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Haecheon Choi - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamic characteristics of flying fish in gliding flight.
The Journal of experimental biology, 2010Co-Authors: Hyungmin Park, Haecheon ChoiAbstract:The flying fish (family Exocoetidae) is an exceptional marine flying vertebrate, utilizing the advantages of moving in two different media, i.e. swimming in water and flying in air. Despite some physical limitations by moving in both water and air, the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight. Hence, the morphological and behavioral adaptations of flying fish to aerial locomotion have attracted great interest from various fields including biology and aerodynamics. Several aspects of the flight of flying fish have been determined or conjectured from previous field observations and measurements of morphometric parameters. However, the detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed yet. Therefore, in the present study, we directly measure the aerodynamic forces and moment on darkedged-wing flying fish (Cypselurus hiraii) models and correlated them with morphological characteristics of wing (fin). The model configurations considered are: (1) both the pectoral and pelvic fins spread out, (2) only the pectoral fins spread with the pelvic fins folded, and (3) both fins folded. The role of the pelvic fins was found to increase the lift force and lift-to-drag ratio, which is confirmed by the jet-like flow structure existing between the pectoral and pelvic fins. With both the pectoral and pelvic fins spread, the Longitudinal Static Stability is also more enhanced than that with the pelvic fins folded. For cases 1 and 2, the lift-to-drag ratio was maximum at attack angles of around 0 deg, where the attack angle is the angle between the Longitudinal body axis and the flying direction. The lift coefficient is largest at attack angles around 30∼35 deg, at which the flying fish is observed to emerge from the sea surface. From glide polar, we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface.
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Aerodynamic characteristics of flying fish in gliding flight
The Journal of Experimental Biology, 2010Co-Authors: Hyungmin Park, Haecheon ChoiAbstract:The flying fish (family Exocoetidae) is an exceptional marine flying vertebrate, utilizing the advantages of moving in two different media, i.e. swimming in water and flying in air. Despite some physical limitations by moving in both water and air, the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight. Hence, the morphological and behavioral adaptations of flying fish to aerial locomotion have attracted great interest from various fields including biology and aerodynamics. Several aspects of the flight of flying fish have been determined or conjectured from previous field observations and measurements of morphometric parameters. However, the detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed yet. Therefore, in the present study, we directly measure the aerodynamic forces and moment on darkedged-wing flying fish ( Cypselurus hiraii ) models and correlated them with morphological characteristics of wing (fin). The model configurations considered are: (1) both the pectoral and pelvic fins spread out, (2) only the pectoral fins spread with the pelvic fins folded, and (3) both fins folded. The role of the pelvic fins was found to increase the lift force and lift-to-drag ratio, which is confirmed by the jet-like flow structure existing between the pectoral and pelvic fins. With both the pectoral and pelvic fins spread, the Longitudinal Static Stability is also more enhanced than that with the pelvic fins folded. For cases 1 and 2, the lift-to-drag ratio was maximum at attack angles of around 0 deg, where the attack angle is the angle between the Longitudinal body axis and the flying direction. The lift coefficient is largest at attack angles around 30∼35 deg, at which the flying fish is observed to emerge from the sea surface. From glide polar, we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface. * A : total planform area (= A 1 + A 2 + A 3) A 1 : planform area of pectoral fins A 2 : planform area of pelvic fins A 3 : planform area of body AR : aspect ratio (= S2/A 1) b : half wing span (= S /2) c : average chord length of pectoral fins (= A 1/ S ) C D : drag coefficient C L : lift coefficient C M : pitching moment coefficient D : drag force h : flight height (distance between the ground and the lower surface of the body) L : lift force L/D : lift-to-drag ratio M : pitching moment r : ratio of flight height to half wing span (= h / b ) Re : Reynolds number (= uc ∞/ν) S : wing span of pectoral fins SL : standard length u ind : wind-induced water velocity u ∞ : freestream velocity x CG : location of the center of gravity α : angle of attack β1 : lateral dihedral angle of pectoral fins β2 : incidence angle of pectoral fins β3 : incidence angle of pelvic fins υ : kinematic viscosity
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Aerodynamic Performance of a Gliding Swallowtail Butterfly Wing Model
Experimental Mechanics, 2010Co-Authors: Hyungmin Park, W. P. Jeon, Kwang-hak Bae, Byoung Do Lee, Haecheon ChoiAbstract:In the present study, we perform a wind-tunnel experiment to investigate the aerodynamic performance of a gliding swallowtail-butterfly wing model having a low aspect ratio. The drag, lift and pitching moment are directly measured using a 6-axis force/torque sensor. The lift coefficient increases rapidly at attack angles less than 10° and then slowly at larger attack angles. The lift coefficient does not fall off rapidly even at quite high angles of attack, showing the characteristics of low-aspect-ratio wings. On the other hand, the drag coefficient increases more rapidly at higher angles of attack due to the increase in the effective area responsible for the drag. The maximum lift-to-drag ratio of the present modeled swallowtail butterfly wing is larger than those of wings of fruitfly and bumblebee, and even comparable to those of wings of birds such as the petrel and starling. From the measurement of pitching moment, we show that the modeled swallowtail butterfly wing has a Longitudinal Static Stability. Flow visualization shows that the flow separated from the leading edge reattaches on the wing surface at α < 15°, forming a small separation bubble, and full separation occurs at α ≥ 15°. On the other hand, strong wing-tip vortices are observed in the wake at α ≥ 5° and they are an important source of the lift as well as the main reason for broad stall. Finally, in the absence of long hind-wing tails, the lift and Longitudinal Static Stability are reduced, indicating that the hind-wing tails play an important role in enhancing the aerodynamic performance.
