CONDITIONS

BACKGROUND OF THE INVENTION

[01] This disclosure relates generally to the field of fluid dynamics and more specifically to fluid dynamic systems and methods for controlling transverse step flow conditions.

[02] Fluid dynamics is replete with examples of flow separation and the associated effects from the separation and associated flow structures such as transverse vortices, separation bubbles and similar conditions. This is true for Newtonian flow conditions, such as air, water and non-Newtonian flow conditions, such as plasma flows.

[03] A particular problem associated with such flows is that they are unsteady over time, and the separation region may alter the flow's location, intensity and even flow direction over time, resulting in significant effects to the overall flow conditions and potentially performance of the device or structure of flow over a surface. Aft facing steps transverse to the flow if included in the surface structure increase the extent of flow disruption, resulting in efficiency losses.

[04] In current art, this disruption to the flow over a surface is not readily or easily controlled, and is accepted as a natural consequence of design engineering constraints. Examples of such structures that result in step conditions with associated efficiency losses are fuselage lap joints, window and door cutouts, flight controls, spoilers/speed brakes, and flaps of an aircraft or plates of a ship's hull, joints of an oil pipeline, and similar devices. Perturbation to the boundary layer is both an inviscid and compressible problem, with greater losses accumulating where shock is involved.

[05] Efforts to minimize flow disruptions of aft facing steps on a body have preoccupied designers throughout history. These efforts have acted at relatively large scales relative to the step heights, on the order of 10 times or greater than the step height, and of a similar relative scale of the boundary later around the body affected by the presence of a step. An example of this is the design of a leading edge lift enhancement device known as a Slat, or Leading Edge Slat. The slat is a beneficial design for low speed, relatively high angles of attack, while deployed by translation forward and generally downwards in an arc from its retracted/stowed position. In the stowed position, the trailing edge of the slat defines an aft facing step on the top and usually rebated lower junction on the wing.

[06] Efforts to reduce the thickness of the step height have been undertaken, but are limited by the out of plane loads that occur in operation that tend to bow a thin section away from the surface. This results in a minimum thickness of a step that can be achieved considering the static and loaded cases. One device that has shown effectiveness at improving the flow effects caused by aft facing steps has been the Conformal Vortex Generator, CVG which can reduce drag at low angles of attack, where the step has the most significant effect on performance outcomes, generally between 1 and 4 degrees' angles of attack.

[07] The CVG can restructure flow effectively behind the step and achieve a flow condition that is described as a hybrid passive boundary layer flow condition, mixing a suction effect for promoting flow towards a surface, and vorticity induced momentum transfer towards the surface of the body, thus reducing drag. A constraint exists however in the effectiveness of the CVG in so far as at high transonic speeds, the CVG effectiveness is reduced by the limitations on CVG height constraints relative to the intensity of the transverse vortex intensity, where the comparative strength of the transverse vortex structure overwhelms the fine scale structure and subtle flow effects of the CVG.

[08] Research visualization testing shows that at low speed, the CVG is able to control a Transverse Vortex, TV, developed by a step, and re-organize the TV into the chord-wise vortex pairs. While this is evident at relatively low speeds, up to 200m/sec, at higher and transonic velocities, the CVG alone has reduced effectiveness. To counter this outcome, a disruptor device or design to improve the effectiveness of flow control devices associated with a step have been designed. These devices act to disrupt the TV and thereby give the CVG or other control device an opportunity to control the flow at higher and transonic and supersonic velocities.

[09] It is within the aforementioned context that a need for the present invention has arisen. Thus, there is a need to address one or more disadvantages of conventional systems and methods, and the present invention meets this need.

BRIEF SUMMARY OF THE INVENTION [10] Various aspects of a disruptor device can be found in exemplary embodiments of the present invention.

[11] In one embodiment, the disruptor device includes a protrusion that is applied to a surface in a flow behind an aft facing step on the surface, wherein the protrusion has a periodic variation in height from the surface behind the aft facing step, wherein the protrusion behind the aft facing step is located in the region of a rear and lower quadrant of the region of separation/transverse vortex, such that the disruptor device interacts with a pressure distribution or flow field of the primary flow developed by the aft facing step. In another embodiment, the disruptor device the protrusion has a flat upper surface that conforms to an upper surface of the surface to which the protrusion is applied. In a further embodiment, a leading edge of the protrusion is shaped in plan-form projection as a series of shapes that achieve disruption of flow conditions that otherwise would exist behind the aft facing step.

