SIMULATION OF THE UNSTABLE OSCILLATORY BEHAVIOR OF SINGLE-PHASE NATURAL CIRCULATION WITH REPETITIVE FLOW REVERSALS IN A RECTANGULAR LOOP USING THE COMPUTER CODE ATHLET
Pk. Vijayan et al., SIMULATION OF THE UNSTABLE OSCILLATORY BEHAVIOR OF SINGLE-PHASE NATURAL CIRCULATION WITH REPETITIVE FLOW REVERSALS IN A RECTANGULAR LOOP USING THE COMPUTER CODE ATHLET, Nuclear Engineering and Design, 155(3), 1995, pp. 623-641
Experiments carried out in three rectangular loops differing in diamet
er showed instability in the loop with the largest diameter. The obser
ved oscillatory behavior involves repetitive flow reversals, the frequ
ency of which is regular (periodic) at low powers and irregular (chaot
ic) at high powers. The flow reversal frequency increases with heater
power. Due to the flow reversals the Reynolds number vary between + 10
000 and - 10 000 causing the flow to pass through the laminar and tur
bulent regime repetitively. Simulation of the oscillatory behavior usi
ng the computer code ATHLET did not show instability with a coarse nod
alization. The nodalization was then progressively refined and with a
fine nodalization ATHLET was able to predict the instability behavior
and to reproduce all the essential characteristics of the observed osc
illatory behavior.