Advance ratio effects on the flow structure and unsteadiness of the dynamic-stall vortex of a rotating blade in steady forward flight

Raghav, Vrishank; Komerath, Narayanan

doi:10.1063/1.4906803

Cited by 18 publications

(7 citation statements)

References 31 publications

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“…Phase-averaged PIV (2D and stereo-) is a standard approach for rotor-wake measurements (2D - Reich et al, 2014aReich et al, , 2017stereo -Raffel et al, 2004;Raghav & Komerath, 2015;Reich et al, 2014aReich et al, , 2018. Note that given the strongly three-dimensional flow-field, stereo-PIV is generally preferred to mitigate the influence of out-of-plane particle motions.…”

Section: Instrumentationmentioning

confidence: 99%

Characterization of a canonical helicopter hub wake

2018

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The current study investigates the long-age wake behind rotating helicopter hub models composed of geometrically simple, canonical bluff body shapes. The models consisted of a 4-arm rotor mounted on a shaft above a 2-arm (scissor) rotor with all the rotor arms having a rectangular cross-section. The relative phase between the 2-and 4-arm rotors was either 0° (in-phase) or 45° (out-of-phase). The rotors were oriented at zero angle-of-attack and rotated at 30 Hz. Their wakes were measured with particle-image-velocimetry within a water tunnel at a hub diameter based Reynolds number of 820,000 and an advance ratio of 0.2. Mean profiles, fluctuating profiles and spectral analysis using time-series analysis as well as dynamic mode decomposition were used to characterize the wake and identify coherent structures associated with specific frequency content.The canonical geometry produced coherent structures that were consistent with previous results using more complex geometries. It was shown that the dominant structures (2 and 4 times per hub revolution) decay slowly and were not sensitive to the relative phase between the rotors.Conversely, the next strongest structure (6 times per hub revolution) was sensitive to the relative

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Section: Instrumentationmentioning

confidence: 99%

Characterization of a canonical helicopter hub wake

2018

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“…12,32 The formulation of U R is adopted from the previous study of Lentink and Dickinson 33 and subsequent studies. 34–36…”

Section: Foil Kinematics and Numerical Methodsmentioning

confidence: 99%

Numerical investigation of the aerodynamic performance of dragonfly-like flapping foil in take-off flight

Shanmugam¹,

Sohn

2019

Proceedings of the Institution of Mechanical Engineers, Part G:

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In this study, the aerodynamic performance of a dragonfly-like flapping foil is investigated in take-off flight using two-dimensional numerical simulations. Two parameters, foil spacing L * ( L/c) and the phase shift between forefoil and hindfoil ψ, which characterize the flow in the tandem configuration, are varied to explore their impact on the resulting aerodynamic performance. Both the vertical and thrust forces generated in one cycle are found to be strongly dependent on ψ and relatively weakly dependent on L *. The tandem configuration is beneficial for the vertical force generation in the range of 0° ≤ ψ ≤ 30°, and further, it aids the thrust force generation for 40° ≤ ψ ≤ 110°. The flow interactions between the forefoil and hindfoil can increase the vertical force generated in a cycle by a maximum of ∼1.2 times when ψ is close to 0° relative to the no foil–foil interaction case (additive effect of two single foils). These interactions can also increase the thrust force generated in a cycle by a maximum of ∼2.8 times when ψ is close to 80°. The vortex structures reveal that the enhancement in thrust force mainly depends on the timing of interactions and how the hindfoil utilizes the vortex detached from the forefoil to benefit from it. Further, we find that dragonflies use in-phase stroking pattern ( ψ = 0 °) with a large downstroke angle of attack, α D ( α D = 86 °), in the initial phase of take-off as it aids in generating additional vertical force. Our findings can significantly contribute to the design of micro aerial vehicles.

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“…Other studies evaluated the influence of the rotation and showed its great influence on the airloads (Refs. [23][24][25][26][27][28] as the rotation kept the stall vortex closer to the blade surface compared to non-rotating configurations.…”

Section: Journal Of the American Helicopter Societymentioning

confidence: 99%

A Numerical Investigation of the Influence of the Blade–Vortex Interaction on the Dynamic Stall Onset

Castells¹,

Richez²,

Costes³

2021

j am helicopter soc

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Recently, fluid–structure coupling simulations of helicopter rotors in high-thrust forward flight suggested that dynamic stall might be triggered by the blade–vortex interaction. However, no clear evidence of a correlation between dynamic stall and blade–vortex interaction has yet been given. We propose in this paper a simplified two-dimensional numerical model that can be used to indicate the role that the blade–vortex interaction plays in dynamic stall onset for different flight conditions. In this model, the rotor blade element is considered in pitching oscillation motion with a nonuniform translation, and a simplified vortex model can be introduced or not in the simulation to highlight the effect of blade–vortex interaction. All flow parameters of this simplified model are deduced from data provided by previous three-dimensional high-fidelity fluid–structure simulations. The method is used for validation and analysis of three flight conditions. The results show that, for the two cases with moderate advance ratio, the dynamic stall event is only triggered when a blade–vortex interaction occurs in the stall region. For the high-speed test case, the dynamic stall event seems to be only triggered by the very high angle of attack due to the motion of the blade.

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Advance ratio effects on the flow structure and unsteadiness of the dynamic-stall vortex of a rotating blade in steady forward flight

Cited by 18 publications

References 31 publications

Characterization of a canonical helicopter hub wake

Characterization of a canonical helicopter hub wake

Numerical investigation of the aerodynamic performance of dragonfly-like flapping foil in take-off flight

A Numerical Investigation of the Influence of the Blade–Vortex Interaction on the Dynamic Stall Onset

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