Porous wall cooling over a selected region can be simulated using this keyword. The region must be identified as a bleed region in the grid file. This option is intended for mass inflow only (i.e., P_t > local P_s). It won't work well for grids that are skewed at the wall, resulting in blowing mass flow errors.

Blowing may also be modeled using the first two forms of the BLEED keyword (i.e., BLEED and BLEED POROSITY).

The definition of the blowing direction is general enough that a blowing region on the upper and/or lower surface of a wing will be treated consistently with a single specification. However, one should avoid specifying a blowing region in more severe cases, such as the normal part of a backward-facing step, where the surface normal is purely in the x direction.

There are four possible blowing 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 blowing is only allowed for perfect gases and non-rotating grids. Also, with unstructured grids, the blowing 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 blowing region with structured and unstructured grids.

BLOW ibreg mdot Tinj [STATIC|TOTAL] \    angle_inc [ABOUT_Z [angle_azi] | ABOUT_NORMAL [angle_azi]] [BLOW FORCING ibreg {MASS|VELOCITY} amp freq phase]

	ibreg		Bleed region number from .cgd file
	mdot		Injected mass flow in region ibreg (lbm/sec)
	Tinj		Temperature of injected flow (°R). Either static or total temperature may be specified, as indicated by the optional choice of STATIC or TOTAL. (However, TOTAL may not be used when VELOCITY is used with BLOW FORCING.) The default is STATIC.
	angle_inc		Blowing inclination angle (degrees); must be > 0
	angle_azi		Blowing azimuthal angle (degrees). The default is 0.0.

The blowing direction is set by the input inclination and azimuthal angles.

The inclination angle is the angle between the blowing direction and the projection of the x axis onto the surface.

If ABOUT_Z is specified, the azimuthal angle is the angle between the blowing direction and the projection of the surface normal onto a constant z plane. Starting from the projection of the x axis onto the surface, the blowing direction is thus determined by rotating about the projection of the surface normal onto a constant z plane by the azimuthal angle, then "up" from the surface by the inclination angle.

If ABOUT_NORMAL is specified, the azimuthal angle is the angle between the blowing direction and the surface normal itself. Again starting from the projection of the x axis onto the surface, the blowing direction is thus determined by rotating about the surface normal by the azimuthal angle, then "up" from the surface by the inclination angle.

If neither ABOUT_Z nor ABOUT_NORMAL is specified, ABOUT_Z is assumed, and angle_azi will have its default value of 0.0.

BLOW FORCING may be used with this blowing mode to add an oscillatory component to the blowing velocity. The added blowing is specified as either a mass flow or velocity, depending on the choice of MASS or VELOCITY. (If VELOCITY is used, the static temperature must be specified with the BLOW keyword.) The direction of the added blowing will be the same as the mean blowing, as determined by angle_inc and angle_azi.

	ibreg		Bleed region number from .cgd file
	amp		Amplitude of the oscillation for the added blowing (lbm/sec for MASS, ft/sec for VELOCITY)
	freq		Frequency of the oscillation (deg/sec)
	phase		Phase offset of the oscillation (deg)

This blowing mode may not be used for multi-species flows.

BLOW PLENUM ibreg Pt T angle [BLOW FORCING ibreg {MASS|VELOCITY} amp freq phase]

	ibreg		Bleed region number from .cgd file
	Pt		Plenum total pressure (psi)
	T		Plenum static temperature (°R)
	angle		Blowing angle relative to x-y plane (degrees)

If the flowfield static pressure P_s becomes greater than the plenum total pressure P_t, the plenum total pressure will be automatically increased to 1.005 P_s to maintain a blowing boundary condition. Setting TEST 52 will notify the user when this occurs.

BLOW FORCING may be used with this blowing mode to add an oscillatory component to the blowing velocity. The added blowing is specified as either a mass flow or velocity, depending on the choice of MASS or VELOCITY. The direction of the added blowing will be the same as the mean blowing, as determined by angle. The input parameters are the same as for the first blowing mode, described above.

