Towards Urban Air Mobility

Overview

Small, electric, multirotor unmanned aerial vehicles (UAVs) have revolutionized the civil and military drone markets. Multirotor configurations provide vertical flight ability and stable control within a compact design. Applications of UAVs are numerous and growing, including surveillance missions, product delivery, photography, and disaster relief. Recently, a new concept for human transportation has emerged, known as Urban Air Mobility (UAM) vehicles. UAMs will be medium-sized rotary wing vehicles with the vertical flight capability of UAVs, designed to transport people in urban areas. UAMs will have full electric propulsion that will eliminate emissions and fuel burn.

Project Details

From small UAVs to medium-sized vehicles for urban air mobility, understanding the complex flow structures generated by the rotors, and their interactions with each other and the vehicle’s fuselage, are crucial for designing quieter, safer, and more efficient vehicles. We run high-fidelity computational fluid dynamics (CFD) simulations on supercomputers at the NASA Advanced Supercomputing (NAS) facility at Ames Research Center to understand the complex physics of multirotor interactions on UAVs.

Two different vehicles are studied here: a classic UAV quadcopter configuration—a NASA-modified DJI Phantom 3 quadcopter design; and an innovative tilt-wing, joined-wing design concept for UAM, the Elytron 4S UAV version of the UAM vehicle. The surfaces of the two rotorcraft, and surrounding air, are modeled using hundreds of millions of grid points with overlapping volume grids. The airflow is then resolved on the Pleiades supercomputer, using the agency’s OVERFLOW high-order Navier-Stokes CFD solver.

Results and Impact

Computational results of the different rotorcraft configurations reveal the structures of the complex flows generated. For the quadcopter configuration, rotor-rotor and rotor-fuselage interactions reduce the thrust and produce high-frequency pressure fluctuations. Other findings show that the presence of a camera and landing gear increases the drag on the vehicle in forward flight, but may help reduce the interactions’ effect on the overall thrust in hover.

For the Elytron configuration, the tilt wing just below the rotors interacts with the wake and results in a fully turbulent flow underneath the body, further reducing the thrust of the vehicle. A fan in the nose is attached for pitch control. In helicopter mode, it spins at maximum velocity, which is almost four times faster than the propellers, providing 20% of the main thrust. We found that the nose fan is the main source of noise below the rotorcraft.

These results help us analyze and understand the complex flow structures of both classic and innovative multirotor vehicles. Using this information, NASA can design UAM vehicles that will someday populate the skies over our cities.

Why HPC Matters

To obtain accurate CFD simulations, hundreds of millions of grid points were necessary in order to correctly capture the complex airflow structures generated by the rotors. The simulations were carried out using thousands of Broadwell processors on the both the Pleiades and Electra supercomputers at the NAS facility.

In addition, NAS’s customized visualizations of the results from our high-fidelity simulations are critically important for understanding the complex, unsteady, turbulent flow interactions of the multirotor UAMs. The facility’s high-memory data analysis nodes were essential for post-processing the unsteady flow simulations.

More Information

• Watch Air Swirl Around a Quadcopter Drone's Rotors
• See additional images/videos related to this demo in our media gallery.
• See the poster for this demonstration (PDF, 4.0MB), as shown in the NASA booth at SC17.