Vortex generator

Abstract

The present application relates to a kind of vortex generators, the vortex generator includes first curved surface S1, second curved surface S2 and reference plane S3;First curved surface S1 is determined shape by first curve COB, second curve BAC and first symmetry line OA, second curved surface S2 is determined shape by second curve BAC, third curve BDC, wherein first curve COB is elliptic curve, second curve BAC is cosine curve, and third curve BDC is parabola.Relative to traditional vortex generator, it can maximize the turbulent airflow of the surface of vehicle into laminar flow, effectively reduce the resistance of vehicle movement.

Description

Technical Field

[0001] This invention relates to an eddy current generator, particularly an eddy current generator suitable for aircraft and submarines. Background Technology

[0002] In many moving devices such as high-speed aircraft (e.g., airplanes, missiles), underwater vehicles (e.g., submarines), high-speed trains, and wind turbine blades, vortex generators are used to induce vortices to disrupt the fluid boundary layer. Existing vortex generators typically have multiple turbulence-inducing blades arranged on the surface of the device, forming a figure-eight shape (e.g., JP2023044715A), or introduce fluid into the vortex generator to generate oscillations, thereby transforming the jet into vortices (e.g., CN216301451U). These technologies can only delay flow separation at solid walls and cannot produce drag reduction. The main reason is that the traditional vortex generator itself, placed in the flow field, increases drag significantly. Furthermore, the vorticity vector of the generated vortices has insufficient components in the flow direction, resulting in limited drag reduction. The combination of these factors often leads to an increase in overall drag. In addition, CN216301451U uses an active jet method to generate vortices, causing additional energy consumption and increasing the difficulty of flow control. Under the condition of delaying separation and achieving the same drag reduction effect, passively controlled vortex generators are more advantageous. Summary of the Invention

[0003] This invention provides an eddy current generator, which includes a first curved surface S1, a second curved surface S2, and a reference plane S3; the first curved surface S1 and the second curved surface S2 are located above the reference plane S3; the reference plane is parallel to the incoming flow direction, which is the x-direction; the direction perpendicular to the reference plane and containing the first curved surface S1 and the second curved surface S2 is the z-direction; and the direction perpendicular to the x-direction and the z-direction is the y-direction.

[0004] With the foremost point of the vortex generator facing the incoming flow as the origin, coordinate axes are formed in the x, y, and z directions respectively, and a rectangular coordinate system is established. The reference plane S3 is the plane containing the x and y coordinate axes.

[0005] The shape of the first surface S1 is defined by the first curve COB, the second curve BAC, and the first line of symmetry OA, where point O is the origin of the coordinate system.

[0006] The first curve COB is a semi-elliptic curve, with C, O, and B being the three vertices of the ellipse. The first curve COB lies on the reference plane S3, and its equation is:

[0007]

[0008] wherein, L is the distance from the foremost end point O to the rearmost end point of the first curve S1 in the incoming flow direction, that is, the length; W is the distance between the two end points B and C of the first curve S1 in the direction perpendicular to the incoming flow direction on the reference plane, that is, the width;

[0009] The point A of the second curve BAC is located above the reference plane, and the points B and C are located on the reference plane. The vertical projection of the second curve BAC on the reference plane is a half-cycle cosine curve BA'C, and the equation of the cosine curve is:

[0010] x=(L1-L)cosπy / W+L

[0011] wherein, point A' is the projection of point A on the reference plane, and L1 is the distance between point O and point A';

[0012] The point O of the first curve and the point A of the second curve are both located on the plane defined by the x coordinate axis and the z coordinate axis. The first symmetry line OA is a quarter cosine curve, which is determined by the following equation:

[0013]

[0014] wherein H is the vertical height from point A of the second curve to the reference plane S3;

[0015] The second curved surface S2 is a symmetrical smooth curved surface as a whole, and its shape is determined by the above-mentioned second curve BAC, third curve BDC and second symmetry line AD, wherein the first curved surface S1 is connected with the second curved surface S2, and the connecting line is the above-mentioned second curve BAC;

[0016] The second symmetry line AD is a straight line, the third curve BDC is located on the reference plane and is a half parabola, D is the vertex of the parabola, which is determined by the following equation:

[0017]

[0018] wherein L2 is the distance between point D of the third curve and point A', which is the projection of point A of the second curve BAC on the reference plane.

