Propeller-based fluid redirection device useful, for example, for reducing resistance of bluff bodies

Abstract

A system includes a bluff body having a trailing end and a wake region and a slipstream direction aft of the trailing end. The system also includes a propeller including a hub and a plurality of blades extending outwardly from the hub. The hub is mounted to the tail end of the bluff body to rotate about an axis. The axis is angled with respect to the slipstream direction in both pitch and yaw aspects such that when fluid flows through the bluff body, at least one of the blades is in the slipstream and extracts energy to rotate the hub, at the same time, at least one of the blades breaks away from the slip flow and redirects fluid from the slip flow into the wake region. This autorotation of the hub causes the blades to continuously move into and out of the slipstream to continuously extract energy and redirect the slipstream fluid into the wake region.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 366,224, filed on June 10, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] Heavy vehicles such as tractor-trailer combinations and buses typically have large front-facing surfaces and blunt rear surfaces. For these vehicles, pressure drag is the main component of aerodynamic drag. For example, as a tractor-trailer moves through the air, pressure increases at its front-facing surface, while pressure drops at its rear surface. Pressure drag is proportional to the difference between the pressure acting on the front-facing surface and the rear surface. Pressure drag can lead to a significant reduction in fuel economy and, therefore, a significant increase in operating costs.

[0004] There are a variety of devices that can be used to reduce pressure drag. Drag reducing devices such as vortex deflectors are installed near the rear end of the vehicle to break up a sheet of passing air into multiple swirling wakes. Drag reducing devices such as tail end drag reducers provide a sharp trailing edge that helps to swirl the air into a wake vortex in a manner that slightly reduces pressure drop. Drag reducing devices such as truncated streamlined tail surfaces help redirect slipstream air into the wake region downstream of the tail surface.

[0005] The disadvantage of these devices is that they provide minimal reduction in tail drag. Some devices are also bulky and relatively heavy. Summary of the invention

[0006] According to one embodiment, a system includes a bluff body having a tail end and a wake region and a slipstream direction behind the tail end. The system also includes a propeller, the propeller including a hub and a plurality of blades extending outward from the hub. The hub is mounted to the tail end of the bluff body to rotate about an axis. The axis is angled relative to the slipstream direction in both pitch and yaw so that when fluid flows through the bluff body propeller, at least one of the blades is in the slipstream and extracts energy to rotate the hub, while at least one of the blades is disengaged from the slipstream and redirects fluid from the slipstream into the wake region. This automatic rotation of the hub causes the blades to continuously move in and out of the slipstream to continuously extract energy and redirect slipstream fluid into the wake region. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Reference will now be made to the accompanying drawings, which reference should be made when read in conjunction with the following specification, wherein like reference numerals refer to like parts throughout the several views, and in which:

[0008] Figure 1 is a 2D top view of a system including a bluff body and a propeller for reducing drag in a wake region downstream of the bluff body according to one embodiment, and Figure 2A yes Figure 1 Partial 3D view of a part of the system.

[0009] Figure 2B is a graphical representation of the angle of attack of the blades of a propeller according to one embodiment.

[0010] Figure 3 and Figure 4 is an illustration of an example of a propeller according to one embodiment.

[0011] Figure 5 is an illustration of an example of a propeller mounted to a bluff body according to one embodiment.

[0012] Figure 6 is an illustration of an example of a mounting structure and a propeller mounted to the structure according to one embodiment.

[0013] Figures 7 to 9 is an illustration of a trailer and a zero-drive propeller-based system for reducing pressure drag at the rear end of the trailer, according to one embodiment.

[0014] Fig.10 is an illustration of a tractor-trailer and a zero-drive propeller-based system for reducing pressure drag in the gap region between the tractor and trailer, according to one embodiment.

[0015] Fig.11 is a diagram comparing a propeller at the tail end of a tractor-trailer to a propeller in the gap area of ​​the tractor-trailer, according to one embodiment.

[0016] Fig.12 is an illustration of a barge and a zero-drive propeller-based system for reducing pressure drag at the aft end of the barge, according to one embodiment.

[0017] Fig.13 is an illustration of a duct and a zero-drive propeller-based system for redirecting fluid flow and reducing pressure drag inside the duct, according to one embodiment.

[0018] Fig.14 is an illustration of an aerodynamic lift structure according to one embodiment. DETAILED DESCRIPTION

[0019] In the following detailed description, reference is made to the accompanying drawings which form a part thereof. In the accompanying drawings, similar symbols generally identify similar components unless the context indicates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized and other changes may be made without departing from the spirit or scope of the subject matter presented herein.

