The paper “Recovery in the wake of in-line axial-flow rotors” co-authored by Drs. Posa and Broglia from CNR-INM and Prof. Balaras from The George Washington University was selected in the Editor’s picks by the editorial board of Physics of Fluids and published on the home page of the journal.
Drs. Posa and Broglia studied – by high-fidelity numerical simulations of axial-flow rotors on cylindrical grids consisting of 3.8 billion points – the influence on the wake development of a downstream turbine by an upstream one. They demonstrated that the wake recovery of the downstream device is much faster than that of the upstream one and weakly affected by their relative distance. This result was found a consequence of the strong sensitivity of the tip vortices shed by axial rotors to even small perturbations of the inflow conditions. Their instability starts the process of momentum replenishment within the wake, having a beneficial effect on the power production of downstream turbines, as verified in recent experiments (see, for instance, the study by Okulov et al. at https://doi.org/10.1016/j.renene.2020.08.148). These phenomena allow decreasing the relative distance between downstream rows of devices in wind and hydrokinetic farms, increasing this way the density of power production per unit land. They also highlight the beneficial effect of free-stream turbulence in accelerating the process of wake recovery and enabling engineers to increase the density of turbines within a site.
More information can be found: https://doi.org/10.1063/5.0085587