Turbulent to Laminar Flow Transition Study in Parallel Plate Geometry Using Direct Numerical Simulation

This study investigates the transition from turbulent to laminar flow regime in channel geometry using Direct Numerical Simulation (DNS). By employing the high-fidelity spectral element CFD code Nek5000, we simulated flow deceleration scenarios in parallel plates geometry to observe the transient behavior of friction factors and Reynolds numbers. Our simulations reveal significant differences between instantaneous friction factors during transients and those predicted by quasi-steady state models. The results show that the transition does not follow a simple linear progression but involves distinct stages characterized by non-monotonic behavior in both friction factors and Reynolds numbers. We also observed a time delay in wall shear stress response to the changes in the flow. This delay is likely due to the time required for the wall layer to adjust to the changing flow conditions through mixing and diffusion processes. The study highlights the necessity for advanced modeling approaches that incorporate the history of flow changes to accurately predict transient behaviors. The findings of this research have implications for various fields, including nuclear reactor safety analysis, where accurate prediction of flow behavior during rapid transients is crucial.