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Home > Teams > EDT team: Two-Phase flows and turbulences > Research activities > Instabilities and interfaces

Air entrainment by plunging jets

J. BERARD, A. CARTELLIER, G. GUYOT, J.-P. MATAS, in collaboration with M. PFISTER (EPFL) et M. RODRIGUEZ (CERG)

Lack of knowledge regarding air entrainment caused by large jets in hydraulic structures, led EDF, in the framework of the La Coche (Savoie) hydro-power plant enhancement project of La Coche (Savoie), to achieve a series of experiments on 10 cm diameter jets with a circa 3m falling height. LEGI, LCH (EPFL), CERG and EDF (CIH) developed a collaboration which aimed at understanding the behavior of such jets for multiple applications (impact, erosion, oxygenation, flood protection, air entrainment,...). In a first stage, the experimental results have been compared to available correlations or theories. The main conclusions are:

  1. the state of the jet upstream the impact is the major parameter governing the downstream consequences
  2. In this case, it is impossible to predict the breaking length, or the state of the jet as a function of the falling height with the parameters used by available models
  3. the studied jets show a oscillating frequency close to 1Hz with an amplitude order of the half jet diameter
  4. the penetration length is poorly understood, and the best existing correlations give results that are significantly different from the measurement.

These observations led us to develop two parallel experiments. The first one in LEGI is aimed at understanding the influence of the amplitude and frequency of the jet oscillations on the penetration depth. The jet diameter is between 0.3 and 2.4 mm, the ejection velocities between 2 and 20 m/s. The fall height is 20 times the nozzle diameter.

The second experiment is realized in the CERG facilities in order to setup large size jets. The nozzle diameter is between 2 and 20 cm, the ejection velocities between 2 and 30 m/s. The free fall height is between 8 and 12 m. The jets impacts a 5 m diameter pool, 5 m deep which change deeper into 2.5 m diameter and 23 m deep. The first goal is to make an extensive study of the various states of the jet. Then we try to identify the relevant parameters that govern the state of the jet.

Illustration of the experiments with oscillating jets:

Illustration of the large size experiments (localized in the CERG facilities):

Jets oscillants