Mario Oertel

Initial stage of two-dimensional dam-break waves: laboratory versus VOF

Since several decades, dam-break waves have been of main research interest. Mathematical approaches have been developed by analytical, physical and numerical models within the past 120 years. During the past 10 years, the number of research investigations has increased due to improved measurement techniques as well as significantly increased computer memories and performances. In this context, the present research deals with the initial stage of two-dimensional dam-break waves by comparing physical and numerical model results as well as analytical approaches. High-speed images and resulting particle image velocimetry calculations are thereby compared with the numerical volume-of-fluid (VOF) method, included in the commercial code FLOW-3D. Wave profiles and drag forces on placed obstacles are analysed in detail. Generally, a good agreement between the laboratory and VOF results is found.

Vertical Slot Fishway: Evaluation of numerical model quality

Numerical modeling is being used with increasing frequency to analyze and design complex hydraulic structures. Especially structures where a standard design or an analytic calculation isn’t applicable, numerical investigations can provide important knowledge of flow parameters. During the past several decades, a number of research investigations have been conducted regarding fish passage structures. However, additional insights are still needed. Vertical Slot Fishways (VSF) have shown a range of applications that are well documented. In particular, these fish passage structures are well suited for slopes less than 5 %, which is needed for most fishes in Europe. Numerical modeling can provide a cost-effective tool to investigate flow on VSF. The present paper deals with an investigation on quality components of numerical 3D simulation of VSF. Four pools constructed as standard design are modeled and examined. A Large-eddy simulation, second order, with three various mesh resolutions was used. Comparison of flow depths showed that a mesh width of 4 cm is sufficient for practical use. The effect of mesh size on velocity distribution was more significant: with a mesh width of 2 cm no convergence could be reached.

Sensitivity Analysis for Discharge Coefficients of Piano Key Weirs

Piano Key Weirs are relatively new weir structures that can be used as a flood release structure at the top of a dam or as a regular weir structure within a river system. The benefit of a PKW is an increased discharge capacity and, hence, lower free surface heads at the upstream reservoir. During the last few years, several experimental and numerical research investigations were carried out to analyze discharge coefficients for various PKW types. Therefore, numerical 3D CFD codes and small-scaled experimental models were used. To identify discharge coefficients, the Poleni formula can be used. By measuring the total discharge and the weir head, discharge coefficients can be calculated. However, results will be sensitive due to the weir head because basically the total energy head includes the velocity head. Hence, the position of the measuring point for the weir head and the associated velocity head must be selected carefully. To show the variation of results for discharge coefficients due to the measurement point and measurement accuracy, a sensitivity analysis for PKW discharge coefficients is given. Measurement data were collected from experimental models at Lubeck University of Applied Sciences’ Water Research Laboratory.

Increasing Piano Key Weir Efficiency by Fractal Elements

Piano Key Weirs (PKW) are hydraulic structures which can be used for flood release systems on dams or for inchannel weir replacement. The efficiency can be increased compared to linear weirs, since the effective overfall length will be majorly increased by arranged piano keys. The present research investigation deals with experimental model results of scaled PKW models and compares resulting discharge coefficients and scale effects. One PKW geometry was manufactured with included fractal elements with the main aim to increase the structure’s efficiency. The paper includes detailed information on the investigated experimental model. The concept of the fractal PKW has a major positive effect on PKW efficiency for very low energy heads. With increasing discharges this advantage gradually decreases. Additionally, the paper focuses on future concepts and possible PKW adaptions.

Scouring Processes Downstream a Crossbar Block Ramp

Crossbar block ramps are hydraulic structures used to conquer large river bottom steps via several pool-stepsystems. Due to reduced velocities and increased flow depths, fish climbing capability can be given. Several authors have investigated crossbar block ramp variations to determine flow resistance, energy dissipation, and bed stability features on the structure. But the downstream end of the structure must also be taken into account concerning scouring processes to guarantee the structure’s stability and to reduce damage during flood events. The present paper presents a comprehensive experimental investigation program dealing with scouring processes downstream a crossbar block ramp. Influences by ramp slope, discharge, and the structure’s geometry are tested. Particularly, for larger discharges and steep slopes, massive scouring takes place. With increasing tailwater depth scouring is reduced and hence the structure’s stability is less affected.

Bemessung von Blocksteinrampen in Riegelbauweise — Hydraulik und Stabilität

Blocksteinrampen in Riegelbauweise werden zur Wiederherstellung der Durchgängigkeit der Fließgewässer benutzt und gewährleisten bei korrektem Einsatz eine Fischpassierbarkeit für zahlreiche Arten. Hierfür ist es erforderlich, sowohl bestimmte geometrische als auch hydraulische Randbedingungen einzuhalten, welche Ruhezonen vorsehen und bestimmte turbulente Verhältnisse ermöglichen. Zur Untersuchung sowohl der hydraulischen Wirksamkeit als auch der Stabilität des Bauwerks existieren nur wenige Forschungsvorhaben, die sich konsequent mit Blocksteinrampen in Riegelbauweise befassen. Die hier vorgestellten Formeln resultierend dabei aus den Ergebnissen von hydraulischen als auch numerischen Modellversuchen der vergangenen Jahre.

Numerical Modeling of Free-Surface Flows in Practical Applications

Nowadays, numerical 1-D and 2-D flow simulations represent state-of-the-art solutions in hydraulic engineering. Hence, 1-D and 2-D as well as coupled simulations are enrooted in consulting companies and used as basic tools to answer various questions from flood protection to flow optimization. An exception are 3-D flow simulations. Due to complex boundary conditions and high calculation requirements, 3-D CFD simulations are expert tools for universities and research institutions. Here, detailed simulation models, e.g. for hydraulic structure flow optimization, are built up under massive time consumption. The present chapter deals with the basics of numerical flow simulations in practical applications. Additionally, various example flow simulations are mentioned to give an impression about the development of numerical modeling in practical application for the past decade.

Artificial stationary breaking surf waves in a physical and numerical model

Surfing is one of the most popular water sports. A number of regional coastal hotspots have naturally breaking surf waves, but wave heights and breaking processes depend on various boundary conditions like seabed geometry, beach formation and swell direction. Since the optimum combination of these conditions is rare in time and place, the formation of surfable waves cannot be guaranteed. In addition, the sports popularity is currently rising even in inland regions, and with it the interest in generating artificial surf waves in rivers or technical constructions to provide surfable waves at any time and place. This research focuses on small-scale surf waves in a physical and numerical model to identify easy-to-handle geometries and to validate numerical simulations as a low-cost solution for varying boundary conditions. Breaking heights and generated tube lengths are analysed for various geometrical and hydraulic conditions to find set-ups for the creation of stationary breaking waves.