Numerical and Experimental Investigations of Darrieus Wind Turbine Start-up and Operation

The performance of small, H-Darrieus vertical axis wind turbines has been investigated numerically and experimentally with particular attention paid to turbine performance at low tip speed ratios (low Reynolds number) and to turbine self-starting. Comprehensive wind tunnel measurements have been performed to provide accurate aerofoil data at low Reynolds numbers and high angles of attack; a unique requirement for vertical axis wind turbine (VAWT) starting studies. Two-dimensional CFD models and blade element momentum (BEM) models were created and assessed to provide new insight into turbine performance for different wind conditions and into different turbine geometries in order to guide the design of the experimental investigation. The experimental and numerical studies have demonstrated that design parameters including turbine solidity, blade profile, blade pitch angle and blade surface roughness have strong influences on turbine performance and turbine self-starting capability. Although other authors have conducted numerical studies of the effect of these parameters, this work represents the first experimental validation for turbine performance at low tip speed ratios. In contrast to some previous studies it is shown that there is no advantage to be gained from the use of cambered blades and that symmetrical blades set at small negative incidence provide the best design solution. It is also shown that increasing the turbine’s solidity can significantly improve self-starting capability and that for a given solidity, increasing the rotor radius with a corresponding increase of blade chord improves performance further. However, these starting performance gains are achieved at the expense of a small loss of peak power output. In addition, bio-inspired blades with tubercle leading edges are demonstrated to be able to significantly improve the turbine self-starting capability by introducing a more gradual stall characteristic. These results are the only reported measurements of the effect of tubercle leading edges on vertical axis wind turbines. Finally, a novel, real-time on-board pressure measurement system was developed and employed to examine the instantaneous blade pressure distribution and its variation when the turbine is rotating. The complex flow physics including dynamic stall, laminar separation and flow curvature were successfully recorded and provide unique, unsteady data to increase our knowledge and understanding of the transient aerodynamics of the H-Darrieus wind turbine. The experimental results were also compared with the available CFD and BEM predictions. It is demonstrated that BEM based approaches are highly sensitive to the quality of the aerofoil data that is provided as input to the model. This thesis provides validation of previous work on the question of whether H-Darrieus wind turbines can start without external assistance and in the light of this research a set of revised design rules are proposed to achieve self-starting turbines

Investigation of bio-aerosol dispersion in a tunnel-ventilated poultry house

Bio-aerosol concentrations in poultry houses must be controlled to provide adequate air quality for both birds and workers. High concentrations of airborne bio-aerosols would affect the environmental sustainability of the production and create environmental hazards to the surroundings via the ventilation systems. Previous studies demonstrate that several factors including the age of the birds, the housing configuration, the humidity and temperature would strongly affect the indoor concentration of bio-aerosols. However, limited studies are performed in the literature to investigate the bio-aerosol dispersion pattern inside poultry buildings. In order to fill a gap of the understanding of the bio-aerosol dispersion behavior, experimental measurements of the indoor bio-aerosol distribution are performed in a tunnel-ventilated poultry house in this paper. Meanwhile a three-dimensional computational fluid dynamics (CFD) model is built and validated to further investigate the effect of flow pattern, turbulence and vortex on the dispersion and deposition of the bio-aerosols. Furthermore, bio-aerosols with various diameters are also examined in the CFD model. It is found that higher concentrations of bio-aerosols are detected at the rear part of the house and strong turbulent flow resulting from the ventilation inlets enhances the diffusion and dispersion of bio-aerosols. Local vortex or disturbed flow is responsible for higher local concentration due to the re-suspension of settled bio-aerosols, which suggests that careful attentions should be paid to these locations during cleaning and disinfection. Results from present study contribute to the optimization of design and operation of the poultry houses from the standing point of reducing airborne bio-aerosol concentrations

A review of H-Darrieus wind turbine aerodynamic research

The H-Darrieus vertical axis turbine is one of the most promising wind energy converters for locations where there are rapid variations of wind direction, such as in the built environment. The most challenging considerations when employing one of these usually small machines are to ensure that they self-start and to maintain and improve their efficiency. However, due to the turbine's rotation about a vertical axis, the aerodynamics of the turbine are more complex than a comparable horizontal axis wind turbine and our knowledge and understanding of these turbines falls remains far from complete. This paper provides a detailed review of past and current studies of the H-Darrieus turbine from the perspective of design parameters including turbine solidity, blade profile, pitch angle, etc. and particular focus is put on the crucial challenge to design a turbine that will self-start. Moreover, this paper summarizes the main research approaches for studying the turbine in order to identify successes and promising areas for future study

Time-accurate blade surface static pressure behaviour on a rotating H-Darrieus wind turbine

Time‐accurate blade pressure distributions on a rotating H‐Darrieus wind turbine at representative tip speed ratios during start‐up are presented here, which allow blade dynamic stall and laminar separation bubbles to be observed clearly and which provide a rare experimental demonstration of the flow curvature effect inherent in H‐Darrieus turbine operation. The convection of a dynamic stall vortex along the blade surface at high reduced frequency has also been clearly identified. This study provides new information of the complex aerodynamics of the vertical axis wind turbines (VAWTs) and provides unique experimental data to validate the transient blade static surface pressure distribution predicted by CFD models. To the best of the authors' knowledge, this is the first time that the instantaneous pressure variation around the blade has been measured and recorded directly for an H‐Darrieus wind turbine

Aerofoil behaviour at high angles of attack and at Reynolds numbers appropriate for small wind turbines

