GB2395524A

GB2395524A - Static pressure regain foil for diverging duct

Info

Publication number: GB2395524A
Application number: GB0320926A
Authority: GB
Inventors: Peter John Bayram
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-09-26
Filing date: 2003-09-08
Publication date: 2004-05-26
Anticipated expiration: 2023-09-08
Also published as: GB0320926D0; GB0222336D0; GB2395524B

Abstract

A static pressure regain foil 4 comprises an aerodynamic or streamlined moulding added to the side of a divergent duct 2 such that the otherwise sharp edge of the juncture 5 at the entry point to the duct 3 is eliminated by the curved leading edge of the aerofoil surface 4 to thereby minimise, or eliminate the eddying air turbulence that would otherwise occur at this sharp edge 5. The foil 4 may be applied to a flat side of a duct, or to the faces of a flap located at the juncture of two ducts. The foil may also be of an annular shape and internally convexly curved. The leading edge of the foil my incorporate turning vanes and the trailing edge may be reflex shaped.

Description

S P R FOIL

This invention relates to the flow of air through diveginq tran-

sitiona1 change-of-section ductwork pieces for ventilation and air conditioning systems, and in particular at tan discharge outlets. standard diverging duct change-of-section piece should have flat sides angled at no more than 10 (ten) degrees, or at no more than additional 10 tten) degree increments if splitters are also used if the static pressure regain 105s factor for the transition section is to be nininised. However, such shallow angles can result in the transition piece being excessively long, and in particular where the transition is from a high velocity fan discharge outlet to an item of conditioning equipment operating at a relatively low face velocity' e.g. as in the case of a 'blow-through' central station air handling unit (0HU). Providing an efficient diverging transition piece from a fan discharge outlet ensures that static pressure regain is eaxiaised and fan sound power levels are niniaised.

Long diverging transition pieces are not always possible due to space considerations and shorter concentric ulti-splitter pieces are impractical. In particular such space and cost considerations can become overridingly prohibitive if applied to a 'blow-

through' central station YOU.

According to the present invention there is provided a means for improving the efficiency of a duct diverging transition piece.

In particular the efficiency of a duct transition piece of rel-

tively short length and with relatively steeply angled sidefs) can be improved without resorting to the use of multi internal splitters, which may not be practically feasible where the di-

vergance is 4-sided.

The losses of a transition piece are almost entirely due to air turbulence that occurs at the sharp edge at the entry to the angled flat sidefs) of a standard transition piece. This sharp edge is eliminated if an aerofoil or streamlined section is added to the inside facets) of the angled sideis) of the transformation piece such that the leading edge of the section is shaped to be be at a tangent to the preceding straight duct or fan discharge outlet. Lift pressure reduction is also generated by the aerofoil

section which (less friction losses) is directly related to sta-

tic pressure regain. The shape, angle and effect of the aerofoil can be analyzed and optimized by use of computational fluid dyn-

aoics (CFD). The addition of an aerofoil, or forming the side of the transition piece into an airfoil shape, permits the side of the transition piece to be More steeply angled (than with a flat surface), and with the addition of internal airfoil curved splitter plates, or leading edge slats J turning vanes even More steeply angled sides become possible. in eMtreoiS a very short and yet relatively efficient transformation section is possible at the fan outlet of a 'blow-through' central station YOU, particularly if it is optiaised by CFO design. reflex curve should be incorporated at the trailing edge of the aerofoil at the juncture to the duct wall where the angle of the tran-

aition side is steep, to thereby oiniaise reverse flow turbu-

lence that would otherwise tend to occur at this juncture.

specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing.

The drawing shows, seei-schevatically, a typical arrangement of inlet and discharge duct connections to a centrifugal fan.

Referring to the drawing the centrifugal fan 1 is connected to the Main discharge duct via a diverging duct transformation piece having flat sides but incorporating an aerofoil element 4 internally. As air is discharged fro. the centrifugal fan 1 some of the air flows over the aerofoil element 4 and due to the coanda (surface) effect this element of the airflow follows the contours of the aerofoil element 4 to diverge the flow of air; not only with little consequential turbulence but also in such a way as to generate a zone of (relatively) low pressure induced by a lifting effect at the surface of the air-

foil 4 such that this low pressure zone accelerates the flow of air out of the fan 1 discharge outlet.

