Wind tunnel design with expanding corners

A wind tunnel may comprise: a flight chamber; a plurality of diffusers; a plurality of expanding corners, wherein the plurality of expanding corners comprises a first expanding corner and a second expanding corner; and a return, the return configured to have disposed therein a fan operatively coupled with a motor.

TECHNICAL FIELD

The present invention relates to the field of wind tunnels; more particularly, to wind tunnels having an improved performance, reduced footprint, and lower cost of construction and operation.

BACKGROUND

Wind tunnels are available in many types and styles depending upon the needs of the user. These include, without limitation, subsonic wind tunnels with and without return flow, transonic wind tunnels with and without return flow, vertical subsonic wind tunnels with and without return flow, supersonic and hypersonic wind tunnels with and without return flow, and compressible flow wind tunnels.

Wind tunnels may be used in the testing of conventional aircraft, helicopters, parachutes, and other aerodynamic devices, wing surfaces, control surfaces, submarines, rockets, and other launch vehicles, ground vehicles such as automobiles and trucks, buildings, other basic flow investigations, and, more recently, amusement (i.e., recreational use). The wind tunnel state of the art may be gleaned from the following patents and patent applications.

U.S. Pat. No. RE43,028 E1 is directed to a vertical wind tunnel amusement device. U.S. Pat. No. 5,655,909 is directed to a skydiving simulator combining a vertical air chamber with a video projection system on the interior wall. U.S. Pat. No. 7,028,542 is directed to a reduced drag cable for use in vertical wind tunnels and other applications with a change in the spacing and/or size of the strands of a standard twisted wire cable. U.S. Pat. No. 7,156,744 is directed to a vertical wind tunnel flight simulator comprising a flight chamber wherein a flyer may experience a freefall simulation. U.S. Patent Number 2012/0312502 is directed to a cooling system for a wind tunnel.

Despite the prior attempts, a need exists for a more efficient, compact, economical wind tunnel, more specifically; a need exists for a more efficient, compact, economical vertical wind tunnel. The present invention facilitates the creation of such wind tunnels.

SUMMARY OF THE INVENTION

The present invention is directed to a more efficient, compact, economical vertical wind tunnel and, in certain aspects, a horizontal wind tunnel.

According to a first aspect, a vertical wind tunnel comprises: a flight chamber; a plurality of diffusers; a plurality of expanding corners, wherein the plurality of expanding corners comprises a first expanding corner and a second expanding corner; and a return, the return configured to have disposed therein a fan operatively coupled with a motor.

In certain aspects, the vertical wind tunnel may further comprise a second return.

In certain aspects, the plurality of expanding corners further comprises a third expanding corner and a fourth expanding corner.

In certain aspects, the flight chamber has a circular cross section and a substantially constant area along the flight chamber's length.

In certain aspects, the expansion ratio of the first expanding corner is not equal to the expansion ratio of the second expanding corner.

In certain aspects, the mean average expansion ratio of the third expanding corner and the fourth expanding corner is greater than the mean average expansion ratio of the first expanding corner and the second expanding corner.

In certain aspects, at least one of said plurality of diffusers or said one or more expanding corners (1) is fabricated using a mold resistant material; or (2) employs mold-resistant sealant.

In certain aspects, each of said plurality of expanding corners has an expansion ratio of between about 1.01 to about 3.00.

In certain aspects, the expansion ratio of at least one of said plurality of expanding corners is between 1.10 and 1.50.

In certain aspects, the plurality of diffusers comprises a first diffuser having a circle to quadrilateral transition.

In certain aspects, the plurality of diffusers further comprises a second diffuser positioned between said first expanding corner and said second expanding corner.

In certain aspects, the return is positioned between the second expanding corner and the third expanding corner.

In certain aspects, the return transitions (1) from a first quadrilateral cross section to a circular cross section, and (2) from the circular cross section to a second quadrilateral cross section.

In certain aspects, the return transitions from a first quadrilateral cross section to a second quadrilateral cross section.

In certain aspects, air traveling through the vertical wind tunnel is cooled using a water cooling technique whereby water is brought into intimated contact with an exterior wall of said vertical wind tunnel.

In certain aspects, the vertical wind tunnel further comprises a contraction nozzle disposed between said fourth expanding corner and said flight chamber, wherein the contraction nozzle transitions from a quadrilateral cross section to a round cross section.

In certain aspects, at least one of said plurality of diffusers utilizes a conical-angle expansion between 0.1 and 7.0 degrees.

In certain aspects, at least one of said plurality of expanding corners comprises a plurality of internally-cooled internal turning vanes.

In certain aspects, said internally-cooled internal turning vanes cooled via a ground-coupled heat exchanger.

In certain aspects, said first quadrilateral cross section is rotated 90 degrees relative to said second quadrilateral cross section.

In certain aspects, the vertical wind tunnel further comprises a netting device positioned at an upstream end of said flight chamber, the netting device being coupled to a net frame via at least one cable, each of said at least one cable having a first distal end and a second distal end, wherein a head end unit is coupled to the first distal end and a receiving end unit is coupled to the second distal end, wherein the head end unit couples the first distal end to a first connection point on said net frame and comprises a first compression spring and a tensioning bolt that is adjustable in length, and wherein the receiving end unit couples the second distal end to a second connection point on said net frame and comprises a second compression spring.

According to a second aspect, a wind tunnel comprises: a chamber; a plurality of diffusers; a plurality of expanding corners, wherein the plurality of expanding corners comprises a first expanding corner and a second expanding corner, wherein each of said plurality of expanding corners has an expansion ratio of between about 1.01 to about 3.00; and a return, the return configured to have disposed therein a fan operatively coupled with a motor.

