Computational Analysis of a Model Coaxial Rotor Hub Wake

A model counter-rotating coaxial rotor hub in free-air was simulated using computational fluid dynamics as a comparison against experimental results. The simulation is performed using NASA's OVERFLOW 2.3d Reynolds averaged Navier-Stokes solver, and flow conditions are based on experiments performed in the 12-inch diameter water tunnel at ARL Penn State. Surface forces were examined, and harmonics in this data were computed and analyzed. The turbulent wake of the rotor hub was analyzed using frequency content as well as turbulent quantities related to the production and transport of turbulent kinetic energy. The lift spectrum showed different dominant frequencies for each counter-rotating hub, and the drag spectrum showed the expected dominant frequency for both parts of the hub. Frequency content of the velocity components in the wake showed positional biases towards the advancing side of each hub, opposing the results from past analyses of similar single rotor hubs. Reynolds stresses showed similar positional biases, and were also consistently concentrated in relatively small areas within the wake. The individual wakes of the hubs did not show signs of interaction until the far wake.