Effects of rotor separation on the axial descent performance of dual-rotor configurations
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 arrange...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Cambridge University Press
2023-01-01
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| Series: | Flow |
| Subjects: | |
| Online Access: | https://www.cambridge.org/core/product/identifier/S2633425922000319/type/journal_article |
| _version_ | 1811156285966516224 |
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| author | Marcel Veismann Christopher Dougherty Morteza Gharib |
| author_facet | Marcel Veismann Christopher Dougherty Morteza Gharib |
| author_sort | Marcel Veismann |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-04-10T04:49:02Z |
| format | Article |
| id | doaj.art-1e7708b0c47e4692aab2d64019393211 |
| institution | Directory Open Access Journal |
| issn | 2633-4259 |
| language | English |
| last_indexed | 2024-04-10T04:49:02Z |
| publishDate | 2023-01-01 |
| publisher | Cambridge University Press |
| record_format | Article |
| series | Flow |
| spelling | doaj.art-1e7708b0c47e4692aab2d640193932112023-03-09T12:34:16ZengCambridge University PressFlow2633-42592023-01-01310.1017/flo.2022.31Effects of rotor separation on the axial descent performance of dual-rotor configurationsMarcel Veismann0https://orcid.org/0000-0001-8106-6738Christopher Dougherty1Morteza Gharib2https://orcid.org/0000-0003-0754-4193Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125, USAGraduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125, USAGraduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125, USARotorcraft 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.https://www.cambridge.org/core/product/identifier/S2633425922000319/type/journal_articleFluid-structure interactionsPropulsion systemsFlow imaging and velocimetryVortex interactionsRotorMultirotorAxial descentVortex ring stateRotor separation |
| spellingShingle | Marcel Veismann Christopher Dougherty Morteza Gharib Effects of rotor separation on the axial descent performance of dual-rotor configurations Flow Fluid-structure interactions Propulsion systems Flow imaging and velocimetry Vortex interactions Rotor Multirotor Axial descent Vortex ring state Rotor separation |
| title | Effects of rotor separation on the axial descent performance of dual-rotor configurations |
| title_full | Effects of rotor separation on the axial descent performance of dual-rotor configurations |
| title_fullStr | Effects of rotor separation on the axial descent performance of dual-rotor configurations |
| title_full_unstemmed | Effects of rotor separation on the axial descent performance of dual-rotor configurations |
| title_short | Effects of rotor separation on the axial descent performance of dual-rotor configurations |
| title_sort | effects of rotor separation on the axial descent performance of dual rotor configurations |
| topic | Fluid-structure interactions Propulsion systems Flow imaging and velocimetry Vortex interactions Rotor Multirotor Axial descent Vortex ring state Rotor separation |
| url | https://www.cambridge.org/core/product/identifier/S2633425922000319/type/journal_article |
| work_keys_str_mv | AT marcelveismann effectsofrotorseparationontheaxialdescentperformanceofdualrotorconfigurations AT christopherdougherty effectsofrotorseparationontheaxialdescentperformanceofdualrotorconfigurations AT mortezagharib effectsofrotorseparationontheaxialdescentperformanceofdualrotorconfigurations |