Structural intrusion, flow disturbance and spillway capacity – CFD modeling

Stockholm (Solna)
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In the intake to the spillway in Torpshammar, there exist two horizontal beams as a measure to stabilize the spillway sidewalls. They intrude in the spillway flow and give rise to disturbance and possible vortex shedding. The discharge capacity is also reduced. Due to measurement difficulties, it is not possible to quantify their effects in the physical model. 3D CFD simulations are undertaken to examine the flow features of the spillway. The main purpose is to understand the flow pattern with the beams and evaluate their effect on the spillway discharge capacity with and without them. Comparisons are made with hydraulic model tests. The flow cases include (1) two bottom outlets, (2) two overflow gates and (3) their combination.
In Älvkarleby, a physical hydraulic model of Torpshammar is now built, including the reservoir, the spillway and the channel downstream, se the figure below. The main purpose of the model study is to twofold, i.e. to determine the spillway discharge capacity and to examine the energy dissipation in the tailwater. The spillway structure is composed of two bottom outlets and two gated overflow openings.
In the flow direction, the spillway gates are located in the middle of the dam body. On each side, the intake to the spillway is surrounded by a sidewall holding the embankment dam. Its length is approximately 26 m. Undesirable displacements are a matter of concern for the long-term stability of the walls. To prevent this, there are two horizontal beams constructed between the sidewalls that take up the sideward loads from the embankments and keep the walls in place, se the figure below.
The reservoir bottom has el. +167.0 m and the normal reservoir water level is at el. 185.6 m. The upper edges of the beams have el. +176.75 m, implying that they are roughly in the mid position of the water depth.
The two beams intrude obviously in the approach flow. The flow velocity between the sidewalls cannot be neglected. This means that the approach flow is always disturbed whether one gate operates or more gates are combined. The spillway discharge capacity is affected. One even suspects that the beams give rise to vortex shedding (oscillating flow) and flow unsteadiness exists.
It is not common that two beams appear in the waterway and intrude in the flow. One would like to know their effect on the flow and understand potential consequences in terms of flow oscillations and discharge capacity. It is practically difficult to document the flow pattern in the model to be built (e.g. with PIV). The accuracy of a flow measurement is normally 2‒5% in a physical model. The effect of the beams might have the same order of magnitude. CFD is considered as a suitable tool to understand and clarify such issues.
The purposes of the study include the following aspects.
▪ To model the flow and discharge capacity without the beams
▪ To reproduce the flow with the beams and examine the discharge
▪ To make comparison with the model testing results
▪ To clarify the differences between the two layouts
For the students
▪ To get familiar with the on-going work with dam safety and dam upgrade projects in the country
▪ To learn about hydraulic model tests
▪ To learn the fundamental knowledge of CFD modelling, including grid generation, grid convergence, model set-up, boundary conditions and numerical convergence
▪ To get familiar with turbulence models including a two-phase water-air flow model
▪ To understand flow phenomena in both overflow spillway and bottom outlet
The project consists of the following aspects.
1. background and literature review
2. Data collection of the spillway and flow data
3. Learning of the use of the Fluent program
4. Based on the spillway geometry, generate 3D models for the waterway
5. Model setup with phase properties and boundary conditions
6. Modelling and
7. Result analyses
8. Comparison with model test results
9. Report writing
The modelling domain starts from the reservoir and terminates at a proper location downstream of the gates.
The project is to be completed within 4 months during 2018, ending up with a report by the diploma work student(s).
✓ The project corresponds to a 30 hp diploma work
✓ It is performed with CFD license (Fluent or CFX), in the first place at KTH
✓ Proper background is civil engineering, engineering physics or similar.
✓ Knowledge of CFD modelling experiences is preferred
✓ Gratitude is paid upon completion.
Your application should contain
1. A cover letter with motivation why you apply for the project
2. List of courses
3. CV with contact information
4. Name of your examiner and contact information
The diploma work is to be carried out at KTH, with professor James Yang as supervisor (KTH Division of Resources, Energy and Infrastructure, Teknikringen 10B, 5th floor),
Potential candidates should directly send in their applications to, phone 070-2723 200. Incomplete applications are not handled. The application is closed April 30, 2018.
Applications are processed on a running basis and the vacancy is filled as long a suitable candidate is found. This is the reason why you should not wait to the deadline to apply. Make up your mind and send in your application now if you are interested.