cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.7507172
title: Detailed Numerical Study on the Aerodynamic Behavior of a Gurney Flapped Airfoil in the Ultra-low Reynolds Regime

description: ABSTRACT: The addition of Gurney flap changes the nature of flow around airfoil by producing asymmetric Von-Karman vortex in its wake. Most of the investigations on Gurney flapped airfoils have modeled the flow using a quasi-steady approach, resulting in time-averaged values with no information on the unsteady features of the flow. Among these, some investigations have shown that quasi-steady approach does a good job on predicting the aerodynamic coefficients and physics of flow. Previous studies on Gurney flap have shown that the calculated aerodynamic coefficients such as lift and drag coefficients from quasi-steady approach are in good agreement with the time averaged values of these quantities in time accurate computations. However, these investigations were conducted in regimes of medium to high Reynolds numbers where the flow is turbulent. Whether this is true for the regime of ultra-low Reynolds number is open to question. Therefore, it is deemed necessary to examine the previous investigations in the regime of ultra-low Reynolds numbers. The unsteady incompressible laminar flow over a Gurney flapped airfoil is investigated using three approaches; namely unsteady accurate, unsteady inaccurate, and quasi-steady. Overall, all the simulations showed that at ultra-low Reynolds numbers quasi-steady solution does not necessarily have the same correlation with the time averaged results over the unsteady accurate solution. In addition, it was observed that results of unsteady inaccurate approach with very small time steps can be used to predict time-averaged quantities fairly accurate with less computational cost.
DOI: 10.6084/m9.figshare.7513433
title: Experimental Investigation of Ionization Sensors under Shock Tube Stagnation Conditions

description: ABSTRACT: Recently, there has been a growing interest in studies concerning ionization sensors for aerospace applications, power generation, and fundamental research. In aerospace research, they have been used for studies of shock and detonation waves. Two key features of these sensors are their short response time, of the order of microseconds, and the fact that they are activated when exposed to high temperature air. In this sense, the present paper describes the development of an ionization sensor to be used in shock tube facilities. The sensor consists of 2 thorium-tungsten electrodes insulated by ceramic, with a stainless steel adapter for proper mounting, as well as 2 copper seal rings. An electrical circuit was also built with 2 main purposes: to provide the electrodes with a sufficient large voltage difference in order to ease ionization of the air and to assure a short time response of the sensor. The tests were carried out in a shock tube with the objective of observing the response of the sensor under stagnation conditions. For that, we chose initial driven pressures of 1.0; 1.2 and 1.5 kgf/cm2, with a constant driver pressure equal to 70 kgf/cm2. We analyzed the response of the sensor as a function of the initial driven pressure, stagnation temperature, and density. For the studied conditions, the results showed that the mean amplitude of the ionization sensor signal varied from 8.29 to 19.70 mV.
DOI: 10.6084/m9.figshare.7513433.v1
title: Experimental Investigation of Ionization Sensors under Shock Tube Stagnation Conditions

description: ABSTRACT: Recently, there has been a growing interest in studies concerning ionization sensors for aerospace applications, power generation, and fundamental research. In aerospace research, they have been used for studies of shock and detonation waves. Two key features of these sensors are their short response time, of the order of microseconds, and the fact that they are activated when exposed to high temperature air. In this sense, the present paper describes the development of an ionization sensor to be used in shock tube facilities. The sensor consists of 2 thorium-tungsten electrodes insulated by ceramic, with a stainless steel adapter for proper mounting, as well as 2 copper seal rings. An electrical circuit was also built with 2 main purposes: to provide the electrodes with a sufficient large voltage difference in order to ease ionization of the air and to assure a short time response of the sensor. The tests were carried out in a shock tube with the objective of observing the response of the sensor under stagnation conditions. For that, we chose initial driven pressures of 1.0; 1.2 and 1.5 kgf/cm2, with a constant driver pressure equal to 70 kgf/cm2. We analyzed the response of the sensor as a function of the initial driven pressure, stagnation temperature, and density. For the studied conditions, the results showed that the mean amplitude of the ionization sensor signal varied from 8.29 to 19.70 mV.
DOI: 10.6084/m9.figshare.7512878
title: Electromagnetic Properties of Multifunctional Composites Based on Glass Fiber Prepreg and Ni/Carbon Fiber Veil

