Patent Description:
A steam turbine includes: a rotating shaft that is rotatable around an axis; a plurality of turbine rotor blade rows that are arranged on an outer peripheral surface of the rotating shaft at intervals in an axis direction; a casing that covers the rotating shaft and the turbine rotor blade rows from an outer peripheral side; and a plurality of turbine stator blade rows that are supported in a radial direction by an inner ring and an outer ring on an inner peripheral side of the casing. Each turbine rotor blade row has a plurality of rotor blades arranged in a circumferential direction of the rotating shaft, and each turbine stator blade row has a plurality of stator blades arranged in the circumferential direction of the rotating shaft. The turbine rotor blade row is disposed adjacent to the turbine stator blade row on a downstream side in the axis direction to form one stage. An intake port connected to an inlet pipe that takes in steam from the outside is formed on an upstream side of the casing, and an exhaust hood is formed on a downstream side. Steam generated by a boiler flows into the turbine after a pressure and a temperature thereof are regulated by a regulating valve and a flow rate thereof is regulated by a turbine inlet valve. The high-temperature and high-pressure steam taken in from the inlet pipe is converted into a rotational force of the rotating shaft by the turbine rotor blade rows after a flow direction and a speed thereof are regulated by the turbine stator blade rows.

The steam passing through the turbine loses energy as the steam goes from an upstream side to the downstream side, and the temperature (and pressure) thereof drops. In particular, a steam turbine for thermal power generation is generally composed of a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine. Two stages (a pair of a turbine stator blade row and a turbine rotor blade row) counting from the most downstream side of the low-pressure turbine provide a gas-liquid two-phase flow environment. Therefore, in the stage on the most downstream side, a portion of the steam is liquefied and exists in an air flow as fine droplets (water droplets), and a portion of the droplets adheres to a surface of the turbine stator blade. The droplets exist on the surface of the turbine stator blade from the upstream side to the downstream side, and the droplets are aggregated on the surface of the blade and grow to form a liquid film. The liquid film is constantly exposed to a high-speed steam flow. When the liquid film further grows and increases in thickness, a portion of the liquid film is torn off by the steam flow and is scattered to the downstream side as coarse droplets. Since the larger the droplet size is, the larger the inertial force is, the droplets cannot ride on the steam flow and pass between the turbine rotor blades, and collide with the turbine rotor blade. A circumferential speed of the turbine rotor blade increases toward a tip side and may exceed a speed of sound. Therefore, in a case where the scattering droplets collide with the turbine rotor blade, erosion may occur on the surface of the turbine rotor blade. In addition, the collision of the droplets may hinder rotation of the turbine rotor blade, resulting in braking loss.

Various techniques have hitherto been proposed in order to prevent the occurrence of such erosion. For example, in a steam turbine described in <CIT> one guide groove is formed on a surface of a turbine rotor blade. It is described that by guiding droplets along the guide groove, the droplets can be prevented from flowing to a tip side of the turbine rotor blade having a high circumferential speed.

<CIT> discloses that a slit-shaped intake opening is provided in the wall of a hollow stationary blade so that it extends lengthwise along the stationary blade. A blade profile above the intake opening is formed so that a passage between the blades is enlarged, that is, a tangent of the surface of the blade profile deflects in sequence to extend into the hollow.

<CIT> discloses a hydrophilic surface pattern on a removal surface of a steam turbine directs surface moisture in at least one predetermined direction to enhance moisture management by enhancing moisture removal or otherwise reducing erosion caused by moisture in the steam turbine. The removal surface is located on the outer surface of a nozzle wall adjacent to an extraction opening. The removal surface is located on the surface of a bucket and directs moisture toward a turbine rotor. The removal surface is located on the surface of a turbine casing or the surface of a nozzle and directs moisture toward a drain in the turbine casing.

<CIT> discloses a turbine stator vane extending in the radial direction which intersects the flow direction of steam, and includes a middle surface facing the upstream side in the flow direction, and a back surface facing the downstream side in the flow direction. A plurality of grooves are formed in at least the middle surface, the grooves extending outward in the radial direction toward the downstream side. At the periphery of the grooves in the middle surface, formed is a hydrophilic uneven region having greater hydrophilic properties than the middle surface.

