Reynolds number dependence of the drag coefficient for laminar flow through fine-scale screens

摘要

The laminar flow downstream of fine-mesh screens is studied experimentally and numerically. Two different screen types are examined experimentally, both with open areas greater than 50% and wire dimensions less than 100 (mu)m. Such screens produce flow disturbances of much smaller scale than those examined in most previous studies of flow-conditioning screens and grid-generated turbulence. Instead of using standard woven-wire screens, high- uniformity screens are used which are fabricated by photoetching holes into 50.8 (mu)m thick Inconel sheets. The holes thus produced are square with rounded corners, arranged to form a square array, with a minimum wire thickness (located halfway between wire crossings) of D = 50.8 (mu)m. A flow facility has been constructed for experiments with these screens. Air at 85 kPa and 295 K is passed through each screen at upstream velocities of 1 to 12 m/s, yielding Reynolds numbers Re(sub D) = (rho)UD/(mu) in the range 2 (le) Re(sub D) (le) 35. Pressure drops across the screens are measured at these conditions using pressure transducers and manometers. From these data, the Reynolds number dependence of the drag coefficient c(sub D) is determined. Three-dimensional flow simulations are performed using the spectral-element code NEKTON. The geometry of the photoetched screens is simulated by a similar geometry with the same open area and minimum wire thickness. The drag coefficients are determined from the computed pressure differences across the screens and are in reasonable agreement with the experimental values, although the agreement degrades slightly with increasing Reynolds number. Such correlations are applicable for the present screens so long as the correct choices for screen open area fraction O and minimum wire thickness D are used in correlation.