GB2145774A

GB2145774A - Bladed rotors and ducts associated therewith

Info

Publication number: GB2145774A
Application number: GB08323266A
Authority: GB
Inventors: Robert Mehew Bass
Original assignee: Dowty Rotol Ltd
Current assignee: Dowty Rotol Ltd
Priority date: 1983-08-31
Filing date: 1983-08-31
Publication date: 1985-04-03
Also published as: GB8323266D0

Abstract

A bladed rotor 1 driven by a prime mover 3, e.g. a gas turbine or piston engine, has an associated duct 6 disposed so that the leading edge 7 thereof lies immediately rearwardly of the tips 9 of the rotor blades 8. The duct is arranged co- axially with respect to the rotor and has an inner wall 11 which is non- convergent rearwardly of the forward end portion 12 thereof and is mounted upon fixed structure 5 through the intermediary of support means, for example tangentially- arranged stator blades 4. The forward end portion of the duct is of such cross-section and so dimensioned that the duct is capable of capturing the peripheral boundary 13 of the slipstream 14 of the rotor during operation thereof. <IMAGE>

Description

SPECIFICATION Bladed rotors and ducts associated therewith This invention relates to bladed rotors, for example engine-driven propellers, and to ducts associated therewith.

In an open, that is non-ducted, bladed rotor having blades of fixed pitch or alternatively of variable pitch the streamlining characteristics are such that the peripheral streamlining boundary of the air flow impelled by the rotor contracts from a zone well ahead of the rotor to a zone well behind it. The magnitude of such contraction reduces with increasing forward speed of the craft or vehicle being propelled by the rotor.

By enclosing a bladed rotor in a duct such contraction is effectively reduced and in consequence a larger air mass flow is induced through the rotor, thereby enhancing its thrust. This is of particular benefit at low forward speeds of the craft or vehicle, but at higher forward speeds there is less to be gained and then the drag resulting from the presence of the duct has an adverse effect.

During operation highly-loaded bladed rotors have a significant swirl in the slipstream which if recovered would considerably increase operational efficiency of those rotors.

One way of achieving such recovery is by providing coaxially-arranged contra-rotating bladed rotors. Another way of achieving recovery is to arranged stator blades or alternatively straightener vanes immediately to the rear of the rotors.

The object of this invention is to provide an improved bladed rotor and associated duct arrangement.

According to this invention a bladed rotor, adapted to be driven by a prime mover, has an associated duct which is so disposed that the leading edge thereof lies immediately rearwardly at least of the tips of the blades of the rotor, said duct being arranged coaxially with respect to the rotor, having an inner wall which is non-convergent rearwardly of the forward end portion of the duct, and being mounted upon fixed structure through the intermediary of support means, said forward end portion of the duct being of such crosssection and so dimensioned that the duct is capable of capturing the peripheral boundary of the slipstream of said rotor during operation thereof.

Preferably said support means comprises a ring of stator blades. The fixed structure may be of circular or annular cross-section and in this case the stator blades are tangentially disposed with respect to said fixed structure.

The advantages offered by the invention are mainly that slipstream contraction downstream of the rotor is substantially reduced and the performance of the rotor and duct assembly, particularly at low rotational speeds of the rotor, is in consequence enhanced.

One way of carrying out the invention is described in detail below with reference to the accompanying diagrammatic drawings which illustrate only one specific embodiment, in which: Figure 1 is a side elevation, partly in crosssection, of a bladed rotor and associated duct, Figure 2 is a view taken in the direction of the arrow II on Fig. 1, and Figure 3 is an enlarged view of part of Fig.

1.

The bladed rotor shown comprises a fourbladed variable-pitch propeller 1 carried on the output shaft 2 of a prime mover in the form of a gas turbine engine 3 for propeiling an aircraft (not shown).

