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Daniel Micallef
Department of Environmental Design, Faculty for the Built Environment, University of Malta, Msida, MSD 2080, Malta

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Journal article
Published: 28 January 2021 in Energies
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The general consensus among academics is that the spatio-temporal humidity distribution is more or less uniform in an indoor space. This has, for the large part, not yet been proven by an academic study; subsequently, this paper aims to demonstrate that this is not always true. The paper makes use of a validated transient CFD model, which uses the Low Reynolds Number k- ϵ turbulence model. The model simulates people in a room at a constant skin temperature and emitting a constant source of humidity using source terms in the species equation. The model is eventually used to predict the implications of having a high source of humidity, in the form of occupancy, on the micro-climate’s spatio-temporal humidity distribution. The results for the high-occupancy case show that different locations experience various amounts of humid air, with a 31% difference between the lowest and highest locations. The amount of water vapor in each person’s proximity is deemed to be highly dependent on the flow of the inlet jet, with the people farthest from the jet having an overall less mass of water vapor in their proximity over the two-hour experimental period. This paper has concluded that there are, in fact, cases where the humidity non-uniformity inside an interior environment becomes substantial in situations of high occupancy. The results of this paper may be useful to improve the design of HVAC systems.

ACS Style

Matthew Bonello; Daniel Micallef; Simon Paul Borg. Humidity Distribution in High-Occupancy Indoor Micro-Climates. Energies 2021, 14, 681 .

AMA Style

Matthew Bonello, Daniel Micallef, Simon Paul Borg. Humidity Distribution in High-Occupancy Indoor Micro-Climates. Energies. 2021; 14 (3):681.

Chicago/Turabian Style

Matthew Bonello; Daniel Micallef; Simon Paul Borg. 2021. "Humidity Distribution in High-Occupancy Indoor Micro-Climates." Energies 14, no. 3: 681.

Journal article
Published: 07 October 2020 in Journal of Wind Engineering and Industrial Aerodynamics
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Navier-Stokes actuator disc models have become a mature methodology for investigating wind turbine rotor performance with numerous articles published annually making use of this approach. Despite their popularity, their ability to predict near wake expansion remains questionable. The objective of this paper is to analyse the predictive ability of actuator disc models and compare results with other popular types of codes. The methodology employs the use of an actuator disc Computational Fluid Dynamics approach to model an actuator disc and a real (finite bladed) turbine case. Results are validated with existing experimental data. In addition, results from an actuator line model with and without tip corrections and a 3D vortex panel method are presented to aid the discussion. Results show that all models give a poor wake expansion prediction particularly in the inboard to mid-board areas. A good prediction is found in the outboard regions. In addition, contrary to the well known positive effects of tip corrections on load prediction, this work shows that this does not bring any particular benefit on wake expansion prediction. The conclusions from this work help to guide the use of actuator disc models in more complex flow scenarios including floating offshore wind turbine analysis.

ACS Style

Daniel Micallef; Carlos Ferreira; Iván Herráez; Leo Höning; Wei Yu; Hugo Capdevila. Assessment of actuator disc models in predicting radial flow and wake expansion. Journal of Wind Engineering and Industrial Aerodynamics 2020, 207, 104396 .

AMA Style

Daniel Micallef, Carlos Ferreira, Iván Herráez, Leo Höning, Wei Yu, Hugo Capdevila. Assessment of actuator disc models in predicting radial flow and wake expansion. Journal of Wind Engineering and Industrial Aerodynamics. 2020; 207 ():104396.

Chicago/Turabian Style

Daniel Micallef; Carlos Ferreira; Iván Herráez; Leo Höning; Wei Yu; Hugo Capdevila. 2020. "Assessment of actuator disc models in predicting radial flow and wake expansion." Journal of Wind Engineering and Industrial Aerodynamics 207, no. : 104396.

Conference paper
Published: 22 September 2020 in Journal of Physics: Conference Series
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ACS Style

Abdolrahim Rezaeiha; Daniel Micallef. CFD Simulation of Two Tandem Floating Offshore Wind Turbines in Surge Motion. Journal of Physics: Conference Series 2020, 1618, 1 .