[0019] Further, 0.3 < L / W < 2.5, α=tan<0x200b>-1(H / L1) is defined to represent the windward angle, 5° < α < 30°, β=tan -1 (H / L2) is defined to represent the leeward angle, 25° < β < 40°.

[0020] Further, the vortex generator is arranged on the surface of a vehicle, and the z direction is the normal direction pointing outward from the surface of the vehicle. Alternatively, the vortex generator is arranged on the surface of a vehicle, and the z direction is the direction opposite to the outward direction of the vehicle surface, 5° < α < 15°.

[0021] The present invention also provides a design method for the above-mentioned eddy current generator, comprising the following steps:

[0022] S1: Arrange the surface dimensions of the vortex generator as needed, and determine the size of the vortex generator and the windward angle α and leeward angle β; the size of the vortex generator is the length L, width W and height H mentioned above.

[0023] S2: According to the equation Determine the shape of the first curve COB;

[0024] S3: Based on the windward angle α and height H, determine L1 = H / tanα, and based on the equation x = (L1 - L)cossπy / W + L, determine the shape of the second curve BAC. Determine the first line of symmetry OA, and then determine the shape of the first surface S1;

[0025] S4: Based on the lee angle β and height H, determine L2 = H / tanβ, and then apply the equation... The shape of the third curve BDC is determined, and the shape of the second surface S2 is determined by combining the second curve BAC and the third curve BDC.

[0026] This invention utilizes a semi-elliptical curve to form the first curve, a semi-parabolic curve to form the third curve, and a cosine curve to design a symmetrical curve and a combined curve (the second curve), thus designing a specially structured vortex generator. Compared to traditional vortex generators, it can maximize the conversion of turbulent airflow on the surface of the aircraft into laminar flow, effectively reducing the aircraft's motion drag. In this invention, the vortex generator has two arrangement forms on the surface of the aircraft: (1) protruding from the surface of the aircraft, i.e., the first curved surface and the second curved surface are located outside the aircraft; (2) embedded in the surface of the aircraft, i.e., a recess is designed on the surface of the aircraft, and the boundary surface of the recess is formed according to the shape of the first curved surface and the second curved surface. Attached Figure Description

[0027] Figure 1 This is a three-dimensional structural schematic diagram of the eddy current generator of the present invention;

[0028] Figure 2 This is a top view of the eddy current generator of the present invention;

[0029] Figure 3 This is a cross-sectional view of the eddy current generator of the present invention;

[0030] Figure 4A This is a schematic diagram of the vortex generator of the present invention arranged on the DLR-F4 wing-body aircraft.

[0031] Figure 4BIt represents the change in lift coefficient under different angles of attack;

[0032] Figure 4C It represents the change in drag coefficient under different angles of attack;

[0033] Figure 4D It represents the change in lift-to-drag ratio under different angles of attack;

[0034] Figure 5 This is a schematic diagram of the vortex generator of the present invention recessed on the surface of the aircraft;

[0035] Figure 6A This is a diagram showing the shear stress distribution on the missile surface when no eddy current generator is installed.

[0036] Figure 6B This is a diagram showing the shear stress distribution on the rear wall surface of the missile after the eddy current generator of this invention is installed.

[0037] Figure 6C It is a comparison of the friction coefficient calculation process with and without eddy current generators on the missile surface;

[0038] Figure 7A This is a friction coefficient distribution diagram when the eddy current generator of this invention is arranged on the surface of a submarine;

[0039] Figure 7B This is a friction coefficient distribution diagram of a submarine surface without vortex generators.

[0040] Figure 7C This is a comparison of the calculation process for the friction coefficient on the surface of a submarine with and without eddy current generators. Detailed Implementation

[0041] For ease of description, in the following text, "front" and "back" are distinguished according to the direction of fluid flow. The fluid flows from "front" to "back", marked by the x-axis in the three-dimensional coordinate system. The reference plane is parallel to the direction of fluid flow and perpendicular to the reference plane. The direction where the first and second curved surfaces are located is "up", marked by the z-axis. The direction perpendicular to the plane formed by the x-axis and y-axis is the z-axis.

