increased heights. Common wind turbine tower designs would generate unjustified costs for transportation and erection leading to inefficient use of materials. In order to reduce these costs, several simplified erection methods have been proposed. One of such is the hybrid lattice-tubular steel tower. For economic feasibility, built-up cold-formed polygonal cross-sections have been proposed for the lattice part. This article presents a numerical investigation of the failure modes of closed polygonal cross-sections. The first part contains a presentation of structural systems which incorporate elements composed of plates and cold-formed members. The evaluation of the polygonal sections is done by means of finite element analysis considering local and global geometrical imperfections and residual stresses generated in the fabrication procedure. A comparative study is performed between several finite element models to propose a corresponding European buckling curve for calculating the flexural buckling resistance. The results show that the design of polygonal sections can be done according to European buckling curves methodology.

Numerical and experimental performance analysis of a four-sided wind tower adjoining parlor and courtyard at different wind incident angles

Ventilation performance of a scaled four-sided wind tower connected to parlor and courtyard at different wind incident angles was studied both numerically and experimentally. Parlor (Talar in Persian) is a large room with one open side that connects the wind tower to the courtyard. The combination of wind tower, parlor, and courtyard forms a typical layout of summer section of vernacular houses in hot-arid regions of Iran. This study aims to uncover ventilation strategies considered in the design of wind tower and its interaction with surrounding architectural elements. The numerical study was conducted on a 1:25 scaled model for 13 wind incident angles with 15° intervals. Interested parameters were the flow rate and the ratio of total extract to supply flow rates at each wind incident angle. A structured grid was generated, and ANSYS Fluent software was employed for simulating the flow field. Wind tunnel experiment was carried out on the same scaled model and a semi-empirical approach was adopted for predicting the air flow rate at each wind angle. Numerical simulation results were validated with the wind tunnel measurements and good agreement was observed. Results indicate that for 61.5% of wind incident angles, the dominant function of four-sided wind tower is extracting air out of the building and at other wind angles, with approximately equal values of supply and extract flow rates, it acts as an air exchanger device. Accordingly, it can be concluded that neglecting stack effect, four-sided wind towers in hot-arid regions of Iran are primarily employed for heat dissipation rather than inducing outdoor breezes to the interior spaces.

Investigation of Airflow Patterns in a New Design of Wind Tower with a Wetted Surface

Passive cooling systems, such as wind towers, can help to reduce energy consumption in buildings and at the same time reduce greenhouse gas (GHG) emissions. Wind towers can naturally ventilate buildings and also can create enhanced thermal comfort for occupants during the warm months. This study proposes a modern wind tower design with a moistened pad. The new design includes a fixed column, a rotating and movable head, an air opening with a screen, and two windows at the end of the column. The wind tower can be installed on roof-tops to take advantage of ambient airflow. The wind tower’s head can be controlled manually or automatically to capture optimum wind velocity based on desired thermal condition. To maximize its performance, a small pump was considered to circulate and spray water on an evaporative cooling pad. A computational fluid dynamics (CFD) simulation of airflow around and inside the proposed wind tower is conducted to analyze the ventilation performance of this new design of wind tower. Thereby, the velocity, total pressure, and pressure coefficient distributions around and within the wind tower for different wind velocities are examined. The simulation results illustrate that the new wind tower design with a moistened pad can be a reasonable solution to improve naturally the thermal comfort of buildings in hot and dry climates.

Performance Evaluation of a Modular Design of Wind Tower with Wetted Surfaces

Wind towers or wind catchers, as passive cooling systems, can provide natural ventilation in buildings located in hot, arid regions. These natural cooling systems can provide thermal comfort for the building inhabitants throughout the warm months. In this paper, a modular design of a wind tower is introduced. The design, called a modular wind tower with wetted surfaces, was investigated experimentally and analytically. To determine the performance of the wind tower, air temperature, relative humidity (RH) and air velocity were measured at different points. Measurements were carried out when the wind speed was zero. The experimental results were compared with the analytical ones. The results illustrated that the modular wind tower can decrease the air temperature significantly and increase the relative humidity of airflow into the building. The average differences for air temperature and air relative humidity between ambient air and air exiting from the wind tower were approximately 10 °C and 40%, respectively. The main advantage of the proposed wind tower is that it is a modular design that can reduce the cost of wind tower construction.

