# time step of twophaseeulerfoam

• Hi guys,
I am using twophaseeulerfoam to simulate liquid-solid pipe flow. The mesh has 180000 cells but I need to use a very very small time step. Do you have any suggestion for how to increse the time step or other ways to make computational time reduced? Thanks a lot!

• Your simulations just blow up

• @东岳 Thanks for your reply. The simulation was not crashed but the time step is small, says 1e-5. I found most of researchers used a smaller time step even than mine in this phenomenon. Thus, it is usual to be like this? If this, I need a lot of computational time?

• Small time step may be possible. But it means too large velocity. If it is incompressible flow, it is not common.

• @东岳 Thanks. My parameters are: Pipe diameter is 0.1 m, mean velocity is 2.5 m/s (ensure fully-suspended), particle size is 1e-4 m, density of particle is 2650 kg/m3, fluid is water. As you can see, the velocity is so small. I cannot imagine if that small time step is used, how much time I need to finish one simulation. There is no way to increase the time step. By the way, I already switch on adjustable time step option, which automatically adjusts the time step to be as large as possible.

• Your simulations just blow up, its difficult to debug the reason from your info.

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