Flow diagnostics and optimal design of vertical axis wind turbines for urban environments

The gap between the supply and the demand of electricity is rapidly increasing throughout the world, due to the decommissioning of old coal-fired power plants, and the stringent regulations on carbon emissions. Power suppliers need renewable energy generating technologies which are both environment friendly and sustainable in a long term. The requirement of renewable technologies is resulting in an increased financing of the research and development in the solar and wind energy sectors. This increase in the research and development in these renewable sectors can be observed all across the developed world and in particular, the European Union, as a result of its commitment to its Renewable Energy Directive. In the United Kingdom, the wind energy sector has predominantly grown in the recent years, with the construction of multiple wind farms, both on-shore and off-shore. This is resulting in significant advancement in the designs of large wind turbines. However, the abundantly available wind energy in the urban areas is still an energy source to be explored. The current research study is aimed at exploring the design and analysis methodologies of small-to-medium sized wind turbines for urban applications, as the published research in this area is severely limited. A drag based Vertical Axis Wind Turbine (VAWT) has been considered in the present study as these types of VAWTs are more suitable for urban environments. Such VAWTs operate at lower wind speeds, have multidirectional structure, simpler construction, lower manufacturing and maintenance costs, robust design, long lasting operational life, smaller size, low level of noise and vibrations, and possess the ability to self-start and be packed closer together. Improvements to the standard drag based VAWT designs are required to make the best use of their inherent design benefits, which coupled with a more refined and effective design can lead to a wide spread use of drag based VAWTs in urban centres, increasing renewable energy production. Detailed investigates on the effects of various innovative geometrical features on the performance of the VAWT have been carried out. This has been achieved through the use of advanced Computational Fluid Dynamics (CFD) based techniques. The first aspect of the study is to carry out a detailed flow diagnostics of a standard drag based VAWT (the baseline model). Various innovative geometrical features have then been integrated with the baseline model to analyse their effects on the performance of the model. For this purpose, three dimensional models of the VAWT have been numerically analysed for the flow of dry and clean air in urban environments. Furthermore, sliding mesh technique has been employed to rotate the rotor of the VAWT. An in-depth qualitative and quantitative analysis of the global and local flow related parameters has been carried out, while instantaneous torque variations have been monitored throughout the rotation of the VAWT. The second aspect of the study is to critically analyse the start-up process (accelerating rotor) in order to determine the entire operating range of a helical VAWT design. Advanced CFD based technique, known as dynamic mesh, has been employed for this purpose. The advantage of dynamic mesh over sliding mesh is that sliding mesh assumes a constant operating point of the VAWT, while dynamic mesh generates the complete performance map of the VAWT; from the start-up to the constant operating point. Hence, the use of dynamic mesh technique is essential in understanding the transient accelerating behaviour of the VAWT. The third aspect of the current study is to develop an innovative in-house built CFD package for aerodynamic design analysis of VAWTs. The developed package is based on existing open source CFD solvers. Predictions from the developed package have been validated against a well-known and widely used commercial CFD software (ANSYS). The developed package has been shown to predict the complex flow structures in the vicinity of the VAWT, and its performance parameters, with reasonable accuracy, and hence can be used as an inexpensive tool for CFD based design analysis of VAWTs for small-to-medium sized enterprises (SMEs)

Silanol-Assisted Carbinolamine Formation in an Amine-Functionalized Mesoporous Silica Surface: Theoretical Investigation by Fragmentation Methods

The aldol reaction catalyzed by an amine-substituted mesoporous silica nanoparticle (amine-MSN) surface was investigated using a large molecular cluster model (Si392O958C6NH361) combined with the surface integrated molecular orbital/molecular mechanics (SIMOMM) and fragment molecular orbital (FMO) methods. Three distinct pathways for the carbinolamine formation, the first step of the amine-catalyzed aldol reaction, are proposed and investigated in order to elucidate the role of the silanol environment on the catalytic capability of the amine-MSN material. The computational study reveals that the most likely mechanism involves the silanol groups actively participating in the reaction, forming and breaking covalent bonds in the carbinolamine step. Therefore, the active participation of MSN silanol groups in the reaction mechanism leads to a significant reduction in the overall energy barrier for the carbinolamine formation. In addition, a comparison between the findings using a minimal cluster model and the Si392O958C6NH361 cluster suggests that the use of larger models is important when heterogeneous catalysis problems are the target

Exact exchange-correlation potential of a ionic Hubbard model with a free surface

We use Lanczos exact diagonalization to compute the exact exchange-correlation (xc) potential of a Hubbard chain with large binding energy ("the bulk") followed by a chain with zero binding energy ("the vacuum"). Several results of density functional theory in the continuum (sometimes controversial) are verified in the lattice. In particular we show explicitly that the fundamental gap is given by the gap in the Kohn-Sham spectrum plus a contribution due to the jump of the xc-potential when a particle is added. The presence of a staggered potential and a nearest-neighbor interaction V allows to simulate a ionic solid. We show that in the ionic regime in the small hopping amplitude limit the xc-contribution to the gap equals V, while in the Mott regime it is determined by the Hubbard U interaction. In addition we show that correlations generates a new potential barrier at the surface

When Ears Drive Hands: The Influence of Contact Sound on Reaching to Grasp

Background Most research on the roles of auditory information and its interaction with vision has focused on perceptual performance. Little is known on the effects of sound cues on visually-guided hand movements. Methodology/Principal Findings We recorded the sound produced by the fingers upon contact as participants grasped stimulus objects which were covered with different materials. Then, in a further session the pre-recorded contact sounds were delivered to participants via headphones before or following the initiation of reach-to-grasp movements towards the stimulus objects. Reach-to-grasp movement kinematics were measured under the following conditions: (i) congruent, in which the presented contact sound and the contact sound elicited by the to-be-grasped stimulus corresponded; (ii) incongruent, in which the presented contact sound was different to that generated by the stimulus upon contact; (iii) control, in which a synthetic sound, not associated with a real event, was presented. Facilitation effects were found for congruent trials; interference effects were found for incongruent trials. In a second experiment, the upper and the lower parts of the stimulus were covered with different materials. The presented sound was always congruent with the material covering either the upper or the lower half of the stimulus. Participants consistently placed their fingers on the half of the stimulus that corresponded to the presented contact sound. Conclusions/Significance Altogether these findings offer a substantial contribution to the current debate about the type of object representations elicited by auditory stimuli and on the multisensory nature of the sensorimotor transformations underlying action