Print Email Facebook Twitter Direct numerical simulation of flow in open rectangular ducts Title Direct numerical simulation of flow in open rectangular ducts Author Yu, Ming (Sapienza Universita di Roma; State Key Laboratory of Aerodynamics) Modesti, D. (TU Delft Aerodynamics) Pirozzoli, Sergio (Sapienza University of Rome) Date 2023 Abstract We study turbulent flow in open channels with a free surface and rectangular cross-section, for various Reynolds numbers and duct aspect ratios. Direct numerical simulations are used to obtain accurate characterization of the secondary motions, which are found to be more intense than in closed ducts, and to scale with the bulk, rather than with the friction velocity. A notable feature of open-duct flows is the presence of a velocity dip, namely the peak velocity is achieved at some depth underneath the free surface. We find that the depth of the velocity peak increases with the Reynolds number, and correspondingly the flow becomes more symmetric with respect to the horizontal midplane. This is also confirmed from the change of the topology of the secondary motions, which exhibit a strong corner circulation at the free-surface/wall corners at low Reynolds number, which, however, weakens at higher. The structure of the mean velocity field is such that the log law applies with good approximation in the direction normal to the nearest wall, which allows us to explain why predictive friction formulae based on the hydraulic diameter concept are successful. Additional analysis shows that the secondary motions account for a large fraction of the frictional drag (up to %). To reference this document use: http://resolver.tudelft.nl/uuid:2be0d401-142a-4e6d-a946-a49f7648a86c DOI https://doi.org/10.1017/jfm.2023.971 ISSN 0022-1120 Source Journal of Fluid Mechanics, 977 (A32) Part of collection Institutional Repository Document type journal article Rights © 2023 Ming Yu, D. Modesti, Sergio Pirozzoli Files PDF direct_numerical_simulati ... _ducts.pdf 6.48 MB Close viewer /islandora/object/uuid:2be0d401-142a-4e6d-a946-a49f7648a86c/datastream/OBJ/view