Efficient CFD Approaches for Coaxial Rotor Simulations
Open Access
- Author:
- Cornelius, Jason
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 01, 2019
- Committee Members:
- Sven Schmitz, Thesis Advisor/Co-Advisor
Michael Kinzel, Committee Member
Amy Ruth Pritchett, Committee Member - Keywords:
- CFD
Computational Fluid Dynamics
Multicopter
Multicopters
Coaxial Rotor
Coaxial Rotors
CFD Simulation
Rotorcraft
Helicopter
STAR-CCM+
RotCFD
Mixing-Plane
Blade-Element
Time-Accurate
Blade-Resolved
Blade-Modeled
Quadcopter - Abstract:
- The advent of small-scale multicopter aircraft, including quad- and octocopter configurations, has opened the door to potential cost-effective vertical flight technology. These aircraft are intended to be used in applications such as public transportation, recreational products, commercial vehicles, military technologies, and even extraterrestrial planetary exploration. As the demand for these aircraft continues to rise, analysis capabilities for their design and performance prediction become increasingly useful. Complex problems such as rotor-rotor interactions call for high-fidelity prediction tools, but conventional approaches using these tools have immense computational demand that commonly leads to running a simulation on the order of days to weeks. In this work, two separate computational fluid dynamics approaches, one blade-resolved and one blade-modeled, are studied using the STAR-CCM+ and RotCFD programs to analyze a coaxial rotor configuration. The blade-resolved approach, which will be referred to as the mixing-plane model, involves the development of a novel modeling method for rotorcraft CFD. The mixing-plane model allows for (1) a smaller cell count due to the ability to utilize periodic boundaries which nearly halve the cell count in the context of a RANS CFD model, (2) enabling the usage of steady algorithms for the rotor solution, (3) and not demanding a highly-resolved rotor wake. The results are compared to that of a baseline time-accurate model, i.e. the current state-of-the-art. The methodology, benchmarking process, and preliminary results indicate that the new modeling approach has potential for future analyses to support engineering design. They reduce the computational cost by more than two orders-of-magnitude over the conventional solution method while still providing a CFD resolved solution that is within 2% of rotor thrust, power, and figure of merit in hover. The physics behind the implementation of the mixing-plane method breaks down in edge-wise flight where the model does not compare as well. Since a highly efficient approach for a coaxial rotor in edge-wise flight was desired, a blade-modeled approach was also explored. The blade-element method was used for this second modeling approach. It represents the rotors with a rotating line of momentum sources that imparts momentum into the flow-field based on the local CFD resolved inflow and the appropriate airfoil performance table. This method is even faster than the first approach discussed, since it is blade-modeled, and still yields rotor performance calculations that agree with time-accurate, i.e. state-of-the-art, simulations. A model incorporating this blade-element method was developed and then used to analyze a coaxial rotor configuration. The coaxial rotor is analyzed in hover, edge-wise flight, and axial climb. The blade-element model was found to provide mid-fidelity results in a fraction of the time as the conventional baseline approach. The model also opens the door for the average user, with only a graphics-card equipped computer, to rotorcraft simulations with CFD resolved inflows and wakes.