An Efficient Wake Modeling Method for Rotorcraft Aeroacoustics
Open Access
- Author:
- Rau, Robert
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 23, 2024
- Committee Members:
- Amy Pritchett, Program Head/Chair
Robert Kunz, Outside Unit & Field Member
Sven Schmitz, Major Field Member
Kenneth Brentner, Major Field Member
Eric Greenwood, Chair & Dissertation Advisor - Keywords:
- aeroacoustics
aerodynamics
rotorcraft
multirotor
wake modeling
wake model - Abstract:
- This dissertation develops a new wake modeling method for the prediction of high temporal resolution blade airloads and acoustics of rotorcraft. This new method is derived from the work on inflow driven wake advection pioneered by Beddoes in 1985. By replacing the prescribed inflow model developed by Beddoes with an physics based model and integrating numerically, the wakes of one or more rotors can be simulated. This approach scales linearly with the number of wake elements and is stable across a breadth of timestep sizes. An implementation of this method, dubbed OpenCOPTER, leverages a potential flow based inflow model and uses the superposition property to create a combined flow field for multiple rotors. This new model is validated by comparing it to other wake models of comparable fidelity as well as comparing to data from conventional helicopters, both with only a main rotor with higher-harmonic loading as well as a coupled main rotor/tail rotor system. The validation results are also compared to other models to provide context for the accuracy of OpenCOPTER results. Finally, the model is applied to study a broad design and operational space of a notional tandem rotor system to study the change in acoustic emissions due to configuration and flight condition. The new model is shown to be capable of capturing the wake distortions of co-planar rotors at a similar degree of fidelity as a contemporary free-wake code. Further, it was shown to predict the performance and acoustics of a helicopter main rotor undergoing higher-harmonic loading. The wake interactions between a main rotor and tail rotor were also able to be simulated with the introduction a hybrid mode, which produced results on the same order of accuracy as a free-wake code. Tail rotor physics were identified that neither code predicts well causing discrepancies in the directivity of the tail rotor acoustics. The new model was also shown to be efficient enough to simulate a large range of rotor configurations as well as flight conditions of a two rotor system demonstrating, its potential as a design tool.