[sensitiveLook]

I am running a simulation with ansys for flow in an aircraft intake. The flow is transient and when I setup FLUENT for getting the solution, the momentum residuals are very low like the x-velocity starts at 1e-10. And the same goes for y-velocity and z-velocity. Then they drop down to 1e-18, and restart from 1e-10 at the beginning of the time-step.
Can anyone tell me why mymomentum residuals so low?
As for settings:
Model: Detached Eddy simulation (RANS model SST k-omega with shielding function as IDDES)
Solver: PISO, 2nd order solvers for all variables,
Transient formulation: bounded second order implicit
Time-step size: 1e-04
Max no. of iteration/time steps=30
I have attached a picture of my residuals for reference

[sbaffini]

We would need a crystall ball to tell. Could you share your velocity initialization and current field, cfl, etc.?

In general, the residual you see at the beginning of the subiterations, if I recall correctly, is still normalized with respect to the max res in the first 5 subiterations of the first time step. If your solution is changing very slowly, it might indeed happen that the following time steps all behave better than the first. But this is just speculation