Aerodynamic performance of a circulating airfoil section for Magnus systems via numerical simulation and flow visualization

Net Power Coefficient of Vertical and Horizontal Wind Turbines with Crossflow Runners

“…In comparison with plain rotating cylinders, higher values of the lift coefficient have been obtained by using spiral fins [21,22], although the lift coefficient substantially decreases as the TSR tends to zero [22]. A drawback of rotating cylinders (both plain and with spirals) is the high value of the drag to lift ratio, which contrasts with the very low ratio recently obtained with a circulating airfoil specifically designed for providing a Magnus force in HAWT [23]. However, the complexity of the previous mechanism motivates the investigation of simpler options for applications in wind energy as, for example, the use of crossflow runners.…”

“…Forces Fx (positive leftwards) and Fy (positive downwards) (see the inset of the CFD simulations box in Figure 2) are also used for calculating the aerodynamic coefficients of lift Cl and drag Cd, as usual [23] For comparison purposes, simulations applying a ∆t equivalent to a 0.2 • turn of the 22 blades turbine were carried out for different values of N and results did not significantly vary (changes in forces less than 0.5%). The numerical algorithm solves the momentum and mass conservation equations with a double precision pressure-based algorithm and second order discretization schemes.…”

“…Since the simulation is 2D, the values of forces and torque reported by the solver are per unit length, being multiplied by L (the length of the turbine) for carrying out the comparison with experimental data. Forces F x (positive leftwards) and F y (positive downwards) (see the inset of the CFD simulations box in Figure 2) are also used for calculating the aerodynamic coefficients of lift C l and drag C d , as usual [23] …”

“…The numerical algorithm solves the momentum and mass conservation equations with a double precision pressure-based algorithm and second order discretization schemes. The shear stress transport (SST) k-ω turbulent model is chosen, as successfully done in [23] for similar conditions, and the pressure-momentum coupling uses the pressure implicit with splitting of operator (PISO) method. Differences of our numerical set up with [9] are that, here: (1) we adapt the time step to have the same angle of rotation per outer iteration for all the cases analyzed; (2) our flow regime corresponds to lower Reynolds numbers (Re = UDρ/µ), as discussed in Section 5; and (3) we use the SST k-ω model as in [23] instead of the realizable k-ε model since it is expected to be more robust and accurate.…”

Visualization of Flow Field: Application of PLIF Technique

“…In the noncontact measurement methods, smokewire technique [2,3], particle image velocimetry (PIV) [4,5], and planar laser-induced fluorescence (PLIF) are the most popular methods to realize flow field visualization.…”