Abstract:
A device for the reduction of aerodynamic drag and for improved performance and stability of ground vehicles by reducing the mass and velocity of the flow passing under a vehicle is described. The device is particularly suited for a tractor-trailer truck system that includes a motorized lead vehicle pulling one or more non-motorized vehicles. The device is designed to control the flow from entering the undercarriage region from the side of a trailer of a tractor-trailer truck system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of prior application U.S. application Ser. No. 11/811,541 titled “Mini Skirt Aerodynamic Fairing Device for Reducing the Aerodynamic Drag of Group Vehicles,” filed on Jun. 11, 2007, now U.S. Pat. No. 7,497,502 which claimed the benefit of U.S. Provisional Application No. 60/814,303, filed Jun. 19, 2006, the entire contents of both of which are incorporated herein by reference. 

   ORIGIN OF THE INVENTION 
   The invention described herein was made by employees of the United States Government, and may be manufactured and used by or for the Government without payment of any royalties thereon or therefore. 

   FIELD OF INVENTION 
   The invention relates to the reduction of aerodynamic drag for moving ground vehicles; specifically to an improved method and device for the reduction of aerodynamic drag and for improved performance and stability of ground vehicles by reducing the mass and velocity of the flow passing under a vehicle. 
   BACKGROUND OF THE INVENTION 
   The flow passing under a ground vehicle imparts a drag force to the vehicle when it impinges on and flows around the vehicle undercarriage components, landing gear, axels, brake components, mud flap systems, wheel wells and fenders, wheels, tires and various other vehicle components attached to or a part of the underside of a vehicle. The ground vehicle class of particular interest is a tractor-trailer truck system consisting of a motorized lead vehicle pulling one or more non-motorized vehicles. The present invention is designed to control the flow from entering the undercarriage region from the side of a trailer of a tractor-trailer truck system. 
   There have been several attempts to reduce the aerodynamic drag associated with the undercarriage of the trailer of a tractor-trailer truck system. Trailer undercarriage drag may comprise 25 percent of the total vehicle drag. 
   The trailer undercarriage is comprised of all the components located below the trailer floor deck surface and the ground or road surface and includes all components attached to the trailer in this region. The flow passing around the tractor-trailer truck vehicle enters the undercarriage region from the trailer side and from the tractor undercarriage region. The undercarriage flow of a trailer is characterized as unsteady and dynamic and comprised of various size and strength eddy currents. The unsteady nature of the undercarriage flow is a result of the flow interacting with the ground or road, rotating wheels, brake systems, axels, tractor undercarriage flow, and the various components comprising the trailer lower surface. Relative to the free stream static pressure, the undercarriage flow imparts an increased pressure on surfaces that face forward and a decreased pressure on surfaces that face aft. The increase in pressure acting on the forward-facing surfaces and the decreased pressure acting on the aft-facing surfaces both generate an aerodynamic drag force. It is estimated that the pressures acting on the trailer wheel assembly accounts for one-half of the undercarriage drag, with the remaining drag being attributed to the flow interacting with numerous small structures comprising the trailer undercarriage. Previous attempts have addressed the undercarriage drag by installing either spanwise or streamwise aerodynamic fairings to the trailer underside to either divert undercarriage flow from the trailer wheel assembly or to block flow from entering the undercarriage region from the trailer side. The flow diverter devices are spanwise fairings that mount to the trailer undercarriage immediately forward of the trailer wheel assembly. The flow diverter fairings are angled downward or outward to divert the undercarriage flow from the wheel assembly. The flow blocking devices are streamwise fairings that mount beneath the trailer outside edge between the trailer wheel assembly and the tractor rear wheel longitudinal position, when the tractor and trailer are joined. Both types of fairings show increased benefit with increased vertical extent of the fairing. 
   Conventional approaches have used the flow diverter undercarriage fairings to reduce the mass of undercarriage flow that impinges onto the trailer wheel assembly, as shown in U.S. Pat. Nos. 4,386,801, 4,486,046, and 4,640,541. These representative fairing devices, while successful in reducing the mass of flow impinging on the trailer wheel assembly and thereby reducing the wheel assembly drag, do not significantly affect the trailer undercarriage drag. The limited effectiveness of these devices is a result of the drag generated by the device, referred to as device drag. The device drag for these fairings may be equal to the wheel assembly drag. These devices only reduce the wheel assembly drag and do not reduce the remaining undercarriage drag associated with the various trailer components. 
   Other approaches have used the trailer undercarriage side fairings to reduce the mass and velocity of the flow entering the undercarriage region of a trailer, as shown in U.S. Pat. Nos. 4,611,847, 4,746,160, 5,280,990, 5,921,617, and 6,644,720. These representative flow blocking devices, while successful in reducing the mass of flow entering the trailer undercarriage region are either simple rigid structures or they are complex active, flexible and variable geometry systems. The simple devices are designed to have a limited vertical and longitudinal extent in order to reduce the impact on operations and maintenance. Limiting the vertical and longitudinal extent of the device significantly reduces the flow blocking capability and results in a minimal aerodynamic drag reduction benefit. The complex devices typically have features that are active, flexible, and/or variable in order to maximize the flow blocking capability while minimizing the impact on operations. The complex devices typically consist of multiple components. The complexity of these devices results in increased weight, maintenance, and cost. Each of the trailer undercarriage flow blocking devices consists of a vertically extended structure that attaches to the trailer lower surface outer side edges. These devices are held in position by various support and bracing structures that are integrated into or attached to the inward facing surface of the flow blocking structure. The support and bracing structures add additional forward and rearward facing undercarriage elements that contribute to the undercarriage drag. These support and bracing structures also collect debris, snow and ice during operation resulting in an increase in maintenance and repair requirements. 
