A Study of Tower Shadow Effect on Fixed-Speed Wind Turbines

This paper studies the impact of tower shadow effect on the power output of a fixed-speed wind farm. A data acquisition unit was placed at a wind farm in Northern Ireland which consists of ten fixed-speed wind turbines. The recording equipment logged the wind farmpsilas electrical data, which was time stamped using the global positioning network. Video footage of the wind farm was recorded and from it the blade angle of each turbine was determined with respect to time. Using the blade angle data and the wind farmpsilas power output, studies where performed to ascertain the extent of tower shadow effect on power fluctuation. This paper presents evidence that suggests that tower shadow effect has a significant impact on power fluctuation and that this effect is increased due to the synchronising of turbine blades around the tower region.

Efficiency improvement study for small wind turbines through flow control

In this study, a constant suction technique for controlling boundary layer separation at low Reynolds numbers was designed and tested. This was later implemented on small wind turbines. Small wind turbines need to operate in low wind speeds, that is, in low Reynolds number regimes – typically in the range 104–105. Airfoils are prone to boundary layer separation in these conditions, leading to a substantial drop in aerodynamic performance of the blades. Under these conditions turbines will have reduced energy output. This paper presents experimental results of applying surface-suction over the suction-surface of airfoils for controlling boundary layer separation. The Reynolds numbers for the experiments are kept in the range 8×104–5×105. The air over the surface of the airfoil is drawn into the airfoil through a slit. It is found that the lift coefficient of the airfoils increases and the drag reduces. Based on the improved airfoil characteristics, an analysis of increase in Coefficient of Power (CP), versus input power for a small wind turbine blade with constant suction is presented.

Testing Tidal Turbines - Part 1: Steady Towing Tests vs Tidal Moored Tests

Tidal turbines have been tested extensively at many scales in steady state flow. Testing medium- or full-scale devices in turbulent flow has been less thoroughly examined. The differences between turbine performances in these two different states are needed for testing method verification and numerical model validation. The work in this paper documents the performance of a 1/10 scale turbine in steady state pushing tests and tidal moored tests. The overall performance of the device appears to decrease with turbulent flow, though there is increased data scatter and therefore, reduced uncertainty. At maximum power performance, as velocity increases the mechanical power and electrical power reduction from steady to unsteady flow increases. The drive train conversion efficiency also decreases. This infers that the performance for this turbine design is affected by the presence of turbulent flow.

Testing Tidal Turbines Part II: Tidal Flow Characterisation Using ADV Data

The study outlined in Testing Tidal Turbines Part 1 explains the variation in performance between turbines operating in steady and turbulent flow conditions. However, the impact of turbulence on devices is generally not well understood. Furthermore, the turbulence characteristics of high velocity marine currents have not been extensively studied. Therefore, knowledge of their characteristics must be expanded and methodologies to predict the impact of the characteristics on devices developed and improved. This study examines the measurement of tidal currents at a site used for testing of medium scale tidal turbines. The data being discussed was collected with a point velocimeter (ADV). The processing procedures implemented are discussed and the resulting estimated turbulence spectra and turbulence intensities are presented. The results contribute to the improvement of knowledge regarding tidal current characteristics. This will be fundamental to the optimisation of the design and operation of tidal stream devices.

Formation and characterization of carbon-radical precursors in char steam gasification

Highly reactive radicals play an important role in high-temperature gasification processes. However, the effect of radicals on gasification has not been systematically investigated. In the present study, the formation of carbon-radical precursors using atomic radicals such as OH, O, and H and molecules such as H₂ and O₂ was characterized, and the effect of the precursors on the adsorption step of steam char gasification was studied using quantum chemistry methods. The results revealed that the radicals can be chemisorbed exothermically on char active sites, and the following order of reactivity was observed: O > H₂ > H > OH > O ₂. Moreover, hydrogen bonds are formed between steam molecules and carbon-radical complexes. Steam molecule adsorption onto carbon-O and carbon-OH complexes is easier than adsorption onto clean carbon surfaces. Alternatively, adsorption on carbon-O₂, carbon-H₂, and carbon-H complexes is at the same level with that of clean carbon surfaces; thus, OH and O radicals accelerate the physical adsorption of steam onto the char surface, H radical and O₂ and H₂ molecules do not have a significant effect on adsorption. © 2010 American Chemical Society.