Towards the sustainability in the design of wind towers

Wind farms are both a renewable energy production alternative and a profitable economic enterprise. At the same time these groups of wind towers can be a social-friendly solution if they solve challenging demands from the society such as integration in landscape, aesthetics, low noise nuisances…This paper presents part of a complete research project that was carried out between 2009 and 2015. First this article presents a new wind tower proposal that has been designed to reduce these social impacts as well as satisfying environmental aspects, economic requirements and boundary conditions such as height, turbine power, soil conditions. This proposal is composed of precast concrete modules joined with high-resistance steel bars that define a post-tension structure. These components define an attractive and transparent tripod that is transversally reinforced with steel profiles. This system holds the Spanish patent “Support structure to wind turbines, number ES 2 319 709 B8” and aims to build 100-120m high towers. At this height there is better wind quality and large turbines of 3 MW can be installed.Second, a sustainability assessment of this new hybrid wind tower has been carried out in order to evaluate its social, environmental and economic impacts compared to other solutions. Steel lattice structures, steel tubular systems, in situ concrete towers and precast concrete structures are the alternatives for wind farms that have been considered. MIVES, a MCDM methodology based on the value function concepts has been used to do this assessment, which has relied upon seminars of experts. This sustainability assessment enabled the identification of the aspects with the lowest sustainability index. These are the maintenance and deconstruction costs and for occupational hazards. Now these weak points can be corrected in the process of bringing the patented technology to market.

Experimental investigation of a modular wind tower in hot and dry regions

Passive cooling systems such as wind towers or wind catchers can create thermal comfort for building residents in hot and dry regions. This paper introduces an experimental study of a modular design of wind tower called the modular wind tower with wetted surfaces. Air temperature, relative humidity (RH) and airflow velocity parameters were measured at different times and at points when the velocity of the ambient air was zero. The results show that the modular wind tower can decrease the air temperature by an average of 10°C and increase the relative humidity of airflow in a building by approximately 36% on average. Additionally, the wind tower can create the airflow velocity entering the building up to around 1.8m/s. Furthermore, the obtained data from the measurements illustrate that the conditions of indoor air improve to the thermal comfort conditions.

Energy efficiency and building environment

With the environmental protection posing as the number one global problem, man has no choice but reducing his energy consumption, one way to accomplish this is to resort to passive and low-energy systems to maintain thermal comfort in buildings. The conventional and modern designs of wind towers can successfully be used in the hot arid regions to maintain thermal comfort (with or without the use of ceiling fans) during all hours of the cooling season, or a fraction of it. Climatic design is one of the best approaches to reduce the energy cost in buildings. Proper design is the first step of defence against stress of climate. Buildings should be designed according to climate of the site for reducing the need of mechanical heating or cooling hence maximum natural energy can be used for creating pleasant environment inside the built envelope. Technology and industry progress of the last decade diffused electronic and informatics’ devices in many human activities and now appear also in building construction. The utilisation and operating opportunities components, increase the reduction of heat losses by varying the thermal insulation, optimise the lighting distribution with louver screens and operate mechanical ventilation for coolness in indoor spaces. In addiction to these parameters the intelligent envelope can act for security control and became an important part of the building demotic revolution. Application of simple passive cooling measure is effective in reducing the cooling load of buildings in hot and humid climates. 43% reductions can be achieved using a combination of well-established technologies such as glazing, shading, insulation, and natural ventilation. More advanced passive cooling techniques such as roof pond, dynamic insulation, and evaporative water jacket need to be considered more closely. The building sector is a major consumer of both energy and materials worldwide, and the consumption is increasing. Most industrialised countries are in addition becoming more and more dependent on external supplies of conventional energy carriers, i.e., fossil fuels. Energy for heating and cooling can be replaced by new renewable energy sources. New renewable energy sources, however, are usually not economically feasible compared with the traditional carriers. In order to achieve the major changes needed to alleviate the environmental impacts of the building sector, it is necessary to change and develop both the processes in the industry itself, and to build a favourable framework to overcome the present economic, regulatory and institutional barriers.

