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Aerodynamic Analysis of Stationary and Flapping Wings in Unsteady Flow Environments at Low Reynolds Numbers.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Aerodynamic Analysis of Stationary and Flapping Wings in Unsteady Flow Environments at Low Reynolds Numbers./
作者:	Poudel, Naresh.
面頁冊數:	1 online resource (149 pages)
附註:	Source: Dissertations Abstracts International, Volume: 83-11, Section: B.
Contained By:	Dissertations Abstracts International83-11B.
標題:	Mechanical engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29168938click for full text (PQDT)
ISBN:	9798438799337

Aerodynamic Analysis of Stationary and Flapping Wings in Unsteady Flow Environments at Low Reynolds Numbers.
Poudel, Naresh.

Aerodynamic Analysis of Stationary and Flapping Wings in Unsteady Flow Environments at Low Reynolds Numbers. - 1 online resource (149 pages)

Source: Dissertations Abstracts International, Volume: 83-11, Section: B.

Thesis (Ph.D.)--University of Maryland, Baltimore County, 2022.

Includes bibliographical references

This thesis investigates nonlinear flow physics of flapping wings in unsteady ambient flow environments at low Reynolds numbers, where most birds, insects, and small unmanned aerial vehicles (UAVs) maneuver or operate, with high-fidelity numerical simulations enabled by high-order accurate computational fluid dynamics (CFD) methods.The first objective of this research is to investigate gust-wing interaction and to unravel the mechanism of gust mitigation with flapping wings. The interaction of a gust with a stationary airfoil produces large undesirable unsteady forces, which exceed the peak static lift coefficient. A simple pitch-down maneuver and oscillating airfoil motion were tested to mitigate the gust. A rapid pitch-down maneuver in response to a gust sometimes exceeds the negative stall angle, causing an inadvertent stall. A step-wise change in the angle of attack, as the gust develops, is shown to be effective at mitigating the negative effects of the gust. However, if the gust continues to grow in magnitude, this strategy may be ineffective. Low amplitude wing oscillations are then tested as a novel method for gust mitigation. Increasing the oscillating airfoil's reduced frequency dominates the gust.The second objective of the research is to examine highly nonlinear flow physics of stationary/flapping wings in unsteady ambient flow environments at low Reynolds numbers. The dependence of a pitching airfoil's thrust on Reynolds and Strouhal numbers is investigated first, and it is discovered that an unsteady flow environment can enhance its thrust production. The thrust scaling law of a pitching airfoil, when operating in highly unsteady flow environments, is extended as a function of Reynolds number, Strouhal number, and turbulence intensity. To quantify the effect of the unsteady flow environment on pitching airfoil thrust production, an effective Reynolds number concept is also introduced. It is also found that moderate freestream turbulence (~5%) can alter the formation of laminar separation bubbles near a stationary wing's leading edge and obtain larger lift coefficients when compared to those in a uniform freestream. This is critical for UAV design and control at low Reynolds numbers as large-scale flow separation can create undesired stall effects over wings at moderate angles of attack due to the weak resistance of unfavorable pressure gradients at low Reynolds numbers.In conclusion, on using high-fidelity numerical simulation tools, this research contributes to novel design and control of future unconventional UAVs by providing key insights into unsteady aerodynamics in highly unstructured real-world flight environments.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798438799337Subjects--Topical Terms:

649730
Mechanical engineering.
Subjects--Index Terms:

Flapping wingsIndex Terms--Genre/Form:

542853
Electronic books.

Aerodynamic Analysis of Stationary and Flapping Wings in Unsteady Flow Environments at Low Reynolds Numbers.
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500 $a Source: Dissertations Abstracts International, Volume: 83-11, Section: B.
500 $a Advisor: Yu, Meilin; Hrynuk, John.
502 $a Thesis (Ph.D.)--University of Maryland, Baltimore County, 2022.
504 $a Includes bibliographical references
520 $a This thesis investigates nonlinear flow physics of flapping wings in unsteady ambient flow environments at low Reynolds numbers, where most birds, insects, and small unmanned aerial vehicles (UAVs) maneuver or operate, with high-fidelity numerical simulations enabled by high-order accurate computational fluid dynamics (CFD) methods.The first objective of this research is to investigate gust-wing interaction and to unravel the mechanism of gust mitigation with flapping wings. The interaction of a gust with a stationary airfoil produces large undesirable unsteady forces, which exceed the peak static lift coefficient. A simple pitch-down maneuver and oscillating airfoil motion were tested to mitigate the gust. A rapid pitch-down maneuver in response to a gust sometimes exceeds the negative stall angle, causing an inadvertent stall. A step-wise change in the angle of attack, as the gust develops, is shown to be effective at mitigating the negative effects of the gust. However, if the gust continues to grow in magnitude, this strategy may be ineffective. Low amplitude wing oscillations are then tested as a novel method for gust mitigation. Increasing the oscillating airfoil's reduced frequency dominates the gust.The second objective of the research is to examine highly nonlinear flow physics of stationary/flapping wings in unsteady ambient flow environments at low Reynolds numbers. The dependence of a pitching airfoil's thrust on Reynolds and Strouhal numbers is investigated first, and it is discovered that an unsteady flow environment can enhance its thrust production. The thrust scaling law of a pitching airfoil, when operating in highly unsteady flow environments, is extended as a function of Reynolds number, Strouhal number, and turbulence intensity. To quantify the effect of the unsteady flow environment on pitching airfoil thrust production, an effective Reynolds number concept is also introduced. It is also found that moderate freestream turbulence (~5%) can alter the formation of laminar separation bubbles near a stationary wing's leading edge and obtain larger lift coefficients when compared to those in a uniform freestream. This is critical for UAV design and control at low Reynolds numbers as large-scale flow separation can create undesired stall effects over wings at moderate angles of attack due to the weak resistance of unfavorable pressure gradients at low Reynolds numbers.In conclusion, on using high-fidelity numerical simulation tools, this research contributes to novel design and control of future unconventional UAVs by providing key insights into unsteady aerodynamics in highly unstructured real-world flight environments.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2023
538 $a Mode of access: World Wide Web
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650 4 $a Fluid mechanics. $3 528155
653 $a Flapping wings
653 $a Gust mitigation
653 $a High-order computational fluid dynamics
653 $a Low Reynolds number
653 $a Non-uniform unsteady environment
653 $a Scaling laws
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