Prediction of Coaxial Rotor Hub Flow Using Mercury Framework

Rotor hubs are predominantly responsible for the parasitic drag encountered by high-speed rotorcraft. To gain a deeper understanding of the fluid dynamics around rotor hubs, simulations of counter-rotating coaxial rotor-hub flows were conducted, which was subsequently followed by a corroborative experiment at Pennsylvania State University. The simulation process employed a computational fluid dynamics framework termed “Mercury,” which utilizes an unstructured⁄Cartesian multimesh paradigm. This process incorporated Spalart–Allmaras delayed detached eddy simulation turbulence modeling for an accurate representation of the flow. The investigation into the coaxial hub flow physics was conducted at two different advance ratios: 0.25 and 0.6, constructed by building up the hub components. The interaction between the hub and fairing components led to an increase in the average hub drag and caused unsteady harmonics in the hub and fairing drags. Furthermore, it was noted that different advance ratios affected the drag and wake structures. The complete hub model was then simulated in a water tunnel with an advance ratio of 0.25. Predictions of mean and unsteady drag, as well as mean wake velocity fields, were compared with the experimental results. Overall, the mean wake velocity field from the simulation qualitatively aligned with the experimental results, especially in the near-wake region. Additionally, the buildup model analysis significantly aided in understanding the intricate wake structures surrounding the hub.