Hyungmin Park - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamic characteristics of flying fish in gliding flight.
The Journal of experimental biology, 2010Co-Authors: Hyungmin Park, Haecheon ChoiAbstract:The flying fish (family Exocoetidae) is an exceptional marine flying vertebrate, utilizing the advantages of moving in two different media, i.e. swimming in water and flying in air. Despite some physical limitations by moving in both water and air, the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight. Hence, the morphological and behavioral adaptations of flying fish to aerial locomotion have attracted great interest from various fields including biology and aerodynamics. Several aspects of the flight of flying fish have been determined or conjectured from previous field observations and measurements of morphometric parameters. However, the detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed yet. Therefore, in the present study, we directly measure the aerodynamic forces and moment on darkedged-wing flying fish (Cypselurus hiraii) models and correlated them with morphological characteristics of wing (fin). The model configurations considered are: (1) both the pectoral and pelvic fins spread out, (2) only the pectoral fins spread with the pelvic fins folded, and (3) both fins folded. The role of the pelvic fins was found to increase the lift force and lift-to-drag ratio, which is confirmed by the jet-like flow structure existing between the pectoral and pelvic fins. With both the pectoral and pelvic fins spread, the Longitudinal Static Stability is also more enhanced than that with the pelvic fins folded. For cases 1 and 2, the lift-to-drag ratio was maximum at attack angles of around 0 deg, where the attack angle is the angle between the Longitudinal body axis and the flying direction. The lift coefficient is largest at attack angles around 30∼35 deg, at which the flying fish is observed to emerge from the sea surface. From glide polar, we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface.
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Aerodynamic characteristics of flying fish in gliding flight
The Journal of Experimental Biology, 2010Co-Authors: Hyungmin Park, Haecheon ChoiAbstract:The flying fish (family Exocoetidae) is an exceptional marine flying vertebrate, utilizing the advantages of moving in two different media, i.e. swimming in water and flying in air. Despite some physical limitations by moving in both water and air, the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight. Hence, the morphological and behavioral adaptations of flying fish to aerial locomotion have attracted great interest from various fields including biology and aerodynamics. Several aspects of the flight of flying fish have been determined or conjectured from previous field observations and measurements of morphometric parameters. However, the detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed yet. Therefore, in the present study, we directly measure the aerodynamic forces and moment on darkedged-wing flying fish ( Cypselurus hiraii ) models and correlated them with morphological characteristics of wing (fin). The model configurations considered are: (1) both the pectoral and pelvic fins spread out, (2) only the pectoral fins spread with the pelvic fins folded, and (3) both fins folded. The role of the pelvic fins was found to increase the lift force and lift-to-drag ratio, which is confirmed by the jet-like flow structure existing between the pectoral and pelvic fins. With both the pectoral and pelvic fins spread, the Longitudinal Static Stability is also more enhanced than that with the pelvic fins folded. For cases 1 and 2, the lift-to-drag ratio was maximum at attack angles of around 0 deg, where the attack angle is the angle between the Longitudinal body axis and the flying direction. The lift coefficient is largest at attack angles around 30∼35 deg, at which the flying fish is observed to emerge from the sea surface. From glide polar, we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface. * A : total planform area (= A 1 + A 2 + A 3) A 1 : planform area of pectoral fins A 2 : planform area of pelvic fins A 3 : planform area of body AR : aspect ratio (= S2/A 1) b : half wing span (= S /2) c : average chord length of pectoral fins (= A 1/ S ) C D : drag coefficient C L : lift coefficient C M : pitching moment coefficient D : drag force h : flight height (distance between the ground and the lower surface of the body) L : lift force L/D : lift-to-drag ratio M : pitching moment r : ratio of flight height to half wing span (= h / b ) Re : Reynolds number (= uc ∞/ν) S : wing span of pectoral fins SL : standard length u ind : wind-induced water velocity u ∞ : freestream velocity x CG : location of the center of gravity α : angle of attack β1 : lateral dihedral angle of pectoral fins β2 : incidence angle of pectoral fins β3 : incidence angle of pelvic fins υ : kinematic viscosity