[0020] Reference now Figure 1 , which is a top view of a bluff body 110 having a front surface 112, a top surface 113, sides 114, 116, a bottom surface (not shown), and a trailing end 118. Bluff body 110 is a body that, due to its shape, has separated fluid flows over most of its surface.

[0021] Bluff body 110 is surrounded by ambient fluid 120. The ambient fluid 120 may be a gas or a liquid, such as air or water. Although reference is made to "fluid," it should be understood that fluid broadly refers to any type of gas, liquid, or combination thereof. Arrow FF indicates the direction of fluid flow over bluff body 110. It should be understood that fluid flow may occur over, around, under, and any combination thereof relative to bluff body 110. The fluid flow may be caused by relative movement between bluff body 110 and ambient fluid 120. The relative movement may be caused by bluff body 110 moving through ambient fluid 120, by ambient fluid 120 moving over bluff body 110, or by movement of both ambient fluid 120 and bluff body 110.

[0022] The wake region W is located behind the tail end 118 of the bluff body 110. When there is relative movement between the bluff body 110 and the ambient fluid 120, a fluid wake is formed in the wake region W. Due to the relative movement, the pressure in the wake region W drops, while the pressure drag increases. Consider an example of a tractor pulling a trailer in a forward direction. When the trailer receives power and moves forward, the air is pushed aside. Since the tail end 118 of the trailer does not generate any air, the surrounding air will try to flow back into it. This is caused by the low pressure there or the few air molecules remaining in the wake region W. The air trying to fill the wake region W is sucked in from all directions, which causes the tail end 118 of the trailer to be pulled back by the air at a lower pressure, which in turn pulls the air further back. If the trailer constantly drives out the air in the wake region W as it moves forward, the amount of time to reposition the air into the wake region W is related to the amount that the residual low pressure can pull back the tail end 118 of the trailer.

[0023] Slipstream refers to fluid moving over bluff body 110, past tail end 118, and over relatively stationary fluid in wake region W. For a slipstream formed by relative movement of ambient air 120 over side 114, the slipstream flows in the direction of arrow S1. For a slipstream formed by relative movement of ambient air 120 over side 116, the slipstream flows in the direction of arrow S2.

[0024] The environment created by the bluff body 110 is different from the environment that conventional fans and propellers operate in. The bluff body 110 creates two distinct zones - the slipstream S1 , S2 where the air moves quickly, and the wake region W where the air moves very little.

[0025] Additional references Figure 2A , which shows propeller-based air redirection that can be used to reduce drag for a bluff body 110. A propeller 130 is mounted to the tail end 118 of the bluff body 110. The propeller 130 includes a hub 210 and blades 220 extending outwardly from the hub 220. The blades 220 have an airfoil-shaped cross-section.

[0026] The hub 210 is mounted to the trailing end 118 of the bluff body 110 for rotation about an axis. The axis is angled relative to the direction of the slipstream so that at least one of the blades 220 can enter the slipstream to extract energy to rotate the hub 210 while at least one of the blades 220 can exit the slipstream to redirect fluid from the slipstream into the wake region W.

[0027] The blade 220, which extracts energy from the slipstream, is positioned in the slipstream at a suitable "angle of attack". As the slipstream fluid flows over the blade 220, lift is generated. As the blade 220 traverses the slipstream, it attempts to rise into the fluid flow, but is ultimately forced to rotate due to the rotational constraints of the hub 210. Once the blade 220 transitions out of the slipstream and into the relatively stationary fluid in the wake region W, it still provides lift, but due to its constrained rotation, the blade pulls the fluid above the blade 220 downward.

[0028] Additional references Figure 2B , which shows the angle of attack α of the blade 220. The angle of attack α is formed by the relative directions of the chord line C of the blade 220 and the slipstream S. The lift is perpendicular to the fluid slipstream direction S. A suitable angle of attack is one that produces lift and provides low drag relative to the energy extracted. The orientation of the blade 220 in the slipstream should not be perpendicular to the slipstream.

[0029] The blades 220 that redirect the fluid from the slipstream into the wake region W are generally parallel to the slipstream. The fluid flowing through such blades 220 is turned from the slipstream into the wake region W in the direction indicated by arrow R1. As the hub 210 rotates, the blades 220 continuously move in and out of the slipstreams S1, S2 to continuously extract energy and redirect the slipstream fluid into the wake region W.