   SUMMARY OF THE INVENTION 
   The invention relates to an aerodynamic device for reducing drag on a ground vehicle. The device includes a first pair of rigid panels attached to the left side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel substantially coplanar with the left surface of the vehicle and an inner panel located inboard of the outer panel; and a second pair of rigid panels attached to the right side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel substantially coplanar with the right surface of the vehicle and an inner panel located inboard of the outer panel. The panels on the left or right side of the vehicle may be comprised of a single panel or of multiple longitudinal segments. Each panel typically extends downward from the vehicle a distance of less than about 90% of the distance from the bottom surface of the vehicle to the surface that the vehicle is moving over. Each panel in the pairs may extend downward a substantially equal distance from the bottom surface of the vehicle, the shape and distance of the downward extension may vary along the length of the panel. 
   In one embodiment, the pair of panels is integrally connected to each other by a horizontal panel. The pair of panels may also be connected by a horizontal panel that is separate from the pair. The panels may also be an integral extension of the side surface of the vehicle. The panels may have various profiles, such as a swept leading or trailing edge. In one embodiment, the panels are connected to the vehicle such that the panels may be folded so as to be substantially adjacent and proximate the bottom surface of the vehicle when not in use. The pairs of panels may also be slidably connected to the vehicle such that the panels slide longitudinally along the vehicle. The distance between at least one of the first or second pairs of panels may be adjustable. The pairs of panels may further include one or more additional panels located inboard from the existing panel pair. For example, a third or more panels may be included in each panel grouping. 
   One aspect of the invention is to prohibit flow from entering the trailer undercarriage region and interacting with the complex geometry comprising the trailer undercarriage and wheel assembly by creating two similar structures that attach to the trailer underside near the two outside edges of the trailer. The two similar structures comprising the present invention are light-weight aerodynamic fairings that attach to the undercarriage of a dry van, refer, flat deck, or tanker trailer near the two outside edges of the trailer. The two similar structures are of minimum vertical extent and include two vertically aligned surfaces and one horizontal surface that attach to the underside of the trailer near the trailer outside edge. The outer edge of each structure is positioned parallel to and below each outer side edge of the trailer. Each structure extends as close as practical to the ground based upon operational and maintenance criteria. Each structure is located longitudinally between the trailer wheel assembly and the tractor aft wheel set. Each structure is variable in length and is capable of covering a variable longitudinal distance between the trailer wheel assembly and the tractor rear wheels. 
   The flow blocking performance of each of the two structures is enhanced through the effective use of three flow control concepts: vortex generation, upwash management, and ground effect interference. Each of the two structures accomplishes the flow control and drag reduction goals with two vertically orientated surfaces and one horizontal surface. The two vertically orientated surfaces are an outer vertical surface located at the outside edge of the trailer and an inner vertical surface located inboard of the first surface. The horizontal surface extends between the two upper edges of the two vertical surfaces to create an inverted “U” shaped channel. The two vertical surfaces of each structure are of equivalent longitudinal and vertical length and the lower edge of both surfaces is aerodynamically sharp. 
   Each of the two structures may be comprised of multiple longitudinal segments. At a minimum each structure is comprised of a single segment. In a preferred embodiment, the structure has a forward longitudinal segment, center longitudinal segment and an aft longitudinal segment. The center longitudinal segment may be further divided into multiple center longitudinal segments to address installation, maintenance, and operational concerns. A single longitudinal segment is comprised of a single outer vertical surface element, a single inner vertical surface element, and a single horizontal surface element. The forward longitudinal segment of each structure has a forward edge that is shaped to meet the operational, maintenance, and performance needs of the user and is aerodynamically sharp. Each center longitudinal segment of the structure has a forward edge that is shaped to join the rear edge of the segment immediately forward of the segment and a rear edge that is shaped to join the forward edge of the segment immediately aft of the segment. The rear longitudinal segment of each structure has a rear edge that is shaped to meet the operational, maintenance, and performance needs of the user and is aerodynamically sharp. The rear longitudinal segment fairing may longitudinally extend forward and rearward to adjustably locate its rearward edge in a selected position forward of the trailer&#39;s wheel assembly. The longitudinal adjustment of the rear segment is by means of a slide engagement with the center longitudinal segment located adjacent and forward of the rear longitudinal segment. 
   The outer vertical surface of the structure is designed to both block flow from entering the undercarriage region and to turn the flow passing under the outer vertical surface upward thereby creating an upwash field between the two vertical surfaces. The upwash field is generated by means of a coherent vortex structure emanating from the aerodynamically sharp lower edge of the outer surface. The inner vertical surface blocks the upwash field from flowing inboard and interacting with the trailer undercarriage and wheel assembly. The horizontal surface blocks the upwash flow from interacting with the trailer undercarriage in the region between the two vertical surfaces. The result of the flow control techniques allows the present invention to block a significantly greater mass of flow from entering the undercarriage region compared to a fairing with a single vertical surface of equal vertical extent. The addition of a horizontal surface between the two vertical surfaces ensures that the blocked upwash flow does not generate a drag force. The invention also takes advantage of the increased turbulence in the flow adjacent to the road surface at the side edge of the trailer to further promote upwash thereby increasing the effective blocking area of the structure. Although upwash is present for all existing trailer undercarriage flow blocking fairings, the present invention is the only device that captures the upwash field and thereby controls a greater mass of air from entering the undercarriage region by means of the inner vertical surface and ensues that the blocked and captured flow does not generate a drag by means of the horizontal surface. The ability of the present invention to block a greater mass of flow with less vertical extent from the trailer undercarriage, compared to existing single surface fairings, allows the present invention to provide a larger vertical gap between the ground or road surface and the invention lower edge, thereby eliminating the need for vertically movable, deflectable, and actuated surfaces to adapt to various surface and/or road structures that may impact the lower edge of the fairing. It also results in a reduced aerodynamic load on the vertical surfaces that eliminates the need for structural bracing and supports, thereby reducing or eliminating device drag. Components of the invention may be smooth and aligned parallel with the vehicle axis, thereby eliminating device associated pressure drag. 
