The effect of an oblique flow entry on the pressure losses in square channels

Flows in square channels are common in applications, such as automotive after-treatment systems and heat exchangers. Flows with axial flow entry are well understood, but for oblique flow entry, there is no clarity on the additional pressure loss magnitude or the flow regime. Laminar flow is often assumed, even though flow separation at the channel entrance can cause a transition to turbulence. Here, the impact of oblique flow entry on the flow is investigated using LES (large eddy simulation) and RANS (Reynolds averaged Navier–Stokes) models, and their advantages and limitations are identified. The LES simulations show that the shear layer at the channel entrance produces continuous shedding of eddies that persist downstream even at moderate channel Reynolds numbers (≈ 2000). The LES predicted pressure losses mostly agree with experimental data, and the differences observed are attributed to the difficulty of accurately replicating the experimental geometry. It is shown that both LES and RANS results are sensitive to the rounding of the leading edge (present in experiments). Including edge rounding improves the pressure predictions. RANS simulations mostly agree with experimens, but unlike LES did not predict transitional flow phenomena for sharp leading edge. This study provides insight into the flow structure and sources of pressure losses in square channels, highlights the importance of understanding key flow and geometric features when using LES to predict complex flows involving flow separation and shear layers, and indicates the need to further investigate the complex instability arising from interactions between secondary flow and shear-layer roll-up.