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Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the retreating rotor blade has a lower relative blade speed, combined with an increased angle of attack, causing a stall and loss of lift. Retreating blade stall is the primary limiting factor of a helicopter's never exceed speed, VNE.
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A blade vortex interaction (BVI) is an unsteady phenomenon of three-dimensional nature, which occurs when a rotor blade passes within a close proximity of the shed tip vortices from a previous blade. The aerodynamic interactions represent an important topic of investigation in rotorcraft research field due to the adverse influence produced on rotor noise, particularly in low speed descending flight condition or maneuver, which generates high amplitude impulsive noise.
An annular lift fan aircraft is a conceptual vertical takeoff and landing (VTOL) aircraft that was first systematically and numerically investigated in 2015. This concept was proposed to offer a VTOL solution for both high hovering efficiency and high cruise speed, using a large annular lift fan instead of the relatively small conventional circular lift fans used in the Ryan XV-5 Vertifan and the F-35B Lightning II (JSF).
The dynamic stall is one of the hazardous phenomena on helicopter rotors, which can cause the onset of large torsional airloads and vibrations on the rotor blades. Unlike fixed-wing aircraft, of which the stall occurs at relatively low flight speed, the dynamic stall on a helicopter rotor emerges at high airspeeds or/and during manoeuvres with high load factors of helicopters, when the angle of attack(AOA) of blade elements varies intensively due to time-dependent blade flapping, cyclic pitch and wake inflow. For example, during forward flight at the velocity close to VNE, velocity, never exceed, the advancing and retreating blades almost reach their operation limits whereas flows are still attached to the blade surfaces. That is, the advancing blades operate at high Mach numbers so low values of AOA is needed but shock-induced flow separation may happen, while the retreating blade operates at much lower Mach numbers but the high values of AoA result in the stall.
References
- ↑ "CFD - CFD support and info - UTS: FEIT Student Intranet". my.feit.uts.edu.au. Retrieved 2023-10-26.
- ↑ K. Jamison, R. Heise, “Evaluating the Release of a Large Store from the BAE Hawk MK120,” International Aerospace Symposium of South Africa, Gordons Bay, 23–25 November 2010.
- ↑ Krzysztof Szilder, Hongyi Xu, “Prediction of Supercooled Droplet Impingement on Helicopter Rotor Blades,” 26th International Conference of the Aeronautical Sciences, ICAS 2008.
- ↑ Liang Jin, Xian Yu Wu, Jing Lei, Li Yan, Wei Huang, Jun Liu, “CFD Analysis of a Hypersonic Vehicle Powered by Triple-Module Scramjets,” Applied Mechanics and Materials, Volume 390, Pages 71-75, August 2013.
- ↑ M. Mamou, M. Khalid, “Steady and unsteady flow simulation of a combined jet flap and Coanda jet effects on a 2D airfoil aerodynamic performance,” Colloque International sur les Energies Renouvelables CER '2007 Oujda, 4 to 5 May 2007, Oujda, Morocco.
- ↑ M. Mamou, M. Khalid, “Time-Accurate Flow Simulations Past Helicopter Rotors in Hover and Forward Flight Conditions Using Chimera Grid Technique,” Canadian Aeronautics and Space Journal, 2006, 52(4): 135-148, 10.5589/q06-016.
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