Late-time growth of an inhomogeneous, turbulent mixing layer subjected to transient compression

• Recent engineering model developments imply that the growth rate exponents of mixing layers may be changed permanently by only a temporary application of strain. • This effect has been demonstrated using Large-Eddy Simulations, with good qualitative agreement with the engineering model. • Under compression, the mixing layer exhibits a substantially reduced growth rate exponent from θ = 0.279 to θ = 0.112 and increased mixing. Recent engineering models of turbulent mixing layers under strain imply that there may be a permanent modification of important mixing layer physics following a temporary application of strain. This paper presents a set of Implicit Large-Eddy Simulations of a canonical Richtmyer-Meshkov instability to explore the validity of this model result. The well-characterised θ -group quarter scale case is modified to include a strain rate which halves domain widths in approximately five eddy turnover times. Following the removal of strain, the observed value of the growth rate exponent θ = 0.112 which is a 2.5 times reduction compared with the unstrained case. Whilst θ is slowly rising at late time, the actual change in θ is qualitatively in good agreement with the engineering model but is quantitatively a much greater change than expected. Mixedness also increases significantly, from Θ = 0.8 for the unstrained to Θ = 0.9 following the application of strain. Turbulent kinetic energy substantially rises during strain, but then dissipates more rapidly following the removal of strain due to the decreased turbulent length-scales. Overall these results demonstrate that modifications to engineering models, such as those proposed by Pascoe et al. (Phys. Rev. Fluids 10 (6), 064609, 2025) are needed to capture these significant variations in flow physics which persist even following the removal of strain. The engineering model further predicts more substantial impacts at high overall compression or expansion as expected in typical applications in inertial confinement fusion, supernovae or explosions.