Abstract
Passive vortex generators (VGs) are widely used to suppress the flow separation of wind turbine blades, and hence, to improve rotor performance. VGs have been extensively investigated on stationary airfoils; however, their influence on unsteady airfoil flow remains unclear. Thus, we evaluated the unsteady aerodynamic responses of the DU-97-W300 airfoil with and without VGs undergoing pitch oscillations, which is a typical motion of the turbine unsteady operating conditions. The airfoil flow is simulated by numerically solving the unsteady Reynolds-averaged Navier-Stokes equations with fully resolved VGs. Numerical modelling is validated by good agreement between the calculated and experimental data with respect to the unsteady-uncontrolled flow under pitch oscillations, and the steady-controlled flow with VGs. The dynamic stall of the airfoil was found to be effectively suppressed by VGs. The lift hysteresis intensity is greatly decreased, i.e., by 72.7%, at moderate unsteadiness, and its sensitivity to the reduced frequency is favorably reduced. The influences of vane height and chordwise installation are investigated on the unsteady aerodynamic responses as well. In a no-stall flow regime, decreasing vane height and positioning VGs further downstream can lead to relatively high effectiveness. Compared with the baseline VG geometry, the smaller VGs can decrease the decay exponent of nondimensionalized peak vorticity by almost 0.02, and installation further downstream can increase the aerodynamic pitch damping by 0.0278. The obtained results are helpful to understand the dynamic stall control by means of conventional VGs and to develop more effective VG designs for both steady and unsteady wind turbine airfoil flow.
Highlights
Airfoil flow control at the high angle of attack (AOA) is of keen interest in a wide range of industrial fluid dynamics applications
The influences of vane height and chordwise installation are investigated on the unsteady aerodynamic responses as well
One can observe that increasing reduced frequencyimpact manifests the of the reduced frequency, likely because the unsteady linear aerodynamic responses have relatively aerodynamic hysteresis of uncontrolled airfoil flow, which is typical of trailing-edge stalling airfoils low sensitivity to the frequency of motion
Summary
Airfoil flow control at the high angle of attack (AOA) is of keen interest in a wide range of industrial fluid dynamics applications. -called low-profile VGs, with a height between 10% and 50% of the boundary-layer thickness, are a remedy for this shortcoming [7,8] Their use, is often limited to applications where the flow-separation points are relatively fixed, which is uncommon on wind turbine blades due to the variable freestream velocity and rotor speed. The idea was to introduce a local flow-dependent forcing term into the momentum equations by means of an analogy to the thin airfoil theory This approach has shown potential to capture the effects of VGs on wind turbine airfoils and blades [16,17]. The performance sensitivity was study in vane height and chordwise installation was conducted on the unsteady airfoil flow as well. Understanding the effect of passive VGs on the unsteady aerodynamic loads of the wind turbine blades
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call