Response regimes in the fluid–structure interaction of wall turbulence over a compliant coating

The interaction between a turbulent boundary layer flow and compliant surfaces is investigated experimentally. Three viscoelastic coatings with different material stiffnesses are used to identify the general surface response conditions. For softest coating, global force measurements show two obvious regimes of an indicated transition at $U_b/C_t\sim 3.5$ , where $U_b$ bulk velocity $C_t$ coating shear velocity. one-way coupled regime shows friction values comparable those rigid wall, while two-way indicate significant increase in fluid friction. Within for $U_b/C_t>1.2$ low level coupling represented by change profile as well Reynolds stresses near-wall region. This supported deformation measurements. Initially, structures induce only imprint on surface, occurs when wave propagation $c_w$ equals (i.e. $c_w/C_t\sim 1$ ). Above growth wavelength observed increasing velocity, most probably due formation generated downstream pressure features flow. stable correlates high-intensity fluctuations layer, $c_w\sim 0.7\unicode{x2013}0.8$ . regime, additional motions downward shift logarithmic region substantial confirm frictional drag increase. Another type initiated phase-lag instability combination undulations that start protrude viscous sublayer, trains 0.17\unicode{x2013}0.18$