In certain aspects, the plurality of expanding corners further comprises a third expanding corner and a fourth expanding corner.

In certain aspects, the expansion ratio of the first expanding corner is not equal to the expansion ratio of the second expanding corner.

In certain aspects, the expansion ratio of at least one of said plurality of expanding corners is between 1.10 and 1.50.

DETAILED DESCRIPTION

Preferred embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail because they may obscure the invention in unnecessary detail. The present invention discloses a more efficient, compact, and economical wind tunnel. While the present invention is generally described as a vertical wind tunnel being intended for indoor skydiving applications, the teachings may be applied to wind tunnels employed for other purposes and therefore should not be limited to those intended for indoor skydiving applications. For this disclosure, the following terms and definitions shall apply:

As used herein, the words “about” and “approximately,” when used to modify or describe a value (or range of values), mean reasonably close to that value or range of values. Thus, the embodiments described herein are not limited to only the recited values and ranges of values, but rather should include reasonably workable deviations, which, unless otherwise indicated, should not exceed a ten percent deviation. Further, the values and ranges of values recited herein describe one embodiment, but other values and ranges of values may be employed to produce a desired wind tunnel for a particular purpose. For example, a person of skill of ordinary skill in the art could adapt the present teachings to construct flight chambers of sizes other than those disclosed. Thus, a person of skill of ordinary skill in the art, upon review of the subject specification, would understand how to apply the subject teachings and determine workable values and ranges of values based upon the values and ranges of values disclosed herein.

As will be appreciated from the following description, the vertical wind tunnel disclosed herein provides a number of improvements relating to customer experience, cost of construction, and cost of operation. First, with regard to customer experience, the present vertical wind tunnel's novel design allows for the flight chamber102to be positioned at the ground floor, thereby enabling easier access for customers. Further, the novel design, as discussed below, produces a better, more laminar (i.e., less turbulent) airflow, which yields a smoother and safer flight experience for customers. The novel design also permits faster wind speeds at nominal power levels, thereby enabling enthusiasts to fly at speeds well above that of free fall. Not only is the present vertical wind tunnel superior in terms of at least customer experience, but both the cost of construction and operations are also reduced, thereby reducing both upfront and ongoing costs. For example, the vertical wind tunnel of the present invention employs about one-third of the land of a comparable, traditional vertical wind tunnel, thus reducing real estate cost.

Within its smaller real-estate footprint, such vertical wind tunnels may be accomplished with a smaller facility, while providing the same approximate size flight chamber102of a much larger facility, thus requiring fewer materials, lower cost of construction, and faster construction for the physical structure. Yet another benefit is that a smaller structure size results in a larger array of potential installation locations, thereby enabling installation of the vertical wind tunnel in crowded places, such as downtown urban areas and other entertainment zones with particularly dense foot traffic.

The cost of operation is mitigated because the vertical wind tunnel need only move a much smaller volume of air than other facilities having flight chambers of the same approximate size, which results in a lower energy expenditure. Moreover, the airflow is designed to travel with greater efficiency, which reduces pressure loss and energy expenditure. Finally, because there are fewer parts to wear or break, the present vertical wind tunnel has a higher mean time between failures (“MTBF”) than traditional vertical wind tunnels, such as multiple-motor systems.

With reference to the Figures, an exemplary embodiment of the vertical wind tunnel100is illustrated having: a flight chamber102, a plurality of diffusers104,108,112,114, (and, in some embodiments, a fifth diffuser117), one or more breather slots122, a fan202operatively coupled with a motor, and a plurality of expanding corners106,110,116,118. The one or more breather slots122may comprise just one slot, or a plurality of slots, which may be arranged horizontally, vertically, or a combination thereof. The plurality of diffusers104,108,112,114and the plurality of expanding corners106,110,116,118are arranged and configured such that they are in closed-loop flow communication with one another (seeFIGS. 1band 2c, where airflow direction is indicated as airflow direction F). More specifically, the vertical wind tunnel100's design is an “open jet” tunnel, which means that the air pressure is equalized with the environment outside the tunnel; thereby obviating the need for pressure locks between the inner tunnel area and external atmosphere. While the subject disclosure is primarily described as applied to a vertical wind tunnel used for recreational purposes, the various novel teachings may be applied to other wind tunnels, including, without limitation, horizontal wind tunnels, such as those utilized for industrial, scientific, and sport testing. To that end, while the term flight chamber throughout this disclosure, when the wind tunnel is configured as a non-flying tunnel (e.g., a wind tunnel utilized for industrial, scientific, and sport testing, whether vertical or horizontal), the flight chamber102would, in those instances, be better described as a test chamber.

As illustrated, the vertical wind tunnel100is arranged to occupy a smaller footprint when the various components are arranged such that the vertical wind tunnel is taller, and less wide. Specifically, an example closed circuit vertical wind tunnel100may include: (1) a flight chamber102with, for example, a circular cross section; (2) a first diffuser104that is also a circle-to-quadrilateral (e.g., a square, as illustrated) transition; (3) four sets of internal turning vanes208designed as expanding corners (e.g., first expanding corner106, second expanding corner110, third expanding corner116, and fourth expanding corner118); (4) a second diffuser108positioned between first expanding corner106and second expanding corner110; (5) a return tower128between the second expanding corner110and the third expanding corner116that also transitions from a rectangular cross section to a circular cross section via a third diffuser112for the power station200and again from a circular cross section to a rectangular cross section via a fourth diffuser114before a third expanding corner116; (6) a single fan202; a fifth diffuser117optionally positioned between the third expanding corner116and a fourth expanding corner118; and (7) a contraction nozzle120that also transitions from a quadrilateral (e.g., a square, as illustrated) cross section to the flight chamber102's round cross section. The vertical wind tunnel100may further comprise a fan nacelle206and a cone210. Moreover, a single netting device (e.g., a screen) and breather slots122may be positioned at the base of the flight chamber102.