[0030] Fluid flowing through the bluff body 110 and past the trailing end 118 is drawn into the wake region W from all directions. However, the propeller 130 increases the flow of fluid into the wake region W and fills the wake region W more quickly. The energy captured from the blades 220 in the slipstream drives the other blades 220 (which redirect the fluid) with a greater force than the low pressure region can provide (the low pressure in the wake region W is not controlled in any way and it has a lower force). In this way, the pressure drop in the wake region W is reduced, and the pressure drag is reduced.

[0031] In the preferred direction of rotation of the propeller 130, the blades 220 in the slipstream create a wash flow that is directed downwardly and inwardly into the wake region W. This is in addition to the flow redirected by the blades 220 out of the slipstream.

[0032] The propeller 130 does introduce some drag. However, the benefits of redirecting the flow into the wake region W outweigh this drag.

[0033] In one embodiment, propeller-based air redirection and drag reduction is performed without the use of a motor or any other external drive device. That is, the propeller 130 provides zero-drive pressure drag reduction. Advantageously, the propeller can be inexpensive because it can be made of a lightweight, flexible, inexpensive material (e.g., plastic).

[0034] According to one embodiment, the use of multiple blades 220 provides redundancy. Consider Figure 2A , which has six blades 220. Even if several blades 220 fail, as long as at least one blade 220 is extracting energy while at least one blade 220 is redirecting fluid into the wake region W, the propeller 130 is still able to reduce pressure drag.

[0035] Although only a single propeller 130 has been described thus far, additional propellers may be mounted to the bluff body 110 (see, e.g., Figure 7 2, all propellers 130 may be mounted to the perimeter of the tail end, such as along the upper horizontal edge and / or both vertical edges. The use of multiple propellers 130 provides additional redundancy, wherein damage to one propeller 130 does not eliminate the array benefit.

[0036] Additional references Figure 3 and Figure 4, which shows an example of a propeller 130. In addition to the blades 220 and the hub 210, the propeller 130 also includes a rigidly mounted shaft 310. A first end 305 of the shaft 310 can be mounted to the bluff body 110. The hub 210 is mounted to a second end 307 of the shaft 310 via a bearing 320. So mounted, the hub 210 can rotate about an axis of rotation A.

[0037] like Figure 3 and Figure 4 As shown, the blades 220 may be angled outward from the hub 210. When the hub 210 rotates, the blades 220 move along the path of a cone. Assume that the hub 210 has a rotation plane R that is perpendicular to the rotation axis A. The blades 220 may be designed to have a cone angle β between 10 degrees and 45 degrees relative to the plane R. In one embodiment, it has been found that a cone angle of 30 degrees significantly reduces pressure drag. This type of propeller 130 is hereinafter referred to as a "conical propeller 130".

[0038] Blade lengths are not limited to any particular range. However, for the examples described below, blade lengths between 4 inches and 12 inches may achieve adequate drag reduction while minimizing the resulting swept diameter and enable the propeller 130 to be used with a variety of bluff bodies 110.

[0039] Longer blades (ie, blades greater than 12 inches in length) may be used to achieve greater air redirection. Alternatively, two or more rows of shorter blades (ie, blades between 4 inches and 12 inches in length) may be used.

[0040] The angle of attack α of the blade 220 is non-zero. Since the tip of the blade rotates faster than the root, the blade 220 is twisted so that the thrust is the same across the length of the blade 220. This has the effect of changing the angle of attack α across the blade 220. The degree of twist, as well as other parameters such as width and chord, can be based on the propeller size and rotational speed, as well as the speed at which the bluff body 110 passes through the ambient fluid 120 to generate sufficient lift.

[0041] Figure 5The pitch of the propeller 130 and the relationship of the blades 220 to the bluff body 110 are shown. Assume that x, y and z represent the coordinate system of the bluff body 110, where the z axis coincides with the longitudinal axis of the bluff body 110 and the y axis extends vertically. The pitch can be described by the pitch angle P and the yaw angle Y relative to the rotation axis A of the propeller 130. The pitch angle P refers to the angle of the axis A relative to the oncoming wind and is in a plane perpendicular to the side of the bluff body 110. The pitch angle P is changed by rotating the propeller 130 about the x axis. The yaw angle Y refers to the angle of the axis A relative to the slipstream direction S in a plane of the side of the bluff body 110. The yaw angle Y is changed by rotating about the y axis. If the cone angle of the propeller 130 is close, it is best to tilt the axis A away from the vertical direction. This places one of the blades 220 in a horizontal direction. The blade should be tilted to one side of the slipstream direction less than 90 degrees; otherwise, the incoming wind will hinder the rotation of the frontmost blade.

