Abstract:
An improved method and device for the reduction of aerodynamic drag and for improved performance of vehicles by increasing the pressure on the rear surface of the vehicle by generating a plurality of vortices along the top and side surfaces that flow in to the base wake region of the vehicle. An improved method and device for generating a reduction in the drag force on a moving object. The present invention is a simple device comprised of a minimum number of thin and slender small surfaces that are attached to or fabricated as part of the side and top exterior surfaces of a vehicle or vehicle component. The spacing and orientation of the small surfaces, comprising the device, are dependent upon the vehicle geometry and vehicle operating conditions. The plurality of adjacent small surfaces are located forward of the base area on the vehicle. The plurality of adjacent small surfaces and are distributed circumferentially over the side and top surfaces of the subject vehicle or vehicle component. To maximize the ability of each of the plurality of adjacent small surfaces to generate a vortex structure the small surfaces are aligned in planes that are perpendicular to the surface of the vehicle. Each of the plurality of adjacent small surfaces extends from the exterior top and side surfaces of the vehicle. The plurality of adjacent small surfaces is applied symmetrically to a vehicle, about a vertical plane passing through the centerline of the vehicle. Each of the plurality of adjacent small surfaces is orientated in a plane or surface that is at an angle to the local flow direction on the vehicle surface in the immediate vicinity of the present invention. The orientation and shape of the plurality of adjacent small surfaces are a function of the vehicle or vehicle component geometry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims a previous provisional patent application, No. 60/496,851 with a filing date of Aug. 21, 2003 and entitled “Vortex strake device and method for reducing the aerodynamic drag of ground vehicles”. 
     
    
     ORIGIN OF THE INVENTION  
       [[0002]]     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. 
     
    
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX  
       [0003]     Not applicable.  
       BACKGROUND  
       [0004]     1. Field of Invention  
         [0005]     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 of ground vehicles by increasing the pressure on the base area of a vehicle or vehicle component by controlling the flow in wake of the vehicle or vehicle component.  
         [0006]     2. Description of Prior Art  
         [0007]     In the prior art there have been attempts to reduce the aerodynamic drag associated with the bluff base of the trailer of a tractor-trailer truck system. The wake flow emanating from the bluff base trailer is characterized as unsteady and dynamic. The unsteady nature of the wake flow is a result of asymmetric and oscillatory vortex shedding of the side surface and top surface flow at the trailing edge of the top and side surfaces of the vehicle. The boundary-layer flow passing along the top and side surfaces of the vehicle is at a low energy state and is unable to expand around the corner defined by the intersection of the side or top surfaces with the base surface. The boundary-layer flow separates at the trailing edge of the top and side surfaces and forms rotational-flow structures that comprise the bluff-base wake flow. The low energy flow separating at the trailing edges of the side surfaces and top surface of the trailer is unable to energize and stabilize the low energy bluff-base wake flow. The resulting bluff-base wake-flow structure emanating from the base area of the vehicle is comprised of the vortex structures that are shed from trailing edges of the side surfaces and top surface of the vehicle. Contributing to the low-energy bluff-base wake is the low-energy turbulent flow that exits from the vehicle undercarriage at the base of the vehicle. The unsteady wake flow imparts a low pressure onto the aft facing surface of the trailer base that results in significant aerodynamic drag. Prior art has addressed these flow phenomena by adding to the bluff base; a pre-defined aerodynamic surface referred to as a boat-tail fairings, surfaces and plates that create a cavity, and surfaces and plates that trap the vortices shed from the trailing edges. Prior art also show the forcing the side surface and top surface flow into the base region through the use of turning vanes or jets of air.  
         [0008]     Prior art has used the aerodynamic boat-tail fairings applied to the trailer base in order to eliminate flow separation and associated drag, see U.S. Pat. Nos. 4,458,936, 4,601,508, 4,006,932, 4,451,074, 6,092,861, 4,741,569, 4,257,641, 4,508,380, 4,978,162 and 2,737,411. These representative aerodynamic boat-tail fairing devices, while successful in eliminating flow separation, are complex devices that are typically comprised of moving parts that require maintenance and add weight to the vehicle. These devices take a variety of form and may be active, passive, rigid, flexible and/or inflatable. These attributes have a negative impact on operational performance and interfere with normal operations of the vehicle.  
         [0009]     Other concepts as documented in U.S. Pat. Nos. 5,348,366, 4,682,808 and 421,478 consist of plates or surfaces that are attached to the base of a trailer or extend from support mechanisms that are attached to the base of a trailer. These devices operate by trapping the separated flow in a preferred position in order to create an effective aerodynamic boat-tail shape. These representative trailer base devices, while successful in reducing the drag due to base flow are complex devices that are typically comprised of moving parts that require maintenance and add weight to the vehicle. All of these devices add significant weight to the vehicle. These attributes have a negative impact on operational performance and interfere with normal operations of the vehicle.  
