[LijieNPIC]

Hi foamers, especially DNSers,

I need your help. I have modified channelFoam to perform DNS of pipe flow. L/D=5, D=0.01m, bulk velocity is 0.53m/s, viscosity is 1e-6, so Re based on D is 5300. The mesh is 4 million, time step is 0.0001. At inlet and outlet boundaries, I set cyclic boundary condition. After 10000 time steps, I sampled the main axial velocity(z direction), very 500 time steps I get 1 sample, so there are 10 samples. I averaged the velocity, and get the following result, seen graph1 attached, the axial velocity seems to oscillate in the radial direction. This behavior will more obvious in instantaneous velocity, seen in graph2. What is more, the inlet instantaneous velocity differs from outlet instantaneous velocity. It is strange, because I applied cyclic bc at the two boundaries. Anyone who has do DNS simulation experience such problem. Please give me your hands, thanks