Method and apparatus for laminar flow control

A method and apparatus for establishing discrete zones of pressure at the surface of a perforated panel of the type typically used for laminar fluid flow control includes a first array of channel members fluidly communicating with perforations in the panel, all of the channel members in the first array extending in a first direction and being substantially parallel to one another, and a second array of channel members fluidly communicating with the fluid in the first array of channel members, all of the channel members in the second array extending in a second direction and being substantially parallel to one another, where the first and second arrays of channel members being disposed in crossing relationship with a source of pressure being applied to the second array of channel members. By this arrangement, control of fluid flow in at least one of the first and second arrays results in discrete zones of pressure at the surface of the panel. Various additional embodiments include variable sized apertures in the second array of channels and various condition-responsive actuators for the apertures.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to laminar flow control apparatus, and more 
particularly to a method and apparatus for defining discrete zones of 
pressure at the surface of a laminar flow control member. 
2. Background of the Invention 
Panels having surface perforations through which compressible and 
incompressible fluids are introduced to control the flow of fluid over the 
surface are well known. Such panels, known as laminar flow control panels, 
are based on the premise that fluid flowing over the surface of the panel 
will be closely entrained along the contour of the surface via a suction 
force generated within the panel and "visible" to and acting on the fluid 
flowing over the panel surface through perforations in the panel. Laminar 
flow control has proven very useful in controlling fluid flow over or 
around surfaces immersed in various fluid environments. 
A typical laminar flow control panel comprises a multi-layer structure 
including inner and outer skins and one or more interior members 
delimiting compartments within the panel. The interior members may be wall 
partitions, honeycomb or truss core structures, or corrugated elements 
bonded at selected regions to the inner and outer skins. The panel skins 
may be of any thickness and material, with emphasis generally being on 
minimized weight, and maximum strength and workability. The skin 
perforations may be provided with hole-spacing tailored for optimum 
suction distribution. 
Factors which typically influence design of these panels include the known 
or anticipated pressure distribution over the region to be laminarized; 
skin perforation patterns, size and spacings; and internal flow 
requirements and capabilities. Control of the latter factor influences the 
pressure distribution required over the suction surface for a range of 
desired conditions. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a novel 
method and apparatus for controlling fluid flow over a surface of a 
laminar flow control panel which will overcome all the deficiencies and 
drawbacks of currently known apparatus of like kind. 
Another object of the present invention is to provide a novel system of 
fluid flow paths within a laminar flow control panel for directing flow of 
fluid from one region of the interior of the panel to another. 
Another object of the invention is to provide dissimilar pressure fields at 
the surface of a laminar fluid control panel to create distinct zones of 
fluid flow over the surface at adjacent regions, such that disturbances in 
the flow of fluid over the entire surface are minimized and laminar flow 
of the fluid over the surface is attainable. 
Still another object of the invention is to provide a novel system of fluid 
flow paths for varying the flow of fluid along the paths within a panel 
such that the pressure of fluid flowing over the panel perforated surface 
is affected by the flow of fluid within the panel. 
These and other objects are achieved by providing a first array of flow 
paths extending in a first direction and a second array of flow paths 
extending in a second direction, where the first and second directions are 
neither parallel nor coincident, and preferably are at substantial angles 
to one another. In a preferred embodiment of the invention, the first and 
second flow path arrays respectively comprise channel members disposed 
immediately atop one another, and one of the first or second arrays is 
located immediately beneath the perforated panel. Apertures of fixed or 
variable size and shape are provided in walls of the channel members at 
predetermined locations to facilitate intercommunication of the flow path 
arrays with one another and with the perforated surface.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, there is shown a laminar flow control panel 100 
of the type contemplated by the present invention. Panels of this type 
have proven useful in such applications as aerodynamic control surfaces, 
nautical control surfaces, and machine control mechanisms. Located below 
the panel is a multi-layered structure 200 defining a first array of 
channels or paths and a second array of channels or paths. It is to be 
understood that the panel and multi-layered structure shown in FIG. 1 is 
only a part of an entire laminar flow control panel assembly. 
The length and width of such a panel assembly can be chosen as required. It 
is further to be understood that the panel assembly will be manufactured 
to have side wall members extending substantially normal to the plane of 
the panel 100 and spanning the outer surface S of the panel and the 
lowermost reaches of the multi-layered structure 200, thereby enclosing 
one or more sides of the panel assembly. 
Panel 100 is shown as having patterns 120 of perforations located at 
specified regions. While discrete patterns have been shown, it is to be 
understood that the entire surface of panel 100 could be provided with 
perforations. These perforations provide means through which fluid located 
beneath (and within the structure defined below) panel 100 can pass. In 
enabling movement of fluid through the perforations either into or out of 
the environment defined beneath panel 100, the pressure of fluid passing 
over the outer surface S of the panel can be altered so as to define 
discrete pressure zones at the surface S. Of course, all of the zones at 
the surface S may have the same pressure; however, it is further 
contemplated, within the scope of teachings of this invention, that the 
zones at the surface S can be distinct, and can be controlled by variation 
of the amount of fluid flowing through the environment beneath the panel 
100. 
