Modelling flow and heat transfer in helically coiled pipes - Part 4: Direct numerical simulation (DNS) of turbulent flow and heat transfer 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 deliverables 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'. The document reports the results of Direct Numerical Simulation of fully turbulent flow and heat transfer in toroidal pipes characterized by different ratio between pipe radius and torus radius (0, 0.1 and 0.3). The calculations have been performed with ANSYS-CFX code using hexahedral volumes.