<CIT> discloses that a turbine blade has a ventral surface that extends in the radial direction, which intersects a vapor flow direction, and faces the upstream side of the flow direction. A slit is formed on the downstream side in the ventral surface and captures droplets generated as a result of the liquefaction of vapor. A region of micro recesses/protrusions, which guides droplets adhered to the ventral surface in the radial direction toward the slit from the upstream side to the downstream side, is formed further upstream than the slit. In the region of micro recesses/protrusions, resistance to the flow of droplets gradually increases from the inside to the outside in the radial direction.

However, restricting the flow of the droplets in the turbine rotor blade as described above does not provide a fundamental solution to erosion. Therefore, there has been an increasing demand for a technique capable of suppressing or collecting droplets in a turbine stator blade.

The present invention has been made to solve the above problems, and an object thereof is to provide a turbine stator blade and a steam turbine capable of suppressing or collecting droplets more efficiently.

In order to solve the above problems, the invention provides a turbine stator blade as set out in independent claim <NUM>, and a steam turbine as set out in independent claim <NUM>. Advantageous developments are defined in the dependent claims.

According to the present invention, it is possible to provide a turbine stator blade and a steam turbine capable of suppressing or collecting droplets more efficiently.

Hereinafter, a steam turbine <NUM> and a stator blade <NUM> (a turbine stator blade) according to an embodiment of the present invention will be described with reference to <FIG> and <FIG>. As shown in <FIG>, the steam turbine <NUM> includes a rotor <NUM> and a casing <NUM>.

The rotor <NUM> has a rotating shaft <NUM> having a circular cross section extending along an axis O, and a plurality of rotor blade rows <NUM> provided on an outer peripheral surface of the rotating shaft <NUM>. The rotating shaft <NUM> is rotatable around the axis O. The plurality of rotor blade rows <NUM> are arranged at intervals in an axis O direction. Each rotor blade row <NUM> has a plurality of rotor blades <NUM> arranged in a circumferential direction of the axis O. The rotor blade <NUM> extends radially outward from the outer peripheral surface of the rotating shaft <NUM>. A detailed configuration of the rotor blade <NUM> will be described later.

The casing <NUM> has a casing body <NUM> that covers the rotor <NUM> from an outer peripheral side, and a plurality of stator blade rows <NUM> supported from the outer peripheral side and an inner peripheral side by an outer ring <NUM> (described later) and an inner ring <NUM> (described later) provided on an inner peripheral side of the casing body <NUM>. The casing body <NUM> has a tubular shape centered on the axis O. The plurality of stator blade rows <NUM> are arranged at intervals in the axis O direction. The steam turbine <NUM> includes the same number of rotor blade rows <NUM> as the stator blade rows <NUM>, and one rotor blade row <NUM> is located between a pair of the stator blade rows <NUM> adjacent to each other in the axis O direction. That is, the rotor blade rows <NUM> and the stator blade rows <NUM> are alternately arranged in the axis O direction. One stator blade row <NUM> and one rotor blade row <NUM> form one "stage". Each stator blade row <NUM> has a plurality of stator blades <NUM> arranged in the circumferential direction of the axis O. The stator blade <NUM> extends in a radial direction with respect to the axis O.

A steam flow path <NUM> for taking high-temperature and high-pressure steam guided from an inlet pipe into the stage of the casing body <NUM> is formed on one side of the casing body <NUM> in the axis O direction. An exhaust hood <NUM> responsible for collecting a pressure of the steam is provided on the other side of the casing body <NUM> in the axis O direction.

The steam that has flowed into the steam flow path <NUM> flows through the stages in the casing body <NUM>, then passes through the exhaust hood <NUM>, and is sent to a condenser (not shown). In the following description, a side on which the steam flow path <NUM> is located as viewed from the exhaust hood <NUM> will be referred to as an upstream side in a flow direction of the steam. A side on which the exhaust hood <NUM> is located as viewed from the steam flow path <NUM> is referred to as a downstream side.

