Marco Geron | Queen's University Belfast (original) (raw)
Papers by Marco Geron
Experimental Thermal and Fluid Science, 2013
Natural convection heat transfer from a heat generating horizontal cylinder enclosed in a square ... more Natural convection heat transfer from a heat generating horizontal cylinder enclosed in a square cavity where a temperature difference exists across its vertical walls has been experimentally investigated for the range 2×10 4 < Ra cyl < 8×10 4 and a Pr of 0.71. Temperature and cylinder Nusselt number measurements were taken for a range of θ *. θ * is defined as a ratio of cylinder and cavity Grashof numbers. It has been found that at the lower values of Ra cyl , the heat transfer from the cylinder compares well with correlations available in literature. As Ra cyl increases however, it deviates away and the overall heat transfer from the cylinder is increased when compared to these correlations due to the interaction from the cavity. 2D-PIV measurements of the flow structures inside the compartment were conducted. They show an increased interaction between the flow structures generated by the cylinder and by the cavity with increasing θ * , corresponding to the increase in the heat transfer from the cylinder. It is observed that the recirculation generated by the temperature gradient imposed on the cavity is broken down as the plume from the cylinder becomes stronger and a transition process is observed, whereby the flow transitions from being dominated by the temperature difference across the cavity to that dominated by the temperature difference due to the cylinder.
Aerospace Science and Technology, 2013
ABSTRACT A Design of Experiments (DoE) analysis was undertaken to generate a list of configuratio... more ABSTRACT A Design of Experiments (DoE) analysis was undertaken to generate a list of configurations for CFD numerical simulation of an aircraft crown compartment. Fitted regression models were built to predict the convective heat transfer coefficients of thermally sensitive dissipating elements located inside this compartment. These are namely the SEPDC and the Route G. Currently they are positioned close to the fuselage and it is of interest to optimise the heat transfer for reliability and performance purposes. Their locations and the external fuselage surface temperature were selected as input variables for the DoE. The models fit the CFD data with R2R2 values ranging from 0.878 to 0.978, and predict that the optimum locations in terms of heat transfer are when the elements are positioned as close to the crown floor as possible (SySy and Ry→min. limitsRy→min. limits), where they come in direct contact with the air flow from the cabin ventilation system, and when they are positioned close to the centreline (SxSx and Rx→CLRx→CL).The methodology employed allows aircraft thermal designers to optimise equipment placement in confined areas of an aircraft during the design phase. The determined models should be incorporated into global aircraft numerical models to improve accuracy and reduce model size and computational time.
Applied Thermal Engineering, 2013
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • Development of a reduced order model for the case of an aircraft crown compartment • A thermal fluid network is generated for its mixed convection regime • Regression analysis utilised to evaluate characteristic parameters • The thermal fluid network is simple but its accuracy is close to the detailed model
Building Simulation Conference Proceedings
In indoor thermal environment modelling applications where dynamic local effects of fluid flows a... more In indoor thermal environment modelling applications where dynamic local effects of fluid flows are critical, classic zonal models are not always suitable. On the other hand, CFD simulations can give accurate solutions at very high computational cost. Reduced-order models (ROMs), extracted from CFD simulations, can preserve CFD model accuracy while being characteristically of low computational cost. The authors propose a method, known as CFD-ROM, capable of rapidly and automatically generating, from CFD simulations, zones, mass, and heat flows, and boundary conditions (BCs) for ROMs. This paper presents a comparative study of automatic zone generation algorithms as a necessary initial step to developing the CFD-ROM method. Zone generation algorithms compared in this paper are: (1) Mean Values Segmentation; (2) Classic Watershed; and (3) Coarse Grid Interpolation. The methods were compared on the bases of their accuracy against the original validated CFD simulation results, and their time to zone generation. The Mean Values Segmentation method yields promising results, providing a mean error below 0.2K for 15-zone models generated in under 28 seconds. The next immediate steps for the development of CFD-ROM are (i) construction of a ROM solver, and (ii) testing its ability to predict thermal conditions when CFD BCs and ROM BCs differ.