         [0010]     U.S. Pat. Nos. 3,010,754, 5,280,990, 2,569,983 and 3,999,797 apply a flow turning vane to the outer perimeter of the trailer base on the sides and top to direct the flow passing over the sides and top of the trailer into the wake in order to minimize the drag penalty of the trailer base flow. These devices provide a drag reduction benefit but they require maintenance and interfere with normal operations of the trailers fitted with swinging doors. These devices also add weight to the vehicle that would have a negative impact on operational performance of the vehicle.  
         [0011]     Several concepts employ pneumatic concepts to reduce the aerodynamic drag of tractor-trailer truck systems. U.S. Pat. No. 5,908,217 adds a plurality of nozzles to the outer perimeter of the trailer base to control the flow turning from the sides and top of trailer and into the base region. U.S. Pat. No. 6,286,892 adds a porous surface to the trailer base and to the sides and top regions of the trailer abutting the trailer base. These porous surfaces cover a minimum depth plenum that is shared by the sides, top and base regions of the trailer. These two patents provide a drag reduction benefit but as with the other devices discussed previously these devices are complex devices, comprised of moving parts, interfere with normal operations of the truck and add weight to the vehicle. These characteristics of the devices result in a negative impact on the vehicle operational performance.  
       SUMMARY OF THE INVENTION  
       [0012]     An object of the invention is to use a limited number of large vortex structures generated on the side and top exterior surfaces of a trailer to energize the flow exiting the trailing edge of the side and top exterior surfaces of the trailer and thereby increasing the ability of the flow on the trailer side and trailer top exterior surfaces to expand into the base region and provide drag reduction, increased fuel economy and improved operational performance. Additionally the vortex structures generated by the subject invention have a preferred angular velocity direction that enhances the mixing of the trailer undercarriage flow with the bluff-base wake flow. Aerodynamic drag reduction is created by increasing the pressure loading on the bluff-base aft-facing surface of the vehicle or vehicle component such as the trailer of a tractor-trailer truck. The invention relates to flow in the base region behind a bluff-base vehicle or vehicle component. The flow in the base region behind a bluff-base vehicle or vehicle component is a function of vehicle geometry, vehicle speed and the free stream flow direction.  
         [0013]     The device provides improved performance for both the no crosswind condition, in which the air is still, as well as the condition when crosswind flow is present. For all moving vehicles that operate on the ground a crosswind flow is always present due to a combination of atmospheric and environmental factors and the interaction of the naturally occurring wind with stationary geological and manmade structures adjacent to the vehicle path as well as interfering flows from adjacent moving vehicles. The device is designed to reduce aerodynamic drag for the all cross wind conditions for single and multiple-component bluff-base vehicles. The subject device uses vortex flows to energize the flow on passing along the exterior top and sides surfaces of a bluff-base ground vehicle to increase the energy of the wake flow and the mixing of the wake flow with the undercarriage flow. The subject device provides reduced aerodynamic drag for all of bluff-base ground vehicles.  
         [0014]     The present invention is a simple device comprised of a minimum number of thin, slender and rigid surfaces that attached to the side and top exterior surfaces of a ground vehicle or vehicle component. The spacing and orientation of the surfaces, comprising the device, are dependent upon the vehicle geometry and vehicle operating conditions.  
         [0015]     The present invention pioneers a novel device that is comprised of a plurality of adjacent surfaces that are attached to the top and side exterior surfaces of a bluff-base vehicle or vehicle component. The plurality of adjacent surfaces are located forward of the base area on the vehicle. The plurality of adjacent surfaces and are distributed circumferentially over the side and top surfaces of the subject vehicle or vehicle component. To maximize the ability of each of the plurality of adjacent surfaces to generate a vortex structure the surfaces are aligned in planes or surfaces that are perpendicular to the surface of the vehicle. Each of the plurality of adjacent surfaces extends from the exterior top and side surfaces of the bluff-base vehicle. The plurality of adjacent surfaces is applied symmetrically to vehicle, about a vertical plane passing through the centerline of the vehicle. Each of the plurality of adjacent surfaces is orientated in a plane or surface that is at an angle to the local flow direction on the vehicle surface in the immediate vicinity of the present invention. The orientation and shape of the plurality of adjacent surfaces are a function of the vehicle or vehicle component geometry.  
