Investigation of the effects of a compliant surface on boundary-layer stability

Abstract

Some of the effects of a passive, single-layer, viscoelastic compliant surface on the stability of a Blasius boundary layer were investigated in a low-turbulence wind tunnel. Measurements of the wavelength and growth rates of vibrating-ribbon-excited harmonic waves were made by hot-wire anemometry. The data for three compliant surfaces with different shear moduli, material damping coefficients, and thicknesses were compared to rigid-surface data. The flow-induced surface displacements were measured using an electro-optic displacement transducer. The results show that the growth rates of unstable Tollmien–Schlichting waves, and the extent of the unstable region in the (F, Rδ*)-plane are reduced over the compliant surfaces relative to those over a rigid surface with the absence of flow-induced surface instabilities. The suppression of the Tollmien–Schlichting waves is accompanied by a surface motion driven by the flow field at the excitation frequency. The experimental results suggest that a delay of the onset to turbulence is possible in air by using appropriately tuned surface characteristics. Further experiments are needed to study the three-dimensional disturbance mode, the flow-induced surface instabilities and the breakdown process.