Claudia Regina de Andrade | Instituto Tecnológico de Aeronáutica (original) (raw)
Papers by Claudia Regina de Andrade
The Aeronautical Journal, 2016
ABSTRACTThis article presents a unified approach to solve steady-state conjugate heat-transfer pr... more ABSTRACTThis article presents a unified approach to solve steady-state conjugate heat-transfer problem including simultaneously gas, liquid and solid regions in just one 3D domain, distinguished by their particular properties. This approach reduces approximation errors and the time to solve the problem, which characterise iterative methods based on separated domains. The formulation employs RANS equations, realisablek-ε turbulence model and near-wall treatment model. A commercial CFD code solves the pressure-based segregated algorithm combined with spatial discretisation of second order upwind. The problem consists of a convergent-divergent metallic nozzle that contains cooling channels divided in two segments along the wall. The nozzle wall insulates the high-speed hot air flow, dealt as perfect gas, from the two low-speed cold water flows, dealt as compressed liquid, both influenced by transport properties dependent of the local temperature. The verification process uses three mes...
The main design requirements of the aircraft environmental control system are the cabin cooling-h... more The main design requirements of the aircraft environmental control system are the cabin cooling-heating loads and the cool-down and warm-up time periods. The cool-down process is the cooling of a heat-soaked aircraft prior to passenger loading and the warm-up process is the heating of a cold-soaked empty aircraft cabin. In this study the aircraft cabin cool-down and warm-up processes are mathematically modeled and numerically solved to study the influence of the air conditioning machine parameters and the cabin external and internal characteristics. The mathematical model couples the lumped parameters method with a differential approach to reduce the computational effort to solve this problem. This computational tool will reduce both the spent design time and the number of experimental tests to adjust the final environmental control system configuration.
This work focuses on a numerical study of a diesel engine valve ports steady-state compressible f... more This work focuses on a numerical study of a diesel engine valve ports steady-state compressible flow to calculate the mixing effects due to the presence of the filling and spiral intake ducts. These valve ports have an important role in engine charge exchange (exhaust and intake mechanisms), air-fuel mixture and combustion processes. Diesel engine industry developed a stationary bench flow tests which has been very useful to improve the preliminary design of valve ports. In this bench methodology, a stationary airflow is induced through valve ports by a exhaust fan where pressure drops and swirl flow patterns are measured maintaining a fixed valve aperture. At this context, the present CFD (Computational Fluid Dynamic) work intends to show fluid flow patterns and to calculate the Swirl number induced by the secondary flow. A 3D turbulent steady compressible flow is solved employing a finite volume technique with a density based approach.
Gas turbine air inlet cooling is a useful method for increasing output for regions where signific... more Gas turbine air inlet cooling is a useful method for increasing output for regions where significant power demand and highest electricity prices occur during the warm months. Inlet air cooling increases the power output by taking advantage of the gas turbine-s feature of higher mass flow rate when the compressor inlet temperature decreases. Different methods are available for reducing gas turbine inlet temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine-s inlet air temperature. The second system employs various ways to chill the inlet air. In this method, the cooling medium flows through a heat exchanger located in the inlet duct to remove heat from the inlet air. However, the evaporative cooling is limited by wet-bulb temperature while the chilling can cool the inlet air to temperatures that are lower than th...
Journal of Solar Energy Engineering, 2017
Microscale numerical modeling is currently the main tool used in wind industry to assess local wi... more Microscale numerical modeling is currently the main tool used in wind industry to assess local wind resources. This paper presents a systematic procedure to adjust computational fluid dynamics (CFD) predicted wind profiles to experimental measurements in order to minimize their differences. It can be applied when wind measurements are available. Data from ten masts with several measurement heights from the well-known Bolund hill experiment provided the observed wind profiles. Simulated profiles were calculated with windsim CFD model for the aforementioned site. Speed-up correction factors were defined through the least squares method to cross-correlate each mast as reference to all the others inside the Bolund hill domain. After, the observed and the adjusted wind profiles at the same position were compared. Moreover, root mean square errors (RMSEs) were used as a metric to evaluate the estimations and the ability of each position to be predicted and predictor. Results have shown th...
