Learning Forum

[ClemensK]

Hi everyone,

I'm doing a steady state simulation (CFX R19.2) on a centrifugal fan with frozen rotor frame change. To avoid that dust adheres to the blade walls, water is injected at two positions. The water droplets are tracked in an Lagrangian manner as particles with fixed diameter (one-way-coupling). In the attached pictures you can see the particle paths, until the particles first hit the blade. Up from this point I want that all droplets stick to the wall and the water (particles) should be transpored outwards (due to wall shear stress and centrifugal forces) to the blade tip, where the particles disengage from the blade tip and are centrifuged outwards. (In these pictures the particles rebound from the wall. I also tried verly low restitution coefficients, but that does not help either. )

For me it is important to know, how long a particle needs from the impact to the tip of the blade as a wall film.

Does anyone know how to model this problem? Is this even possible with the Lagrangian formulation?

[rfblumen]

It's not possible to model the physics you're describing with the Lagrangian Particle Tracking model in CFX. Particles can either reflect off the surface or stick to the wall and become part of the wall film. From the description of the wall film model in the CFX Theory guide:
A so called quasi static wall film model is implemented that neglects the wall film movement due to external forces, such as shear stress, gravity, pressure forces, etc. In this model, wall particles interact only with their surroundings via mass transfer (evaporation) or heat transfer (wall conduction, convection).
One thing you might consider is applying either a mass flow inlet or a mass source to the blade surface with an appropriate mass flow value using a homogeneous multiphase approach. This would enable a "wall film" that could migrate along the blade due to centrifugal effects.