Effect of tip spacing, thrust coefficient and turbine spacing inmulti-rotor wind turbines and farms

Abstract

Large eddy simulations (LES) are performed to study the wakes of a multi-rotor wind turbine configuration comprising of four identical rotors mounted on a single tower. The multi-rotor turbine wakes are compared to the wake of a conventional turbine comprising of a single rotor per tower with the same frontal area, hub height and thrust coefficient. The multi-rotor turbine wakes are found to recover faster, while the turbulence intensity in the wake is smaller, compared to the wake of the conventional turbine. The differences with the wake of a conventional turbine increase as the spacing between the 5 tips of the rotors in the multi-rotor configuration increases. The differences are also sensitive to the thrust coefficients used for all rotors, with more pronounced differences for larger thrust coefficients. The interaction between multiple multi-rotor turbines is contrasted with that between multiple single-rotor turbines by considering wind farms with five turbine units aligned perfectly with each other and with the wind direction. Similar to the isolated turbine results, multi-rotor wind farms show smaller wake losses and smaller turbulence intensity compared to wind farms comprised of conventional single-rotor turbines. The 10 benefits of multi-rotor wind farms over single-rotor wind farms increase with increasing tip spacing, irrespective of the axial spacing and thrust coefficient. The mean velocity profiles and relative powers of turbines obtained from the LES results are predicted reasonably accurately by an analytical model assuming Gaussian radial profiles of the velocity deficits and a hybrid linear-quadratic model for merging of wakes. These results show that a larger planform energy flux can be achieved without significantly increased fatigue loads by using multi-rotor turbines instead of conventional, single-rotor turbines.

Aeroelastic load analysis of a co‐rotating quad‐rotor wind turbine

“…Furthermore, it is observed that closely spacing the rotors on a multi‐rotor wind turbine increases the loading on the blades which requires a further examination by means of aeroelastic simulation of a multi‐rotor wind turbine 7 . An aerodynamic analysis of a multi‐rotor wind turbine comprised of four rotors indicate faster wake recovery as well as reduced turbulence kinetic energy (TKE) compared to a single‐rotor wind turbine with equal swept area 10–13 . The reduction of TKE in multi‐rotor wind turbine wake has the potential of reduced fatigue loads on the downstream wind turbines in a wind farm.…”

“…7 An aerodynamic analysis of a multi-rotor wind turbine comprised of four rotors indicate faster wake recovery as well as reduced turbulence kinetic energy (TKE) compared to a single-rotor wind turbine with equal swept area. [10][11][12][13] The reduction of TKE in multi-rotor wind turbine wake has the potential of reduced fatigue loads on the downstream wind turbines in a wind farm.…”