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Wind energy in the urban environment faces complex and often unfavorable wind conditions. High turbulence, lower average wind velocities and rapid changes in the wind direction are common phenomena in the complex built environments. A possible way to improve the cost-efficiency of urban wind turbines is the application of flowenhancing structures on or near the turbines. For horizontal axis wind turbines (HAWTs), applying a diffuser has shown to have a beneficial impact on the power production, but it is still under development. For a vertical axis wind turbine (VAWT) it is expected that flow augmentation will also strongly increase the performance of the turbine, but very little research has been done in this field. The purpose of this research is to investigate the effects of a diffuser on the airflow through a VAWT. In order to investigate these effects, the turbine (with and without diffuser) is simulated using a 2-D unsteady free-wake potential-flow panel model. The local flow field, local angles of attack, shed vorticity, the shape and strength of the wake, and the rotor torque are investigated for both the case with and without the diffuser. The diffuser used in this research consists of two mirrored airfoil cross-sections. The size of the duct-opening in which the turbine operates is varied. This work shows that unlike for a 1-D actuator disc analysis, the area ratio B of the diffuser exit with respect to the diffuser nozzle area is not the only driving factor in the augmentation of the rotor torque of the VAWT. More important are the effect of the directional change of the rotor inflow and the faster downstream transport of the shed vorticity., Aerodynamics, Wind Energy & Propulsion, Aerospace Engineering

Wind energy in the urban environment faces complex and often unfavorable wind conditions. High turbulence, lower average wind velocities and rapid changes in the wind direction are common phenomena in the complex built environments. A possible way to improve the cost-efficiency of urban wind turbines is the application of flowenhancing structures on or near the turbines. For horizontal axis wind turbines (HAWTs), applying a diffuser has shown to have a beneficial impact on the power production, but it is still under development. For a vertical axis wind turbine (VAWT) it is expected that flow augmentation will also strongly increase the performance of the turbine, but very little research has been done in this field. The purpose of this research is to investigate the effects of a diffuser on the airflow through a VAWT. In order to investigate these effects, the turbine (with and without diffuser) is simulated using a 2-D unsteady free-wake potential-flow panel model. The local flow field, local angles of attack, shed vorticity, the shape and strength of the wake, and the rotor torque are investigated for both the case with and without the diffuser. The diffuser used in this research consists of two mirrored airfoil cross-sections. The size of the duct-opening in which the turbine operates is varied. This work shows that unlike for a 1-D actuator disc analysis, the area ratio B of the diffuser exit with respect to the diffuser nozzle area is not the only driving factor in the augmentation of the rotor torque of the VAWT. More important are the effect of the directional change of the rotor inflow and the faster downstream transport of the shed vorticity., Aerodynamics, Wind Energy & Propulsion, Aerospace Engineering

The Vertical Axis Wind Turbine, in its 2D form, is characterized by a complex unsteady aerodynamic flow, including dynamic stall and blade vortex interaction. Adding to this complexity, the 3D flow causes spanwise effects and the presence of trailing vorticity and tip vortices. The objective of the current paper is to bring insight into the 3D development of the near wake of a H-VAWT, understanding: • The spanwise blade load distribution in the upwind and the downwind blade passages. • The trajectory of tip vortices, including the inboard movement and the radial expansion of the shed and the trailing vorticity. • The impact of the 3D flow phenomena on the efficiency of the VAWT. • The blade vortex interaction of the upwind tip vortex with the downwind blade passage. • The induction due to trailing vorticity. The investigation is composed of experimental wind tunnel research with Stereo-PIV and modeling of the rotor and wake with a 3D unsteady panel method. A two bladed H-Darrieus VAWT model is tested in the low speed/low turbulence wind tunnel at Delft University of Technology. Stereo-PIV measurements are used to visualize the flow in the near wake focusing on the flow field around four tip geometries. The measurement planes cover several sections of the rotor volume, allowing for the reconstruction of the evolution of the tip vortex. The formation, the convection and the dissipation for each tip vortex are quantified. The experimental PIV data is used to validate the 3D, unsteady, multi-body, free-wake panel method. The combination of the results of the panel model validated by experiments, in particular the Stereo PIV results, allows to understand the impact of the near wake development on the upwind blade passage, as well as the energy conversion process during the downwind blade passage., Aerodynamics, Wind Energy & Propulsion, Aerospace Engineering