The cabin pressure control system continuously monitors the ground and flight modes of the airpla... more The cabin pressure control system continuously monitors the ground and flight modes of the airplane (climb, cruise, or descent) as well as holding patterns at various altitudes. It uses this information to allow air to escape continuously from the airplane by further opening or closing the outflow valve. Thus, the cabin internal pressure is controlled by modulating the exhaust airflow through the escape valve (outflow valve). As the airplane changes altitude, the outflow valve repositions itself to allow more or less air to escape. While the external ambient pressure is equivalent to the altitude of 36,000 ft, the cabin pressure is maintained at approximately 8,000 ft due to the physiological human requirements (mainly the respiratory needs). This leads a high differential pressure between the cabin and the external environment implying in more intense structural efforts to the fuselage. The outflow valve is constantly being positioned to maintain cabin pressure as close to sea level as practical, without exceeding a predetermined cabin-to-outside pressure differential. In this context, this work focuses on the determination of the outflow valve opening area of the aircraft cabin pressurization system for ground and flight schedules, considering: (i) the inflow supplied by the airconditioning packs; (ii) cabin leakages and (iii) the pressure change rate. The cabin leakage is modelled using the orifice compressible flow theory and the inflow rate is constant (determined by the cabin ventilation requirements). Results are obtained using a typical aircraft flight mission (schedule).
Journal of Aerospace Technology and Management, 2012
International Review of Mechanical Engineering-IREME, May 31, 2013
This study investigates how an incomplete tranesterification reaction influences the parameters o... more This study investigates how an incomplete tranesterification reaction influences the parameters of quality standards of the produced biodiesel engine performance and exhausts. The parameters evaluated include viscosity, cloud point, acid number and heating value. Biodiesels produced from palm oil were examined in terms of engine performance, where the 3-liter engine with a 4 cylinders 4 strokes, was used. The proportion of methyl ester in biodiesel was varied by adding appropriate amounts of triglyceride. Properties of biodiesel with the methyl ester between 75% and 96.8% by mass were tested against the standard diesel. The engine performance and thermal efficiency when using biodiesels of different qualities were determined under the operating engine speed range between 1,800 and 4,000 rpm. It was found that while the cloud point was raised with methyl ester content the viscosity was decreased. In terms of engine performance, greater proportion of methyl ester provides greater fuel conversion efficiency as well as specific fuel consumption rate.
This research work deals with the application of a hydrous ethanol direct injection spark ignitio... more This research work deals with the application of a hydrous ethanol direct injection spark ignition engine model. Computational Fluid Dynamics (CFD) software is applied in order to create the moving mesh and to solve the governing equations. The research scope includes the airflow characterization during intake and compression stroke and also the charge stratification. The distribution of mixture formation distribution within the combustion chamber is analyzed. The influence of parameters such as fuel injection pressure, start of injection, injected fuel mas, equivalence ratio and wall-wet film are evaluated. The goal is to obtain the fuel concentration within the cylinder during the spray development and the piston movement and also the film formation in the chamber walls. It was analyzed the differences and benefits between different injection strategies considering single and dual pulse injection. Parameters such as injection pressure and fuel mass injected are considered, helping...
Journal of Wind Engineering and Industrial Aerodynamics, 2021
Abstract This paper focuses on the estimation of annual energy production (AEP) by simulating the... more Abstract This paper focuses on the estimation of annual energy production (AEP) by simulating the flowfield on a complex terrain located in the northeast region of Brazil using different numerical approaches: CFD RANS with k-e and k-ω turbulence models (WindSim), simple mass-conserving (WindMap), and refined mesoscale (SiteWind). The last two are run through OpenWind software. Wind observations from five meteorological masts are used to adjust the models. Optimal layouts for a hypothetical wind farm with 50 wind turbines are obtained over each of the four wind fields to predict the power generation. As non-negligible differences are found on the spatial distribution of the winds simulated by the different models, the layouts are also substantially different. The AEP is calculated to compare scenarios varying the layouts over the wind fields. The distinct micrositing generate differences of up to 13 % on AEP prediction, which could mean the impact of an improper siting on the wind farm profitability. It is not plausible to categorically claim the superiority of accuracy of one model over the others. Nonetheless, the observed data provide an indicative that the refined mesoscale model was able to better capture the wind acceleration in the western region of the studied site.
