### 6.7.1. Introduction to Particle-Wall Interaction

Particle-wall interaction involves complex physics and not all aspects are well understood. Dimensional analysis shows that droplet-wall interaction depends on the wall temperature, wall material and roughness, impact angle and impact velocity, the existence of a wall film, and various other parameters.

ANSYS CFX uses advanced particle-wall interaction and quasi-static wall film models to address some of the shortcomings found in ANSYS CFX 11.0 and previous releases (see the background information). The following advanced particle-wall interaction models are available in ANSYS CFX:

- Elsaesser particle-wall interaction model - This model accounts for all of the above listed influencing factors during the particle droplet reflection.

- Stick-to-wall model - This model enforces all particles that hit a wall to become part of the wall film.

For details on the implementation of quasi-static wall film in ANSYS CFX, see Quasi Static Wall Film Model.

#### 6.7.1.1. Background Information

In ANSYS CFX 11.0 and all previous releases, a very simplistic approach is used to describe the process of particles colliding with walls: It is assumed that during the collision process, particles exchange momentum only with the wall. During such collisions, the momentum loss is controlled by constant or time-dependent coefficients of restitution.

In the case of a fully inelastic collision, the particle is collected at a wall; however, the corresponding particle mass or energy is no longer available for the simulation. It is also not possible to explicitly account for the effects of wall roughness or wall temperature during the particle-wall interaction.

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