Aeroacoustics of a High-Fidelity CFD Calculation of a Counter-Rotating Open Rotor in Take-Off Conditions

摘要

A very high-fidelity CFD calculation has been carried out for a 9x7 counter-rotating open rotor setup at take-off conditions. The total setup consisted of roughly 170 million grid cells and was used for a grid study as well as a subsequent acoustic evaluation. The analysis contained farfleld aeroacoustics obtained with the acoustic analogy of Ffowcs Williams and Hawkings as well as nearfield acoustics extracted directly from the flow field data. The grid study showed a low grid dependency for integrated aerodynamic values. The acoustic evaluation in the farfield showed that the main noise characteristics can be resolved sufficiently with all three grid resolutions. Significant errors only occur in the low intensity high frequency range. A comparison of acoustic evaluation in the nearfield with the Ffowcs Williams and Hawkings approach and direct pressure output showed no benefit of the latter justifying the higher computational costs caused by the required grid resolution for the transport of the pressure disturbances. For both approaches the noise characteristics were similar with small discrepancies in the wake of the CROR and at higher frequencies.