Aeroelastic Indicial Response Reduced-Order Modeling for Flexible Flight Vehicles

Hiller, Brett R.; Frink, Neal T.; Silva, Walter A.; Mavris, Dimitri N.

doi:10.2514/1.c035646

Cited by 8 publications

(2 citation statements)

References 33 publications

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“…The general expression for the indicial response, denoted as Φ(t), is used to predict the time-varying output, y(t), in response to the time-varying input, x(t). This prediction is achieved through the convolution with the time derivative of input ẋ(t) (Ghoreyshi & Cummings 2014;Hiller et al 2020):…”

Section: Appendix Amentioning

confidence: 99%

“…This prediction is achieved through the convolution with the time derivative of input (Ghoreyshi & Cummings 2014; Hiller et al. 2020): Here, represents the system input at . By applying the Duhamel superposition integral, as expressed in (A1), we can represent the unsteady lift on a plate with time-varying downwash velocity as Here, is the non-dimensional time scale.…”

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Rapidly pitching plates in decelerating motion near the ground

Adhikari,

Bhattacharya

2024

J. Fluid Mech.

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Birds employ rapid pitch-up motions close to the ground for different purposes: perching birds use this motion to decelerate and come to a complete stop while hunting birds, such as bald eagles, employ it to catch prey and swiftly fly away. Motivated by these observations, our study investigates how natural flyers accomplish diverse flying objectives by rapidly pitching their wings while decelerating near ground. We conducted experimental and analytical investigations focusing on rapidly pitching plates during deceleration in close proximity to the ground to explore the impact of ground proximity on the unsteady dynamics. Initially, we executed synchronous pitch-up motion, where both pitching and deceleration have the same motion duration, at different ground heights. Experimental results demonstrate that as the pitching wing approaches the ground, the instantaneous lift increases by approximately $38\,\%$ compared with a far-from-ground case, while the initial peak drag force remains relatively unchanged. Our analytical model conforms to this trend, predicting an increase in lift force as the wing approaches the ground, indicating enhanced added mass and circulatory lift force due to the ground effect. Next, we examined asynchronous pitch-up motion cases, where rapid pitching motions were initiated at different stages of deceleration. The results reveal that initiating the wing pitch early in the deceleration leads to the formation of larger counter-rotating vortices at the early stage of the manoeuvre. These vortices generate stronger dipole jets that orient backward in the later stages of the manoeuvre after impinging with the ground surface, which hunting birds utilize to accelerate after catching prey. Conversely, when the wing pitch is delayed, smaller vortices form, but their growth is postponed until late in the manoeuvre. This delayed vortex growth produces lift and drag force at the end phase of the manoeuvre that facilitates a smooth landing or perching. Thus, through strategic tuning of a rapid pitch-up motion with deceleration, natural flyers, such as birds, achieve diverse flying objectives.

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Section: Appendix Amentioning

confidence: 99%