Applied Energy, 2019
The application of gasification to thermally treat biomass as carbon neutral resources has been c... more The application of gasification to thermally treat biomass as carbon neutral resources has been constrained by the technical challenges associated with tar formations, which cause operational problems in downstream equipment for syngas processing. Catalysts, such as transition metals, calcined rocks and char, can be used to catalyse tar reforming. Biochars, which are naturally produced during biomass gasification, are particularly attractive as an alternative catalyst due to their catalytic functions, low cost and long endurance. Despite these promising characteristics, adequate knowledge on the relationship between the porous structure of biochar and its deactivation by coking during the steam reforming of tars is not available. In this work, the influence of the porous structure of biochar on its performance across time for reforming tar was investigated in a fixed-bed reactor, over a temperature range from 650 to 850 °C. Regular biochar and physically activated biochar from the same precursor biomass were employed as bed material. The tar samples were the composed mixture of benzene, toluene and naphthalene. Both fresh and spent catalysts were analysed with Brunauer-Emmet-Teller, tplot, Fourier Transform Infrared and Scanning Electron Microscopy/Energy Dispersive Spectroscopy. Results showed that, while at moderate temperatures of 650 and 750 °C, the activated biochar offered a higher tar conversion but more severe deactivation than that of the regular biochar. At the high temperature of 850 °C, the difference in the catalytic performance between the two chars was negligible, and over 90% of the initial tar species were removed throughout the 3-hour long experiments. At 850 °C, the coke deposited in the meso-and macro-pores of both chars was gasified, leading to a stable catalytic performance of both chars. The results indicated that meso-and macro-porous biochars are resilient and active enough to become a viable option for tar steam reforming.
Energy, 2019
The present study aims to develop a systematic tool chain for automatically extracting accurate R... more The present study aims to develop a systematic tool chain for automatically extracting accurate Reduced-Order Models (ROMs) from Computational Fluid Dynamics (CFD) simulations for use in the design and operation of near-zero energy buildings, with a higher accuracy than traditional zonal models but at a fraction of the computational cost of CFD. This study assesses the accuracy and time to solution of ROMs when solved for different Boundary Conditions (BCs) in order to define the usability envelope of the automatically extracted ROMs. The parameters used in this study are inlet temperatures and mass flow rates. Results show that the absolute error can be kept under 0.5K for changes in temperature of up to ±15K and under 0.25K for changes in mass flow rates of up to ±45% of the original value. The results show that this method has potential for applications in the built environment where its accuracy and low computational cost can bridge a gap between low order RC models and high order CFD, further improving energy efficiency in smart buildings.
Energy Procedia, 2019
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Energy and Buildings, 2015
Accurate modelling of the internal climate of buildings is essential if Building Energy Managemen... more Accurate modelling of the internal climate of buildings is essential if Building Energy Management Systems (BEMS) are to efficiently maintain adequate thermal comfort. Computational fluid dynamics (CFD) models are usually utilised to predict internal climate. Nevertheless CFD models, although providing the necessary level of accuracy, are highly computationally expensive, and cannot practically be integrated in BEMS. This paper presents and describes validation of a CFD-ROM method for real-time simulations of building thermal performance. The CFD-ROM method involves the automatic extraction and solution of reduced order models (ROMs) from validated CFD simulations. ROMs are shown to be adequately accurate with a total error below 5% and to retain satisfactory representation of the phenomena modelled. Each ROM has a time to solution under 20 seconds, which opens the potential of their integration with BEMS, giving real-time physics-based building energy modelling. A parameter study was conducted to investigate the applicability of the extracted ROM to initial boundary conditions different from those from which it was extracted. The results show that the ROMs retained satisfactory total errors when the initial conditions in the room were varied by ±5 o C. This allows the production of a finite number of ROMs with the ability to rapidly model many possible scenarios.
