Large-eddy simulation of flow over a rotating cylinder: the lift crisis at ReD=6×10^4
KAUST DepartmentFluid and Plasma Simulation Group (FPS)
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Online Publication Date2018-09-19
Print Publication Date2018-11-25
Permanent link to this recordhttp://hdl.handle.net/10754/630544
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AbstractWe present wall-resolved large-eddy simulation (LES) of flow with free-stream velocity U∞ over a cylinder of diameter D rotating at constant angular velocity Ω , with the focus on the lift crisis, which takes place at relatively high Reynolds number ReD=U∞D/ν , where ν is the kinematic viscosity of the fluid. Two sets of LES are performed within the ( ReD , α )-plane with α=ΩD/(2U∞) the dimensionless cylinder rotation speed. One set, at ReD=5000 , is used as a reference flow and does not exhibit a lift crisis. Our main LES varies α in 0⩽α⩽2.0 at fixed ReD=6×104 . For α in the range α=0.48−0.6 we find a lift crisis. This range is in agreement with experiment although the LES shows a deeper local minimum in the lift coefficient than the measured value. Diagnostics that include instantaneous surface portraits of the surface skin-friction vector field Cf , spanwise-averaged flow-streamline plots, and a statistical analysis of local, near-surface flow reversal show that, on the leeward-bottom cylinder surface, the flow experiences large-scale reorganization as α increases through the lift crisis. At α=0.48 the primary-flow features comprise a shear layer separating from that side of the cylinder that moves with the free stream and a pattern of oscillatory but largely attached flow zones surrounded by scattered patches of local flow separation/reattachment on the lee and underside of the cylinder surface. Large-scale, unsteady vortex shedding is observed. At α=0.6 the flow has transitioned to a more ordered state where the small-scale separation/reattachment cells concentrate into a relatively narrow zone with largely attached flow elsewhere. This induces a low-pressure region which produces a sudden decrease in lift and hence the lift crisis. Through this process, the boundary layer does not show classical turbulence behaviour. As α is further increased at constant ReD , the localized separation zone dissipates with corresponding attached flow on most of the cylinder surface. The lift coefficient then resumes its increasing trend. A logarithmic region is found within the boundary layer at α=1.0 .
CitationCheng W, Pullin DI, Samtaney R (2018) Large-eddy simulation of flow over a rotating cylinder: the lift crisis at ReD=6×10^4. Journal of Fluid Mechanics 855: 371–407. Available: http://dx.doi.org/10.1017/jfm.2018.644.
SponsorsThis work was partially supported by the KAUST baseline research funds of R.S. The Cray XC40, Shaheen, at KAUST was utilized for all the reported LES.
PublisherCambridge University Press (CUP)
JournalJournal of Fluid Mechanics