Investigation of air blowout, geyser, from a bottom outlet

Safe operation of the bottom outlet is vital for many dams and reservoirs and concerns the structural integrity of the whole facility. Through analysing field data from prototype flood tests and performing CFD simulations the project will help understand this hydraulic phenomenon and improve outlet discharge safety.

In water systems, geysers, or air blowouts as they are often called, are a phenomenon that occurs under dynamic flow conditions. The phenomena is so far not well understood. Due to the complexity of the issue including its transient feature, it is difficult to quantify the air amount and blowout frequency. Due to uncontrolled fluctuations in both flow rate and pressure in the system, air entrainment is an issue that affects operation.

Due to the combination of intake geometry and flow conditions, air entrainment and detrainment is inevitable and gives rise to unfavourable flow conditions and in many cases harmful consequences to safety. By analysing the field data from flood tests and CFD simulations knowledge on this phenomenon will be improved. Reliable spillway flow modelling leads to reliable design and refurbishment, which is essential for both discharge safety at extreme floods and daily operation at medium and low floods.

The following aspects are to be addressed to achieve this:

  1. evaluate if CFD can reproduce the hydraulic phenomenon observed in the field tests.
  2. identify major scenarios at different gate openings or flow conditions for prototype operations.
  3. estimate volumes of the trapped air as it is otherwise difficult to quantify it by other means.
  4. predict frequency of air blowouts at various gate openings and compare with prototype observations.

Om projektet


James Yang, KTH


Penghua Teng, KTH
Li Shicheng, KTH
Eric Lillberg, Vattenfall


Yang, James & Teng, Penghua & Nan, Junhu & Li, Shicheng & Ansell, Anders. (2020). Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation. Fluids. 5. 203. 10.3390/fluids5040203.

J. Yang, P. Teng, and S. Li, ‘Prototype Observations and Numerical Modelling of Geysers from A Bottom Outlet’, presented at the ICOLD Symposium on Sustainable Development of Dams and River Basins, 2021.


oktober 2019 - oktober 2020