Unstable interactions of viscoelastic coatings with supersonic turbulent flows

This work demonstrates the occurrence of travelling wave flutter instabilities on viscoelastic coatings in supersonic flows, which forms an important milestone towards developing viscoelastic materials for high-speed flow applications. The flow-induced travelling surface waves were generated by elevating the air speed such that the flow dynamic pressure and the material Young’s modulus are of the similar order, their ratio defined as the compliance parameter. Experimental investigations probed the critical compliance parameter corresponding to surface instability onset across different fluid-structural non-dimensional parameters. The results revealed a strong dependence of the critical compliance parameter on the flow Mach number in addition to other flow and structural parameters that were found to influence the instability onset in earlier studies with aqueous flows. A broader parametric sweep of these parameters was performed using linear stability analysis. Consistent qualitative comparisons were obtained between the experiments and stability calculations on the most amplified wave characteristics. Further investigations revealed that the interaction mechanisms are similar to incompressible flows.