ABSTRACT
Transition from laminar to turbulent flow is a crucial regime change, and is sensitive to duct geometry, surface roughness, and the strength of disturbances in the fluid. The roughness elements change the turbulent pattern near the wall, increase the total solid–fluid surface area, and cause profile drag. The development of velocity, temperature, and concentration boundary layers in turbulent duct flow is qualitatively similar to laminar flow. The hydrodynamic entrance length in turbulent flow is shorter than that in the laminar flow, however, and strongly depends on the entrance conditions, the intensity of disturbances, and surface roughness. The correlations for pressure drop or heat/mass transfer in transition regime are often based on interpolation between well-established correlations for laminar and fully turbulent flow regimes. The turbulent hydrodynamic and transport phenomena in curved ducts are strongly influenced by centrifugal forces that result from the curvature of flow passage.