Claims

À - C L I S

1 An SPR Foil comprises of an aerodynamic, or streamlined aoulding added to the full width and length of an angled flat face side of a ductwork diverging transitional change-

of-section piece such that the leading edge of the SPk Foil is at a tangent to the upstream same side duct wall face.

An SPR Foil as claimed in Claia 1 whereby the angled side

of the duct is not flat but is curved to an aerodynamic, or streamlined contour.

3 An SPR Foil as claimed in Claim 1 or Claim whereby it is not necessarily the full length of the change-of--section piece.

4 An SPR Foil as claimed in Claies 1, 2 or 3 whereby the SPR Foil is applied to both faces of a hinged noveable changeover flap located at the juncture of two (A) alternatively flowing upstream ducts, or fan outlets.

5 An 5PR Foil as claimed in Claim 4 whereby the SPA Foil is not necessarily the full width or length of the flap.

6 An SPR Foil as claimed in Claims 4 5 whereby the flap is a V' shape with the SPR Foil appltied to both outer faces of the flap and the length of each flap face is the same as each of the upstream ducts, or fan outlets.

7 An SPR Foil as claimed in Claim 5 whereby the flap faces are seedcircular and the flap is fitted into a circular conduit.

a An SPR Foil as claimed in any of the preceding Claims where-

by the trailing edge of the SPR Foil has a reflex shape.

An SPR Foil as claimed in any of the preceding Claies where-

by the leading edge of the SPR Foil is not necessarily at a tangent to the upstream duct sidewall.

10 An SPR Foil as claimed in any of the preceding Claims where-

by the SPR Foil is annular, or is a circular tapered diverging fitting that is internally convexly curved.

11 An SPR Foil as claimed in any of the preceding Claies where-

by the leading edge is fitted with turning vanes, or slats.

12 An SPR Foil as claimed in any of the preceding Claims where-

by it may be applied to any fluid, conduit or pump.

13 An SPR Foil substantially as herein described and illustrated in the accompanying drawing

Amendments to the claims have been filed as follows _ I_ L hi = An AFAR Foil comprise a, an a=odiv,,ami=. of- E Eras' Fred n!oulding added to the gill widths or circ'ImferEnce If ant angled str=.ht E,ne or ductwork ciiverDiriu transitional change-of-section piece For fitting) s'.ch that the leaaino edge of the SPR Foil is at a tangent to the 'upstream duct face' or fan case fareoutiet rifting.

On 5PR Foil as claimed in Claim Thereby there iE no, moulair, and the duct side has ar, aerodynamic' or strea.nea shape.

On STIR Foil as claimed in Claims 1 and =, whereby it is not.

necessarily the full length of the change-of-section Apiece.

4 Hn i-'K Foil as riaifl;ed ir'.,,s i' c D;- 'F.-F-r' typo CriG Foil is applied to both faces of a hinged moveable changeover flap located at the juncture of two (Ei alternately flowing upstream ducts, or fan discharge o'.tlets such that. tne flap moves to form two (c.r aiterr,ate angled side diverging t.ran-

sitional changes-of section.

5 On 5PR Foil as claimed in._la3 4 whereby the flap is 89' shape and the SF'R FG ii is applied to both outer faces of tree flap and the length of each flap face is the SORE as the width' of each of the upstream ducts, or fan outlets óSee Figures 4a and 4b of patent application GB A' SB1 835 Ad.

6 En FOR Foil as claimed in Claim wherrby tile flaps is fitted into a circular duct, or fitting.

En SPR Foil as claimed in any of the preceding Claims whereby the trailing edge has a reflex shape.

B On AFAR Foil as claimed in any of the preceding Claims whereby the leading edge is not necessarily at a precise tangent to the Lpstream face, e.g. where the leading edge radials extends above the tangent line to thereby extend into, or above the L'pstrean airflow baludary layer, or as otherwise constrained by prac-

tical application.

Or, SPR Foil as claimed in -.r.'V of the pl-ecP5diT;9 L]aims whereby the leading edge is fitted with turning vanes, or slats.

10 On 5FIR Foil as claimed in any of the preceding Ciaims hereby it may be applied to any fluid, conduit or pump 11 En SPR Foil s'.bstantialiv as described herein, and illustrated in the accompanyi,sg drawing.