description: ABSTRACT: Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S24 = −0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S22 = −0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S22 = −1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for ∼ 1.1 mm) for buildings, aircraft, and space components.
DOI: 10.6084/m9.figshare.7512878.v1
title: Electromagnetic Properties of Multifunctional Composites Based on Glass Fiber Prepreg and Ni/Carbon Fiber Veil

description: ABSTRACT: Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S24 = −0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S22 = −0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S22 = −1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for ∼ 1.1 mm) for buildings, aircraft, and space components.
DOI: 10.6084/m9.figshare.5670727.v1
title: Immersed Boundary Method Based on the Implementation of Conservation Equations along the Boundary using Control-Volume Finite-Element Scheme

description: ABSTRACT In this study conservation equations were implemented along the boundaries via ghost control-volume immersed boundary method. The control-volume finite-element method was applied on a cartesian grid to simulate 2-D incompressible flow. In this approach, mass and momentum equations were conserved in the whole domain including boundary control volumes by introducing ghost-control volume concept. The Taylor problem was selected to validate the present method. Four different case studies of Taylor problem encompassing both inviscid and viscous flow conditions in ordinary and 45º rotated grid were used for more investigation. Comparisons were made between the results of the present method and those obtained from the exact solution. Results of the present method indicated accurate predictions of the velocity and pressure fields in midline, diagonal, and all boundaries. The agreement between the results of the present method and the exact solution was very good throughout the whole temporal domain. Furthermore, comparison of the rate of kinetic energy decay in viscous case showed same level of agreement between the results.
DOI: 10.6084/m9.figshare.5670727
title: Immersed Boundary Method Based on the Implementation of Conservation Equations along the Boundary using Control-Volume Finite-Element Scheme

description: ABSTRACT In this study conservation equations were implemented along the boundaries via ghost control-volume immersed boundary method. The control-volume finite-element method was applied on a cartesian grid to simulate 2-D incompressible flow. In this approach, mass and momentum equations were conserved in the whole domain including boundary control volumes by introducing ghost-control volume concept. The Taylor problem was selected to validate the present method. Four different case studies of Taylor problem encompassing both inviscid and viscous flow conditions in ordinary and 45º rotated grid were used for more investigation. Comparisons were made between the results of the present method and those obtained from the exact solution. Results of the present method indicated accurate predictions of the velocity and pressure fields in midline, diagonal, and all boundaries. The agreement between the results of the present method and the exact solution was very good throughout the whole temporal domain. Furthermore, comparison of the rate of kinetic energy decay in viscous case showed same level of agreement between the results.
DOI: 10.6084/m9.figshare.5670838.v1
title: Evaluation of Filler Effects on the Dynamic Mechanical Behavior of HTPB-Elastomer Used as Binder in Exemplary Composite Formulations

description: ABSTRACT: This study aims to evaluate the dynamic mechanical properties of a binder, used in composite propellants, with increasing amount of different solid fillers. Dynamic Mechanical Analysis (DMA) is performed to determine the region of glass-rubber transition temperature (Tg). Further parameters were obtained from the description of the loss factor curves (tanδ) with models based on exponentially modified Gauss (EMG) distribution function. Polyurethane binders employing the polyol HTPB and diisocyanate were filled with 20, 40, and 60 mass-% of ammonium perchlorate (AP), aluminum (Al) or cyclotrimethylene trinitramine (RDX) particles, using fine and coarse mean sizes. A special turning device manufactured by Fraunhofer ICT was installed inside the curing oven in order to avoid sedimentation during curing. The cured composites were characterized by DMA in torsion mode from -100 °C to 70 °C. The good homogeneous distribution of fillers in the samples was evaluated by computational X-ray micro-tomography. The data on tanδ showed a complex structure describable at first with 2 overlapping peaks. The peak at lower temperatures is due to mobility of unrestricted binder parts (Tgunr) and the second broader peak at high temperature is due to mobility of restricted binder parts (Tgres). Results of tanδ, calculated areas of EMG curves and apparent activation energies of the distinct relaxation processes indicate that Al particles have higher interaction with HTPB-based polyurethane than AP and RDX. Probably Al is bonded to the binder network via isocyanate coupling with OH groups present in the surface. Ammonium perchlorate and cyclotrimethylene trinitramine particle sizes and its morphology influenced the viscoelastic properties. AP and RDX cause more changes in intensity of first peak of loss factor than Al. Increasing amount of these both particles enhances storage (G’) and loss (G”) shear moduli. As a whole tanδ intensity is lowered in the main peak and Al showed an intensity increase in the second apparent peak.
DOI: 10.6084/m9.figshare.5670838
title: Evaluation of Filler Effects on the Dynamic Mechanical Behavior of HTPB-Elastomer Used as Binder in Exemplary Composite Formulations

