# Creating Streamtraces on a No-slip Boundary Surface with Multiple Surrounding Volume Zones

Problem:

How do I create streamtraces on a no-slip boundary surface with multiple surrounding volume zones?

In more detail: In the User’s Manual in the section titled “Surface Streamtraces on No-slip Boundaries”, it describes how to create these surface streamtraces in the context of an ASCII file with one parent (volume) zone. However, if other data file types are used or multiple parent zones, these instructions do not apply.

Solution:

Tecplot 360 can create these surface streamtraces by: calculating the velocity gradient in the volume zones, interpolating the gradient to the surface zones, and dotting it with the unit normal of the surface zones. This method gives the components of the velocity gradient in the surface normal direction, a vector. Using this vector as 360’s vector variables, you can then place surface streamtraces on the surface zones.

Procedure:

1. Select Analyze –> Field Variables, and set the Convective Variables to Velocity, e.g. variables u, v, and w, and click OK.
2. Select Analyze –> Calculate Variables… and calculate Velocity Gradient (tensor) with New Var Location set to Node and deselect “Calculate on Demand”. Click Calculate.
3. Then, also in the Calculate dialog, calculate the Grid K Unit Normal (vector). Similar to step 2, set Var Location to Node and deselect Calculate on Demand. Click Calculate, and close the dialog.
4. Select Data –> Interpolate –> Linear. For Source zone(s), select all the volume zones. For Variables, select all components of velocity gradient, dUdX through dWdZ. For Destination zone, pick the desired surface zone, and click Interpolate. If more than one surface zone is desired, select each as the Destination zone followed by clicking Interpolate. Close the dialog.
5. Select Data –> Alter –> Specify Equations. Enter the following equations and click Compute, then Close:
{Un}={dUdX}*{X Grid K Unit Normal} + {dUdY} * {Y Grid K Unit Normal} + {dUdZ} * {Z Grid K Unit Normal}
{Vn}={dVdX}*{X Grid K Unit Normal} + {dVdY} * {Y Grid K Unit Normal} + {dVdZ} * {Z Grid K Unit Normal}
{Wn}={dWdX}*{X Grid K Unit Normal} + {dWdY} * {Y Grid K Unit Normal} + {dWdZ} * {Z Grid K Unit Normal}
6. Select Plot –> Vector –> Variables and select Un, Vn, Wn as the vector variables. Click OK.
7. Click Streamtrace Details… (on the sidebar) and select the Surface Line format. Close the dialog.
8. Click the streamtrace placement tool and click on the desired surface. You should now see streamtraces.

Note: For this method to work, the nodes of the boundary zone must coincide with nodes on the surfaces of the volume zones.