The various components will now be discussed in greater detail in an order following the airflow direction F, starting with the flight chamber102. As illustrated, the flight chamber102may be a cylinder having a predetermined diameter and a predetermined axial length, with a circular cross-section and substantially constant area along the length of the cylindrical walls. In certain aspects, however, the flight chamber102may diffuse, which would mitigate formation of a bottleneck at the downstream end of the flight chamber102by counterbalancing, either wholly or in part, the growth of the boundary layer along the walls. The foregoing aspect may, moreover, be particular useful in horizontal tunnels where the “flight chamber”102is instead a test chamber and a more constant rate of airflow along the length of the test chamber is desirous for the test conditions. Further, the cross-section of the flight chamber may be polygonal, which, although less ideal from an airflow perspective, does permit for lower cost materials to be used for wall fabrication. In yet other embodiments, the cross-section of the flight chamber may be oval, which, although less ideal from an airflow and customer-experience perspective, would allow for an even smaller physical facility to be built while nominally preserving for customers the “feel” of a bigger tunnel, at least along the longer axis of the oval flight chamber. Thus, while the flight chamber102is illustrated and described as being round and cylindrical, other shapes are possible, including, for example, oval or polygonal.

With reference to a vertical wind tunnel100used for recreational skydiving purposes, the predetermined diameter of the flight chamber102may be, for example, 1 to 40 feet, more preferably 7 to 24 feet, and most preferably about 14 feet in diameter. The predetermined axial length of the flight chamber102may be, for example, 5 to 75 feet, more preferably 25 to 35 feet, and most preferably about 30 feet in length. However, shorter lengths are possible for non-skydiving tunnels and, therefore, the length could be as short as 1 foot. Conversely, longer lengths are contemplated for certain testing wind tunnels where larger test objects must reside within the flight (test) chamber102. A base may be situated at the bottom (upstream) end of the flight chamber102, which may comprise a breather slot122, and a netting device (e.g., a screen—not shown). Unless indicated otherwise, the various geometry measurements disclosed herein (e.g., diameters, dimension, etc.) are interior dimensions.

The netting device may comprise a porous baffle that functions as the floor for the users (e.g., flyers124and instructor126). The porous baffle operates to reduce turbulence of the flow through the screen. In the case of a non-skydiving wind tunnel, the netting device also serves as a debris catcher, providing a “last chance” to catch objects that might otherwise damage a model located in the test chamber. In other embodiments, one or more breather slots122may be located downstream from the end of the flight chamber102, such as in perforations along the walls of the flight chamber102, at the entrance, exit, or along the walls of the first diffuser104, or at the entrance of the first corner106.

The entire length of the flight chamber102may be substantially transparent (e.g., a clear tube/cylinder), and constructed of transparent Plexiglas®, acrylic plastic, glass, or similar high-strength, transparent material. Thus, in certain embodiments, one or more of the walls of the flight chamber102may be fabricated entirely (other than mounting hardware, for example) from a transparent material, whether flat or curved transparent panels, and constructed of any of the aforementioned materials. When present, the transparent panels in the flight chamber102permit an unrestricted view of the activities taking place therein. Adjacent to the flight chamber102may be a loading area (not shown), which communicates with the flight chamber102via one or more openings through which one or more users (or test objects) may enter and exit the flight chamber102. Thus, the loading area and flight chamber102may be transparent, or have transparent windows, so that an observer may view the movement of flyers124(or test objects) within the flight chamber102, without having to enter the loading area. When the wind tunnel is configured as a non-skydiving tunnel (or where visual inspection of the flier or test object is not necessary), the loading area and/or flight chamber102may be constructed from an opaque material.

In some embodiments, the opening between the loading area and the flight chamber102represents the point of lowest pressure in the circuit for the flow of air throughout the length of the wind tunnel. As such, instead of a pressurized air lock, the loading area communicates aerodynamically with the outside environment, which facilitate door-less operation. That is, obviating the need for pressure locks between the inner tunnel (e.g., the flight chamber) and external atmosphere (e.g., the loading area), which, allows users to enter or exit the loading area without first passing through a pressurized-air lock. Alternatively, for purposes of line management—i.e., managing the flow of customers—the loading area may have doors that open periodically to allow people to exit the entire system. Finally, the fan202and other controls can be operated from inside the loading area, inside the flight chamber102, or from an attached or remotely situated control room. The fan202may be controlled to achieve the optimum airflow velocity through the flight chamber102.

As illustrate, a first diffuser104can be coupled to the downstream end of the flight chamber102. The first diffuser104may transition from a circular cross-section shape to a quadrilateral cross-section shape so as to facilitate a connection with a first expanding corner106. The first diffuser104may implement an equivalent conical angle between a value greater than zero degrees (e.g.,0.001and greater) and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably between 2.0 and 4.0 degrees. To facilitate the transition from a circle to quadrilateral, the first diffuser104may employ a cubic-spline transition geometry, as illustrated inFIGS. 7ato 7d. The cubic-spline profile is advantageous over simple lofting because a cubic-spline profile improves pressure recovery and flow uniformity. Thus, the area change along the length of the first diffuser104may follow the cubic-spline profile.