Building and Environment, 2013
Well planned natural ventilation strategies and systems in the built environments may provide hea... more Well planned natural ventilation strategies and systems in the built environments may provide healthy and comfortable indoor conditions, while contributing to a significant reduction in the energy consumed by buildings. Computational Fluid Dynamics (CFD) is particularly suited for modelling indoor conditions in naturally ventilated spaces, which are difficult to predict using other types of building simulation tools. Hence, accurate and reliable CFD models of naturally ventilated indoor spaces are necessary to support the effective design and operation of indoor environments in buildings. This paper presents a formal calibration methodology for the development of CFD models of naturally ventilated indoor environments. The methodology explains how to qualitatively and quantitatively verify and validate CFD models, including parametric analysis utilising the response surface technique to support a robust calibration process. The proposed methodology is demonstrated on a naturally ventilated study zone in the library building at the National University of Ireland in Galway. The calibration process is supported by the on-site measurements performed in a normally operating building. The measurement of outdoor weather data provided boundary conditions for the CFD model, while a network of wireless sensors supplied air speeds and air temperatures inside the room for the model calibration. The concepts and techniques developed here will enhance the process of achieving reliable CFD models that represent indoor spaces and provide new and valuable information for estimating the effect of the boundary conditions on the CFD model results in indoor environments.
Building and Environment, 2013
Natural ventilation is a sustainable solution to maintaining healthy and comfortable environmenta... more Natural ventilation is a sustainable solution to maintaining healthy and comfortable environmental conditions in buildings. However, the effective design, construction and operation of naturally ventilated buildings require a good understanding of complex airflow patterns caused by the buoyancy and wind effects. The work presented in this article employed a 3D computational fluid dynamics (CFD) analysis in order to investigate environmental conditions and thermal comfort of the occupants of a highly-glazed naturally ventilated meeting room. This analysis was facilitated by the real-time field measurements performed in an operating building, and previously developed formal calibration methodology for reliable CFD models of indoor environments. Since, creating an accurate CFD model of an occupied space in a real-life scenario requires a high level of CFD expertise, trusted experimental data and an ability to interpret model input parameters; the calibration methodology guided towards a robust and reliable CFD model of the indoor environment. This calibrated CFD model was then used to investigate indoor environmental conditions and to evaluate thermal comfort indices for the occupants of the room. Thermal comfort expresses occupants' satisfaction with thermal environment in buildings by defining the range of indoor thermal environmental conditions acceptable to a majority of occupants. In this study, the thermal comfort analysis, supported by both field measurements and CFD simulation results, confirmed a satisfactory and optimal room operation in terms of thermal environment for the investigated real-life scenario.
Journal of Biomechanical Engineering-transactions of The Asme, 2009
The urinary catheter is a thin plastic tube that has been designed to empty the bladder artificia... more The urinary catheter is a thin plastic tube that has been designed to empty the bladder artificially, effortlessly, and with minimum discomfort. The current CH14 male catheter design was examined with a view to optimizing the mass flow rate. The literature imposed constraints to the analysis of the urinary catheter to ensure that a compromise between optimal flow, patient comfort, and everyday practicality from manufacture to use was achieved in the new design. As a result a total of six design characteristics were examined. The input variables in question were the length and width of eyelets 1 and 2 (four variables), the distance between the eyelets, and the angle of rotation between the eyelets. Due to the high number of possible input combinations a structured approach to the analysis of data was necessary. A combination of computational fluid dynamics (CFD) and design of experiments (DOE) has been used to evaluate the "optimal configuration." The use of CFD couple with DOE is a novel concept, which harnesses the computational power of CFD in the most efficient manner for prediction of the mass flow rate in the catheter.
International Journal of Computational Fluid Dynamics, 2009
This study is motivated by the use of natural convection correlations in the early stages of ther... more This study is motivated by the use of natural convection correlations in the early stages of thermal design. While correlations are widely available for benchmark geometries, in practice compartments may have many heated surfaces and several heat generating objects. An experimental investigation is undertaken to examine the influence of cavity differential heating on the natural convection flow from an isothermal circular horizontal cylinder. The square compartment, of length (L), contains the centrally positioned cylinder of diameter 0.1L. The vertical walls are differentially heated, while the remainders are assumed adiabatic. Steady-state temperature measurements were taken in 15 different locations inside the cavity. The air flow fields and velocities were measured using a 2D PIV system. Results are presented in the form of Nusselt number correlations, velocity vector maps and boundary layer profiles for different values of the Rayleigh number and temperature difference ratio (T*). A circular airflow was observed inside the compartment. The plume rising from the cylinder interferes with this stream with varying results depending on Ra and T*. The flow structures become increasingly dominated by the presence of the cylinder with increasing Ra and T* despite the Grashof number for the cylinder being several orders of magnitude lower than that for the cavity.
