Aerodynamic Comparisons of Membrane Wings with Cambered and Flat Frames at Low Reynolds Number PDF Download
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Author: Andrew Harley Wrist
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 98
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Book Description
The limited size of micro air vehicles (MAVs) requires small power sources, leading to a need for high aerodynamic efficiency. Flexible membrane wings at the MAV scale can experience improved lift/drag ratios, delays in stall, and decreased time-averaged flow separation when compared to rigid wings. This research thesis examines the effect of frame camber on the aerodynamic characteristics of membrane wings. The frames for the wings were designed in SolidWorks and constructed using an Objet30 Pro 3D printer. The membranes are composed of silicone rubber. Tests were conducted in The University of Alabama low-speed wind tunnel in 135 Hardaway Hall in low Reynolds number flow (Re ~ 50,000). Aerodynamic force and moment measurements were acquired at angles-of-attack varying from -4 to 24°. The results were used to determine whether cambered frames provide membrane wings with aerodynamic advantages when compared to those with flat frames. Additionally, a digital image correlation (DIC) camera system was used to acquire time-averaged shapes for the membrane wings during wind tunnel tests. The wings were mounted vertically at angles-of-attack of 6° and 18° to represent the regions of maximum efficiency and approaching stall, respectively. An in-house MATLAB program was developed to average the deflection plots from the images and produce time-averaged shapes. Lifting-line theory was applied to the time-averaged shapes to calculate theoretical lift and induced drag coefficients. The experimental set-up, results, and conclusions are discussed.
Author: Andrew Harley Wrist
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 98
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Book Description
The limited size of micro air vehicles (MAVs) requires small power sources, leading to a need for high aerodynamic efficiency. Flexible membrane wings at the MAV scale can experience improved lift/drag ratios, delays in stall, and decreased time-averaged flow separation when compared to rigid wings. This research thesis examines the effect of frame camber on the aerodynamic characteristics of membrane wings. The frames for the wings were designed in SolidWorks and constructed using an Objet30 Pro 3D printer. The membranes are composed of silicone rubber. Tests were conducted in The University of Alabama low-speed wind tunnel in 135 Hardaway Hall in low Reynolds number flow (Re ~ 50,000). Aerodynamic force and moment measurements were acquired at angles-of-attack varying from -4 to 24°. The results were used to determine whether cambered frames provide membrane wings with aerodynamic advantages when compared to those with flat frames. Additionally, a digital image correlation (DIC) camera system was used to acquire time-averaged shapes for the membrane wings during wind tunnel tests. The wings were mounted vertically at angles-of-attack of 6° and 18° to represent the regions of maximum efficiency and approaching stall, respectively. An in-house MATLAB program was developed to average the deflection plots from the images and produce time-averaged shapes. Lifting-line theory was applied to the time-averaged shapes to calculate theoretical lift and induced drag coefficients. The experimental set-up, results, and conclusions are discussed.
Author: Zheng Zhang
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 207
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Book Description
To lessen the deterioration of fixed-wing aerodynamic performance associated with Reynolds numbers (Re) below 100,000, flexible membrane wing designs have been studied and proposed as an alternative for micro air vehicle (MAV) use. The beneficial effects of a flexible membrane can include higher lift, steeper lift-curve slope, delayed stall, gentle stall characteristics, and greater efficiency. These benefits have been attributed to both the time-averaged and dynamic deformation of the membrane. The background literature search shows that few investigations regarding membrane wings have focused on low aspect ratio (AR) wings (AR
Author: Trenton James Carpenter
Publisher:
ISBN:
Category : Aerodynamic load
Languages : en
Pages : 118
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Book Description
Through passive adaptation to incidental flow, flexible aerodynamic surfaces exploit effects of increased lift, delayed stall and disturbance rejection. Wings of birds, bats, and insects exhibit these passive effects, and at the same time through the use of structural state feedback sensed from the loads on the wing, active control is applied to achieve stable and highly dynamic maneuvers. The goal of this research is to predict aerodynamic loads on flexible wings, by sensing their structural responses to static and dynamic airflow conditions. Three approaches are presented to estimate aerodynamic loads on highly flexible membrane wings, under static and dynamic conditions, at low Reynolds number. The first applies a linear membrane formulation to correlate the wing's structural strain to lift, through wing-tip vorticity. In the second, the Poisson equation for a 2D linear-elastic membrane with out-of-plane deformation was used to calculate normal pressure distribution from virtual strain sensors using proper orthogonal decomposition basis functions and a recursive least squares minimization. Finally, potential flow theory and a first order state space representation is applied to the transient flow effects around a pitching membrane airfoil to model the time varying loads due to dynamic pitching.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1038
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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author: Wei Shyy
Publisher: Cambridge University Press
ISBN: 1107037263
Category : Science
Languages : en
Pages : 321
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Book Description
For anyone interested in the aerodynamics, structural dynamics and flight dynamics of small birds, bats, insects and air vehicles (MAVs).
