10. AEROPLUME

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General introduction

 The AEROPLUME model can be used to simulate the near-field atmospheric dispersion of high-momentum jets. AEROPLUME is a steady-state model.
Both vapour-only and two-phase jets can be modelled. AEROPLUME uses the standard HGSYSTEM multi-compound, two-phase thermodynamical model.
Dense, neutral and buoyant jets can be simulated for different release angles.

AEROPLUME has its own reservoir discharge model to calculate (steady-state) release rates from a pressurised reservoir. The used relations are identical to the ones used in the SPILL model. The user can specify discharge rates if required.
AEROPLUME will also calculate post-flash conditions using its two-phase thermodynamical model.
Instead of the reservoir calculations, it is also possible to do stack calculations with the AEROPLUME model, where post-flash conditions are user-specified.

AEROPLUME simulates near-field dispersion. In the far field, the code will automatically generate a link file either for PGPLUME or for HEGADAS-S. See documentation on these models. The AEROPLUME model will determine automatically when to make a far-field transition.

AEROPLUME replaces the old PLUME model in HGSYSTEM version 1.0 (also called NOV90 version). PLUME could only describe the dispersion of ideal gas releases.

The HF-specific version of AEROPLUME is a separate model called HFPLUME.

Range of applications and limitations

The AEROPLUME model should not be used for very low-speed jets (slower than ambient wind speed), as wake-effects will be important.

AEROPLUME should not be used for unpressurised releases, or for any releases where exit velocities are small compared to ambient wind speed or where initial momentum is quickly destroyed by impact with the ground. In those cases the evaporating liquid pool model LPOOL should be used.

Jets touching the ground at high speed or very steep angles should also not be simulated with AEROPLUME.

It is very important when interpreting AEROPLUME results to realise that all physical quantities (concentration, density, temperature etc.) are always average quantities over the plume cross-section. As a general rule of thumb, peak (that is, centre-line) concentrations will be about a factor 1.3-1.4 higher than the cross-sectional mean concentrations as given in the AEROPLUME report file.

In the AEROPLUME model it is assumed that all liquid remains within the jet: dropout of large liquid particles is not accounted for. However, it is possible to use the optional deposition model developed by Earth Technology and available in HGSYSTEM. See the MMESOPT input block and Chapter 9 in the HGSYSTEM 3.0 Technical Reference Manual.

Guidance for use

It is very important to realise that when the SPECIES keyword in the GASDATA input block is not specified, AEROPLUME will perform vapour-only calculations (except for any water present in the jet). There is usually a large difference in dispersion results between a vapour-only and a two-phase jet. If any (non-water) two-phase behaviour is relevant then a SPECIES keyword for the corresponding compound must be specified. Serious underpredictions will result if two-phase behaviour is appropriately neglected.

Although the AEROPLUME model is reasonably robust, under certain circumstances the non-linear solver SPRINT used in AEROPLUME, might not be able to find a (physical) solution. This especially occurs for very dense, touch down jets or for plumes which entrain themselves due to strong bending over. Upwind directed releases of dense jets may also cause severe numerical problems.

Numerical difficulties can sometimes be overcome by slightly changing the input parameters.
It should be realised that the influence of atmospheric parameters (wind speed, stability class) and also of surface roughness, on the near-field dispersion is not very strong for high-momentum jets. Therefore changing these parameters will not have large effects on calculated near-field AEROPLUME results, but might solve numerical problems.

For two-phase releases, the calculation time to simulate the first few meters of the jet dispersion can be high compared to calculations further downwind.

AEROPLUME INPUT PARAMETERS

A description of all the input parameters that can occur in an AEROPLUME input file will be given.

The AEROPLUME input file has the DOS filename 'casename.API' where 'casename' is the user-supplied name of the problem.

In the following, actual keywords are given in capitals and in bold. The descriptions of less important parameters or parameters that need not normally be set by the user, are given in a smaller font.

All parameters, except TITLE, occur in blocks preceded by a specific block keyword. For AEROPLUME these block keywords are: RESERVOIR, RELEASE, GASDATA, PIPE, AMBIENT, DISP, MMESOPT, TERMINAT and MATCH.

The TITLE keyword does not occur in a parameter block.

