US3144201A - Blowers and rotary compressors - Google Patents

Description

Aug. 11, 1964 E. w. RUNDLE BLOWERS AND ROTARY COMPRESSORS 2 Sheets-Sheet 1 Filed May 7, 1962 x m wwwwww y u 9 www g w /H v w -m ,mW mu -ww -mw b [W -w -m xmmwmww www Home Aug. 11, 1964 E. w. RUNDLE 3,144,201

BLOWERS AND ROTARY COMPRESSORS Filed May 7, 1962 2 Sheets-Sheet 2 y 3) MM W United States Patent 3,144,201 BLOWERS AND ROTARY COMPRESSORS Eric William Rundle, Leatherhead, England, assignor to Plannair Limited, Surrey, England, a British company Filed May 7, 1962, Ser. No. 193,369 Claims priority, application Great Britain May 9, 1961 2 Claims. (Cl. 230120) This invention relates to blowers and rotary compressors, and is particularly concerned with bladed rotors or impellers for use in such machines.

A common fault among axial-flow blowers and other bladed machines is that they tend to stall at a particular rate of volumetric flow and at a particular delivery pressure-the actual point of stall being dependent on the specific construction of the machine. This necessarily restricts the range of delivery pressures and rates of flow over which the machine will operate satisfactorily.

In many instances this restriction of the operating range is not a severe handicap, but in certain cases it is highly desirable or even essential to use a blower which cannot stall. For example, it is frequently necessary to provide an air filter on the inlet side of a blower, with the result that the resistance to air-flow increases as the filter becomes dirty. A condition is often reached in such installations where the pressure drop across the filter is greater than the maximum pressure rise within the blower, which leads to stalling of the blower and a drastic reduction in the air delivered from it. Similarly, the blower or blowers of an aircraft ventilation system should not stall if all the discharge ports into the passenger cabin are closed.

The present invention has been devised to meet this requirement for a non-stall blower or compressor, and according to the invention a rotor or impeller for use in such machines comprises a number of rotor blades each having flow-surfaces on both sides of the blade which curve in one direction from the leading edge of the blade to a point or line more than half-way towards its trailing edge and which then curve in an opposite direction over the part of the blade adjacent the trailing edge.

The theory behind the invention and a number of other features which can be included in the rotor or impeller will now be explained with reference to the particular example illustrated in the accompanying drawings, in which:

FIGURE 1 is a graph showing the pressure/flow operating range of a typical axial-flow blower in general use at the present time;

FIGURE 2 is a similar graph showing the pressure/ flow operating range of a blower in accordance with the invention;

FIGURE 3 is a rear end view of a rotor or impeller in accordance with the invention;

FIGURE 4 is a side view of the rotor shown in FIG- UREflB;

FIGURE 5 is a front end view of the rotor shown in FIGURE 33;

FIGURE 6 is a diagram showing the cross-section of one of the rotor blades at its root, its tip, and its midheight; and

FIGURE 7 is a vertical section through a typical axialflow blower incorporating the invention.

As indicated above, FIGURE 1 illustrates the operating characteristics of a typical axial-flow blower in general use at the present time, the ordinate X representing the pressure rise within the blower expressed as a percentage and the ordinate Y representing the volume flow through the blower, also expressed as a percentage. It will be seen from inspection of this figure that the blower has an operating range between the points C and D on the line B which is restricted at one end by a so-called breakdown point B of pressure and flow which causes 3,144,201 Patented Aug. 11, 1964 the blower to stall as shown by the broken line A. This is not a serious disadvantage in many installations where blowers or compressors are used, but in certain instances it is most undesirable that the blower should stall once the delivery pressure and rate of volumetric flow reach a certain point.

It is accordingly an aim of the present invention to produce a blower or compressor which has an operating range such as that shown by the line F in FIGURE 2, that is to say, an operating range which is not restricted by the breakdown point E of FIGURE 1.

We have found that a machine which meets this requirement can be provided if the rotor or impeller blades are shaped in a particular manner so as to create a flowpattern through the machine which does not give rise to conditions of stall. FIGURES 3 to 6 show a rotor or impeller ltl having airfoil-section blades 12 shaped in this manner, and it will be noted that the main characteristic of the blades is that the flow-surfaces 14 and 16 adjacent their trailing edges 18 curve in an opposite direction to those parts of the flow-surfaces 14 and 16 which are adjacent the leading edges 20 of the blades, the flow surfaces 14 and 16 being at the same time so disposed that no portion of them produces axial or near-axial flow of the air. It is found that blades of this construction produce a stable air flow at their trailing edges over the whole pressure/flow range of the blower, which is in marked contrast to the unstable air flow which occurs at particular pressures and rates of flow in blowers having rotor blades of conventional design.

