Geometrical layout effect on the main rotor aerodynamic characteristics at the «vortex ring» state modes

Aeronautical and Space-Rocket Engineering


DOI: 10.34759/vst-2023-2-7-16

Аuthors

Makeev P. V.*, Ignatkin Y. M.**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: vaultcity13@gmail.com
**e-mail: k102@mai.ru; ignatkinym@mai.ru

Abstract

Geometric layout affects significantly the aerodynamic characteristics of the helicopter main rotor in various operating modes. When designing a rotor with a given diameter and solidity, various geometry layout solutions are possible, such as, the number of blades, blade twist and relative position of the blades (single or coaxial rotor).

It is common knowledge that the geometrical layout has a significant impact on the efficiency of the rotor in hover [1]. For the other flight modes, the geometry impact on the rotor aerodynamics is of practical interest as well.

The study considers the effect of various options of geometrical layout on rotors aerodynamic characteristics at a vertical descent in the vortex ring state modes range in the range of descent speeds Vy = 0 — 28 m/s. The sharp rotor thrust reduction compared to the hover mode and its non-stationary pulsations are characteristic to the «vortex ring» modes, which makes these modes unsafe for the helicopter.

Wide-scale experimental studies of the vortex ring modes are extremely difficult, thus application of the state-of-the-art computational methods is rational. The studies being presented were performed based on the nonlinear vortex rotor model developed at the Moscow Aviation Institute [19].

Single two- four- and six-bladed rotors, as well as coaxial six-bladed rotor with the same solidity, airfoils and blade twist were considered. The blade twists of 0°, 8° and 16° were considered for the 4-bladed rotor as well.

Computations have been performed at the fixed blade pitch angles, ensuring the equal thrust in hover. The total and distributed aerodynamic characteristics have been obtained and analyzed, including the shapes of the vortex wake and flow-around patterns.

The smallest obtained thrust drop in the vortex ring modes was demonstrated by the two-bladed rotor. The thrusts of the equivalent six-bladed single main rotor and six-bladed coaxial main rotor have similar dependences on the rate of descent, but the coaxial rotor herewith has had lower values of the thrust pulsations amplitude. With the blade twist values growth, the thrust drop and thrust pulsations in vortex ring state increased for the four-bladed rotor. The blade twist effect on the rotor aerodynamic characteristics at the vortex ring modes is in good agreement with the available experimental data [6].

Thus, the considered technical solutions on the rotor geometrical layout (that improve its aerodynamics in hover [1]) do not have a positive effect in the vortex ring modes.

The obtained results may be handy in the rotor aerodynamics analysis in vortex ring state modes.

Keywords:

main rotor, number of blades, blade twist, “vortex ring state” modes, aerodynamic characteristics