[0042] Figure 5 It is also shown that each time the propeller 130 rotates, at least one blade 220 is in the slipstream and at least one blade 220 is out of the slipstream. This allows for continuous extraction of rotational energy and continuous redirection of the flow into the wake region W. These actions are accomplished without the use of a motor or other external drive.

[0043] As used herein, penetration into the slipstream and time in the slipstream refers to less than half of the rotation of the blade 220 in the slipstream extracting rotational energy. The axis A of the conical propeller is tilted to ensure that the blades 220 entering the slipstream are properly oriented in a low drag, high lift position, while also ensuring that the blades 220 leaving the slipstream redirect the flow into the wake region W. This means that the blades should not be flush with the incoming slipstream. If this axis is tilted too much, the back side of the blade will be affected by the slipstream and generate drag instead of lift. Delaying penetration will reduce the time in the slipstream and also change the entry and exit angles relative to the slipstream, which can limit drag.

[0044] In the illustrated embodiment, the hub 210 is offset from the bottom edge of the slipstream by a distance O, but is located within the wake region W. With proper tilt and offset of the conical propeller 130, at least one of those blades 220 that are out of the slipstream is substantially parallel to the slipstream, and at least one of those blades 220 that are in the slipstream has a non-zero angle of attack that enables the propeller 130 to extract energy from the slipstream. By way of example, the offset distance O may be in the range of 0.1 inches to 0.5 inches.

[0045] Additional references Figure 6, which shows an example of a structure for mounting a propeller 130 to a bluff body 110. The structure includes a strut 610 that can be attached to the tail end 118 of the bluff body 110. One end of the mounting shaft 310 of the propeller 130 can be rigidly mounted to the strut 610 at an appropriate inclination. The bearing 320 enables the hub 210 to rotate about the other end of the mounting shaft 310. The strut 610 creates a spacing between the propeller 130 and the tail end 118 to allow the blades 220 to move unhindered. The strut 610 can have a length that enables more than one propeller 130 to be mounted thereto.

[0046] One of ordinary skill in the art will appreciate that a propeller-based fluid redirection device for drag reduction is not limited to any particular bluff body 110 or ambient fluid. The following paragraphs provide some examples of different bluff bodies 110 and different ambient fluids 120.

[0047] refer to Figure 7 and Figure 8 According to one embodiment, Figure 7 A tractor-trailer trailer 710 is shown, and Figure 8 7 is an enlarged partial view of a trailer 710 having a plurality of propellers 130 mounted to an elongated support 720 at a rear end 718. The trailer 710 is an example of a box-type bluff body. The trailer 710 has a front surface 712, a top surface 713, a side 714, an opposing side (hidden from view), a lower surface (also hidden), and a rear end 718. The trailer 710 includes vertical doors 722 and 724 that open outward.

[0048] In one embodiment, air is the ambient fluid surrounding the trailer 710. The wake region W is located directly downstream of the rear end 718 of the trailer 710. When the trailer 710 is pulled in a forward direction at sufficient speed, the air pressure at the front surface 712 increases and a slipstream is formed in the direction of arrow S.

[0049] Elongated posts 720 are mounted to the perimeter of the rear end 718 of the trailer 710 along the opposite vertical edges of the rear end 718. The posts 720 may be attached to the rear end 718, or they may be removable. Posts 720 secured to the edges via a combination of hooks and straps may be removable.

[0050] The mounting shaft 310 of the propeller 130 is attached to the strut 720. The mounting shaft 310 can be rigid. Alternatively, the mounting shaft 310 can be a stiff spring that will be knocked to one side but still strong enough to maintain normal orientation during propeller rotation.

[0051] The propeller 130 may be mounted to each of the struts 720 in an orientation that allows the blades 220 to continually move in and out of the slipstream S during travel of the trailer 710 and continually extract rotational energy and redirect the slipstream fluid into the wake region W. Thus, pressure drag is reduced.

[0052] In addition to the advantages mentioned above (i.e., zero drive, redundancy, low cost, and low drag), the propeller 130 is lighter and smaller than previous attachments. Yet another advantage is that the propeller 130 can be added to the trailer 710 quickly and easily. For example, the propeller 130 can be pre-assembled to the strut 720, and then the strut 720 can be installed to the tail end 718. This is particularly advantageous for truckers who do not own the trailer themselves but are responsible for paying for fuel costs. By attaching the strut 720 to the rear of the trailer before the trip, and removing the strut 720 after the trip, the truck driver can significantly reduce fuel costs.

