Skip navigation links
(Wind-US Documentation Home Page) (Wind-US User's Guide) (GMAN User's Guide) (MADCAP User's Guide) (CFPOST User's Guide) (Wind-US Utilities) (Common File User's Guide) (Wind-US Installation Guide) (Wind-US Developer's Reference) (Guidelines Documents)

(Introduction) (Tutorial) (Geometry and Flow Physics Modeling) (Numerical Modeling) (Boundary Conditions) (Convergence Monitoring) (Files) (Scripts) (Parallel Processing) (Keyword Reference) (Test Options)



CHEMISTRY - Chemistry model selection (block)

CHEMISTRY
   {EQUILIBRIUM
       LIU-VINOKUR |
    FROZEN
       [ADJUST [CURVES FOR 0 K REFERENCE]]
       FILE filename
       SPECIES {AIR | S1 sf1 S2 sf2 ... Sm sfm}
       [DIFFUSION {NONE | SINGLE | EFFECTIVE-BINARY}]
       [THERMO9] |
    FINITE [RATE]
       [ADJUST [CURVES FOR 0 K REFERENCE]]
       FILE filename
       SPECIES {AIR | S1 sf1 S2 sf2 ... Sm sfm}
       [DIFFUSION {NONE | SINGLE | EFFECTIVE-BINARY}]
       [FIXED zone_selector]
       [NOREACT zone_selector]
       [FUEL [AIR] [RATIO] value]
       [OMIT [THIRD-BODY] S1 S2 ... Sm ZONE zone_selector]
       [EDC value]
       [DAMKOHLER Damax]}
   [VISCOSITY {SUTHERLAND | WILKE | KEYE | CONSTANT vis | TUNNEL9 | \
      CUSTOM c1 c2}]
ENDCHEMISTRY

This option allows the user to specify the real gas chemistry mode and input data for the desired species and reactions.

Note: The ARBITRARY INFLOW keyword block, if used, must come after the CHEMISTRY keyword block in the input data (.dat) file.

The various elements of the CHEMISTRY input block are defined as follows:

CHEMISTRY

Defines the beginning of the CHEMISTRY block.

{EQUILIBRIUM | FROZEN | FINITE [RATE]}

The main part of the CHEMISTRY block is divided into three sections, corresponding to input for equilibrium chemistry, frozen chemistry, and finite-rate chemistry. One and only one of the keywords EQUILIBRIUM, FROZEN, and FINITE RATE must be specified.

With the FROZEN chemistry option, it is assumed that rates of chemical reactions are very slow and the time scales of the reactions are much larger than the time scales of the fluid motion. In this case, chemical reaction can be ignored and the species concentrations will only change due to the convection and diffusion processes of the fluid motion. The FINITE RATE option assumes that the chemical reactions occur at time scales that are comparable to those of the fluid motion. Thus, reaction mechanisms are included in the modeled source terms. EQULIBRIUM chemistry essentially means that the rates of chemical reactions are very fast and the time scale of the chemical reactions are very small with respect to the time scales of the fluid motion.

LIU-VINOKUR

Chemical equilibrium is characterized by the minimization of Gibbs free energy subject to the constraint of conservation of atomic species. Rigorous calculation of the free energy state can be very accurate, but also computationally expensive. To improve efficiency, the method of Liu and Vinokur is used to generate a thermodynamic data base as a function of temperature and density for equilibrium air calculations up to 50000 K.

The LIU-VINOKUR option only applies to EQUILIBRIUM chemistry, and is a required keyword. It activates the equilibrium air thermodynamic curve fits. Data for the individual species is not output.

Additional details may be found in the following references:


ADJUST [CURVES FOR 0 K REFERENCE]

In the chemistry data (.chm) file, the WINDNASA and NASA3287 curve fits for the thermodynamic properties use an enthalpy reference state of 298.15 K. When the ADJUST keyword is used, the heat of formation at 0 K is read from the .chm file, and the values of enthalpy and Gibbs free energy returned by the WINDNASA and NASA3287 curve fits are shifted to change the reference state to 0 K. If ADJUST is not used, the enthalpy reference state is left as 298.15 K, and the line in the .chm file containing the heat of formation at 0 K, if present, is ignored.