   An alternative embodiment of the aerodynamic device or structure may have a first pair of rigid panels attached to the left side of the bottom surface of the vehicle, extending downward from the vehicle, with an outer panel substantially coplanar with the left surface of the vehicle and an inner panel located inboard of the outer panel. The first pair of rigid panels is configured with each panel extending downward from the vehicle a desired first vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a first horizontal distance. A second pair of rigid panels is attached to the right side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel substantially coplanar with the right surface of the vehicle and an inner panel located inboard of the outer panel. The second pair of rigid panels is configured with each panel extending downward from the vehicle a desired second vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a second horizontal distance. The first and second pairs of rigid panels are configured so as to form a first and second inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle. In this example, at least a portion of at least one inner panel is inclined inwardly as it extends downward so that the horizontal distance between the inner and outer panels at the lower edge of the panels is greater than the horizontal distance between the inner and outer panels proximate to the bottom surface of the vehicle. 
   Another alternative embodiment of the aerodynamic device or structure has a first pair of rigid panels attached to the left side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel attached inboard and proximate to the left surface of the vehicle and an inner panel located inboard of the outer panel. The first pair of rigid panels are configured with each panel extending downward from the vehicle a desired first vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a first horizontal distance. A second pair of rigid panels attached to the right side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel attached inboard and proximate to the right surface of the vehicle and an inner panel located inboard of the outer panel. The second pair of rigid panels are configured with each panel extending downward from the vehicle a desired second vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a second horizontal distance. The first and second pairs of rigid panels are configured so as to form a first and second inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle, wherein at least a portion the first and second outer panels is inclined outwardly without exceeding the plane of the left or right surfaces of the vehicle, respectively, and the horizontal distance between the inner and outer panels proximate to the bottom surface of the vehicle is less than the horizontal distance between the inner and outer panels at the lower edge of the panels. 
   Another alternative embodiment of the aerodynamic device or structure has a first pair of rigid panels attached to the left side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel substantially coplanar with the left surface of the vehicle and an inner panel located inboard of the outer panel. The first pair of rigid panels is configured with each panel extending downward from the vehicle a desired first vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a first horizontal distance. A second pair of rigid panels is attached to the right side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel substantially coplanar with the right surface of the vehicle and an inner panel located inboard of the outer panel. The second pair of rigid panels is configured with each panel extending downward from the vehicle a desired second vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a second horizontal distance. The first and second pairs of rigid panels are configured so as to form a first and second inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle. In this example, at least a portion of the first and second inner panels is inclined outwardly, and wherein the horizontal distance between the inner and outer panels proximate to the bottom surface of the vehicle is greater than the horizontal distance between the inner and outer panels at the lower edge of the panels. 
   Another alternative embodiment of the aerodynamic device has a first pair of rigid panels attached to the left side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel attached proximate to the left surface of the vehicle and an inner panel located inboard of the outer panel. The first pair of rigid panels is configured with each panel extending downward from the vehicle a desired first vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a first horizontal distance. A second pair of rigid panels is attached to the right side of the bottom surface of the vehicle and extending downward from the vehicle, including an outer panel attached proximate to the right surface of the vehicle and an inner panel located inboard of the outer panel. The second pair of rigid panels is also configured with each panel extending downward from the vehicle a desired second vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel is separated from the inner panel at the lower edges by a second horizontal distance. The first and second pairs of rigid panels are configured so as to form a first and second inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle. In this example, the first and second outer panels are inclined inwardly but substantially proximate to the plane of the left or right surfaces of the vehicle, respectively, and wherein the horizontal distance between the inner and outer panels proximate to the bottom surface of the vehicle is greater than the horizontal distance between the inner and outer panels at the lower edge of the panels. 
   These alternate embodiments may incorporate a number of structural variations. For example, the aerodynamic device may include one or more of the panels on the left or right side of the vehicle that are comprised of multiple longitudinal segments. In one embodiment, each panel may extend downward from the vehicle a distance of less than about 90% of the distance from the bottom surface of the vehicle to the surface that the vehicle is moving over. Each panel of at least one of the first pair or second pair may extend downward a substantially equal distance from the bottom surface of the vehicle. In another example, at least one panel may extend downward a distance that varies along its length. An embodiment may include at least one of the first or second pairs of panels being integrally connected to each other by a horizontal panel. This horizontal panel located between the outer and inner panels may be separate from the pair of panels. At least one of the first or second pairs of panels may be an integral extension of the side surface of the vehicle. In another example, at least one panel has a swept leading edge. Optionally, the panels may be folded so as to be substantially adjacent and proximate the bottom surface of the vehicle when not in use. Also, at least one of the first or second pairs of panels may be slidably connected to the vehicle such that the panels slide longitudinally along the vehicle. In some cases, the distance between at least one of the first or second pairs of panels may be adjustable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood in relation to the attached drawings illustrating preferred embodiments, wherein: 
       FIG. 1A  is a side and lower surface view of a tractor-trailer truck system; 
       FIG. 1B  is a side and lower surface view of a tractor-trailer truck system with the present invention installed on the lower surface of the trailer; 
       FIGS. 2A-B  are cross section views, in a plane perpendicular to the ground, of the undercarriage flow conditions for a tractor-trailer system with and without the present invention installed; 
       FIGS. 3A-3D  are side views of a tractor-trailer truck with alternate embodiments of the invention installed; 
       FIGS. 4A-4C  are side views of a tractor-trailer truck with alternate embodiments of the invention installed; 
       FIGS. 5A-5D  are side views of a tractor-trailer truck with alternate embodiments of the invention installed; 
       FIGS. 6A-6B  is a side view and cross-section views of the present invention illustrating various installation and fabrication concepts; 
       FIGS. 7A-7B  is a side view and cross-section views of the present invention illustrating various edge treatments and fabrication concepts; 
       FIGS. 8A-8B  is a side view, perspective view, and cross-section view of the invention illustrating the preferred stiffening and mounting concept. 
       FIGS. 9A-9B  is a side view, perspective view, and cross-section view of the invention illustrating an alternate stiffening and mounting concept. 
       FIGS. 10A-10B  is a side view, perspective view, and cross-section view of the invention illustrating an alternate stiffening and mounting concept. 