AMA Style

Abdolrahim Rezaeiha, Daniel Micallef. CFD Simulation of Two Tandem Floating Offshore Wind Turbines in Surge Motion. Journal of Physics: Conference Series. 2020; 1618 ():1.

Chicago/Turabian Style

Abdolrahim Rezaeiha; Daniel Micallef. 2020. "CFD Simulation of Two Tandem Floating Offshore Wind Turbines in Surge Motion." Journal of Physics: Conference Series 1618, no. : 1.

Journal article
Published: 13 February 2020 in Building and Environment
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Passive building design involves consideration of a number of design variables which can be optimised with respect to some design objective. The use of optimisation methods in building design is well established but the implementation of the Big Bang-Big Crunch algorithm to passive building design is still as yet unexplored in detail. The aim of this paper is to demonstrate the usefulness of the method as well as to fine-tune its characteristic parameters for its efficient use in building design applications. Two building design scenarios are used to have more than one test case and the number of design variables are limited to an extent that an enumeration search can be performed in a reasonable time frame from which the optimum can be precisely established. The Big Bang-Big Crunch algorithm is used and validated against the true solution from the enumeration search. Results show that the α and β parameters should be set to 0 and around 0.8 respectively. The ratio of the sample size to the number of design variables should ideally be between 2.6 and 2.9 for the algorithm to remain efficient and at the same time successful. The paper also discusses the computational efficiency gain of the Big Bang-Big Crunch algorithm compared to a full enumeration search. Computational savings of more than 90% are possible.

ACS Style

Florian Robic; Daniel Micallef; Simon Paul Borg; Brian Ellul. Implementation and fine-tuning of the Big Bang-Big Crunch optimisation method for use in passive building design. Building and Environment 2020, 173, 106731 .

AMA Style

Florian Robic, Daniel Micallef, Simon Paul Borg, Brian Ellul. Implementation and fine-tuning of the Big Bang-Big Crunch optimisation method for use in passive building design. Building and Environment. 2020; 173 ():106731.

Chicago/Turabian Style

Florian Robic; Daniel Micallef; Simon Paul Borg; Brian Ellul. 2020. "Implementation and fine-tuning of the Big Bang-Big Crunch optimisation method for use in passive building design." Building and Environment 173, no. : 106731.

Journal article
Published: 29 January 2020 in Energies
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One parameter that may affect the performance of a ground source heat pump is the shank-space, the center-to-center distance between the two branches of a vertical U-tube used in a ground heat exchanger. A 3D steady-state computational fluid dynamics (CFD) model of a U-tube ground heat exchanger was used to investigate the influence of varying shank-space on the thermal performance of two isolated vertical shallow U-tubes, one 20 m deep and the other 40 m deep, given that most existing research focuses on systems making use of deeper boreholes. The models adopt an innovative approach, whereby the U-junction at the bottom of the U-tube is eliminated, thus facilitating the computational process. The results obtained show that, although the temperature drop across the U-tube varies for different shank-spaces and is lowest and highest for the closest and the widest shank-spaces, respectively, this temperature drop is not linear with increases in shank-space, and the thermal performance improvement drastically diminishes with increasing shank-space. This indicates that, for shallow U-tubes, the temperature drop is more dependent on the length of the pipework.

ACS Style

Christopher Vella; Simon Paul Borg; Daniel Micallef. The Effect of Shank-Space on the Thermal Performance of Shallow Vertical U-Tube Ground Heat Exchangers. Energies 2020, 13, 602 .

AMA Style

Christopher Vella, Simon Paul Borg, Daniel Micallef. The Effect of Shank-Space on the Thermal Performance of Shallow Vertical U-Tube Ground Heat Exchangers. Energies. 2020; 13 (3):602.

Chicago/Turabian Style

Christopher Vella; Simon Paul Borg; Daniel Micallef. 2020. "The Effect of Shank-Space on the Thermal Performance of Shallow Vertical U-Tube Ground Heat Exchangers." Energies 13, no. 3: 602.