FIGURE 6 shows three cross-sectional views of one of the blades, the first cross-section 22 being taken at the root of the blade, the second cross-section 24 being taken at the mid-height of the blade, and the third cross-section 26 being taken at the tip of the blade. It will be seen that the reverse curvature of the flow-surfaces adjacent the trailing edge of the blade is substantially constant at all heights of the blade, and that the flow-surfaces at the trailing edge are so formed as to throw the air off the blade in a direction which is approximately radial to the axis of the rotor 10.

The actual rotor or impeller shown in the drawings has eight rotor blades, although the number of blades provided is not critical, and it will be seen that the blades overlap each other to a certain extent when the rotor is viewed along its axis. The result is that the width of the gap between adjacent blades measured at right angles to the direction of fluid flow between them is less at the leading edge of one of the blades and at the trailing edge of the other blade than in the central portion of the gap, the best results being obtained when adjacent blades overlap each other by between 15 and 40% of their area when viewed along the axis of the rotor. This ensures that the air is compressed, expanded and then re-compressed as it passes between adjacent blades. Further, it is desirable that the trailing edge 18 of each blade should lie parallel to its leading edge 20, although this does not appear to be a critical requirement as satisfactory results can still be obtained if the leading edge and the trailing edge are out of parallel by as much as 15".

The reverse curvature adjacent the trailing edge 18 of the blades 12 shown in the drawings occurs only over the last quarter of the flow-surfaces 14 and 16. However, in some instances it may be desirable for the reverse curvature to commence directly after the half-way position between the leading and the trailing edges of the blades. In both cases the thickness of the blades along their portions of reverse curvature is no greater at any point than the thickness of the blades at the transition point where the reverse curvature commences.

The invention is applicable to many different kinds of blade, but it has been found particularly advantageous when applied to a rotor blade constructed in accordance with the invention described in British Patent No. 751,954. The rotors or impellers can be manufactured in one piece by a casting, injection moulding or milling operation, and may be made of aluminium-alloy, stainless steel, synthetic plastic and other materials.

it has been found that blowers or compressors in accordance with the invention give improved results if the incoming air or other fluid impinges upon the leading edges of the rotor blades in an axial direction, that is to say, a direction lying parallel to the axis of the rotor. This can be ensured by arranging a honeycomb grille on the inlet side of themachine, the grille thereby serving to counteract any tendency of the incoming air to flow in a non-axial direction. An axial-flow blower of this construction is shown in FIGURE 7 where a grille 28 is arranged on the inlet side of the cylindrical casing 30 of the machine. The rotor 10 is fastened to the shaft 36 of a driving motor 38 arranged in a motor-housing 34, and in this instance a second honeycomb grille 32 is also fitted on the delivery side of the blower around the motorhousing 34. The stator blades of the blower are shown at 40, so that it will be seen that the stator blades are arranged downstream of the rotor blades 12 in the direction of fluid-flow and are separate from the rotor blades.

The invention has been described above primarily in connection with single-stage blowers or compressors, but it is also applicable to multi-stage machines.

I claim:

1. A rotary compressor comprising an axial flow rotor having a central hub, driving means drivingly connected to said hub, a plurality of radially-extending rotor blades peripherally spaced about said hub so as to overlap each other to a substantial extent and having their inner ends extending from said hub, a plurality of stator blades, separate from said rotor blades, arranged downstream of said rotor blades in the direction of fluid flow, a curved forward flow-surface and a curved rear flow-surface on each of said rotor blades, and flow-surfaces being curved in one direction from the leading edge of each of said rotor blades to a transition point at least half-way towards the trailing edge of each of said blades, and being curved in an opposite direction to said first-mentioned direction over the part of each rotor blade adjacent said trailing edge, said blades being fixed relatively to each other on said hub so that the width of the gap between adjacent rotor blades measured at right angles to the direction of fluid flow therebetween is less at the leading edge of one of said blades and at the trailing edge of the other of said blades than in the central portion of said gap, whereby fluid flowing through said gap is compressed, expanded and then re-compressed by said adjacent rotor blades, and flow-surfaces on said rotor blades being at a substantial angle to the rotational axis of said rotor at all points between said leading edges and said trailing edges of said rotor blades, the thickness of said rotor blades along their opposite-curved portions adjacent their trailing edges being no greater at any point than the thickness of said blades at said transition point on each rotor blade; the adjacent rotor blades overlapping each other by between 15 and 40% of their area as viewed along the rotational axis of said rotor; and a honeycomb flow-guiding grille having only axially extending flow passages on the inlet side of said compressor immediately adjacent the leading edges of the rotor blades to guide the incoming fluid in an axial direction and to counteract any tendency of the incoming air to flow in a non-axial direction.

