Evaluation of influence of the inlet swirling flow on the flow field in a triple elbow system

• Flow fields in a triple elbow system are investigated when swirling flows enter.
• At 1st elbow, a stronger swirling inflow causes a smaller separated region.
• There appear separated regions newly downstream of the 2nd elbow.
• Secondary flow distribution of the inflow largely affects a flow separation.

This study evaluated experimentally the influence of the swirling inflow condition upon the flow field in the cold leg piping, which comprises three 90 ° elbows, of the primary cooling system of Japan sodium-cooled fast reactor. Flow visualization experiment was conducted to reveal the velocity fields of the flow in the piping with swirling flow generator. When comparing to the developed turbulent inflow case, the flow separations in the intrados of the 1st elbow became smaller and the swirling flow downstream of the 2nd elbow became stronger, and there appeared separated regions downstream of the 2nd elbow which was not observed in developed turbulent inflow case. Since the flow separation can be considered as the source of the separated vortices which induce pressure fluctuations, these results imply the possibility that pressure fluctuations downstream of the 1st elbow are reduced and those of the 2nd elbow are enhanced by swirling flows as the inlet condition. The separated region is strongly reduced when a suitable swirling inflow enters the 3rd elbow.