variable - Select variables to be processed
variable name [unit-override] [; name [unit-override] ...] |
name | The name of a variable to be selected.
The specified name must either be present in the input files or
must be one that can be derived from other information in the
files.
See the list below for the variables that can be derived.
| ||
---|---|---|---|
unit-override | Specifies one or more unit-specifiers that may be specified
on the unit command, a normalization quantity or a user specified
scale and offset of the form:
[origin origin] [scale scale] |
The variable command is used to define the variables that are to be processed and optionally in what units of measure the data is to be presented. The unit-override specifications only affect the variable being selected; they do not alter the default units of measure.
variable commands accumulate, that is, each variable command adds to the list of variables that will be made available for subsequent processing. The list is passed on in the order that it was created. Up to 128 variables may be selected at any one time. The list of selected variables and their units of measure can be displayed with the show command and cleared with the clear command.
The following list represents variables that, if requested and not present in the input files, will be derived from other information in the files if sufficient information is available. Real gas effects are taken into account if the solution file has the necessary information.
Note that some variables require the specification of a surface, or normal direction into the flow field, and others require knowledge of "up" and "down" axes orientation. Variables denoted with (s) following their description indicate that the normal direction must be specified properly using the subset or surface command. Variables denoted with (o) are affected by the axes orientation set by the orientation command.
name | Description | Direction | ||
---|---|---|---|---|
x | x coordinate | |||
y | y coordinate | |||
z | z coordinate | |||
dx | Δx, measured from first point in subset | |||
dy | Δy, measured from first point in subset | |||
dz | Δz, measured from first point in subset | |||
ds | Arc length, measured from first point in subset | |||
x/c | Normalized x (only valid for GENPLOT files) | |||
y/b | Normalized y (only valid for GENPLOT files) | |||
rho | Density | |||
rho0 | Stagnation density | |||
p | Pressure | |||
p0 | Stagnation pressure | |||
Cp | Pressure coefficient | |||
Cpt | Total pressure coefficient | |||
deltap | Delta pressure | |||
pp | Pitot pressure | |||
q | Dynamic pressure | |||
T | Temperature | |||
T0 | Stagnation temperature | |||
M | Mach number | |||
Ma | Equivalent isentropic Mach number | |||
Mt | Turbulent Mach number | |||
a | Speed of sound | |||
u | x velocity | |||
v | y velocity | |||
w | z velocity | |||
V | Velocity magnitude | |||
Vxy | uv crossflow velocity magnitude | |||
Vyz | vw crossflow velocity magnitude | |||
Vxz | uw crossflow velocity magnitude | |||
e0 | Absolute stagnation energy per unit volume | |||
ek | Kinetic energy per unit volume | |||
ei | Sensible internal energy per unit volume | |||
h | Sensible enthalpy | |||
h0 | Sensible stagnation enthalpy | |||
s | Entropy | |||
S | Strain rate magnitude | |||
Sxx, Sxy, Sxz | Strain rate tensor components | |||
Syx, Syy, Syz | Strain rate tensor components | |||
Szx, Szy, Szz | Strain rate tensor components | |||
W | Rotation rate magnitude or vorticity magnitude | |||
Wxx, Wxy, Wxz | Rotation rate tensor components | |||
Wyx, Wyy, Wyz | Rotation rate tensor components | |||
Wzx, Wzy, Wzz | Rotation rate tensor components | |||
wx | x component of vorticity | |||
wy | y component of vorticity | |||
wz | z component of vorticity | |||
swirl | Swirl | |||
helicity | Helicity | |||
dila | Dilatation | |||
localpha | Local α (angle of attack) | o | ||
locbeta | Local β (sideslip angle) | o | ||
kappa | Thermal conductivity coefficient | |||
Q | Heat transfer rate | s | ||
mu | Total viscosity coefficient | |||
mul | Laminar viscosity coefficient | |||
mut | Turbulent viscosity coefficient | |||
k | k from k-ε or SST turbulence model | |||
epsilon | ε from k-ε turbulence model | |||
omega | ω from SST turbulence model | |||
alphat | Turbulent thermal diffusivity | |||
var_ei, eps_ei | Variance and dissipation rate of internal energy | |||