2. A rotary compressor according to claim 1, in which the portions of said flow-surfaces adjacent the trailing edges of said rotor blades form trailing surfaces directed to throw fluid off said blades in a direction which is approximately radial to the rotational axis of said rotor.

References Cited in the file of this patent UNITED STATES PATENTS 1,448,393 Eastman Mar. 13, 1923 2,161,027 Dollinger June 6, 1939 2,260,169 Couch Oct. 21, 1941 2,784,551 Karlby et al. Mar. 12, 1957 2,931,563 Eggleton Apr. 5, 1960 2,935,246 Roy May 3, 1960 FOREIGN PATENTS 444,206 Great Britain Mar. 17, 1936' 747,750 France Apr. 4, 1933 847,018 France June 19, 1939 937,969 Germany Jan. 19, 1956 955,377 Germany Jan. 3, 1957

Claims (1)

1. A ROTARY COMPRESSOR COMPRISING AN AXIAL FLOW ROTOR HAVING A CENTRAL HUB, DRIVING MEANS DRIVINGLY CONNECTED TO SAID HUB, A PLURALITY OF RADIALLY-EXTENDING ROTOR BLADES PERIPHERALLY SPACED ABOUT SAID HUB SO AS TO OVERLAP EACH OTHER TO A SUBSTANTIAL EXTENT AND HAVING THEIR INNER ENDS EXTENDING FROM SAID HUB, A PLURALITY OF STATOR BLADES, SEPARATE FROM SAID ROTOR BLADES, ARRANGED DOWNSTREAM OF SAID ROTOR BLADES IN THE DIRECTION OF FLUID FLOW, A CURVED FORWARD FLOW-SURFACE AND A CURVED REAR FLOW-SURFACE ON EACH OF SAID ROTOR BLADES, AND FLOW-SURFACES BEING CURVED IN ONE DIRECTION FROM THE LEADING EDGE OF EACH OF SAID ROTOR BLADES TO A TRANSITION POINT AT LEAST HALF-WAY TOWARDS THE TRAILING EDGE OF EACH OF SAID BLADES, AND BEING CURVED IN AN OPPOSITE DIRECTION TO SAID FIRST-MENTIONED DIRECTION OVER THE PART OF EACH ROTOR BLADE ADJACENT SAID TRAILING EDGE, SAID BLADES BEING FIXED RELATIVELY TO EACH OTHER ON SAID HUB SO THAT THE WIDTH OF THE GAP BETWEEN ADJACENT ROTOR BLADES MEASURED AT RIGHT ANGLES TO THE DIRECTION OF FLUID FLOW THEREBETWEEN IS LESS AT THE LEADING EDGE OF ONE OF SAID BLADES AND AT THE TRAILING EDGE OF THE OTHER OF SAID BLADES THAN IN THE CENTRAL PORTION OF SAID GAP, WHEREBY FLUID FLOWING THROUGH SAID GAP IS COMPRESSED, EXPANDED AND THEN RE-COMPRESSED BY SAID ADJACENT ROTOR BLADES, AND FLOW-SURFACES ON SAID ROTOR BLADES BEING AT A SUBSTANTIAL ANGLE TO THE ROTATIONAL AXIS OF SAID ROTOR AT ALL POINTS BETWEEN SAID LEADING EDGES AND SAID TRAILING EDGES OF SAID ROTOR BLADES, THE THICKNESS OF SAID ROTOR BLADES ALONG THEIR OPPOSITE-CURVED PORTIONS ADJACENT THEIR TRAILING EDGES BEING NO GREATER AT ANY POINT THAN THE THICKNESS OF SAID BLADES AT SAID TRANSITION POINT ON EACH ROTOR BLADE; THE ADJACENT ROTOR BLADES OVERLAPPING EACH OTHER BY BETWEEN 15 AND 40% OF THEIR AREA AS VIEWED ALONG THE ROTATIONAL AXIS OF SAID ROTOR; AND A HONEYCOMB FLOW-GUIDING GRILLE HAVING ONLY AXIALLY EXTENDING FLOW PASSAGES ON THE INLET SIDE OF SAID COMPRESSOR IMMEDIATELY ADJACENT THE LEADING EDGES OF THE ROTOR BLADES TO GUIDE THE INCOMING FLUID IN AN AXIAL DIRECTION AND TO COUNTERACT ANY TENDENCY OF THE INCOMING AIR TO FLOW IN A NON-AXIAL DIRECTION.

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