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.

LIU-VINOKUR

Specifies that the Liu and Vinokur equilibrium air curve fits, valid to 50000 K, should be used. Data for the individual species is not output.

This keyword only applies to EQUILIBRIUM chemistry, and must be specified.

FILE filename [LOCAL]

Specifies the chemistry data (.chm) file containing the thermodynamic data, finite rate coefficients, and transport property data for Wilkes' law. If the chemistry data file is located in the same directory as the Wind-US files (.cfl, .cgd, etc.), the LOCAL option must be specified.

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 S_m), and their freestream (reference) mass fractions (sf₁ through sf_m). The specified species must be the same as those in the chemistry data (.chm) file, but not necessarily in the same order.

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. If EFFECTIVE-BINARY is specified, diffusion data must be present 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.

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

FIXED [ZONE] range1[,range2[, ... rangen]]

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.

In the zone specification, the range parameter(s) may be

	zonenum		Selects zone zonenum
	begzone:endzone		Selects all zones from begzone to endzone
	ALL		Selects all zones

This option is intended for use in multi-zone computations with reactions occuring 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.

The FIXED 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 range1[,range2[, ... rangen]]

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 S_m 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.

In the zone specification, the range parameter(s) may be

	zonenum		Selects zone zonenum
	begzone:endzone		Selects all zones from begzone to endzone
	ALL		Selects all zones

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", with the constant set to value.

The EDC keyword only applies to FINITE RATE chemistry, and may only be used (and is required) with ispec = 121 in the chemistry data (.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 and WILKE options are available. See the VISCOSITY keyword for details.

ENDCHEMISTRY

Defines the end of the CHEMISTRY block.

See Also: GAS, PRANDTL, SCHMIDT, VISCOSITY, DEBUG 16, TEST 5, TEST 66, TEST 70, TEST 71, TEST 88, TEST 89, TEST 90, TEST 91, TEST 92, TEST 93, 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 in the table below. [In the table, the symbol e⁻ is electron density, and NO⁺ is ionized nitrogen oxide. Also, T_max 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, OH, H2, H2O, N2	h2air-5sp-std-06k.chm	6000 K	1	2
O2, OH, H2, H2O, N2	h2air-5sp-std-15k.chm	15000 K	3	2
O2, H, H2, H2O, N2	Not yet available
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, CO2, H2O, NO2, N2	Not yet available