Note that the ADJUST keyword has no effect when the SPARKCRV curve fits are used. They always use an enthalpy reference state of 0 K.

The ADJUST keyword applies to both FROZEN and FINITE RATE chemistry. If specified, it must come before the FILE keyword in the .dat file.

FILE filename

Specifies the chemistry data (.chm) file containing the data defining the thermodynamic property, reaction rates, and transport properties. Unless the chemistry data file is located in the same directory as the one in which Wind-US is running (see the -runroot and -runinplace wind script options) the specified filename must be a full path name. And in either case, it should include the .chm extension.

The FILE keyword applies to both FROZEN and FINITE RATE chemistry, and must be specified.

SPECIES {AIR | S1 sf1 S2 sf2 ... Sm sfm}

Specifies the species names (S1 through Sm), and their freestream (reference) mass fractions (sf1 through sfm). The specified species must be the same as those in the chemistry data (.chm) file, but not necessarily in the same order. Multiple SPECIES lines may be used to append to the species list. This is particularly useful in cases where the list is too long to fit on a single line.

AIR may be specified instead of individual species to indicate use of air mass fractions. The species O2 and N2 must be listed in the chemistry data (.chm) file.

The SPECIES keyword applies to both FROZEN and FINITE RATE chemistry, and must be specified.

DIFFUSION {NONE | SINGLE | EFFECTIVE-BINARY}

Specifies the type of species diffusion. The default is SINGLE, which uses a single mixture diffusion coefficient based on the mixture viscosity and the Schmidt number.

If EFFECTIVE-BINARY is specified, an effective binary diffusion model is used, with each species having its own effective diffusion coefficient with respect to the mixture. (For details see Lankford, D. W. and Mani, M. (2003) "Wind Thermochemical Models and Recent Improvements," AIAA Paper 2003-545.) This option requires that the Lennard-Jones parameters used in computing the intermolecular potential be specified in the chemistry data (.chm) file.

The DIFFUSION keyword applies to both FROZEN and FINITE RATE chemistry.

THERMO9

Simulate AEDC's Tunnel 9 facility, using a real gas table look-up of thermodynamic properties. Either nitrogen or hydrogen may be modeled, as specified by the first species listed in the chemistry data (.chm) file. If the first species name is anything other than N2 or H2, the job will abort.

If THERMO9 is specified, it must come after the FILE keyword in the input data (.dat) file. In addition, if the WINDNASA or NASA3287 format is used for the thermodynamic properties in the .chm file, ADJUST must be specified to shift the enthalpy reference state from 298.15 K to 0 K.

The THERMO9 keyword only applies to FROZEN chemistry, and is only available for structured grids.

FIXED zone_selector

Specifies fixed chemistry composition (i.e., a fixed set of mole fractions) in the specified zone(s). Species concentrations are set to the values specified with the SPECIES keyword. This allows the thermodynamic properties to be computed using the correct multi-species models, but the expense of actually solving the species equations is skipped. The chemistry source term is also not computed, since this approach only makes sense where no reactions are taking place.

This option is intended for use in multi-zone computations with reactions occurring in some zones, but not others. An example is an internal/external nozzle flow, where no reactions take place in the external flow upstream of the nozzle exit. Using this option may significantly lower the execution time, but must be used with care.

Specification of the zone_selector is required for this keyword.

The FIXED keyword only applies to FINITE RATE chemistry, and is only available for structured grids.

NOREACT zone_selector

Disables reactions in the specified zone(s), but still allows convection and mixing of the species. This option may be used to reduce compute time in zones where the species concentrations may be changing due to the dynamics of the flow, but no reactions are expected to occur.

Specification of the zone_selector is required for this keyword.

The NOREACT keyword only applies to FINITE RATE chemistry, and is only available for structured grids.

