DEVICE FOR GENERATING VORTICES IN CHANNELS OR PIPES

Abstract

A vortex generator device in channels or ducts that makes it possible to take advantage of the wingtip vortex that is formed in the aerodynamic profiles as a consequence of having a finite wingspan. These aerodynamic profiles have one or two marginal edges from which the wingtip vortex emerges, causing the appearance of an oscillatory movement that subjects the particles that travel with the current to an ascending-descending cycle, and has the fundamental advantage that transverse speeds are produced to the main current, with hardly any pressure drops.

Claims

1. A vortex generator device in channels or ducts comprising: at least one channel or conduit through which a fluid circulates comprising a kinematic viscosity and an average speed of the fluid in the channel or conduit, where the channel or conduit comprises at least two walls and a bottom, at least one fin or aerodynamic profile where the fluid impacts, which in turn comprises a face on which overpressures are produced due to the incidence of the fluid, or high-pressure face, and a face on which there are depressions with respect to the overpressures in the high-pressure face, or low-pressure face, and a maximum chord, wherein the at least one fin or aerodynamic profile is fixed to one of the at least two walls or to the bottom of the channel or duct by means of an edge opposite a marginal edge of the fin or aerodynamic profile, or is fixed to a first solid structure, the solid structure comprising: an angle of attack of said fin or aerodynamic profile between −20° and 20°; a ratio of a sum of the surface of the high-pressure face and the low-pressure face of the fin or aerodynamic profile over the square of its maximum chord is less than 8, and a distance from the marginal edge of the fin or aerodynamic profile to one of the at least two walls or to the bottom of the channel or duct, whichever is the minimum, is greater than a result of multiplying 10000 by a kinematic viscosity of the fluid and divided by an average speed of the fluid in the channel or conduit.

2. The vortex generator device in channels or ducts according to claim 1, wherein the channel or duct comprises a hydraulic diameter and also the distance from the marginal edge of the fin or aerodynamic profile to the first structure solid or a second solid structure is greater than the hydraulic diameter of the channel or conduit divided by 20.

3. The vortex generator device in channels or ducts according to claim 1, wherein the channel or duct comprises an axis and a cross section, where the ratio between an area of the projection of the at least one fin or profile aerodynamic on a plane perpendicular to the direction of the axis of the channel or conduit and the cross-sectional area of the channel or conduit is less than 0.5.

4. The vortex generator device in channels or ducts according to claim 1, wherein the at least one fin or airfoil comprises a root where the at least one fin or airfoil comprises an angle of attack increasing from its root towards the marginal edge.

5. The vortex generator device in channels or ducts according to claim 1, wherein the at least one fin or aerodynamic profile has, in one of its longitudinal sections, a maximum camber between the 25% and 75% of its maximum chord.

6. The vortex generator device in channels or ducts according to claim 1, wherein the marginal edge of the at least one fin or aerodynamic profile comprises a radius of curvature and the at least one fin or aerodynamic profile comprises an average thickness, where an average value of the radius of curvature of the marginal edge is greater than the average thickness of said fin or aerodynamic profile.

7. A method of agitation in channels and ducts comprising generating vortices in channels or ducts by means of the vortex generating device of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows a perspective view of a rectangular section channel or conduit with the vortex generating device in channels or conduits of the present invention anchored to one of the walls of a conduit. The leading edge, trailing edge and marginal edge of the fin are shown, as well as the generated wingtip vortex.

[0034] FIG. 2 shows a longitudinal section of the vortex generating device in channels or ducts of the present invention where the angle of attack is indicated in relation to the direction of the incident current, the chord and the maximum camber for that longitudinal section of said device.

[0035] FIG. 3 shows a longitudinal section of the vortex generating device in channels or conduits of the present invention where the typical pressure distribution on the high and low pressure faces of said device is shown.

[0036] FIG. 4 shows a cross section of the vortex generating device in channels or conduits of the present invention where the pressure distribution on the high and low pressure faces of said device and the edge current are shown.

[0037] FIG. 5 shows a perspective view of a channel or duct of rectangular section with the device of the present invention anchored to one of the walls, where the cross section of the channel or duct and the projection of the device in the direction of the main current on a plane perpendicular to the axis of the duct is shown.

PREFERRED EMBODIMENT OF THE INVENTION

[0038] The references used in the figures of the vortex generator device in channels or ducts of the present invention, which will be explained in detail below, are the following:

[0039] 1: flow with a direction essentially parallel to the walls of the duct or channel.

[0040] 2: channel or duct wall.

[0041] 3: bottom of the canal or duct.

[0042] 4: wingtip vortex generated by the profile.

[0043] 5: fin or aerodynamic profile.

[0044] 6: leading edge.

[0045] 7: trailing edge.

[0046] 8: marginal edge.

[0047] 9: angle of attack.

[0048] 10: chord.

[0049] 11: maximum sag.

[0050] 12: high-pressure face.

[0051] 13: low-pressure face.

[0052] 14: edge current.

[0053] 15: b.

[0054] 16: h.

[0055] 17: Ap.