Conference paper
Published: 03 November 2019 in ASME 2019 2nd International Offshore Wind Technical Conference
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This paper compares the predictions from three independent aerodynamic simulation tools modelling the time varying rotor thrust and shaft power of floating offshore wind turbines (FOWTs) under different sea wave conditions. These include a Blade-Element-Momentum (BEM) model, a Free-Wake Vortex model (FWM) and a Navier-Stokes based Actuator Disc (AD) model. The study is based on the NREL1 5 MW baseline FOWT installed on the OC4 DeepCWind semi-submersible platform. The rotor speed is maintained constant throughout the analysis, though different rotor tip speeds and sea wave heights and periods are considered. While the three aerodynamic models apply different approaches for modelling the wake, they are all based on a blade element theory (BET) approach for simulating the blade loads. A common set of static aerofoil data is used and corrections to the data for unsteady effects such as dynamic stall are ignored. Thus disparity between the predictions for the surging rotor is primarily due to the different numerical approaches used for modelling the FOWT wake. The time-averaged rotor thrust and power coefficients predicted by the three models were found to be in close agreement with one another at low tip speed ratios and the sea state was found to have marginal effect on these results. However, the disparity in such predictions between the three models was found to increase at high tip speed ratios, with the FWM and the AD models yielding the largest and smallest rotor thrust and power coefficients, respectively. Furthermore, the AD model was observed to exhibit the highest sensitivity to sea state, with a significant increase in the time averaged power coefficient being predicted at the most extreme wave condition. The amplitudes in the thrust and power expressed as a percentage of the corresponding time-averaged values estimated by the three aerodynamic models were found to be in close agreement with one another for the optimal and high tip speed ratios. However, at low tip speed ratios, the BEM predictions were significantly smaller than those estimated by the FWM and AD models.

ACS Style

Tonio Sant; Daniel Micallef. Disparity Analysis for Three Floating Wind Turbine Aerodynamic Codes in Comparison. ASME 2019 2nd International Offshore Wind Technical Conference 2019, 1 .

AMA Style

Tonio Sant, Daniel Micallef. Disparity Analysis for Three Floating Wind Turbine Aerodynamic Codes in Comparison. ASME 2019 2nd International Offshore Wind Technical Conference. 2019; ():1.

Chicago/Turabian Style

Tonio Sant; Daniel Micallef. 2019. "Disparity Analysis for Three Floating Wind Turbine Aerodynamic Codes in Comparison." ASME 2019 2nd International Offshore Wind Technical Conference , no. : 1.

Conference paper
Published: 03 November 2019 in ASME 2019 2nd International Offshore Wind Technical Conference
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Significant research in the field of Floating Offshore Wind Turbine (FOWT) rotor aerodynamics has been documented in literature, including validated aerodynamic models based on Blade Element Momentum (BEM) and vortex methods, amongst others. However, the effects of platform induced motions on the turbine wake development downstream of the rotor plane or any research related to such areas is rather limited. The aims of this paper are two-fold. Initially, results from a CFD-based Actuator Disc (AD) code for a fixed (non-surging) rotor are compared with those obtained from a Blade Element Momentum (BEM) theory, as well as previously conducted experimental work. Furthermore, the paper also emphasises the effect of tip speed ratio (TSR) on the rotor efficiency. This is followed by the analysis of floating wind turbines specifically in relation to surge displacement, through an AD technique implemented in CFD software, ANSYS Fluent®. The approach couples the Blade Element Theory (BET) for estimating rotating blade loads with a Navier Stokes solver to simulate the turbine wake. With regards to the floating wind turbine cases, the code was slightly altered such that BET was done in a transient manner i.e. following sinusoidal behaviour of waves. The AD simulations were performed for several conditions of TSRs and surge frequencies, at a constant amplitude. Similar to the fixed rotor analysis, significant parameters including thrust and power coefficients, amongst others, were studied against time and surge position. The floating platform data extracted from the AD approach was compared to the non-surging turbine data obtained, to display platform motion effects clearly. Data from hot wire near wake measurements and other simulation methods were also consulted.

ACS Style

Ryan Bezzina; Tonio Sant; Daniel Micallef. Modelling the Aerodynamics of a Floating Wind Turbine Model Using a CFD-Based Actuator Disc Method. ASME 2019 2nd International Offshore Wind Technical Conference 2019, 1 .