TITLE The title of the current problem to be run with AEROPLUME.
At most 50 alphanumeric characters.
Optional, no default.

The RESERVOIR block contains the parameters which describe the reservoir fluid thermodynamic state.

TRES Temperature of the reservoir fluid (Degrees C).
-50 <= TRES <= 1500.
Mandatory.
PRES Absolute pressure within the reservoir (atm).
-1 <= PRES <= 200.
Mandatory.
  A negative value of PRES serves as a flag to AEROPLUME: the program will calculate the saturation pressure of the specified mixture assuming all compounds are in the liquid-only state and use this as the value for the reservoir pressure. This option is only available when the two-phase (aerosol) thermodynamics model is being used, in other words when the SPECIES keyword is being used in the GASDATA block as discussed below. It is the user's responsibility to judge whether these assumptions in calculating the reservoir pressure are reasonable or not. PRES must always be greater than AIRPRESS of the AMBIENT block.
  The RESERVOIR block can be omitted if the RELEASE block is being specified.

Adding the RELEASE input block to the parameter file causes AEROPLUME to skip the reservoir and discharge calculations. The data of the RESERVOIR block (if specified) is ignored. The pollutant mass flow rate DMDT in the PIPE block must be positive when using the RELEASE block.
This input block is useful for vent stack simulations.

TSTACK Temperature of the stack release fluid (Degrees C).
-50 <=TSTACK <= 1500.
Mandatory.

The GASDATA block contains the pollutant composition and thermodynamic data. The reservoir or initial stack mixture consists of 100 % wet pollutant by definition. Wet pollutant is defined to consist of the dry pollutant plus any water present in pollutant (as specified by WATERPOL).

WATERPOL Mole fraction water (liquid plus vapour) in wet pollutant (-).
0 <= WATERPOL <= 1.0.
Optional, default is 0.0.
CPGAS Specific heat at constant pressure of the dry pollutant (J/(mole K)).
5 <= CPGAS < 300.
Mandatory if SPECIES keyword is not used (gas-only mixture), no default. If SPECIES keyword is used then CPGAS is needed when a link file to HEGADAS is being made. Thus in practice CPGAS must almost always be specified. Using HGSYSTEM module DATAPROP to find CPGAS and other keywords is strongly recommended.
MMGAS Molar mass of dry pollutant (kg/kmole).
2 <= MMGAS <= 200.
Same comments as for CPGAS apply. Again, use of DATAPROP to calculate MMGAS is recommended.
HEATGR Natural convection heat transfer group
5 < HEATGR <= 100.
Optional, no default. Not used by AEROPLUME model but written to HEGADAS link file if this is being made.
  Use of DATAPROP to calculate HEATGR is strongly recommended.
SPECIES Pollutant compound properties. Using this keyword at least once implies the use of the full two-phase (aerosol) model or a mixture consisting of at least one compound (excluding water). If the SPECIES keyword is not specified, ideal gas thermodynamics is used with gas properties given by CPGAS and MMGAS. Condensation or freezing of water is still taken into account.
The SPECIES keyword plus parameters must be specified for every compound in the mixture, except water. The sum of the molar fractions used in the SPECIES keywords (see parameter #2 below) must equal 1.0 - WATERPOL.
The use of DATAPROP to generate the input parameters when the SPECIES keyword is being used, is strongly recommended.
Currently a maximum of 8 species can be specified (excluding water). Please note that DATAPROP allows for more species to be specified. DATAPROP also splits dry air (if specified) up into nitrogen and oxygen, thus generating two compounds instead of one. Thus the AEROPLUME link file generated by DATAPROP could contain the SPECIES keyword more than 8 times. The user should combine or remove compounds if this occurs.
Within the above-mentioned restrictions, there are no restrictions within AEROPLUME concerning the number of aerosols forming or the number of compounds per aerosol. Please note that HEGADAS does have restrictions: either a single two-compound aerosol or a number of separate one-compound aerosols are allowed (not regarding water and dry air), other combinations are not supported. See the description of the SPECIES keyword for the HEGADAS model.
Following the SPECIES keyword of a certain compound a block of 14 parameters (#1 to #14) must be specified:
#1 compound name (maximum of 12 characters).
#2 mole fraction in polutant mixture (-).
0<= #2<= 1.
#3 ;aerosol class (-).
-1<= #3 <= 50.
#4 specific heat of vapour (J/(mole K)).
5<= #4 <=300.
#5 specific heat of liquid (J/(mole K)).
0<= #5 <=10 3 .
#6 heat of vaporisation (J/mole)
0<= #6 <=10 5
#7 critical temperature (K).
0<= #7 <=10 4
#8 critical pressure (atm).
0<= #8 <=10 3
#9 vapour pressure function coefficient B1.
-10 8 <= #9 <=10 8 .
#10 vapour pressure function coefficient B2.
-10 8 <= #10 <= 10 8 .
#11 vapour pressure function coefficient B3.
-10 8 <= #11<= 10 8 .
#12 vapour pressure function coefficient B4.
-10 8 <= #12 <= 10 8 .
#13 molar mass (kg/kmole).
2 <= #13 <= 200.
#14 liquid density (kg/m 3 ).
1<= #14 <= 10 5 .
Note: the saturated vapour pressure of the compound is described by the Wagner function:

