TUFLOW 1D Channels and Hydraulic Structures: Difference between revisions

** The expansion loss (exit loss) can be explicitly handled in 2D provided the 2D cell resolution is sufficiently fine to model the expansion of flow downstream of the culvert.

** The contraction loss (entry loss), which is related to the expansion of water after the ''vena -contracta'' and forms inside at the culvert inlet, won't be picked up well and some additional energy loss (form loss) might be needed to cover this.

** Side and soffit wall friction are not modelled unless Manning's ''n'' varies with depth, i.e. increase Manning's ''n'' with depth to account for the missing Manning's ''n'' on the side and top surfaces.

** The vertical walls not only create extra friction but also straightens the flow in the direction of the wall. Thin breaklines can be used to represent these walls in 2D, but it is likely to cause saw-tooth effect if sub-grid sampling (SGS) is not used, i.e. extra numerical head loss, if there are too few cells between the walls. Sub-grid samplingSGS is recommended in this case.

** Contraction losses (entry losses) are handled better.

** Expansion losses (exit losses) are very dependent on the 2D cell resolution. A 2D cell size much larger than the culvert width will not reproduce the expansion losses very well (even with SGS) and the culvert's exit loss needs to cover this. A finer 2D cell size (several or more cells across the culvert) will reproduce the expansion losses much better and the culvert's exit loss need to be reduced to compensate it. This usually only happens for large 1D culverts with high velocities as there can be losses duplicated in the 2D on the exit side as the 2D flow expands (i.e. duplication of the exit/expansion loss). The latest release has a new feature to automatically adjust 1D culvert losses based on the 2D approach/departure velocities as what happens with a 1D-1D-1D arrangement. See this <u>[https://downloads.tuflow.com/_archive/Publications/Modelling%20of%20Bends%20and%20Hydraulic%20Structures%20in%20a%202D%20Scheme,%20Syme,%202001.pdf paper]</u> for more information.

** HX connections may cause instability, especially with a skewed culvert outlet, but can be demonstrated to produce better velocity patterns downstream of the culvert to model the expansion losses, which will be occurring in the 2D domain.