[0053] Yet another advantage of the conical propellers 130 made of a flexible material and having a minimal swept diameter is that they do not interfere with the opening and closing of the doors 722 and 724. If the doors 722 and 724 have hinge spaces, the propellers 130 can fit into the hinge spaces. Even if the doors 722 and 724 do not have hinge spaces, the blades can still be collapsed into a sufficiently small profile. For example, the conical shape of the blades 220 can be temporarily flattened, or the blades 220 can all be rotated individually toward a common blade so that as a whole, the blades 220 can fit into a smaller space.

[0054] Those skilled in the art will appreciate that the propeller 130 is not limited to the side of the trailer. Instead of or in addition to the side, the propeller 130 may be mounted to the upper edge.

[0055] refer to Fig. 9 In the embodiment of the present invention, the trailer 910 has a row of propellers 130 mounted to an elongated strut extending across the upper edge 912 of the tail end 914. When the trailer 910 is pulled in a forward direction at a sufficient speed, the blades 220 continuously move in and out of the slipstream (along the upper surface 916) to continuously extract energy and redirect the slipstream fluid into the wake region W. There may also be propellers 130 along the sides of the tail end 914.

[0056] The propeller-based fluid redirection for drag reduction may not be limited to the rear end 914 of the trailer. This fluid / air redirection and drag reduction may also be applied to the gap region between the tractor and the front surface of the trailer. The air in this gap region has different characteristics than the air in the wake region W behind the rear end 914 of the trailer. The front of the trailer limits the back pull, but the air in the gap region is in a highly turbulent state. This turbulent air increases drag.

[0057] Reference now Fig.10 , which shows a tractor-trailer 1000 having a gap region G between a tractor 1010 and a trailer 1020. A propeller 1030 is located within the gap region G and is mounted to the periphery of the rear surface of the tractor 1010. The propeller 1030 is configured to exhaust air from the gap region G.

[0058] Additional references Fig.11 , which shows a comparison of one of the propellers 130 used at the tail end 914 of the trailer and one of the propellers 1030 in the gap region G between the tractor 1010 and the trailer 1020, according to one embodiment. Both propellers 130 and 1030 rotate in the same direction and are conical, but they function differently.

[0059] For the propeller 130 at the tail end 914, each blade 220 has an airfoil that, when impacted by the moving air, is pulled away from the propeller hub 210. As the blade 220 rotates into the still air in the wake region W, the aerodynamic forces tend to lift the blade 220 away from the hub 210. Since the hub 210 is held to the mounting shaft by bearings, the air is driven in a direction toward the hub 210 and into the wake region W.

[0060] However, for the propeller 1030 in the gap region G, each blade 1110 has a vertically mirrored airfoil, which retains the leading edge and the same direction of rotation. The force on the blade 1110 still drives the rotation, but with a lift force toward the hub 1120. When the blade 1110 rotates into the stationary fluid, it will try to rise toward the hub 1120. Since its hub 1120 is mounted to the shaft 1130 via bearings 1140, the fluid is driven away from the hub 1120. Thus, turbulent air is expelled from the gap region G and driven into the fast-moving slipstream, and the pressure drag is reduced.

[0061] This propeller-based drag reduction in the gap region G is more advantageous than conventional solutions such as fairings that bridge part of the gap. Fairings do not always bridge the entire gap due to turning clearance issues. Furthermore, fairings can easily collide with trailers.

[0062] Another embodiment of the tractor-trailer may use propeller 130 at tail end 914 and propeller 1030 in gap area G. Propeller 1030 in gap area G may be secured to tractor 1010 and propeller 130 at tail end 914 may be secured to trailer 910.

[0063] Reference now Fig.12, which shows a barge 1210 and a zero-drive propeller-based system for reducing pressure drag at the stern 1212 of the barge 1210. In this example, water is the ambient fluid in the underwater portion of the barge 1210, and air is the ambient fluid above the waterline. Pressure drag is created during movement of the barge 1210. The barge 1210 displaces water to the sides and downward, and a low pressure area is created behind the stern 1212. A water slipstream is created on the opposite side of the low pressure area.

[0064] A plurality of conical propellers 1220 are mounted to the stern 1212 below the waterline of the barge. As with the air device, the extraction of rotational energy from the slipstream is accomplished by airfoil blades in a low drag and lift profile. The blades that break away from the slipstream redirect the water into a low pressure area to reduce pressure drag. Water is denser and can withstand higher pressures without pausing. Therefore, the blades can be more angled, more curved, and have a larger cross section.

[0065] In some cases, the barge 1210 may be moving fast enough to create pressure drag due to the air being displaced. In these cases, the propeller 130 may be mounted to the stern 1212 above the waterline.