References

  1. Ignatkin Yu.M., Makeev P.V., Shomov A.I. Nauchnyi vestnik MGTU GA, 2018, vol. 21, no. 6, pp. 43-53. DOI: 10.26467/2079-0619-2018-21-6-43-53
  2. Akimov A.I. Aerodinamika i letnye kharakteristiki vertoletov (Aerodynamics and Performance of Helicopters), Moscow, Mashinostroenie, 1988, 140 p.
  3. Johnson W. Rotorcraft aeromechanics — Cambridge University Press, New York, 2013, 944 p.
  4. Petrosyan E.A. Aerodinamika soosnogo vertoleta (Aerodynamics of Coaxial Helicopter), Moscow, Poligon-Press, 2004, 820 p.
  5. Drees J.M., Hendal W.P. The Field of Flow through a Helicopter Rotor Obtained from Wind Tunnel Smoke Tests. Journal of Aircraft Engineering, 1951, no. 23, pp. 107-111.
  6. Castles W.Jr., Gray R.B. Empirical Relation between Induced Velocity, Trust, and Rate of Descent of a Helicopter Rotor as Determined by Wind-tunnel Tests on Four Model Rotors. NASA TN-2474, 1951, 74 p. URL: 19930083181.pdf
  7. Washizu K., Azuma A, Koo J., Oka T. Experiments on a Model Helicopter Rotor Operating in the Vortex Ringstate. Journal of Aircraft, 1966, vol. 33, no. 3, pp. 225-230. DOI: 10.2514/3.43729
  8. Empey R.W., Ormiston R.A. Tail-Rotor Thrust on a 5.5-Foot Helicopter Model in Ground Effect. 30th Annual National V/STOL Forum (1974; Washington, D.C.), 13 p.
  9. Xin H., Gao Z. A Prediction of the Helicopter Vortex-ring State Boundary. Journal of Experiments in Fluid Mechanics, 1996, no. 1, pp. 14-19.
  10. Betzina M.D. Tiltrotor Descent Aerodynamics: A Small-Scale Experimental Investigation of Vortex Ring State. 57th Annual Forum (09-11 May 2001; Washington, D.C.), 12 p.
  11. Stack J., Caradonna F.X., Savas Ö. Flow visualizations and extended thrust time histories of rotor vortex wakes in descent. Journal of the American Helicopter Society, 2005, vol. 50, no. 3, pp. 279-288. DOI: 10.4050/1.3092864
  12. Johnson W. Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics. NASA/TP-2005-213477, 2005, 76 p.
  13. Belotserkovskii S.M., Loktev B.E., Nisht M.I. Issledovanie na EVM aerodinamicheskikh i aerouprugikh kharakteristik vintov vertoleta (Computer-Assisted Research into Aerodynamic and Elastic Properties of Helicopter Rotors), Moscow, Mashinostroenie, 1992, 219 p.
  14. Leishman J.G., Bhagwat M.J., Ananthan S. Free-Vortex Wake Predictions of the Vortex Ring State for Single-Rotor and Multi-Rotor Configurations. 58th American Helicopter Society International Annual Forum (11–13 June 2002; Montreal, Quebec, Canada), pp. 956-986.
  15. Anikin V.A. Helicopter Main Rotor Aerodynamic Performance in Descent Conditions. 58th Annual Forum of the American Helicopter Society International (11-13 June 2002$ Montreal, Canada), 15 p.
  16. Bailly J.A Qualitative Analysis of Vortex Ring State Entry Using a Fully Time Marching Unsteady Wake Model. 36th European Rotorcraft Forum (7-9 September 2010; Paris, France), 18 p.
  17. Krymskii V.S., Shcheglova V.M. Nauchnyi vestnik MGTU GA, 2014, no. 200, pp. 86-90. URL: https://avia.mstuca.ru/jour/article/view/15/16
  18. Krymskii V.S., Shcheglova V.M. Nauchnyi vestnik MGTU GA, 2021, vol. 24, no. 5, pp. 60-75. DOI: 10.26467/2079-0619-2021-24-5
  19. Ignatkin Y.M., Makeev P.V., Grevtsov B.S., Shomov A.I. A nonlinear blade vortex propeller theory and its applications to estimate aerodynamic characteristics for helicopter main rotor and anti-torque rotor. Aerospace MAI Journal, 2009, vol. 16, no. 5, pp. 24-31.
  20. Ignatkin Yu.M., Makeev P.V., Shaidakov V.I., Shomov A.I. Izvestiya vysshikh uchebnykh zavedenii. Aviatsionnaya tekhnika, 2018, no. 3, pp. 73-80.
  21. Makeev P.V., Ignatkin Yu.M., Shomov A.I. Numerical investigation of full scale coaxial main rotor aerodynamics in hover and vertical descent. Chinese Journal of Aeronautics, 2021, vol. 34, no. 5, pp. 666-683. DOI: 10.1016/j.cja.2020.12.011
  22. Makeev P.V., Ignatkin Yu.M., Shomov A.I., Ivchin V.A. Comparative Study of 3-Bladed and Scissors Tail Rotors Aerodynamics in Axial Flow. International Review of Aerospace Engineering, 2022, vol. 15, no. 2, pp. 181-191. DOI: 10.15866/irease.v15i2.21284

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