Numerical and Experimental Investigation of Flow in Partially Filled Sewer Pipes

Complex phenomena in wastewater systems, such as flow pattern in sewers and sediment transport could be investigated in detail using computational fluid dynamics (CFD). However, it is not easy to find an appropriate CFD model for a specific problem. This paper aims to develop and validate a CFD model to correctly predict the free-surface turbulent flow passing through a circular pipe.  In this study, the multiphase model Volume of Fluid (VOF) of the software Ansys-Fluent was used to capture the interface between air and water. Different variants of the k-ε turbulence model of the RANS group and meshing approaches were investigated. To validate the CFD model, a set-up of an acryl-glass pipe in a closed system was constructed under laboratory conditions. The centre-plane velocity profile was used to compare the CFD model results and Laser Doppler Velocimetry (LDV) measurements. Furthermore, the values of the average velocity and shear stress from the experiments were compared to the results of the CFD model. The best results were obtained using a Cutcell mesh combined with the RNG k-ε turbulence model. The validated model was used to investigate the influence of the bed roughness on the velocity and shear stress distribution in partially filled pipes. The velocity decreases while increasing the bed roughness, however the shear stress becomes greater over a rough bed than over a smooth bed

Smoothed Particle Hydrodynamics for Navier-Stokes Fluid Flow Application

The aim of this publication is to introduce the particle based computational fluid dynamics (CFD) method smoothed particle hydrodynamics (SPH) and introduce an applicable and valid SPH implementation for practical cases. For this purpose, current research approaches are combined regarding performance and numerical stability.  The principles of the method, the mathematical basics and the discretization of the Navier-Stokes equations are clarified. Furthermore, the implementation of method-specific boundary conditions, wall, inlet and outlet, as well as several correction procedures and a surface tension setup into the present code framework are described. The advantages and validity of the method are shown based on different cases. The free surface fluid behavior of a dam break is compared to experimental data of the time dependent water level of selected positions. A Karman vortex street is validated by its Strouhal number for different Reynolds numbers. The frequency of an oscillating drop is analysed and compared to the analytical solution.  The SPH is utilized for pipe flows influenced by a backward facing step and shows an expected qualitative flow field

Cavitation in Single-Vane Sewage Pumps

Chair fluidsystemdynamics at TU Berlin investigated the cavitation behavior of a full-size single-vane sewage pump. Single-vane pumps are used for raw sewage with high content of dirt and sediments in larger sewage pumping stations. Cavitation measurement was done by using standard NPSH3% and the more sensitive incipient cavitation NPSHIC. Also, vibration and noise where observed. Contrary to very low NPSH3% values, very high NPSHIC values were measured. In a second step, the impeller was modified with special cavitation bores to reduce the cavitation effects. The NPSH3% values increased with cavitation bores, which underlines that this value is not a sufficient criteria describing cavitation. Using the much more sensitive NPSHIC, a significant reduction was obtained. Moreover, the cavitation formation was changed from a relative concentrated cloud to a distributed bubble form, which is much less aggressive in view of noise and erosion. Operational behavior improved with cavitation bores, noise and vibration levels especially came down to acceptable level. Practical experience demonstrates also avoidance of cavitation erosion

Impact of Interface Model on Simulation Results of a Radial Pump at Part Load and Shut-Off Conditions

Computational Fluid Dynamics (CFD) is a well-known tool for predicting and analyzing performance in a variety of engineering branches, including turbomachinery, allowing engineers to partially replace physical experiments with their virtual analog. Nevertheless, numerical analysis should be used carefully regarding possible deviation between simulated and experimental results due to multiple reasons (including but not limited to applied simplifications in the numerical model). These deviations usually have their minima close to the Best Efficiency Point (BEP). The paper deals with analyzing the outcome of steady-state simulations for a radial pump at strong part load and shut-off conditions by switching between three simulation types (steady-state with mixing plane, steady-state with frozen rotor, transient with sliding mesh). A comparison of velocity profiles on the interface surfaces is made, showing how the chosen interface model affects the structures being formed at part load conditions. These effects show particular impact on performance parameters (first of all, head production), which is discussed in the paper. The information provided could be helpful for adjusting the simulation parameters and finding an appropriate compromise between simulation reliability and demand for computational time thereby

zur Erlangung des akademischen Grades

of conducting the dissertation and scientific freedom I have been granted. I am grateful for being part of the Ocean Engineering Group. For further support and taking interest in this work many thanks as well go to the second promoter, Prof. Dr.-Ing. Thamsen and the chair doctoral comity Prof. Dr.-Ing. Holbach. Many thanks go to my colleagues and the staff of the Ocean Engineering Group of the TU-Berlin for great teamwork, vivid discussions, and the great time I have had during the years. Namely, I wish to thank Marco Klein and Dr. Robert Stück and Matthias Dudek for the great cooperation, as well as André Kauffeldt, Sascha Kosleck, Nils Otten, Daniel Testa and Kornelia Tietze. Dr. Janou Hennig and Dr. Christian Schmittner I which to thank for the comments and the encouragement as well as Prof. Guedes Soares and Prof. Molin for valuable advice. Most importantly, I thank my dear wife Mahboubeh and my parents for their everlasting patience and support. i