[12] A further understanding of the nature and advantages of the present invention herein may be realized by reference to the remaining portions of the specification and the attached drawings. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, the same reference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[13] FIG. 1 shows a surface that has a step in surface height that results in an aft facing step.

[14] FIG. 2 shows a surface which is above the surface in FIG. 1, and which is predominately a constant height or conformal elevation above the base surface, such that if considered as a sheet or panel, it would be predominately constant thickness and generally follow the surface curvature of the lower surface.

[15] FIG. 3 shows the trailing edge devices that may be incorporated into the surface that act as conformal vortex generators which have the characteristic vortex generating edges that result in both separation and shear resulting in chord wise vortex structures.

[16] FIG. 4 shows a disruptor constellation as Lozenge forms.

[17] FIG. 5 shows a button form disruptor, with device having a height. [18] FIG. 6 shows a disruptor device, which has a plan form linear leading edge, parallel to the Aft facing step.

[19] FIG. 7 shows the general, average flow conditions at an aft facing step.

[20] FIG. 8 depicts the relative location of the disruptor to the aft facing step, and more specifically the location of the disruptor relative to the primary

separation/vortex structure as depicted in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[21] Reference will now be made in detail to the embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the one embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as to not unnecessarily obscure aspects of the present invention.

[22] In one embodiment, the invention herein described provides a device referred to as a disruptor to assist in control of the transverse vortex or separation field behind an aft facing step. The Disruptor is a device with a periodic or semi periodic raised surface behind the aft facing step, located such as to interfere with the flow field behind the step, being a transverse vortex or separation field, and with such interaction resulting in periodic interference with flow conditions within the transverse vortex or separation field.

[23] The simplest embodiment of the disruptor is a uniform height laminate, which has a periodic or semi periodic plan form leading edge shape such as a sine wave. The peaks of the sine wave are located proximate and behind the aft facing step, within the region of 1 to 10 times the aft facing step height. The height of the disruptor is effective at 10% of the aft facing step, but is not limited by height, however efficiency of the device is best below 50% of the aft facing step height. The peak-to-peak distance of the sine wave is of the order of 2 to 5 times the aft facing step height, but is not limited in the effectiveness at up to 100 times the aft facing step height.

[24] An alternative embodiment of the disruptor can be achieved by scalloping the leading edge of a laminate material such that a variation in height occurs periodically along the width of the leading edge of the disruptor. In this case, the location of the device behind the aft facing step is consistent with the disruptor by means of varying plan form. A further alternative embodiment is a periodic or semi periodic series of perturbations such as a button or series of lozenge shaped perturbations arranged such that the device as a constellation is located to interfere with the aft facing step transverse vortex or separation field, consistent with the plan form type disruptor or the scalloped edge type disruptor described. For all disruptor types described, the periodic span wise spacing, across the free stream flow is not critical but is characteristically 3 to 6 times the aft facing step height.

[25] The device described is located behind the step on the body being any surface in a flow, such as a wing, a hull, a pipe, in such a location and of such design as to cause a disruption of the transverse flow vortex and permit the smaller scale CVG device to control the transverse flow. The CVG itself can be located behind the disruptor, or above the step in front of the disruptor and a further CVG associated with the disruptor. The disruptor is located a distance behind the step so that the flow disruption device is preferentially located to achieve the greatest enhancement of the CVG related control of the flow, which is dependent on the step height, and also the body angle of attack and speed/Mach number. [26] Testing has shown that while a linear forward edge on a CVG, located behind the step can act as a disruptor of the transverse flow, more control can be effected by the use of either a triangular form series, or a sinusoidal leading edge. The non-linear forms indicate greater speed and angle of attack tolerance for being effective in achieving a control of the transverse vortex by the CVG device. Visualizations show clearly defined flow structures indicating that the span-wise pressure distribution are being altered by the disruptor design. Performance measurements show that the disruptor improves the performance enhancements of the CVG alone.

[27] The non- linear disruptor performance exhibits some sensitivity to the phase of any vorticity in front of the step, and also behind the disruptor. When properly aligned, the non-linear disruptor exhibits greater performance in controlling the transverse vortex than the linear disruptor edge. The disruptor can be employed with a CVG applied in front of the disruptor, on and forward of the aft facing step. This configuration results in the vortex pairs from the preceding CVG being controlled down to the lower surface at low and high speeds, and continuing to control the transverse vortex at high speeds. In general, following the disruptor, the trailing edge would incorporate a further CVG for additional flow processing, post control of the transverse vortex or separation area.