The aerodynamic characteristics of a NACA0018 aerofoil have been investigated experimentally for incidence angles ranging from Formula to Formula in closed-jet and open-jet wind tunnels with different blockage coefficients at Reynolds numbers from 60,000 to 140,000. The results provide a comprehensive data set for studying the performance of typical, small-scale Darrieus wind turbine blades which mainly operate at relatively low Reynolds number and experience extreme angles of attack, particularly during start-up. Measurements in both very high and very low blockage, open-jet wind tunnels capture a “second-stall” phenomenon at high angles of attack, but this behaviour is not observed in the closed-jet wind tunnel confirming the sensitivity of aerofoil performance at extreme incidence to wind tunnel configuration. Surface flow visualisation suggests that the “second-stall” occurs when the flow separation point near the leading edge of the aerofoil moves from the suction side to the pressure side which leads to a sudden change of wake structure. In the closed-jet wind tunnel, the tunnel walls constrain the wake and prevent the flow from switching from one regime to another. The measured data are also used to demonstrate that established wind tunnel blockage corrections break down under these extreme, post-stall angles of attack

Computational Fluid Dynamics aided investigation and optimization of a tunnel-ventilated poultry house in China

Ventilation system is crucial for poultry houses to control the indoor climate and air quality. The tunnel ventilation system is widely applied for large-scale poultry buildings in China but only limited scientific researches regarding the flow pattern, temperature distribution and design criteria are available in the literature. Thanks to the fast development of computer technology, Computational Fluid Dynamics (CFD) techniques were used in present study to investigate the indoor air movement, air temperature and relatively humidity. A three-dimensional CFD model was built according to the real dimensions of a laying hen house and the model was validated by comparing the simulation results with the field measurements at 30 positions. Meanwhile, statistical analysis was performed to determine the differences between different boundary conditions regarding the agreement between measured and CFD simulated results. Optimization of air inlet configurations was performed by using the validated CFD model and it was found that the uniformity of indoor air movement could prevent excessive local convective heat losses and reduce the temperature at the end of the house. Furthermore, the air inlets placed at the middle of the side wall could significantly reduce the high temperature expected at the end of the building without using extra energy, which is especially important for large-scale poultry farms with long buildings. The performance of side-wall windows was also examined and preliminary guidance was provided to effectively regulate the indoor climate by using these windows with the help of environmental monitoring systems. The present study contributes to the understanding and design of the tunnel ventilation system used in poultry houses

Construction and verification of an environment and energy prediction model for Controlled Environment Housing

In order to satisfy the healthy growth and performance of livestock and poultry, a large amount of energy is often consumed in the production process of modern livestock and poultry breeding, which is used for automatic feeding management and regulation of breeding environment. In this study, based on the ISO 13790 5R1C equivalent resistance capacitance network computing model, using the henhouse heat balance, water balance, balance of gas (ammonia, carbon dioxide concentration) principle, we developed a simple closed loop control henhouse environment and energy consumption prediction model, Through on-site validation tests, the results show that the model is reliable, and it can assist the farmer for breeding planning, house-design process and increase environmental control and energy management efficiency

Numerical Investigation of the Dynamic Response of a Sand Cushion with Multiple Rockfall Impacts

A shed cave structure with a sand cushion is often used as a protective structure for rockfall disasters. Because of the randomness and unpredictability of rockfall disasters, the cushions of shed caves often suffer multiple impacts from rockfalls. Aiming at the problem of multiple impacts of rockfall, this paper uses the three-dimensional discrete element method to study the dynamic response of multiple rockfall impacts on sand cushions from different heights. Before conducting large-scale simulation studies, the input parameters in the numerical model are verified with data from laboratory experiments. Analyzing the simulation results shows that when the same point is impacted multiple times, the maximum impact force and the maximum penetration depth will increase with the number of impacts. According to the numerical results, a calculation formula of the maximum impact force that considers the number of impacts is fitted. At the same time, considering the impact response when the rockfall impacts different positions multiple times, the distance range that the subsequent impact is not affected by the previous impact is given. The significance of studying the multiple impacts of rockfalls is shown by a numerical study of rockfalls impacting a sand cushion multiple times from different heights, and it provides a reference for the design of rockfall disaster-protection structures in practical engineering

Development and Validation of an Energy Consumption Model for Animal Houses Achieving Precision Livestock Farming

Indoor environmental control is usually applied in poultry farming to ensure optimum growth conditions for birds. However, these control methods represent a considerable share of total energy consumption, and the trend of applying new equipment in the future for precision livestock farming would further increase energy demand, resulting in an increase in greenhouse gas emissions and management costs. Therefore, to ensure optimum efficiency of both energy use and livestock productivity, a customized hourly model was developed in the present study to interpret and analyze the electronically collected data. The modules for estimating indoor gas concentrations were incorporated into the present model, as this has not been properly considered in previous studies. A validation test was performed in a manure-belt layer house using sensors and meters to measure the indoor environmental parameters and energy consumption. The predicted results, including indoor temperature, relative humidity, carbon dioxide and ammonia concentrations, showed good agreement with the measured data, indicating a similar overall trend with acceptable discrepancies. Moreover, the corresponding differences between the measured and simulated energy consumption for heating, tunnel ventilation and base ventilation were 13.7, 7.5, and 0.1%, respectively. The total energy demand estimated by the model showed a limited discrepancy of approximately 10.6% compared with that measured in reality. Although human factors, including inspection, cleaning, vaccination, etc., were not included in the model, the validation results still suggested that the customized model was able to accurately predict the indoor environment and overall energy consumption during poultry farming. The validated model provides a tool for poultry producers to optimize production planning and management strategies, increase the production rate of unit energy consumption and achieve precision livestock farming from an energy consumption standpoint