Suppose we want to create a simulation of a nozzle spraying liquid in to free air. The question arises how to set up such a simulation?
Since inside the nozzle there is internal flow and we require external flow for outside. In SimScale we can choose either an internal flow or external flow simulation.
The following information will help:
The simulation mentioned requires modelling of two media simultaneously, namely water (internal flow) and air (around the nozzle).
In order to perform such analysis, we should use the multiphase simulation type. These simulations allow to model interaction of two non-mixing fluids.You can find more information about multiphase here:
The acquired benefits of using the multiphase approach are quite obvious. They will come with a price of increasing the complexity of the problem tremendously:
- First we need to remember that we cannot run a steady state simulation with multiphase, since we need to resolve the dynamic behavior of the interface between the fluids.
- Secondly, we will need quite a fine mesh to properly capture the flows.Finally, the mesh needs to be good quality, since imperfections will prime the runs to diverge.
Overall we can expect that the multiphase flow simulation will be 10-times more computationally expensive compared to steady state, and still will produce not too much results- a second or two of the real-time behavior is usually maximum of what can be achieved in a reasonable time.
In the end we highly recommend to begin the analysis with steady state, single phase simulations and draw the engineering decisions. After first, “crude” improvements to the model are done, we can move to the verification of the performance using multiphase simulation.
A good example for multiphase project is: