Aeroelastic Divergence Investigation of a Wells Turbine Blade

Computational and experimental investigations into the divergence performance of a low Aspect Ratio Wells turbine blade are presented. The computations were obtained by building a finite element model of a solid NACA0012 blade in MSC/PATRAN and then analyzing it using the MSC/NASTRAN finite element package. Subsonic Doublet Lattice theory was used to model the aerodynamics while the coupling to the s t r u c t u r a l model was achieved through a Surface Splining technique. The p-k method was utilised for the aeroelastic analysis, where damping and frequency values are calculated with respect to free-stream velocity, highlighting the divergence speed when damping value of a mode changes sign while the frequency value decreases to zero. Steady-state wind tunnel experiments were carried out with an aeroelastic rig that allowed rotational motion of a v e r t i c a l l y mounted rigid model that incorporated a spring to provide torsional stiffness. The computations include a modal analysis of the finite element model with and without the torsional spring, and an aeroelastic analysis of the wind tunnel set-up to determine the divergence speed. These results are compared with experiments and also with an analytical value to show that the experimental divergence speed was highest while that computed was lowest. The authors propose that this was due to the computations and analysis overestimating the lift performance of low Aspect Ratio blades in general, thereby underestimating the divergence speed. However, the use of the computational method is advocated for design of Wells turbine blades as these tend to produce more lift than would be expected from single aerofoil data.