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Low-Order Modeling of the Unsteady Aerodynamics in Flapping Wings

Low-Order Modeling of the Unsteady Aerodynamics in Flapping Wings
Author: Juan Carlos Gomez
Publisher:
Total Pages: 96
Release: 2015
Genre:
ISBN:

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The investigation of unsteady aerodynamics is becoming a more attractive topic of research in enhancing flight capabilities. Natural flyers such as birds and insects can undergo flight maneuvers that are very difficult or not possible with current aerodynamic understanding. Modeling the unsteady phenomena produced by flapping wings is important to the understanding of these maneuvers, with possible applications to aircraft flight. We investigate reduced-order modeling of the unsteady aerodynamics generated by flapping wings using the two separate approaches of rotational lift and dynamic stall. A low order quasi steady model based on rotational lift and a revised version incorporating dynamic stall are presented. Both concepts are analyzed using simulated results, with experimental data measured with matching kinematics as a basis of comparison. This combined model is then used to conduct parametric studies of the time averaged aerodynamic forces over varying kinematic variables.


Modeling of Aircraft Unsteady Aerodynamic Characteristics. Part 1

Modeling of Aircraft Unsteady Aerodynamic Characteristics. Part 1
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
Total Pages: 28
Release: 2018-07-05
Genre:
ISBN: 9781722379582

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A short theoretical study of aircraft aerodynamic model equations with unsteady effects is presented. The aerodynamic forces and moments are expressed in terms of indicial functions or internal state variables. The first representation leads to aircraft integro-differential equations of motion; the second preserves the state-space form of the model equations. The formulations of unsteady aerodynamics is applied in two examples. The first example deals with a one-degree-of-freedom harmonic motion about one of the aircraft body axes. In the second example, the equations for longitudinal short-period motion are developed. In these examples, only linear aerodynamic terms are considered. The indicial functions are postulated as simple exponentials and the internal state variables are governed by linear, time-invariant, first-order differential equations. It is shown that both approaches to the modeling of unsteady aerodynamics lead to identical models. Klein, Vladislav and Noderer, Keith D. Langley Research Center RTOP 505-64-52-01...


Evaluation of Unsteady Aerodynamic Forces and Pressure in Wings and Turbines at Low Reynolds Number by Combining Particle Image Velocimetry and Proper Orthogonal Decomposition

Evaluation of Unsteady Aerodynamic Forces and Pressure in Wings and Turbines at Low Reynolds Number by Combining Particle Image Velocimetry and Proper Orthogonal Decomposition
Author: Arturo Villegas Vaquero
Publisher:
Total Pages: 150
Release: 2014
Genre: Unsteady flow (Aerodynamics)
ISBN:

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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.


A Modern Course in Aeroelasticity

A Modern Course in Aeroelasticity
Author: E.H. Dowell
Publisher: Springer Science & Business Media
Total Pages: 724
Release: 2012-12-06
Genre: Technology & Engineering
ISBN: 9401104999

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Aeroelasticity is the study of flexible structures situated in a flowing fluid. Its modern origins are in the field of aerospace engineering, but it has now expanded to include phenomena arising in other fields such as bioengineering, civil engineering, mechanical engineering and nuclear engineering. The present volume is a teaching text for a first, and possibly second, course in aeroelasticity. It will also be useful as a reference source on the fundamentals of the subject for practitioners. In this third edition, several chapters have been revised and three new chapters added. The latter include a brief introduction to `Experimental Aeroelasticity', an overview of a frontier of research `Nonlinear Aeroelasticity', and the first connected, authoritative account of `Aeroelastic Control' in book form. The authors are drawn from a range of fields including aerospace engineering, civil engineering, mechanical engineering, rotorcraft and turbomachinery. Each author is a leading expert in the subject of his chapter and has many years of experience in consulting, research and teaching.


Unsteady Computational Fluid Dynamics in Aeronautics

Unsteady Computational Fluid Dynamics in Aeronautics
Author: P.G. Tucker
Publisher: Springer Science & Business Media
Total Pages: 432
Release: 2013-08-30
Genre: Technology & Engineering
ISBN: 9400770499

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The field of Large Eddy Simulation (LES) and hybrids is a vibrant research area. This book runs through all the potential unsteady modelling fidelity ranges, from low-order to LES. The latter is probably the highest fidelity for practical aerospace systems modelling. Cutting edge new frontiers are defined. One example of a pressing environmental concern is noise. For the accurate prediction of this, unsteady modelling is needed. Hence computational aeroacoustics is explored. It is also emerging that there is a critical need for coupled simulations. Hence, this area is also considered and the tensions of utilizing such simulations with the already expensive LES. This work has relevance to the general field of CFD and LES and to a wide variety of non-aerospace aerodynamic systems (e.g. cars, submarines, ships, electronics, buildings). Topics treated include unsteady flow techniques; LES and hybrids; general numerical methods; computational aeroacoustics; computational aeroelasticity; coupled simulations and turbulence and its modelling (LES, RANS, transition, VLES, URANS). The volume concludes by pointing forward to future horizons and in particular the industrial use of LES. The writing style is accessible and useful to both academics and industrial practitioners. From the reviews: "Tucker's volume provides a very welcome, concise discussion of current capabilities for simulating and modellng unsteady aerodynamic flows. It covers the various pos sible numerical techniques in good, clear detail and presents a very wide range of practical applications; beautifully illustrated in many cases. This book thus provides a valuable text for practicing engineers, a rich source of background information for students and those new to this area of Research & Development, and an excellent state-of-the-art review for others. A great achievement." Mark Savill FHEA, FRAeS, C.Eng, Professor of Computational Aerodynamics Design & Head of Power & Propulsion Sciences, Department of Power & Propulsion, School of Engineering, Cranfield University, Bedfordshire, U.K. "This is a very useful book with a wide coverage of many aspects in unsteady aerodynamics method development and applications for internal and external flows." L. He, Rolls-Royce/RAEng Chair of Computational Aerothermal Engineering, Oxford University, U.K. "This comprehensive book ranges from classical concepts in both numerical methods and turbulence modelling approaches for the beginner to latest state-of-the-art for the advanced practitioner and constitutes an extremely valuable contribution to the specific Computational Fluid Dynamics literature in Aeronautics. Student and expert alike will benefit greatly by reading it from cover to cover." Sébastien Deck, Onera, Meudon, France