Rotary kinetic fluid motors or pumps – Working fluid bypass
Patent
1980-06-05
1982-12-07
Garrett, Robert E.
Rotary kinetic fluid motors or pumps
Working fluid bypass
F02C 792
Patent
active
043624650
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a set of blades for a turbine which includes a group of blades disposed between an upper plate and a lower plate. The group of blades therefore defines a group of passages along which a fluid flows, each passage being delimited by the convex surface of one blade and the concave surface of the blade next to it and by the lower plate and the upper plate.
BACKGROUND OF THE INVENTION
It is known that in a given passage, at points which are sufficiently far from the walls of the passage, the stream lines follow paths which are substantially parallel to the walls of the passage formed by the concave and convex surfaces of the blades. At all points along the path, the centrifugal force which is exerted on a particle is balanced by the pressure forces. The result of this is, generally, that the concave surface of the blade is subjected to a higher pressure than is the convex surface of the other blade which delimits the passage.
It is also known that in the boundary layer near the lower plate and upper plate, the speed of the fluid is low. It follows that the pressure forces are no longer balanced and the stream lines are curves perpendicular to the isobars and follow paths of considerable slippage in each passage from the concave surface to the convex surface as is well known to the person skilled in the art (see, for example, the article in the November 1941 French issue of the Brown Boveri review--p. 356 to 361 and, in particular FIGS. 2 and 3).
The slippage generates a counter-clockwise eddy against the upper plate of the passage and a clock-wise eddy against the lower plate as seen by an observer placed downstream from the set of blades.
These disturbances cause important losses known as secondary losses and the smaller the ratio between the height of the blades and the chord, the more the efficiency of a set of blades is reduced.
A known means for reducing the secondary losses consists in reducing the aerodynamic loading on the blades. This is equivalent to reducing the difference in average pressure between their concave and the convex surfaces e.g. by reducing the blade spacing to chord ratio of the set of blades.
However, the disadvantage of the above method is that it increases the friction losses in the zone of good flow along the passage in such a way that the gain obtained on the secondary losses can be cancelled by increasing the friction losses in the main flow.
SUMMARY OF THE INVENTION
The set of blades in accordance with the present invention which allows the secondary losses to be reduced without having any influence on the friction losses in the main flow is characterized in that for each blade, at least one duct is provided in the upper plate, said duct opening at one end in the neighbourhood of the convex surface of said blade and level with the constriction of the passage which is delimited by the convex surface of said blade and at the other end at a point situated upstream from said set of blades and/or at least one duct is provided in the lower plate and opens at one end in the neighbourhood of the convex surface of the blade and level with the constriction of the passage which is delimited by the convex surface of said blade and at the other end at a point situated upstream from said set of blades. The constriction of the passage is the place where the convex surface of one blade and the concave surface of the blade next to it are the nearest together, said blades delimiting said passage.
The point situated in the neighbourhood of the convex surface of the blade in the constriction of the passage is the point of the passage where the pressure is at its minimum. Due to the set of blades in accordance with the invention, the low pressure on the convex surface is reduced by a duct which leads to a higher-pressure chamber. This reduces the difference in average pressure between the convex surface and the concave surface. However, the reduction in pressure takes place in only a zone adjacent the lower plate and/or the upper plate o
REFERENCES:
patent: 2291828 (1942-08-01), New
patent: 4146352 (1979-03-01), Yasugahira et al.
Bessay Raymond
Riollet Gilbert
Garrett Robert E.
Societe Anonyme dite: Alsthom-Atlantique
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