US20130224037A1

US20130224037A1 - Compound airfoil

Info

Publication number: US20130224037A1
Application number: US13/615,101
Authority: US
Inventors: Dennis Simpson; Jeffrey D. Hoyal
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-09-13
Filing date: 2012-09-13
Publication date: 2013-08-29

Abstract

An airfoil is provided that has an arrangement that improves the lift of an airfoil and that include surface features that change the performance of the airfoil. Protrusions are provided on the top surface of the airfoil such that channels are formed between adjacent protrusions that affect the flow of air there through. In an additional respect, indentations can be provided on the bottom surface of the airfoil that affect the flow of air there through.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S. Patent Application No. 61/534,236, filed Sep. 13, 2011 which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to airfoils, and, more particularly, enhancement of normal airfoils by incorporating venturi and diffusers to increase airfoil effectiveness.

BACKGROUND OF THE INVENTION

An airfoil is a member that has a shape such that when it is moved through a fluid (e.g., air or water) an aerodynamic force (e.g. lift and drag) is produced. Common airfoils include the wing of an airplane, a wind turbine, helicopter rotor blade, or turbine blade for a gas turbine or jet engine, airplane propeller or the sail of a sailboat, for example.
The force or lift produced by an airfoil is primarily a result of the fluid velocity, angle of attack, and the shape of the airfoil. However, other modification to the airfoil may increase the lift. For example, U.S. Patent No. 2,427,972 to Melehior et al., discusses the creation of venturi that are formed via a slot that extends between the upper and lower surfaces of the airfoil. This design, however, relies on directing air flow through the body of the airfoil. The present invention provides fundamental improvements over this design and others.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an airfoil is provided that includes a top surface extending between a leading edge and a trailing edge on a top side of the airfoil and defining a chord length therebetween. A bottom surface extends between the leading edge and the trailing edge on a bottom side of the airfoil. A plurality of protrusions are on the top surface of the air foil. Two adjacent protrusions define a channel therebetween that extends in the direction of the chord length of the airfoil. Each channel has a leading portion, a middle portion, and a trailing portion. The channel is sized and shaped such that the leading portion and the trailing portion are wider than the middle portion.
In a further aspect, each channel extends along a majority of the top surface in the direction of the chord length.
In yet a further aspect, the length of the leading portion of each channel is shorter than the middle portion in the direction of the chord length.
In a still further aspect, the length of the trailing portion of each channel is longer than the middle portion in the direction of the chord length.
In further aspect, each channel extends along less than half of the top surface in the direction of the chord length.
In yet another further aspect, the walls of adjacent protrusions converge along a curved trajectory to define the leading portion of each channel.
In another further aspect, the walls of adjacent protrusions diverge along a generally linear trajectory to define the trailing portion of each channel.
In a further aspect, the walls of adjacent protrusions extend generally parallel to each other to define the middle portion of each channel.
In yet a further aspect, the distance between a top surface of each protrusion and the top surface of the airfoil defines a depth of each channel, and the depth of each channel is greater in the leading portion than the middle portion and the trailing portion.
In a still further aspect, each protrusion extends around the leading edge to the bottom surface of the airfoil such that adjacent protrusions form channels on the bottom surface of the airfoil.
According to another aspect, an airfoil is provided that has a top surface extending between a leading edge and a trailing edge on a top side of the airfoil and defines a chord length therebetween. A bottom surface extends between the leading edge and the trailing edge on a bottom side of the airfoil. A plurality of indentations on the bottom surface of the air foil are provided that define a channel. Each indentation has a leading portion and a trailing portion. The channel is sized and shaped such that the trailing portion is wider than the leading portion.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a graph illustrating the aerodynamic performance of an airfoil showing most of the pressure differential and lift being creating in the forward part of the airfoil;

FIG. 2 is a top plan view on an airfoil with a venturi according to an embodiment of the invention;

FIG. 3 is an isometric view on an airfoil having multiple venturi of FIG. 2;

FIG. 4 is a top plan view on an airfoil with a venturi according to a second embodiment of the invention;

