Numerical methods for unsteady conjugate heat transfer

Thesis

The DPhil thesis enclosed herein addresses key challenges associated with unsteady conjugate heat transfer (CHT) modelling in the context of compressible flows. It establishes a foundation for efficient, high-fidelity simulations of coupled conduction-convection systems and provides insights into transient heat transfer dynamics that are critical to aerospace and energy applications.

First, this work develops a method for generating unsteady inflow conditions in scale-resolving simulations. Most practical CHT applications involve turbulent flows, which require accurate representation of unsteady inflow conditions for capturing complex downstream flow physics. The synthetic inflow generator offers a flexible and efficient solution to this challenge. Validation against experimental data demonstrates superior performance compared to existing methods.

The second contribution focuses on the simulation of unsteady CHT problems. Two primary challenges are addressed: the large disparities in time scales and length scales between solid and fluid domains. To tackle the length scale mismatch, a modal decomposition of the solid temperature field is proposed, which allows for an efficient representation of the unsteady heat conduction problem. The decomposition is coupled with a local, refined solution in the solid domain. To handle the time scale challenge, the decoupled modal equations are accelerated individually based on their respective time constants.

The thesis is concluded with a study of the unsteady effects of CHT in compressible flows. The transient evolution of global flow quantities in a transonic nozzle case is monitored using simulations with different levels of fidelity. Notably, the study reveals that transient thermal drifts are governed by the ratio of thermal capacity to the Stanton number. Results show exponential decay towards steady state, with initial temperature differences dictating drift bounds but not decay rates.

Authors: Drèze, Y

• DOI: 10.5287/ora-kze2wpzgd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: conjugate heat transfer; CFD
• Subjects: CFD