Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 136

6.3.2 Turbulent Flow
Flow is referred to as “turbulent” if the water particles, in addition to their primary
movement, are subjected to a disturbance that leads to an irregular secondary move-
ment. This happens when a critical velocity of the water particles is exceeded.

The dimensionless Reynolds number Re, defi ned as follows, characterizes whether a
laminar or a turbulent fl ow takes place:

(6.21)

The transition from laminar to turbulent fl ow occurs at a critical Reynolds number Re C .
If k/D h

0.0168, the critical Reynolds number for an irrotational one-dimensional fl ow
through a fi ssure is Re C = 2300 (Fig. 6.8, left). According to Wittke (1990), in this
range of relative roughness the following two fl ow equations based on the results of
experiments carried out by Louis (1967) may be applied to irrotational turbulent fl ow
depending on Reynolds number and relative roughness:

≤

(6.22)

(6.23)

Figure 6.8 Types of turbulent fl ow depending on relative roughness and Reynolds number
(Wittke 1990)