       FIG. 11A  is a side view,  FIG. 11B  is a rear view, and  FIG. 11C  is a rear view comparison of various embodiments. 
       FIG. 12A  is a side view,  FIG. 12B  is a rear view, and  FIG. 12C  is a rear view comparison of various embodiments. 
       FIG. 13A  is a side view,  FIG. 13B  is a rear view, and  FIG. 13C  is a rear view comparison of various embodiments. 
       FIG. 14A  is a side view of a flat bed application,  FIG. 14B  is a rear view, and  FIG. 14C  is a rear view of various embodiments. 
       FIG. 15A  is a side view of a flat bed application,  FIG. 15B  is a rear view, and  FIG. 15C  is a rear view comparison of various embodiments. 
       FIG. 16A  is a side view of a flat bed application,  FIG. 16B  is a rear view, and  FIG. 16C  is a rear view comparison of various embodiments. 
       FIG. 17A  is a side view of a tanker application,  FIG. 17B  is a rear view, and  FIG. 17C  is a rear view comparison of various embodiments. 
       FIG. 18A  is a side view of a tanker application,  FIG. 18B  is a rear view, and  FIG. 18C  is a rear view comparison of various embodiments. 
       FIG. 19A  is a side view of a tanker application,  FIG. 19B  is a rear view, and  FIG. 19C  is a rear view comparison of various embodiments. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following descriptions are of exemplary embodiments of the invention only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather the following description is intended to provide a convenient illustration for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the elements described herein without departing from the spirit and scope of the invention. For example, though not specifically described, many shapes, widths, leading edge shapes, spacing and orientation of the forward extended plurality of panels, candidate vehicles that can benefit from the device, fabrication means and material, attachments means and material should be understood to fall within the scope of the present invention. 
   Referring now in detail to the drawings, like numerals herein designate like numbered parts in the figures. 
     FIG. 1  shows a typical ground vehicle or tractor-trailer truck system  1 , for example, comprised of a powered tractor  10  that pulls a trailer  30 . The trailer  30  is comprised of a front surface  31 , side surfaces  32  and  33 , a top surface  34 , a rear surface  36 , and a lower surface  37 .  FIG. 1  shows a side and lower surface view of a typical trailer  30  of a tractor-trailer truck with and without the present invention installed on the lower floor surface  37  of a trailer  30 . The device  40  is comprised of two structures  40   a  and  40   b  that extended downward from the vehicle lower surface  37 . The downward extent of each panel is typically anywhere less than about 90% of the distance from the trailer lower surface to the surface or road that the vehicle is moving over. Each of the two structures,  40   a  and  40   b , are positioned with the outer vertical surface, aligned approximately with the plane of the trailer side surface  32  or  33 . Of course, the present invention may be used with flat bed trailers or vehicles as well, in which the plane of side surfaces  32  or  33  may be somewhat notional. The inner vertical surface of each structure  40   a ,  40   b  is positioned inboard of the outer vertical surface. Each structure has a width W, a transverse Y, and a length L. The leading edge and trailing edge of each structure is swept an angle θ. To facilitate access to the vehicle undercarriage, each panel of the device  40  may be either removed through a quick disconnect mechanism or folded out of the way, so as to be substantially adjacent and proximate the lower surface  30 . The length L of each structure,  40   a  and  40   b , of the device  40  is determined by the geometric characteristics of the vehicle  30 , the operational requirements of the vehicle  30 , and the maintenance requirements of the vehicle  30 . It is desirable that each structure,  40   a  and  40   b , of the device  40  extend between a point forward of the trailer rear wheel assembly to a point aft of the tractor rear wheel set. The width W of each structure,  40   a  and  40   b , of the device  40  is determined by the geometric characteristics of the vehicle  30 , the operational requirements of the vehicle  30 , and the maintenance requirements of the vehicle  30 . The type, size, and structure of the hardware used to attach the invention to the trailer undercarriage is determined by the geometric characteristics of the vehicle  30 , the operational requirements of the vehicle  30 , and the maintenance requirements of the vehicle  30 . 
     FIGS. 2A and 2B  show flow patterns in the undercarriage region of trailer  30  of a tractor-trailer truck with and without the present invention installed. In  FIG. 2A  and  FIG. 2B , the airflow about the vehicle and in the undercarriage region is represented by arrow-tipped lines  100  and  130  and swirl structures  110  and  120 . The arrow-tipped lines  100  represent the free stream flow entering the undercarriage region. The arrow-tipped lines  130  represent the upwash flow entering the region bound by the outer vertical surface and inner vertical surface of the device  40 . The swirl structures  110  represent rotational, random, unsteady eddy flow. The swirl structures  120  represent coherent vortex flow structures. 
     FIG. 2A  shows a cross-section view, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  with side surfaces  32  and  33  and a base or floor surface  37 .  FIG. 2A  also shows the undercarriage flow  100  and  110 , without the present invention installed. For a trailer moving over a surface or road, the free stream flow  100  turns inboard and enters the undercarriage region of the trailer  30 . The freestream flow interacts with the various vehicle components and becomes unstructured and dynamic and includes random size and strength eddies  110 . The dynamic, random undercarriage flow interacts with the vehicle undercarriage structures resulting in a large drag force. 