Journal of Turbomachinery-transactions of The Asme, 2006
ABSTRACT In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable ... more ABSTRACT In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable to reproduce the azimuthal periodicity in the stage of an axial compressor or turbine. Transonic tests in a cascade wind tunnel with open jet boundaries have been shown to suffer from spurious waves, reflected at the jet boundary, that compromise the flow periodicity in pitch. This problem can be tackled by placing at this boundary a slotted tailboard with a specific wall void ratio s and pitch angle alpha. The optimal value of the s-alpha pair depends on the test section geometry and on the tunnel running conditions. An inviscid two-dimensional numerical method has been developed to predict transonic linear cascade flows, with and without a tailboard, and quantify the nonperiodicity in the discharge. This method includes a new computational boundary condition to model the effects of the tailboard slots on the cascade interior flow This method has been applied to a six-blade turbine nozzle cascade, transonically tested at the University of Leicester The numerical results identified a specific slotted tailboard geometry, able to minimize the spurious reflected waves and regain some pitchwise flow periodicity. The wind tunnel open jet test section was redesigned accordingly Pressure measurements at the cascade outlet and synchronous spark schlieren visualization of the test section, with and without the optimized slotted tailboard, have confirmed the gain in pitchwise periodicity predicted by the numerical model.
Aerospace Science and Technology, 2007
The plug nozzle is one of the advanced expansion devices proposed to improve the overall performa... more The plug nozzle is one of the advanced expansion devices proposed to improve the overall performance of launcher liquid rocket engines. The present work investigates the three-dimensional flow field generated on this kind of nozzle by partitioning the primary nozzle into modules. A linear plug nozzle has been designed together with modules having two different geometries: a rectangular cross section and round-to-square module. Numerical simulations have been carried out considering the case where all modules of the primary nozzle are active and the case where one module is turned off. The solutions are compared and specific three-dimensional flow structures taking place inside the modules and on the plug are identified. The relationship between these structures and the skin friction distribution within the module and along the plug surface is investigated. Finally, the effect on performance of these three-dimensional flow features is emphasized.
Experimental Thermal and Fluid Science, 2013
Natural convection heat transfer from a heat generating horizontal cylinder enclosed in a square ... more Natural convection heat transfer from a heat generating horizontal cylinder enclosed in a square cavity where a temperature difference exists across its vertical walls has been experimentally investigated for the range 2×10 4 < Ra cyl < 8×10 4 and a Pr of 0.71. Temperature and cylinder Nusselt number measurements were taken for a range of θ *. θ * is defined as a ratio of cylinder and cavity Grashof numbers. It has been found that at the lower values of Ra cyl , the heat transfer from the cylinder compares well with correlations available in literature. As Ra cyl increases however, it deviates away and the overall heat transfer from the cylinder is increased when compared to these correlations due to the interaction from the cavity. 2D-PIV measurements of the flow structures inside the compartment were conducted. They show an increased interaction between the flow structures generated by the cylinder and by the cavity with increasing θ * , corresponding to the increase in the heat transfer from the cylinder. It is observed that the recirculation generated by the temperature gradient imposed on the cavity is broken down as the plume from the cylinder becomes stronger and a transition process is observed, whereby the flow transitions from being dominated by the temperature difference across the cavity to that dominated by the temperature difference due to the cylinder.
Aerospace Science and Technology, 2013
ABSTRACT A Design of Experiments (DoE) analysis was undertaken to generate a list of configuratio... more ABSTRACT A Design of Experiments (DoE) analysis was undertaken to generate a list of configurations for CFD numerical simulation of an aircraft crown compartment. Fitted regression models were built to predict the convective heat transfer coefficients of thermally sensitive dissipating elements located inside this compartment. These are namely the SEPDC and the Route G. Currently they are positioned close to the fuselage and it is of interest to optimise the heat transfer for reliability and performance purposes. Their locations and the external fuselage surface temperature were selected as input variables for the DoE. The models fit the CFD data with R2R2 values ranging from 0.878 to 0.978, and predict that the optimum locations in terms of heat transfer are when the elements are positioned as close to the crown floor as possible (SySy and Ry→min. limitsRy→min. limits), where they come in direct contact with the air flow from the cabin ventilation system, and when they are positioned close to the centreline (SxSx and Rx→CLRx→CL).The methodology employed allows aircraft thermal designers to optimise equipment placement in confined areas of an aircraft during the design phase. The determined models should be incorporated into global aircraft numerical models to improve accuracy and reduce model size and computational time.
