Flow and thermal transport at porous interfaces

Abstract

In this talk, the influence of porosity and surface microstructure on near-wall turbulence dynamics and their implications for passive flow control strategies aimed at mitigating drag and enhancing thermal transport will be explored. First, the effects of permeability on turbulent heat transfer across a porous interface within a partially porous channel flow setup will be experimentally examined, utilizing commercially available aluminum foams across a range of bulk Reynolds numbers (Reb ≈ 800 − 2500). Point temperature measurements and Particle Image Velocimetry (PIV) measurements within the channel reveal that the increasing permeability of the aluminum foams induces the emergence of large vortex structures associated with the Kelvin-Helmholtz (K-H) instability, thereby enhancing interfacial thermal dispersion. However, this enhancement is accompanied by increased pumping power requirements due to increased friction, prompting the design of anisotropic porous lattices using 3D printing. Subsequently, the thermophysical properties of these custom-designed 3D printed materials were investigated to establish a relationship between microstructure and saturated thermal conductivity and permeability. The findings indicate that empirical models for stochastic foams or isotropic lattices do not adequately predict the thermophysical properties of anisotropic porous lattices. To address this, phenomenological models are developed to predict the principal components of the permeability tensor and effective thermal conductivity, corroborated by experimental measurements. Finally, the effect of anisotropic permeability on drag response for 3D printed porous substrates is experimentally investigated using a benchtop channel for bulk Reynolds number (Reb ≈ 500 − 4000). The results demonstrate that high streamwise permeability leads to the lowest increase in drag, while wall-normal permeability predominantly influences drag increase, correlated with the emergence of spanwise coherent rollers resembling Kelvin-Helmholtz vortices. Overall, these findings demonstrate the potential of streamwise preferential porous materials for passive drag reduction and also for heat transfer enhancement with minimal drag penalties.

Speaker Bio
 Shilpa received her PhD in Mechanical Engineering from the University of Southern California (USC), Los Angeles, and was advised by Dr. Mitul Luhar. For her dissertation, she worked on developing structured porous surfaces for passive flow control, with applications to drag reduction and heat transfer. She also holds an M.S. in Mechanical Engineering from USC and a B.Tech in Civil Engineering from the College of Engineering Pune, India. Her research interests lie in turbulent boundary layer flow, thermal/particle mixing and transport, and applications of experimental techniques to a variety of problems.