Low-Reynolds-number turbulent flows in locally constricted conduits: A comparison study

In numerous internal flow systems the velocity field can undergo all flow regimes, that is, from laminar, via transitional, to fully turbulent. Considering two test conduits with local constrictions, four turbulence models, with an emphasis on low-Reynolds-number (LRN) turbulence models, were compared and evaluated. The objective was to identify a readily available LRN turbulence model with which incompressible laminar-to-turbutent velocity and pressure fields in complex three-dimensional conduits can be directly computed. The comparison study revealed that the renormalization group (RNG) k-epsilon and Menter k-omega models amplify the flow instabilities after tubular constrictions and hence fail to capture the laminar flow behavior at low Reynolds numbers. The LRN k-epsilon model fails to simulate the transition to turbulent flow, and it requires relatively high computational resources because of the slower convergence. The LRN k-omega model adopted for complex three-dimensional tubular flows in this study appears to be capable of reproducing the behavior of laminar, transitional, and fully turbulent flows. Moreover, the LRN k-omega model predicts the maximum turbulence fluctuations quite well. Hence, it is concluded that the LRN k-omega model is suitable for simulating laminar-transitional-turbulent flows in constricted tubes, such as the human upper airways, stenosed blood vessels, obstructed pipes, etc.