This study investigates the wake dynamics and force responses of transversely rotating spheres in isolated and tandem configurations at moderate Reynolds numbers ($\text{Re}=100$, 300, 1000). Using direct numerical simulations of transitional and weakly turbulent flow, we explore how rotation rate ($\alpha =0–5$) and interbody spacing ($L_x=2D, 5D$; $D$ is sphere diameter) influence wake topology, vortex shedding, and fluid forces. At lower $\text{Re}$, rotation suppresses unsteadiness, inducing double-threaded vortical structures, whereas at higher $\text{Re}$, centrifugal effects destabilize shear layers, generating multiscale vortices and weakly turbulent wakes. In tandem configurations, wake-body interactions promote instabilities even when rotation stabilizes the isolated sphere wake. The force coefficients exhibit a nonmonotonic dependence on $\alpha$ due to competing effects of Magnus-induced pressure asymmetry, shear layer separation, and wake unsteadiness.

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• Flow-structure interactions
• Vortex dynamics
• Vortex interactions
• Vortex shedding