Flow Field and Drag for Elliptical Filter Fibers

Filter fibers are now available in many cross-sectional shapes, including elliptical. Assuming viscous flow through a filter, analytical expressions are developed to predict airflow around elliptical fibers and the aerodynamic drag and lift on the fibers. Important variables influencing the velocity field and the drag are the length-to-width ratio of the elliptical cross section, the filter solidity, and the orientation of the fiber's cross section to the incoming airflow. Plots of the streamlines for flow around elliptical fibers show that pressure drop through the filter and particle collection are likely to increase as the length-to-width ratio and filter solidity increase and as more of the fibers are aligned with the cross section's major axis perpendicular to the flow. The expressions developed indicate that drag can vary by more than 4 orders of magnitude as filter properties change.