Helicopter Aerodynamics

A special issue of Aerospace (ISSN 2226-4310). This special issue belongs to the section "Aeronautics".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 14413

Special Issue Editor


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Guest Editor
Chair of Aerodynamics and Fluid Mechanics, Department of Mechanical Engineering, Technical University of Munich, 85748 Munich, Germany
Interests: aerodynamic configuration; turbulent flows and high-lift, highly agile configurations; unsteady aerodynamics and aeroelasticity; helicopter aerodynamics; rotor and propeller aerodynamics; membrane wings and fluid–structure interaction

Special Issue Information

Dear Colleagues,

Helicopters are multi-purpose flight vehicles due to their ability to perform vertical take-off and landing, hovering, and cruise flight at varying speeds. These capabilities are the basis for conducting a unique range of missions from transport up to search and rescue. The forces required for lift and propulsion are created by a rotor consisting of several blades, the number and design of which depending on performance, operational, and mission requirements. Rotor blade aerodynamics phenomena and problems are, among others, related to dynamic stall, Mach number effects, blade-vortex–interaction, transitional flow, and strong interaction phenomena. Methods of aerodynamic drag reduction often concentrate on fuselage and cowling geometries. Rotor and fuselage wake interactions with the stabilizers may cause problems like tail shake. Consequently, a variety of complex aerodynamic interaction phenomena and problems are associated with helicopters addressing a research field of high relevance.

Prof. Christian Breitsamter
Guest Editor

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Keywords

  • dynamic stall
  • blade–vortex-interaction
  • Mach number effects
  • ground effects
  • drag reduction
  • shape optimization
  • aeroelasticity and aeroacoustics
  • tail shake
  • compound configurations
  • active rotor/control

Published Papers (4 papers)

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Research

23 pages, 9734 KiB  
Article
Numerical Study of Coaxial Main Rotor Aerodynamics in Steep Descent
by Pavel Makeev, Yuri Ignatkin and Alexander Shomov
Aerospace 2022, 9(2), 61; https://doi.org/10.3390/aerospace9020061 - 24 Jan 2022
Viewed by 2564
Abstract
Numerical studies of the aerodynamic characteristics of the coaxial main rotor of the Kamov Ka-32 helicopter in steep descent modes, including the area of the vortex ring state (VRS) modes, have been performed. Used in this paper is an original free vortex wake [...] Read more.
Numerical studies of the aerodynamic characteristics of the coaxial main rotor of the Kamov Ka-32 helicopter in steep descent modes, including the area of the vortex ring state (VRS) modes, have been performed. Used in this paper is an original free vortex wake model of the rotor developed by the authors. The angles of attack of the rotor αR = 30 – 90° and the rate of descent in the range of Vy = 0–30 m/s are considered. The calculations have been carried out under the condition of a fixed time-average thrust of the rotor. The visualization of the rotor wake shapes the flow structures using streamlines, and the flow velocities have been received and analyzed. The VRS boundaries in “VxVy” coordinates have been constructed. The criteria used in this paper are: rotor thrust and torque pulsations, rise of rotor torque and induced velocity relative to the hovering mode. The results of the calculations are compared with the experimental and calculated data of other authors, and a satisfactory match has been obtained. The new results presented in this paper can supplement the existing experience of experimental and numerical research in this field. Full article
(This article belongs to the Special Issue Helicopter Aerodynamics)
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19 pages, 6677 KiB  
Article
Transient Thrust Analysis of Rigid Rotors in Forward Flight
by Travis Krebs, Goetz Bramesfeld and Julia Cole
Aerospace 2022, 9(1), 28; https://doi.org/10.3390/aerospace9010028 - 05 Jan 2022
Cited by 4 | Viewed by 2732
Abstract
The purpose of this study was to investigate and quantify the transient thrust response of two small rigid rotors in forward flight. This was accomplished using a distributed doublet-based potential flow method, which was validated against wind-tunnel experimentation and a transient CFD analysis. [...] Read more.
The purpose of this study was to investigate and quantify the transient thrust response of two small rigid rotors in forward flight. This was accomplished using a distributed doublet-based potential flow method, which was validated against wind-tunnel experimentation and a transient CFD analysis. The investigation showed that for both rotors, advancing and retreating blade effects were predicted to contribute to transient thrust amplitudes of 5–30% of the mean rotor thrust. The thrust output amplitudes of individual rotors blades were observed to be 15–45% of the mean rotor thrust, indicating that it is not uncommon for the thrust output variation of an individual rotor blade to approach the same value as the mean thrust output of the rotor itself. In addition to this, the theoretical analysis also illustrated that higher blade thrust oscillations resulted in pronounced asymmetric rotor wake structures. Full article
(This article belongs to the Special Issue Helicopter Aerodynamics)
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19 pages, 4680 KiB  
Article
Wind Tunnel Studies on Hover and Forward Flight Performances of a Coaxial Rigid Rotor
by Chang Wang, Minqi Huang, Xianmin Peng, Guichuan Zhang, Min Tang and Haowen Wang
Aerospace 2021, 8(8), 205; https://doi.org/10.3390/aerospace8080205 - 28 Jul 2021
Cited by 2 | Viewed by 2666
Abstract
The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and [...] Read more.
The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and lift offset. The rotor system featured by 2 m-diameter, four-bladed upper and lower hingeless rotors and was installed in a coaxial rotor test rig. Experiments were conducted in the Φ3.2 m wind tunnel at China Aerodynamics Research and Development Center (CARDC). The rotor system was tested in hover states at collective pitches ranging from 0° to 13° and it was also tested in forward flights at advance ratios up to 0.6, with specific focus on the shaft tilt angle and lift offset sweeps. To ensure that the coaxial rotor was operating in a similar manner to that of the real flight, the torque difference was trimmed to zero in hover flight, whilst the constant lift coefficient was maintained in forward flight. An isolated single-rotor configuration test was also conducted with the same pitch angle setting in the coaxial rotor. The hover test results demonstrate that the figure of merit (FM) value of the lower rotor is lower than that of the upper rotor, and both are lower than that of the isolated single rotor. Moreover, the coaxial rotor configuration can contribute to better hover efficiency under the same blade loading coefficient (CT/σ). In forward flight, the effective lift-to-drag (L/De) ratio of the coaxial rigid rotor does not monotonously change as the advance ratio increases. Increases in the required power and drag in the case with a high advance ratio of 0.6 leads to the decreasing L/De ratio of the rotor. Meanwhile, the L/De ratio of the rotor is relatively high when the rotor shaft is tilted backward. The increasing lift offset tends to result in reduced required rotor power and an increase in the rotor drag. When the effect of the reduced rotor power is greater than that of the increased rotor drag, the L/De ratio increases as the lift offset increases. The L/De ratio can benefit significantly from lift offset at a high advance ratio, but it is much less influenced by lift offset at a low advance ratio. The forward performance efficiency of the upper rotor is poorer than that of the lower rotor, which is significantly different from the case in the hover flight. Full article
(This article belongs to the Special Issue Helicopter Aerodynamics)
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21 pages, 9431 KiB  
Article
Numerical Investigation of an Optimized Rotor Head Fairing for the RACER Compound Helicopter in Cruise Flight
by Patrick Pölzlbauer, Andreas Kümmel, Damien Desvigne and Christian Breitsamter
Aerospace 2021, 8(3), 66; https://doi.org/10.3390/aerospace8030066 - 05 Mar 2021
Cited by 6 | Viewed by 4029
Abstract
The present work is part of the Clean Sky 2 project Full-Fairing Rotor Head Aerodynamic Design Optimization (FURADO), which deals with the aerodynamic design optimization of a full-fairing rotor head for the Rapid And Cost-Effective Rotorcraft (RACER) compound helicopter. The rotor head is [...] Read more.
The present work is part of the Clean Sky 2 project Full-Fairing Rotor Head Aerodynamic Design Optimization (FURADO), which deals with the aerodynamic design optimization of a full-fairing rotor head for the Rapid And Cost-Effective Rotorcraft (RACER) compound helicopter. The rotor head is a major drag source and previous investigations have revealed that the application of rotor head fairings can be an effective drag reduction measure. As part of the full-fairing concept, a new blade-sleeve fairing was aerodynamically optimized for cruise flight. Within this publication, the newly developed blade-sleeve fairing is put to test on an isolated, five-bladed rotor head and compared to an already existing reference blade-sleeve fairing, which was developed at Airbus Helicopters. Numerical flow simulations are performed with ANSYS Fluent 2019 R2 considering a rotating rotor head with cyclic pitch movement. The aerodynamic forces of the isolated rotor head are analyzed to determine the performance benefit of the newly developed blade-sleeve fairing. A drag reduction of 4.7% and a lift increase of 20% are obtained in comparison to the Airbus Helicopters reference configuration. Furthermore, selected surface and flow field quantities are presented to give an overview on the occurring flow phenomena. Full article
(This article belongs to the Special Issue Helicopter Aerodynamics)
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