     FIG. 2B  shows a cross-section view, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  with side surfaces  32  and  33  and a floor surface  37  and the two inverted U-shaped channel structures  40   a  and  40   b  comprising the device  40 . Each structure,  40   a  and  40   b , comprising the device  40  contains three primary surfaces; an outer vertical surface,  40   aa  and  40   ba , an inner vertical surface,  40   ab  and  40   bb , and a base surface,  40   ac  and  40   bc , where the base surface in this embodiment extends between or connecting the upper most edge of the outer vertical surface and inner vertical surface comprising each structure  40   a  and  40   b . This approach may be considered to be an embodiment in which the first or second pairs of vertical surfaces or panels are integrally connected to each other by a base surface  40   ac  and  40   bc  or panel. As an alternative (not shown) to the approach illustrated in  FIG. 2   b , base surfaces  40   ac  (for structure  40   a ) and  40   bc  (for structure  40   b ) may be provided by floor surface  37 . That is, a portion of the floor surface  37  may be exposed to the extent of the transverse Y between, for example with structure  40   a , vertical surfaces  40   aa  and  40   ab .  FIG. 2B  also shows the undercarriage flow  100 ,  110  and  120 , with this embodiment of the device  40  installed. For a trailer moving over a surface or road, the free stream flow  100  is directed aft along the outward facing surface of the outer vertical surfaces,  40   aa  and  40   ba , of the device  40 . A portion of the free stream flow  100  located near the ground or road surface turns inboard and impinges on the lower edge of the outer vertical surface,  40   aa  and  40   ba , of the device  40  and results in a coherent vortex structure  120  that is located between the outer vertical surface,  40   aa  and  40   ba , and inner vertical surface,  40   ab  and  40   bb . The creation of the vortex structure  120  results in the generation of an upwash field  130  that redirects a significant portion of the inward-flowing free stream flow  100  upward and into the channel created by the outer vertical surfaces  40   aa  and  40   ba  and the inner vertical surfaces  40   ab  and  40   bb . The upwash effect reduces the mass of free stream flow entering the undercarriage region and interacting with the undercarriage structure of trailer  30  undercarriage region. Reducing the mass of the dynamic, random undercarriage flow that interacts with the vehicle undercarriage structures results in a reduced drag force. 
     FIGS. 3A-3D  are side and bottom views of a tractor trailer ground vehicles  1  with an embodiment of device  40  installed on the trailer  30  lower surface  37 .  FIG. 3A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly.  FIG. 3B  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 3C  shows a two segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 3D  shows a three segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the rear of the trailer. 
     FIGS. 4A-4C  are side and bottom views of a tractor trailer ground vehicles  1  with an embodiment of device  40  installed on the trailer  30  lower surface  37 .  FIG. 4A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 4B  shows a single segment version of the subject invention  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly and that has a varying vertical extent that varies linearly from a maximum at the forward most position to a minimum at the mid point and to a maximum at the rear most position.  FIG. 4C  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly and that has a varying vertical extent that varies nonlinearly from a maximum at the forward most position to a minimum at the mid point and to a maximum at the rear most position. 
     FIG. 5A-5D  are side and bottom views of a tractor trailer ground vehicles  1  with an embodiment of device  40  installed on the trailer  30  lower surface  37 .  FIG. 5A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with unswept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 5B  shows a multiple-segment version of the device  40  including structures  40   a  and  40   b  with unswept leading and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 5C  shows a single segment version of the device  40  including structures  40   a  and  40   b  with complex curved leading edges, bottom edges and trailing edges installed between the tractor rear wheels and the trailer wheel assembly.  FIG. 5D  shows a single segment version of the device  40  including structures  40   a  and  40   b  with notched leading edges and trailing edges installed between the tractor rear wheels and the trailer wheel assembly and that has a varying vertical extent that varies linearly from a maximum at the forward most position to a minimum at the mid point and to a maximum at the rear most position. 
     FIG. 6A  are side and bottom views of a tractor trailer ground vehicles  1  with the device  40  installed on the trailer  30  lower surface  37 .  FIG. 6A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly. 
     FIG. 6B  shows a cross-section view A-A, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  with the two structures  40   a  and  40   b  comprising the device  40 .  FIG. 6B  shows a cross-section view B-B with details of various embodiments of the device  40  comprised of structures  40   a  and  40   b . Concept A shows each structure  40   a  and  40   b  of the device  40  may be constructed as an integrated unit  41   a  and  41   b , respectively. Concepts B and C show each structure  40   a  and  40   b  of the device  40  may be constructed as individual components with an integrated attachment bracket  42   a ,  43   a ,  44   a  and  42   b ,  43   b ,  44   b , respectively and a separate horizontal surface  50  and  51 . Concepts D and E show each structure  40   a  and  40   b  of the device  40  maybe constructed as individual components  45   a  and  45   b  with attachment brackets  60   a ,  61   a ,  62   a  and  60   b ,  61   b ,  62   b , respectively and a separate horizontal surface  50  and  51 . 
     FIG. 7A  shows side and bottom views of a tractor trailer ground vehicles  1  with the device  40  installed on the trailer  30  lower surface  37 .  FIG. 7A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly. 
     FIG. 7B  shows a cross-section view A-A, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  with the two structures  40   a  and  40   b  comprising the device  40 .  FIG. 7B  cross-section view B-B shows details of various embodiments of the device  40  including structures  40   a  and  40   b . Edge concept A shows that the lower edge of the outer vertical surface and inner vertical surface of each structure  40   a  and  40   b  of the device  40  may be constructed as an integrated unit of the outer and inner vertical surfaces. Edge concept B shows that the lower edge of the outer vertical surface and inner vertical surface of each structure  40   a  and  40   b  of the device  40  maybe constructed as dissimilar material from that composing the outer and inner vertical surfaces. Edge concept C shows that the lower edge of the outer vertical surface and inner vertical surface of each structure  40   a  and  40   b  of the device  40  may be deflected out of the plane of the outer and inner vertical surfaces. 
     FIG. 8A  show side and bottom views of a tractor trailer ground vehicles  1  with the device  40  installed on the trailer  30  lower surface  37 .  FIG. 8A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly. 
     FIG. 8B  shows a cross-section view, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  and the two structures  40   a  and  40   b  comprising the device  40 . The preferred embodiment of the invention is that the device  40  is self-supporting without bracing and bracket. For the preferred embodiment each structure,  40   a  and  40   b , comprising the device  40  contains three primary surfaces; an outer vertical surface,  40   aa  and  40   ba , an inner vertical surface,  40   ab  and  40   bb , and a base surface,  40   ac  and  40   bc , where the base surface extends between the upper most edge of the outer vertical surface and inner vertical surface comprising each structure  40   a  and  40   b . The structures  40   a  and  40   b  mechanically attach to the trailer undercarriage by any suitable attachment device, such as clamps, bolts, weld, interlocking pieces, and the like. 
