Towards Urban Air Mobility: NASA’s Quadcopter Air Taxi Concept

Overview

With many cities around the U.S. growing rapidly, their transportation systems are being pushed to the limits. Urban Air Mobility (UAM) is envisioned to be the future air transportation system over populated areas, where everything from small package-delivery drones to passenger-carrying air taxis are able to interact safely and efficiently. UAM is the new era in air travel that NASA is working on right now.

The capacity of multi-rotor vehicles to perform vertical take-off and landing (VTOL), together with their great maneuverability, make them an excellent choice for UAM aircraft. The accurate prediction of multi-rotor vehicles’ performance and acoustics is very challenging due to the unsteady and complex flows, as well as the aerodynamic interactions of the rotors. High-fidelity computational fluid dynamics (CFD) simulations play a key role in the development of next-generation air vehicles.

Project Details

In this work, we simulate NASA’s quadcopter UAM concept vehicle using high-fidelity CFD, within the scope of NASA’s Revolutionary Vertical Lift Technology (RVLT) project. One of the goals of RVLT is to develop and validate advanced high-fidelity CFD tools with improved physical realism and numerical solution accuracy that can be used in the rotorcraft design process.

The quadcopter and surrounding air are modeled using hundreds of millions of grid points with overset volume grids. The flow is solved using NASA’s OVERFLOW CFD code, a high-order accurate Navier-Stokes solver. Then, the rotorcraft trim and rotor blade motions are predicted with the comprehensive rotorcraft code, CAMRAD II. The final solution is obtained by loosely coupling OVERFLOW and CAMRAD II.

Results and Impact

The quadcopter air taxi is one of NASA’s concept vehicles, intended to focus and guide NASA research activities in support of aircraft development for the emerging UAM market. Advanced CFD tools are being developed to simulate various UAM concepts from NASA. Past work showed that side-by-side rotors increase the cruise performance compared to non-overlapped twin rotors. In this work, we study the performance for a six-passenger quadcopter vehicle. The rotor-rotor and rotor-airframe interactions were analyzed, resulting in a new design where the rear rotors are placed above the front rotors, reducing the interactions while keeping a compact configuration. The advanced CFD tools we are developing will assist in the rotorcraft design process for future multi-rotor UAM vehicles. Coupling these tools with the comprehensive CAMRAD II code provides accurate rotor trim and motion for UAM vehicles.

Why HPC Matters

The performance of the quadcopter vehicle can only be calculated accurately by solving the fluid equations on overset grids, comprising hundreds of millions of grid points. The rotation of the blades makes the problem unsteady, and the quadcopter consists of four three-bladed rotors—making the problem even more complex. In addition, the blades’ design allows for flapping (adding relative in-plane motion). Only with the most powerful supercomputers can such a complex simulation be solved in just a few days.

The simulations were carried out on NASA’s Pleiades and Electra supercomputers at the NASA Advanced Supercomputing (NAS) facility, using 1,200 to 3,000 Intel Xeon Broadwell, Ivy Bridge, and Skylake processors. In addition, NAS’s mass storage system is essential to support this work—the data stored for post-processing a single case can take up to 40 terabytes of memory.

More Information

• SC18 demo: “Towards Urban Air Mobility: The Side-By-Side Air Taxi”
• SC17 demo: “Towards Urban Air Mobility”
• NAS Featured Article: “A Hybrid Quadcopter for Longer Flights, Quieter Skies”
• “The Side-by-Sde Urban Air Taxi
• “Simulations of Ducted and Coaxial Rotors for Air Taxi Operations
• See the poster for this demonstration (PDF, 1MB). As shown in the NASA booth at SC19.