Applied Thermal Engineering, 2013
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • Development of a reduced order model for the case of an aircraft crown compartment • A thermal fluid network is generated for its mixed convection regime • Regression analysis utilised to evaluate characteristic parameters • The thermal fluid network is simple but its accuracy is close to the detailed model
Building Simulation Conference Proceedings
In indoor thermal environment modelling applications where dynamic local effects of fluid flows a... more In indoor thermal environment modelling applications where dynamic local effects of fluid flows are critical, classic zonal models are not always suitable. On the other hand, CFD simulations can give accurate solutions at very high computational cost. Reduced-order models (ROMs), extracted from CFD simulations, can preserve CFD model accuracy while being characteristically of low computational cost. The authors propose a method, known as CFD-ROM, capable of rapidly and automatically generating, from CFD simulations, zones, mass, and heat flows, and boundary conditions (BCs) for ROMs. This paper presents a comparative study of automatic zone generation algorithms as a necessary initial step to developing the CFD-ROM method. Zone generation algorithms compared in this paper are: (1) Mean Values Segmentation; (2) Classic Watershed; and (3) Coarse Grid Interpolation. The methods were compared on the bases of their accuracy against the original validated CFD simulation results, and their time to zone generation. The Mean Values Segmentation method yields promising results, providing a mean error below 0.2K for 15-zone models generated in under 28 seconds. The next immediate steps for the development of CFD-ROM are (i) construction of a ROM solver, and (ii) testing its ability to predict thermal conditions when CFD BCs and ROM BCs differ.
Applied Energy, 2019
The application of gasification to thermally treat biomass as carbon neutral resources has been c... more The application of gasification to thermally treat biomass as carbon neutral resources has been constrained by the technical challenges associated with tar formations, which cause operational problems in downstream equipment for syngas processing. Catalysts, such as transition metals, calcined rocks and char, can be used to catalyse tar reforming. Biochars, which are naturally produced during biomass gasification, are particularly attractive as an alternative catalyst due to their catalytic functions, low cost and long endurance. Despite these promising characteristics, adequate knowledge on the relationship between the porous structure of biochar and its deactivation by coking during the steam reforming of tars is not available. In this work, the influence of the porous structure of biochar on its performance across time for reforming tar was investigated in a fixed-bed reactor, over a temperature range from 650 to 850 °C. Regular biochar and physically activated biochar from the same precursor biomass were employed as bed material. The tar samples were the composed mixture of benzene, toluene and naphthalene. Both fresh and spent catalysts were analysed with Brunauer-Emmet-Teller, tplot, Fourier Transform Infrared and Scanning Electron Microscopy/Energy Dispersive Spectroscopy. Results showed that, while at moderate temperatures of 650 and 750 °C, the activated biochar offered a higher tar conversion but more severe deactivation than that of the regular biochar. At the high temperature of 850 °C, the difference in the catalytic performance between the two chars was negligible, and over 90% of the initial tar species were removed throughout the 3-hour long experiments. At 850 °C, the coke deposited in the meso-and macro-pores of both chars was gasified, leading to a stable catalytic performance of both chars. The results indicated that meso-and macro-porous biochars are resilient and active enough to become a viable option for tar steam reforming.
Energy, 2019
The present study aims to develop a systematic tool chain for automatically extracting accurate R... more The present study aims to develop a systematic tool chain for automatically extracting accurate Reduced-Order Models (ROMs) from Computational Fluid Dynamics (CFD) simulations for use in the design and operation of near-zero energy buildings, with a higher accuracy than traditional zonal models but at a fraction of the computational cost of CFD. This study assesses the accuracy and time to solution of ROMs when solved for different Boundary Conditions (BCs) in order to define the usability envelope of the automatically extracted ROMs. The parameters used in this study are inlet temperatures and mass flow rates. Results show that the absolute error can be kept under 0.5K for changes in temperature of up to ±15K and under 0.25K for changes in mass flow rates of up to ±45% of the original value. The results show that this method has potential for applications in the built environment where its accuracy and low computational cost can bridge a gap between low order RC models and high order CFD, further improving energy efficiency in smart buildings.
