JP2000337101A - Axial flow turbine cascade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress incurring of a cascade back separation loss and to improve performance of an axial flow turbine. SOLUTION: The cascade (a moving blade and a stationary blade) of an axial flow turbine consists of an inlet cascade 11 on the upstream side and an outlet cascade 12 on the wake side. The two blades 11 and 12 are situated to form an overlap region in an axial direction such that the front edge 14 of the outlet cascade 12 is positioned on the upstream side of the rear edge 13 of the inlet cascade 11. A wake 6 generated at the inlet cascade on the upstream side approaches an increased flow 8 occurs between the wake 6 and an inlet cascade back 15, Turning of a flow is decreased compared with a conventional one by the curve of the inlet cascade back 15 and the flow passes through the cascade 11 without the occurrence of separation at the back 15 and is confluent to a flow from an inlet cascade belly 16 and flows through the cascade 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial flow turbine cascade relating to a turbine engine such as a steam turbine and a gas turbine. It was done.

[0002]

2. Description of the Related Art FIG. 5 is a schematic view of a conventional axial turbine blade cascade flow. In FIG. 5, 1 is the wing back surface, 2 is the wing abdominal surface,
Reference numeral 3 denotes a leading edge of the blade, 4 denotes a trailing edge of the blade, 5 denotes a boundary layer having a low flow velocity of the fluid flow, and 6 denotes a wake in a low flow velocity region of the fluid.
The fluid flows from the leading edge 3 of the blade to the trailing edge 4 of the blade in a curved flow path sandwiched between the blade back surface 1 and the adjacent blade abdominal surface 2. A region called a boundary layer 5 having a low flow velocity develops on the blade back surface 1 and the blade abdominal surface 2 under the influence of the viscosity of the fluid.
The developed boundary layer 5 is united at the trailing edge 4 of the blade, and flows out to form a band-like region having a lower flow velocity than the surrounding area. This low flow velocity region generated from the wing trailing edge 4 is called a wake 6,
Flow into the downstream cascade.

FIG. 6 is a schematic view of a conventional axial flow turbine cascade flow showing the influence of the wake described above on the cascade from the upstream side to the downstream side. In FIG. 6, reference numeral 6 denotes a wake generated from the upstream cascade, which moves from left to right relative to the cascade in the figure. When the wake 6 approaches the downstream cascade from the wing back 1 side, the wake 6 and the wing back 1
In the region sandwiched between the two, the effective flow path width becomes narrow and the flow velocity increases. The accelerated flow 8 cannot flow following the curvature of the blade back surface 1, and a loss area 7 due to separation is formed on the blade back surface 1. As the wake 6 moves, when the wake 6 passes from the wing rear surface 1 side to the wing abdominal surface 2 side across the wing leading edge 3, the speed increasing region on the wing rear surface 1 disappears, and the loss region 7 generated by the separation also moves downstream. And outflow. As described above, the conventional axial flow turbine cascade periodically releases the loss due to separation under the influence of the wake 6 generated by the upstream cascade, thereby lowering the performance of the axial flow turbine. .

[0004]

As described above, in the conventional axial flow turbine cascade, the wake generated on the upstream side flows to the downstream cascade, and a loss region due to fluid separation on the back surface of the blade is periodically generated. This loss area is discharged to the downstream and causes a decrease in performance. Therefore, there has been a demand for a measure for eliminating the occurrence of such a fluid loss region and for suppressing a decrease in performance.

Therefore, the present invention suppresses the separation loss on the back surface of the cascade which is periodically generated by the influence of the wake of the upstream cascade as an arrangement or a shape of the wing so as not to wake the fluid flowing through the cascade. It was made to improve the performance of the turbine.

[0006]

The present invention provides the following means (1) and (2) to solve the above-mentioned problems.

(1) In a cascade in which a plurality of blades are arranged around an axial direction of an axial flow turbine, the cascade includes a front cascade and a rear cascade, and the front cascade includes a front cascade in a circumferential direction. An axial flow turbine cascade characterized in that rear cascades are alternately arranged so that the leading edge of the rear cascade is located upstream of the trailing edge of the front cascade in the axial direction.

