When helicopters fly near loose surfaces such as deserts and Gobi terrain, the complex interference flow field formed between the rotor and the ground induces the movement of sand bed particles, easily leading to the brownout phenomenon that obscures the pilot's vision and threatens flight safety. Based on a CFD/DEM coupled numerical analysis method for helicopter brownout, this paper deeply investigates the formation mechanism of brownout driven by the rotor/ground interference flow field from the perspective of “flow structure-particle transport”. The research results indicate that the brownout phenomenon is essentially a continuous process of particle initiation, outward migration, lifting, and suspension under the combined action of the rotor downwash, ground wall jet, and tip vortices. The rotor downwash provides the initial kinetic energy for particle initiation, the ground wall jet dominates the near-ground radial transport of particles, and the tip vortices control the lifting and spatial diffusion of outer particles. The spatiotemporal asynchronous evolution of successive tip vortices creates a significant cumulative effect, enhancing localized particle transport and suspension. Particle diameter has a distinct impact on brownout evolution; larger particles are prone to settling and deposition due to gravity, while smaller particles maintain suspension more easily. Rotor flow field structures, such as the downwash, all have clearly defined dominant interaction zones: 0.8~1.4R is the downwash impingement zone, where the average particle concentration decreases by 99.10% within the flow interaction time; 1.4~2.0R is the ground wall jet displacement zone, where the average particle concentration decreases by 99.03% within the flow interaction time; and the area beyond 2.0R is the zone dominated by tip vortex entrainment.
[1]张卫国, 谭剑锋, 刘亚奎, 等.直升机“沙盲”现象研究进展[J].实验流体力学, 2023, 37(5):56-75
[2]ZHANG W G, TAN J F, LIU Y K, et al.Advances on helicopter brownout[J].Journal of Experiments in Fluid Mechanics, 2023, 37(5):56-75
[3]COWHERD C, Jr.Sandblaster 2: support of see-through technologies for particulate brownout[R]. Defence Advanced Report Research Technical Projects Agency (DARPA), 110565, 2007.
[4]谭剑锋, 闫羽泽, 张卫国, 等.沙盲环境直升机桨叶磨损分析方法[J]., 2025, 46(14):-
[5]TAN J F, YAN Y Z, ZHANG W G, et al.Analyzed method of helicopter blade erosion in brownout condition[J].Acta Aeronautica et Astronautica Sinica, 2025, 46(14):431012-
[6]GANESH B, KOMERATH N.Study of ground vortex structure of rotorcraft in ground effect at low advance ratios[C]//24th AIAA Applied Aerodynamics Conference. Reston, VA: AIAA, 2006.
[7]LEE T E, LEISHMAN J G, RAMASAMY M.Fluid dynamics of interacting blade tip vortices with a ground plane[J].Journal of the American Helicopter Society, 2010, 55(2):022005-
[8]MILLUZZO J I.Effects of blade tip shape on rotor in-ground-effect aerodynamics[D]. Maryland: University of Maryland, 2012: 39-83.
[9]WHITEHOUSE G R, WACHSPRESS D A, QUACK-ENBUSH T R, et al.Exploring aerodynamic methods for mitigating brownout[C]// American Helicopter Society 65th Annual Forum, 2009.
[10]WHITEHOUSE G R，WACHSPRESS D A, QUACK-ENBUSH T R.Aerodynamic design of helicopter rotors for reduced brownout[C]// International Powered Lift Conference, 2010.
[11]JOHNSON B, LEISHMAN J G, SYDNEY A.Investigation of sediment entrainment using two-phase,high-speed particle image velocimetry[J].Journal of the American Helicopter Society, 2010, 55(4):042003-
[12]RAMASAMY M, POTSDAM M, YAMAUCHI G K.Measurements to understand the flow mechanisms contributing to tandem-rotor outwash[J]. Annual Forum Proceedings-AHS International, 2015, 1: 612-647.[J].Annual Forum Proceedings-AHS International, , :-
[13]WANG Y P, LIU P Q, HU T X, et al.Investigation of co-rotating vortex merger in ground proximity[J]. Aerospace Science and Technology, 2016, 53: 116-127.[J].Aerospace Science and Technology, , :-
[14]CHEN Q M, HU T X, LIU P Q, et al.Experiments on asymmetric vortex pair interaction with the ground[J].Experiments in Fluids, 2020, 61(6):150-
[15]WONG O D, TANNER P E.Photogrammetric measure-ments of an EH-60L brownout cloud[J].Journal of the American Helicopter Society, 2016, 61(1):1-10
[16]BRADLEY J, LEISHMAN J G, SYDNEY A, et al.Investigation of sediment entrainment in brownout using high-speed particle image velocimetry[C]//Proc of the 65th Annual Forum of the American Helicopter Society. 2009.