var_h0, eps_h0 | Variance and dissipation rate of total enthalpy | |||
var_h, eps_h | Variance and dissipation rate of static enthalpy | |||
delta | Boundary layer thickness | s | ||
delta1 or delta* | Boundary layer displacement thickness | s | ||
delta2 or THETA | Boundary layer momentum thickness | s | ||
delta3 | Boundary layer energy thickness | s | ||
deltau | Boundary layer velocity thickness | s | ||
THETAinc | Boundary layer incompressible momentum thickness | s | ||
Cf | Skin friction coefficient | s | ||
Cfx | x component of skin friction coefficient | s | ||
Cfy | y component of skin friction coefficient | s | ||
Cfz | z component of skin friction coefficient | s | ||
tau | Total (laminar+turbulent) shear stress | s | ||
taux | x component of total shear stress | s | ||
tauy | y component of total shear stress | s | ||
tauz | z component of total shear stress | s | ||
uu, uv, uw | Turbulent stress components | s | ||
vu, vv, vw | Turbulent stress components | s | ||
wu, wv, ww | Turbulent stress components | s | ||
uu+, uv+, uw+ | Non-dimensional turbulent stress components | s | ||
vu+, vv+, vw+ | Non-dimensional turbulent stress components | s | ||
wu+, wv+, ww+ | Non-dimensional turbulent stress components | s | ||
y+ | Non-dimensional boundary layer wall coordinate | s | ||
u+ | Non-dimensional boundary layer velocity | s | ||
k+ | Non-dimensional turbulent kinetic energy | s | ||
epsilon+ | Non-dimensional turbulent dissipation rate | s | ||
Rt | Turbulent Reynolds number | |||
Ry | Turbulent Reynolds number based on y | |||
cmuRG | C_{μ}, Rumsey-Gatski algebraic stress coefficient | s | ||
fmuJL | f_{μ}, Jones-Launder damping function | s | ||
fmuCH | f_{μ}, Chien damping function | s | ||
fmuSP | f_{μ}, Speziale damping function | s | ||
fmuLB | f_{μ}, Lam-Bremhorst damping function | s | ||
C-species | Mass fraction of species | |||
X-species | Mole fraction of species | |||
Veff | Effective collision frequency | |||
MW | Molecular weight | |||
R | Gas constant | |||
cp | Specific heat at constant pressure | |||
cv | Specific heat at constant volume | |||
gamma | Ratio of specific heats | |||
hf | Heat of formation | |||
beta | Effective gamma | |||
Z | Compressibility factor |
In addition to the above, for flows in a rotating reference frame (computed, for example, using Wind-US with the ROTATE keyword), the following variables may be requested for properties in the rotating reference frame: p0r, T0r, Mr, ur, vr, wr, Vr, and e0r. Note that the names are the same as the corresponding variable from the above list for the inertial (i.e., non-rotating) reference frame.
Also, due to the special significance of conservation variables, any name of the form rho*xxxx will be derived if sufficient information is present to derive rho and xxxx.
In addition to any of the unit-specifiers that may be specified on the units command, any one of the following normalization factors may be supplied:
unit-override | Description | |
---|---|---|
rhoinf | Freestream density | |
rho0inf | Freestream stagnation density | |
pinf | Freestream pressure | |
p0inf | Freestream stagnation pressure | |
ppinf | Freestream pitot pressure | |
qinf | Freestream dynamic pressure | |
Tinf | Freestream temperature | |
T0inf | Freestream stagnation temperature | |
hinf | Freestream enthalpy | |
h0inf | Freestream stagnation enthalpy | |
ainf | Freestream speed of sound | |
Minf | Freestream Mach number | |
uinf | Freestream velocity | |
muinf | Freestream viscosity | |
kinf | Freestream k from the k-ε turbulence model | |
einf | Freestream ε from the k-ε turbulence model |
The use of the origin and scale unit override allows the user to create their own units or nonrmalizations. The values specified for origin and scale are used as follows:
The user must be aware that if x is a dimensional quantity, origin and scale must take into account the fact that x is in SI units. A typical use would be the display of x normalized by the chord length.
Variable names may be preceeded by a minus sign to swap their sign. The minus sign is applied in SI units before any optional origin, scale, unit conversion, or normalization. The minus sign should not be used on variables written to a common file or interpolation file, because CFPOST will not be able to read those variables later. See the interpolate command for more details.
