The numerical prediction of the turbulent flow and heat transfer in the entrance region of a parallel plate duct

The entry flow in a duct is divided into three regions: region I at the inlet, where the flow behaves as an external boundary layer interacting with an inviscid flow; region II, a transition region between external and internal flow; and region III, the fully developed region of internal flow. The flow in region III is described by the classical mixing length model of Nikuradse. A composite eddy viscosity is prescribed in the transition region, which changes smoothly from an external model to an internal model. With this model, the nonlinear eigenvalue procedure of Cebeci and Keller for laminar flows (1974) was used to calculate the developing duct flow. This new composite model gives improved predictions for center line velocity and displacement thickness. In a closure, Emery and Gessner show that by proper matching of initial conditions, their results based on a length-scale model can be brought to closer agreement with experiment, and moreover, the length-scale model has greater flexibility since the constants it requires are also used in a three-dimensional model.