Local wave-number model for inhomogeneous two-fluid mixing

We present a study of two-point spectral turbulence model (Local Wave-Number or LWN model) for the Rayleigh-Taylor (RT) instability. The outcomes are compared with statistical quantities extracted from three-dimensional simulation RT problem. These simulations initialized high wavenumber perturbations at interface heavy fluid placed on top light so that density gradient is in direction opposite to acceleration due gravity. consider flows low medium contrast and compare against data using mix-width evolution as primary metric. original specified physically reasonable but largely \emph{ad hoc} terms account inhomogeneous mechanisms involved growing mixing layer. systematically assess role each equations by comparison simulation. Two these, kinematic source term, introduced maintain finite covariance between specific volume, distortion modifications density-specific-volume covariance, both result severely over-predicting mix layer growth. A simplified eliminating those two shown improve capture well turbulent mass flux velocity profiles across different times. However, this simplification reveals fidelity other metrics such kinetic energy somewhat compromised. implications outcome discussed respect physics problem, we provide guide practical use model.