Flow field obtained by PIV technique for a scaled building-wind tower model in a wind tunnel

Particle image velocimetry (PIV) measurements obtained from air flow distribution in one configuration building-wind tower are analyzed. Experiments were conducted in a wind tunnel tested by dynamic similarity between real and scaled building-wind tower geometries. This concept has been demonstrated technically feasible for producing thermal comfort in popular houses built in arid and semi-arid climates. The objective of this work is providing a PIV data basis, which is a non-intrusive technique, for the design of wind towers. The study used a stream of particles produced by a smoke generator which was injected as part of the air flow entering a scaled model of building-wind tower inserted into the wind tunnel straight section. Velocity data were obtained from several sections in order to reconstruct the whole distribution of the flow in the building-tower configuration assuming a steady state. The results are reproduced with good agreement by numerical simulations conducted with RANS method on a commercial program Fluent. The PIV data provided thus a source of validity for the computational model, which can be used to enhance the design of wind-towers. The PIV technique is used for the first time to study natural ventilation in a building-wind tower configuration.

CFD Simulation and Optimisation of a Low Energy Ventilation and Cooling System

Mechanical Heating Ventilation and Air-Conditioning (HVAC) systems account for 60% of the total energy consumption of buildings. As a sector, buildings contributes about 40% of the total global energy demand. By using passive technology coupled with natural ventilation from wind towers, significant amounts of energy can be saved, reducing the emissions of greenhouse gases. In this study, the development of Computational Fluid Dynamics (CFD) analysis in aiding the development of wind towers was explored. Initial concepts of simple wind tower mechanics to detailed design of wind towers which integrate modifications specifically to improve the efficiency of wind towers were detailed. From this, using CFD analysis, heat transfer devices were integrated into a wind tower to provide cooling for incoming air, thus negating the reliance on mechanical HVAC systems. A commercial CFD code Fluent was used in this study to simulate the airflow inside the wind tower model with the heat transfer devices. Scaled wind tunnel testing was used to validate the computational model. The airflow supply velocity was measured and compared with the numerical results and good correlation was observed. Additionally, the spacing between the heat transfer devices was varied to optimise the performance. The technology presented here is subject to a patent application (PCT/GB2014/052263).

Semi-active control of a wind turbine via magnetorheological dampers

This paper investigates the use of magnetorheological (MR) dampers to semi-actively control wind induced vibrations of a 1/20 scaled wind tower model. The idea consists in realizing a variable restraint at the base of the model, able to modify in real time its mechanical properties according to the instantaneous response of the tower. The restraint is made up of a cylindrical hinge, two springs and two prototype MR devices, the behavior of the latter being driven by control algorithms aiming to reduce the structural demand imposed to the steel tower. The demand is expressed in terms of base bending stress and top displacement.The model has been tested on a shaking table facility at the Denmark Technical University in Copenhagen imposing two different types of accelerograms at the base, equivalent to an extreme short operating gust and a longer high wind speed excitation, respectively. Two distinct control algorithms, each designed according to different philosophies and goals have been adopted to drive the semi-active devices.The results show the effectiveness of the proposed control technique in reducing the stress demand at the base, this at the cost, in the worst case, of a slight increase of top displacement. They encourage investigating further in this direction in order to promote the use of such strategy for a cost effective design of high wind towers.

