Author(s)

X. Boissière, C. Lainé & B. Fourcher

Abstract

In this paper we describe a test loop representative of a feed water nozzle, dedicated to steam generators of nuclear submarines, designed to lower thermal gradients. For that an annulus is around the pipe in the connection zone. One part of the main steam generator flow goes inside that annulus. The behaviour of fluid appeared to be too complex to he determined only by numerical methods. The experimental apparatus aims to improve the understanding and the modelling of our specific configuration in order to have a better knowledge of margins. Actually, thermo mechanical dimensioning of that critical area is made considering a great heat exchange coefficient. This leads to a durability which can be lowered by a precise knowing of the real heat exchanges. Main work consisted in understanding the hydraulic behaviour, to calculate dynamic heat exchanges. Therefore, Particle Image Velocimetry (PIV) is used, because it allows qualitative and quantitative measurements. A first step consisted m developing solutions so that the fluid-flow at the open end of the annulus is regular. Solutions were also developed to take into account the optical distortion of laser beam. When flow in main channel is turbulent, there are periodic flows in the annulus. Those pulses are of a very different period along the axis and circumferentially. The drag is completely disturbed by the water pulsed out of the annulus. Observation and interpretation of flow pattern allows us to build a numerical model. The specification of that model would have been different without tests, and could have never corresponded to reality. It appears that main numerical problem will be to qualify the instability governing the problem. But, knowing that problem, we can imagine a pertinent calculation strategy.

Keywords