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Experiments are conducted in a Ø600 mm tank to analyse the 3D motion of buoyant particles in the free-surface vortex flow. The experiments revealed two stages in the particle motion: stage 1 is the helical motion along the vortex air core and stage 2 is the axial motion inside the vortex core. The stage 1 motion is sensitive to the particle’s initial conditions by showing a chaotic behaviour and quantified by determining the largest Lyapunov exponent. Consequently, the predictability (forecast horizon) of the particle’s motion is limited. A motion parameter is proposed that indicates if a continuous downward motion along the air core occurs. The dynamics in the stage 2 motion is determined by the imbalance between the particle’s buoyancy force and fluid drag force. The drag appears to be determined by the Taylor column drag force as present in rotating fluids. Based on this force, a motion condition is proposed that indicates if axial motion inside the vortex core occurs., Sanitary Engineering

Experiments are conducted in a Ø600 mm tank to analyse the 3D motion of buoyant particles in the free-surface vortex flow. The experiments revealed two stages in the particle motion: stage 1 is the helical motion along the vortex air core and stage 2 is the axial motion inside the vortex core. The stage 1 motion is sensitive to the particle’s initial conditions by showing a chaotic behaviour and quantified by determining the largest Lyapunov exponent. Consequently, the predictability (forecast horizon) of the particle’s motion is limited. A motion parameter is proposed that indicates if a continuous downward motion along the air core occurs. The dynamics in the stage 2 motion is determined by the imbalance between the particle’s buoyancy force and fluid drag force. The drag appears to be determined by the Taylor column drag force as present in rotating fluids. Based on this force, a motion condition is proposed that indicates if axial motion inside the vortex core occurs., Sanitary Engineering

This is an experimental and theoretical research on the motion of buoyant particles in the flow of a free-surface vortex at moderate to high particle Reynolds numbers., Sanitary Engineering

In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers’ assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers’ model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence., Sanitary Engineering, Fluid Mechanics

This is an experimental and theoretical research on the motion of buoyant particles in the flow of a free-surface vortex at moderate to high particle Reynolds numbers., Sanitary Engineering

In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers’ assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers’ model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence., Sanitary Engineering, Fluid Mechanics

The accumulation of FOG (Fat, Oil and Grease) deposits in sewer pumping stations results in an increase in maintenance costs, malfunctioning of pumps and, a potential increase of wastewater spills in receiving open water bodies. It is thought that a variety of parameters (e.g. geometry of the pump sump, pump operation, socioeconomic parameters of the catchment) influences the built-up of FOG. Based on a database containing data of 126 pumping stations located in five Dutch municipalities a statistical model was built. It is shown that 3 parameters are most significant in explaining the occurrence of FOG deposits: mean income of the population in a catchment, the amount of energy (kinetic and potential) per m3 per day and the density of restaurants, bars and hotels in a catchment. Further it is shown that there are significant differences between municipalities that can be traced back to the local ‘design paradigm’. For example, in Amsterdam, the design philosophy of discharging in the pump sump under the water surface (and hence maintaining a low level of turbulence in the pump sump) results in an increase of the probability of the formation of FOG., Sanitary Engineering

The accumulation of FOG (Fat, Oil and Grease) deposits in sewer pumping stations results in an increase in maintenance costs, malfunctioning of pumps and, a potential increase of wastewater spills in receiving open water bodies. It is thought that a variety of parameters (e.g. geometry of the pump sump, pump operation, socioeconomic parameters of the catchment) influences the built-up of FOG. Based on a database containing data of 126 pumping stations located in five Dutch municipalities a statistical model was built. It is shown that 3 parameters are most significant in explaining the occurrence of FOG deposits: mean income of the population in a catchment, the amount of energy (kinetic and potential) per m3 per day and the density of restaurants, bars and hotels in a catchment. Further it is shown that there are significant differences between municipalities that can be traced back to the local ‘design paradigm’. For example, in Amsterdam, the design philosophy of discharging in the pump sump under the water surface (and hence maintaining a low level of turbulence in the pump sump) results in an increase of the probability of the formation of FOG., Sanitary Engineering

Wastewater pumping stations can experience problems due the presence of floating particles of solidified fat and grease. To transport this debris, the ability of free-surface vortices as transport mechanism is investigated. An experimental set-up is developed where the behaviour of large particles (0.02 - 0.04 m) in the vortex flow are analysed. An 3D-particle tracking method based of 6 iPhone® cameras was used to record the position of the particles in the vortex. Based on the measured particle acceleration, the hydrodynamic forces on the particle are derived. This novel 3D-PTV method was found to generate consistent information on the movement of the particles in the vortex flow field., Sanitary Engineering

Wastewater pumping stations can experience problems due the presence of floating particles of solidified fat and grease. To transport this debris, the ability of free-surface vortices as transport mechanism is investigated. An experimental set-up is developed where the behaviour of large particles (0.02 - 0.04 m) in the vortex flow are analysed. An 3D-particle tracking method based of 6 iPhone® cameras was used to record the position of the particles in the vortex. Based on the measured particle acceleration, the hydrodynamic forces on the particle are derived. This novel 3D-PTV method was found to generate consistent information on the movement of the particles in the vortex flow field., Sanitary Engineering