Prediction of the pollutant diffusion discharged from wind tower of the city traffic tunnel

With the increase of the urban traffic volume, a large number of tunnels have been built in many cities; the vehicle emission from the traffic tunnel has a significant impact on the surrounding environment, it has important meaning to study the impact of pollutant diffusion discharged from wind tower on the downwind environment, and to evaluate the air pollution situation and variation tendency around the wind tower. In this study, a reduced scale model of 1:200 is used for three-dimensional numerical simulation and wind tunnel test; results show that the numerical simulation result agrees well with the result of the wind tunnel test. The diffusion of pollutant discharged from the wind tower with the actual size is simulated by the computational fluid dynamics (CFD) program; results show that, the CO concentration ratios of points on building windward side to that of the wind tower outlet (C/C0) are reduced to 1.211%–1.563% on the middle vertical line of building windward side at a distance of 200m when the building is 39m (10m higher than the wind tower), 0.974%–1.215% when the heights of the building and the wind tower are both 29m, and 0.654%–0.834% when the building is 19m. When C/C0 of building windward is lower than the maximum allowable value of 2.67%, the required shortest distances between the building and the wind tower are 50, 150 and 200m for the building heights of 19, 29 and 39m, respectively. The results can be a reference for the design of wind tower of traffic tunnel and the determinations of the location and height of downwind new building.

Preliminary design and structural responses of typical hybrid wind tower made of ultra high performance cementitious composites

Ultra High Performance Cementitious Composites with compressive strength 200MPa (UHPCC-200) is proposed for the structural design of super high hybrid wind turbine tower to gain durability, ductility and high strength design objectives. The minimal wall thickness is analyzed using basic bending and compression theory and is modified by a toque influence coefficient. Two cases of wall thickness combination of middle and bottom segment including varied ratio and constant ratio are considered within typical wall thickness dimension. Using nonlinear finite element analysis, the effects of wall thickness combinations with varied and constant ratio and prestress on the structural stress and lateral displacement are calculated and analyzed. The design limitation of the segmental wall thickness combinations is recommended.

CFD analysis of a heat transfer device integrated wind tower system for hot and dry climate

Increasing emphasis on reducing power consumption has raised public awareness of natural and renewable energy resources, particularly the integration of natural ventilation systems in buildings such as wind towers. The aim of this work is to incorporate heat transfer devices in a wind tower to meet the internal comfort criteria in extreme external conditions. Heat transfer devices were installed inside the passive terminal of the wind tower unit, highlighting the potential to achieve minimal restriction in the external air flow stream while ensuring maximum contact time, thus optimizing the cooling duty of the device. Computational Fluid Dynamics (CFD) was used to develop a numerical model of a new wind tower design and simulate the air flow pattern and pressure coefficients around and through the wind tower to a test room. Results have indicated that the average internal airflow rate was reduced following the integration of the vertical and horizontal heat transfer device configuration, reductions of 7% and 10% was obtained from the achieved numerical models. The work compared the effect of evaporative cooling and heat transfer devices on the thermal performance of the passive ventilation device. The proposed cooling system was capable of reducing the air temperatures up to 15K, depending on the configuration and operating conditions. Furthermore, the study also highlighted that the proposed system was able to provide the recommended rates of fresh supply even at relatively low external wind speeds. The technology presented here is subject to IP protection under the QNRF funding guidelines.

Effects of different internal designs of traditional wind towers on their thermal behavior

The purpose of this study is to investigate the effects of different internal designs of traditional wind towers on their thermal behavior numerically. Among the enormous variety of designs of internal partitions in traditional wind towers, which are used in hot and dry areas of Iran, five main important types were chosen. Calculations were done using evaporative cooling – wet partitions – and without it – dry partitions. In the modeling evaporative cooling, the partitions were considered as the wet surfaces which inject water droplets in the air in a very low speed. The CFD open source package – Open FOAM – was used to produce the current three-dimensional CFD simulation by adopting both the Eulerian approach for the air phase and the Lagrangian approach for the water droplets were adopted. The three dimensional plan of a building and its wind tower were simulated in an analytical space like a tunnel. In addition, to simulate the turbulence flow the k–ɛ standard model was used. The results were compared with some experimental data indicating that whenever the evaporative cooling is used in the best design condition, the air temperature decreases 6.5K and reaches to 311.5K while the temperature of the surrounding is 318K.

