Applicability of flow equation in karst aquifers

摘要

Flow is laminar when the fissure width is narrow and the hydraulic gradient is small. As the fracture aperture increases, velocity increases and the Reynolds number increases rapidly, causing the flow to become turbulent. Darcy's law is applicable under laminar flow, while the Darcy Weisbach equation is used in turbulent flow. The transition to turbulent flow occurs within a range of Reynolds numbers and fissure widths. The Fissure width, fissure length, fissure area and average fissure velocity were measured in 48 sites on karstified limestones in the south of Iran. A cylinder was used to measure the average flow velocity per fissure area in all 48 sites. The results revealed that the onset of turbulence appears at a Reynolds number of 50 and a fissure width of more than 0.8 cm. The onset of turbulence varies on other karstic sites depending on the variation of the fissure width along the flow path, hydraulic gradient, water temperature, roughness of fissure wall, type of representative length dimension in the Reynolds equation, and geometry of the flow path.