AMA Style

Ryan Bezzina, Tonio Sant, Daniel Micallef. Modelling the Aerodynamics of a Floating Wind Turbine Model Using a CFD-Based Actuator Disc Method. ASME 2019 2nd International Offshore Wind Technical Conference. 2019; ():1.

Chicago/Turabian Style

Ryan Bezzina; Tonio Sant; Daniel Micallef. 2019. "Modelling the Aerodynamics of a Floating Wind Turbine Model Using a CFD-Based Actuator Disc Method." ASME 2019 2nd International Offshore Wind Technical Conference , no. : 1.

Journal article
Published: 31 October 2019 in Journal of Building Engineering
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Humidity is an important parameter in understanding the micro-climate in indoor spaces. Existing literature focuses mostly on spatially averaged humidity levels leaving a gap on the spatio-temporal character of this variable. This is contrary to the well populated literature on other environmental parameters such as air temperature and air velocity. The aim of this paper is therefore twofold. First it presents transient humidity and temperature distribution experimental results for a test chamber containing a seated test subject. Secondly, using a validated Computational Fluid Dynamics model, humidity isotropy or lack thereof under conditions of a humidified jet of air was studied. The experimental measurements were carried out at specific points in space over a period of circa 2 h. The CFD model enabled a more complete understanding of the spatial and temporal variations occurring within the space. Comparing the experimental results with those from the CFD model shows that the latter manages to adequately predict the transient specific humidity distribution inside the chamber with a maximum error of 0.0015 g g−1, which, following an initial settling stage, becomes practically homogeneous throughout. Temperature profiles were found difficult to predict with the model. The minor spatial gradients of humidity found are governed by convection and shearing of the flow.

ACS Style

M. Bonello; Daniel Micallef; S.P. Borg. Humidity micro-climate characterisation in indoor environments: A benchmark study. Journal of Building Engineering 2019, 28, 101013 .

AMA Style

M. Bonello, Daniel Micallef, S.P. Borg. Humidity micro-climate characterisation in indoor environments: A benchmark study. Journal of Building Engineering. 2019; 28 ():101013.

Chicago/Turabian Style

M. Bonello; Daniel Micallef; S.P. Borg. 2019. "Humidity micro-climate characterisation in indoor environments: A benchmark study." Journal of Building Engineering 28, no. : 101013.

Journal article
Published: 08 February 2019 in Journal of Building Engineering
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As opposed to steady state characteristics which have been, in the past, estensively investigated, the transient dehumidification characteristics of silica gel under different flat bed configurations, has not been studied in detail with respect to varying mass and air flow rates. Such data is essential in the design of systems employing this method of dehumidification. Moreover, numerical models of the performance of flat bed desiccant configurations generally take the form of fundamental studies with explicit modelling of the desiccant particle geometries. The primary objective of this work aims is to generate dehumidification characteristics in high humidity environments. Secondly, a more simplified and practical approach is proposed here on the basis of experimental calibration. The methodology consists of two main approaches: (i) the development of a test rig for the experimental determination of the transient dehumidification characteristics and, (ii) the development of a Computational Fluid Dynamics (CFD) model using experimental data as input to provide easy extrapolation of experimental data. This paper presents detailed dehumidification results for varying air volume flow rate and desiccant mass. The numerical model, on the other hand, successfully predicts the dehumidification performance of varying silica gel masses by using only a single experimental test case. This proves the validity of using such a model to extrapolate on experimental data.

ACS Style

M. Bonello; D. Micallef; S.P. Borg. Flat bed desiccant dehumidification: A predictive model for desiccant transient characterisation using a species transport model within CFD. Journal of Building Engineering 2019, 23, 280 -290.

AMA Style

M. Bonello, D. Micallef, S.P. Borg. Flat bed desiccant dehumidification: A predictive model for desiccant transient characterisation using a species transport model within CFD. Journal of Building Engineering. 2019; 23 ():280-290.

Chicago/Turabian Style

M. Bonello; D. Micallef; S.P. Borg. 2019. "Flat bed desiccant dehumidification: A predictive model for desiccant transient characterisation using a species transport model within CFD." Journal of Building Engineering 23, no. : 280-290.