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Aerodynamic Performance of a Gliding Swallowtail Butterfly Wing Model
Experimental Mechanics, 2010Co-Authors: Hyungmin Park, W. P. Jeon, Kwang-hak Bae, Byoung Do Lee, Haecheon ChoiAbstract:In the present study, we perform a wind-tunnel experiment to investigate the aerodynamic performance of a gliding swallowtail-butterfly wing model having a low aspect ratio. The drag, lift and pitching moment are directly measured using a 6-axis force/torque sensor. The lift coefficient increases rapidly at attack angles less than 10° and then slowly at larger attack angles. The lift coefficient does not fall off rapidly even at quite high angles of attack, showing the characteristics of low-aspect-ratio wings. On the other hand, the drag coefficient increases more rapidly at higher angles of attack due to the increase in the effective area responsible for the drag. The maximum lift-to-drag ratio of the present modeled swallowtail butterfly wing is larger than those of wings of fruitfly and bumblebee, and even comparable to those of wings of birds such as the petrel and starling. From the measurement of pitching moment, we show that the modeled swallowtail butterfly wing has a Longitudinal Static Stability. Flow visualization shows that the flow separated from the leading edge reattaches on the wing surface at α < 15°, forming a small separation bubble, and full separation occurs at α ≥ 15°. On the other hand, strong wing-tip vortices are observed in the wake at α ≥ 5° and they are an important source of the lift as well as the main reason for broad stall. Finally, in the absence of long hind-wing tails, the lift and Longitudinal Static Stability are reduced, indicating that the hind-wing tails play an important role in enhancing the aerodynamic performance.
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Investigation of Aerodynamic Capabilities of Flying Fish in Gliding Flight
IUTAM Symposium on Unsteady Separated Flows and their Control, 2009Co-Authors: Hyungmin Park, H ChoiAbstract:In the present study, we experimentally investigate the aerodynamic capabilities of flying fish. We consider four different flying fish models, which are darkedged-wing flying fishes stuffed in actual gliding posture. Some morphological parameters of flying fish such as lateral dihedral angle of pectoral fins, incidence angles of pectoral and pelvic fins are considered to examine their effect on the aerodynamic performance. We directly measure the aerodynamic properties (lift, drag, and pitching moment) for different morphological parameters of flying fish models. For the present flying fish models, the maximum lift coefficient and lift-to-drag ratio are similar to those of medium-sized birds such as the vulture, nighthawk and petrel. The pectoral fins are found to enhance the lift-to-drag ratio and the Longitudinal Static Stability of gliding flight. On the other hand, the lift coefficient and lift-to-drag ratio decrease with increasing lateral dihedral angle of pectoral fins.
Maurizio Collu - One of the best experts on this subject based on the ideXlab platform.
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Longitudinal Static Stability requirements for wing in ground effect vehicle
International Journal of Naval Architecture and Ocean Engineering, 2015Co-Authors: Wei Yang, Zhigang Yang, Maurizio ColluAbstract:The issue of the Longitudinal Stability of a WIG vehicle has been a very critical design factor since the first experimental WIG vehicle has been built. A series of studies had been performed and focused on the Longitudinal Stability analysis. However, most studies focused on the Longitudinal Stability of WIG vehicle in cruise phase, and less is available on the Longitudinal Static Stability requirement of WIG vehicle when hydrodynamics are considered: WIG vehicle usually take off from water. The present work focuses on Stability requirement for Longitudinal motion from taking off to landing. The model of dynamics for a WIG vehicle was developed taking into account the aerodynamic, hydroStatic and hydrodynamic forces, and then was analyzed. Following with the Longitudinal Static Stability analysis, effect of hydrofoil was discussed. Locations of CG, aerodynamic center in pitch, aerodynamic center in height and hydrodynamic center in heave were illustrated for a stabilized WIG vehicle. The present work will further improve the Longitudinal Static Stability theory for WIG vehicle.