This blowing mode may not be used for multi-species flows.

BLOW SURFACE ibreg Pt Tt \    angle_inc [ABOUT_Z [angle_azi] | ABOUT_NORMAL [angle_azi]] [BLOW FORCING ibreg {MASS|VELOCITY} amp freq phase]

	ibreg		Bleed region number from .cgd file
	Pt		Plenum total pressure (psi)
	Tt		Plenum total temperature (°R)
	angle_inc		Blowing inclination angle (degrees); must be > 0
	angle_azi		Blowing azimuthal angle (degrees). The default is 0.0.

With this boundary condition, blowing will occur whenever the local flowfield static pressure is less than the specified plenum total pressure. If the flowfield static pressure is greater than the plenum total pressure, the velocity normal to the wall at that point is set to zero (i.e., a solid wall with no blowing or bleed). Unlike the BLOW VALVE capability, with BLOW SURFACE blowing is turned on or off locally, on a point-by-point basis.

The blowing velocity is also constrained to subsonic values.

The blowing direction is set by the input inclination and azimuthal angles. The angles are defined in the same way as when the standard BLOW keyword is used to specify a constant blowing mass flow, as described above.

The BLOW SURFACE keyword may not be used for multi-species flows, except for Liu-Vinokur equilibrium air chemistry.

If the TEST 195 option is set, a message will be written in the list output (.lis) file whenever the blowing is turned off because the flowfield static pressure is too large. Note, however, that this is a five-line message written for each iteration and each "closed" node, and could cause the .lis file to become very large very quickly.

BLOW FORCING may be used with this blowing mode to add an oscillatory component to the blowing velocity. The added blowing is specified as either a mass flow or velocity, depending on the choice of MASS or VELOCITY. The direction of the added blowing will be the same as the mean blowing, as determined by angle_inc and angle_azi. The input parameters are the same as for the first blowing mode, described above.

BLOW WALL ibreg

ibreg

Bleed region number from .cgd file

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

BLOW VALVE ibreg Pt Tt angle [BLOW MASS [FRACTIONS] ibreg sp1 sp2 ... spn]

	ibreg		Bleed region number from .cgd file
	Pt		Plenum total pressure (psi)
	Tt		Plenum total temperature (°R)
	angle		Blowing angle relative to x-y plane (degrees)
	sp1 sp2 ... spn		Mass fractions of injected species. The default values are those specified in the CHEMISTRY keyword block.

This blowing mode is only available for structured grids.

If the flowfield static pressure P_s becomes greater than the plenum total pressure P_t at any point within the blowing region, blowing will be shut off for the entire region, and the surface will be treated as a solid wall. A *VLV* line is written to the list output (.lis) file whenever the valve changes status.

For multi-species flow, when BLOW MASS FRACTIONS is specified the mass fractions should be specified in the same order as the species in the chemistry data (.chm) file. However, if the species have been re-ordered using the SPECIES keyword in the CHEMISTRY keyword block, and the BLOW MASS FRACTIONS keyword comes after the CHEMISTRY keyword block in the input data (.dat) file, then the mass fractions should be specified in the new species order.

BLOW MASS FRACTIONS only works with BLOW VALVE. Note that it is a separate line, not a continuation of the BLOW VALVE keyword.

With BLOW VALVE, the blowing region may extend to more than a boundary surface, and may also be split between zones. Note, however, that when a blowing region is split between multiple processors, the separate sub-regions act independently until the end of a cycle. If the flowfield static pressure grows large enough in one sub-region to close the valve but not in the other sub-region(s), the valve will close for the first sub-region, but not on the others until the end of the cycle. The reverse situation (i.e., opening a closed valve) may also occur. This may be prevented by running one iteration per cycle; as a practical matter, it is not expected to cause problems with the default of five iterations per cycle.

See Also: BLEED, TEST 46, TEST 52, TEST 67, TEST 178, TEST 195