Journal article
Published: 31 October 2018 in Sustainable Buildings
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The present case study sets out to investigate the potential and limitations of passive building design in a typical Mediterranean climate. The Maltese Islands were taken as the case study location. Assuming a fully detached, cuboid-shaped, generic multi-storey office building, one representative storey was modelled by means of the building energy simulation code WUFI®Plus. Thermal comfort was analysed based on the adaptive acceptable operative room temperature concept of EN 15251 for buildings without mechanical cooling systems. Assuming neither artificial heating nor cooling, the free-running operative room temperature was evaluated. By means of a parametric study, the robustness of the concept was analysed and the impact of orientation, window to wall area ratio, glazing, shading, thermal insulation, nighttime ventilation and thermal mass on the achievable level of thermal comfort is shown and discussed. It is concluded that in a well-designed building and by means of decent insulation (present case: Uwall = 0.54 W/(m2 · K)), double glazing, variable external shading devices and passive cooling by nighttime ventilation, a high level of thermal comfort is achievable in this climate using only very minor amounts of energy for artificial heating and cooling or possibly even none at all.

ACS Style

Heinrich Manz; Daniel Micallef; Simon Paul Borg; Vincent Buhagiar. A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta. Sustainable Buildings 2018, 3, 4 .

AMA Style

Heinrich Manz, Daniel Micallef, Simon Paul Borg, Vincent Buhagiar. A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta. Sustainable Buildings. 2018; 3 ():4.

Chicago/Turabian Style

Heinrich Manz; Daniel Micallef; Simon Paul Borg; Vincent Buhagiar. 2018. "A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta." Sustainable Buildings 3, no. : 4.

Journal article
Published: 01 September 2018 in Renewable Energy
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This work presents an investigation on different methods for the calculation of the angle of attack and the underlying induced velocity on wind turbine blades using data obtained from three-dimensional Computational Fluid Dynamics (CFD). Several methods are examined and their advantages, as well as shortcomings, are presented. The investigations are performed for two 10 MW reference wind turbines under axial inflow conditions, namely the turbines designed in the EU AVATAR and INNWIND.EU projects. The results show that the evaluated methods are in good agreement with each other at the mid-span, though some deviations are observed at the root and tip regions of the blades. This indicates that CFD results can be used for the calibration of induction modeling for Blade Element Momentum (BEM) tools. Moreover, using any of the proposed methods, it is possible to obtain airfoil characteristics for lift and drag coefficients as a function of the angle of attack.

ACS Style

H. Rahimi; J.G. Schepers; W.Z. Shen; N. Ramos García; M.S. Schneider; Daniel Micallef; Carlos Simao Ferreira; E. Jost; L. Klein; I. Herráez. Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions. Renewable Energy 2018, 125, 866 -876.

AMA Style

H. Rahimi, J.G. Schepers, W.Z. Shen, N. Ramos García, M.S. Schneider, Daniel Micallef, Carlos Simao Ferreira, E. Jost, L. Klein, I. Herráez. Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions. Renewable Energy. 2018; 125 ():866-876.

Chicago/Turabian Style

H. Rahimi; J.G. Schepers; W.Z. Shen; N. Ramos García; M.S. Schneider; Daniel Micallef; Carlos Simao Ferreira; E. Jost; L. Klein; I. Herráez. 2018. "Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions." Renewable Energy 125, no. : 866-876.

Review
Published: 23 August 2018 in Energies
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Urban wind energy research is crucial for the success or failure of wind turbines installed in the built environment. Research in this field is fragmented into various research groups working on different topics in isolation with seemingly few efforts of integrating the various fields. This review aims at highlighting the synergies between the various advances, particularly in aerodynamics, but also in other areas. Past and current work has been focused on establishing reliable wind statistics at the site of interest. Advances in building aerodynamics have provided new insight on the local flow occurring at the rotor location. An outlook toward future research and the need to treat the different flow scales in a holistic manner is emphasized given also the recent advances in rotor aerodynamics related to the effect of flow skewness and turbulence. This will shed light on the critical issues that need to be addressed by scientists in order to make urban wind energy viable for decentralized generation. Various other present challenges are discussed briefly including structural aspects, noise emissions, economics and visual impact. Research in this field should be the guidepost for more targeted certification standards, in an effort to regularize the small wind energy market.

