Numerical And Experimental Investigation Of 2D Membrane Airfoil Performance

The characteristic feature of a mammalian flight is the use of thin compliant wings as the lifting surface. This unique feature of flexible membrane wings found in flying mammals such as bats and flying squirrel was studied in order to explore its possibility as flexible membrane wings in aerodynamics performance study. The unsteady aspects of the fluid-structure interaction of membrane wings are very complicated and therefore did not receive much attention compared to the rigid wing. Motivated by this, a membrane airfoil consisting of latex sheet mounted on a NACA 643-218 airfoil frame was developed to study effect of membrane flexibility on laminar separation bubble (LSB), effects of membrane thickness, Reynolds number (Re), and membrane rigidity on the aerodynamic performance (lift and drag), meant for low Re applications. Unsteady, two dimensional (2D) simulations were also carried out on rigid and membrane airfoils with the air flow modeled as Laminar and the turbulent cases being modeled using Spalart-Allmaras viscous model. FLUENT 6.3 was employed to study the fluid flow behavior, whereas ABAQUS 6.8-1 was utilized as structural solver, both of which were coupled in real time using the MpCCI 3.1 software. It has been established that, the LSB is greatly influenced by the membrane flexibility, and the membrane airfoil has superior flow separation characteristics over rigid one

An experimental and numerical investigation of flapping and plunging wings

Micro air vehicles, or MAVs, are of current interest for a multitude of uses to which they, being small, unmanned vehicles, are uniquely suited. Among the proposed uses are exploration, reconnaissance, and communications. They can be deployed inside buildings, where their small size, hovering capability, and maneuverability, are important factors. Due to their small size, they operate at low Reynolds numbers where conventional flying mechanisms are not advantageous. Thus, attempts have been made to learn from natural flyers like insects and birds. Natural flight is accomplished by flapping wings, and this idea has been proposed for certain types of MAVs termed ornithopters and entomopters. This dissertation investigates the aerodynamics applicable to low Reynolds number unsteady flow, and consists of four stages. The first stage is CFD for fixed wings at low Reynolds number. In the second and third stage, experiments are conducted on flapping and plunging wings. The final stage consists of dynamic mesh CFD for a plunging airfoil --Abstract, page iii

Flapping wing design for a dragonfly-like micro air vehicle

In this thesis, the aerodynamics of the Quad-Wing Vehicle, a Micro Air Vehicle designed to hover with four flapping wings in a dragonfly-like configuration, is investigated using Computational Fluid Dynamics (CFD), potential flows analysis, and experimental testing. The CFD analysis investigates the kinematics-parameters design space and identifies values of kinematics parameters that maximize the vertical force production in hovering mode while minimizing the aerodynamic power requirement. It also investigates other important considerations, such as the effect of scaling, multi-wing interactions, and comparison with other flapping configurations. In the potential flows analysis, an unsteady 2D panel code is developed and compared with CFD for a broad range of hovering-flight simulations. The results show that, with further development, panel codes may be useful to designers of hovering flapping MAVs because of their time-saving potential compared to CFD. The experimental testing focuses on isolating the aerodynamic forces from other measured forces on a benchtop flapping device, and the findings of the experimental study will be useful for later researchers using experimental methods to study flapping MAV aerodynamics

Numerical And Experimental Investigations Of 2d Membrane Airfoil Performance

The characteristic feature of a mammalian flight is the use of thin compliant wings as the lifting surface. This unique feature of flexible membrane wings found in flying mammals such as bats and flying squirrel was studied in order to explore its possibility as flexible membrane wings in aerodynamics performance study. The unsteady aspects of the fluid-structure interaction of membrane wings are very complicated and therefore did not receive much attention compared to the rigid wing. Motivated by this, a membrane airfoil consisting of latex sheet mounted on a NACA 643-218 airfoil frame was developed to study effect of membrane flexibility on laminar separation bubble (LSB), effects of membrane thickness, Reynolds number (Re), and membrane rigidity on the aerodynamic performance (lift and drag), meant for low Re applications. Unsteady, two dimensional (2D) simulations were also carried out on rigid and membrane airfoils with the air flow modeled as Laminar and the turbulent cases being modeled using Spalart-Allmaras viscous model. FLUENT 6.3 was employed to study the fluid flow behavior, whereas ABAQUS 6.8-1 was utilized as structural solver, both of which were coupled in real time using the MpCCI 3.1 software. It has been established that, the LSB is greatly influenced by the membrane flexibility, and the membrane airfoil has superior flow separation characteristics over rigid one. Besides that, the effects of skin thickness and Re on the aerodynamic performance are investigated. In general, it was observed that, as the membrane thickness decreases, the lift increases and drag decreases, thereby improving the aerodynamic performance; with similar observation reported for the xvii case with increase in Re. Moreover, using experiment, the studies on the effect of ribs on aerodynamic performances were also presented. The results showed that the rigidity of the membrane skins could significantly affect the performance of the membrane airfoils; as the number of rigid ribs decreases, the lift increases and drag decreases. Finally, the displacement and stress of membrane airfoil with incoming flow has been studied by simulation technique. It was found that the membrane airfoils have deformed by the incoming flow and the Von Mises stress was found fluctuating around the membrane airfoil. The current simulation techniques were also validated by suitable wind tunnel experiments and close agreement was obtained

Computational Fluid Dynamics Simulations of Oscillating Wings and Comparison to Lifting-Line Theory

