Small Hole Size High Pressure Gas Leak Definition

 

There is no limitation in the hole size which can be simulated with in:Flux. Commonly very small leaks need to be simulated for various standards. One example, the UK HSE PM84 Guideline for turbine enclosures (and associated HSE CM/04/09 documents) looks at hole sizes as small as 25mm2 (~3.5mm diameter) to 0.25mm2 (0.035mm diameter).

 

Even for very small hole sizes, in:Flux will handle the mesh adaptation in the same way - the mesh will initially be divided into 10 cells divided evenly across the leak. This can result in a very small mesh size which is necessary to maintain accuracy.

 

This tutorial will look to simulate a case similar to the PM84 Guidance but should not be understood as complying or advising on the guideline.

 

Two pure methane gas leaks will be added to the project at the same pressure (40bar) and same location. One will be set to 3mm hole diameter (0.034 kg/s) and the other to 6mm (0.137 kg/s).

 

For the locations of the leaks, turn on the 550s Mean Age-of-Air isosurface defined in the last section, shown in Figure 28 below. We will look at the region of the isosurface which is touching the ride side of the gas turbine (indicated by the blue square). Although this CAD model is an approximation, porosity can be added around the turbine to represent complex pipework that would normally exist in a turbine enclosure. For simplicity, only the loaded CAD model will be used with this tutorial.

Tutorial 9 - Figure 30 - 525s age of air isosurface with indication of leak locations

 

Zoom into the blue square shown in Figure 30 and add a high pressure leak to the project:

  1. From the Add Item tab, select Gas Leak or Emission from the Select Item tab

  2. Change the Name to  "HP Release 01 - 3mm"

  3. Set the Gas as METHANE

  4. Enter a value of "40 bar(g)" as the Upstream Pressure

  5. Set the Upstream Temperature to be "120°C"

  6. Leave the Discharge Coefficient as "0.8"

  7. Set the Diameter of the leak to be "3 mm"

  8. For the location use the pick tool icon to select a point on the gas turbine, facing north, as in the Figure below.

    1. Alternatively, you may enter the coordinate (35.44, 37.42, 6.87)

       

      Tutorial 9 - Figure 31 - location for HP Release 01 - 3mm

       

    2. set the Angle from North as "0 degrees"

    3. and the Elevation as "45 degrees"

  9. Click the Preview checkbox to ensure your leak is similar in location to Figure 31 above.

  10. Click the Add Item button

     

     

The properties of the leak will remain the same after you add the 1mm leak to the project, follow the next steps to replicate the leak for the larger hole size:

  1. Change the Name to "HP Release 02 - 6mm"

  2. Leave all the other properties the same: Gas Upstream Pressure, Upstream Temperature, Discharge Coefficient, Coordinate and Orientation

  3. Enter the Diameter to be "6 mm"

  4. Click the Add Item button.

 

Your screen should now be similar to Figure 32 below with a total of 14 inflows defined: 2 gas leaks and 12 HVACs.

 

Tutorial 9 - Figure 32 - The two gas leaks defined in the project. The Project Items tab is shown with all 14 inflows of the project.

 

Continue to the next section to setup and run the two dispersion cases.