FIG. 5 is an isometric view on an airfoil having multiple venturi of FIG. 4;

FIG. 6 is a top plan view on an airfoil with a venturi according to a third embodiment of the invention;

FIG. 7 is an isometric view on an airfoil having multiple venturi of FIG. 6;

FIG. 8 is a top plan view on an airfoil with a venturi according to a fourth embodiment of the invention;

FIG. 9 is an isometric view on an airfoil having multiple venturi of FIG. 8;

FIG. 10 is a top plan view on an airfoil with a venturi according to a fifth embodiment of the invention;

FIG. 11 is an isometric view on an airfoil having multiple venturi of FIG. 10;

FIG. 12 is a cross-section view on an airfoil with venturi profiles of differing depths according further embodiments of the invention;

FIGS. 13 and 14 are isometric views of airfoils having multiple venturi of FIG. 12;

FIGS. 15 and 16 are isometric views of airfoils having multiple venturi at different spacings;

FIGS. 17 and 18 are views of an airfoil having multiple venturi of a first profile;

FIGS. 19 and 20 are views of an airfoil having multiple venturi of a second profile;

FIGS. 21 and 22 are views of an airfoil having multiple venturi of a third profile;

FIGS. 23-25 are views of an airfoil having multiple venturi of a fourth profile;

FIGS. 26 and 27 are views of an airfoil having multiple venturi of a fifth profile;

FIGS. 28-31 are views of an airfoil having multiple venturi of a sixth profile;

FIG. 32 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 19 and 20;

FIG. 33 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 21 and 22;

FIG. 34 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 19 and 20;

FIG. 35 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 26 and 27;

FIG. 36 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 17 and 18;

FIGS. 37 and 38 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 23-25; and

FIG. 39 is an exemplary schematic of an airfoil that corresponds to the airfoil illustrated in FIGS. 28-31.

DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

By way of overview and introduction, the present invention provides an arrangement that improves the lift of an airfoil. The structures described herein relate to airfoils that include surface features that change the performance of the airfoil. The various arrangements described herein impart a modification of the airflow around the airfoil. Various structures of differing sizes and shapes provide enhanced lift and aerodynamic characteristics to an airfoil by adding a vertical element to airfoils to increase airflow velocity over the top of the wing thereby reducing static pressure and increasing lift. The diffuser aspect of this invention reduces airflow velocity on the underside of the wing thereby increasing static pressure and increasing lift. The figures included herein illustrate airfoils that include venturi on the upper surface of an airfoil. The various figures show venturi of different sizes, shapes, and profiles and at different positions and spacing along the airfoil. The figures included herein are merely illustrative embodiments and venturi having different combinations and variations of the sizes, shapes, profiles, positions and spacing can be made without departing from the invention.
FIGS. 2 and 3 illustrate an airfoil 10 that includes venturi 12. An airfoil having a base shape corresponding to National Advisory Committee for Aeronautics (NACA) airfoil shape designated NACA 0015 was selected as the base airfoil shape. The base shape of the airfoil was selected based on whether the airfoil undergoes trailing edge stall. An airfoil that undergoes trailing edge stall is preferred because 1) a leading edge separation bubble could disrupt the flow into the venturi, and 2) the stream wise vortices created by the venturi will only help suppress stall on the trailing edge. Accordingly, other shape airfoils are contemplated and the invention is not limited to a particular airfoil shape. FIG. 1 shows a typical pressure distribution for a NACA 0015 airfoil at a 10° angle of attack. Cp is the pressure coefficient, and x/c is the distance from the leading edge divided by the airfoil's chord length. For these test conditions the suction peak occurs at approximately 1% chord. The “chord” of an airfoil is the distance between the leading edge and the trailing edge of the airfoil.
FIGS. 2 and 3 illustrate an airfoil 10 that has a venturi 12 with a throat 14, an inlet 16, and a exit 18. The throat of a venturi is the narrow portion of the venturi, as indicated by reference numeral 14. The inlet 16 of the venturi is the leading portion of the venturi presented to the fluid flow ahead of the throat 14. The exit 18 is the portion of the venturi that is aft of the throat 14. The fluid (e.g., air) enters the inlet 16, passes through the constricted throat section 14, and exits through the exit 18. The fluid that exits the throat 14 is at a lower pressure than the fluid on the inlet side of the throat. This low pressure condition can generate increased lift.
The venturi shown in FIGS. 2 and 3 has a throat 14 that extends from 2.5% chord to 7.5% chord (i.e., the throat starts at a distance from the leading edge equal to 2.5% of the chord length of the airfoil and ends at 7.5% of the chord length). This venturi configuration results in a relatively small size inlet 16. As a result of the reduced size inlet 16, there may be reduced airflow into the venturi.
FIGS. 4 and 5 illustrate an airfoil 10 with a venturi 12 that has a throat 14 that starts at 5.0% chord and extends to 10% chord. A venturi of this shape results in a larger inlet 16, which can allow greater airflow into the venturi. As can be seen in FIG. 5, neighboring venturi are closely spaced along the surface of the airfoil 10. However, other spacings can be used in combination with this venturi shape, and other combinations and variations of the venturi parameters can also be used.
FIGS. 6 and 7 illustrate an airfoil 10 with a venturi 12 that has a throat 14 that starts at 7.5% chord and extends to 12.5% chord. An airfoil with venturi of the shape results in the throat 14 of the venturi being located relatively far downstream from the leading edge of the airfoil.
FIGS. 2-7 illustrate airfoils having venturi with different throat and inlet designs. FIGS. 8-11 illustrate airfoils having venturi with different exit structures. The exit 18 shown in FIGS. 8 and 9 has a “diffuser” profile. Accordingly, the walls of the exit 18 flare away from each other along the length of the airfoil such that the walls of the exit 18 are close together near the throat 14 and are further apart near the end of the exit. The angle “a” between the walls of the exit 18 is preferably limited to about 10 degrees in order to reduce the chance of a flow separation. The exit 18 shown in FIGS. 10 and 11 has a “straight” profile. Accordingly, the walls of the exit 18 maintain the same spacing along the length of the airfoil. As can be seen, the exit 18 has the same wall spacing as the throat 14 along its entire length. A diffuser shaped exit can increase the velocity through the throat of the venturi leading to increase suction on the aft side of the throat, and thus increased lift. The straight shaped exit can result in less suction, but a broader region of low pressure along the surface of the airfoil.
FIGS. 12-14 illustrate airfoils that have venturi of differing “floor profiles.” The depth of the floor profile is the depth to which the venturi channel is recessed into the airfoil. Referring to FIG. 12, line 20 shows the depth profile of a shallow floor venturi and line 22 shows the depth profile of a deep floor venturi. In addition, as can be seen, profile 20 more closely approximates the original curvature shape of the airfoil 10, whereas profile 22 is deeper in the throat section of the venturi. Lines 20 and 22 represent the depth of the respective venturi relative to the cross-section of airfoil 10. Line 20 corresponds to the venturi 12′ shown in FIG. 14 and line 22 corresponds to the venturi 12″ shown in FIG. 13. As can be seen by comparison of FIGS. 13 and 14, the throat 14′ in FIG. 14 is shallower than the throat 14″ of FIG. 13. A deep venturi profile can generate a stronger stream wise vortex to help delay stall, but generate less flow velocity through the venturi's throat (resulting in less suction). A shallow venturi profile can yield better flow and suction in the throat, but weaker vortices. Referring to FIG. 12, both the profiles are shaped so as not to reduce the leading edge radius 24 beyond a critical minimum radius, which can result in a leading edge stall. In addition, the profiles are shaped to smoothly exit and transition to the baseline airfoil profile 26 to reduce the chance of flow separation. Accordingly, the profile exits are angled to be smooth and gradual near the reentry to the baseline airfoil profile.
FIG. 15 shows an airfoil 10 with venturi 12 that are closely spaced. FIG. 16 shows an airfoil 10 with venturi 12 that are widely spaced. Accordingly, the distance 28″ between venturi as shown in FIG. 15 is less than the distance 28′ as shown in FIG. 16. Accordingly, the venturi density, i.e., the number of venturi per length of airfoil can be adjusted.
FIGS. 17 and 18 illustrate an airfoil having a base shape corresponding to the national advisory committee for aeronautics (NACA) airfoil shape designated NACA 0015 was selected as the base airfoil shape. Note that the circles on the shown on the airfoil drawings represent rivet holes. The airfoil 110 includes a venturi 112. The venturi 112 are channels that are defined between adjacent protrusions 114. The venturi channels 112 include a leading portion 116, a middle portion 118, and a trailing portion 120. The walls of the adjacent protrusions 114 are curved toward each other in the leading portion 216 of each channel 112, which can have a combination convex concave profile. The walls of protrusions 114 are generally parallel with each other in the middle portion 118 of each channel 112. The walls of the adjacent protrusions 114 are angled away from each other in the trailing portion 120 of each channel 112. The walls of the protrusions 114 in the trailing portion 120 of each channel 112 can either be generally linearly angled away from one another or slightly curved away from one another. The leading portion 116 and the trailing portion 120 of each channel are wider than the middle portion 118. The middle portion 118 is substantially longer than the leading portion 116 and the trailing portion 120. The channel 112 extends along a majority of the chord length of the airfoil. The channel 112 can extend between about 70% and 95% of the chord length. The walls of the protrusions can have a rounding radius to smooth the transition, e.g., the transition from the top wall to a side wall of a protrusion can have a 0.02% radius of rounding. Referring to FIG. 18, the distance between a top surface 122 of the protrusion 114 and the top surface 110 a of the airfoil 110 is greater proximate the leading edge of the airfoil and less proximate the trailing edge of the airfoil. The top surface 122 of the protrusion 114 converges with the top surface 110 a proximate the trailing edge of the airfoil.
FIGS. 19 and 20 show an airfoil 210 with venturi 212. The venturi 212 are channels that are defined between adjacent protrusions 214. The venturi channels 212 include a leading portion 216, a middle portion 218, and a trailing portion 220. The walls of the adjacent protrusions 214 are curved toward each other in the leading portion 216 of each channel 212, which can have a combination convex concave profile. The walls of protrusions 214 are generally parallel with each other in the middle portion 218 of each channel 212. The walls of the adjacent protrusions 214 are angled away from each other in the trailing portion 220 of each channel 212. The walls of the protrusions 214 in the trailing portion 220 of each channel 212 can either be generally linearly angled away from one another or slightly curved away from one another. The leading portion 216 and the trailing portion 220 of each channel are wider than the middle portion 218. The trailing portion 220 is substantially longer than the leading portion 216 and the middle portion 118. The channel 212 extends along a majority of the chord length of the airfoil. The channel 212 can extend between about 70% and 95% of the chord length. Referring to FIG. 20, the distance between a top surface 222 of the protrusion 214 and the top surface 210 a of the airfoil 210 is greater proximate the leading edge of the airfoil and less proximate the trailing edge of the airfoil. The top surface 222 of the protrusion 214 converges with the top surface 210 a proximate the trailing edge of the airfoil.
