Low-pressure section rotor blades for steam turbines, steam turbines, methods, and power plants

Abstract

This disclosure relates to low-pressure section rotor blades for steam turbines, as well as steam turbine arrays, steam turbine rotors, and steam turbines. A method for improving the performance of one or more low-pressure section rotor blades for a steam turbine includes: determining at least one of vibration and aerodynamic instability of the one or more blades, and providing one or more orifices in the blades while they are connected to a rotor. The one or more orifices extend from the tip toward the root. The aerodynamic profile of the one or more blades remains unchanged.

Description

Technical Field

[0001] The present disclosure relates to rotor (moving) blades for a low-pressure section (cylinder) of a steam turbine. The disclosure further relates to rows of low-pressure section rotor blades for a steam turbine, a steam turbine rotor, a steam turbine, and a power plant. The disclosure further relates, in particular, to methods for improving one or more low-pressure section rotor blades for a steam turbine. Prior Art

[0002] A steam turbine is a rotating mechanical device that generates mechanical energy from steam flowing through it. For example, when the turbine is connected to a generator, it can generate electricity. A steam turbine includes a rotor consisting of a shaft and a plurality of rows of blades. A row of blades is also called a wheel. The shaft is arranged in the axial direction of the turbine, and the plurality of rows of blades are connected to the shaft. The rotor is supported by bearings and housed in a housing, such as a cylindrical housing.

[0003] A plurality of nozzles may be mounted to the casing and form part of the stator. Nozzles are also called vanes or diaphragms. Nozzles are arranged between the rows. The casing and the nozzles form a fixed part of the steam turbine.

[0004] One row typically consists of a platform mounted on the shaft and a plurality of blades on the platform. These blades are referred to as moving blades. On the other hand, a stator nozzle comprises a plurality of blades attached to the casing and spaced apart along the casing's circumference. A pair of nozzle rows and a subsequent row of moving blades is typically referred to as a stage of a steam turbine. Steam turbines typically comprise a plurality of stages.

[0005] During steam turbine operation, the nozzles have a fixed position. They direct the flow of steam between the previous row of moving blades and the next. The rows are designed to rotate as steam passes through their moving blades. This rotation of the rows rotates the shaft to which they are attached. This shaft can, for example, turn a generator to generate electricity.

[0006] The size and shape of the moving blades are related to their efficiency, reliability, and lifespan. Both the moving blades and the nozzles typically have an airfoil-shaped cross-section and may include a leading edge, a trailing edge, a pressure side, and a suction side. The cross-section typically varies along the length of the blade (i.e., radial height) to optimize the interaction between the blade and the steam and increase efficiency. Therefore, the blades are often twisted. The blade shape may also vary from one stage to the next, as thermodynamic conditions (temperature, velocity, pressure, etc.) typically vary from stage to stage.

[0007] A blade (i.e., a rotor blade) typically consists of two parts: a root and an airfoil. A blade may also include a shroud at its tip to reduce vibration. The shroud may extend along the circumference of the blade row. The shrouds of adjacent blades may be loosely connected to stabilize the blades. Blades that do not include a shroud at their tip are referred to as shroudless blades or dead-tip blades. Rotor blades with shrouds that span substantially halfway (i.e., along substantially half the length of the blade) are also known.

[0008] Many factors are considered in the design of rotor blades. Rotor blades are also called moving blades. One important aspect is tuning the natural frequency (also known as resonant frequency or eigenfrequency) of the moving blades to avoid frequencies that coincide with certain driving or excitation frequencies of the steam flow. If the excitation frequency coincides with one of the natural frequencies of the moving blades, resonance occurs. As a result, the moving blades begin to vibrate with extremely high amplitudes, potentially damaging or even destroying the moving blades and other parts of the turbine. Tuning the moving blades minimizes or at least reduces the likelihood of resonant vibrations.

