Comparative Study of Coaxial Main Rotor Aerodynamics in the Hover with the Usage of Two Methods of Computational Fluid Dynamics

Abstract

The paper is focused on numerical modeling of the aerodynamic characteristics of a full-scale coaxial main rotor in hover. The simulation was performed using two approaches of computational fluid dynamics (CFD): the original free wake model (FWM) developed by the authors and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations method based on the Ansys Fluent software. The structure of the rotor vortex wake, flow images, vorticity and induced velocity fields, total and distributed aerodynamic characteristics of the rotor, including the rotor performance and figure of merit diagrams, have been analyzed. A comparison between FWM/URANS based calculations and calculated/experimental data by other authors has been performed. A satisfactory match of these data confirms reliability of used methods when modeling the aerodynamic characteristics of coaxial rotors. The FMW demonstrates a significant advantage in speed and resources intensity when calculating the total aerodynamic characteristics of a coaxial rotor. The URANS method makes it possible to model with significant accuracy the effects associated with the blade vortex interactions and pressure distribution over the blade surface. Finally, conclusions about most effectiveness of joint application of considered methods in solving complex problems of coaxial rotor aerodynamics has been made.

Comparative Study of Coaxial Main Rotor Aerodynamics at Forward Flight Based on Free Wake Model and Unsteady ReynoldsAveraged Navier–Stokes Method

“…The URANS-based rotor wake visualizations are performed using isosurfaces for a fixed vorticity ω = 15 s -1 . Such method of a wake visualization gives good results (Ignatkin et al 2020;Kim and Brown 2010;Konstantinov et al 2021;Linton et al 2018;Passe et al 2015) in the case of sufficient resolution of the calculated mesh (in the presented work, mesh has contained about 30 million elements).…”

“…14c) (URANS). Similar pulsations of thrust and torque are characteristics of the coaxial rotors (Kim and Brown 2010;Konstantinov et al 2021;Kritsky et al 2020). It should be noted that for c T = f(n) diagrams, in general, there is a better match between the FWM and URANS calculations than for c Q = f(n) diagrams.…”

“…The paper considers an isolated coaxial main rotor of the Ka-226 helicopter (Bourtsev et al 2007;Konstantinov et al 2021;Vassiliyev et al 2007) Modeling of the coaxial rotor aerodynamics has been performed at horizontal flight modes with speeds V = 30, 40, 50, 60 m•s -1 (μ ≈ 0.15; 0.2; 0.25; 0.3). These velocities correspond to the Mach numbers at the tip of advancing blade M AT = 0.67; 0.7; 0.73 and 0.76.…”

“…The described model uses an approach that allows determining the vorticity field from the vortex segment and the induced velocity from this vorticity field on the basis of an exact solution of the vortex source diffusion. The model with its basic equations is described in detail in previous works (Ignatkin et al 2009;Konstantinov et al 2021).…”

“…Previously, these approaches had been used and validated by the authors in comparative numerical studies of helicopter rotor aerodynamics at the different flight modes. The cases having been under consideration: conventional rigid model-scale rotor at hover and forward flight in the range of μ = 0.1-0.45 (Konstantinov et al 2020); full-scale coaxial main rotor at hover (Ignatkin et al 2021). Thus, this present work is a continuation and development of the mentioned researches.…”