As shown in <FIG>, the rotor blade <NUM> includes a platform <NUM>, a rotor blade body <NUM>, and a shroud <NUM>. The platform <NUM> is installed on the outer peripheral surface of the rotating shaft <NUM> (rotating shaft outer peripheral surface 6A). The rotor blade body <NUM> is provided on an outer peripheral side of the platform <NUM>. The rotor blade body <NUM> extends in the radial direction and has a blade-shaped cross-sectional shape when viewed in the radial direction. As an example, the rotor blade body <NUM> is formed so that a dimension in the axis O direction gradually decreases from an inner side to an outer side in the radial direction. The shroud <NUM> is provided at an end portion on a radially outer side of the rotor blade body <NUM>. The shroud <NUM> has a substantially rectangular cross-sectional shape having the axis O direction as a longitudinal direction. An outer peripheral surface of the shroud <NUM> faces an inner peripheral surface (casing inner peripheral surface 3A) of the casing body <NUM> at an interval in the radial direction.

The stator blade <NUM> has the outer ring <NUM>, a stator blade body <NUM> (blade body), and the inner ring <NUM>. In addition, the stator blade body <NUM> has a central region <NUM>, an outer region <NUM>, an inner region <NUM>, and a slit <NUM> (collecting portion <NUM>). The outer ring <NUM> has an annular shape centered on the axis O. The outer ring <NUM> is supported by the casing body <NUM> via a support member (not shown). The stator blade body <NUM> is fixed between the outer ring <NUM> and the inner ring <NUM>. The stator blade body <NUM> extends radially inward from an outer ring inner peripheral surface 21A and has a blade-shaped cross-sectional shape when viewed in the radial direction. That is, the stator blade body <NUM> extends in a direction intersecting the flow direction of the steam. As an example, a dimension of the stator blade body <NUM> in the axis O direction gradually decreases from the outer side to the inner side in the radial direction. The inner ring <NUM> is provided at an end portion on a radially inner side of the stator blade body <NUM>. The inner ring <NUM> has a substantially rectangular cross-sectional shape having the axis O direction as a longitudinal direction. An inner peripheral surface of the inner ring <NUM> faces the rotating shaft outer peripheral surface 6A at an interval in the radial direction.

The central region <NUM>, the outer region <NUM>, the inner region <NUM>, and the slit <NUM> are formed on a surface of the stator blade body <NUM> (more specifically, a surface facing the upstream side of both surfaces of the stator blade body <NUM> in a thickness direction: a pressure side). A plurality of fine grooves <NUM> recessed inward from the surface of the stator blade body <NUM> are formed in the central region <NUM>, the outer region <NUM>, and the inner region <NUM>. The fine grooves <NUM> are provided to transfer droplets generated on the surface of the stator blade body <NUM> to the downstream side along a flow of the steam. The fine grooves <NUM> are arranged at intervals in the radial direction.

Regarding the fine grooves <NUM> (first fine grooves <NUM>) formed in the central region <NUM>, intervals between the first fine grooves <NUM> adjacent to each other decrease from a leading edge 22a side to a trailing edge 22b side of the stator blade body <NUM>. That is, a dimension of the central region <NUM> gradually decreases in the radial direction from the leading edge 22a side toward the trailing edge 22b side. End portions of the first fine grooves <NUM> on the downstream side communicate with the slit <NUM> described later.

The outer region <NUM> is formed radially outward of the central region <NUM>. The fine grooves <NUM> (second fine grooves <NUM>) formed in the outer region <NUM> are curved toward the outer side in the radial direction from the leading edge 22a side toward the downstream side. End portion of the second fine grooves <NUM> on the downstream side are connected to the inner peripheral surface of the outer ring <NUM>.

The inner region <NUM> is formed radially inward of the central region <NUM>. The fine grooves <NUM> (third fine grooves <NUM>) formed in the inner region <NUM> are curved toward the inner side in the radial direction from the leading edge 22a side toward the downstream side. End portion of the third fine grooves <NUM> on the downstream side extend to a radially inner region (vicinity of the inner ring <NUM>) in the trailing edge 22b.

On the leading edge 22a side, the central region <NUM> (first fine grooves <NUM>) occupies the largest ratio, and the outer region <NUM> and the inner region <NUM> occupy a smaller area than the central region <NUM>.

