  This study investigates a novel phenomenon of lift generation around a sphere
by pneumatically manipulating its surface topology with an asymmetric roughness
distribution. A comprehensive series of systematic experiments were conducted
for Reynolds numbers ($Re = U_{\infty} d/\nu$, where $U_{\infty}$ is the fluid
velocity, $d$ is the sphere diameter, and $\nu$ is the fluid kinematic
viscosity) ranging from $6\times10^4$ to $1.3\times10^5$, and dimple depth
ratios ($k/d$, where $k$ is the dimple depth) from $0$ to $1\times10^{-2}$
using a smart morphable sphere with one smooth and one dimpled side. The
findings show that an asymmetrically rough sphere can generate lift forces up
to 80\% of the drag, comparable to those produced by the Magnus Effect. The
dimple depth ratio affects both the $Re$ at which lift generation begins and
the maximum lift coefficient ($C_L$) achievable. The optimal $k/d$ for maximum
lift varies with $Re$: deeper dimples are needed at low $Re$, while shallower
dimples are more effective at high $Re$. For a fixed $Re$, increasing $k/d$
monotonically increases lift until a critical $k/d$ is reached, beyond which
lift decreases. Particle Image Velocimetry (PIV) revealed that dimples delay
flow separation on the rough side while the smooth side remains unchanged,
resulting in asymmetric boundary layer separation, leading to wake deflection
and lift generation. Beyond the critical $k/d$, the flow separation location
moved upstream, increasing the size of the rear wake, reducing wake deflection,
and thus decreasing lift. Overall, this study establishes the foundation for
wake control over bluff bodies and paves the way for real-time manoeuvring
applications.
