There are two variants of simulation: Steady state and Transient flow.
In order to account for time-dependent effects, consider a transient simulation. If you are only interested in the converged steady state solutions where the flow condition does not change over time, consider a steady state simulation.
- Steady state simulations are not time dependent, hence cheaper than transient simulations. But generally sufficient enough to do design comparisons at design phase.
- Transient simulations are computationally expensive, but for applications like moving turbines or high vortex flows, they give us more insight.