     FIG. 9A  shows side and bottom views of a tractor trailer ground vehicles  1  with the device  40  installed on the trailer  30  lower surface  37 .  FIG. 9A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly. 
     FIG. 9B  shows a cross-section view, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  and the two structures  40   a  and  40   b  comprising the device  40 . An alternate embodiment of the invention is that the device  40  employs a minimal sized bracing to provide the necessary rigidity. For this embodiment, each structure,  40   a  and  40   b , comprising the device  40  contains three primary surfaces; an outer vertical surface,  40   aa  and  40   ba , an inner vertical surface,  40   ab  and  40   bb , and a base surface,  40   ac  and  40   bc , where the base surface extends between the upper most edge of the outer vertical surface and inner vertical surface comprising each structure  40   a  and  40   b . Bracing may be applied in the form of an angle bracket  80  that attaches to the inward facing surface of the inner vertical surface  40   ab  and  40   bb  and to the trailer undercarriage. Support may be supplied to the outer vertical surface by means of a minimum-diameter support rod or member  70 . The structures  40   a  and  40   b  mechanically attach to the trailer undercarriage by any suitable attachment device, such as clamps, bolts, weld, interlocking pieces, and the like. 
     FIG. 10A  shows side and bottom views of a tractor trailer ground vehicle  1  with the device  40  installed on the trailer  30  lower surface  37 .  FIG. 10A  shows a single segment version of the device  40  including structures  40   a  and  40   b  with swept leading and trailing edges installed between the trailer landing gear and the trailer wheel assembly. 
     FIG. 10B  shows a cross-section view, in a plane perpendicular to the ground, of the undercarriage of a trailer  30  and the two structures  40   a  and  40   b  comprising the device  40 . A further alternate embodiment of the invention is that the device  40  employs a minimal sized bracing to provide the necessary rigidity to the outer vertical surface  40   aa  and  40   ba . For this embodiment, each structure,  40   a  and  40   b , comprising the device  40  contains three primary surfaces; an outer vertical surface,  40   aa  and  40   ba , an inner vertical surface,  40   ab  and  40   bb , and a base surface,  40   ac  and  40   bc , where the base surface extends between the uppermost edge of the outer vertical surface and inner vertical surface comprising each structure  40   a  and  40   b . Bracing may be applied in the form of minimum-sized angle bracket  81  that attaches to the inward facing surface of the outer vertical surface  40   aa  and  40   ba  and to the horizontal surface. The structures  40   a  and  40   b  mechanically attach to the trailer undercarriage by any suitable attachment device, such as clamps, bolts, weld, interlocking pieces, and the like. 
     FIG. 11A  shows a side view of tractor trailer  1  with structure  40   a  visible.  FIG. 11B  shows a rear view of tractor trailer  1 , along lines A-A in a plane perpendicular to the ground, with structures  40   a  and  40   b  visible.  FIG. 11C  shows a rear view detail of structure  40   b  from  FIGS. 11   a - 11   b , along with alternative embodiments of structure  40   b  designated structures  40   b   1 - 40   b   4 .  FIGS. 12 and 13  provide similar illustrations for alternative embodiments of structure  40   b  with structures  40   b   5 - 40   b   12 .  FIGS. 14-16  illustrate these alternative embodiments installed with a flat bed tractor trailer  1 , while  FIGS. 17-19  illustrate these alternative embodiments with a tanker tractor trailer  1 . The alternative embodiments illustrated herein for structure  40   b  may be similarly applied to structure  40   a . Thus, references made to the panels of structure  40   b  in  FIGS. 11C-19C  are for convenience of illustration, and should be construed as applicable or suitable for the respective panels of companion structure  40   a.    
   These alternative embodiments of device  40  each define different profiles for the inverted U-shaped channels of structures  40   a  and  40   b  that open in the downward direction. As noted above, the panels of device  40  are configured to generate a vortex (not shown) within the channel when the ground vehicle or tractor trailer  1  is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle. Changing the shape or profile of the U-shaped channel as shown herein may change the boundary of the trapped vortex in minor ways, but does not substantially impair the functional ability of the structures to generate the vortex described above. On the other hand, the shape changes disclosed herein do enable the accommodation of the device  40  to certain operational concerns described below. As may be seen from structures  40   b   1 - 40   b   12 , the profile of device  40  may be modified by varying the value of the transverse Y while approaching the lower surface  37 , which means creating some incline apart from completely vertical in some portion of one or more of the vertical panels  40   ba ,  40   bb , or both  40   ba  and  40   bb . In general, however, transverse Y at the mouth of the structure is configured (along with panels  40   aa ,  40   ab ,  40   ac ,  40   ba ,  40   bb , and  40   bc ) in each of these embodiments to form the inverted U-shaped channel for generating a vortex. The phrase “inverted U-shaped channel” is thus intended to be construed so as to include these profile modifications. In some embodiments, as may be seen with structures such as  40   b   1 ,  40   b   3 ,  40   b   4 ,  40   b   5 ,  40   b   7 ,  40   b   9 , and  40   b   11 , the incline of vertical panels  40   ba  and  40   bb  may be so configured as to reduce  40   bc  to a transverse point of connection to lower surface  37 . Thus, for purpose of description, panel  40   bc  describes the transverse or horizontal, with panels  40   ba  and  40   bb  being vertical, whether inclined or completely vertical. 
