Sanath Kotturshettar | Searcharxiv

arXiv2026

A global mass-preserving numerical method for low-Mach-number real-gas flows in closed systems

A mass-preserving low-Mach-number framework is proposed for closed-system real-fluid flows governed by general nonlinear equations of state. The formulation enforces consistency between the spatially uniform thermodynamic pressure, the equation of state, and global mass conservation. Moreover, the numerical algorithm employs a segregated strategy in which the thermodynamic state is updated before the momentum equations, and the velocity field is advanced using a pressure-correction method. This approach enables an efficient solution procedure by decoupling the thermodynamic and momentum updates and retaining the use of FFT-based solvers for the pressure correction. The resulting formulation is implemented with second-order spatial accuracy. The implementation is first verified using the method of manufactured solutions, in which the thermodynamic state is prescribed through analytical density and thermodynamic-pressure fields, enabling verification of the nonlinear equation of state, thermodynamic-pressure evolution, and the low-Mach-number divergence constraint. The framework is subsequently validated against benchmark laminar and turbulent flows for both ideal and real fluids, particularly transcritical CO$_2$ channel flow, demonstrating its accuracy and robustness in the presence of strong thermodynamic nonlinearities.

physics.flu-dyn↗

arXiv2025

Mean velocity profile in stably stratified turbulent channel flow

The Monin-Obukhov Similarity Theory (MOST) is a cornerstone of atmospheric science for describing turbulence in stable boundary layers. Extending MOST to stably stratified turbulent channel flows, however, is non-trivial due to confinement by solid walls and the much smaller turbulent length scales involved. In this study, we investigate the applicability of MOST in closed channels and identify where and to what extent the theory remains valid. A key finding is that the ratio of the half-channel height to the Obukhov length serves as a governing parameter for identifying distinct flow regions and determining the scaling of the mean velocity within them. Hence, we propose a closure relation to estimate this ratio directly from the governing input parameters: friction Reynolds and friction Richardson numbers ($Re_τ$ and $Ri_τ$). The framework is tested against a series of direct numerical simulations (DNS) across a range of $Re_τ$ and $Ri_τ$. The reconstructed velocity profiles enable accurate prediction of the skin friction coefficient crucial for quantifying pressure losses in stratified flows in engineering applications.

physics.flu-dyn↗