CFD_VAR Schema

The idea here is that datasets use differently named variables for the same entities. This makes it difficult for EnSight to "guess" that a variable might be pressure or density. As a result, it is difficult to write GUI utilities that provide domain specific computation with datasets from different formats. The CFD_VAR schema defines some fundamental variable quantities and tags the variables to let the GUI know that while this variable might be named "HELLO", it should be treated as "CFD_Velocity". The schema includes a tag 'CFD_VAR' that is specified on the case object itself that reports that the case supports the schema and the version number of the schema employed.

Notes: It would be nice if the Meta Data included a way to tell it which direction was the axial_direction for use with RectToCyl to define the coordinate transformation X, Y, or Z, default is Z). It would also be nice to define things like symmetry plane so that symmetry could be automatically turned on.

Note: if you use a format that supports CFD_VAR schema (EnSight or Fluent), then you must turn it on. To turn it on, click on the User Defined Tools icon. Then open the Utilities folder. Then double click the Extended CFD variables. Then in that pop up window choose on File>Enable. This pop up window will tell you all the CFD variables which the schema is capable of enabling.

Dependencies

There are a number of variable quantities defined by the schema and they are listed here, along with their dependencies (in parenthesis) and the formulas. One interesting feature of this schema is that there is an extension that can automatically figure out what other CFD variables can be computed based on the tagged variables present in the variable list. For example, if the extension detects the presence of "Pressure_absolute", "Temperature", and "Density", it can automatically generate an "R_mass" variable for the user, using the table below. The extension is also capable of chaining expressions from the table, using two or more sub-expressions to create the final variable.

Units are described as M=mass, L=length, K=temperature, T=time. The first description of each variable has a => with units.

R_mass = (Pressure_absolute, Temperature, Density) = Pressure_absolute/(Density*Temperature) => MM/TTK
R_mass = (Temperature, Gamma, Speed_sound) = Speed_sound^2/(Gamma*Temperature)
R_mass = (R_ref) # this defaults to constant reference value
Cp_mass = (Gamma,R_mass) = Gamma*R_mass/(Gamma - 1) => same as R_mass
Cp_mass = (Cp_ref) # this defaults to constant reference value
Gamma = (R_mass,Cp_mass) = 1 / ( 1 - (R_mass/Cp_mass)) => dimensionless
Gamma = (Speed_sound, R_mass, Temperature) = Speed_sound^2/(Rmass*Temperature)
Gamma = (Speed_sound, Pressure_absolute, Density) = (Speed_sound^2)*Density/Pressure_absolute
Gamma = (Gamma_ref) # this defaults to constant reference value
Pressure_absolute = (Pressure_relative, Pressure_absolute_const) = Pressure_absolute_const + Pressure_relative => M/LTT
Density = (Pressure_absolute,Temperature, R_mass) = Pressure_absolute/(R_mass*Temperature) => M/LLL
Temperature = (Speed_sound, Gamma, R_mass) = Speed_sound^2 / (Gamma * R_mass) => K
Temperature = (Mach, Velocity, Gamma, R_mass) = (Velocity/Mach)^2 / (R_mass * Gamma)
Temperature = (Pressure_absolute,Density,R_mass) = Pressure_absolute / (Density * R_mass)
Speed_sound = (Gamma, R_mass, Temperature) = sqrt(Gamma * R_mass * Temperature) => L/T
Speed_sound = (Velocity, Mach) = Velocity / Mach
Energy_total = (Density, Pressure_absolute, Velocity, Gamma) = Pressure_absolute/(Gamma -1) + (Density * Velocity^2)/2 # from the user manual for this calculator function => M/LTT
Mach = (Velocity, Speed_sound) = Velocity / Speed_sound => dimensionless
Mach = (Density, Energy_total, Velocity, Gamma) = # see User manual for calculator function

Pressure_stagnation = (Presure_absolute, Mach, Gamma)= # See calculator function equation PresStag => M/LTT
Pressure_stagnation = (Density, Energy_total, Velocity, Gamma) = # see calculator function equation PresStag
Temperature_stagnation = (Temperature, Mach, Gamma) = # see calculator function TemperStag equation listed in user manual => K
Temperature_stagnation = (Density, Energy_total, Velocity, Gamma) - #use calculator function TemperStag

Vorticity = (Velocity) = # use Vorticity function in Calculator => /T
Velocity_grad = (Velocity) # use gradient function in calculator. => /T
Velocity_x = (Velocity) = Velocity[X] in calculator => L/T
Velocity_y = (Velocity) = Velocity[Y] from calculator => L/T
Velocity_z = (Velocity) = Velocity[Z] from calculator => L/T
Velocity_x_grad = (Velocity_x) = #calculator gradient of Velocity_x => /T
Velocity_y_grad = (Velocity_y) = #calculator gradient of Velocity_y => /T
Velocity_z_grad = (Velocity_z) = #calculator gradient of Velocity_z => /T
Pressure_grad = (Pressure_absolute) = # calculator function gradient on Pressure_absolute => M/LLTT
Pressure_grad = (Pressure_relative) = # calculator function gradient of Pressure_relative => M/LLTT

EleSize = () # calculator function EleSize. => LL or LLL depending on 2D or 3D elements
Wall_shear_force = Wall_shear_stress * Element_size # for 2D elements only
Wall_pressure_force = (P) = Multi-step Pressure force calculation. Create an elemental pressure scalar, calculate Wall_pressure_force = Normal * pressure * area => ML/TT
Wall_total_force = (Wall_pressure_force, Wall_shear_force) = vector sum of these vectors. => ML/TT

Velocity_axial = (Velocity,Axial_direction) = RectToCyl[Z] #RectToCyl only can use Z = axial => L/T
Velocity_radial = (Velocity,Axial_direction)= RectToCyl[X] => L/T
Velocity_tangential = (Velocity,Axial_direction) = RectToCyl[Y] => L/T
Coordinates_axial = (Coordinates,Axial_direction) = RectToCyl[Z] => L
Coordinates_radial = (Coordinates,Axial_direction) = RectToCyl[X]
Coordinates_tangential = (Coordinates,Axial_direction) = RectToCyl[Y]
Coordinate_x = (Coordinates) = Coordinates[X]
Coordinate_y = (Coordinates) = Coordinates[Y]
Coordinate_z = (Coordinates) = Coordinates[Z]
Total_Surface_Heat_Flux = Boundary_heat_flux / EleSize => M/TTT (commonly W/m^2).
Wall_shear_stress = Wall_shear_force / EleSize => M/TTL
Wall_shear_force = Wall_shear_stress * EleSize => ML/TT

Example XML mapping for Fluent

Example XML mapping for STARCCM Plus

STAR3 - discontinued around 2003. Export EnSight Case Gold to read.

STAR4 = STARCCM - transition product between 3 and plus uses .ccm. Can be read by VKI.

STARCCM Plus is fifth generation product released 2004. Cannot be read by VKI (3/09), users must export case gold. uses .sim file.

All three export EnSight case gold and all name variables differently. This work is for STARCCM Plus.

CFD_VAR Schema

CFD_VAR Schema

Dependencies

Example XML mapping for Fluent

Example XML mapping for STARCCM Plus

Example XML mapping for CFX5