Wind-US User's Guide - Keyword Reference, BLEED

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BLEED - Bleed region flow rate

Structured Grids

BLEED {ibrg blv1 | POROSITY ibrg blv1 blv2 [blv3] | \ MODEL ibrg mode blv1 blv2 blv3 blv4 | \ FORCING ibrg blv1 blv2 blv3 | WALL ibrg | AEDC ibrg}

Unstructured Grids

BLEED {ibrg blv1 | POROSITY ibrg blv1 blv2 blv3 | \ FORCING ibrg blv1 blv2 blv3 | WALL ibrg}

The effect of bleed on the flow can be modeled, if bleed regions were identified in the grid file. The parameters discussed below identify the bleed rate for each region, for a specific solution. If a bleed region is not named in this file, its bleed rate is set to zero.

There are five possible bleed modes for structured grids, and three for unstructured grids, as described below. Unless noted otherwise, the keywords apply to both structured and unstructured grids.

However, with unstructured grids bleed is only allowed for perfect gases and non-rotating grids. Also, with unstructured grids, the bleed boundary condition is applied at the cell faces, but the flow field values written to the .cfl file for post-processing are at the nodes. The results may thus be slightly different around the edges of the bleed region with structured and unstructured grids.

BLEED ibrg blv1

ibrg Bleed region number from .cgd file
blv1 Normalized bleed flow rate

blv1 can also be thought of as the mass flow ratio for the bleed region. The actual bleed mass flow is calculated as

m_bleed = blv1 (ρ_∞U_∞A_c)
where A_c is an arbitrarily set reference "capture area" that you must specify, in either GMAN (using the CAPTURE AREA command, or the BOUNDARY COND. menu) or MADCAP (using Set Capture Area from the Boundary Conditions menu), in each zone of the grid file that contains bleed areas.

The bleed velocity will automatically be limited to Mach 1.

Although this is intended as a bleed model, it can also be used for blowing by setting blv1 to a negative value.

BLEED POROSITY ibrg blv1 blv2 blv3

[There are some questions about the coding for the porous bleed model that need to be resolved. This model should be therefore used with caution.]

ibrg Bleed region number from .cgd file
blv1 Back pressure p_plen, in psia
blv2 Porosity
blv3 Discharge coefficient; may be defaulted for structured grids

With this model, the velocity at the wall will be computed from the local pressure p in the flow field, and the specified back pressure p_plen. If p > p_plen, the flow will be out of the computational domain (i.e., bleed). If p < p_plen, the flow will be into the computational domain (i.e., blowing).

For unstructured grids, the discharge coefficient must be specified. For structured grids, however, it may be omitted. In this case, for bleed a default value is computed from the specified back pressure and the local flow conditions, using the empirically-based method of Dittrich and Graves [Dittrich, Ralph T., and Graves, Charles C. (1956) "Discharge coefficients for combustor-liner air-entry holes", NACA TN 3663]. For blowing, the default value for the discharge coefficient is 0.6.

BLEED MODEL ibrg mode blv1 blv2 blv3 blv4

This bleed mode is only available for structured grids.

This keyword specifies use of the empirical bleed model of 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], and allows the bleed mass flow rate to vary in response to local flow conditions.

The input parameter ibrg is the bleed region number from the .cgd file. The input data for the bleed model is given by the values of blv1 through blv4. Various combinations of values may be specified, depending on the mode, as described below.

mode blv1 blv2 blv3 blv4
1 p_plen Porosity qsmode N_bl
2 p_plen Porosity qsmode
3 p_plen Porosity qsmode M
4 Q_sonic Porosity M

In the above table, p_plen is the bleed plenum static pressure, N_bl is the number of grid points in the boundary layer, Q_sonic is the sonic mass flow coefficient (described below), and M is the local Mach number at the edge of the boundary layer. The parameter qsmode is an integer from 1 to 3 defining how Q_sonic is to be computed, as follows:

1 Set Q_sonic = 1
2 Compute Q_sonic for 90° holes
3 Compute Q_sonic for 20° holes

In the Mayer-Paynter model, the bleed velocity is given by the formula

V_bleed = Q_sonicφGT (p_T/p) (T_T)^−1/2
where φ is the porosity, p and T are the local static pressure and temperature, and p_T and T_T are the local total pressure and temperature. "Local" means at the edge of the boundary layer at the location of the grid point within the bleed region. The parameter G is a function of the specific heat ratio γ.

G = [1 + (γ−1)/2]^{−[(γ+1)/2(γ−1)]}

Central to the model is Q_sonic, the sonic mass flow coefficient, defined as

Q_sonic = m_bleed / m_max = f (α, M, p_plen/p )
where m_bleed is the actual bleed flow rate and m_max is the maximum theoretical bleed flow rate.

Q_sonic is a function of the bleed hole angle α, the local Mach number M, and the ratio of the plenum pressure p_plen to the local pressure p. The functional relationship is in the form of tabulated experimental data for circular bleed holes at angles of 20° and 90°. The 20° data were taken by McLafferty and Ranard [McLafferty, G., and Ranard, E. (1958) "Pressure Losses and Flow Coefficients of Slanted Perforations Discharging from Within a Simulated Supersonic Inlet," United Aircraft Corporation, Report R-0920-1, Dec. 1958], and the 90° data were taken by Syberg and Hickox [Syberg, J., and Hickox, T. E. (1972) "Design of a Bleed System for a Mach 3.5 Inlet," NASA CR-2187, Sept. 1972].

BLEED FORCING ibrg blv1 blv2 blv3

This mode allows an oscillating normal velocity bleed boundary condition to be specified.

ibrg Bleed region number from .cgd file
blv1 Amplitude of the normal velocity oscillation (ft/sec)
blv2 Frequency of the oscillation (Hz)
blv3 Phase offset of the oscillation (deg)

BLEED WALL ibrg

ibrg Bleed region number from .cgd file

This keyword may be used to explicitly turn bleed off in a specific bleed region, and to treat the boundary as a viscous solid wall.

BLEED AEDC ibrg

ibrg Bleed region number from .cgd file

This bleed mode is only available for structured grids.

When the AEDC keyword is specified, the bleed region uses the AEDC wind tunnel wall correction correlations. (Note: the entire boundary must be flagged as bleed, not only the porous region.) This condition is hard-wired for the j = 1 boundary and the AEDC wind tunnel and is not intended for general use.

See Also: BLOW, MASS FLOW, TEST 46, TEST 67

	ibrg		Bleed region number from .cgd file
	blv1		Normalized bleed flow rate

mode	blv1	blv2	blv3	blv4
1	p_plen	Porosity	qsmode	N_bl
2	p_plen	Porosity	qsmode
3	p_plen	Porosity	qsmode	M
4	Q_sonic	Porosity		M

	1		Set Q_sonic = 1
	2		Compute Q_sonic for 90° holes
	3		Compute Q_sonic for 20° holes