HYDRODYNAMICS AND FLOW STRUCTURES OF A UNIFORMLY ROTATING CIRCULAR CYLINDER

Flow past a uniformly rotating circular cylinder in laminar regime is modeled by the lattice Boltzmann method (LBM), so as to obtain variations of the wake mode with the rotational speed α between 0 and 10. The dynamic mode decomposition (DMD) is then adopted to establish the reduced order model and to figure out the flow stability characteristics. The effect of rotary control on the hydrodynamic force exerted on the cylinder as well as the vorticity field are highlighted. According to the growth rate computed by the DMD, detailed trend of the impact of control parameters on the flow stability is presented. Results show that as the rotational speed increases, five modes can be observed: the Kármán vortex street mode, the shear layer mode, the reverse shear layer mode, the single-side vortex mode, and the attached vortex mode. As the rotational speed increases, the mean drag decreases first, but encounters a dramatic increase when the single-side vortex mode occurs. Meanwhile, the mean lift and mean moment coefficient retain the increasing trend. Within the two rotational speeds intervals where vortex shedding occurs, the hydrodynamic force fluctuates with higher amplitudes than those accompanied with the secondary instability. Results of the DMD show that flow structures in the downstream of the cylinder is mainly affected by the rotary motion of the cylinder wall that leads to new modes. As evidenced by the DMD growth rate, the rotary control also significantly affects the flow stability: in the underdevelopment stage, the effect of rotation on flow stability is not significant. After the full development, the flow field instability modes at each rotational speed are far less than those in the underdevelopment stage. With the increase of the rotational speed, the flow stability will be enhanced or weakened to varying degrees. In general, the flow stability without vortex shedding is better than that with vortex shedding. Therefore, the flow stability can be effectively enhanced via suppressing the vortex shedding using rotary control.