Improving the Flight Efficiency of Helicopters
NASA's Revolutionary Vertical Lift Technology (RVLT) Project is working toward increasing a helicopter's forward-flight speed and performance in an environmentally responsible manner, for example, by reducing noise levels and fuel consumption through better designs and hybrid propulsion systems. However, new high-performance designs can lead to the introduction of blade vortex interaction (BVI), where a helicopter’s blade-tip vortices strike and interact with the other spinning rotor blades, and dynamic stall, which causes a sudden reduction in thrust that is dangerous and limits a helicopter's lifting capability and flight speed. Using NASA's Pleiades supercomputer, researchers are running high-fidelity computational fluid dynamics (CFD) simulations combined with adaptive mesh refinement methods to improve BVI and dynamic stall prediction accuracy, as well as provide greater insight into the fundamental causes of these events.
Imagine reducing airport congestion and noise by conveniently taking short-haul flights closer to your home, or commuting to work in an autonomous rotorcraft. RVLT research, boosted by the computational power of NASA's high-performance computing resources, can make these dreams a reality.
Neal M. Chaderjian, Senior Research Scientist, NASA Ames Research Center
Quick Facts
- Because it was previously thought that a rotor blade pitching up to a high angle of attack was the sole cause of dynamic stall, experiments and CFD validation studies have for decades focused on the simpler two-dimensional problem of a pitching airfoil. The findings of this study indicate that BVI increases a rotor blade’s local angle of attack, and may prematurely trigger dynamic stall. Therefore, three-dimensional models provide greater insight into the cause of dynamic stall and when it may occur.
- The study found that predicted aerodynamic loads did not depend on refining the rotor wake beyond what is normally done for engineering calculations. This surprising result is good news for design engineers who must compute many CFD simulations on coarser grids to reduce analysis time and cost.
- These flow simulations were conducted on the Pleiades supercomputer using 5,628 Intel Xeon "Broadwell" cores for 1 – 2 weeks using the NASA-developed OVERFLOW CFD flow solver. Grid sizes varied from 78 million to 1.8 billion grid points, and the solutions required 6 – 36 hours of wall-clock time per rotor revolution.
Key Image
Image Caption
CFD simulation of dynamic stall for a Blackhawk helicopter rotor in forward flight. In this oblique view, the vortex wake is colored by vorticity magnitude (red is high, blue is low). Neal M. Chaderjian, NASA/AmesDownload High-Res Image
Contacts
Neal M. Chaderjian, NASA Ames Research Centerneal.chaderjian@nasa.gov