(2) In a cascade in which a plurality of blades are arranged around the axial flow turbine in the axial direction, a cavity is provided on the back surface of the blade upstream of the throat of each blade, and a recirculating flow of fluid is provided in the cavity. An axial flow turbine cascade characterized in that it is held constantly.

In (1) of the present invention, when the wake of the fluid generated in the upstream cascade approaches the front cascade, the effective flow path width between the wake and the back of the front cascade is reduced, and the flow velocity is reduced. Increase. This increased flow velocity flows from the leading edge of the trailing cascade to the trailing cascade, but since the leading cascade is arranged so that the flow direction is smaller than before, the flow is With no separation on the upper side, the accelerated flow passes through the front cascade, joins the flow from the front cascade ventral surface, and passes through the rear cascade. In this way, the blade cascade back surface separation loss periodically generated by the influence of the upstream cascade wake is suppressed, and the performance of the axial turbine can be improved.

In (2) of the present invention, a recirculating flow is constantly generated in a cavity provided on the back surface of the blade. When the wake generated on the upstream side approaches from the back side of the wing, an accelerated flow is generated in a region sandwiched between the wake and the back side of the wing. When this flow goes around the recirculating flow in the cavity, the boundary line of the recirculating flow expands to the accelerated flow side due to the decrease in static pressure due to the accelerated flow, but when the accelerated flow disappears as the wake passes, It contracts to the recirculation flow side. In this way, the boundary line of the recirculating flow expands and contracts irregularly, causing separation loss at the back of the blade,
Reduce spills. As described above, it is possible to suppress the generation and outflow of separation loss on the blade back surface due to the passage of the upstream cascade wake, and to improve the performance of the axial turbine.

[0011]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an airfoil sectional view of an axial flow turbine cascade according to a first embodiment of the present invention. In the figure, 11 is a front cascade, 12 is a rear cascade, 1
Numeral 3 is a trailing edge of the leading cascade, and numeral 14 is a leading edge of the trailing cascade. As shown in FIG. 1, the axial turbine cascade according to the first embodiment of the present invention comprises a front cascade 11 and a rear cascade 12 which are alternately arranged.
Consists of The two cascades are arranged so as to have an overlapping area A in the turbine axial direction such that the trailing edge 14 of the trailing cascade is located upstream of the trailing edge 13 of the leading cascade. This cascade is applied to both moving blades and stationary blades.

FIG. 2 is a schematic diagram showing the internal flow of the axial turbine cascade according to the first embodiment of the present invention. In the figure, reference numerals 11 to 14 are the same as those in FIG. 3, reference numeral 15 is the front cascade rear surface, and reference numeral 16 is the front cascade ventral surface. Reference numeral 6 denotes a wake, and reference numeral 8 denotes a speed increasing flow.

In FIG. 2, when the wake 6 generated in the upstream cascade approaches the axial turbine cascade according to the present invention,
The effective flow path width in a region sandwiched between the wake 6 and the front cascade back surface 15 is reduced, and the flow velocity is increased. Since the flow diverting in the front cascade 11 is smaller than that in the conventional axial turbine cascade, the flow 8 without separation on the front cascade back surface 15 passes through the front cascade 11, It passes through the rear cascade 12 together with the flow from the front cascade abdominal surface 16 side. As described above, it is possible to suppress the loss due to the separation of the back surface of the cascade, which is periodically generated due to the influence of the wake 6 in the upstream cascade, and to improve the performance of the axial flow turbine.

FIG. 3 is an airfoil sectional view of an axial flow turbine cascade according to a second embodiment of the present invention. In the figure, 1 is the back surface of the blade, 2 is the blade surface, 9 is the throat between adjacent blades, and 21 is a cavity formed in the blade. As illustrated, the axial flow turbine cascade according to the second embodiment of the present invention is configured by forming a cavity 21 on the blade back surface 1 upstream of the throat 9.

FIG. 4 is a schematic diagram showing the internal flow of an axial turbine cascade according to a second embodiment of the present invention. In the figure, reference numerals 1, 2, and 21 are the same as those in FIG. 3, 6 is a wake, 8 is an accelerating flow, 22 is a recirculating flow, and 23 is a recirculating flow boundary line.