[0009] Another important aspect is aerodynamic instabilities, such as fluttering, rotating stall, and buffeting. The moving blades can be tuned to avoid or at least reduce the presence of aerodynamic instabilities during turbine operation.

[0010] The severity of a moving blade's vibration response can be difficult to predict using theoretical tools because it depends on the intensity of the excitation. Therefore, frequency testing is often performed to determine the actual vibration response of the moving blade. In some cases, a turbine is operated to investigate how the turbine rotor's moving blades behave under different conditions, such as varying steam flow rates. Blade vibration can be measured, for example, by attaching strain gauges to the moving blades. In other cases, test equipment or a rotor can be used. For example, the blades can be attached to a test rig or rotor to perform blade frequency testing. After performing blade frequency testing, modifications can be made to the moving blades (for example, the external shape of the blade's airfoil portion).

[0011] Blade tuning can be achieved in a number of ways. Blade tuning can, for example, involve changing the profile of the blade tip, or generally changing the outer shape of the blade. To tune the blade, the tip region of the blade can be cut, machined, and / or ground. However, such blade tuning can adversely affect other important parameters, such as the stress distribution throughout the blade. Cutting, machining, and grinding can cause irreversible damage to the blade. The aerodynamic performance of the rotor blades can also significantly affect, reducing the overall efficiency of the turbine. Furthermore, thermal efficiency can be reduced, and the blades can be made more susceptible to corrosion. Furthermore, if the blades are tested while attached to the turbine rotor, the blades requiring tuning must be removed from the rotor for modification, which complicates and labors the tuning process.

[0012] Another way to limit the negative effects of resonance is to use hybrid tuning. Hybrid tuning involves providing two different groups of moving blades for the same stage or row of blades. The blades of the first group have a different external shape than the blades of the other group, for example, a different airfoil profile for the airfoil portion. Consequently, each group of moving blades has its own natural frequency, which differs from the natural frequency of the other group. The two groups of moving blades are arranged alternately around the shaft in the circumferential direction. In this way, two circumferentially adjacent moving blades have different natural frequencies. It is known in the art that aerodynamic instabilities (such as flutter, rotating stall, and buffeting) can be reduced by using hybrid-tuned moving blade groups. However, since the external shape of the blade airfoils differs between the two groups, this can negatively impact the aerodynamic performance of the blades and, therefore, the efficiency of the turbine. Furthermore, hybrid tuning can be time-consuming and expensive because it requires two separate manufacturing processes, such as two different molds for each type of blade.

[0013] Another relevant parameter for steam turbines is the pitch-to-chord ratio, as it can significantly affect efficiency and losses, particularly for the last-stage blades. A suboptimal pitch-to-chord ratio at the tips of the last-stage blades can reduce aerodynamic efficiency. Increasing the chord of the blades can help increase efficiency but can compromise mechanical integrity. Dynamic and static criteria for mechanical integrity can include, for example, resonant free blades, allowable bending stresses, and adequate mechanical damping; and allowable tensile stresses and local (notch) stresses in the airfoil, as well as proper root attachment. It should be noted that a portion of a blade is also referred to as a blade segment.

[0014] For different turbine configurations, the pitch-to-chord ratio can have an optimal value between 0.55 and 0.85, depending, for example, on whether impulses and / or reactions will be used to move the row of moving blades. Due to mechanical integrity limitations, the pitch-to-chord ratio can approach 1.0 or even exceed this value at the tip region of the last-stage blades. If the pitch-to-chord ratio is too high, blade-to-blade passages are absent, and effective steam flow control can become very difficult, which can lead to reduced efficiency.

[0015] A steam turbine may include sections operating at different pressures. A turbine section is also called a turbine. For example, a steam turbine may include at least one of a high-pressure (HP) section, an intermediate-pressure (IP) section, and a low-pressure (LP) section. The blade size increases toward the low-pressure section. In this disclosure, the moving blades used in the low-pressure section of a steam turbine are generally referred to as low-pressure section rotor blades. It is also possible for a steam turbine to include only low-pressure section rotor blades and, therefore, have only a single section, in these examples, the low-pressure section.