Sumps of wastewater pumping station can experience problems due the formation of (solid) floating layers of fat and scum as a result of insufficient current guidelines for sump design with respect to transport of floating debris. To complimentary the guidelines, the use of free-surface vortices is defined as a potential transport mechanism for floating debris. The transport ability and capacity of vortices is investigated in an experimental set-up and experimental data will be used to design and validate a theoretical vortex transport model describing the transport ability and capacity of a free-surface vortex. Two theoretical vortex models describing the vortex flow field are used as a base for the transport model. Experimental results show that both models needs adaptation to match experimental results. Furthermore, the experiments show that the ability to transport buoyant material is highly sensitive on the flow field in the vortex (core) and on the particle density. Particles can either get stuck in the vortex core with no or less transport or either translated around the core with efficient transport. Before designing and validating the vortex transport model, extensive future research is needed to capture the observed phenomena’s., Sanitary Engineering

Sumps of wastewater pumping station can experience problems due the formation of (solid) floating layers of fat and scum as a result of insufficient current guidelines for sump design with respect to transport of floating debris. To complimentary the guidelines, the use of free-surface vortices is defined as a potential transport mechanism for floating debris. The transport ability and capacity of vortices is investigated in an experimental set-up and experimental data will be used to design and validate a theoretical vortex transport model describing the transport ability and capacity of a free-surface vortex. Two theoretical vortex models describing the vortex flow field are used as a base for the transport model. Experimental results show that both models needs adaptation to match experimental results. Furthermore, the experiments show that the ability to transport buoyant material is highly sensitive on the flow field in the vortex (core) and on the particle density. Particles can either get stuck in the vortex core with no or less transport or either translated around the core with efficient transport. Before designing and validating the vortex transport model, extensive future research is needed to capture the observed phenomena’s., Sanitary Engineering

Nowadays flooding because of a dike breach can be simulated with high accuracy by use of computer models. Delft FLS, which stands for DELFT Flooding System, developed by WL - Delft Hydraulics, is such a model. The hydrodynamic processes occurring during a flooding are complex, for example moving hydraulic jumps and propagating bores. The implementation of the hydrodynamic laws in the computer model must be done correctly to be able to calculate these processes accurately. To verify the accuracy of the model an experiment was developed and executed in which these hydrodynamic processes occurred. The experimental results were compared with the numerical results to allow statements about the accuracy of the model. The experiment concerned the flooding of a basin of 8 m by 23 m. When a gate was lifted a reservoir emptied into the basin, which was thereby flooded. Three experiments were executed, two with different initial water layers in the basin and one with an initially dry basin. A video camera above the basin recorded the development of the flooding in the horizontal plane. The water depths were registered with wave gauges. The first numerical results seemed to agree reasonably well with the experimental data. However the calculated lateral flow velocity was too high. The dike-break is modelled in the computer program as a linear in time decreasing height of a dam. A numerical momentum conservative method is normally used in Delft FLS to calculate the flow through the breach. In the experiment a lifted gate represented the dike-break. The flow could not be calculated with the momentum conservative method because of a loss of momentum due to a force against the gate. An energy conservative numerical method is needed to calculate the flow. After applying the energy conservative numerical method the calculated results agreed very well with the experimental results. Verification of the computer model Delft FLS showed that the numerical methods used in the computation c, Environmental Fluid Dynamics, Hydraulic Engineering, Civil Engineering and Geosciences

Nowadays flooding because of a dike breach can be simulated with high accuracy by use of computer models. Delft FLS, which stands for DELFT Flooding System, developed by WL - Delft Hydraulics, is such a model. The hydrodynamic processes occurring during a flooding are complex, for example moving hydraulic jumps and propagating bores. The implementation of the hydrodynamic laws in the computer model must be done correctly to be able to calculate these processes accurately. To verify the accuracy of the model an experiment was developed and executed in which these hydrodynamic processes occurred. The experimental results were compared with the numerical results to allow statements about the accuracy of the model. The experiment concerned the flooding of a basin of 8 m by 23 m. When a gate was lifted a reservoir emptied into the basin, which was thereby flooded. Three experiments were executed, two with different initial water layers in the basin and one with an initially dry basin. A video camera above the basin recorded the development of the flooding in the horizontal plane. The water depths were registered with wave gauges. The first numerical results seemed to agree reasonably well with the experimental data. However the calculated lateral flow velocity was too high. The dike-break is modelled in the computer program as a linear in time decreasing height of a dam. A numerical momentum conservative method is normally used in Delft FLS to calculate the flow through the breach. In the experiment a lifted gate represented the dike-break. The flow could not be calculated with the momentum conservative method because of a loss of momentum due to a force against the gate. An energy conservative numerical method is needed to calculate the flow. After applying the energy conservative numerical method the calculated results agreed very well with the experimental results. Verification of the computer model Delft FLS showed that the numerical methods used in the computation c, Environmental Fluid Dynamics, Hydraulic Engineering, Civil Engineering and Geosciences