   In a first example of an operational consideration, device  40  may be adapted for use with certain trailers used in inter-modal systems. Alternative structures  40   b   3 ,  40   b   4 ,  40   b   9 ,  40   b   10 , and  40   b   11  of  FIGS. 11C and 13C  provide an inverted U-shaped channel that opens in the downward direction, while exposing a corner  37   c  of trailer  30 . This exposed corner  37   c  of trailer  30  can be gripped by cranes or other moving equipment (not shown). Such a configuration is particularly well suited for trailers used in “piggy-back” inter-modal system in which wheeled trailers are lifted and placed on railroad flatcars. To accommodate this consideration, the alternative structures may feature a transverse Y that decreases at the vicinity of contact with lower surface  37 , creating an incline in  40   bb  and optionally  40   ba , so as to expose a corner  37   c  of trailer  30 . Outer panel  40   bb  is thus attached to lower surface  37  inboard and proximate to right surface  32 . In retrofit embodiments, such modifications may also be useful for the avoidance of pre-existing undercarriage structure (not shown) that may depend from lower surface  37  near right surface  32 . Of course, device  40  may be modified similarly in structure  40   a  with respect to the left surface  33 . 
   Thus, with reference to  FIGS. 11C and 13C , alternative structures  40   b   3 ,  40   b   4 , and  40   b   9 - 40   b   11 , for example, have a pair of rigid panels  40   ba ,  40   bb  attached to the right side of the bottom surface of the vehicle  30  and extending downward, including an outer panel  40   bb  attached inboard and proximate to the right surface  32  of the vehicle and an inner panel  40   ba  located inboard of the outer panel  40   bb . The pair of rigid panels are configured with each panel extending downward from the vehicle  30  a desired vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel  40   bb  is separated from the inner panel  40   ba  at the lower edges by a second horizontal distance. The pair of rigid panels  40   ba ,  40   bb  are configured so as to form an inverted U-shaped channel open to the downward direction, with the panels  40   ba ,  40   bb  further configured to generate a vortex within the channel when the ground vehicle  30  is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle  30 , wherein at least a portion of the outer panel  40   bb  is inclined outwardly without exceeding the plane of the right surface  32  of the vehicle, and the horizontal distance Y between inner and outer panels  40   ba ,  40   bb  proximate to the bottom surface  37  of the vehicle is less than the horizontal or transverse distance Y between the inner and outer panels  40   ba ,  40   bb  at the lower edge of the panels. Modified structures for  40   a  (not shown) could be similarly configured with respect to the left surface  33 . 
   As noted above, alternative structures  40   b   9 - 40   b   11  provide free space on lower surface  37  near corner  37   c , which can be useful in retrofitting applications. In some embodiments of device  40   b , it may be desirable to reduce the attachment area on lower surface  37  to avoid preexisting undercarriage structure (not shown) depending from lower surface  37  inboard of structure  40   b . Alternative structures  40   b   1 - 40   b   7  all provide a smaller point of attachment to lower surface  37  and provides free space to accommodate the presence of preexisting undercarriage structure inboard. Alternative structures  40   b   3  and  40   b   4  notably provide free space both inboard and outboard of the structure. 
   Thus, alternative structures  40   b   1 - 40   b   7  show a pair of rigid panels  40   ba ,  40   bb  attached to the right side of the bottom surface  37  of the vehicle  30  and extending downward, including an outer panel  40   bb  substantially coplanar with the right surface of the vehicle and an inner panel  40   ba  located inboard of the outer panel  40   bb . The pair of rigid panels  40   ba ,  40   bb  is configured with each panel extending downward from the vehicle  30  a desired vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel  40   bb  is separated from the inner panel  40   ba  at the lower edges by a horizontal or transverse distance Y. The rigid panels  40   ba ,  40   bb  are configured so as to form an inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle  30  is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle  30 . In this example, at least a portion of inner panel  40   ba  is inclined inwardly (inboard) as it extends downward so that the horizontal distance between the inner panel  40   ba  and the outer panel  40   bb  at the lower edge of the panels is greater than the horizontal distance between them proximate to the bottom surface  37  of the vehicle  30 . Modified structures for  40   a  (not shown) could be similarly configured with respect to the left surface  33 . 
   Such modifications may have additional benefits. Some of the foregoing embodiments of device  40  have a reduced complexity for the inverted U-shaped channel profile, which simplifies manufacture. In addition, a simpler profile generally reduces the amount of material used in manufacture, which also reduces material expense and weight, making it cheaper to use in operation. For example, alternative structures  40   b   5  and  40   b   9  may be fabricated from a single piece of material with a single crease, such that base surface  40   bc  is reduced to a minimum horizontal required for attachment to lower surface  37 . In other words, the value of the transverse Y may be reduced as it approaches the lower surface  37 , leaving the point of attachment. In addition, some of the simpler embodiments of device  40   b , such as structures  40   b   3  or  40   b   4 , may be desirable for avoiding the buildup of dirt and/or ice within the inverted U-shaped channel during operation. 
   A number of the alternative structures discussed above provide free space on lower surface  37 , either inboard, outboard, or both. In some embodiments of device  40   b , it may be desirable to reduce the value of the transverse Y without the need for reducing the area of attachment on lower surface  37 . This need may arise in avoiding pre-existing undercarriage structure that might otherwise interfere with the panels forming the inverted U-shaped channel, but the attachment of the pre-existing undercarriage structure is located elsewhere on lower surface  37 . Alternative structures  40   b   8  and  40   b   12  illustrate two examples enabling additional free space inboard or outboard, as may be desired. 
   Alternative structure  40   b   8  has a pair of rigid panels  40   ba ,  40   bb  attached to the right side of the bottom surface  37  of the vehicle  30  and extending downward, including an outer panel  40   bb  substantially coplanar with the right surface  33  of the vehicle and an inner panel  40   ba  located inboard of the outer panel  40   bb . The pair of rigid panels  40   ba ,  40   bb  is configured with each panel extending downward from the vehicle  30  a desired vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel  40   bb  is separated from the inner panel  40   ba  at the lower edges by a horizontal distance. The pair of rigid panels  40   ba ,  40   bb  are configured so as to form an inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle  30  is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle  30 . At least a portion of inner panel  40   ba  is inclined outwardly, and wherein the horizontal distance between the inner and outer panels  40   ba ,  40   bb  proximate to the bottom surface  37  of the vehicle  30  is greater than the horizontal distance between the inner and outer panels  40   ba ,  40   bb  at the lower edge of the panels. 