[0016] The previously discussed disadvantages can be particularly detrimental to low pressure section rotor blades.

[0017] Therefore, the present disclosure provides low-pressure section rotor blades, rotors, and steam turbines that can mitigate or eliminate one or more of the above-mentioned disadvantages. Summary of the Invention

[0018] In one aspect of the present disclosure, a method for improving one or more low-pressure section rotor blades for a steam turbine is provided. The method includes determining at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades. The low-pressure section rotor blades have a root end, a tip end, and an airfoil portion between the root end and the tip end, the root end being used to attach the low-pressure section rotor blade to a rotor. The method further includes providing one or more holes in the tip end of the one or more low-pressure section rotor blades while the one or more low-pressure section rotor blades are connected to the rotor, thereby reducing at least one of the determined vibration and the determined aerodynamic instability. The one or more holes extend from the tip end toward the root end. An aerodynamic profile of the one or more low-pressure section rotor blades remains unchanged.

[0019] In one embodiment, the aerodynamic profile can be understood to include or consist of the pressure and suction sides of the low-pressure section rotor blade. In this or other embodiments, the aerodynamic profile includes or consists of the outer shape of the airfoil portion. In a further embodiment, the aerodynamic profile includes or consists of the outer shape of the airfoil portion and the outer shape of the root end.

[0020] Based on this, at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades is determined. Subsequently, one or more holes are provided in the one or more low-pressure section rotor blades while the blades are attached to the rotor. The aerodynamic profile of the blades is not modified; for example, the blades are not ground, machined, or cut. Thus, the one or more low-pressure section rotor blades are improved because the provision of the one or more holes reduces or prevents at least one of the previously determined vibration and aerodynamic instability. Furthermore, the possibility of providing the holes while the blades are attached to the rotor avoids the problems and time associated with detaching the blades from the rotor and subsequently reattaching them to the rotor. These problems arise because rotor blades are often firmly attached to the rotor; that is, during detachment from the rotor, blades may even be irreversibly damaged. Time is a crucial factor in any repair or upgrade, as reducing the time required for repair or upgrades shortens any downtime.

[0021] In a further aspect of the present disclosure, a low-pressure section rotor blade for a steam turbine is provided. The blade includes a root end, a tip end, and an airfoil portion between the root end and the tip end, the root end being used to attach the low-pressure section rotor blade to a rotor. The blade also includes one or more holes for reducing at least one of vibration and aerodynamic instability, the one or more holes being provided only in the tip end and extending from the tip end toward the root end. The aerodynamic profile of the low-pressure section rotor blade remains unchanged. In one embodiment, the most convenient way to maintain this aerodynamic profile is by placing the one or more holes on a camber line of the tip end. This is particularly relevant for blades with complex shapes, such as those with a high degree of twist. This can be achieved, for example, by defining the camber line at the tip end and then providing the one or more holes on the camber line. This allows the one or more holes to be placed at equal distances from both the pressure side and the suction side.

[0022] In all aspects of the present disclosure, because the aerodynamic profile of the one or more low-pressure section rotor blades remains unchanged, the blades are improved without sacrificing aerodynamic efficiency and erosion resistance, for example, compared to cutting, machining, or grinding the blades. This results in aerodynamically efficient low-pressure section rotor blades and an aerodynamically efficient rotor for a steam turbine. Because the provision of one or more holes allows for tunability of the rotor blades, the rotor blades can be manufactured using a single mold rather than two different molds.

[0023] Furthermore, because the one or more low-pressure section rotor blades, and in particular the last stage blades, may be longer than the rotor blades used in other sections of the steam turbine and therefore may be more susceptible to damage from aerodynamic instabilities and vibrations, this method may be particularly suitable for improving the one or more low-pressure section rotor blades.

