Numerical Simulation of Vortex Ring State Phenomenon for the Mi2 Type Helicopter Tail Rotor

Zalewski, Wiesław

doi:10.5604/12314005.1213772

Cited by 3 publications

(2 citation statements)

References 1 publication

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“…As the descent velocity increases starting from hover, the cores of these vortex rings can be observed to move upward, closer to the rotor disks (see collection of all streamline patterns in the supplementary material). In accordance with single-rotor studies from the rotorcraft literature (Castles, 1958;Liangquan, Guohua, & Yongjie, 2018;Veismann et al, 2022;Zalewski, 2016), the cores of the vortex ring systems can be seen to be located within the rotor plane and close to the rotor blade tips during the fully established VRS, where thrust losses and fluctuations peak (v c /v h ≈ −1.3). Similar critical descent rate ratios (v c /v h = −1.35), for when the cores are located within the rotor plane, were found in single rotor studies (Green et al, 2005).…”

Section: Flow Field Analysissupporting

confidence: 81%

Effects of rotor separation on the axial descent performance of dual-rotor configurations

Veismann

Dougherty

Gharib

2023

Flow

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Rotorcraft can encounter highly unsteady flow when descending at a steep angle, leading to a flow condition called vortex ring state, which is associated with strong oscillatory airloads and substantial losses in mean rotor thrust. This study examines the aerodynamic coupling between closely arranged rotors in vertical flight and assesses the extent to which rotor–rotor interactions affect the rotor performance in this flight stage. Wind tunnel experiments were performed on a small-scale, dual-rotor set-up with adjustable rotor spacing, and the effect of rotor separation on thrust generation was quantified. Pairs of 4 in., 5 in. and 6 in. rotors ( $3.0 \times 10^4< Re<8.1 \times 10^4$ ) were investigated, with load cell measurements showing significant thrust losses and concomitantly increased thrust oscillations as descent rate increased. Peak losses and fluctuations were consistently recorded at descent rates of 1.2–1.3 times the hover induced velocity for all rotor sizes and separations. While tests showed that the mean aerodynamic performance of dual-rotor systems is generally similar to that of single rotors, appreciable changes to the descent characteristics could be observed at low rotor separations. Particle image velocimetry flow visualization suggests considerable changes to the flow field as rotor separation decreases, where individual vortex ring systems merge into a single vortex ring structure.

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Section: Flow Field Analysissupporting

confidence: 81%

Effects of rotor separation on the axial descent performance of dual-rotor configurations

Veismann

Dougherty

Gharib

2023

Flow

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“…Some research was conducted and published on the topic as well 6 – 8 . Although not part of the four notable milestones, we briefly mention this body of literature.…”

Section: Introductionmentioning

confidence: 99%

Data-driven analysis and new findings on the loss of tail rotor effectiveness in helicopter accidents

Saleh

Guvir

et al. 2022

Sci Rep

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Loss of tail rotor effectiveness (LTE) is an unstable dynamic phenomenon that affects single-rotor helicopters and frequently leads to accidents. LTE accidents recur with troubling regularity and show no sign of abatement. This work uncovers new data-driven findings pertaining to LTE and risk factors. First, a scorecard is developed covering a broad range of results to better understand LTE accidents. Second, the risk of LTE is derived for current helicopters. Third, a Deep Learning model is developed that captures the dependence between LTE risk and helicopter features. A danger zone is discovered in the design space for short tail rotor arm and high tail rotor RPM. The results challenge the prevailing narrative of LTE accidents as mere pilot errors and demonstrate an intrinsic propensity to these accidents is embedded in part in the helicopter design. The findings open the door to new, more effective safety interventions for LTE accident prevention.

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Mechanism analysis of the vortex ring and its effects on an axial descending rotor

Zeng,

Gao,

et al. 2024

International Journal of Fluid Engineering

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A vortex ring is a flow phenomenon involving a complex toroidal vortex system. When a rotor is in descending flight, it may enter the vortex ring state (VRS), which will affect the rotor’s aerodynamic characteristics and even endanger it. In this paper, to clarify the aerodynamic mechanism by which the vortex ring exerts its effects on an axial descending rotor, an unsteady numerical simulation method for the rotor integrated with structured moving overset grids is proposed and validated using experimental data. This numerical simulation method is then applied to analyze the aerodynamic characteristics of the rotor in descending flight. The variations of the aerodynamic forces and the flow characteristics in the slipstream are analyzed to elucidate the physical mechanisms responsible for the relationships between the aerodynamic loads, flow field, and vortices when the rotor is in the VRS. The effects of the VRS cause a sharp drop in the average aerodynamic forces, which directly affects the safety and reliability of a rotor aircraft. In the slipstream of the descending rotor, a distinct vortex ring forms and moves upward as the velocity of descent increases. The most severe VRS occurs at a nondimensional velocity of descent of 1.13 when the center of the highly unsteady vortex ring is right at the blade tip, and this can be used as an indicator of the VRS. The physical mechanism by which the VRS exerts its effects can be attributed to the low pressure induced by strong vortices. The VRS decreases the pressure on the lower surface of the blade and increases the pressure on the upper surface, resulting in a reduction in the aerodynamic loads. In comparison with the hovering state, the VRS results in a much larger vortex strength and possesses a different vortex structure.

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Numerical Simulation of Vortex Ring State Phenomenon for the Mi2 Type Helicopter Tail Rotor

Cited by 3 publications

References 1 publication

Effects of rotor separation on the axial descent performance of dual-rotor configurations

Effects of rotor separation on the axial descent performance of dual-rotor configurations

Data-driven analysis and new findings on the loss of tail rotor effectiveness in helicopter accidents

Mechanism analysis of the vortex ring and its effects on an axial descending rotor

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