Numerical simulation of laminar breakdown and subsequent intermittent and turbulent flow in parallel-plate channels: Effects of inlet velocity profile and turbulence intensity

The nature of flow development in a parallel plate channel has been investigated by making use of a newly developed model of intermittency. That model, taken together with the RANS equations of momentum conservation, the continuity equation, and the SST turbulence model, was employed to provide a complete chronology of the development processes and the derived practical results. A major focus of the work is the effect of inlet conditions on the downstream behavior of the developing flow. It was observed that the flow development process depends critically on the specifics of the inlet conditions characterized here by the shape of the velocity profile and the magnitude of the turbulence intensity. Two velocity profile shapes (flat and parabolic), are regarded as limiting cases. Similarly, two turbulence intensities, Tu = 1% and 5%, are employed. From the standpoint of practice, the relationship between the friction factor and the Reynolds number is most significant. It was found that this relationship reflects that of standard practice for only one of the investigated cases (flat velocity profile, Tu = 5%). For the other cases (flat profile, Tu = 1% and parabolic profile, Tu = 1% and 5%), the breakdown of laminar flow is delayed and the onset of full turbulence occurs rather abruptly at Re ∼10,000. Three unique fully developed flow regimes are existent, depending on the inlet conditions and on the value of the Reynolds number. In addition to the standard laminar and fully turbulent regimes, another regime, fully developed intermittent, can occur. Specifically, in the latter regime, laminar and turbulent flows occur intermittently.