Implementierung eines schräg angeströmten Rechens in die 3D-numerische Berechnung mit FLOW-3D

Abstract

Zusammenfassung In den letzten Jahren hielt vermehrt die dreidimensionale (3D-)numerische Strömungssimulation im Bereich der Grundlagenforschung und der Planung von hydraulischen Anlagen Einzug. Rechen im Bereich von Kraftwerkseinläufen stellen jedoch für die numerische Simulation eine besondere Herausforderung dar. Dies ist der, im Vergleich zu anderen Bauteilen, kleinteiligen Rechenstabgeometrie geschuldet. Als alternativer Lösungsansatz zur Modellierung der Rechenverluste in der Software FLOW-3D bietet sich als Flächenobjekt eine Baffle an. Der Beitrag baut auf den Erkenntnissen von Waldy et al. (Österreichische Wasser-und Abfallwirtschaft 67:1-2, 2015) auf, welcher unterschiedliche Konzepte zur vereinfachten Modellierung der Verluste an Rechen untersucht hat. Dabei zeigt sich, dass die Verwendung einer Baffle als erfolgversprechende Variante gesehen werden kann. Diese Vergleiche erfolgten jedoch unter der Einschränkung eines gerade angeströmten Rechens, bei dem die Netzausrichtung immer in der Rechenebene lag. Der aktuelle Beitrag befasst sich mit der Modellierung der Rechenverluste mithilfe einer Baffle am schräg gestellten Rechen und erweitert somit den Beitrag Waldy et al. (Österreichische Wasser-und Abfallwirtschaft 67:1-2, 2015). Implementation of an angled trash rack in the 3D-numerical simulation with FLOW-3D Summary Over the last years, scientists and engineers have used more and more 3D-numerical flow simulations for basic research and the planning of hydraulic constructions. However, trash racks in front of the intakes of hydroelectric power plants represent a particular problem for numerical simulations. The reason for this is the especially fragmented geometry of the trash rack bars in comparison to other construction elements. As an alternative approach to include trash rack losses into a 3Dnumerical simulation with FLOW-3D a baffle can be used. Waldy et al. (Österreichische Wasser-und Abfallwirtschaft 67:1-2, 2015) demonstrated that such a baffle is a promising method to model the losses at trash racks. These comparisons of different concepts were limited to a vertical trash rack, which had its grid orientation along the computational plane. The actual paper focuses on the modelling of the trash rack losses by means of a baffle at an angled trash rack and thus upgrades the survey of Waldy et al. (Österreichische Wasser-und Abfallwirtschaft 67:1-2, 2015).

Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables

“…An attempt was made to estimate the head loss of both rack options by applying the methods according Equation 5provided by Kirschmer [20] and Equation (6) modified by Meusburger [18]. Both methods are developed for vertical (inclined) rack types and it is known that the approaching velocity at the inclined trash rack can change significantly over the cross section with a peak at the far end of the inclined structure [25,33]. Nevertheless, it was assumed that the vertical inclination β of Equation (5) and Equation (6) can be replaced by the horizontal angle α.…”

Determining the Flow Resistance of Racks and the Resulting Flow Dynamics in the Channel by Using the Saint-Venant Equations

“…Admittedly, the flow in the channel section, where the rack is installed, can be studied in more detail with 2D or 3D computational models [5,12,17,18,47]. By automatically considering lateral and vertical flow components, seminal insights into the turbulent flow around the bars or ethohydraulic effects [12,13] can be elaborated.…”

“…Furthermore, new designs and optimisation of racks have been keeping research and development activities going. Using sophisticated measurements techniques [15,31,[42][43][44][45][46] and computational fluid dynamics simulations [5,17,18,47] served to better understand the flow conditions, especially for studying partially blocked trash racks and conducting ethohydraulic investigations [12][13][14]45,46]. Some references offer specific empirical equations, tables, or graphs to determine the depth difference or hydraulic head loss depending on a vast range of rack configurations [1,36,48,49].…”

“…Computational models can be used to overcome the requirement of empirical equations since the flow is usually simulated based on differential equations. Although recent studies utilised computational models to study racks [12,13,[17][18][19], the workflow with 2D and 3D simulations is commonly too laborious and time-consuming to serve as a suitable design tool in everyday engineering practice.…”