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1、11 1 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Chapter 11 CFX Expression Language CEL Introduction to CFX CFX Expression Language 11 2 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual CEL CFX Express
2、ion Language Allows the user to create equations can be functions of solution system variables that can be used in CFX Pre and CFD Post Example CEL CFX Expression Language 11 3 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual The syntax rules ar
3、e the same as those for conventional arithmetic Operators are written as addition subtraction multiplication division exponentiation Variables and expressions are case sensitive example t vs T Expressions must be dimensionally consistent for addition and subtraction operations example 1 0 mm 0 45 yd
4、s is OK You cannot add values with inconsistent dimensions Fractional and decimal powers are allowed example a 1 2 1 0 0 5 Units of expressions are not declared they are the result of units in the expression example a kg m 3 b m s 1 has units of kg m 2 s 1 Some constants are also available in CEL fo
5、r use in expressions e Constant 2 7182818 g Acceleration due to gravity 9 806 m s 2 pi Constant 3 1415927 R Universal Gas Constant 8314 5 m 2 s 2 K 1 CEL Rules CFX Expression Language 11 4 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual Numeric
6、al functions and operators are also available in CEL Right click when creating expressions for a complete list Custom functions with User Fortran can also be created Function Operand s Dimensions x Operand s ValuesResult s Dimensions sin x Angle Any Dimensionless cos x Angle Any Dimensionless tan x
7、Angle Any Dimensionless asin x Dimensionless 1 x 1 Angle acos x Dimensionless 1 x 1 Angle atan x Dimensionless Any Angle exp x Dimensionless Any Dimensionless loge x Dimensionless 0 x Dimensionless log10 x Dimensionless 0 1 m 1 0 In this case if the result is precisely equal to 1 m the result is res
8、1 res2 2 step x is 0 for negative x 1 for positive x and 0 5 for x 0 note that tan x is undefined for np 2 where n 1 3 5 both x and y must have the same dimensions Built In Functions CFX Expression Language 11 5 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598
9、Training Manual xDirection 1 in Reference Coordinate Frame yDirection 2 in Reference Coordinate Frame zDirection 3 in Reference Coordinate Frame rRadial spatial location r x 2 y 2 0 5 thetaAngle arctan y x tTime uVelocity in the x coordinate direction vVelocity in the y coordinate direction wVelocit
10、y in the z coordinate direction p absolute Pressure keTurbulent kinetic energy edTurbulent eddy dissipation TTemperature sstrnrShear strain rate densityDensity rNoDimNon dimensional radius rotating frame only viscosityDynamic Viscosity CpSpecific Heat Capacity at Constant Pressure condThermal Conduc
11、tivity AV nameAdditional Variable name mfMass Fraction Solver variables are available for use in any expression Below is a partial list of the available system variables When creating expressions right click to access a full list Depending on your physics some variables will not be valid e g you nee
12、d to solver heat transfer to use T Solver Variables CFX Expression Language 11 6 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual How To Create Expressions CFX Expression Language 11 7 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved Apr
13、il 28 2009 Inventory 002598 Training Manual To add more expressions similar method in CFD Post How To Create Expressions Right click in the Definition window to access Variables Constants Functions Locators and existing Expressions CFX Expression Language 11 8 ANSYS Inc Proprietary 2009 ANSYS Inc Al
14、l rights reserved April 28 2009 Inventory 002598 Training Manual where is the shear strain rate Creating a variable viscosity Viscosity of a shear thickening fluid Solver Variable and Expression Name are both accessed via the right mouse button CEL in CFX Pre Example 1 CFX Expression Language 11 9 A
15、NSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual Alternatively an expression can be entered directly into a field CEL in CFX Pre Example 1 CFX Expression Language 11 10 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Invent
16、ory 002598 Training Manual Using an if Function Set inlet temperature to 300 K for the first 19 iterations then raise it to 320 K after 20 iterations Solver variable accessed with the right mouse button Note On the 21st iteration inlet temp 310 K CEL in CFX Pre Example 2 CFX Expression Language 11 11 ANSYS Inc Proprietary 2009 ANSYS Inc All rights reserved April 28 2009 Inventory 002598 Training Manual You can also define your own 1 D linear or 3 D cloud of points interpolation functions Import
