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Paper IPM / P / 16236  


Abstract:  
We study hydrodynamic fluctuations in a compressible and viscous fluid film confined between two rigid, noslip, parallel plates, where one of the plates is kept fixed, while the other one is driven in smallamplitude, translational, displacements around its reference position. This jiggling motion is assumed to be driven by a stochastic, external, surface forcing of zero mean and finite variance. Thus, while the transverse (shear) and longitudinal (compressional) hydrodynamic stresses produced in the film vanish on average on either of the plates, these stresses exhibit fluctuations that can be quantified through their equaltime, twopoint, correlation functions. For transverse stresses, we show that the correlation functions of the stresses acting on the same plate (selfcorrelators) as well as the correlation function of the stresses acting on different plates (crosscorrelators) exhibit universal, decaying, powerlaw behaviors as functions of the interplate separation. At small separations, the exponents are given by 1, while at large separations, the exponents are found as 2 (selfcorrelator on the fixed plate), 4 (excess selfcorrelator on the mobile plate) and 3 (crosscorrelator). For longitudinal stresses, we find much weaker powerlaw decays in the large separation regime, with exponents 3/2 (excess selfcorrelator on the mobile plate) and 1 (crosscorrelator). The selfcorrelator on the fixed plate increases and levels off upon increasing the interplate separation, reflecting the nondecaying nature of the longitudinal forces acting on the fixed plate.
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