A set of seven fixed stator blades 4 is carried by non-rotative forward engine structure 5 which is of annular cross-section, these blades being arranged tangentially in the manner shown in Fig. 2 with respect to structure 5. The blades 4 carry a duct 6 which is disposed with its leading edge 7, that is its foremost extremity, disposed slightly rearwardly of the tips 9 of the blades 8 of the propeller 1, clearance thereby formed being indicated at 10.

The duct 6, which is arranged coaxially with respect to the propeller, is of the aerofoil cross-sectional shape shown in Figs. 1 and 3 and the inner wall 11 of the duct is nonconvergent rearwardly of the forward end portion 1 2 of the duct.

The diameter of the leading edge 7 of the duct is only slightly larger than the diameter of the propeller, and the axial length of the duct is in this embodiment a little greater than half the propeller diameter.

The stator blades 4 in this embodiment slope rearwardly somewhat from the forward engine structure 5, that is in the direction away from the propeller.

The dimensions and the position of duct 6, with leading edge 7 lying immediately rearwardly of the tips 9 of blades 8, and the cross-sectional shape of the forward end portion 1 2 of the duct ensure that during operation of the propeller the duct captures the peripheral boundary 1 3 of the propeller slipstream 14. The wake 1 5 is entrained by the inner wall 11 of the duct and slipstream contraction is thus at least substantially reduced, thereby accelerating flow through the stators and enhancing mass flow. In consequence performance of the propeller/duct assembly is enhanced and particularly so at lower aircraft forward speeds.

The stator blades 4 have a straightening effect on the mass flow leaving the propeller and afford removal of the effects of swirl in the slipstream thereby contributing to the improvement in performance of the propeller/ duct assembly. Further, the stator blades im prove the structural stiffness of the duct assembly, their tangential arrangement affording desired torsional resistance in the assembly.

The arrangement is such that stator blades of relatively thin cross-section can be used giving a relativelv iiqhtweiaht structure. yet retaining desired rigidity as well as avoiding vibration.

As shown in dotted detail at -l 6 in Fig. 3, the inner wall of the duct may in other embodiments be in part slightly divergent in the direction rearwardly away from the propeller, and aerodynamic advantages thereby obtained.

Further, in other embodiments the stator blades may be of variable pitch and advantages in operation accordingly obtained thereby.

Again, instead of providing stator blades, in other embodiments straightener vanes may be provided for supporting the duct, or any other suitable support means, which have the effect of avoiding the setting up of swirl in the slipstream, may be provided.

Although in the embodiment above described with reference to the drawings the bladed rotor is of variable pitch, in other embodiments it may be of fixed pitch.

Further, although the bladed rotor above described with reference to the drawings has four blades, in other embodiments of the invention the rotor may have a suitable number of blades less than four or alternatively more than four, and the number of stator blades can be other than seven to suit the particular installation.

Finally, although in the embodiment above described with reference to the drawings the propeller and duct are associated with a gas turbine engine, in other embodiments they may be associated with other forms of prime mover, for example piston ennines.

Claims

1. A bladed rotor, adapted to be driven by a prime mover, havinq an associated duct which is so disposed that the leading edge thereof lies immediately rearwardly at least of the tips of the blades of the rotor, said duct being arranged coaxially with respect to the rotor, having an inner wall which is nonconvergent rearwardly of the forward end portion of the duct, and being mounted upon fixed structure through the intermediary of support means, said forward end portion of the duct being of such cross-section and so dimensioned that the duct is canable of capturing the peripheral boundary of the slip- stream of said rotor during operation thereof.

2. A bladed rotor and associated duct as claimed in claim 1, in which said support means comprises a rinq of stator blades.

3. A bladed rotor and associated duct as claimed in claim 2, in which said fixed structure is of circular or annular cm-,s-section and said stator blades are tangentially disposed with respect to said fixed structure.

4. A bladed rotor and associated duct as claimed in any one of the preceding claims, in which said inner wall of said duct is in part slightly divergent in the direction rearwardly away from said rotor.

5. A bladed rotor and associated duct substantially as hereinbefore described with reference to the accompanying drawings.