Abstract:
The aviation industry currently faces unique multi-domain challenges with a global
push to reduce environmental impacts and increase efficiency. Blended Wing Body
(BWB), a bio-inspired design, is the next innovation with the potential to fulfill these
goals simultaneously. However, BWB aircraft may exhibit wing rock phenomenon with
a different triggering mechanism. The current research therefore aims to investigate the
wing rock characteristics for a BWB UCAV and further evaluate the efficacy of Active
Flow Control (AFC) techniques for its suppression. A validated computational
framework based on rigid body single DOF dynamic mesh motion, as well as forced
roll sliding mesh motion employing unsteady Reynolds Averaged Navier Stokes
(RANS) equations has been developed. Free-to-roll simulations predicted the onset
angle of attack and various wing rock characteristics which were dependent on
Reynolds number and inertial properties. Jet blowing was effective in suppression of
wing rock amplitude as well as mean roll angles within a certain range of angle of attack
after which its momentum coefficient has to be increased. However, after a certain
threshold of blowing coefficient and incidence angle, steady jet maintains only limited
effectiveness. Liutex-based flow analysis revealed complex tip-separated flow
interactions and coalescence of multiple vortex systems as a primary cause of wing rock
initiation which were replaced by symmetric coherent flow features with the application
of AFC. Dynamic stability analysis highlighted that the configuration loses roll
damping when it is given a certain initial roll suggesting that the model can undergo
limit cycle oscillations only at a specific roll angle. Finally, Large Eddy Simulations
(LES) helped in better understanding of flow features. The developed framework can
be extended to multi DOF analyses, flow adaptive blowing or to investigate other
dynamic instabilities e.g. tumbling.