description: ABSTRACT: This study aims to evaluate the dynamic mechanical properties of a binder, used in composite propellants, with increasing amount of different solid fillers. Dynamic Mechanical Analysis (DMA) is performed to determine the region of glass-rubber transition temperature (Tg). Further parameters were obtained from the description of the loss factor curves (tanδ) with models based on exponentially modified Gauss (EMG) distribution function. Polyurethane binders employing the polyol HTPB and diisocyanate were filled with 20, 40, and 60 mass-% of ammonium perchlorate (AP), aluminum (Al) or cyclotrimethylene trinitramine (RDX) particles, using fine and coarse mean sizes. A special turning device manufactured by Fraunhofer ICT was installed inside the curing oven in order to avoid sedimentation during curing. The cured composites were characterized by DMA in torsion mode from -100 °C to 70 °C. The good homogeneous distribution of fillers in the samples was evaluated by computational X-ray micro-tomography. The data on tanδ showed a complex structure describable at first with 2 overlapping peaks. The peak at lower temperatures is due to mobility of unrestricted binder parts (Tgunr) and the second broader peak at high temperature is due to mobility of restricted binder parts (Tgres). Results of tanδ, calculated areas of EMG curves and apparent activation energies of the distinct relaxation processes indicate that Al particles have higher interaction with HTPB-based polyurethane than AP and RDX. Probably Al is bonded to the binder network via isocyanate coupling with OH groups present in the surface. Ammonium perchlorate and cyclotrimethylene trinitramine particle sizes and its morphology influenced the viscoelastic properties. AP and RDX cause more changes in intensity of first peak of loss factor than Al. Increasing amount of these both particles enhances storage (G’) and loss (G”) shear moduli. As a whole tanδ intensity is lowered in the main peak and Al showed an intensity increase in the second apparent peak.
DOI: 10.6084/m9.figshare.5670967
title: Aerofoil Design for Unmanned High-Altitude Aft-Swept Flying Wings

description: ABSTRACT In this paper, 12 new aerofoils with varying thicknesses for an aft-swept flying wing unmanned air vehicle have been designed using a MATLAB tool which has been developed in-house. The tool consists of 2 parts in addition to the aerodynamic solver XFOIL. The first part generates the aerofoil section geometry using a combination of PARSEC and Bezier-curve parameterisation functions. PARSEC parametrisation has been used to represent the camber line while the Bezier-curve has been used to select the thickness distribution. This combination is quite efficient in using an optimisation search process because of the capability to define a range of design variables that can quickly generate a suitable aerofoil. The second part contains the optimisation code using a genetic algorithm. The primary target here was to design a number of aerofoils with low pitching moment, suitable for an aft-swept flying wing configuration operating at low Reynolds number in the range of about 0.5 × 106. Three optimisation targets were set to achieve maximum aerodynamic performance characteristics. Each individual target was run separately to design several aerofoils of different thicknesses that meet the target criteria. According to the set of result obtained so far, the initial observation of the aerodynamic performance of the newly designed aerofoils is that the lift/drag ratio in general is higher than that of the existing ones used in many current-generation high-altitude long-endurance aircraft. Another observation is that increasing the maximum thickness of the aerofoil leads to a decrease in the maximum lift/drag ratio. In addition, as expected, this ratio sharply drops after the maximum value of some of these aerofoils.
DOI: 10.6084/m9.figshare.5670967.v1
title: Aerofoil Design for Unmanned High-Altitude Aft-Swept Flying Wings