With reference to a vertical wind tunnel100used for recreational skydiving purposes having a 14-foot circular flight chamber102with a constant diameter, the length of the first diffuser104may be between, for example, 5 and 35 feet, more preferably 10 and 25 feet, and most preferably about 15 and 20 feet. That is, testing indicates that a 15-foot length was very good, but a 20-foot length was nearly ideal. The dimension of the first diffuser104's quadrilateral end may be, for example, about 14 feet by about 14 feet (e.g., 13 to 15 feet, more specifically, 14 to 14.5 feet, even more specifically 14.25 feet). To the extent necessary, and in view of the present teachings, one of ordinary skill in the art would know to adjust the values and ranges of values of these dimensions to correspond with flight chambers of a desired size and shape. In certain embodiments, fillets may be inserted into the corners of the first diffuser104in order to reduce the introduction of non-uniformities into the airflow at the point of intersection between the four walls of the first diffuser104.

The first expanding corner106may be an expanding corner with an expansion ratio of about 1.01 to 10.00, more preferably about 1.01 to 7.00, even more preferably about 1.10 to 1.50, or about 1.31, and most preferably about 1.25. Generally speaking, an expanding corner functions by increasing the cross section of the tunnel so as to expand the flow of air. Thus, for example, if the first expanding corner106has a 1.25 expansion ratio, the input cross-sectional area would be X, the output cross-sectional area would be 1.25(X). Though larger ratios may be used and can result in a smaller structure that requires less real estate and saves on construction costs, the smaller size has the risk of adversely affecting flow quality through the introduction of non-uniformities, particularly in the high-speed first expanding corner106. In certain embodiments, however, it may be desirous to sacrifice flow quality in exchange for a shorter return circuit. In such embodiments, the ratio of expansion for the first expanding corner106may be increased. To compensate for the resulting introduction of non-uniformities into the airflow, the airflow may be treated downstream of the first expanding corner106, such as by passing the airflow through a flow straightener composed of hexagonal comb and placed before (e.g., immediately before) the contraction nozzle120, in an example. A smaller ratio, however, is advantageous in that the resulting slight increase in the overall size of the airflow circuit (versus higher ratios) may reduce risk of introducing non-uniformities into the airflow.

The first expanding corner106may have a first quadrilateral end configured to couple with the quadrilateral end of the first diffuser104, and a second quadrilateral (e.g., rectangular) end configured to couple with the rectangular end of the second diffuser108.

A second diffuser108may provide an expansion in a horizontal axis only and couples the rectangular end of said first expanding corner106with a second expanding corner110's rectangular entrance end. The second diffuser108may implement an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees, where the area change may follow a cubic-spline profile. In some embodiments, a second diffuser108may provide an expansion in a vertical axis, a horizontal axis, or both a vertical and a horizontal axis. In certain embodiments, fillets may be inserted into the corners of the second diffuser108in order to reduce the introduction of non-uniformities into the airflow at the point of intersection between the four walls of the second diffuser108.

The second expanding corner110may have expansion ratio of about 1.01 to 10.00, more preferably about 1.01 to 7.00, even more preferably about 1.10 to 1.50, or about 1.31. Thus, the expansion ratio of the first expanding corner106need not be equal to the expansion ratio of the second expanding corner110. For example, the expansion ratio of the first expanding corner106may be less than the expansion ratio of the second expanding corner110. If desired, however, the expansion ratio of the second expanding corner110may also be 1.25. In certain embodiments, it may be desirous to sacrifice flow quality in exchange for a shorter return circuit. In such embodiments, the ratio of expansion for the second expanding corner110may be increased. To compensate for the resulting introduction of non-uniformities into the airflow the airflow may be treated downstream of the second expanding corner110. A smaller ratio, however, is advantageous in that the resulting slight increase in the overall size of the airflow circuit (versus higher ratios) may reduce risk of introducing non-uniformities into the airflow.

The second expanding corner110may comprise a rectangular end configured to couple with said second diffuser108and a rectangular end configured to couple with the rectangular end of a third diffuser112.

The third diffuser112may couple the second expanding corner110with a fourth diffuser114and may transition from a first rectangular shape to a circular shape, with an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees, where the area change may follow a cubic-spline profile. As the equivalent conical angle increases in degrees, however, the risk of introducing flow separation and other non-uniformities into the wind stream also increases. For example, equivalent conical angles of 2 or 2.5 degrees may be used. Nevertheless, in certain embodiments, the use of higher equivalent conical angles may be advantageous as a means to shorten the overall length of the return circuit. The resulting non-uniformities introduced into such embodiments may be ameliorated through, for example, an air treatment applied downstream, such as the passing the airflow through a flow straightener composed of hexagonal comb immediately before the contraction nozzle120.

With reference to a vertical wind tunnel100having a 14 foot flight chamber102used for recreational purposes, the diameter of the circular ends of the third diffuser112and the fourth diffuser114may be, for example, 10 to 80 feet, more preferably 20 to 40 feet, and most preferably about 30 feet. However, as discussed above, one of skill in the art would understand that these values are relative to the size tunnel one is building. The fourth diffuser114may transition from the circular shape to a second rectangular shape, with an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees, where an area change follows a cubic-spline profile. The second rectangular shape at the exit of the fourth diffuser114may be rotated 90 degrees relative to the first rectangular shape at the entrance of the third diffuser112. By rotating the rectangular airflow by 90 degrees, this geometric transition enables the use of a shallow, wide excavation when those sections are located underground rather than a narrow, deep excavation, which would tend to cost more to perform during construction. Said 90-degree geometric rotation also facilitates returning the rectangular airflow to a square-shaped (or other quadrilateral) airflow after the airflow passes through the third expanding corner116, the (optional) fifth diffuser117, and the fourth expanding corner118.