[0024] At least one of aerodynamic instability and vibration may occur during a process aimed at reducing rotor blade weight. In other words, a rotor blade undergoing weight reduction must limit or prevent at least one of aerodynamic instability and vibration for use in a steam turbine. The present invention allows for the achievement and application of rotor blade weight reduction. This allows for rotor blade designs that were previously impossible to manufacture.

[0025] The aerodynamic instabilities may include at least one of flutter, rotating stall, and buffeting. The vibrations may include at least one of a first mode, a second mode, and a third mode of blade resonance vibration.

[0026] The one or more low-pressure section rotor blades may be unshrouded low-pressure section rotor blades. The method may be particularly applicable to blades of this type because they may be more susceptible to aerodynamic instabilities and vibrations than shrouded low-pressure section rotor blades.

[0027] In a further aspect of the present disclosure, a low-pressure section rotor blade for a steam turbine is provided that is improved by the method of the aforementioned aspect. As previously explained, when the aforementioned method is performed on one or more low-pressure section rotor blades for a steam turbine, the one or more low-pressure section rotor blades are improved by reducing at least vibration and / or aerodynamic instabilities.

[0028] In a further aspect of the present disclosure, a rotor is provided comprising at least one low pressure section rotor blade according to the previous aspect.

[0029] In some examples, all blades in a row are modified according to the methods described herein. In some examples, at least some low-pressure section rotor blades do not contain any holes. In some examples, a distribution or size of the holes varies between low-pressure section rotor blades.

[0030] In some examples, each row of rotors including the low-pressure section rotor blades of the prior embodiment also includes one or more additional low-pressure section rotor blades. Each additional low-pressure section rotor blade includes a narrower tip than the tip of the low-pressure section rotor blade of the prior embodiment. In each row, every two low-pressure section rotor blades are separated by one additional low-pressure section rotor blade.

[0031] In a further aspect of the present disclosure, a steam turbine is provided comprising a rotor according to the previous aspect.

[0032] In a further aspect of the present disclosure, a fossil power plant, a renewable energy power plant, a waste-to-energy power plant, a combined cycle power plant, and a nuclear power plant are provided that include the steam turbine of the previous aspect or the rotor of the previous aspect.

[0033] Elements of these aspects and examples may be combined to form new aspects and examples within the scope of the present disclosure. Simple diagram description

[0034] [ FIG. 1A ] A schematic diagram shows an example of a low-pressure section rotor blade for a steam turbine. FIG1B schematically illustrates a cross-section of the airfoil portion of the low-pressure section rotor blade of FIG1A taken along line AB. [FIG. 2A] Schematically illustrates a perspective top view of a low-pressure section rotor blade including a hole. [ FIG. 2B ] A perspective side view schematically showing the tip region of the low-pressure section rotor blade of FIG. 2A . [Figure 3] A flow chart showing a method for improving one or more low-pressure section rotor blades of a steam turbine. Implementation Method

[0035] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only and not limitation. In fact, various modifications and variations will be apparent to those skilled in the art. For example, features illustrated or described as part of one embodiment can be used with another embodiment to produce a still further embodiment. Therefore, the present disclosure intends that such modifications and variations come within the scope of the appended claims and their equivalents.

[0036] A schematic example of a low-pressure section rotor blade, particularly an unshrouded low-pressure section rotor blade, is shown in FIG1A . A low-pressure section rotor blade 1 typically comprises two parts: a root or root end 2 and an airfoil portion 3. The root 2 is used to connect the low-pressure section rotor blade to the shaft, for example by forming a joint or welding the root to the hub. The airfoil portion 3 is an aerodynamic portion configured to interact with the passing steam. This interaction can result in forces that contribute to the rotation of the row in which the low-pressure section rotor blade 1 is located. As the row of steam turbines rotates, the tip or point 4 of the low-pressure section rotor blade 1 rotates closer to the stator casing.