Procceedings of the 24th ABCM International Congress of Mechanical Engineering, 2017
SAE Technical Paper Series, 2017
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
International Communications in Heat and Mass Transfer, 2013
Pultrusion is a manufacturing method for fiber-reinforced composite with constant cross-section. ... more Pultrusion is a manufacturing method for fiber-reinforced composite with constant cross-section. In this process, a fiber creel is impregnated in a resin bath and passes through a heated die with a constant pulling force and the elevated die temperature induces the curing-resin process. At the present work the effect of variable properties (thermal conductivity and volumetric heat capacity) during the pultrusion process of thermosetting composite materials is numerically studied. The thermal properties are considered as a function of both temperature and degree of cure distributions inside the carbon/epoxy matrix composites. A two-dimensional parabolic model using the finite element method to solve the energy and degree of cure transport equations was used. These two equations are coupled by a source term from resin curing exothermic reaction. The resin cure kinetics and the properties that are temperature-dependent are both modeled by expressions obtained from the literature. The computational domain is discretized using an unstructured mesh with triangular elements and an adaptive refinement. Iterative algorithms are used to solve the algebraic equation system. Results showed that as the temperature and degree of cure along the die extension increase the volumetric heat capacity and the thermal conductivity also elevate. The influence of the pulling speed and the die temperature in the thermal property variation is also analyzed. It is verified that the temperature profile at the pultruded bar centerline for the variable property case is smoother than the constant one, similarly when the pulling speed is increased. The degree of cure development is delayed for the variable property simulation, requiring a larger die length to reach a suitable degree of cure design value. Moreover, the proper knowledge of these characteristics allows a better pultrusion process design.
Pressure loss in ductworks is an important factor to be considered in design of engineering syste... more Pressure loss in ductworks is an important factor to be considered in design of engineering systems such as power-plants, refineries, HVAC systems to reduce energy costs. Ductwork can be composed by straight ducts and different types of fittings (elbows, transitions, converging and diverging tees and wyes). Duct fittings are significant sources of pressure loss in fluid distribution systems. Fitting losses can be even more significant than equipment components such as coils, filters, and dampers. At the present work, a conventional 90<sup>o</sup> round elbow under turbulent incompressible airflow is studied. Mass, momentum, and k-e turbulence model equations are solved employing the finite volume method. The SIMPLE algorithm is used for the pressure-velocity coupling. In order to validate the numerical tool, the elbow pressure loss coefficient is determined using the same conditions to compare with ASHRAE database. Furthermore, the effect of Reynolds number variation on ...
International Journal of Thermodynamics, 2014
This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft airconditio... more This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft airconditioning purposes. The ACM configuration mainly includes two compact heat exchangers, a compressor and an expander. The energy to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan. Results showed that the computational tool implemented to solve the ACM mathematical model allows an understanding of the air cycle machine performance when flight aircraft and cabin human comfort parameters are changed to attain an optimized aircraft environmental control system (ECS) design.
Engevista, 2012
Foram efetuadas diversas simulações numéricas para o escoamento do tipo jato livre axissimétrico,... more Foram efetuadas diversas simulações numéricas para o escoamento do tipo jato livre axissimétrico, incompressível e turbulento, no intuito de avaliar numericamente as afirmações de Taulbee (1989), George (1989) e George e Davidson (2004) as quais convergem na afirmação de que a modelagem single-point RANS (Reynolds-averaged Navier–Stokes) não possui a física necessária para contabilizar a dependência assintótica da origem do jato no seu desenvolvimento. O objetivo principal deste trabalho limita-se a mostrar alguns resultados, sem tentar solucionar tal afirmação. Adicionalmente é apresentada uma breve análise da influência das condições de origem do jato sobre a região completamente desenvolvida do escoamento. Os resultados das simulações corroboram a afirmação dos referidos autores e também indicam que não há um conjunto geral de constantes dos modelos de turbulência que se apresente universalmente válido. Foi verificado que a região completamente desenvolvida mostra-se dependente ...