The wind towers of Bastakiya: assessing the role of the towers in the whole house ventilation system using dynamic thermal modelling

A thermal model of the complex wind environments in and around a traditional wind tower house in Bastakiya, Dubai, was constructed using Virtual Environment Software. The original house with its three wind towers was simulated and the potential to increase comfort in it using adaptive comfort criteria was explored with varying iterations of the wind tower design. The height of one tower was increased and reduced by 33%, and the cross-sectional area of a tower increased and reduced by 50%. This article presents the results of these simulations and the three key methodological conclusions reached. Firstly, that only by using the adaptive comfort model was it possible to understand how the buildings actually operated in terms of the comfort they provide for tradition populations in this historic building. Secondly, that the whole house behaves as a self-regulating thermal system in which the internal ventilation system operates around on modal shifts in each of the three towers from updraft to downdraft airflows. Thirdly that these modal shifts occur around thermal thresholds that are a direct result of the cross-sectional area and height of the towers and that by changing the dimensions of the towers these thresholds can be raised or lowered. Thus, the geometry of the towers themselves provides some control over the temperatures experienced in the home and its indoor comfort environment.

Research on Dynamic Behaviour of Wind Tower under Ambient Excitation Based on DASP

By means of site test of horizontal-axis wind turbine tower under different working conditions, the paper make a further analysis by DASP system and obtained the acceleration spectrum and characteristic frequency; Again to build finite element model of the tower and calculated it's dynamic characteristics. The measured results and calculative results provide a basis for avoiding resonance and further study of structure dynamic response of wind turbines tower; In addition, it can provide valuable modal parameter data for wind tower design and structural vibration control.

Two-phase Euler-Lagrange CFD simulation of evaporative cooling in a Wind Tower

A new design of Wind Tower is investigated numerically under different structural parameters and environmental conditions. The new design is some wetted columns, consisting of wetted curtains hung in the tower column, which are modeled as surfaces that inject droplets of water with very low speed. The CFD open source package – Open FOAM – is used. The current three-dimensional CFD simulation has adopted both the Eulerian approach for the air phase and the Lagrangian approach for the water phase. The effects of water droplet diameter and water droplet temperature on the thermal performance of the Wind Tower are investigated at specific inlet air velocity and relative humidity and height of wetted columns. Also, the effects of wind velocity, temperature, and relative humidity inlet to Wind Tower are studied. Changing the height of the wetted columns and its effect on the evaporative cooling in other specific parameters is studied. The results obtained from the present CFD study are compared with the analytical data taken from the literature and a good agreement is observed. As a result, the height of 10 m of wetted columns decreases 12 K of the ambient air temperature and increases 22% of its relative humidity.

Experimental investigation of new designs of wind towers

Two new designs of wind towers were tested side by side with a conventional wind tower in the city of Yazd, Iran. All the towers were of identical dimensions. The two new designs were one with wetted column, consisting of wetted curtains hung in the tower column, and the other one with wetted surfaces, consisting of wetted evaporative cooling pads mounted at its entrance. The air temperature leaving the wind towers with evaporative cooling provisions were much lower than the air temperature leaving the conventional design, and its relative humidity much higher. The air-flow rate was reduced slightly in these new towers. It was found that the wind tower with wetted column performs better with high wind speeds whereas the tower with wetted surfaces performs better with low wind speeds. It is recommended that these new designs of wind towers should be manufactured in different sizes and incorporated in the designs of new buildings. They can replace the evaporative coolers currently employed in Iran, and other hot arid regions, with considerable saving in electrical energy consumption.