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Author: Siddarth Kolluru Venkata
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Siddarth Kolluru Venkata
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Mustafa Serdar Genç
Publisher: BoD – Books on Demand
ISBN: 9535104926
Category : Science
Languages : en
Pages : 176
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Book Description
This book reports the latest development and trends in the low Re number aerodynamics, transition from laminar to turbulence, unsteady low Reynolds number flows, experimental studies, numerical transition modelling, control of low Re number flows, and MAV wing aerodynamics. The contributors to each chapter are fluid mechanics and aerodynamics scientists and engineers with strong expertise in their respective fields. As a whole, the studies presented here reveal important new directions toward the realization of applications of MAV and wind turbine blades.
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: Anya Rachel Jones
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Arturo Villegas Vaquero
Publisher:
ISBN:
Category : Unsteady flow (Aerodynamics)
Languages : en
Pages : 150
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Book Description
Aerodynamic unsteady forces in stationary and rotating wings are analyzed in this dissertation by using a combination of time-resolved particle image velocimetry (TR-PIV) and proper orthogonal decomposition (POD) techniques. Recent progress in experimental measurements has demonstrated the use of TR-PIV to calculate forces by applying the integral conservation of momentum equation in its different forms. However, a more accurate and robust method is needed for unsteady forces calculations. With this in mind, a modified pressure Poisson method is developed and applied in this work, showing its superior behavior compared to other methodologies described in the past. The independence of the calculated forces shows the robustness and stability of the method. Whereas force calculations have been recently considered, the role of flow structures in force fluctuations has not been revealed yet and it is the main focus of this study. To elucidate these relations, a hybrid PIV-POD analysis is applied to reconstruct the velocity field from the most energetic modes of the flow. A model describing the vortex-force relations is proposed in terms of lift and drag variations during the vortex shedding process. A spectral analysis of the calculated forces suggests symmetric periodic lift, drag and circulation variations at the shedding frequency. Moreover, lift, drag and circulation signals are in phase, which supports lift-circulation proportionality. However, non-symmetric drag fluctuations are found at double the shedding frequency within a shedding cycle. For instance, when a positive or negative circulation vortex detaches, different values in the maximum and minimum drag are obtained. The data and physical relations obtained in this work such as main frequencies, vortex-force fluctuations and behavior of reduced-order models can aid in the development of CFD applications at low Rey . The methodology described can be applied to any moving or stationary wing at different Reynolds numbers and angles of attack which would provide additional data for numerical codes. Furthermore, accurate measurements of unsteady forces allow determining narrower and more precise safety margins. Moreover, these measurements could be of application in flow control since forces are related to flow features simultaneously.
Author: Charles William Pitt Ford
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Ashok Gopalarathnam
Publisher:
ISBN:
Category : Reynolds number
Languages : en
Pages : 42
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Book Description
Unsteady motions of airfoils at low Reynolds numbers were studied computationally using low-order vortex lattice methods and using two high-order methods: a Reynolds Averaged Navier-Stokes code and an Immersed Boundary method. Results from the low-order methods compared well with experimental and computational results in the literature for small reduced amplitudes and frequencies. The high-order methods were compared with experiments on high intensity pitch and plunging motions at Reynolds numbers of 10,000 and 40,000. The pitch (rotation about the quarter chord) and plunge motions were at reduced frequencies of 3.93 and with kinematically equivalent amplitudes of effective angle of attack at the quarter-chord location. For the plunge cases, agreement between computation and experiment was qualitatively excellent and quantitatively acceptable, but for the pitch cases, the wake structure in the experiment was markedly different from that predicted by both computations, which were however similar among one another. In all cases, Reynolds number effects were found to be negligible. On-going research aims to determine the parameters necessary for pitch-plunge equivalence and also resolve the poor experiment-computation agreement for pitch.
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: Rudd Deakins
Publisher:
ISBN: 9781632403315
Category : Aerodynamics
Languages : en
Pages : 0
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Book Description
This book elucidates information regarding the low Reynolds number aerodynamics. It discusses the recent advancements and trends in the low Re number aerodynamics, transition from laminar to turbulence, unsteady low Reynolds number flows, experimental studies, numerical transition modelling, control of low Re number flows, and MAV wing aerodynamics. It includes contributions by fluid mechanics and aerodynamics scientists and engineers proficient in their respective fields. The studies included in the book demonstrate significant new methods for the realization of the functions of MAV and wind turbine blades.
Author: Pavan Kumar Shivaram
Publisher:
ISBN:
Category : Oscillating wings (Aerodynamics)
Languages : en
Pages : 108
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Book Description
"The present study is an attempt to understand the unsteady aerodynamics about a stationary wing. This study is undertaken so as to obtain useful information about such flows and make intelligent decisions that can be used beneficially for developing efficient flapping wing flying machines."--Introduction, p. 7.