         [0016]     For ground vehicles such as tractor-trailer trucks, which have a cross-section shape that is predominately rectangular or square, the plurality of adjacent surfaces will be planar. The flow passing over this class of vehicle is parallel to the vehicle centerline and moving aft along the vehicle surface. The number, shape, width and orientation of the plurality of adjacent surfaces that comprise the invention are determined by; the vehicle geometry and vehicle average operating speed. The preferred embodiment of the invention is to have each of the surfaces, comprising the invention, located on the sides of the vehicle will be orientated with the leading edge positioned above the trailing edge. The surfaces located on the side of the vehicle will be evenly distributed from the lowest edge of the side surface to the highest edge of the side surface. The trailing edge of the surface located nearest the lowest edge of the side surface will be approximately coincident with the lowest edge of the side surface. The vertical position of adjacent surfaces, increasing vertical position, on the side of the vehicle will be such that the trailing edge of the adjacent surfaces is located at a vertical position that is equal to or less than the vertical position of the leading edge of the previous surface. Additional surfaces are positioned on the side of the vehicle in a similar manner with each additional surface being located at an ever-increasing vertical position. The final surface is located on the side of the vehicle with the leading edge at a vertical position coincident with the highest edge of the side of the vehicle. The preferred embodiment of the invention is to have each of the surfaces, comprising the invention, that are located on the top of the vehicle will be orientated with the leading edge positioned inboard of the trailing edge. The surfaces distributed over the top of the vehicle will be evenly and symmetrically distributed about the vehicle centerline from the outer edge of the top surface to the vehicle centerline. The trailing edge of the surface located nearest the outer edge of the top surface will be coincident with the outer edge. The position of the adjacent surface on the top of the vehicle will be such that the trailing edge is located at a lateral position that is equal to or greater than the lateral position of the leading edge of the previous surface. Additional surfaces are positioned on the top of the vehicle in a similar manner with each additional surface located at an ever-increasing inboard position. The final surface that is located on the top of the vehicle will have the leading edge at a lateral position coincident with the vehicle centerline. This arrangement of the surfaces comprising the invention ensures that the surfaces are aligned at an angle to the surface flow for this class of ground vehicle.  
         [0017]     The reduction of aerodynamic drag, improved operational performance and improved stability of multiple component vehicles is obtained by increasing the pressure loading on the bluff base of the vehicle or vehicle component. The pressure loading on the bluff base is increased by vortex structures that are generated on the exterior surfaces of the top and sides of a vehicle. The vortex structures flow into the bluff-base region of the vehicle and energize the wake flow emanating from the bluff base. The vortex structures have a preferred rotation direction that increases the mixing of the undercarriage flow with the bluff-base wake flow. The plurality of adjacent surfaces comprising the invention, extend perpendicularly from the exterior sides and top surfaces of the vehicle. More specifically, this invention relates to a device and method for reducing aerodynamic drag utilizing a plurality of adjacent surfaces that are specifically shaped, sized, and orientated to generate vortex structures that energizes the bluff-base wake and improves mixing of the undercarriage flow with the bluff-base wake. The vortex structures energize and stabilize the wake resulting in reduced unsteady flow separation, increased pressures acting on the bluff base area and reduced vehicle aerodynamic drag. The number of surfaces, the spacing between adjacent surfaces, the length of the surfaces, the width of the surfaces and the incidence of the surfaces to the flow are the primary design variables that are used to determine vortex strength and the drag reduction capability of the device. To ensure that a vortex is formed by the interaction of the side and top surface flow with the side edge of each surface, the thickness of each surface is minimized and the leading and side edges of each surface are made aerodynamically sharp.  
         [0018]     The invention may be used to reduce the drag of all existing and future ground vehicles (i.e., cars with trailers, tractor-trailer trucks, trains, etc.).  
       OBJECTS AND ADVANTAGES  
       [0019]     Several objects and advantages of the present invention are: 
        (a) to provide a novel process to reduce the aerodynamic drag of vehicles;     (b) to provide a means to use vortex structures to reduce aerodynamic drag;     (c) to provide a means to reduce the aerodynamic drag and improve the operational efficiency of vehicles;     (d) to provide a means to reduce the aerodynamic drag and improve the fuel efficiency of vehicles;     (e) to provide a means to conserve energy and improve the operational efficiency of vehicles;     (f) to provide a means to reduce the aerodynamic drag without a significant geometric modification to existing vehicles;     (g) to provide an aerodynamic drag reduction device that uses a plurality of adjacent surfaces;     (h) to allow the surface contour of each of the plurality of adjacent surfaces to be variable to meet the specific needs of the application;     (i) to allow the spacing, location, and orientation of each of the plurality of adjacent surfaces to be variable to meet the specific needs of the application;     (j) to create a number of high pressure and low aerodynamic drag forces on the bluff base of a vehicle that are used to reduce the aerodynamic drag of the subject vehicle;     (k) to allow the device to be fabricated as a number of independent surfaces that may be applied to an existing vehicle;     (l) to allow the device to be fabricated as a single independent unit that may be applied to an existing vehicle;     (m) to allow the device to be fabricated as an integral part of a vehicle;     (n) to allow for optimal positioning of each of the plurality of adjacent surfaces on the vehicle side surface;     (o) to allow for optimal positioning of each of the plurality of adjacent surfaces on the vehicle top surface;     (p) to have minimum weight and require minimum volume within the vehicle;     (q) to have minimum maintenance requirements;        
 
         [0037]     Further objects and advantages are to provide a device that can be easily and conveniently used to minimize aerodynamic drag on any ground vehicle for the purposes of improving the operational performance of the vehicle. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]      FIG. 1  is a rear perspective view of the aft most portion of a trailer of a tractor-trailer truck system with the subject invention installed on the two side surfaces and top surface of the trailer.  
         [0039]      FIG. 2   a  to  2   b  are cross section views, in planes horizontal to the ground ( FIG. 2   a ) and perpendicular to the ground ( FIG. 2   b ), of the wake flow conditions for a tractor-trailer system without the subject invention installed.  