The third and fourth diffusers112,114define a return tower128that may house a power station200to accelerate the air. The power station200may include a single fan202, motor-support vanes204, a motor (not shown), and a gear box (not shown) that may be used to increase torque of a large-mass fan. In certain embodiments, as discussed below, the power station200may employ a plurality of fans. In certain embodiments, fillets may be inserted into the corners of the third and/or fourth diffusers112,114in order to reduce the introduction of non-uniformities into the airflow at the point of intersection between the four walls of the third and/or fourth diffusers112,114.

The power station200may further comprise a cone210and a fan nacelle206, which may be used to house the motor and the gear box. For example, as illustrated inFIG. 1b, the power station200may be positioned at or near the connection point between the third diffuser112and the fourth diffuser114. In other embodiments, the power station200may be located in the base (e.g., an underground plenum) located between the third expanding corner116and the fourth expanding corner118, possibly in the fifth diffuser117. Alternately, the power station200may be located in the second diffuser108or the first diffuser104, or the connection points between said first and second diffusers and the surrounding sections. In yet other embodiments, the power station200may be located after the fourth expanding corner118and before the contraction nozzle120.

A fan202may be provided with an area ratio of between 1:1 and 10:1 (fan202to flight chamber102cross area). For example, a low-acoustic fan may be designed with a large hub diameter and nacelle geometry. The use of a single fan generally results in higher MTBF, as well as a much quieter operation when compared to systems using multiple fans. However, in some embodiments multiple smaller fans may be utilized. In some embodiments, such as when the fan202and attached motor are located in the return tower128, the fan202and attached motor may be configured so as to be removable from the top so as to facilitate easy replacement and/or repair. Anti-swirl vanes may employ, for example, a constant thickness, swept chord, and swept thickness-to-chord ratio.

While a single return tower128is illustrated, one of skill in the art would appreciate that plural return towers128may be employed. For example, a designer may employ two or more return towers128to reduce the depth of the underground excavation required to build a wind tunnel with a flight chamber at or near ground level—for example, instead of a single return to a depth of 50 feet underground, the facility could utilize two returns each at a depth of approximately 25 feet. However, with the increased number of return towers128comes an increase in air turbulence as well as a potential increase in the above-ground construction cost and an adverse impact on the MTBF due to the increased number of components to manufacture, assemble and maintain. When plural return towers128are employed, each return tower128may comprise a power station200.

A third expanding corner116and a fourth expanding corner118may be coupled to one another, possibly by a fifth diffuser117positioned therebetween, and configured to function as, or define, the base130(e.g., a plenum) of the vertical wind tunnel100's structure. As illustrated, the third expanding corner116may be coupled with a second rectangular-shaped end of the fourth diffuser114. The third expanding corner116and a fourth expanding corner118may be fabricated as a single unit separated by a channel, or as two separate components coupled at their rectangular ends, either directly, or, or illustrated, via a fifth diffuser117positioned between the third expanding corner116and the fourth expanding corner118. The third expanding corner116and fourth expanding corner118may each have an expansion ratio of about 1.01 to 10.00, more preferably about 1.01 to 7.00, even more preferably about 1.10 to 1.50, or about 1.31. Thus, in certain embodiments the expansion ratio of the third expanding corner116and the fourth expanding corner118may be the same as the expansion ratio of the second expanding corner110, but greater than that of the first expanding corner106. As a result, the mean average expansion ratio of the third expanding corner106and the fourth expanding corner118is generally greater than the mean average expansion ratio of the first expanding corner106and the second expanding corner110. If desired, however, the expansion ratios of the third expanding corner116and the fourth expanding corner118may equal to or smaller than the expansion ratio of the third expanding corner106and/or the fourth expanding corner118.

In certain embodiments, the third expanding corner116and fourth expanding corner118may be located below ground, requiring excavation for their construction. Generally, the cost of excavation increases arithmetically along the horizontal axis (the length of the dig) and increases disproportionately higher along the vertical axis (the depth of the dig). To mitigate the cost of excavation, the expansion ratio one or both of the third expanding corner116and the fourth expanding corner118may be increased. The increased ratio will cause the introduction of non-uniformities into the air flow that, if advantageous, can be treated downstream, typically through the use of a flow straightener before the contraction nozzle120, as previously described above.

The base130may be installed below ground so as to reduce the height of the overall structure, reduce the temperature of the air (e.g., due to ground cooling), and enable entry of the flight chamber102by users at, or near, ground level. Thus, when installed, certain components, such as the fourth diffuser114, third expanding corner116, fifth diffuser117, fourth expanding corner118, and contraction nozzle120, may be buried (e.g., within the ground) such that the breather slot122is positioned at, or just above, ground level. For example, the fourth diffuser114, third expanding corner116, fifth diffuser117, fourth expanding corner118, and contraction nozzle120may be substantially underground (indicated via line A inFIG. 2c), or just the third expanding corner116, the fifth diffuser117, and the fourth expanding corner118may be substantially underground (indicated via line B inFIG. 2c). In some embodiments, the base130may expand along its length at an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees. However, as discussed above with regard to the potential for flow separation and other non-uniformities, the equivalent conical angles may be greater.

