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Creation of a pneumatic component for Flowmaster

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A standard is a document that provides requirements, specifications, guidelines or characteristics that can be used consistently to ensure that materials, products, processes and services are fit for their purpose. It also helps to harmonize technical specifications of products and services making industry more efficient and breaking down barriers to international trade.

ISO 6358:2013 standard
In pneumatic fluid power systems, energy is controlled by a gas under pressure circulating in a circuit. The constitutive elements of such a circuit basically present dispersing characteristics. Consequently it is necessary to carry out experiments to determine this characteristics and the match of the component with the circuit.

The ISO 6358:2013 standard specifies a method for testing components which use gases to enable their flow-characteristics to be compared. It defines three constants described on the table 1 which completely characterize the component.


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Fig. 1 - Diagram of the component

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The downstream mass flow rate 2 of the component shown in figure 1 is calculated with the following equations.

  • For P2/P1≤b (Choked flow):
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  • For P2/P1=1 there is no flow:
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  • For 1>P2/P1 >b (Subsonic flow):
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With the law of conservation of mass it also gives 2= -2
Those equations are going to be used in Flowmaster.
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Procedure to create the component
It requires two stages: first the component analytical model (CAM) needs to be created and then it needs to be associated with an actual component.

The CAM is created directly on Flowmaster which creates a stub code asking the user what kind of component is to be created. In this way the name, the number of arms (here 2), the inputs and outputs of the component are chosen.
Figure 2 shows the data sheet of the created CAM. Then Flowmaster creates a « .cs » file which must be modified with the previous equations that the CAM is going to verify.

Flowmaster solves the following type of system:
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Fig. 2 - Table of data (inputs)

The standard equations need to be linearised and then the solution on the code is generated and this will create a « .dll » file that need to be moved in the Flowmaster folder.

Then the component itself is created choosing a symbol and associating the CAM.

Results
The created component has been tested and the model converges in each case with a maximum relative error of 0,1%. Figure 3 shows the evolution of the theoretical and evaluated downstream mass flow rate depending on the upstream pressure.
(With P2=1 bar, b=0,5, C=8.10-7 s.m4/kg and m=0,5)

A parallel with a component created with 3D CFD has also been carried out. The standard coefficients of a 3D piece have been calculated:
b=0,388 ,C=1,17.10-6 s.m4/kg and m=0,5585.

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Figure 4 - Mass flow rate depending on the downstream pressure

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Figure 3 - Mass flow rate depending on the upstream pressure

These coefficients have then been set as inputs for the component on Flowmaster and the results found compared with those of the CFD.
Figure 4 shows the obtained mass flow rate results as a function of downstream pressure. The maximum relative error is of 3% which is in accordance with the norm.

Conclusion
A pneumatic component in accordance with the ISO 6358:2013 standard has been created and can be used in Flowmaster networks.

For any real element of a pneumatic system, having its coefficients b, C and m (which should be on the technical data sheet) allows a user to understand the flow through the component with Flowmaster and without the need of doing real experiments on a test bench. This allows the user to do economy of time and money during the study of pneumatic systems.

Furthermore this shows the adaptability of the software regarding the needs of the clients. If in this case a component has been created to be in accordance the last standard, the previous procedure allows any user to create the component he needs and add it to the Flowmaster catalogue.

Articolo pubblicato sulla Newsletter EnginSoft Anno 10 n°3

Philippe Gessent
EnginSoft

 
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