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COMPRESSOR FACE - Outflow boundaries, compressor face

Structured Grids

COMPRESSOR [FACE] {[CHUNG] mach | BOEING mode val1 [val2] | \
                   PAYNTER mach val1 val2 | SAJBEN mach angh angc} zone_selector

This keyword allows an outflow boundary in a structured grid to be modeled as a compressor face.

Specification of the zone_selector is required for this keyword.

There are several models available, as described below. All are based on the observation that turbine engine conditions set the corrected mass flow, and that this corresponds directly to the average Mach number at the compressor face. These boundary conditions have been implemented mainly for the analysis of unsteady flow; however, this option has also been shown to be robust for the establishment of steady-state, supercritical inlet flows.

COMPRESSOR [FACE] [CHUNG] mach zone_selector

The CHUNG keyword option uses the Chung-Cole model [Chung, J. and Cole, G. L. (1996) "Comparison of Compressor Face Boundary Conditions for Unsteady CFD Simulations of Supersonic Inlets," NASA TM-107194]. Based on the specified mass-averaged Mach number mach, and using the computed local Mach number and total pressure, a new local static pressure is computed.

Note: This boundary condition is identical in its effect on the flow to the DOWNSTREAM MACH keyword.

COMPRESSOR [FACE] BOEING mode val1 [val2] zone_selector

The BOEING keyword option uses uses a model developed by Mayer and Paynter [Mayer, D. W. and Paynter, G. C. (1994) "Boundary Conditions for Unsteady Supersonic Inlet Analyses," AIAA Journal, Vol. 32, No. 6, pp. 1200-1206]. The parameters to be specified as val1 and val2 depend on mode, as shown in the following table.

    mode   val1   val2
1Average Mach number-
2Corrected mass flux per unit area, lbm/sec/ft2-
3Nominal Mach numberNominal total temperature, degrees Rankine

Modes 1 and 2 are equivalent, and are useful in obtaining initial flow fields, and for simulating instantaneous changes at the compressor face via a restart. Mode 3 is used to set a constant volumetric flow condition. Typically, an initial condition is obtained using mode 1 and becomes the nominal condition. Then val1 is set to the Mach number used in mode 1 and val2 is set to the freestream total temperature, i.e., it is assumed that the total temperature at the compressor face is equal to the freestream value. If the average total temperature at the compressor face does not change, then modes 1 and 3 will yield identical results. However, if the average total temperature at the compressor face changes due to a freestream disturbance, for example, then the corrected flow rate will be adjusted to maintain a constant volumetric flow rate.

COMPRESSOR [FACE] PAYNTER mach val1 val2 zone_selector

The Paynter compressor face model computes unsteady acoustic reflections from a compressor face subjected to acoustic and convective disturbances [Paynter, G. C. (1998) "Modeling the Response from a Cascade to an Upstream Convective Velocity Disturbance", AIAA Paper 98-3570]. This model is intended to be used for time-accurate simulations of unsteady inlet flow. The CFL number should be less than one. The flow is assumed to be subsonic and axial as it enters the compressor face.

The model assumes the compressor face is positioned within an annular duct with a hub and case, and consists of a single row of axial flow compressor blades. The conditions at the compressor face are determined by the convective velocity response coefficient α, and the acoustic response coefficient β. The definitions of α and β depend on the passage Mach number Mpassage, which is given by

Mpassage = Mcf / cos G

where Mcf is the compressor face Mach number, and G is the local stagger angle.

For subsonic flow (Mpassage < 1),

α = γ [M2cf / (1 − Mcf)] tan (G/2) tan G

β = tan2 (G/2) [ (1 + Mcf) / (1 − Mcf) ]

where γ is the specific heat ratio. For supersonic flow (Mpassage > 1),

α = γMcf

β = 1.0

Details on the implementation of this boundary condition are given by Slater and Paynter [Slater, J. W. and Paynter, G. C. (2000) "Implementation of a Compressor Face Boundary Condition Based on Small Disturbances", ASME Paper 2000-GT-0005].

In Wind-US, α and β may be treated as constant and specified directly, or computed using the above equations. The local stagger angle G is determined by assuming a linear variation between specified values of the stagger angles at the hub and case. The solidity of the blade row is assumed to be greater than one.

The absolute value of the keyword parameter mach sets the nominal or average compressor face Mach number Mcf. The meanings of val1 and val2 depend on the sign of mach:

    mach   val1   val2
> 0 Stagger angle (degrees) of the compressor fan blade at the hub Stagger angle (degrees) of the compressor fan blade at the case
< 0 Constant convective velocity response coefficient, α Constant acoustic response coefficient, β

COMPRESSOR [FACE] SAJBEN mach angh angc zone_selector

The Sajben compressor face model is basically the same as the Paynter model, except that Sajben's expression for the acoustic response coefficient is used for subsonic flow [Sajben, M. (1999) "Prediction of Acoustic, Vorticity and Entropy Waves Generated by Short-Duration Acoustic Pulses Incident on a Blade Row", ASME Paper 1999-GT-148].

Sajben's expression for the acoustic response coefficient may be written as

β = Mcf tan2 G / [2(1 + Mcf) + Mcf tan2 G]

where Mcf is the compressor face Mach number, and G is the local stagger angle.

With the COMPRESSOR [FACE] SAJBEN keyword, the keyword parameter mach is the nominal or average compressor face Mach number Mcf, and angh and angc are the stagger angles in degrees of the compressor fan blade at the hub amd case.




Last updated 1 Apr 2016