Jl. Lage et al., 2 TYPES OF NONLINEAR PRESSURE-DROP VERSUS FLOW-RATE RELATION OBSERVEDFOR SATURATED POROUS-MEDIA, Journal of fluids engineering, 119(3), 1997, pp. 700-706
Previous reports of experiments performed with water (Fand et al., 198
7 and Keceioglu and Jiang, 1994) indicated that beyond the Forchheimer
regime the rate of change of the hydrostatic pressure gradient along
a porous medium suddenly decreases. This abnormal behavior has been te
rmed ''transition to turbulence in a porous medium.'' We investigate t
he relationship between the hydrostatic pressure gradient of a fluid (
air) through a porous medium and the average seepage fluid velocity. O
ur experimental results, reported here, indicate an increase in the hy
drostatic pressure rate beyond a certain transition speed nor a decrea
se. Physical arguments based on a consideration of internal versus ext
ernal incompressible viscous flow are used to justify this distinct be
havior, a consequence of the competition between a form dominated tran
sition and a viscous dominated transition. We establish a criterion fo
r the viscous dominated transition from consideration of the results o
f three porous media with distinct hydraulic characteristics. A theore
tical analysis based on the semivariance model validation principle in
dicates that the pressure gradient versus fluid speed relation indeed
departs from the quadratic Forchheimer-extended Darcy flow model, and
can be correlated by a cubic function of fluid speed for the velocity
range of our experiments.