In other embodiments, the expansion of the base130may be generated, at least in part, by adding a slope to the flooring between the third expanding corner116, the optional fifth diffuser117, and the fourth expanding corner118, which the shallow end at the third expanding corner116and the deep end at the fourth expanding corner, said slope serving a second purpose, which is to channel water to a drain hole located about the fourth expanding corner118. In yet other embodiments, such as construction into a hillside, only the third expanding corner116or, alternately, the fourth expanding corner118may need to be substantially underground, thus saving excavation costs. In another embodiment, the fourth diffuser114, third expanding corner116, fifth diffuser117, fourth expanding corner118, and contraction nozzle120may be substantially above underground, with customers utilizing stairs or some other conveyance to reach the elevation of the flight chamber102.

A contraction nozzle120may be used to provide a quadrilateral (e.g., a square, as illustrated) to circular transition and couple the fourth expanding corner118's square end to the circular flight chamber102. The contraction nozzle120may employ a predetermined cross-sectional area contraction ratio (e.g., about 2:1 to 10:1, more preferably about 3:1 to 6:1, and most preferably about 5:1) and a predetermined length-to-width ratio (e.g., about 0.50 to 2.0, or more preferably 0.75 to 1.25, and most preferably, about 1.0). The area change may follow the cubic-spline profile and it may also follow the fifth order polynomial profile. Thus, to improve pressure recovery and flow uniformity, at each geometric transition (e.g., from a polygon to circle, and vice versa) an equivalent, conical angle between 0.1 and 10.0 degrees is combined with a cubic-spline profile, rather than simple lofting.

A breather slot122may be located immediately upstream of a safety net, which may attach to net pulleys, as illustrated inFIG. 8, that adjust the tautness and/or facilitate replacement of the netting device or supporting cables. In some embodiments, the breather slot122may be located downstream from the safety net and either at the entrance of or upstream of the first expanding corner106, such as at the connection point between the flight chamber102and the first diffuser104.

As illustrated, the expanding corners of the vertical wind tunnel100(e.g., first expanding corner106, second expanding corner110, third expanding corner116, and fourth expanding corner118) may comprise a plurality of internal turning vanes208. The plurality of internal turning vanes208are configured to assist in changing the airflow direction by 90 degrees. The internal turning vanes208may also providing cooling functionality using fluid-cooling techniques (e.g., water-cooling or air-cooling). For example, the internal turning vanes208may be hollow and have heat transfer fluid (e.g., cool water, other liquids, or air) pumped therethrough. In operation, the air passes through the anti-swirl vanes, which redirects the air from a substantially vertical to a substantially horizontal path (or vice versa, depending on the corner).

Generally, it is advantageous to mitigate energy needed to cool air passing through a wind tunnel. Existing systems typically rely on energy to circulate and cool heat transfer fluid through, for example, a heat exchanger. However, such heat exchanging systems require a significant amount of energy to circulate and cool the heat transfer fluid. To mitigate this cost, a wind tunnel as disclosed herein may harness the cooling effects of the earth through a ground-coupled heat exchanger. A ground-coupled heat exchanger uses an underground heat exchanger that can capture heat from and/or dissipate heat to the ground. Such ground-coupled heat exchangers use the Earth's near constant subterranean temperature to cool heat transfer fluid that is then used to cool air circulating through the wind tunnel. In certain aspects, ground-coupled heat exchanger may also use air, water, and/or antifreeze as a heat transfer fluid, often in conjunction with a geothermal heat pump.

Such a ground-coupled heat exchanger may be constructed using a pipe buried underground where the year-round ambient earth temperature is, depending on region, typically 10 to 23° C. (50-73° F.) at 1.5 to 3 meters (5 to 10 feet). However, because ground temperature becomes more stable with depth, the pipe may be positioned deeper to provide a cooler, more stable, temperature. For instance, the pipes may be buried about half way between the surface of the base130and the ground level. For example, the pipe may be positioned about 20 feet below the earth's surface, where the temperature is more stable. In operation, heat transfer fluid is communicated through the subterranean pipe where the earth's temperature cools the heat transfer fluid prior to being sent to the heat exchanger (e.g., turning vanes208or, in an alternate example, vertical vanes running from the ceiling to the floor in the underground plenum defined by third expanding corner116, fifth diffuser117(optional), fourth expanding corner118), where the cooled heat transfer fluid is then used to cool the air in the wind tunnel. In certain embodiments, the ground-coupled heat exchanger may be positioned solely in the submerged portion of the vertical wind tunnel100(e.g., third expanding corner116, the fifth diffuser117, and/or fourth expanding corner118) so as to obviate the need to pump the fluid vertically, thus saving even more energy. That is, lateral movement of the heat transfer fluid requires less energy. For water adjacent facilities, a water-to-air heat exchanger may be used, whereby a large body of water (e.g., lake, ocean, river, etc.) is used to cool the fluid within the tube.

Another method to mitigate the energy needed to cool the airflow is to pass a heat-transfer fluid, such as described above, over the outside shell of the return, and particularly the underground plenum. Such a system may be combined advantageously with a ground-coupled heat exchanger for cooling the returned fluid. The shell of the return should be thin and non-rusting with a low insulation value, such as stainless steel sheet.

During normal operation, wind tunnels may generated mold growth due to any number of factors, such as being located in a humid area, internal condensation due to cooling vanes, and the use of water for an evaporative-cooling system. To address potential mold issues, the various components of the vertical wind tunnel100(e.g., the expanding corner, diffusers, etc.) may be fabricated from, or otherwise incorporate, mold-resistant materials. For example, the various components may be fabricated from extruded aluminum, injection molded plastic, or the like, and, importantly, sealed with mold-resistant sealant (e.g., caulking). In an example, the internal turning vanes208may be fabricated from, for example, a composite material (e.g., fiberglass, carbon fiber, etc.) metals, metal alloys, etc., and/or sealed with a mold-resistant sealant.

