Comparative analysis of the results obtained with 3d orthogonal and non-orthogonal grids in the 3d-flow models: Part 1

Abstract

Application of orthogonal and non-orthogonal grids in numerical models of the three-dimensional flow is considered. A river confluence is chosen as an example due to strong three-dimensional flow effects occurring at the confluence and the complex bathymetry of the river bed. In addition to the type of numerical method/scheme used, the quality of the numerical simulation results depends on the choice of the computational grid, too. In contrast to orthogonal grids, the non-orthogonal ones are better aligned with the boundary. Hence, they are more suitable for discretisation of the complex flow domains such as the river confluence than the orthogonal ones. The paper aims at investigating the difference in the numerical simulation results obtained with the two types of grids. The investigation is rather qualitative than the quantitative one. The results are discussed in terms of the type of the secondary flow patterns developed in the confluence and the post-confluence channel under different flow conditions at the confluence. .

Razmatra se primena ortogonalnih i neortogonalnih mreža u modelima prostornog tečenja. Za analizu je izabrano rečno ušće, jer je na ušću tečenje izrazito prostorno, a korito ima složen oblik. Na kvalitet rezultata dobijenih numeričkim simulacijama pored pravilnog izbora numeričke metode, bitno utiče i izbor tipa računske mreže. Neortogonalna mreža se svojim oblikom bolje prilagođava čvrstoj granici od ortogonalne, pa je pogodnija za predstavljanje računskih oblasti složenog oblika kakvo je ušće. Cilj rada je da se kroz uporednu kvalitativnu analizu rezultata utvrde razlike između dva tipa računskih mreža. Poređenje rezultata je obavljeno na osnovu tipa sekundarnog strujanja koje nastaje na ušću i nizvodno od ušća pri različitim odnosima inercijalnih sila reke i pritoke. .