On a trailing edge 22b side of the central region <NUM>, the slit <NUM> is formed as a collecting portion <NUM> for collecting a liquid film that has flowed through the first fine grooves <NUM>. The slit <NUM> extends along the trailing edge 22b. The slit <NUM> is one or more elongated holes communicating with an inside of the stator blade body <NUM>. That is, the stator blade body <NUM> is hollow. It is desirable that an internal space of the stator blade body <NUM> is brought into a negative pressure state by a device (not shown).

Next, dimensions of the fine grooves <NUM> will be described with reference to <FIG>. As shown in the figure, in the present embodiment, the fine groove <NUM> has a rectangular cross-sectional shape. In a case where the interval (pitch) between the adjacent fine groove <NUM> is p, a depth of the fine groove <NUM> is h, a width of an opening is w, and a width of a bottom surface part is b, it is desirable that a value of w is <NUM> to <NUM>. In addition, it is desirable that a value of b/w is <NUM> to <NUM> (although details will be described later, a case where the value is <NUM> corresponds to a case where the fine groove <NUM> has a triangular cross section). Furthermore, it is desirable that a value of h/w is <NUM> to <NUM>. A value of p/w is desirably <NUM> to <NUM>.

Subsequently, an operation of the steam turbine <NUM> and a behavior of the droplets on the stator blade <NUM> according to the present embodiment will be described. In operating the steam turbine <NUM>, first, high-temperature and high-pressure steam is introduced into an inside of the casing body <NUM> through the steam flow path <NUM>. The steam alternately passes through the above-described stator blade rows <NUM> and rotor blade rows <NUM> while flowing toward the downstream side inside the casing body <NUM>. The stator blade row <NUM> rectifies the flow of the steam to cause the steam to flow into the adjacent rotor blade row <NUM> on the downstream side. By the steam acting on the rotor blade row <NUM>, torque is applied to the rotating shaft <NUM> through the rotor blade row <NUM>. Due to this torque, the rotor <NUM> rotates around the axis O. Rotational energy of the rotor <NUM> is taken out from a shaft end and is used for driving a generator (not shown) or the like.

Here, energy of the steam passing through the stage in a main flow path of the turbine is converted into rotational energy each time the steam passes through the stage from the upstream side toward the downstream side, resulting in a decrease in temperature (and pressure). Therefore, in the stator blade row <NUM> on the most downstream side, a portion of the steam is liquefied and exists in an air flow as fine droplets, and a portion of the droplets adheres to the surface of the stator blade <NUM> (the stator blade body <NUM>). These droplets grow to form a liquid film. Furthermore, when the liquid film flows downstream and increases in thickness as the number of droplets continues to increase, a portion of the liquid film is torn off by the steam flow, or the liquid film that remains adhering to the stator blade row scatters as coarse droplets from the trailing edge of the stator blade. The scattering droplets flow toward the downstream side while gradually accelerating due to the steam flow. When the coarse droplets collide with the rotor blade <NUM> on the downstream side, erosion may occur on a surface of the rotor blade <NUM>. In addition, the collision of the droplets may hinder rotation of the rotor blade <NUM> (rotor <NUM>), resulting in braking loss.

Therefore, in the present embodiment, the plurality of fine grooves <NUM> are formed on the surface of the stator blade body <NUM> as described above. The droplets captured in the fine grooves <NUM> flow toward the downstream side along with the flow of the steam. In the central region <NUM>, the droplets flow toward the slit <NUM> along the first fine grooves <NUM>. The droplets are collected by a negative pressure of the slit <NUM>. In addition, in the outer region <NUM>, the droplets flow toward the outer side in the radial direction along the second fine grooves <NUM> and are guided to the inner peripheral surface of the outer ring <NUM>. That is, the droplets do not reach the rotor blade <NUM> on the downstream side. Similarly, in the inner region <NUM>, the droplets flow toward the inner side in the radial direction along the third fine grooves <NUM>. Accordingly, the droplets do not reach a tip portion of the rotor blade <NUM> having a high circumferential speed.

In particular, according to the above configuration, the intervals between the first fine grooves <NUM> decrease from the upstream side toward the collecting portion <NUM> (slit <NUM>). Accordingly, the liquid film or droplets can be guided toward the collecting portion <NUM> from a wider range on the upstream side. In addition, accordingly, a size of the collecting portion <NUM> itself can be minimized. As a result, a possibility that the collecting portion <NUM> affects a mainstream of the steam can be reduced compared to a case where a large collecting portion <NUM> is secured.

