Residual circulation budget analysis in a Wells turbine with leading-edge micro-cylinders

To further interpret the control mechanisms of leading-edge micro-cylinders for flow separation in a Wells turbine, the residual circulation budget was performed through an improved triple decomposition method that the computational cost was reduced by 38.2%.The intensity of the leading-edge vortex (LEV), free of shear effects, was tracked under typical conditions. Meanwhile, disturbance physics was dissected by splitting the contributions of shear, swirling, and straining motions to the flow from dominant modes, captured by the proper orthogonal decomposition method under typical working conditions. The influence of micro-cylinders on the spatiotemporal evolution of the LEV has been discussed in detail. The results indicate that the accumulative shaft power of the turbine is improved by 54.2% through the micro-cylinders operating by suppressing the swirling intensity near the leading edge and weakening the instability of the boundary layer. Moreover, low-frequency disturbances could be significantly weakened and tended to transfer to higher-order modes with lower energy. Under the stall condition, the shear layer flux and diffusive flux dominated the LEV circulation rate. In contrast to the referential model, as the cylinders blocked the LEV trajectory after falling, the annihilation slowed down with an intensified accumulative circulation of the LEV.