[kharih3]

Hello, I am currently working on a project that mixes two compounds. One being water and another being air (for the time being), the next phase would be water with a powdered solid. I have designed a preliminary simple mixer a closed cylinder with a 4 fin propeller with a shaft that rises above the top of the cylinder (tank). I have tried to simulate mixing through rotating with just water with a simpler design which worked. Now when I try two different fluids I get a lot of errors (mainly geometrical errors). I was wondering if I have to specify the fluid boundary + air boundry within the tank in SpaceClaim or if I can just skip that step and set the inlet flow rate to a specific value.

If anyone has any advice on how to simulate mixing of two fluids on cfx, please do let me know. I tried using the cfx manual with chapter 17 for multiphase mixing (not using the given mixer model from ANSYS cfx) but I have been stuck at this stage for a while.

[ghorrocks]

There are many ways of modelling air+water mixtures, depending on what regime your mixture is in - clear water/air interface, bubble, droplets, foam, mist - these are all modelled differently. So you need to understand what regime your simulation is in and select an appropriate multiphase model.

You also mention that there is a powdered solid as well - this suggests you could have 3 phases (air, water, powdered solid). There are similar regimes for solid/fluid flow so you need to select an appropriate model for your case. And note that multiphase models involving 3 or more phases are very difficult and the models often have limited accuracy as the physics of what happens for these cases is not well understood.

You sound like a CFD beginner, so start with single phase flows and make sure you understand them well and can get accurate solutions single phase before starting multiphase models. Multiphases models are much more complex than single phase.