         [0040]      FIG. 2   c  to  2   d  are cross section views, in planes horizontal to the ground ( FIG. 2   c ) and perpendicular to the ground ( FIG. 2   d ), of the wake flow conditions for a tractor-trailer system with the subject invention installed  
         [0041]      FIG. 3   a  to  3   d  are side and top views of various ground vehicles with and without the subject invention installed.  
         [0042]      FIG. 4   a  to  4   c  are a perspective view and two cross section views of a fabrication and attachment technique for the subject invention applied to a vehicle.  
         [0043]      FIG. 4   d  to  4   f  are a perspective view and two cross section views of a fabrication and attachment technique for the subject invention applied to a vehicle.  
         [0044]      FIG. 5   a  to  5   c  are a perspective view and two cross section views of a fabrication and attachment technique for the subject invention applied to a vehicle.  
         [0045]      FIG. 5   d  to  5   f  are a perspective view and two cross section views of a fabrication and attachment technique for the subject invention applied to a vehicle.  
         [0046]      FIG. 6   a  to  6   c  are a perspective view and two cross section views of the subject invention fabricated as an integral part of a vehicle.  
         [0047]      FIG. 6   d  to  6   f  are a perspective view and two cross section views of the subject invention fabricated as an integral part of a vehicle.  
         [0048]      FIG. 7   a  to  7   d  are side views of alternate embodiments of the subject invention installed on a tractor-trailer truck.  
         [0049]      FIG. 8   a  to  8   d  are side views of alternate embodiments of the subject invention installed on various ground vehicles.  
         [0050]      FIG. 9  is a side rear perspective view of the aft portion of a trailer showing an alternate embodiment of the subject invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]     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 surfaces, 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.  
         [0052]     Referring now in detail to the drawings, like numerals herein designate like numbered parts in the figures.  
         [0053]      FIG. 1  is a rear perspective view of the aft portion of a typical trailer  30  of a tractor-trailer truck with the subject invention  40  installed on the exterior side surfaces  32  and  33  and exterior top surface  34  of a trailer  30 . The number, shape, size, and orientation of the plurality of outward extended adjacent surfaces comprising the subject invention  40  are a function of the geometry of the trailer side surfaces  32  and  33 , geometry of the trailer top surface  34  and the geometry of the trailer base surface  36 . The subject invention  40  is comprised of a plurality of outward extended surfaces that are evenly distributed circumferentially about the aft portion of the vehicle. Each surface is inclined at an angle δ to the direction of the local flow  100  passing along the side surfaces  32  and  33  and the top surface  34  of the trailer  30 .  
         [0054]     The plurality of outward extended adjacent surfaces  40  that are attached to the side surfaces  32  and  33  of the vehicle are positioned forward of the base surface  36  a distance Xa. The distance Xa is determined by operational and maintenance requirements of the vehicle. The length La of the plurality of outward extended adjacent surfaces  40  attached to the side surfaces  32  and  33  of the trailer  30  is a function of the geometry of the side surface  32  and  33 , the incidence angle δ and operational and maintenance requirements of the vehicle.  
         [0055]     The plurality of outward extended adjacent surfaces  40  attached to the top surface  34  of the trailer  30  are positioned forward of the base surface  36  a distance Xb. The distance Xb is determined by operational and maintenance requirements. The length Lb of the plurality of outward extended adjacent surfaces comprising the invention  40  attached to the top surface  34  of the trailer  30  is a function of the geometry of the top surface  34 , the incidence angle δ and operational and maintenance requirements of the vehicle.  
         [0056]     The subject invention  40  provides aerodynamic drag reduction for all free stream flow  100  conditions including crosswind conditions. The subject invention  40  takes advantage of all flow  100  conditions to provide increased aerodynamic drag reduction. Aerodynamic drag reduction occurs when flow  100  encounters the leading edge and outward facing side edge of each of the plurality of outward extended surfaces comprising the subject invention  40 . The flow  100  impinging on the leading edge and outward facing side edge of each surface separates and forms and a vortex. The vortex shed from each surface comprising the invention  40  flows downstream and exits the trailing edge of both exterior side surfaces  32  and  33  and the trailing edge of the exterior top surface  34 . The vortices generated by the subject invention  40  then pass into the vehicle base area and energize the bluff-base wake flow. The vortices generate a stable bluff-base wake flow and a high pressure that acts on the exterior base surface  36  of the trailer  30 . The strength of the vortices formed by the device  40  and thus the aerodynamic drag reduction will increase with increasing velocity of the flow  100 . The vortex structures generated by the invention  40  have a preferred rotation in order to increase the mixing of the undercarriage flow with the bluff-base wake flow. The subject invention is comprised of a plurality of outward extended adjacent surfaces  40  that are evenly distributed circumferentially about the vehicle.  
         [0057]      FIG. 2   a  through  FIG. 2   d  show flow patterns in the wake of a bluff-base tractor-trailer truck with and without the present invention  40  installed. In  FIG. 2   a  through  FIG. 2   d  the airflow about the vehicle and in the base region is represented by arrow tipped lines and swirl structures  100 ,  110 ,  120 ,  130  and  140 . The conical shaped structures with arrow tipped lines represent vortices  130  generated by the subject invention  40 . The shaded swirl structures represent rotational wake flow  110 . The small swirl structures represent turbulent flow structures  120  in the base area and from the vehicle undercarriage.  