In FIG. 4, a cavity 21 provided in the blade back surface 1 of the axial flow turbine cascade according to the second embodiment of the present invention is shown.
Inside, a recirculating flow 22 is constantly generated. Wing back 1
When the wake 6 in which the upstream cascade is generated approaches from the side, an accelerated flow 8 is generated in a region between the wake 6 and the blade back surface 1. When the accelerated flow 8 wraps around the recirculation flow 22 in the cavity 21, the boundary line 2 of the recirculation flow 22
3 swells toward the accelerated flow 8 side due to a decrease in the static pressure due to the accelerated flow 8, but increases with the passage of the wake 6.
Disappears, it contracts to the recirculation flow 22 side. As described above, the boundary line 23 of the recirculation flow expands and contracts unsteadily, thereby preventing generation and outflow of separation loss at the blade back surface 1. Therefore,
It is possible to suppress the generation and outflow of separation loss on the blade back surface due to the passage of the upstream cascade wake 6, and to improve the performance of the axial turbine.

[0017]

According to the present invention, there is provided an axial flow turbine cascade comprising: (1) a cascade in which a plurality of blades are arranged around an axial flow turbine in an axial direction, wherein the cascade is a front cascade and a rear cascade. That the front cascade and the rear cascade are alternately arranged in the circumferential direction, and that the front cascade front edge is located in the axial direction so as to be located upstream of the front cascade rear edge, respectively. It is characterized by. With this configuration, the fluid does not separate at the back of the front cascade, the flow smoothly flows from the front cascade to the rear cascade, and the blades are periodically generated by the influence of the upstream cascade wake. The separation loss at the back of the row can be suppressed, and the performance of the axial turbine can be improved.

An axial flow turbine cascade according to (2) of the present invention is characterized in that, in a cascade in which a plurality of blades are arranged around the axial flow turbine in the axial direction, a cavity is provided on the back surface of the blade upstream of the throat of each blade. A feature is that the recirculation flow of the fluid is constantly maintained in the cavity. With such a configuration, the boundary line of the recirculating flow in the cavity expands when the fluid passes, and contracts when the flow disappears. These expansion and contraction are repeated, thereby suppressing the occurrence of separation loss and outflow at the back surface of the blade. be able to. In this way, the occurrence of separation loss on the back surface of the wing due to the passage of the upstream cascade wake,
Outflow can be suppressed, and the performance of the axial turbine can be improved.

[Brief description of the drawings]

FIG. 1 is an airfoil sectional view of an axial turbine cascade according to a first embodiment of the present invention.

FIG. 2 is a schematic internal flow diagram of the axial turbine blade cascade according to the first embodiment of the present invention.

FIG. 3 is a blade cross-sectional view of an axial flow turbine cascade according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram of the internal flow of an axial turbine cascade according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram of a conventional axial turbine cascade flow.

FIG. 6 is a schematic diagram of the internal flow of a conventional axial flow turbine cascade affected by a wake generated by an upstream cascade.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wing back surface 2 Wing abdominal surface 6 Wake 8 Acceleration flow 9 Throat 11 Front cascade 12 Rear cascade 13 Front cascade trailing edge 14 Rear cascade front edge 15 Front cascade back surface 16 Front cascade Ventral surface 21 Cavity 22 Recirculating flow 23 Recirculating flow boundary

Claims (2)

[Claims] In a cascade in which a plurality of blades are arranged around an axial flow turbine in an axial direction, the cascade includes a front cascade and a rear cascade, and a front cascade and a rear cascade in a circumferential direction. Alternately with the cascade,
An axial flow turbine cascade characterized in that the leading edge of the trailing cascade is located in the axial direction upstream of the trailing edge of the leading cascade. 2. A cascade in which a plurality of blades are arranged around an axial direction of an axial flow turbine, a cavity is provided on a back surface of the blade upstream of a throat portion of each blade, and a fluid recirculation flow is steadily maintained in the cavity. An axial flow turbine cascade characterized in that the turbine blade cascade is held.