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How To Assess a Pressure Drop in the Post-Processor?

This article shows how to determine a pressure drop value with SimScale using the online post-processor.


Let’s first obtain the values of the pressure in the areas within the fluid domain where we aim to study the changes in pressure. In the following figure, we have a representation of a flow through junction pipe with different regions to help us explain this process, going step-by-step:

pipe model with a representation of the internal flow
Figure 1: Pipe model flow situation. The fluid enters through the horizontal and vertical inlet and leaves through the outlet.

1. Cutting Plane

In order to determine the drop in pressure between the inlet and outlet region of the pipe, we need to open the post-processor and create two cutting planes in those regions, with the Scalar value as Pressure or Pressure[node].


In case you want to know the difference between the Pressure and Pressure[node], read this article where we explain the difference between cell and node values.

post processor steps to create a cutting plane in the model to analyze pressure drop
Animation 1: Post-processor workflow to generate cutting planes

Using the cutting planes we have the average values of the pressure in the selected areas of the model. By subtracting the values in the two regions we obtain the pressure drop of the simulation.

pressure results of a cutting plane in the post-processor for pressure drop analysis
Figure 2: Average pressure values are presented in the form of a small box with the exported data

$$\Delta\ P=P_1-P_2=1.48e+3\ – 4.227e+2 =1.057e+3 $$

Applying the averaged values available above, we determine the value of the pressure drop in this model between the inlet and outlet regions. It is approximately 1057 \(Pa\).

2. Surface Data

Another available option to obtain the pressure drop more precisely between the inlet and outlet face is to use the Surface data item under Result control and directly obtaining the pressure values on the inlet and outlet faces.

surface data setup simscale
Figure 3: Surface data setup in SimScale Workbench for area average on the inlet and outlet of the pipe model

Once the simulation finishes, you can access these results controls and extract the pressure values from the plots available under Run -> Area averages.

area average results for pressure differences
Figure 4: Pressure value on the inlet and outlet face (averaged over face area) for every iteration. The values are fairly converged and the difference can be considered as a drop.

By calculating the difference between the two pressure values of the last iteration, we get the pressure drop of the model.

Try It Yourself

If the above article has sparked interest in you then we are happy to refer you to the Fluid Flow Simulation tutorial where you can learn to simulate the pipe junction flow and also try the new post-processor.


If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.

Last updated: January 6th, 2021

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