FUEL [AIR] [RATIO] value

value specifies the fuel-air ratio for H2-air combustion (two-reaction global model).

The FUEL AIR RATIO keyword only applies to FINITE RATE chemistry, with ispec = 2 in the chemistry data (.chm) file.

OMIT [THIRD-BODY] S1 S2 ... Sm ZONE zone_selector

This keyword allows control of the reacting species in a finite-rate chemistry solution on a zonal basis. Reactions leading to the production or destruction of the species given by S1 through Sm will be eliminated in the selected zones. In addition, if the THIRD-BODY keyword parameter is used, any reaction involving the named species will be eliminated. The species will still be convected and diffused, maintaining conservation at zone boundaries.

Eliminating reactions in zones where they aren't relevant improves the overall efficiency of the calculation in two ways. First, the time required to perform the unnecessary computations is eliminated. And second, the stiffness of the system of equations is reduced, leading to faster convergence and greater stability.

Specification of the zone_selector is required for this keyword. In addition, the ZONE keyword must be included.

Multiple OMIT keywords are allowed, with conflicting input resolved by using the latter of the conflicting entries.

Currently, you cannot omit the final species specified with the SPECIES keyword.

The OMIT keyword only applies to FINITE RATE chemistry.

EDC value

Specifies use of the "eddy dissipation concept" when computing the reaction rate for finite-rate chemistry, and sets the value of the eddy dissipation coefficient Cedc. See the description of the chemistry data (.chm) file, Format 2, for more detail about the eddy dissipation concept.

The EDC keyword only applies to FINITE RATE chemistry solutions using the SST turbulence model. It may only be used when ispec = 121 or 137 in the .chm file.

DAMKOHLER Damax

Specifies use of the Damkohler rate limiter when computing the reaction rate for finite-rate chemistry. This is intended to improve the solution convergence rate by reducing the stiffness of the governing equations. Both forward and backward reaction rates will be limited such that the ratio

Da = τFD / τCHDamax

where τFD and τCH are the fluid dynamic and chemical reaction time scales, respectively. A reasonable value for Damax is 10. See the description of the chemistry data (.chm) file, Format 2, for more detail about the Damkohler rate limiter

The DAMKOHLER keyword may only be used when ispec = 137 in the .chm file.

MASS [FRACTIONS] {AIR | sf1 sf2 ... sfn}

Specifies the freestream (reference) mass fractions of the species. The mass fractions are specified in the same order as the species in the chemistry data (.chm) file.

AIR may be specified instead of individual species to indicate use of air mass fractions. The species O2 and N2 must be listed in the chemistry data (.chm) file.

The MASS FRACTIONS keyword may be used instead of the SPECIES keyword to specify the species mass fractions, but its use is discouraged. It has been retained for compatibility with input data (.dat) files used with earlier versions of Wind-US.

VISCOSITY {SUTHERLAND | WILKE | KEYE | CONSTANT vis | TUNNEL9 | \
      CUSTOM c1 c2}

Selects the transport property equations. For unstructured grids, only the SUTHERLAND, WILKE, and CONSTANT options have been extensively exercised. See the VISCOSITY keyword for details.

ENDCHEMISTRY

Defines the end of the CHEMISTRY block.

See Also: GAS, PRANDTL, SCHMIDT, VARIABLE PRANDTL, VARIABLE SCHMIDT, VISCOSITY, DEBUG 16, TEST 5, TEST 66, TEST 69, TEST 70, TEST 71, TEST 76, TEST 88, TEST 90, TEST 91, TEST 92, TEST 94, TEST 95, TEST 96, TEST 99, TEST 164, TEST 172, TEST 178

General and Standard Chemistry Packages

The chemistry data files supplied with Wind-US are summarized below.

Wind-US Recommended Chemistry Files

The following table lists the recommended Wind-US chemistry files. These files all contain thermodynamic data in the preferred NASA3287 format. Most of the elementary species have three thermodynamic curve fits and are valid to 20000 K, while other species such as H2O and CO2 only have two curve fits and are only valid to 6000 K. As a result, note that Tmax shown in the table is the maximum temperature for which all of the curve fits are valid.