   Alternative structure  40   b   12  has a pair of rigid panels  40   ba ,  40   bb  attached to the right side of the bottom surface  37  of the vehicle  30  and extending downward, including an outer panel  40   bb  substantially coplanar with the right surface  33  of the vehicle and an inner panel  40   ba  located inboard of the outer panel  40   bb . The pair of rigid panels  40   ba ,  40   bb  is configured with each panel extending downward from the vehicle  30  a desired vertical distance and having a lower edge that is aerodynamically sharp and wherein the outer panel  40   bb  is separated from the inner panel  40   ba  at the lower edges by a horizontal distance. The pair of rigid panels  40   ba ,  40   bb  are configured so as to form an inverted U-shaped channel open to the downward direction, with the panels further configured to generate a vortex within the channel when the ground vehicle  30  is in motion, wherein the vortex has an axis of rotation aligned with the direction of motion of the ground vehicle  30 . At least a portion of outer panel  40   bb  is inclined inwardly but substantially proximate to the plane of the right surface  37  of the vehicle  30 , and wherein the horizontal distance between the inner and outer panels  40   ba ,  40   bb  proximate to the bottom surface  37  of the vehicle  30  is greater than the horizontal distance between the inner and outer panels  40   ba ,  40   bb  at the lower edge of the panels. 
   These alternate embodiments may incorporate a number of structural variations. For example, the aerodynamic device may include one or more of the panels on the left or right side of the vehicle that are comprised of multiple longitudinal segments. In one embodiment, each panel may extend downward from the vehicle a distance of less than about 90% of the distance from the bottom surface of the vehicle to the surface that the vehicle is moving over. Each panel of at least one of the first pair or second pair may extend downward a substantially equal distance from the bottom surface of the vehicle. In another example, at least one panel may extend downward a distance that varies along its length. An embodiment may include at least one of the first or second pairs of panels being integrally connected to each other by a horizontal panel. This horizontal panel located between the outer and inner panels may be separate from the pair of panels. At least one of the first or second pairs of panels may be an integral extension of the side surface of the vehicle. In another example, at least one panel has a swept leading edge. Optionally, the panels may be folded so as to be substantially adjacent and proximate the bottom surface of the vehicle when not in use. Also, at least one of the first or second pairs of panels may be slidably connected to the vehicle such that the panels slide longitudinally along the vehicle. In some cases, the distance between at least one of the first or second pairs of panels may be adjustable. 
   While the invention has been described and illustrated using two pairs or panels on the bottom surface of the vehicle, those of skill in the art will understand that the invention is not so limited. For example, a third or more panels may be included in each panel grouping on the bottom surface of the vehicle. It is believed that such additional panels would further enhance the aerodynamic drag reduction of the device. 
   From the description provided above, a number of features of the mini-skirt aerodynamic fairing become evident: 
   The invention provides a process to reduce the drag of a ground vehicle. 
   (a) The invention uses vortices to generate upwash to reduce undercarriage flow and reduce drag. 
   (b) The invention reduces the aerodynamic drag and improves the operational efficiency of bluff-base vehicles. 
   (c) The invention reduces the aerodynamic drag and improves the fuel efficiency of bluff-base vehicles. 
   (d) The invention conserves energy and improves the operational efficiency of bluff-base vehicles. 
   (e) The invention reduces the aerodynamic drag without a significant geometric modification to existing ground vehicles. 
   (f) The invention may be easily applied to any existing ground vehicle or designed into any new ground vehicle. 
   (g) The invention may be efficiently operated with a limited number of components. 
   (h) The invention permits the matching of complex surface shapes by the shaping and placement of the components. 
   (i) Large reductions in drag force may be achieved with a large vertical spacing between the lower edge of the invention and the road surface. 
   (j) The structure, placement, and shape of each component may be adapted to meet specific performance or vehicle integration requirements. 
   (k) The leading edge shape of each surface may be linear or complex to meet specific performance or vehicle integration requirements. 
   (l) The lower edge shape of each surface may be linear or complex to meet specific performance or vehicle integration requirements. 
   (m) The trailing edge shape of each surface may be linear or complex to meet specific performance or vehicle integration requirements. 
   (n) Each component of the device may be optimally positioned on the vehicle undercarriage. 
   (o) The device minimizes weight and volume requirements within the vehicle. 
   (p) The device has minimal maintenance requirements. 
   (q) The device has minimal impact on operational and use characteristics of the vehicle door system. 
   (r) The device provides for maximum safety of vehicle operation. 
   Accordingly, the reader will see that the mini-skirt aerodynamic fairing device can be used to easily and conveniently reduce aerodynamic drag on any ground vehicle for the purposes of improving the operational performance of the vehicle. For example, ground vehicles may include busses, rail cars, automobiles, etc., so long as such vehicle would benefit from the present invention&#39;s implementation of the three flow control concepts of vortex generation, upwash management, and ground effect interference. 
   Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, the outer and inner vertical surfaces can be composed of various planar shapes such as ellipsoid, quadratic, and the like; the outer and inner vertical surfaces can be rotated from the vertical axis or may be curvilinear surfaces that are parallel with the axis of the vehicle; the thickness and width can vary along the length; the material can be any light-weight and structurally sound material such as wood, plastic, metal, composites, and the like; the substrate can be any metal, wood, plastic, composite, rubber, ceramic, and the like; the application surface can be that of a metal, wood, plastic, composite, rubber, ceramic, and the like. The attachment and actuation hardware can be either conventional off the shelf or designed specifically for the subject invention. Further, the present invention may be incorporated or integrated within the structure of the vehicle, so as to require no separate attachment. 
   The invention has been described relative to specific embodiments thereof and relative to specific vehicles, it is not so limited. The invention is considered applicable to any road vehicle including race cars automobiles, trucks, buses, trains, recreational vehicles and campers. The invention is also considered applicable to non-road vehicles such as hovercraft, watercraft, aircraft and components of these vehicles. It is to be understood that various modifications and variation of the specific embodiments described herein will be readily apparent to those skilled in the art in light of the above teachings without departing from the spirit and scope. 
   Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.