Coupling of a multibody simulation tool for the analysis of rotary systems with a panel based flow solver and a navier-stokes flow solver

Soğancı, Semih
In rotorcraft design, aeroelastic effects on the main rotor blades play a critical role in the accurate estimation of the external loading acting on the structure. The external loading is mainly due to the aerodynamic loads and the inertial loads on the main rotor blades. High aspect ratio blades largely deform in flapping direction on top of rigid body flapping, and due to the rigid and elastic flapping motion, the airloads acting on the blades change continuously. Hence, the rotor blade loads analysis should be interdisciplinary relying on the nonlinear structural dynam ics, the aerodynamics and the control. A flexible multibody dynamics solver, DYMORE, is used as a comprehensive analysis tool for rotor simulations. Aerodynamic loads are internally calculated from two dimensional aerodynamic tables which give the aerodynamic coefficients based on the angle of attack and the Mach number. In the aerodynamic shape optimization of blade profiles, at each iteration in the shape optimization, sections are perturbed and for the perturbed sections aerodynamic loads can not be calculated using the look-up tables since these tables are for a certain airfoil shape. Therefore, there is a need for an aerodynamic solver to provide the solution for the perturbed sections. In this study, the internal aerodynamic module of DYMORE is replaced first with a panel based flow solver, XFOIL, and then a Reynolds Averaged Navier-Stokes (RANS) solver, SU2. At each section, the aerodynamic load coefficients obtained from XFOIL and SU2 are used instead of interpolated table coefficients. XFOIL and SU2 source codes are embedded into DYMORE and compiled together using the C-FORTRAN interoperability functions and the external data structures with assigned pointers. The simulations are carried out for an isolated rotor in hover. UH-60 main rotor architecture is modeled and NACA 0012 profile is used for blade sections. Validation studies are carried out at Mach numbers of 0.4 and 0.7 for the angle of attack range of 0 to 15 degrees. The lift and drag coefficients obtained from XFOIL and SU2 are in good agreement with the table values. Hub airloads and blade angles obtained from the coupled analyses are also in close correlation with the internal aerodynamic results.