P v (T) = P c x exp { [ B 1 x Q + B 2 x Q 1.5 + B 3 x Q 3 + B 4 x Q 6 ] / T r }
where T is the vapour temperature, P c the critical pressure, T c the critical temperature, T r = T/T c and Q = 1 - T r .

The PIPE block contains the release pipe/orifice exit-plane conditions.

DMDT Steady wet pollutant mass discharge rate (kg/s).
-103 <= DMDT <= 10 5 .
Mandatory.
  A non-positive value for DMDT serves as a flag to AEROPLUME: the program will in this case use a literature correlation to calculate DMDT. However, the maximum value of DMDT, calculated using AEROPLUME's own discharge model, will never be exceeded.
If the user has specified the RELEASE block, then DMDT must be positive.
DEXIT Effective orifice diameter of the discharge pipe (m).
0.001 <= DEXIT <= 10.
Mandatory.
ZEXIT Height above ground level of discharge opening (m).
0.0 <= ZEXIT <= 600.
Mandatory.
  ZEXIT should be greater than ZR in the DISP block because otherwise model assumptions used in some atmospheric correlations will be violated.
ANGLE Inclination of release opening with respect to horizontal (degrees).
-180 <= ANGLE <=180.
Optional, default is 0 degrees (downwind horizontal release).
  Therefore for a vertically upward release ANGLE is 90 degrees
DURATION Duration of pollutant release (s).
-106 <= DURATION <= 10 6 ..
Optional, default is -1 (steady release).
  If DURATION <= 0, then a steady release is assumed (infinite duration). Please note that this is not always a realistic scenario as the total amount of released pollutant can become very large.
  AEROPLUME does not use DURATION itself as it only simulates steady releases, but for a proper transition to HEGADAS-S or HEGADAS-T the value of DURATION is needed.
CDG Discharge coefficient for vapour only releases (-).
0.0 <= CDG <= 1.0.
Optional, default is 1.0.
  AEROPLUME uses discharge coefficients to estimate value for DMDT, the user might want to change the default values of these coefficients.
CDL Discharge coefficient for liquid or two-phase releases (-).
0.0 <= CDL <= 1.0.
Optional, default is 0.61.
  AEROPLUME uses discharge coefficients to estimate value for DMDT, the user might want to change the default values of these coefficients.

The AMBIENT block contains parameters describing the conditions of the ambient atmosphere.

Z0 Reference height for atmospheric data in this block (m).
0.1 <= Z0 <= 200.
Mandatory.
U0 Ambient wind velocity at height Z0 (m/s).
0.0 < U0 <= 20.
Mandatory.
  Please note that U0 can be small but never equal to 0.
AIRTEMP Ambient air temperature at height Z0 (Degrees c)
-50 <= AIRTEMP <= 50
Mandatory.
AIRPRESS Ambient air pressure at release height ZEXIT (atm).
0.7 <= AIRPRESS <= 1.1.
Optional, default is 1.0 atm.
  AIRPRESS must be less than PRES of the RESERVOIR block.
RHPERC Relative air humidity at release height ZEXIT (%).
0.0 <= RHPERC <= 100.
Mandatory.

