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ABSTRACT: The crossflow instability of a three-dimensional boundary layer is a main factor affecting the transition around the swept-wing.
The three-dimensional boundary layer flow affected by the saturated crossflow vortex is very sensitive to the high frequency
disturbances, which foreshadows that the swept wing flow transition will happen. The primary instability of the compressible
flow over a swept wing is investigated with nonlinear parabolized stability equations (NPSE). The Floquet theory is then applied
to the analysis of the influence of localized steady suction on the secondary instability of crossflow vortex. The results
show that suction can significantly suppress the growth of the crossflow mode as well as the secondary instability modes.
Keywordsboundary layer suction–crossflow instability–secondary instability
Science China: Physics, Mechanics and Astronomy 04/2012; 54(11):2040-2052. · 0.78 Impact Factor
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ABSTRACT: The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition
over a swept-wing. In this report, the primary instability of the incompressible flow over a swept wing is investigated by
solving nonlinear parabolized stability equations (NPSE). The Floquet theory is applied to study the dependence of the secondary
and high-frequency instabilities on curvature, Reynolds number and angle of swept (AOS). The computational results show that
the curvature in the present case has no significant effect on the secondary instabilities. It is generally believed that
the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow vortex. But, at a certain
state, when the Reynolds number is 3.2 million, we find that the secondary instability growth rate becomes smaller even when
the magnitude of the nonlinear mode of the crossflow vortex is larger. The effect of the angle of swept at 35, 45 and 55 degrees,
respectively, is also studied in the framework of the secondary linear stability theory. Larger angles of swept tend to decrease
the spanwise spacing of the crossflow vortices, which correspondingly helps the stimulation of ‘z’ mode.
Keywordscrossflow instability–secondary instability–curvature–angle of swept
Science China: Physics, Mechanics and Astronomy 04/2012; 54(4):724-736. · 0.78 Impact Factor
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ABSTRACT: Flows around vortex generators (VGs), which serve as one of the important flow control methods, are investigated by solving
Reynolds-averaged Navier-Stokes (RANS) equations. The influences on the main flow of VGs are intended to explore. Firstly,
the flow around a single VG on a flat plane is computed to validate the schemes and to acquire basic knowledge of this kind
of flow. Secondly, transonic flow past a standard model, named by ONERA-M6 wing, is predicted to investigate the flow features
of shockwave/boundary-layer interactions (SWBLI). Thirdly, the effects of a row of VGs mounted about 25% local chord on a
supercritical wing are analyzed in transonic condition with strong SWBLI. Lastly, VGs are mounted more upwind (about 3.5%
local chord) to explore the effects at low speed and high incidence condition. The numerical results show that seven VGs can
effectively suppress the separations behind the strong SWBLI and decrease spanwise flow and wing-tip vortex in transonic condition.
VGs also can decrease the large scope of separation over the wing at low speed with high angle of attack.
Keywordssupercritical wing-vortex generator (VG)-shockwave/boundary-layer interactions (SWBLI)
Science China Technological Sciences 04/2012; 53(8):2038-2048. · 0.75 Impact Factor
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ABSTRACT: Unsteady supersonic base flows around three afterbodies, cylindrical (Cy), boattailed (BT) and three-step (MS), are investigated
in this paper. Reynolds-averaged Navier–Stokes (RANS) and two RANS/LES (large-eddy simulation) hybrid methods, detached eddy
simulation (DES) and delayed-DES (DDES), are used to predict the base flow characteristics around the baseline Cy afterbody.
All the RANS and hybrid methods are based on the two-equation SST (shear-stress transport) model with compressible corrections
(CC). According to the comparison of measurements, both DES and DDES can produce more satisfactory results than RANS. RANS
can only present the “stable” flow patterns, while the hybrid methods can demonstrate unsteady flow structures. DDES and DES
results are little different from one another although the latter exhibits better agreement with the experiment. DES is taken
to investigate the 5° BT andthree-step afterbodies. The mean flow data and the instantaneous turbulent coherent structures
are compared against available measurements.
KeywordsCylindrical-Boattailed and three-step afterbodies-DES and DDES-Unsteady flow
Acta Mechanica Sinica 04/2012; 25(4):471-479. · 0.86 Impact Factor
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SCIENCE CHINA, Physics, Mechanics & Astronomy. 01/2012; 55:260-271.
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ABSTRACT: This paper presents hybrid Reynolds-averaged Navier–Stokes (RANS) and large-eddy-simulation (LES) methods for the separated
flows at high angles of attack around a 6:1 prolate spheroid. The RANS/LES hybrid methods studied in this work include the
detached eddy simulation (DES) based on Spalart–Allmaras (S–A), Menter’s k–ω shear-stress-transport (SST) and k–ω with weakly nonlinear eddy viscosity formulation (Wilcox–Durbin+, WD+) models and the zonal-RANS/LES methods based on the
SST and WD+ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation
of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode
for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid
methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme
with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower–upper symmetric-Gauss–Seidel
with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried
out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting
for the effect on grids and fundamental turbulence models, is obtained for the separation flows.
Acta Mechanica Sinica 07/2007; 23(4):369-382. · 0.86 Impact Factor