[0066] Reference now Fig.13 , which shows a duct 1310 in which propeller-based fluid redirection and drag reduction are performed according to one embodiment. Fig.13 In the illustrated embodiment, the pipe 1310 has a sharp bend 1312 (e.g., a 90 degree bend or a similar angle bend). As indicated by the directional arrows, the fluid flows into the pipe 1310 and changes direction at the bend 1312. Thereafter, the fluid flows out of the pipe 1310. Similar to the wake region W behind the bluff body 110, the change in direction of the fluid may cause a pressure drop at the bend 1312.

[0067] In one embodiment, the pressure drop can be reduced by a row of conical propellers 1320 arranged along the inner corner of the bend 1312. Each of the conical propellers 1320 can be positioned so that at least one of the propeller blades will extract energy from the flowing fluid flowing into the pipe 1310 in a manner that rotates the blade, while at least one other blade redirects the fluid around the bend 1312. In the case where the propellers 1320 bring low drag, they divert the fluid in this low pressure area, and the combined drag is less than if there were no propellers. Therefore, a reduction in pressure occurs in the area B after the bend 1312.

[0068] Consider the four blades of the conical propeller 1320. At a certain moment in the rotation, one blade has just entered the fluid flow and is trying to rise, which creates a rotational torque. The next blade is just about to leave the fluid flow and has just provided a rotational torque. The next blade has passed out of the fluid flow and is now passing through the relatively static fluid just behind the bend 1312, and as it tries to rise, it pulls air from the side of the fluid flow into the low pressure area B. The last blade continues this action and drives more fluid into the low pressure area B. Each blade performs these functions in turn.

[0069] Reference now Fig.14 , which shows an aerodynamic lift structure 1410 including a strut 1420 and a conical propeller 1430. The strut 1420 has a rounded nose 1422 that forms the leading edge of the structure 1410. A plurality of ribs 1440 are arranged in parallel along the length of the strut 1420. Each rib 1440 has an end 1442 attached to the strut 1420, and each rib 1440 has a free end 1444 downstream of the strut 1420. The ribs 1440 can incorporate the airfoil shape of a wing. Each conical propeller 1430 is mounted at the free end 1444 of the corresponding rib 1440. The propeller 1430 has a mounting shaft 1432 that can be fixed to one side of the corresponding rib 1440 and is tilted so that at least one propeller blade 1434 can extract rotational energy from the air flowing through the strut 1420, while at least one other blade 1434 can redirect the air. The air is redirected downward to create lift.

[0070] In one embodiment, struts 1410 may be configured as an airplane wing. In another embodiment, struts 1410 may be configured as blades for a wind turbine.

[0071] Example 1 may include a system comprising: a bluff body having a tail end and a wake region and a slipstream direction behind the tail end; and a propeller comprising a hub and a plurality of blades extending outwardly from the hub, the hub mounted to the tail end of the bluff body to rotate about an axis, the axis being angled relative to the slipstream direction in both pitch and yaw so that when fluid flows over the bluff body, at least one of the blades is in the slipstream and extracts energy to rotate the hub, while at least one of the blades is out of the slipstream and redirects fluid from the slipstream into the wake region, whereby automatic rotation of the hub causes the blades to continually move in and out of the slipstream to continually extract energy and redirect slipstream fluid into the wake region.

[0072] Alternatively and / or additionally, Example 2 includes Example 1, further comprising additional propellers to the propeller, wherein the bluff body has a box-like geometry, and wherein all of the propellers are mounted to a periphery of the tail end of the bluff body.

[0073] Alternatively and / or additionally, Example 3 includes one or more of Examples 1-2, wherein the propeller includes six blades.

[0074] Alternatively and / or additionally, Example 4 includes one or more of Examples 1 to 3, wherein the propeller further comprises a rigidly mounted shaft having a first end and a second end, the first end being mounted to the bluff body, the hub being mounted to the second end for rotation about the axis of rotation, the blades being angled outwardly from the hub.

[0075] Alternatively and / or additionally, Example 5 includes one or more of Examples 1 to 4, wherein the hub has a rotation plane perpendicular to the rotation axis; and wherein the blades have a cone angle between 10 degrees and 45 degrees relative to the plane.

[0076] Alternatively and / or additionally, Example 6 includes one or more of Examples 1-5, wherein the cone angle is approximately 30 degrees.

[0077] Alternatively and / or additionally, Example 7 includes one or more of Examples 1-6, wherein each of the blades has a length of approximately 4 inches to 12 inches.