[0042] See Figure 1-3 The eddy current generator of the present invention includes a first curved surface S1, a second curved surface S2, and a reference plane S3.

[0043] The first curved surface S1 is a symmetrical smooth curved surface as a whole, and its shape is determined by the symmetrical first curve COB, the second curve BAC and the first symmetry line OA. The two end points of the first curve COB and the second curve BAC coincide respectively (the coincidence points are B and C). The second curve BAC is located behind the first curve BOC, the connecting line between the foremost end point O of the first curve and the foremost end point A of the second curve is the first symmetry line OA, the first symmetry line OA is a curve, and the projection OA' of the first symmetry line OA on the reference plane coincides with the x-axis.

[0044] The first curve COB is a semi-elliptical curve;

[0045] The equation thereof is:

[0046]

[0047] wherein L is the distance from the foremost end point O of the first curve to the rearmost end point (B or C) in the incoming flow direction, that is 1 / 2 of the major axis of the ellipse; W is the distance between the two end points B and C of the first curve in the direction perpendicular to the incoming flow direction on the reference plane, that is the minor axis of the ellipse.

[0048] wherein 0.3<L / W<2.5. This ratio directly affects the downwind extension angle of the device, and this angle is affected by incoming flow conditions, which is basically consistent with barchan dunes in nature. When L / W is large, the dune presents a relatively narrow and long shape. In this case, the dune rises rapidly on the windward side and slides slowly on the leeward side, forming an obvious arc; airflow generates streamwise vortices on the device, and this shape is similar to traditional vortex generators in terms of profile. When the incoming flow velocity is higher, the flow Reynolds number is higher, the generated differential pressure force is larger, the intensity of the generated streamwise vortex is stronger, and the drag reduction effect is more obvious. When L / W is small, the device presents a relatively wide shape. In this case, the ascending angle of the windward side and the inclination angle of the leeward side are relatively gentle. When the incoming flow velocity is lower and the flow Reynolds number is lower, a better drag reduction effect can be obtained.

[0049] The vertical projection BA'C of the second curve BAC on the reference plane is a half-cycle cosine curve, and the equation thereof is:

[0050] x=(L1-L)cosπy / W+L (2)

[0051] wherein L1 is the distance between the foremost point O of the first curve and the projection A' of the foremost point A of the second curve on the reference plane.

[0052] wherein 0.1<L1 / L<0.8. When L1 / L is small, the length of the windward slope is short, the vortex generation area is smaller, the vortex tube is smaller, the streamwise vortex intensity is lower, the vortex is difficult to maintain stably, the effect of suppressing turbulence deteriorates, but at the same time, the overall device is relatively gentle, which can reduce the shape drag of the device itself exposed to the air; on the contrary, the larger the vortex generation area, the higher the streamwise vortex intensity, and the stronger the suppression effect of the streamwise vortex on turbulence, but it will additionally increase the shape drag. Therefore, it is necessary to maintain this ratio in a suitable range.

[0053] See Figure 3 , the projection of the first symmetry line OA on the xz plane is a quarter cosine curve, which is determined by the following equation:

[0054]

[0055] wherein, H is the vertical distance between the foremost point A of the second curve and the reference plane S3. α=tan-1(H / L1) is defined to represent the windward angle, and the range of α is 5-30°. A certain windward angle α is set to generate a leeward low-pressure (negative pressure) area with a sufficient range; the leeward low-pressure area and the high-pressure fluid on the windward side converge at the "swallowtail" section and rub out a streamwise vortex with sufficient intensity. When α<5°, the leeward area is too small to generate sufficiently strong negative pressure, which leads to failure to generate sufficiently strong streamwise vortex, and turbulence cannot be eliminated for drag reduction in the downstream if the streamwise vortex index cannot meet the requirement; when α>20°, although the leeward area can generate strong negative pressure, the benefit of increasing the angle to improve negative pressure weakens or even disappears (especially in the case of high-speed incoming flow), the drag reduction benefit of eliminating turbulence in the downstream is almost unchanged, while an excessively large windward angle will make the vortex generator too high, resulting in too much increase in induced drag generated by the vortex generator itself, which is not worth the loss.