Disposed below panel 100 is a first array 200 of channels, and a second 
array 300 of channels. The channels in each array are delimited by channel 
members, which are depicted in FIG. 1 as having substantially similar 
configurations. It is to be understood that the channel members may be 
comprised of corrugated structural elements as shown in FIG. 1, or the 
channel members may be a series of partition walls of any similar or 
dissimilar shape or configuration which divide the space between the panel 
100 and the second array 300 of channels into discrete fluid flow paths. 
Each of the channel members in the first array of channels comprise base 
members 210, a hat member 220, and interconnecting side wall members 230, 
240. Adjacent base members 210 of neighboring channel members run into, 
and may be unitary with (as shown in FIG. 1 of the drawing), one another, 
so that the channel members in their side-by-side disposition form the 
first array. 
Disposed below the first array of channel members 200 is a second array of 
channel members 300. Preferably, the first and second arrays of channel 
members have the same configuration; however, this is not mandatory. Each 
of the channel members in the second array of channels comprises a base 
member 310, a hat member 320, and interconnecting side wall members 330, 
340. Adjacent base members 310 of neighboring channel members extend 
toward, and may be unitary with (as shown in FIG. 1 of the drawing), one 
another, so that the channel members in their side-by-side disposition 
form the second array. In addition, the second array of channel members is 
preferably secured or joined, as by bonding or welding, to the first array 
of channel members. This is accomplished, as shown in FIG. 1, by 
attachment of the hat members 320 of the second array of channel members 
to the base members 210 of the first array of channel members, where the 
first and second arrays are disposed at angles to one another, and 
preferably at about right angles to one another. 
Referring to FIGS. 1 and 2, side wall members 230 and 240 include apertures 
232 and 242, respectively. The location and size of the apertures are 
determined according to mathematical and computer models and as a function 
of known or desired pressure distributions and gradients on the surface of 
panel 100 and desired pressure distributions and gradients in each of the 
pressure zones P.sub.i, where i=1, 2, 3, . . . (as shown in FIG. 1). 
Apertures are also provided in the hat members 320 of the second array of 
channel members. The location and size of these apertures are 
predetermined in the same manner and based on the same criteria as for the 
apertures provided in the side wall members of the first array. The 
apertures in the side wall members of the first array communicate the 
fluid environment located above the panel 100 with the successive 
channel-configured fluid environments defined within the first array 200 
of channel members. The apertures in the hat members 320 of the second 
array of channel members communicate the fluid environment located below 
the panel 100 disposed within the successive channel-configured fluid 
environments of the first array 200 with alternating channel-configured 
fluid environments disposed within each of respectively alternating 
channel members 300 defining the second array of channel members. 
In use, a source of pressure, either positive or negative, is fluidly 
connected with the second array of channel members, and through the unique 
arrangement (i.e., size and location) of apertures disclosed above, 
discrete zones of pressure are established at the surface of the 
perforated panel thereby enabling laminar fluid flow control of the fluid 
passing over the surface. 
Referring to FIG. 3 now, there is generally shown structure capable of 
altering the size of the apertures 232 in each of the channel members of 
the first array. As shown in this example, a plate 250 is slidably 
supported on a side wall member 230 in which the apertures 232 have been 
formed. Plate 250 is provided with openings 252 which preferably 
correspond in location and size with the apertures 232. The plate is 
slidably movable along the axis of the channel member so that the openings 
252 can be displaced at various locations between one position in which 
each of the openings substantially overlap a corresponding one of the 
apertures 232 to a second position in which each of the openings is 
substantially removed from a corresponding one of the apertures 232. Thus, 
the "effective" size of the apertures 232 can be varied between being 
substantially entirely open to substantially entirely closed. 
Movement of the plate 250 relative to the side wall member 230 of the 
channel member can be effected through various mechanisms. For example, 
the plate 250 could be controlled using a remote actuator, such as radio 
or microwave actuators. The plate could alternatively be controlled using 
an ambient condition actuator, i.e., one which reacts in response to an 
ambient condition such as temperature, air flow speed, turbulence, etc. 
Mechanisms for effecting movement of the plate can be electrical, 
pneumatic, mechanical or hydraulic and such mechanisms are collectively 
represented in FIG. 3 by the block 260. 
Thus it is apparent that there has been provided, in accordance with the 
present invention, an apparatus and method for controlling pressure at the 
surface of a perforated panel which fully satisfies the objectives, aims, 
and advantages set forth above. While the invention has been described in 
conjunction with specific embodiments thereof, it is evident that many 
alternatives, modifications, and variations will be apparent to those 
skilled in the art in light of the foregoing description. Accordingly, the 
present invention is intended to embrace all such alternatives, 
modifications, and variations which fall within the spirit and scope of 
the appended claims.