Wind-US Recommended Chemistry Files
Species File(s) Tmax Description
CO2, H2O, O2, C2H4, N2 eth-air-5sp-3287.chm 6000 K Ethylene-air, 5 species, 1 global reaction, Westbrook-Dryer
C2H4, O2, CO, CO2, H2, H2O, N2 eth-air-7sp-3287.chm 6000 K Ethylene-air, 7 species, 3 reactions, taken from Baurle and Eklund, J. Prop. and Power, Vol. 18, No. 5, 2002, pp. 990-1002.
He,  O2, N2 he-air-3sp-3287.chm 20000 K 3 species, no reactions, for Helium-air mixing
O2, H, H2, H2O, OH, O, N2 h2-air-7sp-3287.chm 6000 K 7 species, 8 reactions, same as h2air-7sp-std-15k.chm but uses NASA3287 format.
O2, H, H2, H2O, OH, O, N2 h2-air-7sp-mbody-3287.chm 6000 K 7 species, 8 reactions, same as h2-air-7sp-3287.chm but has increased third body efficiencies for H2 and H2O which should enable faster combustion.
H2, O2, OH, H, O, H2O, HO2, H2O2, CO, CO2, HCO, HCHO, N2 h2-air-13sp-3287.chm 6000 K 13 species, 27 reactions, from Peters and Rogg, Lecture Notes in Physics, 1993, for modeling H2-air combustion with steam and carbon-based vitiation.


Older Wind-US Chemistry Files

The table below describes chemistry file data sets that use the older SPARKCRV or WINDNASA format for the thermodynamic data curve fits from previous versions of Wind-US. While still valid, they are now considered deprecated and might not be supported in the future. TEST 19 must be active to use these older format chemistry files. In many of these older files, the transport data (i.e. Sutherland viscosity and thermal conductivity coefficients) for 'O' species has been updated relative to previously released files.

In the table, the symbol e is electron density, and NO+ is ionized nitrogen oxide. Also, Tmax is the maximum temperature at which the curve fits are valid, Nc is the number of thermodynamic curve fit segments, Nr is the number of reaction equations, and 3d denotes Variable or Average 3rd-body efficiency.

General and Standard Chemistry Packages
Species File(s) Tmax Nc Nr 3d
O2, NO, O, N, N2 air-5sp-std-06k.chm
air-5sp-gen-06k.chm
6000 K 1 5 V
O2, NO, O, N, N2 air-5sp-std-15k.chm
air-5sp-gen-15k.chm
15000 K 3 5 V
O2, NO, O, N, N2 air-5sp-std-30k.chm
air-5sp-gen-30k.chm
30000 K 5 5 V
O2, NO, O, N, NO+, e, N2 air-7sp-std-06k.chm 6000 K 1 6 V
O2, NO, O, N, NO+, e, N2 air-7sp-std-15k.chm
air-7sp-gen-15k.chm
15000 K 3 6 V
O2, NO, O, N, NO+, e, N2 air-7sp-std-30k.chm
air-7sp-gen-30k.chm
30000 K 5 6 V
O2, H, H2, H2O, OH, O, N2 h2air-7sp-std-15k.chm
h2air-7sp-gen-15k.chm
h2air-7sp-bak-15k.chm
15000 K 3 8  
O2, H, H2, H2O, OH, O, N2 h2-air-7sp-mbody-spark.chm 6000 K 3 8  

The last entry in the table, h2-air-7sp-mbody-spark.chm, is similar to h2air-7sp-std-15k.chm but with increased third body efficiencies for H2 and H2O which should enable faster combustion. Note that h2-air-7sp-mbody-3287.chm and h2-air-7sp-3287.chm from the first table contain the same reaction sets, but use the preferred NASA3287 thermodynamic data format.

Obsolete Wind-US Chemistry Files

Three previously released chemistry files have been removed from distribution and should no longer be used:


Last updated 30 Sep 2016