BLEED {ibrg blv1 | POROSITY ibrg blv1 blv2 blv3 | \
       MODEL ibrg mode blv1 blv2 blv3 blv4 | \
       FORCING ibrg blv1 blv2 blv3}

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 four possible bleed models, as follows:

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

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. Note, however, that if the resulting blowing velocity exceeds Mach 1, the logic in the code that is used to limit the bleed velocity to Mach 1 will reset blv1 to a positive value, resulting in bleeding instead of blowing.

BLEED POROSITY ibrg blv1 blv2 blv3

	ibrg		Bleed region number from .cgd file
	blv1		Back pressure pplen, in psia
	blv2		Porosity
	blv3		Discharge coefficient

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).

BLEED MODEL ibrg mode blv1 blv2 blv3 blv4

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		pplen		Porosity		qsmode		Nbl
	2		pplen		Porosity		qsmode
	3		pplen		Porosity		qsmode		M
	4		Qsonic		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 Qsonic = 1
	2		Compute Qsonic for 90° holes
	3		Compute Qsonic for 20° holes

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

Q_sonic is a function of the bleed hole angle alpha, 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)

See Also: BLOW, MASS FLOW