WRL technology used in speed record of air-water flow measurements

During a three-year collaboration project, researchers from the Laboratory of Hydraulics, Hydrology and Glaciology at ETH Zürich, Switzerland (Dr Benjamin Hohermuth and Professor Robert Boes) together with WRL’s Dr Stefan Felder developed an air-water flow measurement system that can be used under extreme conditions.

Stefan, a leading expert in the field of air-water flows in hydraulic structures, described the achievement of the project team as ground-breaking. “Nobody has been able to measure air-water flows under such extreme conditions.”

WRL’s state-of-the-art air-water conductivity probes were modified by toolmaker Robert Jenkins to withstand air-water flows exceeding 40 m/s. An array of 16 of these probes were installed in the tunnel spillway of the 225 m high Luzzone Dam in Switzerland during two measurement campaigns in 2019 and 2020. “The last comparable air-water flow measurements with velocities of up to 20 m/s were conducted on a dam in New Zealand in the 1970s. We now have unique validation data of air-water flows. I would like to give great credit to my collaborator Dr Benjamin Hohermuth who lead this project and undertook the prototype measurements.” Stefan said.

High-velocity air-water flows often occur in hydraulic structures such as spillways or low-level outlets at dams. Entrained air affects the flow properties of the air-water flows and must therefore be considered in the design of such structures. Existing design guidelines are primarily based on laboratory-scale model tests. However, since certain relevant air-water flow processes cannot be scaled in the laboratory models, so-called scale effects may occur when upscaling from the laboratory to prototype structures. Validation data from prototypes is essential for the safe design of dams and other large water infrastructure.

This study is an important step toward a better understanding of scale effects in air-water flows. The results confirm a good agreement of some bulk air-water flow properties such as mean air concentration with existing empirical design equations, while others such as droplet sizes are significantly influenced by scale effects. These findings are significant since they enhance confidence in the safe design of hydraulic structures.

High-velocity air-water flow measurement

Published research:

Benjamin Hohermuth, Robert M. Boes, and Stefan Felder (2021). High-Velocity Air–Water Flow Measurements in a Prototype Tunnel Chute: Scaling of Void Fraction and Interfacial Velocity. Journal of Hydraulic Engineering 147(11): 04021044, doi: 10.1061/(ASCE)HY.1943-7900.0001936

News and further reading:

For further information contact:

Dr Stefan Felder | Senior Lecturer | s.felder@wrl.unsw.edu.au

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