[0037] Compared to the upstream pressure section, the low-pressure section rotor blades 1 of the example of FIG1A may have increased length. The height or length of low-pressure section rotor blades, particularly those in the final stage of a steam turbine, may exceed one meter. Blade length may be measured between the root and tip of the blade along the radial direction of the row, rotor, or steam turbine. Increased blade length may make the blade more susceptible to vibration and aerodynamic instability.

[0038] FIG1B schematically shows a cross section of the airfoil portion 3 of FIG1A along line AB. When the blade 1 is mounted on the rotor, line AB will be perpendicular to the radial and axial directions of the steam turbine and thus corresponds to the circumferential direction.

[0039] The cross section of Figure 1B shows the leading edge 5 and trailing edge 6 of the airfoil portion 3. Also shown are the pressure side 7 and suction side 8 of the airfoil portion 3. The imaginary line 9 connecting the leading edge 5 to the trailing edge 6 is called the chord of the airfoil portion 3. A camber line 10 is also shown.

[0040] Low-pressure section rotor blades can be manufactured using metal alloys such as steel or titanium alloys. Low-pressure section rotor blades and nozzles can be manufactured, for example, by overcasting. A negative mold of the blade shape can be provided, and the inner wall of the mold can then be overlaid with a material such as wax to form the blade pattern. The blade pattern can then be coated with a heat-resistant material to create a shell, which can then be filled with the metal alloy to form the blade.

[0041] According to one aspect of the present disclosure, a method 30 is provided. The flow chart of Figure 3 illustrates the method 30, which is a method for improving one or more low-pressure section rotor blades for a steam turbine.

[0042] At block 31, the method includes determining at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades. As previously explained, the low-pressure section rotor blade 1 has a root end 2, a tip end 4, and an airfoil portion 3 between the root end 2 and the tip end 4, the root end being used to attach the low-pressure section rotor blade to a rotor. At block 32, the method further includes providing one or more holes 11 in the one or more low-pressure section rotor blades 1 while the one or more low-pressure section rotor blades are connected to the rotor, thereby preventing at least one of the determined vibration and the determined aerodynamic instability. The one or more holes extend from the tip end 4 toward the root end 2.

[0043] In this manner, one or more low pressure section rotor blades have one or more holes such that at least one of vibrations and aerodynamic instabilities are limited or prevented.

[0044] Furthermore, the modification can be performed in situ without removing the low-pressure section rotor blades. Rather than having to remove multiple low-pressure section rotor blades from the rotor to modify them (e.g., frequency-tune them after determining at least one of vibration and aerodynamic instability), for example, by dismantling the turbine, transporting the blades to storage, changing the external shape of the airfoil portion, transporting the blades back, and reinstalling them. This allows for faster assembly and operation of the rotor. Aerodynamic instabilities are tested using steam and thus in a steam turbine, such as at a power plant. Vibrations, particularly resonances, can be tested outside the steam turbine, such as by testing the rotor at a factory. The present invention applies to both testing performed in the steam turbine (including testing at a power plant) and testing performed at a factory.

[0045] Furthermore, the overall centrifugal force on the low-pressure section rotor blade containing the hole can be reduced. A reduction in root attachment can also be achieved.

[0046] The aerodynamic instabilities may include at least one of flutter, rotating stall, and buffeting. The vibrations may include at least one of a first mode, a second mode, and a third mode of blade resonance vibration.

[0047] By providing one or more holes, the characteristic frequency of one or more low-pressure section rotor blades can be tuned, i.e., set to a desired value, without modifying the aerodynamic profile. Because the aerodynamic profile of the one or more low-pressure section rotor blades remains unchanged, aerodynamic efficiency can be maintained and the low-pressure section rotor blades can be made less susceptible to erosion.

[0048] Tuning or adjusting the eigenfrequency may refer to modifying one or more low-pressure section rotor blades to achieve a desired eigenfrequency. However, the aerodynamic profile of the blade or blades is not modified. In other words, tuning or adjusting the eigenfrequency goes beyond simply changing the eigenfrequency of one or more blades and involves achieving a desired eigenfrequency.