The DISP block contains parameters describing the dispersion characteristics.
ZR Land surface roughness (m).
10-5 <= ZR<= 1.
Mandatory.
ZR must be less than ZEXIT of the PIPE block.
PQSTAB Pasquill/Gifford stability class.
PQSTAB = A, B, C, D, E or F (character).
Mandatory.

The MMESOPT block contains the 'switches' which indicate the use of the extra options developed by Earth Technology and sponsored by Martin Marietta Energy Systems. An indicator value of 1 means that the corresponding option is used, a value of 0 means that the option is inactive.

IMETP Indicator for use of meteorological pre-processor (-).
IMETP = 0 or 1.
Optional, default is 0.
  For IMETP = 1, an additional file 'casename.MET' must be supplied. See Chapter 18 for a description of the data which must be given in this file.
IDEP Indicator for use of wet and dry deposition model (-).
IDEP = 0 or 1.
Optional, default is 0.
  For IDEP = 1, an additional file 'casename.DEP' must be supplied. See Chapter 18 for a description of the data which must be given in this file.
ICANY Indicator for calculation of canyon effects (-).
ICANY = 0 or 1.
Optional, default is 0.
For ICANY = 1, an additional file 'casename.CNY' must be supplied. See Chapter 18 for a description of the data which must be given in this file.
IFLUC Indicator for calculation of centre-line concentration fluctuations (-).
IFLUC = 0 or 1.
Optional, default is 0.
  For IFLUC = 1, an additional file 'casename.PTL' must be supplied. See Chapter 18 for a description of the data which must be given in this file.
ILIFT Indicator for use of plume lift-off description (-).
ILIFT = 0 or 1.
Optional, default is 0.
  No additional data needed.
When ILIFT = 0, AEROPLUME will stop program execution when plume lift-off is detected for a plume after touch-down. When ILIFT = 1, a plume is allowed to become air-borne again after touch-down. See Chapter 9 in the HGSYSTEM 3.0 Technical Reference Manual for details.

The TERMINAT block sets reservoir release termination criteria. Normally these are all inactive (by setting them to a negative value) and the AEROPLUME run will only end when the reservoir is exhausted or when the reservoir pressure falls below the ambient pressure. Sometimes, however, it can be useful to stop the run before this occurs. The TERMINAT parameters can be used for this purpose.
DLST Last required plume diameter (m).
-1000 <= DLST <= 1000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
SLST Last required displacement measured along the plume axis (m).
-1000 <= SLST <= 2000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used
ZLST Last required plume centroid height (m).
-1000 <= ZLST <= 2000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
XLST Last required horizontal displacement (m).
-1000 <= XLST <= 2000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
ULST Last required plume velocity (m/s).
-1000 <= ULST <= 500.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
CPOLST Last required pollutant concentration (kg/m^3).
-1000 <= ULST <= 1000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
VPOLST Last required volumetric pollutant concentration (%).
-1000 <= ULST <= 100.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.

The MATCH block parameters contain the criteria that determine when the transition from AEROPLUME to one of the far-field models (HEGADAS and PGPLUME) will occur.
Normally the user should not change these parameters.
However, if the user wants to influence the transition location, then the MATCH parameters should be modified. This is only recommended for expert users or after seeking expert advice.

RULST Excess velocity ratio (-).
10-3 <= RULST <= 1.0.
Optional, default is 0.1.
RELST Entrainment ratio (-).
10-3 <= RELST <= 1.0.
Optional, default is 0.3.
RGLST Buoyancy effect for advection (-).
10-3 <=RGLST <=1.0.
Optional, default is 0.3.
RNLST Buoyancy effect for passive diffusion (-).
10-3 <= RNLST <= 1.0.
Optional, default is 0.1.
RALST Aspect ratio for passive diffusion (-).
10-3 <=RALST <= 1.0.
Optional, default is 0.2.

The CONCS block contains the minimum and maximum volumetric concentrations that are used to generate extra plume information concerning the contents of pollutant and total mixture within the cloud.

VCMAX Maximum volumetric concentration (%).
0 <= VCMAX <=100.
Optional, default is 100.
  e.g. higher flammability limit.
VCMIN Minimum volumetric concentration (%).
0 <= VCMIN <=100.
Optional, default is 0.
  E.g. lower flammability limit.

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