Abstr:Induced flow in a T-junction

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Application Area 3: Chemical & Process, Thermal Hydraulics & Nuclear Safety

Application Challenge AC3-02

Abstract

A dedicated test rig comprising a T-junction has been tested in the Research and Development Division of Electricité de France in Chatou, France. A high Reynolds number flow is maintained in the main pipe while very small incoming mass flow rates are imposed in the auxiliary pipe (or “dead leg”). In such a configuration, a vortex is generated at the junction. Due to the shear, the flow is recirculating in the dead leg. The symmetry of this recirculation with respect to the plane including the axes of the two pipes may break down, then a swirling flow extends along the dead legs.

The objective here is to predict the appearance of the swirl, and to describe it (for example predict its height in the dead leg).

Two RANS turbulence models have been used for calculations : the k-epsilon model and the Reynolds Stress Model (or “Second Moment Closure”, SMC).

The primary circuit of Pressurized Water Reactors is connected to a large number of auxiliary lines in which the fluid is usually colder than in the main pipe. Most of the time, the mass flow rate is small in the part of the auxiliary line located between the main circuit and the first valve. Hence, this zone might show temperature fluctuations if hot fluid coming from the main pipe is recirculating due to the shear at the junction. Previous analyses in Robert (1992) have shown that the swirl power in the dead leg is directly affected by the Reynolds number in the main pipe and by geometric details of the junction, whereas the influence of thermal effects is comparatively negligible. This is the reason why the application challenge proposed here focuses on the isothermal study of this flow : the motivation, for safety reasons, is to understand and be able to model the hydraulic behavior of auxiliary lines connected to the primary circuit of Pressurized Water Reactors.

The main parameter which will allow to assess the quality of the calculations is the height of the swirl. We put the stress on the necessity to define properly the extremity of the swirl, since it is highly subjective, in the experiment as well as in the calculations. All definitions are of course purely conventional.

Velocity profiles along a diameter of dead leg sections could also be a good parameter. Unfortunately, these data are not available.


Contributors: Frederic Archambeau - EDF - R&D Division


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