         [0058]      FIG. 2   a  show a top view of the aft portion of a trailer  30  and a cross section view, in a plane horizontal to the ground, of the bluff-base wake flow, without the subject invention installed. For this condition, a surface flow  100  develops on the trailer that separates at the trailing edge of the side surfaces  32  and  33 , and forms rotational-flow structures  110  that comprise the bluff-base wake flow. The rotational-flow structures  110  are shed asymmetrically from the opposing side surfaces  32  and  33 . These rotational-flow structures  110  continue to move downstream in a random pattern. The asymmetric shedding of the rotational-flow structures  110  produce low pressures that act on the base surface  36  of the trailer. These low pressures result in a high aerodynamic drag force. The low energy flow  100  separating at the trailing edges of the side surfaces  32  and  33  of the trailer  30  is unable to energize and stabilize the low energy bluff-base wake flow. The resulting bluff-base wake-flow structure emanating from the base area of the vehicle is comprised of the vortex structures  110  that are shed from trailing edges of the side surfaces  32  and  33  of the trailer  30 . Contributing to the low-energy bluff-base wake is the low-energy turbulent flow  120  that exits from the vehicle undercarriage at the base of the vehicle.  
         [0059]      FIG. 2   b  show a side view of the aft portion of a trailer  30  and a centerline cross-section view of the bluff-base wake flow, without the subject invention installed. For this condition, a surface flow  100  develops on the trailer that separates at the trailing edge of the top surface  34  and forms rotational-flow structures  110  that comprise the bluff-base wake flow. The rotational-flow structures  110  that are shed from the trailing edge of the top surface  34  are asymmetrically located in the wake. These rotational-flow structures  110  continue to move downstream in a random pattern. The unsteady shedding of the rotational-flow structures  110  produce low pressures that act on the base surface  36  of the trailer. These low pressures result in a high aerodynamic drag force. The low energy flow  100  separating at the trailing edges of the top surface  34  of the trailer  30  is unable to energize and stabilize the low energy bluff-base wake flow. Contributing to the low-energy bluff-base wake is the low-energy turbulent flow  120  that exits from the vehicle undercarriage at the trailing edge of the vehicle. The resulting bluff-base wake-flow structure emanating from the base area of the vehicle is comprised of the vortex structures  110  that are shed from trailing edges of the side surfaces  32  and  33  and the top surface  34  of the vehicle. The low-energy turbulent flow  120  that exists from the vehicle undercarriage also enters into the bluff-base wake flow. The unsteady wake flow imparts a low pressure onto the aft facing surface  36  of the trailer base that results in significant aerodynamic drag.  
         [0060]      FIG. 2   c  and  FIG. 2   d  show a top view and a side view of the aft portion of a trailer  30  and cross section views in a plane horizontal to the ground and along the vehicle centerline of the bluff-base wake flow, with the subject invention  40  installed. For this condition, a surface flow  100  develops on the trailer  30  exterior top surface  34  and exterior side surfaces  32  and  33  that impinge on the leading edge and outward facing side edge of each outward-extended surface comprising the subject invention  40 . The flow  100  impinging on the plurality of outward-extended adjacent surfaces separates and forms vortices  130 . The plurality of outward-extended adjacent surfaces, comprising the subject invention  40 , is symmetrically positioned on the trailer  30  top exterior surface  34  and side exterior surfaces  32  and  33  about the vehicle centerline. Each surface of the subject invention  40  is inclined at an angle δ to the direction of the local flow  100 . Each surface  40  of the subject invention is designed to generate a coherent vortex structure  130 . The invention  40  generates a plurality of vortices  130  that are symmetrically orientated about the centerline of the trailer  30 . The vortices  130  move downstream in a symmetric pattern and exit the top surface  34  and side surfaces  32  and  33  at the trailing edge of the vehicle  30  and enter into the base region of the vehicle  30 . The vortices  130  energize the bluff-base wake flow. The vortices  130  generate a stable bluff-base wake flow and a high pressure that acts on the base surface  36  of the trailer  30 . The strength of the vortices  130  formed by the device  40  and thus the aerodynamic drag reduction benefit will increase with increasing velocity of the flow  100 . The vortex structure generated by the invention  40  has a preferred rotation in order to increase the mixing of the undercarriage flow with the bluff-base wake flow.  
