Another application of the user state point function could be to calculate the isentropic expansion efficiency of a device. The following example code shows the usage of the USER_STATEPT function to accomplish this task. Input arguments for this routine are the mass flow averaged values of total enthalpy () and entropy () at a reference plane 1 as well as the mass flow averaged values of total enthalpy () and total pressure () at a second reference plane, such as an outlet. The isentropic expansion efficiency is defined as:

(19–6)

With the isentropic enthalpy, , being the enthalpy .

To calculate the isentropic efficiency, the following input data is provided to USER_STATEPT:

The CCL that is required to plot the efficiency in the CFX-Solver Manager is as follows:

LIBRARY:
  USER ROUTINE DEFINITIONS:
    USER ROUTINE: User Routine 1
      Calling Name = my_eff
      Library Name = efficiency
      Library Path = ..
      Option = User CEL Function
    END
  END
  CEL:
    FUNCTION: Function 1
      Argument Units = [J/kg],[J/kg],[J/kg/K],[Pa]
      Option = User Function
      Result Units = []
      User Routine Name = User Routine 1
    END
    EXPRESSIONS:
      H1 = massFlowAve(Total Enthalpy in Stn Frame)@Inflow
      H2 = massFlowAve(Total Enthalpy in Stn Frame)@Outflow
      S1 = massFlowAve(Static Entropy)@Inflow
      P2 = massFlowAve(Total Pressure in Stn Frame)@Outflow
#
      Eff = Function 1(H1,H2,S1,P2)
    END
  END
END
FLOW: Flow Analysis 1
  OUTPUT CONTROL:
    MONITOR OBJECTS:
      MONITOR BALANCES:
        Option = Full
      END
      MONITOR FORCES:
        Option = Full
      END
      MONITOR PARTICLES:
        Option = Full
      END
      MONITOR RESIDUALS:
        Option = Full
      END
      MONITOR TOTALS:
         Option = Full
      END
      MONITOR POINT: Eff1
        Option = Expression
        Expression Value = Eff
      END
    END
    RESULTS:
      File Compression Level = Default
      Option = Standard
    END
  END
END

The Fortran source code for the expansion efficiency calculation is given below:

#include "cfx5ext.h"
dllexport(my_eff)
      SUBROUTINE MY_EFF ( 
     &  NLOC,NRET,NARG,RET,ARGS,CRESLT, CZ,DZ,IZ,LZ,RZ)
CC
CD User routine: Compute isentropic efficiency
CC
CC --------------------
CC        Input
CC --------------------
CC
CC  NLOC   - size of current locale
CC  NRET   - number of components in result
CC  NARG   - number of arguments in call
CC  ARGS() - (NLOC,NARG) argument values
CC
CC --------------------
CC      Modified
CC --------------------
CC
CC  Stacks possibly.
CC
CC --------------------
CC        Output
CC --------------------
CC
CC  RET()  - (NLOC,NRET) return values
CC  CRESLT - 'GOOD' for success
CC
CC --------------------
CC       Details
CC --------------------
CC
CC  Template routine for user state point code
CC
CC======================================================================
C
C ------------------------------
C        Argument list
C ------------------------------
C
      INTEGER   NLOC,NARG,NRET
      CHARACTER CRESLT*(*)
      REAL      ARGS(NLOC,NARG), RET(NLOC,NRET)
C
      INTEGER IZ(*)
      CHARACTER CZ(*)*(1)
      DOUBLE PRECISION DZ(*)
      LOGICAL LZ(*)
      REAL RZ(*)
C
C ------------------------------
C        External routines
C ------------------------------
C
C ------------------------------
C        Local Parameters
C ------------------------------
C
C ------------------------------
C        Local Variables
C ------------------------------
C
      INTEGER        NPROPIND
      CHARACTER*(80) CPROPCALC, CPROPIND(2)
C
      REAL           RPROPIND(2), H1, H2, HIS, S1, SN, P2, DHIS, DHLOC,
     &               ETA_E
C
C ------------------------------
C        Stack pointers
C ------------------------------
C
C=======================================================================
C
C ---------------------------
C    Executable Statements
C ---------------------------
C
C---- Initialize RET(1:NLOC*NRET) to zero.
C
      CALL SET_A_0(RET,NLOC*NRET)
C
C-----------------------------------------------------------------------
C     Averaged values of inlet total enthalpy, inlet entropy, outlet
C     total enthalpy and outlet total pressure are passed into his
C     routine. 
C     Mass flow averaging is used.
C-----------------------------------------------------------------------
C
      H1 = ARGS(NLOC,1)
      H2 = ARGS(NLOC,2)
      S1 = ARGS(NLOC,3)
      P2 = ARGS(NLOC,4)
C
C-----------------------------------------------------------------------
C     Compute isentropic efficiency
C-----------------------------------------------------------------------
C
C---- Number of input properties
C
      NPROPIND    = 2
C
C---- Input properties are entropy and pressure
C
      CPROPIND(1) = 'Static Entropy'
      CPROPIND(2) = 'Pressure'
C
C---- Input values are s1 and p2
C
      RPROPIND(1) = S1
      RPROPIND(2) = P2
C
C---- Compute isentropic enthalpy, h = h(s1,p2)
C
      CPROPCALC = 'Air Ideal Gas.Static Enthalpy'
      CALL USER_STATEPT(HIS,CPROPCALC,CPROPIND,RPROPIND,
     &                  NPROPIND,'SKIP',CRESLT, CZ,DZ,IZ,LZ,RZ)
C
C---- Expansion efficiency
C
      DHIS = HIS - H1
      DHLOC = H2 - H1
C
      IF (DHIS.LT.0.0 .AND.DHLOC.LT.0.0 .AND.DHIS.LT.DHLOC) THEN
        ETA_E = (H2 - H1)/(HIS - H1 + SN)
      ELSE
        ETA_E = 1.0
      ENDIF
C
C-----------------------------------------------------------------------
C
C---- Copy output property value to RET(1:NLOC,1).
C     --> NLOC = 1
C
      RET(1,1) = ETA_E
C
C---- Set success flag.
C
      CRESLT = 'GOOD'
C
C-----------------------------------------------------------------------
      END