As noted above, the wind tunnel may further employ a tilted floor to direct any water resulting from condensation (and other moisture sources) to a drain. For example, the base defined by the third expanding corner116, fifth diffuser117, and the fourth expanding corner118may be tilted (e.g., up to 10.0 degrees, more preferably, up to 2.0 degrees, and most preferably about 0.5 to 1.0 degree). The wind tunnel may further comprise debris netting and, optionally, a tray to collect the debris. In some embodiments, the debris netting and optional tray are located in the area between the first diffusing corner106and the second diffusing corner110and, more preferably, at the exit of the second diffuser108.

Testing and computational modeling was performed to confirm that the forgoing vertical wind tunnel100's design was advantageous over existing systems. The results indicate that the present design provides premium air quality, lower operating cost (e.g., electric consumption), higher wind speeds, is easier to maintain, has a reduced (e.g., small) footprint, requires fewer parts to manufacture, is faster to build/assemble, and is less costly to build. Further, testing indicates that the first diffuser104produced improvements in pressure recovery and in flow uniformity when utilizing a cubic-spline profile. Analysis was focused on assessment of flow velocity and total pressure across the cross section at the end of first diffuser104and along symmetry planes of the section, including through the corners of the square end. The results indicate that a first diffuser104utilizing a cubic-spline profile provides both improvements in pressure recovery and in flow uniformity.

Within a particular design (standard or cubic-spline) pressure recovery is similarly driven by length with no clear improvement at each discrete length over the theoretical pressure recovery or the round (non-transitioning) diffuser. Similarly, flow uniformity for an empty flight chamber102(a/k/a, a clean configuration) does not appear to be impacted significantly by the first diffuser104's length. With flyers in the flight chamber102, however, diffuser length does have an impact on flow uniformity with additional length providing better uniformity. This effect is more pronounced as more flyers124are introduced into the flight chamber102. Looking at the data downstream of the diffuser outlet for a 14 foot circular flight chamber, it appears the improvement in flow uniformity is substantial from diffuser lengths of 10 to 12 feet and from 12 to 15 feet, with a further (but less drastic) improvement from 15 to 20 feet. However, the ideal diffuser length varies with the width and shape of the flight chamber. Though these variations are not linear, a person of skill would understand how to determine the ideal diffuser length for a flight chamber of a particular size and shape.

As explained above, the first expanding corner106may have an expansion ratio of less than 1.25:1; while the second expanding corner110, the third expanding corner116, and the fourth expanding corner118each have an expansion ratio of about 1.25:1. This particular arrangement may be selected in order to minimize risk of flow separation in the first expanding corner106that can be attributed to large wakes from the flyers in the flight chamber. Further, each of the first diffuser104, the second diffuser108, the third diffuser112, and the fourth diffuser114were configured such that they expand at an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees. In some embodiments utilizing a fifth diffuser117between the third expanding corner116and fourth expanding corner118, said diffuser may be configured such that expands at an equivalent conical angle between 0.1 and 10.0 degrees, more preferably between 1.0 and 7.0 degrees, most preferably 2.0 and 4.0 degrees. However, as discussed above with regard to the potential for flow separation and other non-uniformities, the equivalent conical angle may be greater.

Initial testing was performed using computational fluid dynamics (“CFD”) analysis with the vertical wind tunnel100with an empty flight chamber102at both 116 mph and at 180 mph in order to verify and validate that circuit flow quality is adequate. The CFD analysis initially identified a number of areas of poor flow quality, with the worst flow quality found in the return tower128when standard diffuser geometry was employed. For example, the area upstream of the fan in the return tower128(i.e., within the third diffuser122) was found to have a very low flow velocity and thus an area where flow is separated. To address this issue, a cubic-spline profile was applied to each of the third diffuser112and the fourth diffuser114in the return tower128. All area ratios and inlet and outlet cross-sectional profiles were otherwise unchanged, but the area change could be updated for systems with plural return towers. Once updated, the CFD analysis was reassessed with the cubic-spline profile and a noticeable improvement in flow quality and flow uniformity was identified.

The results from the CFD analysis allows for the estimation of power consumption for each condition. Power estimation was based on the calculation that [fan ideal power]=[volumetric flow rate]×[system pressure drop]. The fan ideal power was then aggressively de-rated to account for a 90% efficiency for the aerodynamics of the fan and a 90% efficiency for the electric motor and VFD combination for an overall system efficiency of 81% (90%×90%). However, an overall system efficiency of about 90% efficiency is expected at many speeds based on the known efficiencies of VFDs and premium-efficiency motors available in the market today. The resultant power estimations are consistent with the expectations for an efficient wind tunnel circuit design of this nature. The power estimates for conditions with an empty flight chamber102are valid off the CFD analysis as it was solved.

The power estimates for the conditions with flyers included, however, may require further refinement since the body attitude of the flyers included in the analysis creates more drag at the assessed test velocities than the anticipated weight of the flyers. For example, at 180 mph with four flyers in the test section, the measured drag of each of the four flyers is ˜390 pound force (lbf), which is substantially greater than the expected weight of a flyer (about 160 lbs). Since a hover condition requires that the drag of the flyers be equal to their weight, power estimations for hovering flight for any combination of flyers and flight velocity can be estimated from the baseline by determining the amount of power required to overcome the aerodynamic drag of the flyers for a given condition.

