To investigate the near-wall rotating cylindrical wake and hydrodynamic characteristics, flow around cylinder at typical gap ratios is investigated.

A numerical simulation of flow around a near-wall rotating cylinder with different gap ratios (G/D = 0.2, 0.8, 1.4) and rotation rates at Reynolds number$Re = 200$ was carried out to compare the cylindrical wake and hydrodynamic characteristics at different gap ratios and rotation rates.

The results show that: For $G/D = 0.2$, the cylindrical vortex shedding is significantly suppressed and the lift and drag force on the cylindrical surface remain steady. For $G/D = 0.8$ and $G/D = 1.4$, at low rotation rates, the "wake vortex" is shed and is similar to the 2S pattern, with sinusoidal periodic fluctuations in the lift and drag coefficients and small amplitude; at higher positive rotation rates, the cylindrical wake pattern is the stable D pattern with no vortex shedding (changing from D⁺ to D^- pattern as the rotation rate increases), the "wake vortex layer" is separated from the "wall vortex layer", the "wall vortex" is shed multi-periodically, the lift and drag coefficients are fluctuating multi-periodically and the amplitude is increasing significantly; at higher reverse rotation rates, the cylindrical surface is wrapped by a positive boundary layer, with no vortex shedding and no fluctuations in lift and drag.

The results can provide a reference for the development of high efficient flow control technology.