Numerical Investigation of the Effect of an Oblique Flow Entry on the Pressure Losses in Square Channels

TL;DR

This study investigates how oblique flow entry affects pressure losses in square channels using LES and RANS simulations, revealing flow separation effects, the importance of geometric details, and the accuracy of different modeling approaches.

Contribution

It provides a detailed comparison of LES and RANS models in predicting pressure losses due to oblique flow entry in square channels, emphasizing the impact of geometric features.

Findings

LES shows persistent eddy shedding at moderate Reynolds numbers.

RANS predicts pressure losses within 5% of experiments except during transitional flow.

Edge rounding significantly improves pressure loss predictions.

Abstract

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 predicted pressure losses mostly agree with experimental data. The differences observed for some parameters are attributed to the difficulty of accurately replicating the experimental geometry. It is shown that LES results are susceptible to the rounding of the leading edge (present in experiments). Including edge rounding improves the pressure predictions. RANS simulations predicted pressure losses within 5% of experimental values for most cases, apart from where transitional flow was observed (resulting in differences up to 40%). This study provides insights into the flow structure and sources of pressure losses in square channels and highlights the importance of understanding key flow and geometric features when using LES to predict complex flows involving flow separation and shear layers.