Aircraft Engineering and Aerospace Technology, 2016
Purpose-This paper aims to determine the halon concentration time-evolution inside an aircraft ca... more Purpose-This paper aims to determine the halon concentration time-evolution inside an aircraft cargo compartment to design fire extinguishing systems. Design/methodology/approach-A fire suppression system is numerically simulated using the lumped parameter approach. Findings-The halon volumetric concentration, halon and air mass fluxes and the cargo compartment pressure are numerically calculated. It also determines the time to halon concentration to achieve the fire suppressant value (high pressure bottle) as well as its inerting volumetric concentration (low pressure bottle). Research limitations/implications-In the lumped parameter approach, the dependent variables of interest are a function of time alone, and its spatial distribution is neglected. Practical implications-This study predicts the fire extinguishing agent behavior aiming to satisfy cargo compartment certification requirements. Originality/value-This paper uses a simplified methodology, but it represents a very useful tool during the preliminary stages of the aircraft fire suppression systems design.
Acta Scientiarum. Technology, 2011
No presente trabalho, o problema de jato livre circular axissimétrico foi resolvido numericamente... more No presente trabalho, o problema de jato livre circular axissimétrico foi resolvido numericamente. A equação da conservação de massa, momento, energia e da modelagem da turbulência foram discretizadas aplicando o método de volumes finitos. Três modelos RANS de turbulência sem modificações foram testados, k-ε padrão, k-ε realizável e v2-f para determinar quais modelos proveem a melhor previsão do campo de escoamento de um jato livre turbulento nos seguintes regimes de escoamento: incompressível, subsônico e supersônico sobrexpandido. Os resultados numéricos para cada caso simulado foram comparados com dados experimentais disponíveis na literatura. Nenhum modelo de turbulência testado previu satisfatoriamente os três regimes de escoamentos, e o modelo k-ε realizável mostrou melhor concordância frente aos dados experimentais para o regime incompressível e supersônico, enquanto o modelo v2-f mostrou melhor previsão do escoamento para o regime subsônico. Palavras-chave: dinâmica dos fluidos computacional, volume finito, jato livre turbulento, modelos RANS de turbulência. ABSTRACT. Assessment of turbulence RANS models for axysimmetric round free jet problem. In the present study, the problem of axisymmetric round free jet was numerically solved. The governing equations (continuity, momentum, energy and turbulence) were discretized using the finite volume method. In order to determine which models provide the best prediction for the flow field of a turbulent free jet, three models (standard k-ε, realizable k-ε and v2-f) were tested on the following flow regimes: incompressible, subsonic and over-expanded supersonic. The numerical results from each simulated case were compared with experimental available data in the literature. None of the turbulence models tested predicted adequately the three flow regimes. Nevertheless, according to results, the k-ε realizable model presented better agreement to the experimental data for the incompressible and supersonic regimes, whereas the v2-f model better predicted the flow for subsonic regime.
Volume 3: Cycle Innovations; Education; Electric Power; Fans and Blowers; Industrial and Cogeneration, 2012
For geographic regions where significant power demand and highest electricity prices occur during... more For geographic regions where significant power demand and highest electricity prices occur during the warm months, a gas turbine inlet air cooling technique is a useful option for increasing output. Inlet air cooling increases the power output by taking advantage of the gas turbine’s feature of higher mass flow rate, due the compressor inlet temperature decays. Industrial gas turbines that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, the increases of the air density results in a higher air mass flow rate once the volumetric rate is constant. Consequently, the gas turbine power output enhances. Different methods are available for reducing compressor intake air temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine...
