16.2.1. Common Variables Relevant for Most CFD Calculations

The following table contains a list of variables (with both long and short variable names) that can be used when working with CFD calculations. For an explanation of the column headings, see List of Field Variables.

Note: Variables with names shown in bold text are not output to CFD-Post. However, some of these variables can be output to CFD-Post by selecting them from Extra Output Variables List on the Results tab of the Solver > Output Control details view of CFX-Pre.

Long Variable Name	Short Variable Name	Units	Availability	Definition
Density	density	[kg m^-3]	1 A, C, M, P, R, TS	Mass per unit volume. Note that for fixed composition, variable composition, and reacting mixtures, when density is governed by the `Ideal Mixture` option, the density is determined by a mass-fraction-weighted harmonic average:
Dynamic Viscosity	viscosity	[kg m^-1 s^-1]	2 A, C, M, P, R, TS	Dynamic viscosity (), also called absolute viscosity, is a measure of the resistance of a fluid to shearing forces, and appears in the momentum equations. Using an expression to set the dynamic viscosity is possible. For details, see Non-Newtonian Flow in the CFX-Solver Modeling Guide.
Velocity^[a]	vel	[m s^-1]	1 A, C, M, P, R, TS	Velocity vector.
Velocity u Velocity v Velocity w	u v w	[m s^-1]	1 A, C, M, P, R, TS	Components of velocity.
Pressure	p	[kg m^-1 s^-2]	1 A, C, M, P, R, TS	Both `Pressure` and `Total Pressure` are measured relative to the reference pressure that you specified on the Domains panel in CFX-Pre. Additionally, `Pressure` is the total normal stress, which means that when using the k-e turbulence model, `Pressure` is the thermodynamic pressure plus the turbulent normal stress. `Static Pressure` is the thermodynamic pressure, in most cases this is the same as `Pressure`. For details, see Modified Pressure in the CFX-Solver Theory Guide.
Static Pressure	pstat	[kg m^-1 s^-2]	3	CFX solves for the relative `Static Pressure` (thermodynamic pressure) in the flow field, and is related to `Absolute Pressure` .
Total Pressure	ptot	[kg m^-1 s^-2]	2 A, C, M, P, R, TS	The total pressure, , is defined as the pressure that would exist at a point if the fluid was brought instantaneously to rest such that the dynamic energy of the flow converted to pressure without losses. The following three sections describe how total pressure is computed for a pure component material with constant density, ideal gas equation of state and a general equation of state (CEL expression or RGP table). For details, see Scalable Wall Functions in the CFX-Solver Theory Guide.
Wall Shear	wall shear	Pa	3,B	For details, see Scalable Wall Functions in the CFX-Solver Theory Guide.
Volume of Finite Volume			3 C, DT, R, TS	Volume of finite volume. For details, see Discretization of the Governing Equations in the CFX-Solver Theory Guide.
X coordinate	x	[m]	2 C	Cartesian coordinate components.
Y coordinate	y	[m]	2 C
Z coordinate	z	[m]	2 C
Kinematic Diffusivity	visckin		2 C, M, P, R, TS	Kinematic diffusivity describes how rapidly a scalar quantity would move through the fluid in the absence of convection. For convection-dominated flows, the kinematic diffusivity can have little effect because convection processes dominate over diffusion processes.
Shear Strain Rate	sstrnr	[s^-1]	2 A, C, M, R, TS	For details see Non-Newtonian Flow in the CFX-Solver Modeling Guide.
Specific Heat Capacity at Constant Pressure	Cp	[m^2 s^-2 K^-1]	2 A, C, M, R, TS	For details, see Specific Heat Capacity in the CFX-Solver Modeling Guide.
Specific Heat Capacity at Constant Volume	Cv	[m^2 s^-2 K^-1]	2 A, C, M, P, R, TS
Thermal Conductivity	cond	[kg m s^-3 K^-1]	2 A, C, M, R, TS	Thermal conductivity, , is the property of a fluid that characterizes its ability to transfer heat by conduction. For details, see Thermal Conductivity in the CFX-Solver Modeling Guide.
Temperature	T	[K]	1 A, C, DT, M, P, R, TS	The static temperature, , is the thermodynamic temperature, and depends on the internal energy of the fluid. In CFX, depending on the heat transfer model you select, the flow solver calculates either total or static enthalpy (corresponding to the total or thermal energy equations). For details, see Static Temperature in the CFX-Solver Theory Guide.
Total Temperature	Ttot	[K]	1 A, C, M, P, R, TS	The total temperature is derived from the concept of total enthalpy and is computed exactly the same way as static temperature, except that total enthalpy is used in the property relationships. For details, see Total Temperature in the CFX-Solver Theory Guide.
Wall Heat Flux	Qwall	[W m^-2]	2,B C, DT, R, TS	A heat flux is specified across the wall boundary. A positive value indicates heat flux into the domain. For multiphase cases, when the bulk heat flux into both phases is set, this option is labeled Wall Heat Flux instead of Heat Flux. When set on a per fluid basis, this option is labelled Heat Flux.
Wall Heat Transfer Coefficient	htc	[W m^-2 K^-1]	2,B C, R, TS	For details, see Heat Transfer Coefficient and Wall Heat Transfer Coefficient in the CFX-Solver Modeling Guide.
Total Enthalpy	htot	[m^2 s^-2]	A, C, M, R, TS	For details, see Transport Equations in the CFX-Solver Theory Guide.
Static Enthalpy	enthalpy	[m^2 s^-2]	2 A, C, M, P, R, TS	For details, see Static Enthalpy in the CFX-Solver Theory Guide.

^[a]When a rotating frame of reference is used, all variables in the CFX-5 results file are relative to the rotating frame, unless specified as a Stn Frame variable.