### 1.9.6. Wall

#### 1.9.6.1. Mass and Momentum

##### 1.9.6.1.1. No Slip (Not Moving, No Wall Velocity)

The velocity of the fluid at the wall boundary is set to zero, so the boundary condition for the velocity becomes:

| (1–250)

##### 1.9.6.1.2. Free Slip

In this case, the velocity component parallel to the wall has a finite value (which is computed), but the velocity normal to the wall, and the wall shear stress, are both set to zero:

| (1–251)

| (1–252)

##### 1.9.6.1.3. Finite Slip

For details on finite slip wall, see Finite Slip Wall in the CFX-Solver Modeling Guide

##### 1.9.6.1.4. Specified Shear

For details on specified shear wall, see Specified Shear in the CFX-Solver Modeling Guide

##### 1.9.6.1.5. No Slip (Moving, with Wall Velocity)

In this case, the fluid at the wall boundary moves at the same velocity as the wall. There are three different options for the wall velocity:

- Cartesian Components: You can directly specify Cartesian components in a local coordinate frame or the global coordinate frame:

  | (1–253)

- Cylindrical Components: You can directly specify cylindrical components in a local cylindrical coordinate system:

  | (1–254)

  and the solver automatically transforms the cylindrical velocity components into the global Cartesian coordinate system.

- Counter-rotating Wall and Rotating Wall : A counter-rotating wall can be specified for walls in rotating frames. In this case, the wall is stationary in the absolute frame; in the relative frame, it moves with a velocity:

  | (1–255)

  where is the radial vector from the domain axis of rotation to the wall and is the domain angular velocity.

  A rotating wall can be specified in both stationary and rotating frames. This option is useful to use in stationary domains when you would like to create a spinning wall. In this case, you enter a local rotation axis for the wall boundary and the wall velocity:

  | (1–256)

The solver automatically transforms the specified wall velocity into Cartesian components. This option could be used to duplicate the counter rotating wall option in rotating frames by explicitly setting the angular velocity equal to minus one times the domain angular velocity.

#### 1.9.6.2. Turbulence

The treatment of wall boundary conditions for turbulent flow is the same as for laminar flow, except for No Slip. For details, see Modeling Flow Near the Wall.

#### 1.9.6.3. Heat Transfer

##### 1.9.6.3.1. Adiabatic

The Adiabatic Wall boundary condition allows no heat transfer across the Wall boundary:

| (1–257)

##### 1.9.6.3.2. Fixed Temperature

Static Temperature is specified at the wall boundary:

| (1–258)

##### 1.9.6.3.3. Heat Flux

Heat flux at the wall boundary is specified:

| (1–259)

##### 1.9.6.3.4. Heat Transfer Coefficient

Heat flux at the wall boundary is calculated using:

| (1–260)

where is a specified heat transfer coefficient, is the specified boundary temperature, (that is, outside the fluid domain) and is the temperature at the internal near-wall boundary element center node. For details, see Heat Transfer in the CFX-Solver Modeling Guide.

#### 1.9.6.4. Additional Variables

The options for specifying Additional Variable quantities at wall boundaries are analogous to those for heat transfer.

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