ACS Style

Daniel Micallef; Gerard Van Bussel. A Review of Urban Wind Energy Research: Aerodynamics and Other Challenges. Energies 2018, 11, 2204 .

AMA Style

Daniel Micallef, Gerard Van Bussel. A Review of Urban Wind Energy Research: Aerodynamics and Other Challenges. Energies. 2018; 11 (9):2204.

Chicago/Turabian Style

Daniel Micallef; Gerard Van Bussel. 2018. "A Review of Urban Wind Energy Research: Aerodynamics and Other Challenges." Energies 11, no. 9: 2204.

Conference paper
Published: 18 June 2018 in Journal of Physics: Conference Series
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A sheared wind profile creates an asymmetric wind field and an asymmetric wind turbine wake. Both of these have been described in the past but a study on their implications on the out-of-plane moment on the rotor is still a gap which needs to be addressed. A numerical assessment has been undertaken using a lifting-line free-wake vortex code. Owing to the lack of experimental validation, two other modelling approaches are used to assess the consistency of results - an actuator disc approach and a blade element momentum approach. Results were found to show acceptably good agreement. The line of action of the thrust force is found to be shifted by around 10% upwards above the rotor axis for the extreme shear case of α = 0.55. The wake was found to add to the asymmetry of the wind field by increasing the vertical shift in the line of action by 100% compared to the wind field alone. The results have important implications on the role of the out-of-plane bending moment on the wake kinematics as well as other issues related to fatigue performance of the rotor.

ACS Style

Daniel Micallef; Tonio Sant. Rotor aerodynamics in sheared inflow: An analysis of out-of-plane bending moments. Journal of Physics: Conference Series 2018, 1037, 022027 .

AMA Style

Daniel Micallef, Tonio Sant. Rotor aerodynamics in sheared inflow: An analysis of out-of-plane bending moments. Journal of Physics: Conference Series. 2018; 1037 (2):022027.

Chicago/Turabian Style

Daniel Micallef; Tonio Sant. 2018. "Rotor aerodynamics in sheared inflow: An analysis of out-of-plane bending moments." Journal of Physics: Conference Series 1037, no. 2: 022027.

Conference paper
Published: 18 June 2018 in Journal of Physics: Conference Series
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As part of the AVATAR and Mexnext projects, this study compares several methods used to derive lifting line variables from CFD simulations of the MEXICO rotor in yawed inflow. The results from six partners within the AVATAR/Mexnext consortium using five different methods of extraction were compared. Overall comparison of the induced velocities at the mid and tip parts of blade shows fairly good agreement between the tested methods, where the derived angle of attack differs within 1°, within the linear range this accounts to ˂ 10% uncertainty on the aerodynamic forces. The presented comparison shows inadequate agreement between the methods for application towards the root.

ACS Style

K. Vimalakanthan; J.G Schepers; W.Z Shen; H. Rahimi; D. Micallef; C.J. Simao Ferreira; E. Jost; L. Klein. Evaluation of different methods of determining the angle of attack on wind turbine blades under yawed inflow conditions. Journal of Physics: Conference Series 2018, 1037, 022028 .

AMA Style

K. Vimalakanthan, J.G Schepers, W.Z Shen, H. Rahimi, D. Micallef, C.J. Simao Ferreira, E. Jost, L. Klein. Evaluation of different methods of determining the angle of attack on wind turbine blades under yawed inflow conditions. Journal of Physics: Conference Series. 2018; 1037 (2):022028.

Chicago/Turabian Style

K. Vimalakanthan; J.G Schepers; W.Z Shen; H. Rahimi; D. Micallef; C.J. Simao Ferreira; E. Jost; L. Klein. 2018. "Evaluation of different methods of determining the angle of attack on wind turbine blades under yawed inflow conditions." Journal of Physics: Conference Series 1037, no. 2: 022028.

Preprint
Published: 13 September 2017
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This work presents an investigation on different methods for the calculation of the angle of attack and the underlying induced velocity on wind turbine blades using data obtained from three dimensional computational fluid dynamics. Several methods were examined and their advantages as well as shortcomings were presented. The investigations were performed for flows past two 10MW reference wind turbines under axial inflow conditions, namely the 10MW turbines designed in the EU AVATAR and INNWIND.EU projects. The results shown that the evaluated methods are in good agreement with each other at the mid-span, though some deviations were observed at the root and tip regions of the blades. Using any of the proposed methods, it is possible to obtain airfoil characteristics for lift and drag coefficients as a function of the angle of attack. Furthermore, by using the extracted data new correction models can be derived for blade element momentum calculations.