[28] The disruptor device may be fabricated from various materials, and by various methods. It can be formed as a tape of thermoplastic polyurethane or ultrahigh molecular weight polyethylene for example using an adhesive interface to the main surface. It can also be made of metal, or ceramic materials, or ceramic metal mixes as may be preferable for the conditions encountered. The disruptor as a non-linear device can be added to a linear edge of a CVG that is installed, by fabricating the disruptor with a non- linear disruptor edge, and a linear edge abutting the disruptor rear to the CVG front.

[29] The disruptor when applied with a configuration including a conformal vortex generator that precedes the disruptor benefits from permitting the vortex pair form the preceding vortex generator being aligned stream-wise with the disruptor 's forward protuberance. This allows a surface for the vortex pairs to touch down while assisting the disruption of the transverse vortex or stagnation field, which becomes integrated by induced flow into the flow of the vortex pairs. This permits a greater step height related transverse flow field to be controlled by the preceding vortex pairs, improving the efficiency of the conformal vortex generators performance. This is the case for an additive vortex generator, to a surface, or a generator that is integral to the surface. [30] A practitioner versed in the art will note that the disruptor does not develop the flow conditions that a turbulator does, as the disruptor alters the transverse vortex flow of the aft facing step by breaking down the coherent flow of the transverse vortex in a span wise or cross flow and converts that into a series of chord- wise vortex structures not just turbulent flow. Testing has shown that the plan form shape of the disruptor does alter the effectiveness of the device, with a sinusoidal shape being more effective than a pointed shape, however position relative to the step is more significant as a factor.

[31] The device is located at a distance behind the aft facing step that is dependent on the step height, viscosity of the fluid, and the flow, essentially being dependent on the location being such that the leading edges of the disruptor result in local flow and pressure variations that are within the region of influence of the span wise flow or separation field. CFD modeling and flow visualization has shown that the offset distance from the aft facing step of the disruptor is of the order of 2 to 3 times the step height, however this is not limiting. Offset distances greater than 10 times the step height has shown the disruptor effect to be reduced.

[32] FIG. 1 shows a surface (1) that has a step in surface height (2) that results in an aft facing step (3). The flow direction of the figure is from left to right, such that the step (3) is facing away from the direction of flow.

[33] FIG. 2 shows a surface (4) which is above the surface (1) in FIG. 1, and which is predominately a constant height or conformal elevation above the base surface, such that if considered as a sheet or panel, it would be predominately constant thickness and generally follow the surface curvature of the lower surface. The leading edge shapes (5), with vertical extent (6), of the surface (4) are arranged at a distance behind the aft facing step (3) of FIG. 1 such that they interfere with the transverse vortex or separation field that exists immediately behind the aft facing step (2).

[34] FIG. 3 shows the trailing edge devices that may be incorporated into the surface (4) that act as conformal vortex generators (CVG) (15) which have the characteristic vortex generating edges (16) that result in both separation and shear resulting in chord wise vortex structures. The plan form of the device results in the surface (4) having a predominately vertical extent (6). [35] FIG. 4 shows a disruptor constellation as Lozenge forms. The disruption is achieved by device (5) having a vertical extent (6). FIG. 5 shows a button form disruptor, with device (5) having a height (6).

[36] FIG. 6 shows a disruptor device, which has a plan form linear leading edge, parallel to the Aft facing step, and where the variation to the flow conditions of the transverse vortex or separation field is achieved by variation in height of the leading edge by scalloping the leading edge resulting in varying height in the transverse direction and also in the flow wise direction. The general characteristics of a disruptor remain evident, the device (5) and a vertical height (6).

[37] FIG. 7 shows the general, average flow conditions at an aft facing step. A fluid with a vertical velocity profile (7) within the boundary layer flows over the surface (8), resulting in separation (9), which may become a transverse vortex flow with sufficient shear being present, which will be commonly the case. Counter flow structures exist (10) (11) (12) which are either small scale vortex (10) (11) or stagnation flow structures (12). The general flow will be affected on average over the top of the primary separation/vortex structure (9).

[38] This is not the case for the time study outcome, where the separation/vortex structure (9) is unsteady behind an aft facing step, and which convects downstream in an unsteady manner disrupting the flow extensively. FIG. 8 depicts the relative location of the disruptor to the aft facing step, and more specifically the location of the disruptor relative to the primary separation/vortex structure (9) as depicted in FIG. 7.

[39] While the above is a complete description of exemplary specific embodiments of the invention, additional embodiments are also possible. Thus, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims along with their full scope of equivalents.