[0056] the second curved surface S2 is also a symmetrical smooth curved surface on the whole, and its shape is determined by the above-mentioned second curve BAC, the third curve BDC and the second symmetry line AD. Wherein the first curved surface S1 is connected with the second curved surface S2, and the connecting line is the second curve BAC; the foremost point D of the third curve BDC is located on the reference plane S3 and on the x-axis. The third curve is a semi-parabola; the second symmetry line AD is a straight line.

[0057] See Figure 2 , the third curve BDC is determined by the following equation:

[0058]

[0059] wherein L2 is the distance between the projection point A' of the foremost point A of the second curve BAC on the reference plane S3 and the foremost point D of the third curve BDC.

[0060] β is defined as tan -1(H / L2) represents the lee angle, and β ranges from 25 to 40°.

[0061] See Figure 1 When the airflow passes over the surface S1 of the object, the fluid is obstructed by the surface and a local high-pressure area is formed on the windward side. When the fluid passes over the surface S2, the airflow pressure gradually decreases as the flow cross-section gradually expands, thus forming a pressure difference between the windward and leeward areas. In the tail area of ​​the vortex generator (such as points B and C), the fluid forms a continuous flow vortex under the action of the pressure difference. The flow vortex inhibits the occurrence of turbulence (maximizing the laminar flow range). The frictional resistance of turbulence is much greater than that of laminar flow, so the downstream flow remains laminar, thereby reducing frictional resistance. As a result, the overall resistance of the vehicle also decreases.

[0062] Figure 4A This is a schematic diagram of the vortex generator of the present invention arranged on a DLR-F4 wing-body aircraft. Multiple vortex generators are arranged on the wing, and the vortex generators protrude from the wing surface. Figure 4B The figure shows a comparison of the lift coefficient at different angles of attack. It can be seen from the figure that after adding the vortex generator, the lift increases at all angles of attack except 0°. The increase in lift becomes more and more obvious as the angle of attack increases, with the largest increase of 12.1% at an angle of attack of 3°. Figure 4C The figure compares the drag coefficients at different angles of attack. It can be seen from the graph that after installing the eddy current generator, the drag increases slightly at small angles of attack and decreases at large angles of attack. Furthermore, the rate of change of the drag coefficient with the angle of attack after installing the eddy current generator shows a significant decreasing trend. In summary, the eddy current generator has a significant drag reduction capability at large angles of attack, and the drag reduction effect becomes more significant as the angle of attack increases. Figure 4D The figure shows the trend of lift-to-drag ratio under different angles of attack. As can be seen from the figure, the lift-to-drag ratio is significantly improved when the angle of attack is 2-5° compared with that without the eddy current generator.

[0063] Therefore, it is evident that adding vortex generators to the wing surface generates small vortices on the wing-body assembly surface, increasing boundary layer energy and stabilizing the flow field to suppress airflow separation. At low angles of attack, lift increases while drag also increases, so the lift-to-drag ratio does not significantly improve compared to when the generator is not installed. As the angle of attack increases, lift increases rapidly while drag increases more steadily, resulting in a higher lift-to-drag ratio. This means that the wing-body assembly at this point has better aerodynamic performance, is more conducive to climb, and also improves the aircraft's fuel efficiency, helping to reduce energy consumption and environmental pollution.

[0064] It should be noted that when the vortex generator is arranged on the surface of an air wing or other aircraft, the surface of the aircraft is generally curved. In this case, the reference plane in this invention is the projection of the surface of the aircraft at the location of the vortex generator onto the horizontal plane. The edge of the first curved surface naturally extends (for example, along the tangent direction of the edge) to the surface of the aircraft, and the edge of the second curved surface also naturally extends to the surface of the aircraft, so that the vortex generator fits into the surface of the aircraft and forms a closed surface.