ACS Style

Hamid Rahimi; Gerard Schepers; Wen Zhong Shen; Néstor Ramos García; Marc Schneider; Daniel Micallef; Carlos Simao Ferreira; Eva Jost; Levin Klein; Iván Herráez. Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions. 2017, 1 .

AMA Style

Hamid Rahimi, Gerard Schepers, Wen Zhong Shen, Néstor Ramos García, Marc Schneider, Daniel Micallef, Carlos Simao Ferreira, Eva Jost, Levin Klein, Iván Herráez. Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions. . 2017; ():1.

Chicago/Turabian Style

Hamid Rahimi; Gerard Schepers; Wen Zhong Shen; Néstor Ramos García; Marc Schneider; Daniel Micallef; Carlos Simao Ferreira; Eva Jost; Levin Klein; Iván Herráez. 2017. "Evaluation of different methods for determining the angle of attack on wind turbine blades with CFD results under axial inflow conditions." , no. : 1.

Conference paper
Published: 01 May 2017 in Journal of Physics: Conference Series
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The presence of conservative forces on rotor blades is neglected in the blade element theory and all the numerical methods derived from it (like e.g. the blade element momentum theory and the actuator line technique). This might seem a reasonable simplification of the real flow of rotor blades, since conservative loads, by definition, do not contribute to the power conversion. However, conservative loads originating from the chordwise bound vorticity might affect the tip vortex trajectory, as we discussed in a previous work. In that work we also hypothesized that this effect, in turn, could influence the wake induction and correspondingly the rotor performance. In the current work we extend a standard actuator line model in order to account for the conservative loads at the blade tip. This allows to isolate the influence of conservative forces from other effects. The comparison of numerical results with and without conservative loads enables to confirm qualitatively their relevance for the near wake and the rotor performance. However, an accurate quantitative assessment of the effect still remains out of reach due to the inherent uncertainty of the numerical model.

ACS Style

I. Herráez; D. Micallef; G.A.M. Van Kuik. Influence of the conservative rotor loads on the near wake of a wind turbine. Journal of Physics: Conference Series 2017, 854, 12022 .

AMA Style

I. Herráez, D. Micallef, G.A.M. Van Kuik. Influence of the conservative rotor loads on the near wake of a wind turbine. Journal of Physics: Conference Series. 2017; 854 (1):12022.

Chicago/Turabian Style

I. Herráez; D. Micallef; G.A.M. Van Kuik. 2017. "Influence of the conservative rotor loads on the near wake of a wind turbine." Journal of Physics: Conference Series 854, no. 1: 12022.

Journal article
Published: 01 December 2016 in Energy and Buildings
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ACS Style

Daniel Micallef; Vincent Buhagiar; Simon P. Borg. Cross-ventilation of a room in a courtyard building. Energy and Buildings 2016, 133, 658 -669.

AMA Style

Daniel Micallef, Vincent Buhagiar, Simon P. Borg. Cross-ventilation of a room in a courtyard building. Energy and Buildings. 2016; 133 ():658-669.

Chicago/Turabian Style

Daniel Micallef; Vincent Buhagiar; Simon P. Borg. 2016. "Cross-ventilation of a room in a courtyard building." Energy and Buildings 133, no. : 658-669.

Conference paper
Published: 30 September 2016 in Journal of Physics: Conference Series
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The performance of a wind turbine located above a cubic building is not well understood. This issue is of fundamental importance for the design of small scale wind turbines. One variable which is of particular importance in this respect is the turbine height above roof level. In this work, the power performance of a small wind turbine is assessed as a function of the height above the roof of a generic cubic building. A 3D Computational Fluid Dynamics model of a 10m x 10m x 10m building is used with the turbine modelled as an actuator disc. Results have shown an improvement in the average power coefficient even in cases where the rotor is partially located within the roof separation zone. This goes against current notions of small wind turbine power production. This study can be of particular importance to guide the turbine installation height on building roof tops.