[0049] In some examples, determining at least one of vibration and aerodynamic instability can include obtaining an indication of how one or more low-pressure section rotor blades vibrate under load. The load can represent an operational load. In some examples, this determination can allow for the measurement or calculation of one or more characteristic frequencies, i.e., one or more frequencies at which one or more low-pressure section rotor blades resonate. This determination can also help estimate under what circumstances, for example, under what loads, one or more blades may be damaged or may break.

[0050] An example of a low-pressure section rotor blade 1 provided with one or more holes 11 (e.g., a first plurality of holes 11) is shown in Figures 2A and 2B. Figure 2A schematically shows a perspective top view of a steam turbine blade 1, and Figure 2B schematically shows a perspective side view of the tip region of the steam turbine blade 1 of Figure 2A. As used herein, the tip region of a turbine blade may refer to the region of the blade closest to the tip 4 of the blade, having a length that is one-third of the blade length, or less than one-third of the blade length.

[0051] The one or more low pressure section rotor blades may be shroudless low pressure section rotor blades.

[0052] In some examples, one or more low-pressure section rotor blades may have the same external shape. That is, within normal manufacturing tolerances, all low-pressure section rotor blades (e.g., a rotor row) may have the same external shape. For example, all low-pressure section rotor blades may be manufactured using the same mold.

[0053] In some examples, one or more holes 11 may extend longitudinally from the tip 4 to a longitudinal position 12 of the airfoil portion. Providing longitudinally extending holes may be easier than providing holes in other directions. The holes may be provided by drilling or other mechanical processes. Throughout this disclosure, "longitudinally extending" may refer to extending along the radial direction of the row (and therefore along the steam turbine). A longitudinal position in this context may be understood as a position along the airfoil portion that is separated from the tip of the low-pressure section rotor blade. In some examples, at least one of the one or more holes may extend at least partially to the root end. In some examples, the step of determining at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades may be performed while the one or more low-pressure section rotor blades are connected to the rotor. For example, the method may further include connecting the one or more low-pressure section rotor blades to the rotor, for example, to the steam turbine shaft, before the step of determining at least one of vibration and aerodynamic instability.

[0054] The step of determining at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades may include rotating the rotor at a speed within a range between a design speed of the steam turbine and a speed equal to 150% of the design speed of the steam turbine. The method may further include tuning the torsional modes of one or more low-pressure section rotor blades, particularly the third natural mode. Providing one or more holes tunes the third torsional mode of the corresponding low-pressure section rotor blade. Thus, the third mode can be tuned and positioned within the correct frequency range without cutting or grinding the low-pressure section rotor blades. Consequently, the low-pressure section rotor blades are less susceptible to erosion. Furthermore, because the aerodynamic profile of the blade is correlated with aerodynamic efficiency, if the aerodynamic profile of the blade remains unchanged, aerodynamic efficiency can be maintained while avoiding resonant vibration, particularly in the third natural mode.

[0055] One or more low-pressure section rotor blades may include a pitch-to-chord ratio less than 0.9, optionally less than 0.87, and optionally equal to 0.86. The efficiency of the low-pressure section rotor blades can be increased because the chord of the low-pressure section rotor blades is also increased, and grinding / machining of the external surface is not required. Providing one or more holes also facilitates compliance with mechanical integrity constraints: a desired pitch-to-chord ratio can be employed, and efficiency can be increased without creating mechanical integrity issues. This is particularly applicable to the tip region of the low-pressure section rotor blades, and more specifically, the tip region of the last-stage blades.

[0056] In some examples, one or more holes may be provided on alternating blades within a row of low-pressure section rotor blades. For example, one or more holes may be provided on each second low-pressure section rotor blade within the row of blades. A row of low-pressure section rotor blades may generally include a plurality of low-pressure section rotor blades, which are connected to a shaft of a steam turbine.

