Rotor Airloads Prediction Using Loose Aerodynamic/Structural Coupling

Abstract

A computational fluid dynamics (CFD) code and rotorcraft computational structural dynamics (CSD) code are coupled to calculate helicopter rotor airloads across a range of flight conditions. An iterative loose (weak) coupling methodology is used to couple the CFD and CSD codes on a per revolution, periodic basis. The CFD code uses a high fidelity, Navier-Stokes, overset grid methodology with first principles-based wake capturing. Modifications are made to the CFD code for the aeroelastic analysis. For a UH-60A Blackhawk helicopter, three challenging level flight conditions are computed: 1) high speed, μ = 0.37, with advancing blade negative lift, 2) low speed, μ = 0.15, with blade-vortex interaction, and 3) high thrust with dynamic stall, μ = 0.24. Results are compared with UH-60A Airloads Program flight test data. For all cases the loose coupling methodology is shown to be stable, convergent, and robust with full coupling of normal force, pitching moment, and chord force. In comparison with flight test data, normal force and pitching moment phase and magnitude are in good agreement. The shapes of the airloads curves are well captured. Overall, the results are a noteworthy improvement over lifting line aerodynamics used in rotorcraft comprehensive codes. ρ = air density σ = rotor solidity ψ = rotor azimuth angle, 0 aft, deg

Investigation of Rotor Performance and Loads of a UH-60A Individual Blade Control System

“…This algorithm, called the delta coupling technique, was pioneered by Tung et al [27] and implemented in OVERFLOW 2 by Nygaard et al [28]. Significantly improved airloads prediction capability was demonstrated for the UH-60A rotor (without IBC) using a loosely coupled CAMRAD II/OVERFLOW-D in steady level flight conditions by Potsdam et al [11].…”

“…However, in-depth correlation studies have not been performed. In recent years, there has been significant progress in aeromechanics prediction capability using coupled computational fluid dynamics (CFD) / rotorcraft computational structural dynamics (CSD) analyses [11,12]. The CFD methods, which use a high fidelity, Navier-Stokes, overset grid methodology with first-principles-based wake capturing, overcame the limitations of the conventional lifting line aerodynamics used in rotorcraft comprehensive codes.…”

Computational Investigation of Gurney Flap Effects on Rotors in Forward Flight

“…The periodic blade deformations obtained from this run are transferred to the CFD solver using a fluid-structure interface. The CFD solver deforms the blade mesh and computes the periodic airloads, which is subsequently transferred to the structural dynamics system using the delta airloads method, explained in detail in [5][6][7][8]. The delta airloads are first recast in a shaft-fixed frame as three components of forces and moments at each radial location before its use in the CSD analysis.…”

Computational-Fluid-Dynamics- and Computational-Structural-Dynamics-Based Time-Accurate Aeroelasticity of Helicopter Rotor Blades

“…The arrow related to complexity indicates the ease with which complex geometries can be modeled using lower-fidelity models. As reported in [13], the current validated state of the art is the quasi-steady or loosely coupled approach based on hybrid CFD and CC methods [14]. Computational structural dynamics used in the CC method are limited to simple beam models, mostly in harmonic motions.…”