[0078] Alternatively and / or additionally, Example 8 includes one or more of Examples 1-7, wherein the hub is located offset within the wake region.

[0079] Alternatively and / or additionally, Example 9 includes one or more of Examples 1-8, wherein the mounting axis is inclined relative to the bluff body such that at least one blade exiting the slipstream is substantially parallel to the slipstream and at least one blade in the slipstream is at an angle of attack that produces lift.

[0080] Alternatively and / or additionally, Example 10 includes one or more of Examples 1-9, wherein the bluff body comprises a trailer, wherein the system comprises struts mounted to a perimeter of a trailing end of the trailer along opposing vertical edges of the trailing end, and wherein the propeller and a plurality of additional propellers of the propeller are mounted to the struts, whereby the blades continually move in and out of the slipstream during travel of the trailer to continually absorb energy and redirect slipstream fluid into the wake region as the trailer travels.

[0081] Alternatively and / or additionally, Example 11 includes one or more of Examples 1-10, wherein the propeller is zero drive.

[0082] Example 12 may include a propeller comprising: a disc-shaped hub having a longitudinal axis of rotation; and a plurality of aerodynamically shaped blades arranged around the hub and extending outward from the hub at a taper angle between 15 degrees and 50 degrees relative to a plane perpendicular to the longitudinal axis.

[0083] Alternatively and / or additionally, Example 13 includes Example 12, wherein the cone angle is approximately 30 degrees.

[0084] Alternatively and / or additionally, Example 14 includes one or more of Examples 12-13, wherein the blade is configured to generate lift toward the hub.

[0085] Alternatively and / or additionally, Example 15 includes one or more of Examples 12-13, wherein the blade is configured to generate lift away from the hub.

[0086] Alternatively and / or additionally, Example 16 includes a strut and a plurality of propellers of the propeller of one or more of Examples 12-15 mounted to the strut.

[0087] Alternatively and / or additionally, Example 17 includes a bluff body and the propeller of one or more of Examples 12 to 16, the bluff body having a tail end and a slipstream region behind the tail end, wherein the propeller further comprises a mounting shaft, the hub being mounted to a first end of the shaft for rotation about the longitudinal axis, the second end of the shaft being mounted to the bluff body at a certain tilt angle, the tilt angle allowing those blades in the slipstream region to extract rotational energy and allowing those blades not in the slipstream region to redirect flow from the slipstream region.

[0088] Alternatively and / or additionally, Example 18 includes a duct having a curved portion, and the propeller of one or more of Examples 12 to 17, the propeller being mounted at an inner corner of the curved portion.

[0089] Alternatively and / or additionally, Example 19 includes a method for the propeller of one or more of Examples 12 to 18, comprising mounting a shaft of the propeller to a bluff body having a tail end and a wake region and a slipstream region behind the tail end, such that those blades that exit the slipstream region are substantially parallel to the slipstream region.

[0090] Example 20 may include a vehicle box-shaped bluff body having a tail end and a slipstream region downstream of the tail end; and a plurality of propellers mounted to opposing vertical edges of the tail end, each propeller including a hub and a plurality of blades extending outwardly from the hub at a taper angle between 10 degrees and 45 degrees, each hub having an axis of rotation angled relative to the tail end and the blades angled relative to the axis such that those blades that are disengaged from the slipstream region redirect air out of the slipstream region.

[0091] Alternatively and / or additionally, Example 21 includes Example 20, wherein the bluff body is part of a trailer.

[0092] Alternatively and / or additionally, Example 22 includes one or more of Examples 20 to 21, and further includes: a tractor for the trailer, a gap region between the tractor and the trailer, and a slipstream region outside the gap region; and a second plurality of propellers, the second plurality of propellers being mounted to the tractor and located within the gap region, each propeller of the second plurality of propellers comprising a hub and a plurality of blades extending outwardly from the hub at a taper angle between 10 degrees and 45 degrees, each hub being mounted to the tractor for rotation about an axis, the axis being angled relative to the tractor such that those blades that are out of the slipstream region redirect air out of the gap region.

[0093] Alternatively and / or additionally, Example 23 includes one or more of Examples 20-22, wherein the bluff body is part of a barge.

