GB2545153A

GB2545153A - Bridging Seal

Info

Publication number: GB2545153A
Application number: GB1514750.7A
Authority: GB
Inventors: John Evans Timothy
Original assignee: ESTRESS Ltd
Current assignee: ESTRESS Ltd
Priority date: 2015-08-19
Filing date: 2015-08-19
Publication date: 2017-06-14
Anticipated expiration: 2035-08-19
Also published as: GB201514750D0; GB2545153B

Abstract

A corrosion and erosion resistant seal 1 placed under a load is used to bridge a gap or aperture [4, fig. 1] between two surfaces 2, 3 exposed to smooth or laminar fluid flow. The exposed thickness of the seal and its profile should be such that they do not undermine laminar flow, and there should be low friction at the seal-to-surface contact 5. The seal may contact the surface at an inclined plane, and the seal might only contact the surface at the extremities of the seal. The seal may contact the plane via a low-friction substance. The seal may comprise thin sheets or layers 13 bonded with adhesive to form a laminate. The seal may be fabricated with the profile of a T-section [14, fig. 5]. A spring may provide the load to the seal. The seal may be bonded together to a surface using adhesive. The seal may accommodate surface curvatures, and may be applied to a surface using an automated process. The surfaces may be the external surfaces of hulls, wings or blades, where a gap or other imperfection may cause turbulence.

Description

Bridging Seal

This invention relates to a seal for the concealment of external surface gaps, steps and discontinuities.

The efficiency of movement of a body through a fluid (liquids and gases) is improved by the smoothness of the external surfaces of the body. Conversely the presence and exposure of roughness, imperfections, gaps and steps on the external surfaces of the body impairs efficiency. More specifically, the reduction in external surface-friction drag in boats, aircraft or any other structural body passing through a fluid is to maintain a condition called laminar flow, in which water or air slides smoothly over the surfaces of hulls, wings, blades or other external surfaces of a structure. With regard to practical engineered structures fabricated from many components, moving through a fluid, the typical presence of surface roughness, imperfections, surface waviness, gaps and steps leads to a transition from laminar flow to turbulent flow resulting in increased surface-friction drag and a loss in speed, power and efficiency. Surface seals and fillers can be used to restore surface smoothness, but currently both suffer inherent limitations: the step size introduced by the thickness of seal, and the durability of filler with respect to the long term operating environment (fluid pressure, surface temperature, surface strain matching compliance and in-service surface treatments). The current state of the art regarding fluid-structure interaction defines permissible seal step heights, seal-to-surface relief profiles (both waviness and interaction of neighbouring steps) and seal roughness characteristics that do not undermine laminar flow.

To overcome these limitations the present invention proposes a corrosion and erosion resistant seal under pre-load which bridges the gap between two surfaces which are exposed to laminar fluid flow where the exposed seal surface thickness and the resulting seal-to-surface relief profile do not undermine laminar flow and where relative movements between the sealed surfaces are facilitated by the low frictional tribological nature at one or both of the seal-to-surface contacts and the nonparallelism of one or both of the seal-to-surface contact planes.

The non-parallelism of a surface contact plane with respect to the plane of the seal allows the seal to accommodate relative movements between the two surfaces to be sealed without incurring infringement of allowable laminar flow step heights and surface relief profile limitations, and also enables a seal design which respects seal material mechanical strength limits.

Preferably, the non-parallelism of one or both of the seal-to-surface contact planes is that of an inclined plane with respect to the plane of the seal, thus ensuring that at that location the seal-to-surface contact only occurs at the extremities of the seal.

The gradient of an inclined plane with respect to the plane of the seal is such that laminar flow step height limitations and surface relief profile limitations are observed.

The seal-to-surface contact at an inclined plane involves a low frictional substance to facilitate relative movements between the seal and contact surface and mitigates seal stresses due to surface strain matching compliance.

The seal pre-load is induced mechanically, thermally or electrically or in combination.

Preferably, the seal instantaneous pre-load is quantifiable and engaged for all service life operational and environmental conditions.

Preferably, the seal is manufactured, machined or fabricated with the profile of a T-Section positioned such that the surface exposed to fluid flow is the horizontal face of the T-Section, or possesses an alternative profile such as a flat plate.

Preferably, the seal consists of a layup of thin sheets bonded together with adhesive, thus forming a laminate and with at least the exposed surface sheet layer possessing the necessary corrosion and erosion resistant qualities.

Preferably, the seal will accommodate surface curvatures.

Preferably, the application of the seal to the external surfaces will be automated.

Figure 1 to Figure 3 present the typical features of the seal. Examples of the invention are then described by referring to Figure 4 to Figure 6. The seal may comprise combinations of the features in all Figures.

As depicted in Figure 1, a structural seal 1 is attached to the external surfaces of two bodies 2 and 3 concealing the surface gap, step or discontinuity 4. Bodies 2 and 3 may comprise dissimilar materials and may be subject to fluid pressures, temperatures and mechanical strains. A foot 5 consisting of low friction material is depicted in Figure 2. The foot 5 facilitates relative translational movements in directions X, Y and Z of the seal relative to the contact surface plane. The combined step thickness of features 5 and 6 (8) is chosen so as not to undermine laminar flow and one or both of the contact surfaces is inclined 7 such that the seal can accommodate these relative movements whilst respecting the allowable laminar flow step heights and seal-to-surface relief profile of both 8 and 9 for all relative movement configurations of the seal and contact surface.

Figure 3 depicts the seal 1 consisting of a layup of thin sheets 10 bonded together with adhesive, thus forming a laminate, with at least the exposed surface sheet layer possessing corrosion and erosion resistant qualities. The sheets are stepped such that the thickness of the laminate at critical sections is sufficient to react bending without exceeding seal material mechanical strength limits whilst maintaining contact only at the extremity of the seal 5.

Figure 4 depicts one example configuration of the seal where the seal is bonded only to the surface of body 3 at contact plane 11, and contacts at 5 the inclined surface of body 2 as described for Figure 2. The step height 12 at the bonded surface is chosen so as not to undermine laminar flow. The seal comprises thin sheets 13 bonded together with adhesive, thus forming a laminate and with at least the exposed surface sheet layer possessing corrosion and erosion resistant qualities. The thin sheets forming the laminate possess different coefficients of thermal expansion and are disposed throughout the laminate so as to generate beneficial deformation of the laminate in the Y-Z plane under changes of temperature causing pre-load at 5. Preferably, the mechanical properties of the seal in the bonded region will mitigate thermal expansion and strain compatibility effects at the bonded interface 11.

Figure 5 depicts an alternative configuration of the seal where both seal-to-surface contact planes are inclined relative to the plane of the seal and the cross section of the seal is that of a T-section with the web of the seal 14 lying in the X-Z plane. The seal is retained by passing a clip 15 through a slotted bracket 15 which is attached to one of the bodies 2, 3. The clip 15 exerts pre-load in the Z-axis maintaining seal to surface contacts only at the extremities of the seal. A spring 17 exerts a force in the Y-axis producing a mechanical couple which acts in combination with the pre-load to maintain seal-to-surface contact at the more remote seal-to-surface contact 5.

Another alternative configuration is depicted in Figure 6 in which a pre-load device such as a conical spring 18 provides the clamping force necessary to maintain contact at the seal-to-surface interface, preferably exerting a constant force for the full range of anticipated possible relative dispositions of bodies 2, 3. The seal comprises a stiffening web 19 in the X-Z plane in order to maintain seal-to-surface contact between the locations of discrete pre-load attachments as illustrated in the plan view.

In all such configurations the seal is designed to take account of the operating environment: in particular and with respect to Figure 1, mechanical bending of the seal across gap 4 under fluid pressure, any thermal mismatch of the seal relative to the surfaces of bodies 2 and 3, strain matching compliance of the seal with respect to surfaces of bodies 2 and 3 and anticipated relative movements of bodies 2, 3.

Claims

Claims

1 - A corrosion and erosion resistant seal under pre-load which bridges the gap between two surfaces which are exposed to laminar fluid flow where the exposed seal surface thickness and the resulting seal-to-surface relief profile do not undermine laminar flow and where relative movements between the sealed surfaces are facilitated by the low frictional tribological nature at one or both of the seal-to-surface contacts and the non-parallelism of one or both of the seal-to-surface contact planes.
2 - A seal according to claim 1 in which the non-parallelism of one or both of the seal-to-surface contact planes comprises an inclined plane with respect to the plane of the seal ensuring that at that location the seal-to-surface contact occurs only at the extremities of the seal and in which the gradient of the inclined plane with respect to the plane of the seal is such that both laminar flow step height and surface relief profile limitations are observed and also enables a seal design which respects seal material mechanical strength limits.
3 - A seal according to claim 1 and claim 2 in which the seal-to-surface contact at an inclined plane involves a low friction substance to facilitate relative movements between the seal and contact surface and which mitigates seal stresses due to surface strain matching compliance.
4 - A seal according to claim 1 in which the pre-load is induced mechanically, thermally or electrically or in combination.
5 - A seal according to claim 1 and claim 4 for which the instantaneous pre-load can be quantified and engaged for all operational and environmental conditions throughout the service life of the seal.
6 - A seal according to claim 1 consisting of a layup of thin sheets bonded together with adhesive, thus forming a laminate and with at least the exposed surface sheet layer possessing corrosion and erosion resistant qualities.
7 - A seal according to claim 1, claim 5 and claim 6 in which the thin sheets forming the laminate possess different coefficients of thermal expansion and are disposed throughout the laminate so as to generate beneficial pre-load due to deformation of the laminate across the gap under changes of temperature.
8 - A seal according to claim 1 comprised of a smart material where beneficial pre-load due to deformation of the seal across the gap can be achieved through temperature dependant material shape memory or through application of a voltage or via a combination of both.
9 - A seal according to claim 1 and claim 5 manufactured, machined or fabricated with the profile of a T-Section positioned such that the surface exposed to fluid flow is the horizontal face of the T-Section.
10 - A seal according to claim 1 and claim 5 where a spring is used as a pre-load device.
11 - A seal according to claim 1 where one of the seal-to-surface contact planes is bonded together with adhesive.
12 - A seal according to claim 1 which will accommodate surface curvatures.
13 - A seal according to claim 1 in which the application to the external surfaces will be automated.