On the formation of thermal caustics in turbulent particle-laden flows

This study investigates the development of thermal caustics within particle-laden turbulent flows, a concept recently proposed to elucidate the non-smooth behavior of particle temperature during fluid–particle thermal interactions, drawing a parallel to the creation of caustics. The temperature variations observed between closely spaced particles, which are linked to thermal caustics, stem from the history of their different paths. This work delves into the emergence of thermal caustics by analyzing the dynamics of the gradient of particle temperature in the configuration space, highlighting the influence of both particle and thermal inertia. The analysis indicates that thermal caustics arise concurrently with caustics, with the exception of the condition of zero thermal inertia, which represents a singular scenario where particle temperature decouples from velocity.