Franz Nestmann

Determination of the drag coefficients of emergent and just submerged willows

This paper presents results regarding the flow resistance and the drag coefficient of floodplain vegetation. According to the literature review, most of the investigations concerning the interaction between flow and woody vegetation are based on laboratory experiments where the vegetation is idealized with a high level of abstraction. However, the vegetations resistance behaviour depends on many natural parameters, such as the flexural rigidity, the manner of contraction in the current, the degree of foliation and the vibration behaviour. Furthermore the varying shape of the vegetation elements due to the current forces has to be observed. The drag coefficients of three kinds of willow species depending on the flow conditions and the effect of the plants flexibility and foliation on the projected plant area and thus on the drag coefficient are presented in this paper. The results show that it is very important to distinguish between leafy and leafless condition as the drag coefficient is a result of different physical effects.

From intermittent to continuous water distribution: a proposed conceptual approach and a case study of Béni Abbès (Algeria)

Centralised water distribution systems in developing countries currently are operated intermittently to a very large extent. As a consequence of the numerous negative impacts associated with intermittent water distribution, functioning water supplies in the long run absolutely require the introduction of a continuous mode of water distribution. This article presents a conceptual approach to the successive introduction of a continuous water distribution. The approach is based on existing systems originally designed for continuous distribution but currently run in the intermittent mode. The focus is on the difficulties in planning and implementing the complex processes of database organisation, restructuring and changing the mode of operation, which are harmonised in a comprehensive process. The approach is explained for the case of the water distribution system in Béni Abbès, Algeria.

Numerische und physikalische Modelluntersuchungen für ein innovatives Fischaufstiegskonzept am Ruhrwehr Baldeney@@@Numerical and Physical Model Studies for an Innovative Fish Pass Concept at the Weir Baldeney (Ruhr)@@@Цифровые и физические модели исследований для разработки инновационной концепции рыбоподъемного сооружения на рурской плотине Бальденей (Baldeney)

Im Auftrag des Ruhrverbandes und gefördert durch das Land NRW wird derzeit am Standort Baldeney ein innovatives Fischliftsystem entwickelt, welches der aquatischen Fauna die Überwindung des Stauwehres ermöglichen soll. Die Positionierung dieser Fischaufstiegsanlage sowie die geometrische Ausgestaltung der Anlagenperipherie basieren auf umfangreichen Voruntersuchungen im Rahmen eines iterativen Optimierungsprozesses. Aufgrund der komplexen hydraulischen Randbedingungen sowie der hohen schökologischen Anforderungen kam ein hybrides Untersuchungskonzept zum Einsatz basierend auf detaillierten 3-D-Strömungssimulationen in Verbindung mit physikalischen (gegenständlichen) Modellversuchen sowie ethohydraulischen Tests. Im vorliegenden Beitrag werden schwerpunktmäßig die eingesetzten numerischen Methoden vorgestellt und in Bezug auf ihre Prognosefähigkeit diskutiert.

Applications of CFD in Hydraulics and River Engineering

In this paper, various applications and developments of CFD technology in hydraulics and river engineering are presented. Numerical studies of three-dimensional turbulent flow fields in open channels and rivers are carried out by CFD packages such as the finite element code FIDAP and finite volume code COMET. Meshing procedures are implemented by GAMBIT or CFD-GEOM. To calculate the position of the free surface two methods are applied, free surface tracking and volume-of-fluid, and some comparisons of these methods are discussed.

Three-dimensional computation of turbulent flow in meandering channels and rivers

In this paper, a three–dimensional (3D) numerical model for the computation of turbulent meandering flow is developed. A finite element calculation procedure combined with the two–equation k–ε and mixing length model are applied to the problem of simulating the 3D turbulent flow in closed and open curved channels. Near the wall a special approach is applied in order to overcome the weakness of the standard k–ε model in the viscous sub–layer. A special shape function is used in the near wall elements to accurately describe the strong variations of the mean flow variables in the viscosity–affected near wall region. At the free surface, a moving boundary condition combined with the surface tracking procedure is applied to determine the position of the free surface. Eventually, in order to solve a large nonlinear equation system, which is obtained from the discretization of the continuity and momentum equations, a segregated approach is applied. The segregated solver is guaranteed to have substantially reduced disk storage in comparison with a fully coupled solver.