[17]SYDNEY A, LEISHMAN J G.Measurements of rotor/ airframe interactions in ground effect over a sediment bed[C]//Proc of the 69th Annual Forum of the American Helicopter Society. 2013.
[18]SYDNEY A, BAHARANI A, LEISHMAN J G.Understanding brownout using near-wall dual-phase flow measurements[C]//Proc of the 67th Annual Forum of the American Helicopter Society. 2011.
[19]SYDNEY A, LEISHMAN J G.Measurements of the plumelike three-dimensionality of rotor-induced dust fields[C]// Proc of the 70th Annual Forum of the American Helicopter Society. 2014.
[20]SYAL M, LEISHMAN J G.Modeling of bombardment ejections in the rotorcraft brownout problem[J].AIAA Journal, 2013, 51(4):849-866
[21]WACHSPRESS D A, QUACKENBUSH T R, BOSCHI-TSCH A H.First-principles, free-vortex wake model for helicopters and tiltrotors[C]//The American Helicopter Society 59th Annual Forum. Alexandria: AHS, 2003: 307-330.
[22]WACHSPRESS D A, WHITEHOURSE G R, KELLER J D, et al.A high fidelity brownout model for real-time flight simulations and trainers[C]∥The American Helicopter Society 65th Annual Forum. Alexandria: AHS, 2009: 1281-1304.
[23]THOMAS S, AMIRAUX M, BAEDER J D.Modeling the two-phase flowfield beneath a hovering rotor on graphics processing units using a FVM-RANS hybrid methodology[C]//21st AIAA Computational Fluid Dynamics Conference. Reston, VA: AIAA, 2013.
[24]HANCE B T.Effects of body shapes on rotor in-ground-effect aerodynamics[D]. Maryland: University of Maryland, 2012: 42-66.
[25]胡健平, 徐国华, 史勇杰, 等.基于-耦合数值模拟的全尺寸直升机沙盲形成机理[J].航空学报, 2020, 41(3):154-168
[26]HU J P, XU G H, SHI Y J, et al.Formation mechanism of brownout in full-scale helicopter based on CFD-DEM couplings numerical simulation[J].Acta Aeronautica et Astronautica Sinica, 2020, 41(3):154-168
[27]HU J P, XU G H, SHI Y J, et al.A numerical simulation investigation of the influence of rotor wake on sediment particles by computational fluid dynamics coupling discrete element method[J]. Aerospace Science and Technology, 2020, 105: 106046.[J].Aerospace Science and Technology, 2020, :-
[28]LIN H Y, XU C H, JIANG C W, et al.Finite particle approach for high-fidelity simulation on helicopter brownout[J].AIAA Journal, 2024, 62(1):193-208
[29]谭剑锋, 何龙, 于领军, 等.基于黏性涡粒子沙粒 的直升机沙盲建模[J].航空学报, 2022, 43(8):351-361
[30]TAN J F, HE L, YU L J, et al.Helicopter brownout modeling based on viscous vortex particle and sand particle DEM[J].Acta Aeronautica et Astronautica Sinica, 2022, 43(8):351-361
[31]谭剑锋, 杨宇霄, 张卫国等.侧风对直升机沙盲特性影响[J].北京航空航天大学学报, 2024, 50(10):1-12
[32]TAN J F, YANG Y X, ZHANG W G, et al.Influence of crosswind on the helicopter brownout[J].Journal of Beijing University of Aeronautics and Astronautics, 2024, 50(10):1-12
[33]TAN J F, GAO J E, BARAKOS G N, et al.Novel approach to helicopter brownout based on vortex and discrete element methods[J]. Aerospace Science and Technology, 2021, 116: 106839.
[34]CUNDALL P A, STRACK O D L.A discrete numerical model for granular assemblies[J].Géotechnique, 1979, 29(1):47-65
[35]MINDLIN R D, DERESIEWICZ H.Elastic spheres in contact under varying oblique forces[J].Journal of Applied Mechanics, 1953, 20(3):327-344
[36]DI RENZO A, DI MAIO F P.Comparison of contact-force models for the simulation of collisions in DEM-based granular flow codes[J].Chemical Engineering Science, 2004, 59(3):525-541
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