description: ABSTRACT In this paper, 12 new aerofoils with varying thicknesses for an aft-swept flying wing unmanned air vehicle have been designed using a MATLAB tool which has been developed in-house. The tool consists of 2 parts in addition to the aerodynamic solver XFOIL. The first part generates the aerofoil section geometry using a combination of PARSEC and Bezier-curve parameterisation functions. PARSEC parametrisation has been used to represent the camber line while the Bezier-curve has been used to select the thickness distribution. This combination is quite efficient in using an optimisation search process because of the capability to define a range of design variables that can quickly generate a suitable aerofoil. The second part contains the optimisation code using a genetic algorithm. The primary target here was to design a number of aerofoils with low pitching moment, suitable for an aft-swept flying wing configuration operating at low Reynolds number in the range of about 0.5 × 106. Three optimisation targets were set to achieve maximum aerodynamic performance characteristics. Each individual target was run separately to design several aerofoils of different thicknesses that meet the target criteria. According to the set of result obtained so far, the initial observation of the aerodynamic performance of the newly designed aerofoils is that the lift/drag ratio in general is higher than that of the existing ones used in many current-generation high-altitude long-endurance aircraft. Another observation is that increasing the maximum thickness of the aerofoil leads to a decrease in the maximum lift/drag ratio. In addition, as expected, this ratio sharply drops after the maximum value of some of these aerofoils.
DOI: 10.6084/m9.figshare.5671045
title: Reduced Order Modeling of Composite Laminates Through Solid-Shell Coupling

description: ABSTRACT: Composite laminates display a complex mechanical behavior due to their microstructure, with a through-thickness variation of the displacement and stress fields that depends on the fiber orientation in each layer. Aiming to develop reduced-order numerical models mimicking the real response of composite structures, we investigated the capability and accuracy of finite element analyses coupling layered shell and solid kinematics. This study represents the first step of a work with the goal of accurately matching stress evolution in regions close to possible impact locations, where delamination is expected to take place, with reduced computational costs. Close to such locations, a 3-D modeling is adopted, whereas in the remainder of the structure, a less computationally demanding shell modeling is chosen. To test the coupled approach, results of numerical simulations are presented for a quasi-statically loaded cross-ply orthotropic plate, either simply supported or fully clamped along its boundary.
DOI: 10.6084/m9.figshare.5671045.v1
title: Reduced Order Modeling of Composite Laminates Through Solid-Shell Coupling

description: ABSTRACT: Composite laminates display a complex mechanical behavior due to their microstructure, with a through-thickness variation of the displacement and stress fields that depends on the fiber orientation in each layer. Aiming to develop reduced-order numerical models mimicking the real response of composite structures, we investigated the capability and accuracy of finite element analyses coupling layered shell and solid kinematics. This study represents the first step of a work with the goal of accurately matching stress evolution in regions close to possible impact locations, where delamination is expected to take place, with reduced computational costs. Close to such locations, a 3-D modeling is adopted, whereas in the remainder of the structure, a less computationally demanding shell modeling is chosen. To test the coupled approach, results of numerical simulations are presented for a quasi-statically loaded cross-ply orthotropic plate, either simply supported or fully clamped along its boundary.
DOI: 10.6084/m9.figshare.5671204
title: Orthotropic Elastic Properties Assessment of Sandwich Laminates

description: ABSTRACT: Sandwich structures are nowadays widely used due its excellent characteristics of matching light weight with high bend stiffness. However the complex nature of its composition turns the estimation of its mechanical elastic properties challenging. The objective of the present article is to propose an analytical/experimental model to estimate the orthotropic elastic properties of this composite material. To accomplish this objective a theory of anisotropic plates is used together to an extensometric experimental approach. A sandwich laminate specimen, instrumented with strain gages, was submitted through pure bending loading by a mechanical testing machine on a 4-point bending apparatus. The result of this research was the determination of 4 orthotropic elastic properties of the sandwich laminate specimen, namely: the longitudinal and transversal Young moduli, the shear modulus, and the Poisson's ratio.
DOI: 10.6084/m9.figshare.5671204.v1
title: Orthotropic Elastic Properties Assessment of Sandwich Laminates

description: ABSTRACT: Sandwich structures are nowadays widely used due its excellent characteristics of matching light weight with high bend stiffness. However the complex nature of its composition turns the estimation of its mechanical elastic properties challenging. The objective of the present article is to propose an analytical/experimental model to estimate the orthotropic elastic properties of this composite material. To accomplish this objective a theory of anisotropic plates is used together to an extensometric experimental approach. A sandwich laminate specimen, instrumented with strain gages, was submitted through pure bending loading by a mechanical testing machine on a 4-point bending apparatus. The result of this research was the determination of 4 orthotropic elastic properties of the sandwich laminate specimen, namely: the longitudinal and transversal Young moduli, the shear modulus, and the Poisson's ratio.