Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Reexamination Certificate
2001-02-01
2002-12-10
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
C415S210100
Reexamination Certificate
active
06491493
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a turbine nozzle, and more particularly to a turbine nozzle having an array of nozzle blades disposed circumferentially in an annular passage defined between an inner ring and an outer ring of a diaphragm and fixed to the inner and outer rings of the diaphragm.
BACKGROUND ART
It has been recognized in recent years that it is important to improve the performance of a turbine in order to improve energy consumption for mechanical operation or improve the efficiency of power generation in a power generating plant.
In order to improve the performance of a turbine, it is necessary to reduce the internal losses in each of the turbine stages. The internal losses in each of the turbine stages include a blade profile loss, a secondary flow loss, and a leakage loss.
The proportion of the secondary flow loss is large in a turbine stage where an aspect ratio (blade height/blade chord) is small and a blade height is small. Therefore, it is effective to reduce the secondary flow loss for thereby improving the performance of the turbine.
The mechanism of generation of the secondary flow will be described below.
As shown in
FIG. 15
of the accompanying drawings, a flow G flowing in between nozzle blades
1
is subject to a force caused by a pressure gradient from a pressure surface F to a suction surface B in each of the nozzle blades
1
. In a main flow-away from a turbine end wall, the force caused by the pressure gradient and a centrifugal force caused by the turning of the flow are in balance. However, a flow in a boundary layer near the turbine end wall has a low level of kinetic energy, and hence is carried from the pressure surface F to the suction surface B by the force caused by the pressure gradient as indicated by the arrows J. In a latter half of the flow passage, the flow collides with the suction surface B and rolls up, thus forming a flow passage vortex W. The flow passage vortex W accumulates a low-energy fluid in the end wall boundary layer to thereby generate a non-uniform energy distribution downstream of the nozzle blade. Although the non-uniform energy distribution is uniformized downstream of the nozzle blade, a large energy loss is generated during its uniformization. In
FIG. 15
, E represents a radial line, and L represents a hub end wall.
Various attempts have heretofore been made to suppress the above secondary flow.
For example, as shown in FIG,
16
of the accompanying drawings, bales
1
are inclined at an angle &thgr; to the radial line E for thereby weakening any blade-to-blade pressure gradient near the hub end wall of the blade. In
FIG. 16
, reference numeral
2
represents an outer ring, and reference numeral
3
represents an inner ring. Further, as shown in
FIGS. 17 and 18
of the accompanying drawings, nozzle blades
1
are curved at their opposite ends to orient the pressure surfaces F to the end wall. In
FIG. 17
, U represents an outer diameter surface. In
FIG. 18
, &thgr;t represents the angle between the tangent to the blade stacking line
1
at the tip end wall and radial line E, &thgr;r represents the angle between the tangent to the blade stacking line
1
at the hub end wall and radial line E, and h represents a blade height. According to the conventional attempts, while the same blade profile is employed, blade stacking lines are cured or inclined in a direction to weaken the blade-to-blade pressure gradient near the end walls, thereby controlling the secondary flow to reduce the loss.
Another conventional technology involves an inclined or curved surface imparted to a nozzle blade across its entire height for thereby controlling the secondary flow, as disclosed in Japanese laid-open patent publication No. 10-77801.
In order to control the pressure gradient with the above conventional arrangements, the nozzle blade needs to be largely inclined or curved, and hence efforts to meet such a requirement tend to cause problems in the manufacturing process or in the mechanical strength of the nozzle blades.
Further, according to such curved or inclined blades, a flow distribution at the outlet of the blades is liable to differ greatly from a flow distribution on blades which are neither curved nor inclined.
For example,
FIG. 19
of the accompanying drawings shows a graph having a horizontal axis representative of positions along the height of a blade, which are expressed as a dimensionless ratio with respect to the height h, and a vertical axis representative of circumferential velocities Vt and meridional velocities Vm, which are expressed as a dimensionless ratio with respect to the absolute velocity V (=(Vt
2
+Vm
2
)
0.5
). The graph shown in
FIG. 19
indicates that flow velocity distributions of an ordinary blade (indicated by the solid-line curves) and those of a curved blade (indicated by the broken-line curves) differ at the opposite ends of the blades.
If nozzle blades are of a curved shape and are combined with conventional rotor blades positioned downstream of the nozzle blades, then flows from the nozzle blades do not match the rotor blades, and the curved nozzle blades may not be effective. In such a case, new rotor blades capable of matching flows from the outlet of the curved nozzle blades are required, and thus such an arrangement cannot meet a wide range of applications.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide a turbine nozzle which is capable of reducing a secondary flow loss and producing an outlet flow that is the same as an outlet flow from ordinary blades, and does not adversely affect rotor blades positioned downstream of the turbine nozzle.
According to one aspect of the present invention, there is provided a turbine nozzle comprising: an array of nozzle blades (
1
) disposed circumferentially in an annular passage (
4
) defined between inner and outer rings of a diaphragm and fixed to the inner and outer rings of the diaphragm; and a flow passage defined between a pressure surface (F) and a suction surface (B) of adjacent ones of the nozzle blades, a cross section of the flow passage including predetermined ranges extending along a blade height from the inner and outer diameter surfaces (hub and tip end walls) and defined by a curved line, and another range defined by a substantially straight line.
Since the cross section of the flow passage in the predetermined ranges on the pressure surface and the suction surface includes a region defined by the curved line and a region defined by the substantially straight line, the turbine nozzle according to the present invention is clearly different in structure from the nozzle blade disclosed in Japanese laid-open patent publication No. 10-77801.
According to another aspect of the present invention, there is also provided a turbine nozzle comprising: an array of nozzle blades (
1
) disposed circumferentially in an annular passage (
4
) defined between inner and outer rings of a diaphragm and fixed to the inner and outer rings of the diaphragm; a pressure surface (F) in each of the nozzle blades facing the tip end wall of the turbine diaphragm in a predetermined range in the meridional direction of the nozzle blade and in a predetermined range between the tip end wall and a midspan of a blade, and the pressure surface facing the hub end wall of the turbine diaphragm in a predetermined range between the hub end wall and the midspan of the blade; a suction surface (B) in each of the nozzle blades facing the hub end wall of the turbine diaphragm in a predetermined range in the meridional direction of the nozzle blade and in a predetermined range between the tip end wall and a midspan of the blade, and the suction surface facing the tip end wall of the diaphragm in a predetermined range between the hub end wall and the midspan of said blade.
Here, the predetermined range may comprise a range corresponding to at least 30% of a meridional width (Cx) of the nozzle blade from a leading edge (
1
f
) of the nozzle blade in a meridional direction (x). The predetermined range may comprise
Harada Hideomi
Watanabe Hiroyoshi
Armstrong Westerman & Hattori, LLP
EBARA Corporation
Ryznic John E.
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