The Aeronautical Journal, 2016
ABSTRACTThis article presents a unified approach to solve steady-state conjugate heat-transfer pr... more ABSTRACTThis article presents a unified approach to solve steady-state conjugate heat-transfer problem including simultaneously gas, liquid and solid regions in just one 3D domain, distinguished by their particular properties. This approach reduces approximation errors and the time to solve the problem, which characterise iterative methods based on separated domains. The formulation employs RANS equations, realisablek-ε turbulence model and near-wall treatment model. A commercial CFD code solves the pressure-based segregated algorithm combined with spatial discretisation of second order upwind. The problem consists of a convergent-divergent metallic nozzle that contains cooling channels divided in two segments along the wall. The nozzle wall insulates the high-speed hot air flow, dealt as perfect gas, from the two low-speed cold water flows, dealt as compressed liquid, both influenced by transport properties dependent of the local temperature. The verification process uses three mes...
The main design requirements of the aircraft environmental control system are the cabin cooling-h... more The main design requirements of the aircraft environmental control system are the cabin cooling-heating loads and the cool-down and warm-up time periods. The cool-down process is the cooling of a heat-soaked aircraft prior to passenger loading and the warm-up process is the heating of a cold-soaked empty aircraft cabin. In this study the aircraft cabin cool-down and warm-up processes are mathematically modeled and numerically solved to study the influence of the air conditioning machine parameters and the cabin external and internal characteristics. The mathematical model couples the lumped parameters method with a differential approach to reduce the computational effort to solve this problem. This computational tool will reduce both the spent design time and the number of experimental tests to adjust the final environmental control system configuration.
This work focuses on a numerical study of a diesel engine valve ports steady-state compressible f... more This work focuses on a numerical study of a diesel engine valve ports steady-state compressible flow to calculate the mixing effects due to the presence of the filling and spiral intake ducts. These valve ports have an important role in engine charge exchange (exhaust and intake mechanisms), air-fuel mixture and combustion processes. Diesel engine industry developed a stationary bench flow tests which has been very useful to improve the preliminary design of valve ports. In this bench methodology, a stationary airflow is induced through valve ports by a exhaust fan where pressure drops and swirl flow patterns are measured maintaining a fixed valve aperture. At this context, the present CFD (Computational Fluid Dynamic) work intends to show fluid flow patterns and to calculate the Swirl number induced by the secondary flow. A 3D turbulent steady compressible flow is solved employing a finite volume technique with a density based approach.
Gas turbine air inlet cooling is a useful method for increasing output for regions where signific... more Gas turbine air inlet cooling is a useful method for increasing output for regions where significant power demand and highest electricity prices occur during the warm months. Inlet air cooling increases the power output by taking advantage of the gas turbine-s feature of higher mass flow rate when the compressor inlet temperature decreases. Different methods are available for reducing gas turbine inlet temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine-s inlet air temperature. The second system employs various ways to chill the inlet air. In this method, the cooling medium flows through a heat exchanger located in the inlet duct to remove heat from the inlet air. However, the evaporative cooling is limited by wet-bulb temperature while the chilling can cool the inlet air to temperatures that are lower than th...
Journal of Solar Energy Engineering, 2017
Microscale numerical modeling is currently the main tool used in wind industry to assess local wi... more Microscale numerical modeling is currently the main tool used in wind industry to assess local wind resources. This paper presents a systematic procedure to adjust computational fluid dynamics (CFD) predicted wind profiles to experimental measurements in order to minimize their differences. It can be applied when wind measurements are available. Data from ten masts with several measurement heights from the well-known Bolund hill experiment provided the observed wind profiles. Simulated profiles were calculated with windsim CFD model for the aforementioned site. Speed-up correction factors were defined through the least squares method to cross-correlate each mast as reference to all the others inside the Bolund hill domain. After, the observed and the adjusted wind profiles at the same position were compared. Moreover, root mean square errors (RMSEs) were used as a metric to evaluate the estimations and the ability of each position to be predicted and predictor. Results have shown th...
