BLOW {ibreg mdot Tinj angle_inc [angle_azi] | \
      PLENUM ibreg Pt T angle | \
      VALVE ibreg Pt Tt angle | \
      SURFACE ibreg Pt Tt angle_inc angle_azi}

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 is currently implemented for j-boundaries only, and the flow must be in the +x direction (u > 0).

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

There are four possible blowing modes, as follows:

BLOW ibreg mdot Tinj angle_inc [angle_azi]

	ibreg		Bleed region number from .cgd file
	mdot		Injected mass flow in region ibreg (lbm/sec)
	Tinj		Static temperature of injected flow (°R)
	angle_inc		Blowing inclination angle (degrees); must be > 0
	angle_azi		Blowing azimuthal angle (degrees)

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

If angle_azi is not specified, angle_inc is interpreted as the rotation about the z axis into the flow.

If angle_azi is specified, starting from the projection of the x axis onto the surface, the blowing direction is determined by rotating about the surface normal by the azimuthal angle, then "up" from the surface by the inclination angle. If this results in blowing in the "upstream" (defined as negative x) direction, the azimuthal angle psi is automatically changed to 180° - psi, while maintaining the specified inclination angle. This reverses the x component of the blowing velocity vector, so that blowing is in the "downstream" direction, while keeping the other components unchanged.

Note that specifying both angles, with angle_azi = 0, is not the same as specifying just angle_inc, except on surfaces with no curvature in the z direction.

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

TEST option 191, mode 1, may be used to specify that the blowing angles are to be measured relative to the projection of the surface normal onto a constant z plane, rather than relative to the normal itself.

TEST option 191, mode 4, allows an earlier one-angle form of the BLOW keyword to be used. However, this is not recommended. Due to an implementation error, this option only considers mass flow in the x-y plane, and therefore does not provide the requested mass flux for surfaces whose normal vector contains components in the z direction (i.e., surfaces with transverse curvature).

Important: The change from the one-angle form to the two-angle form of this keyword was made in WIND 5.204. Specifying just one angle is still allowed, but will in general give slightly different results, due to the implementation error in earlier versions described above.

BLOW PLENUM ibreg Pt T angle

	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 VALVE ibreg Pt Tt angle

	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)

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.

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.

The BLOW VALVE keyword may not be used for multi-species flows.

BLOW SURFACE ibreg Pt Tt angle_inc angle_azi

	ibreg		Bleed region number from .cgd file
	Pt		Plenum total pressure (psi)
	Tt		Plenum total temperature (°R)
	angle_inc		Blowing inclination angle (degrees)
	angle_azi		Blowing azimuthal angle (degrees)

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, except that the one-angle form is not available.

TEST option 191 may be used to specify that the blowing angles are to be measured relative to the projection of the surface normal onto a constant z plane, rather than relative to the normal itself.

TEST option 191 may also be used to allow surface blowing with Liu-Vinokur equilibrium air chemistry. The BLOW SURFACE keyword may not otherwise be used for multi-species flows.

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.

The implementation of this boundary condition is general enough that one can specify a blowing region on the upper and/or lower surface of a wing. However, one should avoid specifying a blowing region in more severe cases, such as the normal part of a backward-facing step.

See Also: BLEED, TEST 52, TEST 191, TEST 195