ACS Style

Daniel Micallef; Tonio Sant; Carlos Ferreira. The influence of a cubic building on a roof mounted wind turbine. Journal of Physics: Conference Series 2016, 753, 22044 .

AMA Style

Daniel Micallef, Tonio Sant, Carlos Ferreira. The influence of a cubic building on a roof mounted wind turbine. Journal of Physics: Conference Series. 2016; 753 ():22044.

Chicago/Turabian Style

Daniel Micallef; Tonio Sant; Carlos Ferreira. 2016. "The influence of a cubic building on a roof mounted wind turbine." Journal of Physics: Conference Series 753, no. : 22044.

Review
Published: 27 July 2016 in Wind Turbines - Design, Control and Applications
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The fundamental physics of HAWT aerodynamics in yaw is reviewed with reference to\ud \ud some of the latest scientific research covering both measurements and numerical\ud \ud modelling. The purpose of this chapter is to enable a concise overview of this important\ud \ud subject in rotor aerodynamics. This will provide the student, researcher or industry\ud \ud professional a quick reference. Detailed references are included for those who need to\ud \ud delve deeper into the subject. The chapter is also restricted to the aerodynamics of single\ud \ud rotors and their wake characteristics. Far wake and wind turbine to turbine effects\ud \ud experienced in wind farms are excluded from this review. Finally, a future outlook is\ud \ud provided in order to inspire further research in yawed aerodynamics.peer-reviewe

ACS Style

Daniel Micallef; Tonio Sant. A Review of Wind Turbine Yaw Aerodynamics. Wind Turbines - Design, Control and Applications 2016, 1 .

AMA Style

Daniel Micallef, Tonio Sant. A Review of Wind Turbine Yaw Aerodynamics. Wind Turbines - Design, Control and Applications. 2016; ():1.

Chicago/Turabian Style

Daniel Micallef; Tonio Sant. 2016. "A Review of Wind Turbine Yaw Aerodynamics." Wind Turbines - Design, Control and Applications , no. : 1.

Journal article
Published: 01 March 2016 in Journal of Renewable and Sustainable Energy
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Lifting line vortexmodels have been widely used to predict flow fields around wind turbine rotors. Such models are known to be deficient in modelling flow fields close to the blades due to the assumption that blade vorticity is concentrated on a line and consequently the influences of blade geometry are not well captured. The present study thoroughly assessed the errors arising from this approximation by prescribing the bound circulation as a boundary condition on the flow using a lifting line free-wake vortex approach. The bound circulation prescribed to free-wake vortexmodel was calculated from two independent sources using (1) experimental results from SPIV and (2) data generated from a 3D panel free-wake vortex approach, where the blade geometry is fully modelled. The axial and tangential flow fields around the blades from the lifting line vortexmodel were then compared with those directly produced by SPIV and the 3D panel model. The comparison was carried out for different radial locations across the blade span. The study revealed the cumulative probability error distributions in lifting line model estimations for the local aerofoil flow field under both 3D rotating and 2D non-rotating conditions. It was found that the errors in a 3D rotating environment are considerably larger than those for a wing of infinite span in 2D flow. Finally, a method based on the Cassini ovals theory is presented for defining regions around rotating blades for which the lifting line model is unreliable for estimating the flow fields.

ACS Style

T. Sant; V. Del Campo; D. Micallef; C. S. Ferreira. Evaluation of the lifting line vortex model approximation for estimating the local blade flow fields in horizontal-axis wind turbines. Journal of Renewable and Sustainable Energy 2016, 8, 023302 .

AMA Style

T. Sant, V. Del Campo, D. Micallef, C. S. Ferreira. Evaluation of the lifting line vortex model approximation for estimating the local blade flow fields in horizontal-axis wind turbines. Journal of Renewable and Sustainable Energy. 2016; 8 (2):023302.

Chicago/Turabian Style

T. Sant; V. Del Campo; D. Micallef; C. S. Ferreira. 2016. "Evaluation of the lifting line vortex model approximation for estimating the local blade flow fields in horizontal-axis wind turbines." Journal of Renewable and Sustainable Energy 8, no. 2: 023302.