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the Longitudinal Static Stability of an aerodynamically alleviated marine vehicle a mathematical model
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2010Co-Authors: Maurizio Collu, M. H. Patel, Florent TrarieuxAbstract:An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic an...
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The Longitudinal Static Stability of an aerodynamically alleviated marine vehicle, a mathematical model
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2009Co-Authors: Maurizio Collu, M. H. Patel, Florent TrarieuxAbstract:An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high-speed marine vehicle equipped with aerodynamic surfaces is one such concept. In 1904, Bryan & Williams (Bryan & Williams 1904 Proc. R. Soc. Lond. 73 , 100–116 (doi:10.1098/rspl.1904.0017)) published an article on the Longitudinal dynamics of aerial gliders, and this approach remains the foundation of all the mathematical models studying the dynamics of airborne vehicles. In 1932, Perring & Glauert (Perring & Glauert 1932 Reports and Memoranda no. 1493) presented a mathematical approach to study the dynamics of seaplanes experiencing the planing effect. From this work, planing theory has developed. The authors propose a unified mathematical model to study the Longitudinal Stability of a high-speed planing marine vehicle with aerodynamic surfaces. A kinematics framework is developed. Then, taking into account the aerodynamic, hydroStatic and hydrodynamic forces, the full equations of motion, using a small perturbation assumption, are derived and solved specifically for this concept. This technique reveals a new Static Stability criterion that can be used to characterize the Longitudinal Stability of high-speed planing vehicles with aerodynamic surfaces.
Florent Trarieux - One of the best experts on this subject based on the ideXlab platform.
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the Longitudinal Static Stability of an aerodynamically alleviated marine vehicle a mathematical model
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2010Co-Authors: Maurizio Collu, M. H. Patel, Florent TrarieuxAbstract:An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic an...
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The Longitudinal Static Stability of an aerodynamically alleviated marine vehicle, a mathematical model
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2009Co-Authors: Maurizio Collu, M. H. Patel, Florent TrarieuxAbstract:An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high-speed marine vehicle equipped with aerodynamic surfaces is one such concept. In 1904, Bryan & Williams (Bryan & Williams 1904 Proc. R. Soc. Lond. 73 , 100–116 (doi:10.1098/rspl.1904.0017)) published an article on the Longitudinal dynamics of aerial gliders, and this approach remains the foundation of all the mathematical models studying the dynamics of airborne vehicles. In 1932, Perring & Glauert (Perring & Glauert 1932 Reports and Memoranda no. 1493) presented a mathematical approach to study the dynamics of seaplanes experiencing the planing effect. From this work, planing theory has developed. The authors propose a unified mathematical model to study the Longitudinal Stability of a high-speed planing marine vehicle with aerodynamic surfaces. A kinematics framework is developed. Then, taking into account the aerodynamic, hydroStatic and hydrodynamic forces, the full equations of motion, using a small perturbation assumption, are derived and solved specifically for this concept. This technique reveals a new Static Stability criterion that can be used to characterize the Longitudinal Stability of high-speed planing vehicles with aerodynamic surfaces.
Joris Degroote - One of the best experts on this subject based on the ideXlab platform.
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Multi-objective optimization of a wing fence on an unmanned aerial vehicle using surrogate-derived gradients
Structural and Multidisciplinary Optimization, 2019Co-Authors: Jolan Wauters, Nicolas Knudde, Ivo Couckuyt, Tom Dhaene, Joris DegrooteAbstract:In this paper, the multi-objective, multifidelity optimization of a wing fence on an unmanned aerial vehicle (UAV) near stall is presented. The UAV under consideration is characterized by a blended wing body (BWB), which increases its efficiency, and a tailless design, which leads to a swept wing to ensure Longitudinal Static Stability. The consequence is a possible appearance of a nose-up moment, loss of lift initiating at the tips, and reduced controllability during landing, commonly referred to as tip stall. A possible solution to counter this phenomenon is wing fences: planes placed on top of the wing aligned with the flow and developed from the idea of stopping the transverse component of the boundary layer flow. These are optimized to obtain the design that would fence off the appearance of a pitch-up moment at high angles of attack, without a significant loss of lift and controllability. This brings forth a constrained multi-objective optimization problem. The evaluations are performed through unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations. However, since controllability cannot be directly assessed through computational fluid dynamics (CFD), surrogate-derived gradients are used. An efficient global optimization framework is developed employing surrogate modeling, namely regressive co-Kriging, updated using a multi-objective formulation of the expected improvement. The result is a wing fence design that extends the flight envelope of the aircraft, obtained with a feasible computational budget.