[0094] The description of various embodiments herein has been presented for illustrative purposes and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, practical applications or technical improvements over technologies found on the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A system comprising: a bluff body having a tail end and a wake region and a slipstream direction behind the tail end; as well as A propeller comprising a hub and a plurality of blades extending outwardly from the hub, the hub being mounted to the trailing end of the bluff body for rotation about an axis, the axis being angled in both pitch and yaw relative to the direction of the slipstream, such that as fluid flows over the bluff body, at least one of the blades is in the slipstream and extracts energy to rotate the hub, while at the same time at least one of the blades is out of the slipstream and redirects fluid from the slipstream into the wake region, whereby automatic rotation of the hub causes the blades to continually move in and out of the slipstream to continually extract energy and redirect slipstream fluid into the wake region.

2. The system of claim 1 further comprising additional propellers to said propeller, wherein said bluff body has a box-like geometry, and wherein all of said propellers are mounted to a periphery of said tail end of said bluff body.

3. The system of claim 1, wherein the propeller comprises six blades.

4. The system of claim 1, wherein the propeller further comprises a rigidly mounted shaft having a first end and a second end, the first end being mounted to the bluff body, the hub being mounted to the second end for rotation about an axis of rotation, the blades being angled outwardly from the hub.

5. The system of claim 4, wherein the hub has a plane of rotation perpendicular to the axis of rotation; and wherein the blades have a taper angle between 10 and 45 degrees relative to the plane.

6. The system of claim 5, wherein the cone angle is approximately 30 degrees.

7. The system of claim 5, wherein each of the blades is approximately 4 inches to 12 inches in length.

8. The system of claim 5, wherein the hub is offset within the wake region.

9. The system of claim 8, wherein the mounting axis is inclined relative to the bluff body such that at least one blade exiting the slipstream is substantially parallel to the slipstream and at least one blade in the slipstream is at an angle of attack that produces lift.

10. The system of claim 1 wherein the bluff body comprises a trailer, wherein the system comprises struts mounted to a perimeter of the aft end of the trailer along opposed vertical edges of the aft end, and wherein the propeller and a plurality of additional ones of the propellers are mounted to the struts whereby the blades continually move in and out of the slipstream during travel of the trailer to continually absorb energy and redirect slipstream fluid into the wake region as the trailer travels.

11. The system of claim 10, wherein the propeller is zero drive.

12. A propeller, comprising: a disk-shaped propeller hub having a longitudinal axis of rotation; as well as A plurality of aerodynamically shaped blades are disposed about the hub and extend outwardly from the hub at a taper angle between 15 and 50 degrees relative to a plane perpendicular to the longitudinal axis.

13. The propeller of claim 12, wherein the cone angle is approximately 30 degrees.

14. The propeller of claim 12, wherein the blades are configured to generate lift toward the hub.

15. The propeller of claim 12, wherein the blades are configured to generate lift away from the hub.

16. A system comprising a strut and a plurality of propellers of the propeller of claim 12 mounted to the strut.

17. A system comprising a bluff body and the propeller of claim 12, the bluff body having a tail end and a slipstream region behind the tail end, wherein the propeller further comprises a mounting shaft, the hub being mounted to a first end of the shaft for rotation about the longitudinal axis, the second end of the shaft being mounted to the bluff body at an angle of inclination that allows those blades in the slipstream region to extract rotational energy and allows those blades not in the slipstream region to redirect fluid from the slipstream region.

18. A system comprising a pipe having a curved portion and the propeller of claim 12, the propeller being mounted at an inner corner of the curved portion.

19. A method for a propeller as claimed in claim 12, comprising mounting a shaft of the propeller to a bluff body having a trailing end and a wake region and a slipstream region behind the trailing end so that those blades that exit the slipstream region are substantially parallel to the slipstream region.

20. A vehicle comprising: a box-shaped bluff body having a tail end and a slipstream region downstream of the tail end; as well as a plurality of propellers mounted to opposed vertical edges of the tail end, each propeller including a hub and a plurality of blades extending outwardly from the hub at a taper angle between 10 and 45 degrees, each hub having an axis of rotation angled relative to the tail end and the blades angled relative to the axis such that those blades disengaged from the slipstream region redirect air from the slipstream region.

21. The vehicle of claim 20, wherein the bluff body is part of a trailer.

22. The vehicle of claim 21 further comprising: a tractor for the trailer, a gap region between the tractor and the trailer, and a slipstream region outside the gap region; as well as and a second plurality of propellers mounted to the tractor and located in the gap region, each propeller of the second plurality of propellers comprising a hub and a plurality of blades extending outwardly from the hub at a taper angle between 10 and 45 degrees, each hub mounted to the tractor for rotation about an axis, the axis being angled relative to the tractor such that those blades that are out of the slipstream region redirect air out of the gap region.

23. The vehicle of claim 20, wherein the bluff body is part of a barge.

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