Computational fluid dynamics (CFD) analysis was performed in order to compare the solutions of oscillating wings with Prandtl’s lifting-line theory. Quasi-steady and steady-periodic simulations were completed using the CFD software Star-CCM+. The simulations were performed for a number of frequencies in a pure plunging setup. Additional simulations were then completed using a setup of combined pitching and plunging at multiple frequencies. Results from the CFD simulations were compared to the quasi-steady lifting-line solution in the form of the axial-force, normal-force, power, and thrust coefficients, as well as the efficiency obtained for each simulation. The mean values were evaluated for each simulation and compared to the quasi-steady lifting-line solution. It was found that as the frequency of oscillation increased, the quasi-steady lifting-line solution was decreasingly accurate in predicting solutions

Practical Flapping Mechanisms for 20cm-span Micro Air Vehicles

[[abstract]]In the body of research relevant to high-performance flapping micro air vehicles (MAV), development of light-weight, compact and energy-efficient flapping mechanisms occupies a position of primacy due to its direct impact on the flight performance and mission capability. Realization of such versatile flapping mechanism with additional ability of producing thrust levels that fulfill requirements of cruising forward flight and vertical take-off and landing (VTOL) conditions demand extensive design validation and performance evaluation. This paper presents a concerted approach for mechanism development of a 20 cm span flapping MAV through an iterative design process and synergistic fabrication options involving electrical-discharge-wire-cutting (EDWC) and injection molding. Dynamic characterization of each mechanism is done through high speed photography, power take-off measurement, wind tunnel testing and proof-of-concept test flights. The research outcome represents best-in-class mechanism for a 20 cm span flapping MAV with desirable performance features of extra-large flapping stroke up to 100°, minimal transverse vibrations and almost no phase lag between the wings.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]US

Quantitative analysis of take-off forces in birds

The increasing interest on Unmanned Air Vehicles (UAV’s) and their several utilities blended with the need of easy carrying and also the stealth, lead to the need to create the concept of Micro Air Vehicles (MAV’s) and the Nano Air Vehicles (NAV’s). Due to the current interest and the present lack of knowledge on the insect’s and bird’s flight, this study was intended to interpret the forces involved on the moment of the take-off of a bird, recurring to an experiment involving a fast data acquisition force sensor and high speed camera, in addition known facts from earlier studies. In order to do that a bibliographic revision was done, to know what was already studied and to find what could yet be studied. That way could be formed a link on the factors involved on the propulsion of a bird at the moment of take-off. The main conclusions obtained by this work is that the bird can produce movements that will enhance the total moment when the bird stretches its neck forward and moving head down followed by stretching even more its neck and moving head up impelling himself into the air, resulting in a main role on the mechanical forces (against perch) for the bird first moments momentum. Columba livia can generate about 4 times its weight worth mechanic force (against perch) and above 8 times its weight during the 2nd downstroke.O interesse crescente nos Veículos Aéreos não Tripulados “Unmanned Air Vehicles (UAV’s)” e suas diversas utilidades em conjunto com a necessidade de seu fácil transporte e furtividade, levaram à necessidade de criar o conceito dos Micro Veículos Aéreos “Micro Air Vehicles (MAV’s)” e os Nano Veículos Aéreos “Nano Air Vehicles (NAV’s)”. Este tipo de veículos tem como fonte inspiradora os insetos e aves devido à necessária produção simultânea de sustentação e propulsão. Tal como no voo convencional, também no voo animal podem ser identificadas as fases de levantamento (descolagem) e aterragem como diferenciadas do voo longe de uma superfície de apoio. Este trabalho é dedicado ao estudo da fase de levantamento de voo de uma ave columba livia. Foram realizadas experiências para medir a força inicial produzida pela ave para iniciar o voo e a respetiva trajetória na zona próxima do ponto de apoio inicial. Estas medidas foram efetuadas com um sensor de força dotado de elevada velocidade de aquisição de dados e uma camara de alta velocidade. As principais conclusões obtidas com a realização deste trabalho é o facto de que a ave consegue produzir movimentos, que aumentar o momento total quando a ave estica o pescoço para a frente e movendo a cabeça para baixo seguido por continuação de esticamento do pescoço e movimento da cabeça para cima impelindo-se para o ar, resultando num papel principal relativamente às forças mecânicas (contra o poleiro) para o momento linear actuante nos primeiros momentos. Columba livia consegue gerar cerca de 4 vezes o seu peso em força mecânica e acima de 8 vezes o seu peso durante o 2º downstroke

Development, Design, Manufacture and Test of Flapping Wing Micro Aerial Vehicles

The field of FlappingWing Micro Air Vehicles (FWMAV) has been of interest in recent years and as shown to have many aerodynamic principles unconventional to traditional aviation aerodynamics. In addition to traditional manufacturing techniques, MAVs have utilized techniques and machines that have gained significant interest and investment over the past decade, namely in additive manufacturing. This dissertation discusses the techniques used to manufacture and build a 30 gram-force (gf) model which approaches the lower limit allowed by current commercial off-the-shelf items. The vehicle utilizes a novel mechanism that minimizes traditional kinematic issues associated with four bar mechanisms for flapping wing vehicles. A kinematic reasoning for large amplitude flapping is demonstrated namely, by lowering the cycle averaged angular acceleration of the wings. The vehicle is tested for control authority and lift of the mechanism using three servo drives for wing manipulation. The study then discusses the wing design, manufacturing techniques and limitations involved with the wings for a FWMAV. A set of 17 different wings are tested for lift reaching lifts of 38 gf using the aforementioned vehicle design. The variation in wings spurs the investigation of the flow patterns generated by the flexible wings and its interactions for multiple flapping amplitudes. Phase-lock particle image velocimetry (PIV) is used to investigate the unsteady flows generated by the vehicle. A novel flow pattern is experimentally found, namely “trailing edge vortex capture” upon wing reversal for all three flapping amplitudes, alluding to a newly discovered addition to the lift enhancing effect of wake capture. This effect is believed to be a result of flexible wings and may provide lift enhancing characteristics to wake capture