Journal
COMPUTERS & FLUIDS
Volume 99, Issue -, Pages 1-17Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.compfluid.2014.03.011
Keywords
Nonslender delta wing; Leading-edge vortex flap; Vortex breakdown control; Modified turbulence model
Funding
- National Natural Science Foundation of China [10972183, 11002116]
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The aim of this paper is to numerically and experimentally evaluate the control efficiency of a series of leading-edge vortex flaps for a nonslender delta wing at a moderate Reynolds number. Both downward and upward deflected leading-edge vortex flaps are examined by experimental measurements and numerical simulations. It has been found in the wind tunnel experiments that the upward deflected vortex flap increases the vortex lift at low angles of attack due to the enhancement of the vortex strength while at high angles of attack the aerodynamic performances are significantly deteriorated due to a premature flow stall. Meanwhile the flap deflected downward has an excellent performance at high angles of attack, especially with a flap deflection angle of -70 degrees. Consequently, numerical simulations of this optimal configuration are conducted to explore the mechanism of aerodynamic performance improvement and the vortical structures. A recently modified turbulence model has been demonstrated to be suitable to capture the complex vortex structures in this type of flow. In addition, the numerical results are in good agreement with those of the PIV data. Obviously the lift enhancement is due to the fact that the stall phenomenon of the baseline wing is significantly delayed by the vortex flap. This has been proved by the comparisons of vortical topologies, mean pressure coefficients and the limiting streamlines between the experimental measurements and the numerical simulations. Besides, the drag coefficient is reduced by an additional vortex system generated at the leeside of the flap. Furthermore, our simulations are capable of discerning the classical dominant frequencies of helical mode instability, Kelvin-Helmholtz instability and vortex wandering. Correspondingly some unsteady phenomena encountered in the two cases are investigated by the distributions of high levels of turbulent kinetic energy. (C) 2014 Elsevier Ltd. All rights reserved.
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