The viscous flow over a thick permeable circular disk in the Reynolds number (Re) range of
10 to 130 and in the Darcy number (Da) range of 10− 9 to 1 is examined. Direct numerical
simulations are performed on a 2D grid with axisymmetric boundary conditions. Three flow
regimes are observed: I, II, and III. In regime I (effectively impervious; D a< 1 0− 6⁠), the
wake is characterized by the presence of a toroidal vortex whose length is approximately
equal to that of an impervious disk. In regime II (transition; 1 0− 6< D a< 1 0− 3⁠), the …

… 9(b) should correspond to a disk diameter downstream rather than a disk radius
downstream. … (a) The streamwise velocity u z profiles across the wake for an axial position
z: (a) on the disk’s face and (b) a distance of one disk diameter downstream of the disk’s
rear face, for three values of Da = 10 −9 , 2.5 × 10 −4 , and 10 −3 , corresponding to regimes
I, II, and III, respectively. The experimental data in (b) are redrawn from Figs. 6(a) and 6(b) of
Ref. … (a) The streamwise velocity u z profiles across the wake for an axial position z: (a) on …