Wall Calculator
The Wall Calculator in the Results task calculates flow-induced forces on solid and wall surfaces. Such forces are useful in many situations, and examples include:
- Assessing the hydrodynamic force on internal valve components for determining spring rate
- Calculating the lift and drag on aerodynamic bodies
In addition, the Wall dialog calculates:
- Wall temperatures
- Pressures
- Heat flux
- Film coefficients
- Torque about an axis and the center of force
The resid_heat_flux_calc flag causes thermal results to be calculated using residuals on the surface.
The Wall Results tab is broken into two tabs:
- Selection and Result: select surfaces and the quantities to calculate
- Output: display the results
Using the Wall Calculator
Click Results (tab) > Results Tasks (panel) > Wall Calculator to open the Wall Calculator.
When this dialog is open, surfaces on the model highlight as the mouse hovers near them.
Step 1
Select surfaces on which to assess wall results. Valid surfaces are any wall surface as well as openings (inlets and outlets).
When the Selection Mode is Volume, volumes highlight when hovered over, and can be selected. The surfaces belonging to a selected volume are actually selected, not the volume itself. The IDs of selected surfaces are shown in the list region.
Select groups of surfaces using the Group Operation button. The group must exist prior to running the last set of iterations. If not, simply run 0 iterations to force the model to re-process.
Step 2
Select the quantities and desired units to output.
Force is the overall stress tensor. Pressure and shear are integrated over the surface. Force components and magnitude are computed for each selected surface. The total (summed) force for all selected surfaces is also computed. Note that forces are reported in the global coordinate system.
To remove very low wall pressures (which may indicate the on-set of cavitation) from the force calculation, check the Cutoff Pressure box, and specify a minimum pressure value. This value will be assigned to all locations with pressures that fall below the Cutoff. (This cutoff does not affect the displayed results fringes or any other output quantity.)
For moving solids, the computed force and torque are the hydraulic values, and do not include the effect of specified driving and resistance forces or torque as part of the Motion definition.
Pressure is the average pressure exerted by the fluid on the wall surface.
Temperature is the average temperature on the wall surface. Note that temperatures values from intermediate saved iterations or time steps are not accessible on the Wall dialog.
Temperature values on walls are not available while the analysis is running. They are computed after the analysis has stopped.
Heat Flux is based on the thermal residual from the heat transfer solution. Note that heat flux values from intermediate saved iterations or time steps are not accessible on the Wall dialog. Also, heat flux values from moving objects are not available.
Film coefficient can be calculated in two ways:
- Enter a value for the Ref. temperature. The film coefficient is calculated based on the heat flux and the temperature difference between the specified reference temperature and the wall temperature.
- Use the near wall temperature at every wall node as the local reference temperature. Check the Use near-wall temperatures box. The film coefficient will be based on the difference between the wall temperature and temperature at the closest non-wall (flow) node for every node on the wall.
To calculate the Torque about an axis, enter the coordinates of one point on the axis of revolution in the Point on Axis group, and enter a unit vector that defines the Direction of the axis in. When Force is selected, the wall forces, the center of force about each global axis, and the torque about the selected axis are computed and displayed on the Output tab.
Step 3
Click Calculate from either the Wall Results dialog or from the Wall context panel.
Output Tab
Click the Output tab to view calculated wall results. The requested values from the Selection and Result tab are displayed on this dialog for every selected surface.
A Summary section lists the total quantities for all of the selected surfaces.
Save this data to an Excel csv file by clicking Write to file. The output file is in Excel csv format.
Click View file to open a saved wall results file. The contents of the file are displayed in the Output region.
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