In addition, according to the above configuration, the liquid film generated on the outer side in the radial direction from the central region <NUM> can be further guided toward the outer side in the radial direction (for example, the inner peripheral surface of the outer ring <NUM>) by the second fine grooves <NUM>. Accordingly, a possibility that the droplets are scattered toward a downstream side of the stator blade body <NUM> can be further reduced.

Furthermore, according to the above configuration, the liquid film generated on the inner side in the radial direction from the central region <NUM> can be further guided toward the inner side in the radial direction by the third fine grooves <NUM>. Accordingly, the possibility that the droplets are scattered toward the downstream side of the stator blade body <NUM> can be further reduced.

Hereinabove, the embodiment of the present invention has been described. In addition, various changes and modifications of the above-described configuration can be made without departing from the scope of the present invention, which is solely defined in the literal language of the claims.

According to the invention, a configuration shown in <FIG> can be adopted as a first modification example of the stator blade <NUM>. According to the invention, first fine grooves 51b are curved toward the outer side in the radial direction from the leading edge 22a side toward the slit <NUM> side. Furthermore, according to the invention, a turning angle, which is an angle formed by a direction in which the first fine grooves 51b extend with respect to a flow direction F of the steam, gradually decreases toward the slit <NUM>. That is, a portion of the first fine grooves 51b on the slit <NUM> side has a larger radius of curvature than a portion of the first fine grooves 51b on the leading edge 22a side. In other words, according to the invention, a rate of increase in the turning angle gradually decreases from the leading edge 22a side toward the slit <NUM> side. It is also possible to form the portion of the first fine grooves 51b on the slit <NUM> side as a clothoid curve.

According to the above configuration, the direction in which the first fine grooves 51b extend changes along the flow direction of the steam toward the slit <NUM>. Accordingly, a flow velocity of the liquid film increases toward the slit <NUM>, and the liquid film can be collected more efficiently.

Furthermore, it is also possible to adopt a configuration shown in <FIG> as a second modification example of the stator blade <NUM>. In the second modification example, main grooves 51c and sub-grooves 51d are formed as the fine grooves <NUM> in the central region <NUM>. The main grooves 51c extend from the leading edge 22a side toward the slit <NUM>, and an interval between the main grooves 51c adjacent to each other decreases. The sub-grooves 51d join one of the main grooves 51c at an end point starting from the leading edge 22a side. Even with such a configuration, it is possible to collect the liquid film in a wider range on the leading edge 22a side.

In addition, in the above-described embodiment, which is not according to the present invention, the example in which the fine groove <NUM> has a rectangular cross-sectional shape has been described. However, the shape of the fine groove <NUM> can be variously changed as long as the above-mentioned dimensional conditions are satisfied. For example, as shown in <FIG>, the width b of the bottom surface part can also be made larger than the width w of the opening (b > w). As shown in <FIG>, the width b of the bottom surface part can also be made smaller than the width w of the opening (b < w). As shown in <FIG>, the cross-sectional shape of the fine groove <NUM> can be made triangular (b = <NUM>). Furthermore, as shown in <FIG>, the bottom surface part can be made in an arc shape.

Claim 1:
A turbine stator blade (<NUM>) comprising:
a stator blade body (<NUM>) extending in a radial direction intersecting a flow direction of steam;
a collecting portion (<NUM>; <NUM>) formed on a surface of the stator blade body (<NUM>) and collecting a liquid film flowing along the surface; and
a central region (<NUM>) formed on the surface of the stator blade body (<NUM>) and formed with a plurality of first fine grooves (<NUM>) extending from an upstream side in the flow direction toward the collecting portion (<NUM>; <NUM>),
wherein intervals between the first fine grooves (<NUM>) adjacent to each other decrease from the upstream side toward the collecting portion (<NUM>; <NUM>),
characterized in that a turning angle, which is an angle formed by a direction in which the first fine grooves (51b) extend with respect to the flow direction, gradually decreases toward the collecting portion (<NUM>; <NUM>).