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ACTUATOR | SCREEN - Actuator disk / screen model (block)

{ACTUATOR | SCREEN}
   ZONE iz1 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX | U surface} \
        [SUBSET I range J range K range]
   ZONE iz2 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX | U surface} \
        [SUBSET I range J range K range]
   TURNING {CONSERVE {ANGLE | PARALLELU} | \
            ZERO PARALLELU | \
            {SOLIDBODY | VORTEX} val xc yc zc | \
            SPECIFY ANGLE α [ROTATE β]}
   TIP-EFFECT r1 r2 r3 r4
   POWER {{DPS | DPT | DPOWER} val | \
          TURNING | \
          {SOLIDBODY | VORTEX} val xc yc zc}
   EFFICIENCY {ETA val | \
               CLOSS val | \
               VORTEX val | \
               SCREEN {NORMAL | TOTAL} SOLIDITY sol}
{ENDACTUATOR | ENDSCREEN}

This keyword enables the user to model an actuator disk or screen by specifying a discontinuous change in properties across a zone boundary or portion of a zone boundary. The following restrictions apply:

The various elements of the ACTUATOR | SCREEN input block are defined as follows:

{ACTUATOR | SCREEN}

Defines the beginning of the actuator or screen block.

ZONE iz1 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX | U surface} \
     [SUBSET I range J range K range]
ZONE iz2 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX | U surface} \
     [SUBSET I range J range K range]

These two lines define the location of the actuator disk or screen. The relevant zones are given by the values of iz1 and iz2, and the relevant boundaries within zones iz1 and iz2 are specified via the BOUNDARY keyword parameter.

    iz1   Zone to which increments will be added when passing information to iz2
iz2 Zone receiving positive increments, increments will be subtracted when passing information back to zone iz1

BOUNDARY specification for structured zones is done via the I, J, or K parameters. For unstructured zones, U surface is used to specify the surface ID number.

The SUBSET parameter may be used to specify that the change in properties occurs only over a part of the structured zone boundary. Otherwise (and for unstructured zones), it is assumed that the change occurs over the entire boundary. The range parameters define the part of the zone boundary over which the change occurs, and take one of the following forms:

    index1 index2   Starting and ending indices in the specified direction. LAST may be used for the last index.
ALL Equivalent to 1 LAST.

The starting and ending indices for the appropriate I, J, or K parameter (depending on the boundary specified) must be the same, and correspond to that boundary. In addition, for two-dimensional cases, the K parameter must be specified as either K 1 1 or K ALL.

TURNING {CONSERVE {ANGLE | PARALLELU} | \
         ZERO PARALLELU | \
         {SOLIDBODY | VORTEX} val xc yc zc | \
         SPECIFY ANGLE α [ROTATE β]}

Defines the net change in parallel velocity across the zone boundary.

    CONSERVE   Conserves the net flow angle (ANGLE) or the parallel velocity components (PARALLELU) across the zone boundary. (The ANGLE option is currently not implemented.)
 
ZERO PARALLELU Sets the parallel components of velocity across the zone boundary to zero
 
SOLIDBODY Defines a solidbody rotation increment to the parallel velocity, where:

    val   Rotation rate in degrees/second (positive by right hand rule). (Note: in earlier versions of the code, this input was in radians per second. Old input data files using this keyword may need to be changed if used with the current version of the solver.)
xcyczc   Center of rotation (must be in the plane, requires the zone boundary to lie in a x-, y-, or z-constant plane) (inches)

VORTEX Defines free vortex flow increment to parallel velocity, where:

    val   Vortex strength &kappa (ft2/sec), where κ = ωa2 = Γ/2π, and Γ is the circulation, ω is the rotation rate of the solidbody core, and a is the radius of the solidbody core (required to avoid P = 0 at axis), a2 = κ2ρ / (0.9 P) (assumes Pmin = 0.1 P)
xcyczc   Center of rotation (inches)

SPECIFY ANGLE Allows the user to specify the flow turning angle.

    α   The flow angle giving the rotation of the iz2 boundary normal, projected onto the xy-plane, about the z-axis (degrees)
β   An optional rotation of the resulting vector about the y-axis

TIP-EFFECT r1 r2 r3 r4

Forces increments to go to zero at hub and/or tip to avoid solution discontinuities at the boundaries. A scalar, (0-1) multiplies the turning and power when this option is on. This is required for engine face models (where the wall velocity at the tip must be zero in the diffuser frame of reference). r1-r4 define linear regions ranging from 0 to 1 between r1 and r2, and from 1 to 0 between r3 and r4. r1, r2, r3, and r4 define the distance from the center of rotation (inches).

This keyword requires that TURNING SOLIDBODY, TURNING VORTEX, or POWER SOLIDBODY be specified.

