We present wall-resolved large-eddy simulation (LES) of flow with free-stream velocity
$\boldsymbol{U}_{\infty }$
over a cylinder of diameter
$D$
rotating at constant angular velocity
$\unicode[STIX]{x1D6FA}$
, with the focus on the lift crisis, which takes place at relatively high Reynolds number
$Re_{D}=U_{\infty }D/\unicode[STIX]{x1D708}$
, where
$\unicode[STIX]{x1D708}$
is the kinematic viscosity of the fluid. Two sets of LES are performed within the (
$Re_{D}$
,
$\unicode[STIX]{x1D6FC}$
)-plane with
$\unicode[STIX]{x1D6FC}=\unicode[STIX]{x1D6FA}D/(2U_{\infty })$
the dimensionless cylinder rotation speed. One set, at
$Re_{D}=5000$
, is used as a reference flow and does not exhibit a lift crisis. Our main LES varies
$\unicode[STIX]{x1D6FC}$
in
$0\leqslant \unicode[STIX]{x1D6FC}\leqslant 2.0$
at fixed
$Re_{D}=6\times 10^{4}$
. For
$\unicode[STIX]{x1D6FC}$
in the range
$\unicode[STIX]{x1D6FC}=0.48{-}0.6$
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
$\boldsymbol{C}_{\boldsymbol{f}}$
, 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
$\unicode[STIX]{x1D6FC}$
increases through the lift crisis. At
$\unicode[STIX]{x1D6FC}=0.48$
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
$\unicode[STIX]{x1D6FC}=0.6$
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
$\unicode[STIX]{x1D6FC}$
is further increased at constant
$Re_{D}$
, 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
$\unicode[STIX]{x1D6FC}=1.0$
.
ASYMMETRY AND SKEWNESS IN THE BOTTOM BOUNDARY LAYER : SMALL SCALE EXPERIMENTS AND NUMERICAL MODEL