Untersuchungsmethodik zur Systemoptimierung von Sonderbauweisen am Beispiel Baldeney@@@Research Methodology for System Optimization of Special Constructions Methods for Fish Passages, Case Study Baldeney@@@Методика исследования для оптимизации системы специальных методов строительства на примере плотины Бальденей (Baldeney)

Die oftmals unterschiedlichen geometrischen und hydraulischen Randbedingungen an den verschiedenen Standorten von Fischaufstiegsanlagen führen dazu, dass in der Planungspraxis die vorhandenen Richtlinien und Regelwerke nicht immer angewandt werden können und stattdessen Sonderbauweisen zum Einsatz kommen. Dies kann sich z. B. auf die Ausgestaltung von Umlenkbecken oder aber auch auf innovative Wanderhilfen z. B. in Form von Fischaufzügen oder ähnlichen Bauwerken, beziehen. Am Ruhrwehr Baldeney nahe Essen soll eine solche Sonderbauweise in Form eines innovativen Fischliftsystems zur Herstellung der ökologischen Durchgängigkeit errichtet werden. Der Nachweis der Funktionsfähigkeit wurde im Rahmen eines Untersuchungsprogramms am Institut für Wasser und Gewässerentwicklung des KIT erbracht, bei dem neben den klassischen physikalischen und numerischen Modellen auch ethohydraulische Tests zum Einsatz kamen. Mit dieser Vorgehensweise kann aus Sicht des IWG die im DWA-Merkblatt M 509 geforderte Qualitätssicherung zur Gewährleistung einer optimalen Funktion schon während der Planungsphase entsprochen werden.

Settling behavior of fine-grained materials in flocs

This paper contributes to the understanding of the effect of suspended sediment deposition and turbidity on aquatic systems. The influence of the cohesive properties of clay on its settling behaviour was quantified in still distilled water with ion addition. Two different model materials, alumina and quartz, were used, as their identical presentation in the mineral composition of clay affects the flocculation of suspended fine particles. The suspended concentrations were measured in a 1m settling column using a CCD Camera. The settling rates of alumina and quartz increased with salinity, with the settling rates for alumina being higher than those for quartz at any given salinity. The settling velocities for alumina were higher at pH 9, whereas the opposite was true for quartz. Conversely, the settling velocities for quartz were higher at pH 4, while the velocities for alumina were then low.

EXPERIMENTAL AND COMPUTATIONAL STUDIES OF THE EFFECT OF 'CASING EYE RIB' ON THE SWIRL FLOW AT THE EXIT OF A PUMP AS TURBINE

This paper presents a detailed hydraulic analysis of the effects of the casing eye rib on a pump operating as a turbine. It describes a flow-zone approach within a pump as turbine and lays out the build up for the experimental and numerical techniques applied. The pump as turbine exhibits very good characteristics with a maximum operating efficiency over 82%. The similitude between experimental and numerical results has been satisfactory. The two stages namely the ‘casing rib present’ and the ‘casing rib absent’ stage are compared at 6 different load points encompassing the entire characteristics. Both methods reveal that the performance of the PAT has enhanced without the presence of the rib. However the two methods show different causes for this behaviour. The comparison of the swirl profiles reveal that the fluid in the ‘casing rib absent’ stage has greater rotational momentum in the part-load and overload region compared to the ‘casing rib present’ stage. However the ‘casing rib absent stage’ displays more symmetric swirl profiles. At the end of the paper, an uncertainly analysis for the experimental efficiency is carried out.Copyright

Bed load transport modeling of a secondary flow influenced curved channel with 2D and 3D numerical models

Due to the complex physical interactions that affect the flow processes in curved channel sections, measuring and simulating the morphological processes has been the object of scientific studies for quite a long time. The occurring secondary flow exerts a major influence on bed formation and on bed load transport in channel bends. To analyze these effects, numerical simulations of a meandering laboratory channel were performed by means of the open-source Telemac–Sisyphe program system. The study focuses on the importance of two-dimensional (2D) or three-dimensional (3D) approaches for the flow simulation underlying the morphological investigations. Hence, the numerical studies were performed in a 2D and 3D model and the morphological development was analyzed. The differentiated model studies showed local differences in the morphological results as a consequence of the different spatial resolution of flow modeling. The 3D model provided an improved description of the situation observed in the laboratory especially in the regions of development and decay of secondary flow. Regarding the maximum sedimentation and erosion as well as the bed development tendencies within the whole model area, the 2D and 3D model determine the laboratory observations.

Hybride Modelluntersuchungen zum Ein- und Auslaufbauwerk im Unterbecken des Pumpspeicherwerks Atdorf

Die Schluchseewerk AG plant den Bau des größten Pumpspeicherwerks (PSW) in Deutschland. Am Institut für Wasser und Gewässerentwicklung in Karlsruhe wurden hybride wasserbauliche Untersuchungen zur Optimierung des Einund Auslaufbauwerks im Unterbecken durchgeführt. Dabei wurden umfangreiche Vergleiche zwischen dem numerischen und dem physikalischen Modell angestellt sowie die Modellübertragbarkeit vom Modellmaßstab in den Naturmaßstab untersucht. Als Ergebnis konnte ein Bauwerksentwurf gestaltet werden, der sowohl über geringe Abmessungen als auch über gute Strömungseigenschaften verfügt.