[0056] The behavior of a fuselage profile immersed in a fluid current is very well described by its applications in aeronautical engineering. The most important aerodynamic characteristics of a profile are its coefficient of lift, CL, and its coefficient of aerodynamic drag, CD, defined as

[00003]$\begin{array}{cc}{C}_L=\frac{L}{\frac{1}{2}\rho v^{2}S}y& \left(1\right)\\ C_D=\frac{D}{\frac{1}{2}\rho v^{2}S},& \left(2\right)\end{array}$

[0057] where L and D are, respectively, the lift forces and aerodynamic drag on the profile and S is the wing surface.

[0058] These two coefficients vary as a function of the Reynolds number, although it is generally sufficient to consider the asymptotic values for very high Reynolds numbers in fully developed turbulence. In addition, the coefficients also vary depending on the angle of attack of the fin or aerodynamic profile. When the boundary layer on the profile is adhered and the wake that emerges from the trailing edge is very narrow, the coefficient of aerodynamic resistance, CD, is much less than unity, since in this case the losses are produced by friction with profile walls, a generally negligible effect at high Reynolds numbers. In the same situation, the lift coefficient CL, is usually of unit order, presenting an increasing dependence with the angle of attack, until for a certain critical angle the so-called lift crisis occurs, in which the boundary layer on the low-pressure face detaches before reaching the trailing edge. From that angle, the lift of the aerodynamic profile decreases sharply as the angle of attack increases as a result of the detachment of the boundary layer and a lower pressure difference between the high-pressure face (overpressure face) and the low-pressure face (depression). To achieve higher lift values, profiles with a certain thickness and curvature can be used, which allows the boundary layer not to detach at higher angles of attack.

[0059] As explained above, to increase the intensity of the wingtip vortex that occurs on a profile, it is convenient that the pressure difference between the high-pressure and the low-pressure face be high along the entire chord of the fin or aerodynamic profile. As a consequence of the aforementioned, the aerodynamic profile should work with high angles of attack, but without reaching the critical value in which the lift crisis occurs due to the detachment of the boundary layer.

[0060] The type of vortex that emerges from the marginal edge of the fin or airfoil can be modeled as a cylindrical vortex, which in the case of a channel or conduit stream would have an axis essentially parallel to the axis of the same channel or conduit.

[0061] In specialized literature, cylindrical vortex models such as the Rankine vortex or the Burgers vortex are often used (Dávila J. & Hunt J. C. R. 2001, Settling of small particles near vortices and in turbulence. J. Fluid Mech. 440, 117-145). These models describe a dependence of the azimuth velocity (around the vortex axis) as a function of the distance from the vortex axis.

[0062] The most important parameters of cylindrical vortices are their viscous radius, Rv, and the circulation of the vortex. The first of these parameters determines the distance to the vortex axis at which the azimuth velocity is maximum. When the Reynolds number is high, the viscous radius is very small (typically on the order of one millimeter) and the vortex circulation is approximately constant. From the point of view of agitation, it is important that the circulation of the vortex is high, which is closely related to high values of the lift coefficient of the fin or aerodynamic profile and the angle of attack.

[0063] The technical problem solved by the present invention is to favor the agitation of an essentially parallel stream (1) that flows through a conduit or a channel formed by side walls (2) and a bottom or hearth (3) (FIG. 1). To do this, the generation of wingtip vortices (4) is used through the use of fins or aerodynamic profiles, without a substantial increase in the intensity of the turbulence.

[0064] For this, the vortex generator device in channels or ducts of the present invention comprises at least one fin or aerodynamic profile (5), anchored to one of the side walls (2) or to the bottom (3) of the channel or duct by means of the edge opposite the marginal edge (8) of the fin or aerodynamic profile (5), or anchored to a first solid structure, by means of fixing means, so that a controlled incorporation of intense wingtip vortices (4) to the main flow (1) of the duct or channel is produced.

[0065] The foundation of the device is the use of the wingtip vortex (4) that is formed in the aerodynamic profiles (5) as a consequence of having a finite wingspan. In said profiles, the leading edge (6) is defined as the edge on which the main current (1) falls and the trailing edge (7) is the one that is downstream in the direction of the current (1) (FIG. 1). These profiles consist of one or two marginal edges (8), which are the lateral edges in the direction of the main stream (1). The profiles will have a single marginal edge when it is attached directly to one of the solid walls of the conduit or channel, or one of its sides protrudes through the surface in a channel or conduit.

[0066] The wingtip vortex (4) detaches from the marginal edge (8) of the fin or aerodynamic profile (5) and causes the appearance of an oscillatory movement that subjects the particles that travel with the current to an ascending-descending cycle. For this reason, the present invention has the fundamental advantage that transverse speeds to the main current are produced with little introduction of head losses, instead of starting from a strong increase in turbulent intensity through any other procedure, which is key to that energy efficiency can be maximized.

[0067] The device designed, therefore, tries to promote the wingtip vortex (4), for which the angle of attack of the fin or aerodynamic profile must be small, since otherwise the boundary layer would be detached and, consequently, the lift force would be much lower and the hydraulic losses would be much higher, against the objective that is being sought. Therefore, the angle of attack must be between −20° and 20°. As shown in FIG. 2, the angle of attack of a longitudinal section (9) is that formed by the incident current with the reference line of a fuselage body, which is the line that joins the leading edge of the at least one fin or aerodynamic profile with the trailing edge and that defines the so-called chord (10) of the fin or aerodynamic profile (5) in said longitudinal section (FIG. 2).

