Setting a leak

1. In the Scenario Settings tab select Run Wizard -> Leak wizard

   or

2. Expand the Leaks tab, right click and select Leak wizard

1. Phase: Gas or Liquid (flashing)

2. Type: Point or Area

3. Position: 3D coordinates

4. Direction: direction of leak outflow or diffuse leak

5. Manual entry of leak properties: upon selection allows the user to set parameters for the leak outlet (see below)

1. Composition: by default, the value for this field is taken from the volume fractions in the Gas composition and volume section of the scenario (refer to the Gas composition and volume article for further information). This value can be changed manually for gas leaks. For liquid-phase releases, only one species can be selected. For AIR type leaks, the value should be "AIR".

2. Volume: of reservoir, used when a volume limited steady state release is specified

3. Pressure

4. Temperature

1. Select release type: can modelled based on hole size or release rate. For releases based on hole sizes Nozzle diameter must be specified. For release rate based releases, Release rate must be specified.

   

2. Nozzle diameter: only available for point leaks

3. Discharge coefficient: value between 0 and 1, default is 0.85

4. Pseudo-source model:

   1. Single planar shock: default for dispersion (recommended for all gases apart from hydrogen)

   2. Single planar shock + air entrainment: as above with the air-entrainment option

   3. Ewan-Moodie: gives better agreement with experiments in general however, requires greater CPU time. Recommended for fire simulations and hydrogen releases (only). Not available for liquid releases.

   4. Ewan-Moodie + air entrainment: as above with the air-entrainment option 

      

5. Time dependency: 

   1. Steady state: continuous release based on calculated or input mass flow rate

   2. Steady state (volume limited): as above but limited by volume specified in reservoir properties

   3. Time dependent: simulates depressurisation of a reservoir

      

      
      

6. Start time: start time of leak in seconds

7. Duration: duration of leak in seconds

1. Temperature

2. Pressure

Advanced options are only required under certain circumstances and are used for advanced control of heat transfer and turbulence parameters.

The area leak input menu is shown upon proceeding from the first part of the leak wizard menu only if Type is set to Area in the Leak Properties section. The following inputs are required:

1. Size: dimensions of the leak in metres

2. Shape: elliptic or rectangular

3. Profile: gaussian (for elliptical shaped leaks only), uniform or parabolic

1. Start time

2. Duration

3. Leak type:

   1. Diffuse: no momentum leak, gas has the same velocity as the surrounding flow

   2. Entraining: entrainment of air into a jet can be captured empirically for considerable computational savings but can only be applied in certain circumstances (see section 3.7.16.2.3 of the User's Manual)

   3. Jet: a point or area leak with momentum

   4. Air: similar to a jet leak but with air only (based on ER9)

   5. Suction: negative point sources, gas and air are removed at the leak location

   6. Fan: does not add or remove mass but assigns a fixed momentum to the gas in the concerned control volume

4. Area: effective cross-sectional area of the leak outlet

5. Velocity: at the leak outlet, can be specified instead of mass flow rate

6. Mass flow rate: at the leak outlet, takes priority if mass flow rate and velocity are specified

7. Relative turbulence intensity: normally between 0.01 (low turbulence) and 0.10 (high turbulence)

8. Turbulence length scale: normally in the range of 10-20% of the nozzle diameter

Automatic refinement of the grid in the cells around the leak control volume can be performed by right-clicking on the leak in question and selecting Refine grid. The grid guidelines should be referred to with respect to refining in the direction of the leak (the size of the grid cells in the direction of and directly in front of the leak should not be any greater than 5x the size of that in the plane of the leak).