The cabin pressure control system continuously monitors the ground and flight modes of the airpla... more The cabin pressure control system continuously monitors the ground and flight modes of the airplane (climb, cruise, or descent) as well as holding patterns at various altitudes. It uses this information to allow air to escape continuously from the airplane by further opening or closing the outflow valve. Thus, the cabin internal pressure is controlled by modulating the exhaust airflow through the escape valve (outflow valve). As the airplane changes altitude, the outflow valve repositions itself to allow more or less air to escape. While the external ambient pressure is equivalent to the altitude of 36,000 ft, the cabin pressure is maintained at approximately 8,000 ft due to the physiological human requirements (mainly the respiratory needs). This leads a high differential pressure between the cabin and the external environment implying in more intense structural efforts to the fuselage. The outflow valve is constantly being positioned to maintain cabin pressure as close to sea level as practical, without exceeding a predetermined cabin-to-outside pressure differential. In this context, this work focuses on the determination of the outflow valve opening area of the aircraft cabin pressurization system for ground and flight schedules, considering: (i) the inflow supplied by the airconditioning packs; (ii) cabin leakages and (iii) the pressure change rate. The cabin leakage is modelled using the orifice compressible flow theory and the inflow rate is constant (determined by the cabin ventilation requirements). Results are obtained using a typical aircraft flight mission (schedule).
Journal of Aerospace Technology and Management, 2012
International Review of Mechanical Engineering-IREME, May 31, 2013
This study investigates how an incomplete tranesterification reaction influences the parameters o... more This study investigates how an incomplete tranesterification reaction influences the parameters of quality standards of the produced biodiesel engine performance and exhausts. The parameters evaluated include viscosity, cloud point, acid number and heating value. Biodiesels produced from palm oil were examined in terms of engine performance, where the 3-liter engine with a 4 cylinders 4 strokes, was used. The proportion of methyl ester in biodiesel was varied by adding appropriate amounts of triglyceride. Properties of biodiesel with the methyl ester between 75% and 96.8% by mass were tested against the standard diesel. The engine performance and thermal efficiency when using biodiesels of different qualities were determined under the operating engine speed range between 1,800 and 4,000 rpm. It was found that while the cloud point was raised with methyl ester content the viscosity was decreased. In terms of engine performance, greater proportion of methyl ester provides greater fuel conversion efficiency as well as specific fuel consumption rate.
This research work deals with the application of a hydrous ethanol direct injection spark ignitio... more This research work deals with the application of a hydrous ethanol direct injection spark ignition engine model. Computational Fluid Dynamics (CFD) software is applied in order to create the moving mesh and to solve the governing equations. The research scope includes the airflow characterization during intake and compression stroke and also the charge stratification. The distribution of mixture formation distribution within the combustion chamber is analyzed. The influence of parameters such as fuel injection pressure, start of injection, injected fuel mas, equivalence ratio and wall-wet film are evaluated. The goal is to obtain the fuel concentration within the cylinder during the spray development and the piston movement and also the film formation in the chamber walls. It was analyzed the differences and benefits between different injection strategies considering single and dual pulse injection. Parameters such as injection pressure and fuel mass injected are considered, helping...
Journal of Wind Engineering and Industrial Aerodynamics, 2021
Abstract This paper focuses on the estimation of annual energy production (AEP) by simulating the... more Abstract This paper focuses on the estimation of annual energy production (AEP) by simulating the flowfield on a complex terrain located in the northeast region of Brazil using different numerical approaches: CFD RANS with k-e and k-ω turbulence models (WindSim), simple mass-conserving (WindMap), and refined mesoscale (SiteWind). The last two are run through OpenWind software. Wind observations from five meteorological masts are used to adjust the models. Optimal layouts for a hypothetical wind farm with 50 wind turbines are obtained over each of the four wind fields to predict the power generation. As non-negligible differences are found on the spatial distribution of the winds simulated by the different models, the layouts are also substantially different. The AEP is calculated to compare scenarios varying the layouts over the wind fields. The distinct micrositing generate differences of up to 13 % on AEP prediction, which could mean the impact of an improper siting on the wind farm profitability. It is not plausible to categorically claim the superiority of accuracy of one model over the others. Nonetheless, the observed data provide an indicative that the refined mesoscale model was able to better capture the wind acceleration in the western region of the studied site.