FIGS. 21 and 22 show an airfoil 310 with venturi 312. The venturi 312 are channels that are defined between adjacent protrusions 314. The venturi channels 312 include a leading portion 316, a middle portion 318, and a trailing portion 320. The walls of the adjacent protrusions 314 are curved toward each other (following a concave curve portion 317 and a convex curve portion 319) in the leading portion 316 of each channel 312. The concave curve portion 317 is shorter than the convex curve portion 319. The walls of protrusions 314 are generally parallel with each other in the middle portion 318 of each channel 312. The walls of the adjacent protrusions 314 are angled away from each other in the trailing portion 320 of each channel 312. The walls of the protrusions 314 in the trailing portion 320 of each channel 312 can either be generally linearly angled away from one another or slightly curved away from one another. The leading portion 316 and the trailing portion 320 of each channel are wider than the middle portion 318. The trailing portion 320 and the middle portion 318 are about the same length and both are substantially longer than the leading portion 316. The channel 312 extends along a majority of the chord length of the airfoil. The channel 312 can extend between about 70% and 95% of the chord length. Referring to FIG. 22, the distance between a top surface 322 of the protrusion 314 and the top surface 310 a of the airfoil 310 is greater proximate the leading edge of the airfoil and less proximate the trailing edge of the airfoil. The top surface 322 of the protrusion 314 converges with the top surface 310 a proximate the trailing edge of the airfoil.
FIGS. 23-25 show an airfoil 410 with venturi 412 a on the top surface 410 a of the airfoil and a diffuser 412 b on the bottom surface 410 b of the airfoil. The venturi 412 a and diffuser 412 b are channels that are defined between adjacent protrusions 414 a that extend from the top surface 410 a and extend around the leading edge of the airfoil to the bottom surface 410 b to form protrusions 414 b. The venturi channels 412 a on the top surface include a leading portion 416 a, a middle portion 418 a, and a trailing portion 420 a. The walls of the adjacent protrusions 414 a are curved toward each other in the leading portion 416 a of each channel 412 a. The walls of protrusions 414 a are generally parallel with each other in the middle portion 418 a of each channel 412 a. The walls of the adjacent protrusions 414 a are angled away from each other in the trailing portion 420 a of each channel 412 a. The walls of the protrusions 414 a,b in the trailing portion 420 a,b of each channel 412 a,b can either be generally linearly angled away from one another or slightly curved away from one another. The leading portion 416 a and the trailing portion 420 a of each channel are wider than the middle portion 418 a. The leading portion 416 a and the middle portion 418 a are about the same length and the trailing portion 420 a is longer than each of the leading portion 416 a and the middle portion 418 a. The channel 412 a extends along a majority of the chord length of the airfoil. The channel 412 a can extend between about 70% and 95% of the chord length.
Referring to FIG. 24, the diffuser 412 b on the bottom surface 410 b has a different profile than venturi 412 a on the top surface. The diffuser channels 412 b on the bottom surface include a leading portion 416 b, a middle portion 418 b, and a trailing portion 420 b. The walls of the adjacent protrusions 414 a are generally parallel with each other in the leading portion 416 b of each channel 412 b. The walls of protrusions 414 b are curve away from each other in the middle portion 418 b of each channel 412 b. The walls of the adjacent protrusions 414 b are angled away from each other in the trailing portion 420 b of each channel 412 b. The leading portion 416 b is the narrowest part of the channel 412 b. The leading portion 416 b and the middle portion 418 b are about the same length and the trailing portion 420 b is longer than each of the leading portion 416 b and the middle portion 418 b. The channel 412 b extends along a majority of the chord length of the airfoil. The channel 412 b can extend between about 70% and 95% of the chord length.
Referring to FIG. 25, the distance between a top surface 422 a of the protrusion 414 a and the top surface 410 a of the airfoil 410 is greater proximate the leading edge of the airfoil and less proximate the trailing edge of the airfoil. Similarly, the distance between a top surface 422 b of the protrusion 414 b and the bottom surface 410 b of the airfoil 410 is greater proximate the leading edge of the airfoil and less proximate the trailing edge of the airfoil. The top surfaces 422 a and 422 b of the protrusions 414 a and 414 b converge with the top surface 410 a and bottom surface 410 b, respectively, proximate the trailing edge of the airfoil
FIGS. 26 and 27 show an airfoil 510 with venturi channels 512 formed by protrusions 514 that are similar in profile to venturi 312, except that venturi 512 are shorter than venturi 312 such that the leading, middle, and trailing portion of venturi 512 are all disposed on the airfoil leading portion. The channels 512 extend along a less than half majority of the chord length of the airfoil. The channels 512 can extend between about 20% and 45% of the chord length.
FIGS. 28-31 show an airfoil 610 that have diffusers 612 that are formed by indentations in the airfoil surface. As can be seen in FIG. 30, the diffusers 612 do not extend beyond the bottom surface 610b of the airfoil 610. The diffusers 612 are narrow near the leading edge of the airfoil 610 and expands along a divergently curving profile toward the trailing edge. The diffusers 612 extend between about 30% and 60% of the chord length of the airfoil. The walls 613 are generally perpendicular to the surface of the airfoil. The walls of the indentations can have a rounding radius to smooth the transition, e.g., the transition from the top wall to a side wall of an indentation can have a 0.02% radius of rounding.
A number of examples are provided below that illustrate possible dimensions that can be used to construct airfoils with venturi and diffusers. The dimensions are provided assuming an airfoil with a nine inch chord and the dimensions are alternatively provided as a percentage of chord length for airfoils having different chord lengths. These dimensions are only provided as non-limiting examples and variations of these dimensions are contemplated.

EXAMPLE 1

FIG. 32 shows an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 19 and 20 with exemplary dimensions as follows:


		Value	Value
Refer-		for a 9″	as a
ence		chord	percent
No.	Description	airfoil	of chord

1A	Airfoil chord length	9.000	100.00
1B	Distance from airfoil leading edge to start of	0.062	0.69
	venturi Leading Portion
1C	Overall length of venturi	8.422	93.58
1D	Distance from end of venturi Trailing	0.516	5.73
	Portion to airfoil trailing edge
1E	Length of venturi Leading Portion	1.839	20.43
1F	Length of venturi Middle Portion	2.020	22.44
1G	Length of venturi Trailing Portion	4.562	50.69
1H	Width of venturi at start of Leading Portion	0.040	0.44
1I	Width of venturi throughout Middle Portion	0.527	5.86
1J	Width of channel between Middle Portions	0.675	7.50
	of adjacent venturis
1K	Center-to-center distance between adjacent	1.202	13.36
	venturis
1L	Width and Height of venturi at Trailing	0.000	0.00
	Portion
1M	Height of venturi from airfoil surface at the	0.322	3.58
	start of the Leading Portion
1N	Height of venturi from airfoil surface at the	0.200	2.22
	start of the Middle Portion
1O	Height of venturi from airfoil surface at the	0.164	1.82
	start of the Trailing Portion

EXAMPLE 2

FIG. 33 shows an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 21 and 22 with exemplary dimensions as follows:

2A	Airfoil chord length	9.000	100.00
2B	Distance from airfoil leading edge to start of	0.062	0.69
	venturi Leading Portion
2C	Overall length of venturi	8.422	93.58
2D	Distance from end of venturi Trailing	0.516	5.73
	Portion to airfoil trailing edge
2E	Length of venturi Leading Portion	1.091	12.12
2F	Length of venturi Middle Portion	2.768	30.76
2G	Length of venturi Trailing Portion	4.562	50.69
2H	Width of venturi at start of Leading Portion	0.040	0.44
2I	Width of venturi throughout Middle Portion	0.527	5.86
2J	Width of channel between Middle Portions	1.125	12.50
	of adjacent venturis
2K	Center-to-center distance between adjacent	1.652	18.36
	venturis
2L	Width and Height of venturi at Trailing	0.000	0.00
	Portion
2M	Height of venturi from airfoil surface at the	0.322	3.58
	start of the Leading Portion
2N	Height of venturi from airfoil surface at the	0.233	2.59
	start of the Middle Portion
2O	Height of venturi from airfoil surface at the	0.164	1.82
	start of the Trailing Portion

EXAMPLE 3

FIG. 34 shows an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 19 and 20 with similar dimensions to Example 1, except that the distance between adjacent venturi (Ref No. K) is varied, as follows:

3A	Airfoil chord length	9.000	100.00
3B	Distance from airfoil leading edge to start of	0.062	0.69
	venturi Leading Portion
3C	Overall length of venturi	8.422	93.58
3D	Distance from end of venturi Trailing	0.516	5.73
	Portion to airfoil trailing edge
3E	Length of venturi Leading Portion	1.839	20.43
3F	Length of venturi Middle Portion	2.020	22.44
3G	Length of venturi Trailing Portion	4.562	50.69
3H	Width of venturi at start of Leading Portion	0.040	0.44
3I	Width of venturi throughout Middle Portion	0.527	5.86
3J	Width of channel between Middle Portions	1.125	12.50
	of adjacent venturis
3K	Center-to-center distance between adjacent	1.652	18.36
	venturis
3L	Width of venturi at end of Trailing Portion	0.000	0.00
3M	Height of venturi from airfoil surface at the	0.322	3.58
	start of the Leading Portion
3N	Height of venturi from airfoil surface at the	0.200	2.22
	start of the Middle Portion
3O	Height of venturi from airfoil surface at the	0.164	1.82
	start of the Trailing Portion

EXAMPLE 4

FIG. 35 shows an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 26 and 27 with exemplary dimensions as follows:

4A	Airfoil chord length	9.000	100.00
4B	Distance from airfoil leading edge to start of	0.062	0.69
	venturi Leading Portion
4C	Overall length of venturi	2.970	33.00
4D	Distance from end of venturi Trailing	5.968	66.31
	Portion to airfoil trailing edge
4E	Length of venturi Leading Portion	0.613	6.81
4F	Length of venturi Middle Portion	0.449	4.99
4G	Length of venturi Trailing Portion	1.908	21.20
4H	Width of venturi at start of Leading Portion	0.040	0.44
4I	Width of venturi throughout Middle Portion	0.527	5.86
4J	Width of channel between Middle Portions	1.125	12.50
	of adjacent venturis
4K	Center-to-center distance between adjacent	1.652	18.36
	venturis
4L	Width and Height of venturi at Trailing	0.000	0.00
	Portion
4M	Height of venturi from airfoil surface at the	0.283	3.14
	start of the Leading Portion
4N	Height of venturi from airfoil surface at the	0.196	2.18
	start of the Middle Portion
4O	Height of venturi from airfoil surface at the	0.150	1.67
	start of the Trailing Portion

EXAMPLE 5

FIG. 36 shows an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 17 and 18 with exemplary dimensions as follows:

5A	Airfoil chord length	9.000	100.00
5B	Distance from airfoil leading edge to start of	0.062	0.69
	venturi Leading Portion
5C	Overall length of venturi	8.364	92.93
5D	Distance from end of venturi Trailing	0.574	6.38
	Portion to airfoil trailing edge
5E	Length of venturi Leading Portion	1.839	20.43
5F	Length of venturi Middle Portion	5.597	62.19
5G	Length of venturi Trailing Portion	0.928	10.31
5H	Width of venturi at start of Leading Portion	0.040	0.44
5I	Width of venturi throughout Middle Portion	0.527	5.86
5J	Width of channel between Middle Portions	1.125	12.50
	of adjacent venturis
5K	Center-to-center distance between adjacent	1.652	18.36
	venturis
5L	Width of venturi at end of Trailing Portion	0.040	0.44
5M	Height of venturi from airfoil surface at the	0.322	3.58
	start of the Leading Portion
5N	Height of venturi from airfoil surface at the	0.200	2.22
	start of the Middle Portion
5O	Height of venturi from airfoil surface at the	0.092	1.02
	start of the Trailing Portion
5P	Height of venturi from airfoil surface at the	0.031	0.34
	end of the Trailing Portion

EXAMPLE 6

FIGS. 37 and 38 show an example of an airfoil with venturi that have a profile that corresponds to the airfoil illustrated in FIGS. 23-25 with exemplary dimensions as follows:

6A	Airfoil chord length	9.000	100.00
6B	Distance from leading edge of venturi to	0.400	4.44
	leading edge of airfoil
6C	Length of lower venturi Trailing Portion	7.972	88.58
6D	Distance from end of venturi Trailing	0.574	6.38
	Portion to airfoil trailing edge
6E	Length of upper venturi Leading Portion	2.513	27.92
6F	Length of upper venturi Middle Portion	1.786	19.84
6G	Length of upper venturi Trailing Portion	4.527	50.30
6H	Width of venturi at leading edge	1.155	12.83
6I	Width of venturi throughout Middle Portion	1.798	19.98
6J	Width of channel between Middle Portions	1.506	16.73
	of adjacent venturis
6K	Center-to-center distance between adjacent	3.304	36.71
	venturis
6L	Width of venturi at end of Trailing Portion	0.000	0.00
6M	Height of venturi from airfoil surface at the	0.319	3.54
	start of the lower Trailing Portion
6N	Height of venturi from airfoil surface at the	0.209	2.32
	start of the upper Middle Portion
6O	Height of venturi from airfoil surface at the	0.196	2.18
	start of the upper Trailing Portion
6P	Length of lower venturi Leading Portion	0.854	9.49

EXAMPLE 7

FIG. 39 shows an example of an airfoil with diffusers that have a profile that corresponds to the airfoil illustrated in FIGS. 28-31 with exemplary dimensions as follows:

7A	Airfoil chord length	9.000	100.00
7B	Distance from airfoil leading edge to start of	0.362	4.02
	cavity
7C	Length of cavity	4.438	49.31
7D	Distance from end of cavity to airfoil trailing	4.200	46.67
	edge
7E	Width of cavity at exit	2.642	29.36
7F	Width of cavity at entrance	1.352	15.02
7G	Distance from airfoil leading edge	1.000	11.11
7H	Distance from airfoil leading edge	2.000	22.22
7I	Distance from airfoil leading edge	3.000	33.33
7J	Depth of cavity 1.0 inch from airfoil leading	0.080	0.89
	edge
7K	Depth of cavity 2.0 inches from airfoil	0.109	1.21
	leading edge
7L	Depth of cavity 3.0 inches from airfoil	0.079	0.88
	leading edge
	Center-to-center spacing between cavities	2.642	29.36

While the invention has been described in connection with a certain embodiment and variations thereof, the invention is not limited to the described embodiment and variations but rather is more broadly defined by the recitations in the claims below and equivalents thereof.

Claims

What is claimed is:

1. An airfoil for a vehicle, comprising:

a top surface extending between a leading edge and a trailing edge on a top side of the airfoil and defining a chord length therebetween;

a bottom surface extending between the leading edge and the trailing edge on a bottom side of the airfoil;

a plurality of protrusions on the top surface of the air foil, wherein two adjacent protrusions define a channel therebetween that extends in the direction of the chord length;

wherein each channel has a leading portion, a middle portion, and a trailing portion, the channel being sized and shaped such that the leading portion and the trailing portion are wider than the middle portion.

2. An airfoil of claim 1, wherein each channel extends along a majority of the top surface in the direction of the chord length.

3. An airfoil of claim 1, wherein the length of the leading portion of each channel is shorter than the middle portion in the direction of the chord length.

4. An airfoil of claim 3, wherein the length of the trailing portion of each channel is longer than the middle portion in the direction of the chord length.

5. An airfoil of claim 1, wherein each channel extends along less than half of the top surface in the direction of the chord length.

6. An airfoil of claim 1, wherein the walls of adjacent protrusions converge along a curved trajectory to define the leading portion of each channel.

7. An airfoil of claim 1, wherein the walls of adjacent protrusions diverge along a generally linear trajectory to define the trailing portion of each channel.

8. An airfoil of claim 1, wherein the walls of adjacent protrusions extend generally parallel to each other to define the middle portion of each channel.

9. An airfoil of claim 1, wherein distance between a top surface of each protrusion and the top surface of the airfoil defines a depth of each channel, and the depth of each channel is greater in the leading portion than the middle portion and the trailing portion.

10. An airfoil of claim 1, wherein each protrusion extends around the leading edge to the bottom surface of the airfoil such that adjacent protrusions form channels on the bottom surface of the airfoil.

11. An airfoil for a vehicle, comprising:

a plurality of indentations on the bottom surface of the air foil each defining a channel, wherein

each indentation has a leading portion and a trailing portion, the channel being sized and shaped such that the trailing portion is wider than the leading portion.