Density Functional Study on Reaction Activity of Steam Decomposition Products Adsorbed on Carbonaceous Surface

A systematic theoretical study on the adsorption of steam and its thermal decomposition products on carbon both zigzag and armchair surface was performed to provide molecular-level understanding of the reaction activity of all these reactants in biomass steam gasification process. All the calculations were carried out using density functional theory (DFT) at the B3LYP/6-31+g(d,p) level. The structures of carbonaceous surfaces, all reactants and surface complexes were optimized and characterized. Based on the value of adsorption heat been obtained from the calculation, the activity of all reactants can be ordered as: O > O2 >H2 >H >OH >H2O for both zigzag and armchair surface, and the adsorption style is physisorption to water molecule and chemisorption to the other dissociated components.

Investigation into the potential of using micro gas turbines in plug-in hybrid electric vehicles

The transport sector is considered to be one of the most dependent sectors on fossil fuels. Meeting ecological, social and economic demands throughout the sector has got increasingly important in recent times. A passenger vehicle with a more environmentally friendly propulsion system is the hybrid electric vehicle. Combining an internal combustion engine and an electric motor offers the potential to reduce carbon dioxide emissions. The overall objective of this research is to provide an appraisal of the use of a micro gas turbine as the range extender in a plug-in hybrid electric vehicle. In this application, the gas turbine can always operate at its most efficient operating point as its only requirement is to recharge the battery. For this reason, it is highly suitable for this purpose. Gas turbines offer many benefits over traditional internal combustion engines which are traditionally used in this application. They offer a high power-to-weight ratio, multi-fuel capability and relatively low emission levels due to continuous combustion.

Field test of multiple 1/10 scale tidal turbines in steady flows

Queen's University Belfast and Wave Barrier Ltd have developed a tidal testing platform to test hydrokinetic turbines at medium scale. Multiple turbines can be pushed through still water conditions, in steady-state pushing tests. Experiments were conducted to evaluate the interactions between two identical, mono-strut, horizontal axis tidal turbines (HATTs) of 1.5 m diameter (D) rotor. Their relative performance when located individually, in-plane and in-line are investigated. The data shows a high consistency in the power curves at different flow speeds, which indicates high repeatability in this Reynolds range. For an individual turbine, there is no performance difference when the rotor is mounted either upstream or downstream of the supporting structure. When placed in-plane, the turbines have no adverse effect on one another. When spaced in-line with 2D separation, there is a 63% reduction in the performance of the downstream turbine. At 6D downstream this performance reduction is still 59%, indicating some wake recovery between 2D and 6D, though the influence from the upstream rotor persists to at least 6D downstream of the first device. In contrast the performance of the downstream turbine when placed at 1.5D offset of the upstream device at 6D downstream is approximately recovered to the individual turbine performance.

Ethanol Steam Reforming on Rh Catalysts: Theoretical and Experimental Understanding

Through combined theoretical and experimental efforts, the reaction mechanism of ethanol steam reforming on Rh catalysts was studied. The results suggest that acetaldehyde (CH3CHO) is an important reaction intermediate in the reaction on nanosized Rh catalyst. Our theoretical work suggests that the H-bond effect significantly modifies the ethanol decomposition pathway. The possible reaction pathway on Rh (211) surface is suggested as CH3CH2OH -> CH3CH2O -> CH3CHO -> CH3CO -> CH3 + CO -> CH2 + CO -> CH + CO -> C + CO, followed by the water gas shift reaction to yield H-2 and CO2. In addition, we found that the water-gas shift reaction, not the ethanol decomposition, is the bottleneck for the overall ethanol steam reforming process. The CO + OH association is considered the key step, with a sizable energy barrier of 1.31 eV. The present work first discusses the mechanisms and the water effect in ethanol steam reforming reactions on Rh catalyst from both theoretical and experimental standpoints, which may shed light on designing improved catalysts.

