Passive removal of suction air for laminar flow control, and associated systems and methods
Passive removal of suction air for producing a laminar flow, and associated systems and methods are disclosed. One such method includes forming a laminar flow region over an external surface of an aircraft by drawing air through the external surface and into a plenum. The method can further include passively directing the air from the plenum overboard the aircraft. For example, the air can be passively directed to a region external to the aircraft having a static pressure lower than a static pressure in the plenum, as a result of the motion of the aircraft. Flows from different sections of the external surface can be combined in a common plenum, and the corresponding massflow rates can be controlled by the local porosity of the external surface.
1. A method for controlling aircraft external flow, comprising:
forming a laminar flow region over an external surface of an aircraft by drawing air through the external surface into a plenum, wherein drawing air through the external surface into the plenum includes:
drawing a first portion of the air through a first section of the external surface having a first porosity;
drawing a second portion of the air through a second section of the external surface having a second porosity different than the first porosity; and
collecting the first and second portions of air in a common plenum; and
passively directing the air from the plenum overboard the aircraft, wherein passively directing the air from the plenum includes:
directing the air from the plenum through an exit opening via a pressure difference between a region interior to the plenum and a region exterior to the exit opening, the pressure difference resulting from motion of the aircraft; and
controlling the amount of air drawn through the external surface by controlling an area of the exit opening.
2. The method of claim 1 wherein drawing air through the external surface includes drawing air through the external surface at a region where the pressure at the external surface is less than a static pressure of the freestream air though which the aircraft is flying.
3. The method of claim 1 wherein passively directing the air from the plenum includes directing the air without passing the air through a compressor.
4. The method of claim 1 wherein passively directing the air from the plenum includes directing the air through a scoop having the exit opening, and wherein the exit opening is aft facing.
5. The method of claim 4 wherein directing the air through a scoop includes directing the air through a scoop having a fixed exit opening.
6. The method of claim 4 wherein the scoop includes a door adjacent the exit opening, and wherein controlling an area of the exit opening includes controlling an amount by which the door is opened.
7. The method of claim 6 wherein controlling an area of the exit opening is performed by computer-based instructions.
8. The method of claim 1 wherein the external surface includes an airfoil surface having a leading edge, and wherein drawing the first portion of the air includes drawing the first portion of the air at a first rate at a first location relative to the leading edge, and drawing the second portion of the air includes drawing the second portion of the air at a second rate less than the first rate at a second location aft of the first location.
9. The method of claim 1 wherein drawing air includes drawing air at a rate of about 1% or less of the air passing over the surface.
10. The method of claim 1 wherein drawing air includes drawing air at a rate of about 0.1% or less of the air passing over the surface.
11. The method of claim 1 , further comprising controlling a rate at which air is drawn through the external surface as a function of a static pressure external to the aircraft.
12. The method of claim 1 , further comprising controlling a rate at which air is drawn through the external surface via a static pressure external to the aircraft.
13. A method for controlling aircraft external flow, comprising:
forming a laminar flow region over an external surface of an aircraft airfoil by:
passing a flow of air over the external surface;
drawing a first portion of the air through a first section of the external surface having a first porosity;
drawing a second portion of the air through a second section of the external surface having a second porosity different than the first porosity;
collecting the first and second portions of air in a common plenum;
passively directing the air from the plenum overboard the aircraft via an exit opening, without adding energy to the air between the external surface and the exit opening; and
controlling the amount of air drawn through the external surface by controlling an area of the exit opening.
14. The method of claim 13 wherein passively directing the air from the plenum includes directing the air without pressurizing the air with a compressor.
15. The method of claim 13 wherein controlling the amount of air drawn through the external surface includes automatically controlling the area of the exit opening as a function of static pressure external to the aircraft.
16. The system of claim 13 wherein passively directing the air includes directing the air through a scoop having the exit opening, and wherein the exit opening faces aft.
17. An aircraft system, comprising:
an aircraft external flow surface positioned to be exposed to an external airstream during flight, the external flow surface having multiple openings, the multiple openings forming a first region having a first porosity and a second region having a second porosity different than the first;
a common plenum positioned interior to the external flow surface and in fluid communication with the multiple openings in both the first and second regions; and
a passive flow removal device in fluid communication with the plenum, the passive flow removal device having an exit opening positioned to remove air from the plenum to the external airstream, the passive flow removal device being configured to remove the air from the plenum without adding energy to the air between the openings in the external flow surface and the exit opening, the passive flow removal device including a flow regulator positioned along a flowpath between the exit opening and the multiple openings in the external surface.
18. The system of claim 17 wherein the passive flow removal device includes a scoop having an aft-facing region at which the exit opening is positioned.
19. The system of claim 17 , further comprising a controller operatively coupled to the flow regulator, the controller having instructions for directing a change in a setting of the regulator as a function of ambient pressure.
20. The system of claim 17 wherein the flow regulator includes a door positioned at least proximate to the exit opening, the door being movable between a first position and a second position, the exit opening having a first area when the door is in the first position and a second area different than the first area when the door is in the second position.
21. The system of claim 17 wherein the openings in at least one of the first and second regions have a diameter of about 0.0025 inches.