Turbulent airflow above a full-scale macroporous material: Boundary layer characterization and conditional statistical analysis

• Full-scale investigation and characterization of airflow above a macroporous material.
• Significant presence of organized turbulent structures observed at low air speed.
• Sensitivity of sweeps and ejections to surface porosity observed only at high air speed.
• No generally valid scaling law is found, demonstrating need for full scale studies.

Convective drying of macroporous materials is governed by the complex interaction between airflow above and into the material, the roughness of the air–material interface and the characteristics of the material pore system. In this study, we experimentally investigate this interplay in detail and at full-scale, using porous asphalt (PA) as a model material. The characteristics of the turbulent flow in the immediate vicinity of the material surface are studied with full-scale wind tunnel experiments at three flow speeds over two types of PA with different surface porosities and surface pore sizes, and are compared to similar measurements over a smooth and impermeable reference material. It is shown that, above a certain wall-normal distance, turbulence profiles can be scaled to make them independent of the flow speed. However, at low speed, the scaling breaks down due to a combination of organized turbulent structures of high intensity and a low turbulence background. No generally valid scaling applicable at all tested air speeds is found close to the surface, where drying occurs. Hence, realistic drying experiments must be performed at full scale and for the entire range of velocities of interest.