Example 1
! select pressure normalized by the freestream pressure ! also select Mach number variable p pinf; M ! select u in feet/second (assume second is default time unit) variable u feet ! select turbulent shear stress, swapping the sign variable −rho*uv ! four variables have been selected!
Example 2
! select u velocity normalized by freestream velocity variable u uinf ! enable English units units english ! select v velocity in feet/second variable v ft sec ! select w velocity in centimeters/second variable w cm
Example 3
! select pressure in psi. Note that if one simply selected ! English units then the result would be in psf! variable p lbf inches ! select heat transfer rate in BTU/(foot^2-hour) variable Q feet hour BTU
Example 4
! Select Cp and x. x is normalized by the chord. ! The chord is 100 inches = 2.54 meters, therefore ! scale = 1/2.54 = .3937 ! The leading edge was at 250 inches = 6.35 meters, therefore ! origin = 6.35 variable x origin 6.35 scale .3937
See Also: The units command for how to define units of measure; the show command for how to display the variable list; the clear command for how to clear the variable list; the subset and surface commands for how to specify the surface and normal direction into the flow field for variables marked with (s); the orientation command for how to specify the axes orientation for variables marked with (o); "Equations Used by CFPOST" for the formulas used for deriving variables.
vector - Define a vector variable
vector variable [unit-override] |
variable | The name of a vector variable.
| ||
---|---|---|---|
unit-override | A normalization quantity or one or more unit-specifiers that may be specified on the units command. |
The vector command is used to specify the variable to be included in the plot file for generating a vector plot. The following vector variables are available:
variable | Description | |
---|---|---|
V | Velocity | |
Cf | Skin friction | |
W | Vorticity |
See Also: The units command for how to define units of measure; the genplot surface command for how to generate a file for vector plotting; the plot vectors command for how to perform vector plotting.
units - Specify default dimensional units of output data
units unit-specifier unit-specifier ... |
unit-specifier | The name of a unit or system of units. |
---|
The units command defines the default units of measure to be used for the subsequent presentation of data. CFPOST maintains units of measure for four basic units (mass, length, time and temperature), and two derived units (force and energy). All other units are derived from these basic units. For instance, units of pressure are derived from the force unit and the length unit. Similarly, velocity is derived from length and time units. CFPOST uses SI units internally as its default system of units. The default output system of units is FSS.
If a "system of units" is specified as a unit-specifier, all six of the units of measure are set to the values defined for the selected "system of units". If a "unit name" is specified as a unit specifier, only the corresponding unit of measure is modified.
Some commands produce geometry information with the geometry variables being explicitly requested (e.g.: artis, plot3d). On some other commands the user is providing locations, lengths, or areas (e.g.: cut, integrate, rake). In these situations, CFPOST needs to know the length unit in which the information is being given. The program does this by maintaining a default length unit. The default length unit is the length unit that is in effect just before the first variable is added to the variable list or, if no variables have been selected, at the time that a command that requires the default length unit is executed. Note that the first variable is either the first one added in an execution of CFPOST or the first one added after the variable list has been cleared.
Valid values for "system of units" are:
unit-specifier | Description | |
---|---|---|
SI | System International (meter, kilogram, second, degrees Kelvin, Newton, Joule) | |
MKS | A synonym for SI | |
metric | A synonym for SI | |
CGS | Centimeter, gram, second, degrees Kelvin, dyne and erg | |
FSS | Foot, slug, second, degrees Rankine, pound force, foot-pound force | |
british | A synonym for FSS | |
english | A synonym for FSS | |
FPS | Foot, pound mass, second, degrees Rankine, pound force, foot-pound force |
Valid values for mass units are:
kg, kilogram gram slug lb, lbm, poundValid values for length units are:
m, meter cm, centimeter mm, millimeter ft, feet, foot in, inchValid values for temperature units are:
K, Kelvin C, Centigrade, Celsius R, Rankine F, FahrenheitValid values for force units are:
N, Newtons dynes lbf (pounds force)Valid values for energy units are:
Joule erg lbf-ft, ft-lbf BTU
Example
! English system, but override energy unit units english BTU
See Also: The variable command for how to override the current units of measure.
Last updated 4 Sep 2019