Author: Luke Tregidgo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Albert Medina
Publisher:
ISBN:
Category :
Languages : en
Pages : 183
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Book Description
Flapping flight has gained much attention in the past decade driven by the desire to understand capabilities observed in nature and the desire to develop agile small-scale aerial vehicles. Advancing our current understanding of unsteady aerodynamics is an essential component in the development of micro-air vehicles (MAV) intended to utilize flight mechanics akin to insect flight. Thus the efforts undertaken that of bio-mimicry. The complexities of insect wing motion are dissected and simplified to more tractable problems to elucidate the fundamentals of unsteady aerodynamics in biologically inspired kinematics. The MAV's fruition would satisfy long established needs in both the military and civilian sectors. Although recent studies have provided great insight into the lift generating mechanisms of flapping wings the deflection response of such wings remains poorly understood. This dissertation numerically and experimentally investigates the aerodynamic performance of passively and actively deflected wings in hover and rotary kinematics. Flexibility is distilled to discrete lines of flexion which acknowledging major flexion lines in insect wings to be the primary avenue for deformation. Of primary concern is the development of the leading-edge vortex (LEV), a high circulation region of low pressure above the wing to which much of the wing's lift generation is attributed. Two-dimensional simulations of wings with chord-wise flexibility in a freestream reveal a lift generating mechanism unavailable to rigid wings with origins in vortical symmetry breaking. The inclusion of flexibility in translating wings accelerated from rest revealed the formation time of the initial LEV was very weakly dependent on the flexible stiffness of the wing, maintaining a universal time scale of four to five chords of travel before shedding. The frequency of oscillatory shedding of the leading and trailing-edge vortices that develops after the initial vortex shedding was shown to be responsive to flexibility satisfying an inverse proportionality to stiffness. In hover, an effective pitch angle can be defined in a flexible wing that accounts for deflection which shifts results toward trend lines of rigid wings. Three-dimensional simulations examining the effects of two distinct deformation modes undergoing prescribed deformation associated with root and tip deflection demonstrated a greater aerodynamic response to tip deflection in hover. Efficiency gains in flexion wings over rigid wing counterpart were shown to be dependent on Reynolds number with efficiency in both modes increasing with increased Reynolds number. Additionally, while the leading-edge vortex axis proved insensitive to deformation, the shape and orientation of the LEV core is modified. Experiments on three-dimensional dynamically-scaled fruit fly wings with passive deformation operating in the bursting limit Reynolds number regime revealed enhanced leading-edge vortex bursting with tip deflection promoting greater LEV core flow deceleration in stroke. Experimental studies on rotary wings highlights a universal formation time of the leading-edge vortex independent of Reynolds number, acceleration profile and aspect ratio. Efforts to replicate LEV bursting phenomena of higher aspect ratio wings in a unity aspect ratio wing such that LEV growth is no limited by span but by the LEV traversing the chord revealed a flow regime of oscillatory lift generation reminiscent of behavior exhibited in translating wings that also maintains magnitude peak to peak.
Author: Michael S. Selig
Publisher: Soartech
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 320
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Book Description
Author: Csaba Hefler
Publisher: Cambridge University Press
ISBN: 110887522X
Category : Technology & Engineering
Languages : en
Pages : 104
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Book Description
Insect-scale flapping wing flight vehicles can conduct environmental monitoring, disaster assessment, mapping, positioning and security in complex and challenging surroundings. To develop bio-inspired flight vehicles, systematic probing based on the particular category of flight vehicles is needed. This Element addresses the aerodynamics, aeroelasticity, geometry, stability and dynamics of flexible flapping wings in the insect flight regime. The authors highlight distinct features and issues, contrast aerodynamic stability between rigid and flexible wings, present the implications of the wing-aspect ratio, and use canonical models and dragonflies to elucidate scientific insight as well as technical capabilities of bio-inspired design.
Author: Thomas J. Mueller
Publisher: Springer Science & Business Media
ISBN: 3642840108
Category : Science
Languages : en
Pages : 456
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Book Description
Current interest in a variety of low Reynolds number applications has focused attention on the design and evaluation of efficient airfoil sections at chord Reynolds numbers from about 100,000 to about 1,000,000. These applications include remotely piloted vehicles (RPVs) at high altitudes, sailplanes, ultra-light man-carrying/man powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers. The purpose of this conference was to bring together those researchers who have been active in areas closely related to this subject. All of the papers presented are research type papers. Main topics are: Airfoil Design and Analysis, Computational Studies, Stability and Transition, Laminar Separation Bubble, Steady and Unsteady Wind Tunnel Experiments and Flight Experiments.
