arXiv subjects

M. Bernades

Publications and source records attributed to M. Bernades.

2 recordsLinked to original sources

arXiv2025

Data-Augmented Resolvent Analysis of Wall-Bounded High-Pressure Transcritical Flow

High-pressure transcritical fluid flows are central to modern energy and propulsion systems. A key challenge arises in confined configurations, where optimizing performance requires a detailed understanding of the coupled hydrodynamic and thermodynamic nonlinearities governing these flows. In this context, low-order decomposition techniques, particularly resolvent analysis, provide an interpretable linear input-output framework to identify and quantify dominant amplification mechanisms of coherent flow structures. This work pursues two main objectives: (i) to establish a resolvent-based framework tailored to high-pressure transcritical fluid flows, and (ii) to characterize the spatio-temporal sensitivity of the resolvent operator using data-driven turbulent base flows. These analyses identify flow responses and forcings that optimally enhance mixing and heat transfer, along with their characteristic scales. Results show that amplification is dominated by streamwise-elongated structures with spanwise periodicity, associated with peak singular values at normalized spanwise wavenumbers of order unity. Unlike ideal-gas or incompressible flows, the dominant forcings originate from thermodynamic fluctuations in the pseudo-boiling region. Linearization about the turbulent mean flow yields intensified responses in the form of coherent counter-rotating vortex pairs. Energetic-scale motions are constrained by the low-Reynolds-number and non-isothermal conditions considered, with a dominant spectral mode reaching streamwise lengths comparable to instantaneous structures. Data-driven analyses further reveal coherent motions propagating at phase speeds absent from classical incompressible wall-bounded turbulence, intensified near the pseudo-boiling region and constrained toward the hot wall.

physics.flu-dyn↗

arXiv2024

Non-dissipative large-eddy simulation of wall-bounded transcritical turbulent flows

A posteriori analysis based upon a recently proposed non-dissipative large-eddy simulation framework for transcritical wall-bounded turbulence has been carried out. Due to the complexities arisen in such flows, the discretization requires kinetic-energy- and pressure-equilibrium-preservation schemes to yield stable and non-dissipative scale-resolving simulations. On the basis of this framework, the objectives are to (i) compute wall-resolved and wall-modeled large-eddy simulations of a high-pressure transcritical turbulent channel flow, and (ii) assess the thermofluid performance with respect to a direct numerical simulation. In this regard, three different subgrid-scale stress tensor models have been considered, together with models for the unresolved scales of the filtered pressure transport equation and equation of state. In terms of wall-modeling, models based on the "standard law of the wall" and velocity-temperature coupled approaches have been assessed. The results show that for the wall-resolved approaches, the subgrid-scale stress tensors examined slightly deviate from the time-averaged velocity and temperature reference profiles. In terms of bulk performance, it has been found that the Nusselt number and skin-friction coefficient are relatively well captured at the cold and hot walls, respectively. While heat transfer phenomena are fairly well reproduced, particularly the Prandtl and heat flux trends along wall-normal direction. Additionally, the wall-modeled strategies improve the recovery of first-order statistics, although they do not attain the profile in the log-law region. However, they enhance the wall metrics and the heat flux prediction. It is, thus, concluded that dedicated efforts by the research community are needed to improve the prediction accuracy of existing subgrid-scale and wall models for wall-bounded transcritical turbulence.

physics.flu-dyn↗