Energy Procedia, 2019
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Energy and Buildings, 2015
Accurate modelling of the internal climate of buildings is essential if Building Energy Managemen... more Accurate modelling of the internal climate of buildings is essential if Building Energy Management Systems (BEMS) are to efficiently maintain adequate thermal comfort. Computational fluid dynamics (CFD) models are usually utilised to predict internal climate. Nevertheless CFD models, although providing the necessary level of accuracy, are highly computationally expensive, and cannot practically be integrated in BEMS. This paper presents and describes validation of a CFD-ROM method for real-time simulations of building thermal performance. The CFD-ROM method involves the automatic extraction and solution of reduced order models (ROMs) from validated CFD simulations. ROMs are shown to be adequately accurate with a total error below 5% and to retain satisfactory representation of the phenomena modelled. Each ROM has a time to solution under 20 seconds, which opens the potential of their integration with BEMS, giving real-time physics-based building energy modelling. A parameter study was conducted to investigate the applicability of the extracted ROM to initial boundary conditions different from those from which it was extracted. The results show that the ROMs retained satisfactory total errors when the initial conditions in the room were varied by ±5 o C. This allows the production of a finite number of ROMs with the ability to rapidly model many possible scenarios.
Building and Environment, 2013
Well planned natural ventilation strategies and systems in the built environments may provide hea... more Well planned natural ventilation strategies and systems in the built environments may provide healthy and comfortable indoor conditions, while contributing to a significant reduction in the energy consumed by buildings. Computational Fluid Dynamics (CFD) is particularly suited for modelling indoor conditions in naturally ventilated spaces, which are difficult to predict using other types of building simulation tools. Hence, accurate and reliable CFD models of naturally ventilated indoor spaces are necessary to support the effective design and operation of indoor environments in buildings. This paper presents a formal calibration methodology for the development of CFD models of naturally ventilated indoor environments. The methodology explains how to qualitatively and quantitatively verify and validate CFD models, including parametric analysis utilising the response surface technique to support a robust calibration process. The proposed methodology is demonstrated on a naturally ventilated study zone in the library building at the National University of Ireland in Galway. The calibration process is supported by the on-site measurements performed in a normally operating building. The measurement of outdoor weather data provided boundary conditions for the CFD model, while a network of wireless sensors supplied air speeds and air temperatures inside the room for the model calibration. The concepts and techniques developed here will enhance the process of achieving reliable CFD models that represent indoor spaces and provide new and valuable information for estimating the effect of the boundary conditions on the CFD model results in indoor environments.
Building and Environment, 2013
Natural ventilation is a sustainable solution to maintaining healthy and comfortable environmenta... more Natural ventilation is a sustainable solution to maintaining healthy and comfortable environmental conditions in buildings. However, the effective design, construction and operation of naturally ventilated buildings require a good understanding of complex airflow patterns caused by the buoyancy and wind effects. The work presented in this article employed a 3D computational fluid dynamics (CFD) analysis in order to investigate environmental conditions and thermal comfort of the occupants of a highly-glazed naturally ventilated meeting room. This analysis was facilitated by the real-time field measurements performed in an operating building, and previously developed formal calibration methodology for reliable CFD models of indoor environments. Since, creating an accurate CFD model of an occupied space in a real-life scenario requires a high level of CFD expertise, trusted experimental data and an ability to interpret model input parameters; the calibration methodology guided towards a robust and reliable CFD model of the indoor environment. This calibrated CFD model was then used to investigate indoor environmental conditions and to evaluate thermal comfort indices for the occupants of the room. Thermal comfort expresses occupants' satisfaction with thermal environment in buildings by defining the range of indoor thermal environmental conditions acceptable to a majority of occupants. In this study, the thermal comfort analysis, supported by both field measurements and CFD simulation results, confirmed a satisfactory and optimal room operation in terms of thermal environment for the investigated real-life scenario.