         [0061]      FIG. 3   a  through  FIG. 3   d  are side and top views of example ground vehicles with and without the subject invention installed.  FIG. 3   a  shows a typical tractor-trailer truck system  1 , comprised of a powered tractor  10  that pulls a trailer  30 . The tractor  10  is comprised of a cab  11  and an aerodynamic fairing system  20  that may be an integral part of the tractor  10 .  FIG. 3   b  shows the same tractor-trailer truck system  1  as that of  FIG. 3   a  with the subject invention  40  installed on the side surfaces  32  and  33  and the top surface  34  of the trailer  30 . The plurality of outward extend adjacent surfaces that comprise the invention  40  are symmetrically distributed in a circumferential row located at the rear of the trailer  30 .  FIG. 3   c  and  FIG. 3   d  show an automobile  50  pulling a trailer  60  with and without the subject invention  40  installed on both the automobile exterior side surfaces  52 ,  53  and the exterior top surface  54  and the trailer exterior side surfaces  62 ,  63  and the exterior top surface  64 . The plurality of outward extend adjacent surfaces that comprise the invention  40  are symmetrically distributed in a circumferential row located at the rear of the automobile  50  and the trailer  60 . The various vehicles depicted in  FIG. 3  shows a powered vehicle towing/pulling an un-powered towed vehicle. Additionally, other multiple component vehicles may be considered than those depicted.  
         [0062]      FIG. 4   a  through  FIG. 4   f  are perspective views and cross section views of the subject invention  40  fabricated as a single independent unit that may be applied or attached to an existing vehicle or vehicle component.  FIG. 4   a  through  FIG. 4   c  show the subject invention  40  fabricated as a single independent unit for attachment to the exterior surface of a vehicle.  FIG. 4   a  show the invention  40  fabricated as a single independent unit consisting of a plurality of outward extended adjacent surfaces  41 , a base plate  42  and means  43  to attach the outward extended adjacent surfaces  41  to the base plate  42 . Each of the plurality of outward extended adjacent surfaces  41  have a length La and are orientated on the base plate  42  at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 4   b  show a cross section cut of the invention  40 , fabricated as a single independent unit, attached to the exterior surface  202  of a vehicle  200 .  FIG. 4   c  show a cross section cut of one outward extended adjacent surfaces  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Ha. The angle δ and dimensions La and Ha are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  and the base plate  42  may be any light-weight and structurally sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the base plate  42  may differ or may be of the same material and fabricated as a single component. The attachment means  43  may consist of bonding, welding or other appropriate structural attachments. The subject invention  40  is attached to the exterior surface  202  of a vehicle  200  by a means  45 . The attachments means  45  may consist of bonding, mechanical fasteners or other appropriate means.  
         [0063]      FIG. 4   d  through  FIG. 4   f  show the subject invention  40  fabricated as a single independent unit for attachment to the exterior surface  204  of a vehicle  200 .  FIG. 4   d  show the invention  40  fabricated as a single independent unit consisting of a plurality of outward extended adjacent surfaces  41 , a base plate  42  and means  43  to attach the outward extended adjacent surfaces  41  to the base plate  42 . The plurality of outward extended adjacent surfaces  41  is orientated in a symmetric pattern about the centerline A of the vehicle  200 . Each of the plurality of outward extended adjacent surfaces  41  have a length Lb and are orientated on the base plate  42  at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 4   e  show a cross section cut of the invention  40 , fabricated as a single independent unit, attached to the exterior surface  204  of a vehicle  200 .  FIG. 4   f  show a cross section cut of one outward extended adjacent surfaces  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Hb. The angle δ and dimensions Lb and Hb are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  and the base plate  42  may be any light-weight and structurally sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the base plate  42  may differ or may be of the same material and fabricated as a single component. The attachment means  43  may consist of bonding, welding or other appropriate structural attachments. The subject invention  40  is attached to the exterior surface  204  of a vehicle  200  by a means  45 . The attachments means  45  may consist of bonding, mechanical fasteners or other appropriate means.  
         [0064]      FIG. 5   a  through  FIG. 5   f  are perspective views and cross section views of the subject invention  40  fabricated as a plurality of independent structures that may be applied or attached to an existing vehicle or vehicle component.  FIG. 5   a  through  FIG. 5   c  show the subject invention  40  fabricated as a plurality of independent structures for attachment to the exterior surface  202  of a vehicle  200 .  FIG. 4   a  show the invention  40  fabricated as a plurality of independent structures with each structure consisting of an outward extended adjacent surface  41 , a base plate  42  and means  43  to attach the outward extended adjacent surface  41  to the base plate  42 . Each outward extended adjacent surface  41  has a length La and a height Ha. Each of the plurality of independent structures is orientated on the side of vehicle at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 5   b  show a cross section cut of the invention  40 , fabricated as a plurality of independent structures, attached to the exterior surface  202  of a vehicle  200 .  FIG. 5   c  show a cross section cut of one outward extended adjacent surfaces  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Ha. The angle δ and dimensions La and Ha are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  and the base plate  42  may be any light-weight and structurally sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the base plate  42  may differ or may be of the same material and fabricated as a single component. The attachment means  43  may consist of bonding, welding or other appropriate structural attachments. The plurality of independent structures comprising the subject invention  40  is attached to the exterior surface  202  of a vehicle  200  by a means  45 . The attachments means  45  may consist of bonding, mechanical fasteners or other appropriate means.  
