Physical Review Fluids
Effective viscosity of a suspension of hot particles
Author(s): Osher Arbib and Naomi Oppenheimer
When particles suspended in a fluid are heated, their localized temperature modifies the fluid’s viscosity in nontrivial ways. Einstein famously showed that adding particles to a fluid increases its viscosity. This work demonstrates that heating these particles can cause the viscosity to increase, decrease, or remain unchanged, depending on the temperature gradient. Moreover, an uneven heat distribution on the particles gives rise to surprising effects — making the fluid’s behavior directionally dependent and inducing what is known as odd viscosity. These findings open new avenues for controlling fluid flow.
[Phys. Rev. Fluids 10, 013301] Published Thu Jan 23, 2025
Tumbling elimination induced by permeability: An experimental approach
Author(s): J. Sánchez-Rodríguez and F. Gallaire
Archetypal falling behaviors of impervious objects are classified into four modes: fluttering, tumbling, steady descent, and chaotic motion. We present in this paper an experimental result of stability induced by porosity and permeability. We discover that by drilling different porosity patterns, we can avoid tumbling and chaotic behavior in plates that, due to their inertia and Reynolds values, should tumble while falling according to the regime diagram of impervious plates. Instead, the majority of the plates flutter and a few even descend steadily.
[Phys. Rev. Fluids 10, 013904] Published Tue Jan 21, 2025
Linear model for secondary motions in stratified flows
Author(s): Abdelhalim Abdeldayem, Thijs Bon, Raúl Bayoán Cal, and Johan Meyers
The valley-mountain arrangement excites secondary vortices when interacting with the atmospheric boundary layer. In this paper we develop an analytical model to predict these secondary vortices in the case of thermal stratification. The model was compared to recent direct numerical simulations available in the literature which studied secondary motions in channel flow for a wide range of Reynolds and Richardson numbers. The model showed robust performance for the range of cases considered, showing error less than 5% for the temperature and below 20% for velocity in most cases.
[Phys. Rev. Fluids 10, 014605] Published Tue Jan 21, 2025