Rotors Aerodynamic Simulation via Coupled FEA (MBD)/CFD Method: Aeroelastic Behavior Assessment
FEA & CFD Based Simulation Design Analysis Virtual prototyping MultiObjective Optimization
The prediction of the flow around rotors by means of CFD methods is one of the most challenging problems in aerodynamics. This is due to unsteadiness of the flow and the large number of flow phenomena which must be accurately resolved, e.g. the transonic flow regions on the advancing rotor blade, dynamic stall and reverse flow areas on the retreating blade, tip vortices of the main and tail rotors and their interaction with other rotor blades and the fuselage.
The blade vortex interactions (BVI) generate high load peaks and represent one of the main noise sources of a helicopter. In contrast to the rotors the flow around the fuselage is basically incompressible and many helicopters have a blunt body with large flow separations behind the fuselage. Depending on the flight conditions there may be strong interactions between main and tail rotors, rotor head, fuselage and the empennage, e.g. the tail shake phenomenon which is mainly caused by separations behind the rotor head.
In order to resolve accurately the flow phenomena described above, MSC Cradle, Fluent or Star-ccm+ is used with strong coupling procedure using the multibody simulation code such as MSC Adams, Simulia SIMPACK or FEA software such as Nastran and Abaqus.
During one rotor revolution the unsteady airloads and centrifugal forces cause blade flapping and lead/lag motions as well as large aeroelastic blade deformations. A rotor trim procedure and a method to calculate the elastic deformations (FEM and MBD) are therefore needed to get the correct blade shape and to adjust the rotor controls for the desired flight state.
- Blades and flybar roll e pitch angle variation for collective pitch in static conditions
- Blades and flybar roll e pitch angle variation for cyclic pitch in static conditions
- Destabilizing torque on the swashplate
- Destabilizing torque on the Blade carriers
- Change in cyclic input tilt (stepped function)
- Identify the natural frequencies of the system in the linearized configuration of the rotating frame.
- Minimum peak acceleration on blades for destabilizing torque on blades
- Minimum time to equilibrium for destabilizing torque on blades
- Simulation in hovering flight without the presence of lift forces and the blades modeled with flexible bodies, using as an input only the cyclic pitch.
- Simulation in hovering flight with the presence of lift forces and the blades modeled with flexible bodies, using as an input only the cyclic pitch. This simulation has been made to assess the effect of the lift force on the blades as a source of destabilization.
- Complete simulation with as input cyclic and collective pitch.