The power required to overcome aerodynamic drag is as follows: [power]=[velocity]×[drag]. If drag must equal weight, then the total power requirement for a given condition is equal to the baseline power for the condition plus the power required to overcome the weight of a flyer multiplied by the number of flyers or [total power]=[baseline power]+([flyers]×[velocity]×[weight of each flyer]) As a validation of the CFD prediction, the same methodology was used to calculate the power of the circuit operating at 180 mph with four flyers who have a weight of 160 lbs. The resultant calculation comes out to 2,622.84 HP compared to the 2,677.12 HP measured directly in CFD. The relatively small delta 54.28 HP (or about two percent) can potentially be attributed to inefficiencies brought about by the propagation of wakes of the flyers throughout the circuit. Using the simplified calculation described above, the power estimation of various tunnel velocities and number of flyer combinations has been prepared, indicating that the efficiency of the subject vertical wind tunnel100's design for single flyers is about twice as efficient as that of conventional vertical wind tunnels.

An example net pulley arrangement800for supporting the netting device is illustrated inFIG. 8, which may be used in connection with vertical wind tunnel100, or any other net system. Thus, the pulley arrangement800disclosed inFIG. 8should not be construed as being limited to use with the vertical wind tunnel100, but rather, may be employed with traditional wind tunnels, or any other system employing a cable supported net or screen, or where cable tautness is to be maintained. The pulley arrangement800is advantageous in that it permits a quick installation, can be installed without requiring a second installer, may be periodically adjusted generate a consistent tension on the cable even as said cable fatigues, which results in a longer cable life and a safer net. Finally, it is easy to spot damage to, sabotage, or accidental mis-installation of, the cable or other component of the pulley arrangement800.

As illustrated, such a pulley arrangement800may comprise a head end unit801positioned at an end (or both ends) of a cable814, and may comprise: (1) a pulley block802, which may be a replaceable part that absorbs sawing; (2) a jam nut804to prevent bolt movement; (3) a tensioning bolt806that is adjustable in length; (4) a compression spring808that allows for visual measurement, and inspection; (5) a washer (preferably a capture washer)810; (6) one or more (most preferably two) swages812; (7) a bolt head820(or bolt head portion or coupling nut), which may comprise a deep countersink to act as a first spring guide818; and (8) a fixturing nut822, which may be bolted to net frame816. The frame may also comprise a countersink to act as a second spring guide824. The pulley arrangement800may further comprise a receiving end unit826positioned at an end of a cable814opposite a head end unit801, and may comprise: (1) a second compression spring828; (2) a washer (preferably a capture washer)810; and (3) one or more (most preferably two) swages812. As illustrated, the pulley arrangement800may comprise a plurality of cables814configured in a planar parallel arrangement, where the proximal ends of the cables814alternate between comprising a head end unit801and a receiving end unit826. In certain embodiments, each cable814comprising a head end unit801connected to an end of the cable814may further comprise a receiving end unit826connected to the opposite end of the cable826. In certain embodiments, the fixturing nut822may be integrated with the frame816, such as through welding. For example, the frame816may be threaded and configured to directly receive the tensioning bolt806. The bolt head814's material may be hardened (e.g., hardened steel) to increase strength and usable life. As illustrated at points X, Y, and Z, the component adjacent the cable814(e.g., through-holes) may be filleted to reduce sawing by the cable814. Further, the cable ring818(e.g., the vertical wind tunnel100's wall) may be slotted to avoid sawing by the cable814. A suitable distance between the tensioning bolts806, when used with the vertical wind tunnel100, may be about 4 inches on center, but one of skill in the art would recognize that other distances may be employed depending on the particular need. For example, according to one embodiment, a 1″ threaded stainless bolt806may be used with 3/32″ stainless cable814. In certain aspects, a threaded rod may be used in lieu of a bolt, with a coupling nut (e.g., a tall nut, such as a 2 to 3 inch nut) that functions as the bolt head. The coupling nut may be screwed to the threaded rod about half down the nut's length and secured to the rod using, for example, a tack weld. The open end of the coupling may be configured to fit the spring.

Another consideration wind tunnel fabrication is sound absorption. During operation of the vertical wind tunnel100, a considerable amount of sound resonates from, for example, the motor, the fan blades, and the movement of air. To address such noise from the wind tunnel, perforated sheet metal of specified open area ratio and sound absorbing material may be provided along the walls of the tunnel. The hole size, hole pattern and open area ratio may be selected to address a particular need. The sound absorbing material, which may be shaped to include a plurality of protrusions, may be fabricated from, inter alia, plastic. The plurality of protrusions may employ one or more shaped profiles, including, for example, pyramidal, conical, rounded, etc.

An issue that can arise, however, is the potential for the accumulation of contaminants, such as dust and/or debris, on the sound absorbing material. Such an accumulation of contaminants reduces the effectiveness of the sound absorbing material, while also exposing the user of the wind tunnel to such contaminants, which may contain allergens. Thus, to mitigate this accumulation, an acoustically transparent layer (e.g., a fabric, screen, resin, or other material) may be provided between the perforated sheet metal and the sound absorbing material. The term “acoustically transparent” means that acoustic energy is able to enter and transit through the material with a minimal amount of reflection. The acoustically transparent layer would effectively block the contaminants from encountering the sound absorbing material, while also allowing sound waves to pass and be absorbed by the sound absorbing material. In certain aspects, the fan may be a ducted fan whereby the fan blades are mounted within a cylindrical shroud or duct. In such an example, the cylindrical shroud or duct may be acoustically transparent.

The above-cited patents and patent publications are hereby incorporated by reference in their entirety. Although various embodiments have been described with reference to a particular arrangement of parts, features, and like, these are not intended to exhaust all possible arrangements or features, and indeed many other embodiments, modifications, and variations will be ascertainable to those of skill in the art. Thus, it is to be understood that the invention may therefore be practiced otherwise than as specifically described above.