Sebastian Schwindt

Numerical Modelling Of Plunge Pool Scour Evolution In Non-Cohesive Sediments

Abstract Turbulences in liquids caused by jets can be of interest for numerous applications. For one, it concerns flood spillway structures within civil engineering but also is key in any area where turbulent mixing is present. The numerical simulations of jets that impinge into plunge pools are still in an early phase of their development. This paper verifies the accuracy of the Flow-3D software package in regards to simulating 3D scouring processes generated by turbulent water jets impinging on a sediment bed. Scour calculations are performed based on previously examined laboratory experiments. The results of the numerical model compare well with the experimental results in terms of the scour depth and the ridge height which accumulates downstream of the scour hole. The impact angle of the jet is identified as a driving parameter for the establishment of steady state conditions of scour depth and ridge height.

Effects of Lateral and Vertical Constrictions on Flow in Rough Steep Channels with Bedload

AbstractTwo-phase flows occurring at flow constrictions such as bridges or open sediment check dams are complex, especially for steep rivers with bedload transport. Dangerous bedload deposition and...

Bottom slope influence on flow and bedload transfer through contractions

ABSTRACT In-stream open check dams are essential for flood protection at mountain rivers that are characterized by steep slopes (>1%) and sediment-laden flood discharges. These structures comprise an opening acting as a lateral or vertical flow contraction to force sediment retention when floods occur. Otherwise, the contraction should not affect the run-off. Design criteria for the discharge capacity referring to the size and geometry of the opening were previously established. This experimental study reviews the existing formulae for the discharge capacity and analyses the beginning of sediment deposition, with varying channel slopes. The effects of the channel slope on backwater, sediment deposition and local head losses are relevant when free surface flow conditions persist in the opening. A channel slope-sensitive correction factor is introduced for calculating the discharge capacity. The sediment transfer rate through the contraction decreases with increasing backwater and is most sensitive for trans-critical flow conditions. The findings are validated against a case study in the Swiss Alps.

The influence of the opening width of check dams on bedload continuity of mountain rivers

The design of open check dams at mountain rivers for flood protection has an essential impact on the sediment budget of downstream river reaches. A key issue is the bedload transfer hindering and retention which can be influenced by the geometry of the openings of check dams. Contemporary design concepts provoke the retention of too much or insufficient bedload with regard to the downstream transport capacity. This dysfunction can cause continuous maintenance works or endanger downstream infrastructures, respectively. Herein an experimental analysis of the influence of check dam openings on the bedload transport capacity is made as a function of the constriction ratio of the opening width and the mean width of the undisturbed channel. Constriction ratios of more than 0.9 have no significant influence on the bedload transport capacity, while constriction ratios of less than about 1/3 block every grain larger than 1/40 of the channel width.

Psamathe – Alternatives Konzept der Entsanderspülung

Die vollstandige Spulung von Dufour-Sandfangen geht einher mit erheblichen Verlusten des Triebwassers, wodurch der Anlagenertrag geschmalert wird. Die Effizienz eines neuartigen Spulsystems wird durch numerische Simulationen anhand einer Fallstudie eines Dufour-Sandfangs bewiesen. Das System ermoglicht gleichmasige Geschwindigkeitsverteilungen entlang des Spulkanals im Bereich einer ausreichenden Sedimenttransportkapazitat, im Gegensatz zu bestehenden Systemen, die erst im letzten Drittel des Spulkanals ausreichende Fliesgeschwindigkeiten erreichen.