Review of measurement techniques for unsteady helicopter rotor flows

Gardner, Anthony Donald; Wolf, Christian; Raffel, Markus

doi:10.1016/j.paerosci.2019.100566

Cited by 34 publications

(15 citation statements)

References 89 publications

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“…With the increase of the vortex age angle, the vortex core of blade tip vortex becomes larger. This is consistent with most conclusions [5].…”

Section: Blade Tip Vortex Flow Structuresupporting

confidence: 94%

“…A strong blade tip vortex will appear in the wake of each blade tip, occupying a leading role in wake flow, and is the "skeleton" of the wake flow field. These vortices are always close to the rotor, generating a complex three-dimensional induced flow field, which affects the aerodynamic load of the rotor, aerodynamic performance, vibration level, aeroelasticity and acoustic performance [1,[5][6][7].…”

Section: Introductionmentioning

confidence: 99%

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Research on Rotorcraft Blade Tip Vortex Identification and Motion Characteristics in Hovering State

Kong

Wang

et al. 2020

Symmetry

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The rotorcraft blade tip vortex rolled up by the blade tip when the rotor rotates at high speed will produce a complex induced velocity field, which will have an important impact on the aerodynamic load and performance of the rotor. For this reason, this paper carries out the research on the identification of blade tip vortex and the motion characteristics of the vortex. Through the time-resolved particle image velocimetry (TR-PIV) experiment, the flow field of the rotor at a fixed rotate speed (2100 r/min) with a collective pitch of 6° and 9° was obtained. Based on the vorticity field, Q criterion, and Ω criterion, the research on vortex identification and vortex motion characteristics are realized. The results show that with the increase of blade motion azimuth, the radial position of blade tip vortex gradually contracts inward and the axial position moves downward in hovering state. As the collective pitch of the rotor increases, the radial contraction becomes more obvious, and the axial displacement increases, at the same time, the blade tip vortex intensity increases. Comparative study results show that different vortex identification methods have obtained certain deviations in the vortex center. Compared with other vortex identification methods, the Ω criterion method has a smaller deviation and can accurately identify the vortex core radius and vortex boundary.

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“…With the increase of the vortex age angle, the vortex core of blade tip vortex becomes larger. This is consistent with most conclusions [5].…”

Section: Blade Tip Vortex Flow Structuresupporting

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Research on Rotorcraft Blade Tip Vortex Identification and Motion Characteristics in Hovering State

Kong

Wang

et al. 2020

Symmetry

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show abstract

“…Rudmin and co-workers [10][11] measured the separation and transition locations for a pitching airfoil based on the cross-correlation and spectra of the hot-film data. Gardner and co-workers [12][13][14] investigated laminar, transitional, and turbulent BL over a pitching airfoil from the hot-film raw voltages.…”

Section: Nomenclaturementioning

confidence: 99%

Time-Frequency Analysis and Transitional Boundary Layer Investigation over a Pitching Airfoil

2020

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Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2.7×10 5) is experimentally investigated through the space-frequency and time-frequency analyses of hot-film signals. Boundary layer events are visualized based on the spacefrequency and time-frequency plots. The precursor phenomena for turbulent as well as fully separated flows are presented based on the time-frequency analysis. A new technique based on the time-frequency analysis of hot-film signals is presented to measure the transition onset as well as the relaminarization locations. This technique is based on the analysis of highfrequency disturbances of the measured data. Special attention is focused on the spatial/temporal progression of the transition onset and the relaminarization points, compared to the static values, for different oscillation frequencies and amplitudes. Investigations are performed prior to, within and beyond the static stall angle of attack conditions. The results obtained by the new technique will be discussed and compared with the observations from the previous investigators.

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“…Obviously, in helicopter technology, rotor aerodynamics plays an important role. However, the existence of a tip vortex makes the flow field of the rotor extremely complex [1,2]. In the field of helicopter aerodynamics and computational fluid dynamics (CFD), the accurate prediction for rotor flow field with vortex wake is still one of the most complex and challenging problems [3].…”

Section: Introductionmentioning

confidence: 99%

A Modified Fifth-Order WENO-HLLC Riemann Solver for Transonic Viscous Flows around Helicopter Rotor in Hover

Zhao

Cai

2022

Shock and Vibration

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This paper presents a modified fifth-order WENO-HLLC Riemann solver for the transonic compressible viscous flows around the helicopter rotor in hover. The HLLC approximate Riemann solver is proposed to discrete the convection term involving grid velocity of the Navier-Stokes equations. In order to solve the interface flow accurately, a modified fifth-order WENO scheme is presented by designing the smoothness indicators based on L 1 norm measurement. The improved WENO scheme can provide the optimal approximation order even at critical points. Numerical accuracy and robustness are validated by several benchmark inviscid flow problems. Then the numerical properties of the WENO-HLLC solver in conjunction with the implicit LU-SGS time integration method with high efficiency are further validated by simulating transonic viscous flows over RAE2822 airfoil and ONERA-M6 wing. The results show that the accuracy of calculating shock, discontinuity, and the vortex is significantly improved. Finally, the method is developed to compute the transonic vortex flow around the helicopter rotor with a domain discretized by overset grids. The results indicate that the proposed method is very robust and effective in acquiring high resolution for vortex wake.

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Review of measurement techniques for unsteady helicopter rotor flows

Cited by 34 publications

References 89 publications

Research on Rotorcraft Blade Tip Vortex Identification and Motion Characteristics in Hovering State

Research on Rotorcraft Blade Tip Vortex Identification and Motion Characteristics in Hovering State

Time-Frequency Analysis and Transitional Boundary Layer Investigation over a Pitching Airfoil

A Modified Fifth-Order WENO-HLLC Riemann Solver for Transonic Viscous Flows around Helicopter Rotor in Hover

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