[0068] As a consequence of the operation of the profile as a fuselage body, there is a notable difference in pressure between the two faces of the fin or aerodynamic profile (5) (FIG. 3). The face on which the overpressures occur is called high-pressure face (12) and the face on which a depression occurs with respect to the pressure of the incident current is called low-pressure face (13). This allows us to explain why a finite wingspan aerodynamic profile (5) produces wingtip vortices, since from the high-pressure face (12) towards the low-pressure face (13) a favorable pressure gradient is generated which in turn generates a current around of the marginal edge (8) called edge current (14), as indicated in FIG. 4.

[0069] If the wingspan of the profile is much greater than the maximum chord, the pressures in the high-pressure face (12) and the low-pressure face (13) are very uniform and the effect of the wingtip vortex (4) on the lift force of said profile is reduced. Since the present invention intends to intensify the wingtip vortex (4), fins or aerodynamic profiles will be used in which the ratio of the sum of the surface of the high-pressure face (12) and the low-pressure face (13) of the fin or aerodynamic profile over the square of its maximum chord (10) is less than 8. Therefore, in these profiles the wingspan is of the same order of magnitude as the maximum chord.

[0070] In the field of hydraulic engineering, the hydraulic diameter of a hydraulic duct or channel (DH) is defined as four times the area of its cross-section (A) divided by the perimeter wetted by the fluid (p), which is the length of the contour of the section that is in contact with the fluid flowing through the duct or channel:

D.sub.H=4A/p   (3)

[0071] For circular ducts, DH matches the inside diameter of the duct. In the case of square section ducts, it matches the height of the duct. When a channel or conduit has a section with a base, b (13), much greater than its height h (14), (b>>h) the hydraulic diameter is of the order of the height of the conduit, h, that is, of the smallest of the dimensions that define the cross section (FIG. 5).

[0072] The losses of mechanical energy per unit volume in a channel or duct with a cross section of area A, which occur as a consequence of a narrowing of the section produced by the existence of a submerged device whose area Ap, of the projection of the device (15) on a plane perpendicular to the direction of the axis of the duct or channel (FIG. 5), can be determined as

[00004]$\begin{array}{cc}\Delta H\approx -\frac{1}{2}\rho v^2\frac{A_p^2}{A^2}& \left(4\right)\end{array}$

[0073] Therefore, for the losses produced by the vortex generating device to be small in relation to the inertia of the fluid, it is necessary that Ap be less than 0.5 times the section of the duct, A. Thus, the head loss coefficient, k, which is defined as

[00005]$\begin{array}{cc}K=\Delta H\text{/}\left(\frac{1}{2}\rho v^2\right)& \left(5\right)\end{array}$

it will be much less than unity, which means that the losses produced by the device are negligible, thus maximizing the efficiency of the process.

EXAMPLE OF PRACTICAL EMBODIMENT OF THE INVENTION

[0074] A practical embodiment of the invention is shown in the attached figures, where the device requires the supply of a flow of gas or liquid to be stirred. This flow rate must be high enough so that the Reynolds number associated with the flow around the profiles that form the vortex generating device is high. On the other hand, the number of fins or profiles and/or their surface will be increased if necessary to achieve the levels of agitation required for each specific application. Likewise, the angle of attack, the chord or the curvature of the profiles will be increased if more agitation is required.

[0075] The flow rate of the fluid to be stirred must be as homogeneous as possible upstream of the aerodynamic profiles to avoid detachment of the boundary layer near the leading edge.

[0076] The materials in which the vortex generating device can be manufactured are multiple (metal, plastic, composites, etc.), the choice of material mainly depending on the specific application in which the device is to be used.

[0077] FIGS. 1 and 2 show the diagram of a prototype installed in a hydrodynamic channel or wall duct (2) and base (3), in which an aerodynamic profile with parallel sides has been fixed to the bottom of said channel or duct (4) by the edge opposite its marginal edge (8). In this prototype we have worked with water velocities of the incident current of between 0.3 and 0.5 m/s. The width of the profile was 15 cm, the length of its marginal edge also 15 cm and its average thickness 4 mm. Tests have been carried out in a range of attack angles (9) of the aerodynamic profile (5) of between 0° and 20°. The marginal edge of the profile was at a distance from the nearest wall equivalent to 0.5 times the hydraulic diameter of the conduit, which in this case was 30 cm.

[0078] For the hydrodynamic channel or duct, the thickness of the boundary layers of the walls can be estimated at 5000 times the kinematic viscosity of the fluid (water) divided by average velocity. In this case, the thickness is therefore of the order of one centimeter, so that the marginal edge of the fin does not interact with these areas of high energy dissipation.

[0079] As shown in FIG. 5, to ensure a minimum pressure drop in this prototype, the projection of the section of the profile in the direction of the current had an area between 0 and 20 cm2.