Rotary kinetic fluid motors or pumps – With means for re-entry of working fluid to blade set – Cross flow runner
Patent
1985-03-22
1986-12-23
Croyle, Carlton R.
Rotary kinetic fluid motors or pumps
With means for re-entry of working fluid to blade set
Cross flow runner
415213C, F04D 500
Patent
active
046309934
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an axial-flow fan comprising a rotor and a surrounding casing. The rotor includes a hub and a plurality of rotor blades extending radially outwards from the hub, and the casing comprises an inlet section located in its entirety upstream of the rotor blades, an outlet section of substantially the same diameter as the inlet section and arranged with its upstream end located in a plane intermediate the leading and trailing edges of the rotor blades, and an intermediate section of larger diameter than the inlet and outlet sections to which it is connected airtight at the downstream and upstream ends, respectively, of those sections whereby the intermediate section defines an annular chamber partly overlapping the tips of the rotor blades. A plurality of stationary guide vanes are secured to the walls of the annular chamber and extend from the upstream to the downstream end thereof, whereby they divide the chamber into a plurality of compartments distributed along its circumference.
In an axial-flow fan of this type, which is known from the published specification of International Application No. PCT/AU81/00181 (WO82/01919), the annular chamber, which partly overlaps the rotor blade tips, is provided for obviating or at least mitigating some undesirable phenomena occurring when the rotor operates in the so-called stalling region or regime, i.e. at a low delivery rate and corresponding high angles of attack at the leading edges of the rotor blades. When stalling occurs at a rotor blade the air flow becomes separated or detached from the convex side of the blade profile, and the resulting stall vortices will move outwardly, due to centrifugal forces, into the annular chamber and be directed back therefrom into the flow upstream of the rotor and mixed therewith. As a consequence of this recycling or backflow the axial inflow velocity at the leading blade edge increases and the angle of attack decreases correspondingly. The quoted specification discloses a plurality of fixed guide vanes disposed within the annular chamber and oriented radially relative to the rotor axis with their radial dimension decreasing to zero at the downstream end wall of the annular chamber. It has been explained in the specification that at low delivery rates there will be obtained a somewhat higher delivery pressure with the stationary guide vanes than without them.
According to the present invention an axialflow fan of the type defined in the opening paragraph above is characterized in that the radially innermost edge zone of each stationary guide vane is oriented towards the direction of rotation of the rotor and includes an angle of between 65.degree. to 40.degree. with a radius from the rotor axis to the inner edge of the vane.
It has been found that by inclining the innermost edge zone of each vane, as provided by the invention, it is possible, inter alia, to eliminate the pressure drop which according to the above discussed prior specification occurs at very low delivery rates, even with guide vanes in the annular chamber. The pressure-versus-volume curves of the fan then exhibit a pressure maximum at or adjacent zero delivery, similar to the characteristics of a centrifugal fan. If the operational conditions of the fan include a risk of substantial overload due to temporarily increased flow resistance, the fan may then still operate at a correspondingly reduced delivery rate without stalling and at a reasonable efficiency.
The advantages obtained by inclining the inner edge zones of the guide vanes are believed to be due to the fact that as soon as an outwardly traveling stall vortex loses contact with the tip of a rotor blade, the mass of air within the vortex is so to speak intercepted by an edge zone of a guide vane and guided, by the vane, into one of the compartments, into which the annular chamber is subdivided by the vanes. At the blade tip each stall vortex has, in addition to its proper swirl, a tangential and a radial velocity component. The tangential velocity component can be regarded as consta
REFERENCES:
patent: 2327841 (1943-08-01), Hagen
patent: 2653754 (1953-09-01), McDonald
patent: 3677660 (1972-07-01), Taniguchi et al.
patent: 4375937 (1983-03-01), Cooper
patent: 4511308 (1985-04-01), Russell et al.
Croyle Carlton R.
Nordisk Ventilator Co.
Stout Donald E.
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