POWER {{DPS | DPT | DPOWER} val | \
       TURNING | \
       {SOLIDBODY | VORTEX} val xc yc zc}

Defines the power increment across the zone boundary. Screens require setting the power to zero. i.e., POWER DPOWER 0.

    DPS   val specifies the static pressure increment across the actuator boundary (psi). Requires that the efficiency be specified, using EFFICIENCY ETA.
 
DPT val specifies the total pressure increment across the actuator boundary (psi). Requires that the efficiency be specified, using EFFICIENCY ETA.
 
DPOWER val specifies a (constant) power per unit area increment (ft-lb/sec-ft2). (Corresponds to unsteady (rotor) free vortex turning)

DPOWER = ρucp (Tt2Tt1)
 
TURNING Specifies work corresponding to the net turn across the zone boundary (specified in the TURNING element). Assumes all turning is done in an unsteady process (by the rotor), i.e., no stator.

dW = cp (Tt2Tt1) = ωr (w2w1)

where ω is the rotation rate of the rotor, r is the local radius from the center of the rotor, and w is the local circumferential velocity.

This option requires that TURNING SOLIDBODY be specified.

 
SOLIDBODY | VORTEX Defined as in the TURNING element. This defines the turning accomplished by the rotor. The net turning may be altered by another process (e.g., by a stator).

dW = cp (Tt2Tt1) = ωr (w2w1)

Note: Currently vortex turning (i.e., POWER VORTEX) is not allowed. This would correspond to constant work across the rotor. However, currently, the procedure used to eliminate the vacuum at the core (setting Pmin = 0.1 P) makes the work input independent of the strength of the vortex, so the user could not vary the work input by changing κ.


EFFICIENCY {ETA val | \
            CLOSS val | \
            VORTEX val | \
            SCREEN {NORMAL | TOTAL} SOLIDITY sol}

Defines the efficiency of the actuator disk or screen.

    ETA   Compressor efficiency, val = [(Pt2 / Pt1)(γ − 1)/γ − 1] / [(Tt2 / Tt1) − 1]
 
CLOSS Loss coefficient, val = (Pt1 - Pt2) / q, where q = ρU2/2 (U based on normal Mach number)
 
VORTEX Free vortex total pressure loss. val is the maximum value of (Pt2Pt1) / (Pt) (i.e., the loss at the center of the vortex). A linear distribution is assumed from the vortex center to the radius a, where a is determined by the strength value specified using TURNING VORTEX, or directly using TEST 180.

This option requires that TURNING VORTEX be specified.

 
SCREEN Use screen loss relations to define total pressure loss, where

    NORMAL   Use normal component of Mach number
TOTAL Use total Mach number. (This option is not currently implemented.)
sol Solidity of screen = Ab / (Ab + Ao), where Ab is the blocked area, and Ao is the open area.

If solidity is specified, the screen loss coefficient associated with the screen model is defined by the solidity correlation of Cornell [Cornell, W. G. (1958) "Losses in Flow Normal to Plane Screens," Transactions of the ASME, May 1958, pp. 791-799.], unless the optional CLOSS value is specified.

The screen model is not intended for use with choked screens, where the screen is significantly limiting the mass flow rate. During the solution start-up phase, it may be necessary to specify a low solidity, then increase it to the desired value to avoid strong choking in transients.

This option requires that the power be zero. i.e., POWER DPOWER 0.


{ENDACTUATOR | ENDSCREEN}

Ends actuator or screen input block

Examples

The following examples illustrate the use of the ACTUATOR | SCREEN input block for an engine face and for a screen.

Engine face model

   ACTUATOR
      ZONE 1 BOUNDARY IMAX
      ZONE 2 BOUNDARY I1
      TURNING SOLIDBODY 240000. 312. 54. 0.
      TIP-EFFECT 5. 5.1 39.8 40.0
      POWER TURNING
      EFFICIENCY ETA 0.85
   ENDACTUATOR
   BOUNDARY TVD FACTOR 0 ZONE 1 BOUNDARY IMAX
   BOUNDARY TVD FACTOR 0 ZONE 2 BOUNDARY I1
Screen
   SCREEN
      ZONE 3 BOUNDARY K1
      ZONE 2 BOUNDARY IMAX
      TURNING ZERO PARALLELU
      POWER DPOWER 0.0
      EFFICIENCY SCREEN NORMAL SOLIDITY 0.1
   ENDSCREEN
   BOUNDARY TVD FACTOR 0 ZONE 3 BOUNDARY K1
   BOUNDARY TVD FACTOR 0 ZONE 2 BOUNDARY IMAX

See Also: BOUNDARY TVD, TEST 180


Last updated 1 Apr 2016