Date of Award
Winter 2025
Project Type
Dissertation
Program or Major
Mechanical Engineering
Degree Name
Doctor of Philosophy
First Advisor
Greg Chini
Second Advisor
John Gibson
Third Advisor
Jeff Oishi
Abstract
This dissertation focuses on wall-bounded shear-driven turbulence with temperature-dependentviscosity. Direct numerical simulations and quasilinear reduction have been used to establish the asymmetric variation of turbulent statistics in the wall-normal direction. A comparison of energy spectra in the cold and hot halves of the channel reveals that large scale motions are amplified in the more viscous half while small scale motions are amplified in the less viscous half. Interestingly, the threshold wavenumber distinguishing these scales remains independent of stratification. This observation has been verified via a low-order reconstruction of the turbulent kinetic energy profile using resolvent analysis. Fourier modes that selectively amplify kinetic energy in the two halves of the channel have been identified and the reconstructed turbulent kinetic energy profiles reproduce the characteristic asymmetries of viscosity stratified turbulence. Varying the relative magnitudes of thermal and momentum diffusivity is then shown to alter the characteristic asymmetry. The modified asymmetry can be attributed to a variation in the range of wavenumbers which selectively amplify in the cold half of the channel. The results demonstrate the applicability of quasilinear and resolvent analyses and provide new insights into viscosity stratified turbulence.
Recommended Citation
Dubey, Pulkit Kumar, "Viscosity Stratified Turbulence: Insights from Direct Numerical Simulations, Quasilinear Reduction and Resolvent Analysis" (2025). Doctoral Dissertations. 2974.
https://scholars.unh.edu/dissertation/2974