Modelling flow and heat transfer in helically coiled pipes - Part 2: Direct numerical simulations for laminar, transitional and weacly turbulent flow in the case of zero pitch

That report has been issued in the frame of the second research programme of ENEA-MSE agreement and it is one of the deliverabies of the task G 'Theoretical and experimental studies on IRIS critical components (SG, EHRS)' of the work-programme 2 'Evolutionary INTD reactors' of the research theme on 'Nuovo Nucleare da Fissione'. This document deals with the results of time-dependent numerical simulation carried out for evaluating flow and heat transfer in toroidal pipes. The analysis has been performed for two different curvatures (0.1 and 0.3) and for a wide range of Reynolds number so that to obtain flow ranging from laminar to chaotic. The report gives particular emphasis to quasi-periodic and periodic flow regimes that can be obtained for intermediate values of Reynolds number, which are poorly or not at all documented in literature.