Theoretical and experimental understanding on ethanol steam reforming for H-2 production

H2 is considered to be a potential alternative fuel due to its high energy density by weight and working with pollution free. Currently, ethanol conversion to hydrogen has drawn much attention because it provides a viable way for H2 production from renewable resources. In this work, we combined theoretical and experimental efforts to study the reaction mechanism of ethanol steam reforming on Rh catalysts. The results suggest that acetaldehyde (CH3CHO) is an important reaction intermediate in the reaction on nano-sized Rh catalyst. Our theoretical work suggests that the H-bond effect significantly modifies the ethanol decomposition pathway. The possible reaction pathway on Rh (211) surface is suggested as: CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3+CO → CH2+CO → CH+CO → C+CO, followed by the water gas shift reaction to yield H2 and CO2. It was found that that the water gas shift reaction is paramount in the ethanol steam reforming process.

A numerical study of trailing edge geometry for low inertia automotive mixed flow turbines

Abstract. Mixed flow turbines can offer improvements over typical radial turbines used in automotive turbochargers, with respect to transient performance and low velocity ratio efficiency. Turbine rotor mass dominates the rotating inertia of the turbocharger’s rotating assembly, and any reductions of mass in the outer radii of the wheel, including the rotor back-disk, can significantly reduce this inertia and improve the acceleration of the assembly. Off-design, low velocity ratio conditions are typified by highly tangential flow at the rotor inlet and a non-zero inlet blade angle is desirable for such operating conditions. This is achievable in a Mixed Flow Turbine without increasing bending stresses within the rotor blade, which is beneficial in high speed and high inlet temperature turbine designs.
This study considers the meridional geometry of Mixed Flow Turbines using a multi-disciplinary study to assess both the structural and aerodynamic performance of each rotor, incorporating both CFD and FEA. Variations of rotor trailing edge were investigated at different operating conditions representing both on- and off-design operation within the constraints of existing hardware geometries. In all cases, the performance is benchmarked against an existing state-of-the-art radial turbocharger turbine with consideration of rotor inertia and its benefit for engine transient performance. The results indicate the influence of these parameters and this report details their benefits with respect to turbocharging a downsized, automotive engine.

Emotional response to images of wind turbines: A psychophysiological study of their visual impact on the landscape

Social acceptance for wind turbines is variable, providing a challenge to the implementation of this energy source. Psychological research could contribute to the science of climate change. Here we focus on the emotional responses to the visual impact of wind turbines on the landscape, a factor which dominates attitudes towards this technology. Participants in the laboratory viewed images of turbines and other constructions (churches, pylons and power-plants) against rural scenes, and provided psychophysiological and self-report measures of their emotional reactions. We hypothesised that the emotional response to wind turbines would be more negative and intense than to control objects, and that this difference would be accentuated for turbine opponents. As predicted, the psychophysiological response to turbines was stronger than the response to churches, but did not differ from that of other industrial constructions. In contrast with predictions, turbines were rated as less aversive and more calming compared with other industrial constructions, and equivalent to churches. Supporters and non-supporters did not differ significantly from each other. We discuss how a methodology using photo manipulations and emotional self-assessments can help estimate the emotional reaction to the visual impact on the landscape at the planning stage for new wind turbine applications.

Facts, Hacks and Turbines: Media Analysis of Irish Wind Energy

Wind energy projects face increasing opposition from host communities throughout the western world. Governments have responded in a range of ways, including enhanced local control over consenting (England), reform of planning regulations (Australia) or community ownership (Denmark). However, there is no effective mechanism for monitoring levels of social acceptance and thus, no means of evaluating the effectiveness of these approaches. There have been attempts to understand how social framing of wind energy in the media (e.g. Van de Velde et al 2010, Barry and Ellis, 2008, Hindmarsh 2014), highlighting how this changes over time. However, no research has focussed on Ireland and critically, none have examined whether this can help monitor overall levels of social acceptance. In order to explore this, this paper will present a media analysis of wind energy in the Republic of Ireland, which witnessed a rapid increase in wind energy capacity and has the highest energy penetration of wind in the world (19%). However, this has been accompanied by increasing public opposition and (assumed) declining levels of social acceptance.

This paper will describe the results of analysing over 8000 articles on wind energy that have appeared in three Irish newspapers. These are assessed through historical-diachronic (over time) and comparative –synchronic (differences between newspapers) analyses (Carvalho 2007) to highlight changing trends in framing wind energy and changing concerns over wind energy in Ireland. The paper will consider whether such media analysis could form a tool for monitoring the trends in social acceptance of wind energy.