Journal of Biomechanical Engineering-transactions of The Asme, 2009
The urinary catheter is a thin plastic tube that has been designed to empty the bladder artificia... more The urinary catheter is a thin plastic tube that has been designed to empty the bladder artificially, effortlessly, and with minimum discomfort. The current CH14 male catheter design was examined with a view to optimizing the mass flow rate. The literature imposed constraints to the analysis of the urinary catheter to ensure that a compromise between optimal flow, patient comfort, and everyday practicality from manufacture to use was achieved in the new design. As a result a total of six design characteristics were examined. The input variables in question were the length and width of eyelets 1 and 2 (four variables), the distance between the eyelets, and the angle of rotation between the eyelets. Due to the high number of possible input combinations a structured approach to the analysis of data was necessary. A combination of computational fluid dynamics (CFD) and design of experiments (DOE) has been used to evaluate the "optimal configuration." The use of CFD couple with DOE is a novel concept, which harnesses the computational power of CFD in the most efficient manner for prediction of the mass flow rate in the catheter.
International Journal of Computational Fluid Dynamics, 2009
This study is motivated by the use of natural convection correlations in the early stages of ther... more This study is motivated by the use of natural convection correlations in the early stages of thermal design. While correlations are widely available for benchmark geometries, in practice compartments may have many heated surfaces and several heat generating objects. An experimental investigation is undertaken to examine the influence of cavity differential heating on the natural convection flow from an isothermal circular horizontal cylinder. The square compartment, of length (L), contains the centrally positioned cylinder of diameter 0.1L. The vertical walls are differentially heated, while the remainders are assumed adiabatic. Steady-state temperature measurements were taken in 15 different locations inside the cavity. The air flow fields and velocities were measured using a 2D PIV system. Results are presented in the form of Nusselt number correlations, velocity vector maps and boundary layer profiles for different values of the Rayleigh number and temperature difference ratio (T*). A circular airflow was observed inside the compartment. The plume rising from the cylinder interferes with this stream with varying results depending on Ra and T*. The flow structures become increasingly dominated by the presence of the cylinder with increasing Ra and T* despite the Grashof number for the cylinder being several orders of magnitude lower than that for the cavity.
Journal of Turbomachinery-transactions of The Asme, 2006
ABSTRACT In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable ... more ABSTRACT In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable to reproduce the azimuthal periodicity in the stage of an axial compressor or turbine. Transonic tests in a cascade wind tunnel with open jet boundaries have been shown to suffer from spurious waves, reflected at the jet boundary, that compromise the flow periodicity in pitch. This problem can be tackled by placing at this boundary a slotted tailboard with a specific wall void ratio s and pitch angle alpha. The optimal value of the s-alpha pair depends on the test section geometry and on the tunnel running conditions. An inviscid two-dimensional numerical method has been developed to predict transonic linear cascade flows, with and without a tailboard, and quantify the nonperiodicity in the discharge. This method includes a new computational boundary condition to model the effects of the tailboard slots on the cascade interior flow This method has been applied to a six-blade turbine nozzle cascade, transonically tested at the University of Leicester The numerical results identified a specific slotted tailboard geometry, able to minimize the spurious reflected waves and regain some pitchwise flow periodicity. The wind tunnel open jet test section was redesigned accordingly Pressure measurements at the cascade outlet and synchronous spark schlieren visualization of the test section, with and without the optimized slotted tailboard, have confirmed the gain in pitchwise periodicity predicted by the numerical model.
Aerospace Science and Technology, 2007
The plug nozzle is one of the advanced expansion devices proposed to improve the overall performa... more The plug nozzle is one of the advanced expansion devices proposed to improve the overall performance of launcher liquid rocket engines. The present work investigates the three-dimensional flow field generated on this kind of nozzle by partitioning the primary nozzle into modules. A linear plug nozzle has been designed together with modules having two different geometries: a rectangular cross section and round-to-square module. Numerical simulations have been carried out considering the case where all modules of the primary nozzle are active and the case where one module is turned off. The solutions are compared and specific three-dimensional flow structures taking place inside the modules and on the plug are identified. The relationship between these structures and the skin friction distribution within the module and along the plug surface is investigated. Finally, the effect on performance of these three-dimensional flow features is emphasized.