         [0065]      FIG. 5   d  through  FIG. 5   f  show the subject invention  40  fabricated as a plurality of independent structures for attachment to the exterior surface  204  of a vehicle  200 .  FIG. 5   d  show the invention  40  fabricated as a plurality of independent structures with each independent structure consisting of an outward extended adjacent surface  41 , a base plate  42  and means  43  to attach the outward extended adjacent surface  41  to the base plate  42 . Each of the plurality of independent structures comprising the invention  40  is orientated in a symmetric pattern about the centerline A of the vehicle  200 . Each of the plurality of independent structures comprising the invention  40  has a length Lb and are orientated on the exterior surface  204  of the vehicle  200  at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 5   e  show a cross section cut of the invention  40 , fabricated as a plurality of independent structures, attached to the exterior surface  204  of a vehicle  200 .  FIG. 5   f  show a cross section cut of one outward extended adjacent surface  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Hb. The angle δ and dimensions Lb and Hb are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  and the base plate  42  may be any light-weight and structurally sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the base plate  42  may differ or may be of the same material and fabricated as a single component. The attachment means  43  may consist of bonding, welding or other appropriate structural attachments. The subject invention  40  is attached to the exterior surface  204  of a vehicle  200  by a means  45 . The attachments means  45  may consist of bonding, mechanical fasteners or other appropriate means.  
         [0066]      FIG. 6   a  through  FIG. 6   f  are perspective views and cross section views of the subject invention  40  fabricated as an integral part of an existing vehicle  200  or vehicle component.  FIG. 6   a  through  FIG. 6   c  show the subject invention  40  fabricated as an integral part of the exterior surface  202  of a vehicle  200 .  FIG. 6   a  show the invention  40  fabricated as an integral part of an existing vehicle  200  with the subject invention consisting of a plurality of outward extended adjacent surfaces  41  fabricated as part of the surface  202 . Each outward extended adjacent surface  41  has a length La and a height Ha. Each of the plurality of independent structures is orientated on the vehicle at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 6   b  show a cross section cut of the invention  40 , fabricated as an integral part of the surface  202  of a vehicle  200 .  FIG. 6   c  show a cross section cut of one outward extended adjacent surfaces  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Ha. The angle δ and dimensions La and Ha are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  may be any light-weight and structurally-sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the vehicle  200  may differ or may be of the same material and fabricated as a single component. The plurality of independent structures comprising the subject invention  40  is fabricated as part of the exterior surface  202  of a vehicle  200 .  
         [0067]      FIG. 6   d  through  FIG. 6   f  show the subject invention  40  fabricated as an integral part of the exterior surface  204  of a vehicle  200 .  FIG. 6   d  show the invention  40  fabricated as an integral part of the surface  204  of a vehicle  200  consisting of a plurality of outward extended adjacent surfaces  41 . Each of the plurality of outward extended adjacent surfaces  41  comprising the invention  40  is orientated in a symmetric pattern about the centerline A of the vehicle  200 . Each of the plurality of outward extended adjacent surfaces  41  comprising the invention  40  has a length Lb and is orientated on the surface  204  of the vehicle  200  at an angle δ. Each of the plurality of outward extended adjacent surfaces  41  have a leading edge  46  and an outward facing side edge  47 .  FIG. 6   e  show a cross section cut of the invention  40 , fabricated as a plurality of outward extended adjacent surfaces  41 , attached to the top surface  204  of a vehicle  200 .  FIG. 6   f  show a cross section cut of one outward extended adjacent surface  41  of the invention  40 . The sketch show the surface  41  extends perpendicularly from the surface of the vehicle a distance Hb. The angle δ and dimensions Lb and Hb are determined by the geometry of the vehicle  200  and direction of the air flow  100 . Example material for the outward extended adjacent surfaces  41  may be any light-weight and structurally sound wood, metal, plastic, composite or other suitable material. The material for the outward extended adjacent surfaces  41  and the vehicle  200  may differ or may be of the same material. The subject invention  40  is attached to the exterior surface  204  of a vehicle  200 .  
         [0068]      FIG. 7   a  to  7   d  are side views of various embodiments of the subject invention  40  installed on a tractor-trailer truck  1 .  FIG. 7   a  is a side view of a tractor-trailer truck  1  with the subject invention  40 , comprised of a minimal number of outward projected adjacent surfaces orientated with a large incidence angle δ, installed in the furthest aft position on the trailer  30  exterior side surfaces  32  and  33  and exterior top surface  34 .  FIG. 7   b  is a side view of a tractor-trailer truck  1  with the subject invention  40 , comprised of a minimal number of outward projected adjacent surfaces orientated with a large incidence angle δ, installed in a forward position on the trailer  30  exterior side surfaces  32  and  33  and exterior top surface  34 .  FIG. 7   c  is a side view of a tractor-trailer truck  1  with the subject invention  40 , comprised of a increased number of outward projected adjacent surfaces orientated with a reduced incidence angle δ, installed in an aft position on the trailer  30  exterior side surfaces  32  and  33  and exterior top surface  34 .  FIG. 7   d  is a side view of a tractor-trailer truck  1  with the subject invention  40 , comprised of a increased number of outward projected adjacent surfaces with a reduced length La and Lb and a large incidence angle δ, installed in the aft position on the trailer  30  exterior side surfaces  32  and  33  and exterior top surface  34 .  
