As part of the cloudburst water management plan for the City of Copenhagen, HOFOR will construct the Kalvebod Brygge cloudburst tunnel and pumping station. The physical model we created of the pumping station helped to optimise and validate its efficient performance, with all safety conditions in place.

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Challenge

The new Kalvebod cloudburst tunnel will be established under the central part of Copenhagen, Denmark, in order to handle extreme cloudburst rain fall events and prevent flooding in the city. A key element in the new tunnel system is the Kalvebod pumping station that will be constructed at the Copenhagen harbourfront at Kalvebod Brygge. When the tunnel reaches Kalvebod Brygge, it will be at approximately 20 m below ground level. In order to discharge the cloudburst water into the harbour via an overflow structure, the pumping station will lift the water up to ground level, and from here it will flow into the harbour.

The Kalvebod Brygge cloudburst tunnel with the pumping station on the extreme right. © HOFOR

The pumping station’s layout is based on a semi-circle geometry with the tunnel inlet in one side, and six propeller pumps with vertical column pipes and bell mouth inlets distributed around the half circle well above the inlet. The diameter of the circular pump house will be 17.5 m and the height of the pump house will be about 20 m from the bottom to the ground level at Kalvebod Brygge. The pumps will each have a rated capacity of 5.1 m3/s. With four pumps in operation at the time (and two in reserve), the total capacity will be 20.4 m3/s.

Validating the hydraulic performance
Our client Grundfos A/S will deliver the six pumps for which they have also designed the bell mouth inlet and will deliver the column pipes. Furthermore, they have also validated and optimised the electrical design of the pumping station. As part of this deliverable for the Kalvebod pumping station, Grundfos A/S has the responsibility to validate and optimise the hydraulic performance of the pumping station. For this, Grundfos A/S contacted DHI for assistance on the hydraulic assessment and physical scale model tests.

Solution

To ensure safe and efficient hydraulic function and performance under all operating conditions, the pumping station physical scale model was put through an intensive and comprehensive test campaign at the model test facilities at DHI’s headquarters in Hørsholm, Denmark. The model tests were carried out in close collaboration with our client who contributed greatly to the project development and successful execution. In addition, both HOFOR and HOFOR’s consulting team consisting of NIRAS A/S and Jacobs followed the project closely.

The model of the pumping station was designed and built at scale 1:11.81. The model was manufactured for complete transparency in acrylic glass, which gave maximum freedom for observing any flow features in the model. It was instrumented to measure the rotation of the water and the velocity distribution inside the vertical pumping pipes, vertical velocity profiles in the main pump chamber, water level variations in the pump chamber, and flow rates in each pump, as well as flow visualisations to document the flow patterns.

The Kalvebod pumping station scale model. © DHI
View of the bell mouth inlet to the pumps. The bell mouth shape was designed by Grundfos A/S. © DHI

During the course of the test campaign, modifications were introduced to the layout of the interior of the pump chamber to improve the hydraulic performance. This included baffle columns, which is vertical columns that slow down the flow and dissipate energy as water enters the pump chamber. Here, a calm and well distributed flow is achieved in the pump chamber, which ensured that all evaluation parameters were well within the acceptable limits according to international guidelines.

For this project, DHI made use of our expertise within physical scale model tests of hydraulic structures and pumping stations. At our model test facilities, we perform tests with pumping stations in a dedicated test bench, making sure all equipment is in place for a full hydraulic assessment, forming the basis for verification against relevant standards. In addition to physical model tests, DHI also has the expertise to perform detailed numerical CFD simulations of pumping stations, which is often a valuable approach in combination with physical model tests.

Results

Improved
hydraulic performance

Validated the safety and efficiency of the basic design of the pumping station

Helped the client meet all international guidelines

‘The DHI team responded to our request for physical scale model tests with a technical high-quality proposal. They managed to carry out a complex model build and instrumentation of the pumping station model and provided detailed and continuous feedback on performance during fabrication, instrumentation and testing.’

Jens Bjerritsgaard, Head of Project Department
Karl Norbert Kiniger, Application Manager
Grundfos A/S

‘HOFOR and our consultant NIRAS found it necessary to have the untraditional and extreme design verified before initiating the construction. In addition to CFD simulations, a scale model test was specified. HOFOR is very satisfied with the way the model was built, and with the tests conducted by DHI and Grundfos. The tests resulted in some optimisations and finally in a satisfying result. HOFOR is now fully confident the design will work in full scale. The cooperation has been excellent and the delivery was on time.’

Niels Eriksen, Chief Consultant
HOFOR

About the client

Grundfos has a global presence and is a full range supplier within pumps for heating, air conditioning, irrigation, industry, groundwater, boosting and water treatment. Know more about the Kalvebod Cloud Burst tunnel project: https://www.hofor.dk/driftsinfo/kalvebod-brygge-skybrudstunnel/

Case story - Highlights flyer

Optimising Kalvebod Brygge cloudburst pumping station

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