Numerical investigation on evolutionary characteristics of the leading-edge vortex induced by flapping caudal fin

2019 ◽  
Vol 31 (12) ◽  
pp. 125117
Keyword(s):  
Numerical Investigation ◽  
Leading Edge ◽  
Caudal Fin ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Flapping Caudal Fin

scholarly journals Numerical Investigation of a Dynamic Stall on a Single Rotating Blade

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 90
Author(s):  
Yin Ruan ◽  
Manfred Hajek
Keyword(s):  
Numerical Investigation ◽  
Vortex Structure ◽  
Leading Edge ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Dynamic Stall ◽  
Leading Edge Vortex ◽  
Pitching Airfoil ◽  
Edge Vortex ◽  
High Reynolds

Dynamic stall is a phenomenon on the retreating blade of a helicopter which can lead to excessive control loads. In order to understand dynamic stall and fill the gap between the investigations on pitching wings and full helicopter rotor blades, a numerical investigation of a single rotating and pitching blade is carried out. The flow phenomena thereupon including the Ω-shaped dynamic stall vortex, the interaction of the leading edge vortex with the tip vortex, and a newly noticed vortex structure originating inboard are examined; they show similarities to pitching wings, while also possessing their unique features of a rotating system. The leading edge/tip vortex interaction dominates the post-stall stage. A newly noticed swell structure is observed to have a great impact on the load in the post-stall stage. With such a high Reynolds number, the Coriolis force exerted on the leading edge vortex is negligible compared to the pressure force. The force history/vortex structure of the slice r/R = 0.898 is compared with a 2D pitching airfoil with the same harmonic pitch motion, and the current simulation shows the important role played by the swell structure in the recovery stage.

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Abstract

Vorticity transport in the leading-edge vortex on a rotating blade

2014 ◽  
Vol 743 ◽  
pp. 249-261 ◽  
Author(s):  
Craig J. Wojcik ◽  
James H. J. Buchholz
Keyword(s):  
Leading Edge ◽  
Quasi Equilibrium ◽  
Transport Mechanisms ◽  
Leading Edge Vortex ◽  
Rotating Blade ◽  
Edge Vortex ◽  
Rotation Motion ◽  
Vorticity Transport ◽  
Control Volumes ◽  
Quiescent Fluid

AbstractVorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

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