Numerical Investigation Of Synthetic Jet Assisted Flow Control Over Horizontal Axis Wind Turbines

Due to their increasing size,horizontal axis wind turbines(HAWT)operates in the atmospheric boundary layer where aerodynamic losses due to flow separation effects could significantly reduce their performance and lifespan over time,leading to an increase in the Levelized Cost of Energy(LCOE).Synthetic Jet Actuators(SJAs)have been extensively studied as an active flow control method in aerospace applications due to their fast response rate,low power requirements,and reduced geometrical complexities compared to other control methods.However,the actuation effects of SJAs on Horizontal Axis Wind turbines have not been fully studied.The current thesis aims to carry out the numerical investigation of the characteristics of SJA as a promising approach for active flow control over commercial wind turbines(using the NREL-5MW baseline wind turbine at rated conditions as a case study).The NREL-5MW horizontal axis wind turbine is a three-blade configuration with a 63 m radius and a hub height of 90 m.The rated power of this turbine is five megawatts.The cut-in and cut-out wind speeds are 3 and 25 m/s,respectively.In order to reduce the computational cost,the periodicity assumption was used so that only one of the blades was modeled.The Computational mesh was made using the ICEM meshing software.The Reynolds Averaged Navier Stokes(RANS)three-dimensional equations in rotating frames of reference are solved using the commercially available ANSYS software package for computational fluid dynamics.The steady-state analysis was conducted using the SST k-ω turbulence model due to its numerical stability and ability to perform well in flows with adverse pressure gradients such as the one understudied.By monitoring the average torque results,continuity,and the x,y,and z momentum equations,the convergence of the simulation was obtained and verified based on existing data.The following results have been obtained;(1)From the aerodynamic investigation of the full-scale NREL-5MW wind turbine,it is pointed out that while the separation effect is reduced at the blade tip,the flow over the blade root is severely separated or stalled with massive reverse flow due to the local increase in the angle of attack.This results in poor aerodynamic performance of the blade even under rated conditions.(2)Through the numerical simulation of the full-size turbine rotor without any form of control,it is pointed out that the flow separation effect at the root of the blade will expand radially along the blade span and affect the aerodynamic characteristics of the whole blade.(3)Through a 2.5D numerical simulation,the influence of flow separation on the aerodynamic performance of the turbine sections was investigated.Furthermore,further investigations were carried out for the synthetic jet actuator(SJA)based flow control of the blade root separation.The following parameters were used;the jet angle was 20 degrees,the non-dimensional frequency,F+= 0.8,and the Jet momentum coefficient,C(?) = 1.5×10-3 respectively,which yielded a178% increase in the baseline lift coefficient and an 18% decrease in the drag coefficient respectively.Conclusively,it has been shown that the impact of the blade root phenomenon on aerodynamic performance is more severe than is curren tly thought of in literature.Also,it is pointed out that the appropriate synthetic jet control can significantly improve the turbine aerodynamic performance.