Procceedings of the 24th ABCM International Congress of Mechanical Engineering, 2017
SAE Technical Paper Series, 2017
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
International Communications in Heat and Mass Transfer, 2013
Pultrusion is a manufacturing method for fiber-reinforced composite with constant cross-section. ... more Pultrusion is a manufacturing method for fiber-reinforced composite with constant cross-section. In this process, a fiber creel is impregnated in a resin bath and passes through a heated die with a constant pulling force and the elevated die temperature induces the curing-resin process. At the present work the effect of variable properties (thermal conductivity and volumetric heat capacity) during the pultrusion process of thermosetting composite materials is numerically studied. The thermal properties are considered as a function of both temperature and degree of cure distributions inside the carbon/epoxy matrix composites. A two-dimensional parabolic model using the finite element method to solve the energy and degree of cure transport equations was used. These two equations are coupled by a source term from resin curing exothermic reaction. The resin cure kinetics and the properties that are temperature-dependent are both modeled by expressions obtained from the literature. The computational domain is discretized using an unstructured mesh with triangular elements and an adaptive refinement. Iterative algorithms are used to solve the algebraic equation system. Results showed that as the temperature and degree of cure along the die extension increase the volumetric heat capacity and the thermal conductivity also elevate. The influence of the pulling speed and the die temperature in the thermal property variation is also analyzed. It is verified that the temperature profile at the pultruded bar centerline for the variable property case is smoother than the constant one, similarly when the pulling speed is increased. The degree of cure development is delayed for the variable property simulation, requiring a larger die length to reach a suitable degree of cure design value. Moreover, the proper knowledge of these characteristics allows a better pultrusion process design.
Pressure loss in ductworks is an important factor to be considered in design of engineering syste... more Pressure loss in ductworks is an important factor to be considered in design of engineering systems such as power-plants, refineries, HVAC systems to reduce energy costs. Ductwork can be composed by straight ducts and different types of fittings (elbows, transitions, converging and diverging tees and wyes). Duct fittings are significant sources of pressure loss in fluid distribution systems. Fitting losses can be even more significant than equipment components such as coils, filters, and dampers. At the present work, a conventional 90<sup>o</sup> round elbow under turbulent incompressible airflow is studied. Mass, momentum, and k-e turbulence model equations are solved employing the finite volume method. The SIMPLE algorithm is used for the pressure-velocity coupling. In order to validate the numerical tool, the elbow pressure loss coefficient is determined using the same conditions to compare with ASHRAE database. Furthermore, the effect of Reynolds number variation on ...
International Journal of Thermodynamics, 2014
This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft airconditio... more This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft airconditioning purposes. The ACM configuration mainly includes two compact heat exchangers, a compressor and an expander. The energy to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan. Results showed that the computational tool implemented to solve the ACM mathematical model allows an understanding of the air cycle machine performance when flight aircraft and cabin human comfort parameters are changed to attain an optimized aircraft environmental control system (ECS) design.
Engevista, 2012
Foram efetuadas diversas simulações numéricas para o escoamento do tipo jato livre axissimétrico,... more Foram efetuadas diversas simulações numéricas para o escoamento do tipo jato livre axissimétrico, incompressível e turbulento, no intuito de avaliar numericamente as afirmações de Taulbee (1989), George (1989) e George e Davidson (2004) as quais convergem na afirmação de que a modelagem single-point RANS (Reynolds-averaged Navier–Stokes) não possui a física necessária para contabilizar a dependência assintótica da origem do jato no seu desenvolvimento. O objetivo principal deste trabalho limita-se a mostrar alguns resultados, sem tentar solucionar tal afirmação. Adicionalmente é apresentada uma breve análise da influência das condições de origem do jato sobre a região completamente desenvolvida do escoamento. Os resultados das simulações corroboram a afirmação dos referidos autores e também indicam que não há um conjunto geral de constantes dos modelos de turbulência que se apresente universalmente válido. Foi verificado que a região completamente desenvolvida mostra-se dependente ...