Virtual Reality (VR) has been constantly evolving since its early days, and is now a fundamental technology in different application areas. User evaluation is a crucial step in the design and development of VR systems that do respond to users’ needs, as well as for identifying applications that indeed gain from the use of such technology. Yet, there is not much work reported concerning usability evaluation and validation of VR systems, when compared with the traditional desktop setup. The paper presents a user study performed, as a first step, for the evaluation of a low-cost VR system using a Head-Mounted Display (HMD). That system was compared to a traditional desktop setup through an experiment that assessed user performance, when carrying out navigation tasks in a game scenario for a short period. The results show that, although users were generally satisfied with the VR system, and found the HMD interaction intuitive and natural, most performed better with the desktop setup., Electrical Engineering, Mathematics and Computer Science

Virtual Reality (VR) has been constantly evolving since its early days, and is now a fundamental technology in different application areas. User evaluation is a crucial step in the design and development of VR systems that do respond to users’ needs, as well as for identifying applications that indeed gain from the use of such technology. Yet, there is not much work reported concerning usability evaluation and validation of VR systems, when compared with the traditional desktop setup. The paper presents a user study performed, as a first step, for the evaluation of a low-cost VR system using a Head-Mounted Display (HMD). That system was compared to a traditional desktop setup through an experiment that assessed user performance, when carrying out navigation tasks in a game scenario for a short period. The results show that, although users were generally satisfied with the VR system, and found the HMD interaction intuitive and natural, most performed better with the desktop setup., Electrical Engineering, Mathematics and Computer Science

Virtual and Augmented Reality are developing rapidly: there is a multitude of environments and experiments in several laboratories using from simple HMD (Head-Mounted Display) visualization to more complex and expensive 6-wall projection CAVEs, and other systems. Still, there is not yet a clear emerging technology in this area, nor commercial applications based on such a technology are used in large scale. In addition to the fact that this is a relatively recent technology, there is little work to validate the utility and usability of Virtual and Augmented Reality environments when compared with the traditional desktop set-up. However, usability evaluation is crucial in order to design better systems that respond to the users’ needs, as well as for identifying applications that might really gain from the use of such technologies. This paper presents a preliminary usability evaluation of a low-cost Virtual and Augmented Reality environment under development at the University of Aveiro, Portugal. The objective is to assess the difference between a traditional desktop set-up and a Virtual/Augmented Reality system based on a stereo HMD. Two different studies were performed: the first one was qualitative and some feedback was obtained from domain experts who used an Augmented Reality set-up as well as a desktop in different data visualization scenarios. The second study consisted in a controlled experiment meant to compare users’ performances in a gaming scenario in a Virtual Reality environment and a desktop. The overall conclusion is that these technologies still have to overcome some hardware problems. However, for short periods of time and specific applications, Virtual and Augmented Reality seems to be a valid alternative since HMD interaction is intuitive and natural., Electrical Engineering, Mathematics and Computer Science

Virtual and Augmented Reality are developing rapidly: there is a multitude of environments and experiments in several laboratories using from simple HMD (Head-Mounted Display) visualization to more complex and expensive 6-wall projection CAVEs, and other systems. Still, there is not yet a clear emerging technology in this area, nor commercial applications based on such a technology are used in large scale. In addition to the fact that this is a relatively recent technology, there is little work to validate the utility and usability of Virtual and Augmented Reality environments when compared with the traditional desktop set-up. However, usability evaluation is crucial in order to design better systems that respond to the users’ needs, as well as for identifying applications that might really gain from the use of such technologies. This paper presents a preliminary usability evaluation of a low-cost Virtual and Augmented Reality environment under development at the University of Aveiro, Portugal. The objective is to assess the difference between a traditional desktop set-up and a Virtual/Augmented Reality system based on a stereo HMD. Two different studies were performed: the first one was qualitative and some feedback was obtained from domain experts who used an Augmented Reality set-up as well as a desktop in different data visualization scenarios. The second study consisted in a controlled experiment meant to compare users’ performances in a gaming scenario in a Virtual Reality environment and a desktop. The overall conclusion is that these technologies still have to overcome some hardware problems. However, for short periods of time and specific applications, Virtual and Augmented Reality seems to be a valid alternative since HMD interaction is intuitive and natural., Electrical Engineering, Mathematics and Computer Science