[0065] Furthermore, the vortex generator of the present invention can also embed the first and second curved surfaces into the interior of the aircraft surface, i.e., an embedded type. This is equivalent to designing a recess on the original aircraft surface, the shape of which is equivalent to the vortex generator being placed in reverse as described above; when placed in reverse, the boundary of the recess is formed according to the shapes of the first and second curved surfaces. If the aircraft surface is flat, then the plane is the reference plane, and the recess is entirely composed of the first and second curved surfaces; if the aircraft surface is curved, then the reference plane is tangent to the original aircraft surface, and the recess is formed according to the shapes of the first and second curved surfaces. In this case, the boundary of the recess is a portion of the first and second curved surfaces, specifically determined by the curvature of the aircraft surface.

[0066] See Figure 5 The "upper" orientation of the vortex generator refers to the direction extending from the surface of the aircraft inwards. With this structure, when the vortex generator is externally placed on an object, it generates directional vortices under the influence of the high-pressure area on the windward side and the low-pressure area on the leeward side. These directional vortices suppress turbulence (maintaining the laminar flow region to the maximum extent), thus achieving low drag. When the vortex generator is embedded inside the aircraft, forming a groove, a pressure difference is created between the interior of the groove and the outer surface of the aircraft. On one hand, the airflow forms directional vortices under the pressure difference, which further suppresses turbulence and reduces drag. On the other hand, embedding the vortex generator inwards in the opposite direction eliminates the pressure drag caused by the addition of a convex vortex generator, further achieving drag reduction. For the embedded structure, the preferred windward angle α is 5-15°.

[0067] See Figures 6A-6C The image shows the configuration of the vortex generator of the present invention on a Pershing II missile. Three vortex generators are evenly arranged axially on the circumferential surface at the missile's nose, with an incoming flow Mach number of 5, during flight at an altitude of 20 kilometers. Figures 6A-6B In the wall shear stress cloud diagram, the darker the color, the smaller the surface friction, and vice versa. Figure 6A It can be seen that the transition from laminar to turbulent flow in the mid-course phase of the missile occurs at approximately the 20% mark, and the frictional resistance after the transition is relatively high (lighter in color). Figure 6BAs can be seen, after adding the eddy current generator, the downstream flow is almost entirely laminar, corresponding to lower surface friction (darker color). Clearly, the addition of the eddy current generator suppresses turbulence and significantly reduces frictional resistance. See also... Figure 6C The drag coefficient of the prototype (without the eddy current generator) is 3.1692e-2, while the drag coefficient after adding the eddy current generator is 2.9077e-2, achieving a drag reduction effect of 8.25%.

[0068] See Figures 7A-7C This is a schematic diagram of the vortex generator of the present invention arranged on a submarine. When the submarine speed is 12 knots, after installing the vortex generator, the surface flow downstream of the vortex generator is almost entirely laminar (see [reference]). Figure 6A The drag reduction effect is as high as 38.12%.

[0069] The design process of the eddy current generator of the present invention is as follows:

[0070] Based on the surface dimensions required for the placement of the vortex generator on the aircraft, determine the size of the vortex generator (i.e., length L, width W, and height H), as well as the angle of attack α and the angle of leeward β.

[0071] The shape of the first curve COB is determined according to equation (1); L1 is determined according to the windward angle α and the height H; the shape of the second curve BAC is determined according to equation (2); the first symmetry line OA is determined according to equation (3); and the shape of the first surface S1 is determined.

[0072] Based on the lee angle β and the height H, determine L2, determine the shape of the third curve BDC according to equation (4), and combine the second curve BAC and the third curve BDC to determine the shape of the second surface S2.

[0073] When making specific arrangements, the vortex generator is fully integrated with the aircraft, depending on its arrangement (protruding from or recessed into the surface of the aircraft) and the shape of the aircraft's surface.

[0074] The present invention also provides a vehicle having a plurality of the aforementioned vortex generators on its surface, the vehicle being a missile, submarine, aircraft, automobile, etc.

[0075] This invention utilizes a semi-elliptical curve to form the first curve, a semi-parabolic curve to form the third curve, and a cosine curve to design a symmetrical curve and a combined curve (the second curve), thus designing a specially structured vortex generator. Compared to traditional vortex generators, it can maximize the conversion of turbulent airflow on the surface of the aircraft into laminar flow, effectively reducing the aircraft's motion drag. In this invention, the vortex generator has two arrangement forms on the surface of the aircraft: (1) protruding from the surface of the aircraft, i.e., the first curved surface and the second curved surface are located outside the aircraft; (2) embedded in the surface of the aircraft, i.e., a recess is designed on the surface of the aircraft, and the boundary surface of the recess is formed according to the shape of the first curved surface and the second curved surface.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An eddy current generator, characterized in that, The eddy current generator includes a first curved surface S1, a second curved surface S2, and a reference plane S3; the first curved surface S1 and the second curved surface S2 are located above the reference plane S3; The reference plane is parallel to the incoming flow direction, which is the x-direction; the direction perpendicular to the reference plane and containing the first surface S1 and the second surface S2 is the z-direction; the direction perpendicular to the x-direction and the z-direction is the y-direction. With the foremost point of the vortex generator facing the incoming flow as the origin, coordinate axes are formed in the x, y, and z directions respectively, and a rectangular coordinate system is established. The reference plane S3 is the plane containing the x and y coordinate axes. The shape of the first surface S1 is defined by the first curve COB, the second curve BAC, and the first line of symmetry OA, where point O is the origin of the coordinate system. The first curve COB is a semi-elliptic curve, with C, O, and B being the three vertices of the ellipse. The first curve COB lies on the reference plane S3, and its equation is: Where L is the length from the foremost point O to the last endpoint of the first curve COB in the direction of the incoming flow, and W is the distance between the two endpoints B and C of the first curve COB in the direction perpendicular to the direction of the incoming flow on the reference plane, which is also the width. Point A of the second curve BAC is located above the reference plane S3, and points B and C are located on the reference plane. The vertical projection of the second curve BAC onto the reference plane is a half-period cosine curve BA'C, and the equation of this cosine curve is: Where A' is the projection of point A onto the reference plane S3, and L1 is the distance between point O and point A'. Point O of the first curve and point A of the second curve both lie on the plane defined by the x-coordinate axis and the z-coordinate axis. The first line of symmetry OA is a quarter-cosine curve, which is determined by the following equation: Where H is the vertical height from point A of the second curve to the reference plane S3; The second surface S2 is a symmetrical and smooth surface as a whole, and its shape is determined by the second curve BAC, the third curve BDC and the second symmetry line AD. The first surface S1 and the second surface S2 are connected by the second curve BAC. The second line of symmetry, AD, is a straight line. The third curve, BDC, lies on the reference plane and is a semi-parabola. Point D is the vertex of the parabola, which is determined by the following equation: Where L2 is the distance between point D of the third curve and point A' of the second curve BAC projected onto the reference plane.

2. The eddy current generator according to claim 1, characterized in that, 0.3<L / W<2.5, α is defined as tan -1 (H / L1) represents the windward angle, 5°<α<30°, β is defined as tan -1 (H / L2) represents the leeward angle, 25°<β<40°.

3. The eddy current generator according to claim 2, characterized in that, The vortex generator is arranged on the surface of the vehicle, with the z-direction being the normal direction of the vehicle surface outward.

4. The eddy current generator according to claim 2, characterized in that, The vortex generator is arranged on the surface of the vehicle, and the z-direction is the direction opposite to the normal direction of the surface of the vehicle to the outside.

5. The eddy current generator according to claim 4, characterized in that, 5°<α<15°。 6. A design method for an eddy current generator as described in any one of claims 2-5, characterized in that, Includes the following steps: S1: Arrange the surface dimensions of the vortex generator as needed, and determine the size of the vortex generator, as well as the windward angle α and the leeward angle β; the size of the vortex generator is the length L, width W and height H mentioned above. S2: According to equation Determine the shape of the first curve COB; S3: Based on the windward angle α and the height H, determine L1 = H / tanα, and then use the equation... Determine the shape of the second curve BAC according to the equation. Determine the first line of symmetry OA, and then determine the shape of the first surface S1; S4: Based on the lee angle β and height H, determine L2 = H / tanβ, and then apply the equation... The shape of the third curve BDC is determined, and the shape of the second surface S2 is determined by combining the second curve BAC and the third curve BDC.

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