Aircraft Engineering and Aerospace Technology, 2016
Purpose-This paper aims to determine the halon concentration time-evolution inside an aircraft ca... more Purpose-This paper aims to determine the halon concentration time-evolution inside an aircraft cargo compartment to design fire extinguishing systems. Design/methodology/approach-A fire suppression system is numerically simulated using the lumped parameter approach. Findings-The halon volumetric concentration, halon and air mass fluxes and the cargo compartment pressure are numerically calculated. It also determines the time to halon concentration to achieve the fire suppressant value (high pressure bottle) as well as its inerting volumetric concentration (low pressure bottle). Research limitations/implications-In the lumped parameter approach, the dependent variables of interest are a function of time alone, and its spatial distribution is neglected. Practical implications-This study predicts the fire extinguishing agent behavior aiming to satisfy cargo compartment certification requirements. Originality/value-This paper uses a simplified methodology, but it represents a very useful tool during the preliminary stages of the aircraft fire suppression systems design.
Acta Scientiarum. Technology, 2011
No presente trabalho, o problema de jato livre circular axissimétrico foi resolvido numericamente... more No presente trabalho, o problema de jato livre circular axissimétrico foi resolvido numericamente. A equação da conservação de massa, momento, energia e da modelagem da turbulência foram discretizadas aplicando o método de volumes finitos. Três modelos RANS de turbulência sem modificações foram testados, k-ε padrão, k-ε realizável e v2-f para determinar quais modelos proveem a melhor previsão do campo de escoamento de um jato livre turbulento nos seguintes regimes de escoamento: incompressível, subsônico e supersônico sobrexpandido. Os resultados numéricos para cada caso simulado foram comparados com dados experimentais disponíveis na literatura. Nenhum modelo de turbulência testado previu satisfatoriamente os três regimes de escoamentos, e o modelo k-ε realizável mostrou melhor concordância frente aos dados experimentais para o regime incompressível e supersônico, enquanto o modelo v2-f mostrou melhor previsão do escoamento para o regime subsônico. Palavras-chave: dinâmica dos fluidos computacional, volume finito, jato livre turbulento, modelos RANS de turbulência. ABSTRACT. Assessment of turbulence RANS models for axysimmetric round free jet problem. In the present study, the problem of axisymmetric round free jet was numerically solved. The governing equations (continuity, momentum, energy and turbulence) were discretized using the finite volume method. In order to determine which models provide the best prediction for the flow field of a turbulent free jet, three models (standard k-ε, realizable k-ε and v2-f) were tested on the following flow regimes: incompressible, subsonic and over-expanded supersonic. The numerical results from each simulated case were compared with experimental available data in the literature. None of the turbulence models tested predicted adequately the three flow regimes. Nevertheless, according to results, the k-ε realizable model presented better agreement to the experimental data for the incompressible and supersonic regimes, whereas the v2-f model better predicted the flow for subsonic regime.
Volume 3: Cycle Innovations; Education; Electric Power; Fans and Blowers; Industrial and Cogeneration, 2012
For geographic regions where significant power demand and highest electricity prices occur during... more For geographic regions where significant power demand and highest electricity prices occur during the warm months, a gas turbine inlet air cooling technique is a useful option for increasing output. Inlet air cooling increases the power output by taking advantage of the gas turbine’s feature of higher mass flow rate, due the compressor inlet temperature decays. Industrial gas turbines that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, the increases of the air density results in a higher air mass flow rate once the volumetric rate is constant. Consequently, the gas turbine power output enhances. Different methods are available for reducing compressor intake air temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine...