Numerical Analysis of the Influence of Rotor Wake on Hub Drag for a Coaxial Rigid Rotor

Hub system of coaxial rigid rotor has a significant contribution to the total vehicle parasite drag. Prior efforts have explored various faring designs to reduce flow separation and interference drag between each components of hub system. The aerodynamic interference physics of rotor wake on the hub fairing system components is still need to be resolved to examine its practicability. A numerical investigation was carried out to predict the influence of rotor wake on hub drag for a coaxial rigid rotor. The investigation was based on the solution of RANS equations in three dimensions using unstructured grids and main rotor modelled by an actuator disc. Results are presented for baseline configuration and optimized lower drag configuration under various forward flight velocities. The analysis shows that the presence of rotor wake has remarkable interference on hub drag, the swirl and downwash component of rotor wake have significant interference effect on each parts of hub fairing system. With the increase of wind speed, interference effects have been altered by the movement of rotor wake. The additional rotor wake remarkably increases the hub system drag in low speed range, and makes the hub system drag slightly reduction at higher speed. The drag of optimized model is still lower than base model in the interference of rotor wake, reveals that the optimized technique which is to reshape the shaft fairing and pylon is effective in the presence of rotor wake.