         [0069]      FIG. 8   a  to  8   d  are side views of various embodiments of the subject invention  40  installed on various ground vehicles.  FIG. 8   a  is a side view of a surface truck  130  with the subject invention  40 , comprised of a minimal number of outward projected adjacent surfaces orientated with a large incidence angle δ, installed in the furthest aft position on the truck  130  exterior side surfaces  132  and  133  and exterior top surface  134 .  FIG. 8   b  is a side view of a pick-up truck  1  with the subject invention  40 , comprised of a large number of outward projected adjacent surfaces orientated with a small incidence angle δ, installed on the pick-up cab exterior side surfaces  142  and  143  and exterior top surface  144  and the pick-up bed exterior side surfaces  145  and  146 .  FIG. 8   c  is a side view of a van  150  with the subject invention  40 , comprised of a increased number of outward projected adjacent surfaces orientated with a reduced incidence angle δ, installed in an aft position on the van  150  exterior side surfaces  152  and  153  and exterior top surface  154 .  FIG. 8   d  is a side view of a bus  160  with the subject invention  40 , comprised of a increased number of outward projected adjacent surfaces with a reduced length and a large incidence angle δ, installed in the aft position on the bus  160  exterior side surfaces  162  and  163  and exterior top surface  164 .  
         [0070]      FIG. 9  is a rear perspective view of the aft portion of a typical trailer  30  of a tractor-trailer truck showing an alternate embodiment of the subject invention  40  installed on the exterior side surfaces  32  and  33  and exterior top surface  34  of a trailer  30 . The number, shape, size, and orientation of the plurality of outward extended adjacent surfaces comprising the subject invention  40  are a function of the geometry of the trailer exterior side surfaces  32  and  33 , geometry of the trailer exterior top surface  34  and the geometry of the trailer exterior base surface  36 . The subject invention  40  is comprised of a plurality of outward extended surfaces that are evenly distributed circumferentially about the aft portion of the vehicle. Each surface is inclined at an angle δ to the direction of the flow  100  passing along the exterior side surfaces  32  and  33  and the exterior top surface  34  of the trailer  30 . The leading edge of each outward projected surface, comprising the invention  40 , located on the exterior side surfaces  32  and  33  of the trailer  30  are orientated with the leading edge of each surface at a vertical position that is below the trailing edge of each surface. The leading edge of each outward projected surface, comprising the invention  40 , located on the exterior top surface  34  of the trailer  30  are orientated with the leading edge of each surface positioned outboard of the trailing edge of each surface.  
         [heading-0071]     Advantages  
         [0072]     From the description provided above, a number of advantages of the vortex strakes become evident:  
         [0073]     The invention provides a novel process to reduce the drag of a bluff-base body. 
        (a) The invention provides a means to use vortices generated on the top and side surfaces of a bluff-base body to reduce drag.     (b) The invention provides a means to reduce the aerodynamic drag and improve the operational efficiency of bluff-base vehicles.     (c) The invention provides a means to reduce the aerodynamic drag and improve the fuel efficiency of bluff-base vehicles.     (d) The invention provides a means to conserve energy and improve the operational efficiency of bluff-base vehicles.     (e) The invention provides a means to reduce the aerodynamic drag without a significant geometric modification to existing bluff-base vehicles.     (f) The invention may be easily applied to any existing bluff-base vehicle or designed into any new bluff-base vehicle.     (g) The invention allows for the efficient operation of the invention with a limited number of outward extended surfaces.     (h) The invention allows for the matching of complex surface shapes by the shaping and placement of the plurality of outward extended surfaces.     (i) Large reductions in drag force can be achieved by the plurality of vortices.     (j) The structure of each outward extended surface may be adapted to meet specific performance or vehicle integration requirements.     (k) The shape of each single outward extended surface may be planar, cylindrical, or combinations thereof to meet specific performance or vehicle integration requirements.     (l) The ability to optimally position each outward extended surface on the vehicle top surface and side surfaces.     (m) The ability to minimize weight and volume requirements within the vehicle.     (n) The ability to minimize maintenance requirements.     (o) The ability to maximize the safety of vehicle operation. 
 
 Conclusion, Ramifications, and Scope 
       
 
         [0090]     Accordingly, the reader will see that the vortex strake 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. Furthermore, the plurality of outward extended adjacent surfaces comprising the vortex strake device has the additional advantages in that: 
        it provides a aerodynamic drag reduction force over the base of the vehicle;     it allows the contour of the host surface to be easily matched;     it allows easy application to any existing vehicle or designed into any existing vehicle;     it allows the device to be fabricated as an independent unit that may be applied to an existing surface;     it allows for optimal positioning of each outward extended surface on the vehicle side surfaces and top surface;     it allows the design of a system with minimum weight and to require minimum volume within the vehicle;     it allows minimum maintenance requirements;     it allows for the maximum safety of vehicle operation;        
 
         [0099]     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 outward projected surfaces can have various non-planar shapes such as ellipsoid, complex, etc.; 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, etc.; the substrate can be any metal, wood, plastic, composite, rubber, ceramic, etc.; the application surface can be that of a metal, wood, plastic, composite, rubber, ceramic, etc.  
         [0100]     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 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.  
         [0101]     Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.