Unsteady Pressures Analysis of an Oscillating Airfoil Exhibiting Nonsynchronous Vibrations as Applied to Turbomachinery
When an unsteady aerodynamic instability interacts with the natural modes of vibration of a rigid body, lies a phenomenon known as Non-Synchronous Vibrations (NSV), also known as Vortex-Induced Vibrations (VIV). These vibrations cause blade failure in jet engines and turbomachinery; however, the underlying flow physics are much less understood compared to other aeroelastic phenomenon such as flutter or forced response. When the buffeting frequency of the flow around a body nears a natural frequency of said body, the former locks on to the latter in a process known as “lock on”. Within this “lock on” region there is only one main frequency, while outside of it there are two. Although this phenomenon has been documented experimentally and computationally, the unsteady pressures associated with this phenomenon have not measured. First, we collected the spectra of pressure frequencies around a NACA 0012 airfoil exhibiting NSV in a low-speed wind tunnel. Then the time domain pressure data is Fast Fourier Transformed into frequency domain results. Finally, the unsteady pressure content from the aerodynamics is separated from the content from the motion of the airfoil, allowing for greater understanding of the unsteady aeroelastic behavior. The results are compared to previous experiments as well as Computational Fluid Dynamics (CFD) simulations. Understanding the pressures and how they affect the flow physics of NSV allows for further studies into this phenomenon, paving the way for the design of more efficient and safer jet engines.