[0057] By staggering the holes, hybrid tuning can be achieved. The presence of multiple holes in alternating low-pressure section rotor blades provides two groups of blades, each group having its own characteristic frequency that differs from the characteristic frequency of the other group, rather than having two groups of low-pressure section rotor blades with different external shapes, such as different shapes of the airfoil portions. The first blade group can be formed from low-pressure section rotor blades that include holes, while the second blade group can be formed from low-pressure section rotor blades that do not include such holes. The two groups of low-pressure section rotor blades can be arranged alternately around the shaft in a circumferential direction of the shaft.

[0058] In some examples, the method may further include providing one or more additional holes 13 through the airfoil portion 3 of one or more of the low-pressure section rotor blades, for example on each second (unshrouded) low-pressure section rotor blade, such that the additional holes 13 extend from longitudinal position 12 of the airfoil portion 3 to an additional longitudinal position 14 of the airfoil portion 3. In this manner, the vibration frequency may be more easily controlled. The additional longitudinal position 14 may be closer to the blade root 2 than the (first) longitudinal position 12.

[0059] One or more holes may be empty. For example, one or more first holes 11 and one or more additional holes 13 may be empty.

[0060] At least one of the hole distribution, depth, and size can be determined based on at least one of excitation measurements and calculations. For example, the size (e.g., diameter), depth, spacing between holes (e.g., along the arc line 10 of the blade 1), and number of holes can be adjusted to the desired low-pressure section rotor blade, such as tuning. The shape and size of the low-pressure section rotor blade, such as its length, twist, and / or external shape, can influence one or more of the aforementioned characteristics of the holes. Some aspects of incorporating the first hole 11 and / or the additional holes 13 are further indicated below.

[0061] In addition to being applicable to manufacturing and operating steam turbine rotors or steam turbines without scratching, method 30 can also be used to retrofit at least one train of steam turbines. In some examples, all old low-pressure section rotor blades of the train can be removed. New low-pressure section rotor blades can be connected to the rotor shaft and tested, i.e., to determine at least one of vibration and aerodynamic instability. One or more holes can then be provided in one or more low-pressure section rotor blades, such as each second low-pressure section rotor blade, to improve the low-pressure section rotor blades.

[0062] In other examples, half of the old low-pressure section rotor blades in the row may be removed. For example, previously cut or ground (e.g., for frequency tuning) low-pressure section rotor blades may be removed. Unmodified low-pressure section rotor blades, e.g., uncut and / or unground blades, may remain attached to the rotor. New pressure section rotor blades having the same external shape as the low-pressure section rotor blades that remained attached to the rotor may replace the old, removed blades. The new blades may be interleaved with the old blades. After determining at least one of vibration and aerodynamic instability, one or more of the holes may be provided in the new or old blades.

[0063] In still other examples, the old blades may not be removed, and one or more holes may be provided in one or more of the array of old blades.

[0064] In the above example of a method for improving a steam turbine train, a more efficient train, and therefore a more efficient steam turbine, can be obtained. Further examples of improved methods may be possible.

[0065] The row may be the row of the last stage of a steam turbine. The low-pressure section rotor blades of the row of the last stage of the steam turbine may be longer than the low-pressure section rotor blades of other stages of the steam turbine and, therefore, may be more susceptible to aerodynamic instabilities, vibrations, and resonances. The low-pressure section rotor blades of the last stage may particularly benefit from having one or more first holes and, optionally, one or more additional holes provided therein.

[0066] According to a further aspect of the present disclosure, there is provided a low pressure section rotor blade for a steam turbine improved by the method described herein.

[0067] The blade may, for example, include a root end, a tip end, and an airfoil portion between the root end and the tip end, the root end being used to attach the low-pressure section rotor blade to a rotor. The blade may include one or more holes provided only in the tip end and extending from the tip end toward the root end, so that when the blade is attached to a rotor for or belonging to a steam turbine and the rotor rotates, at least one of vibration and aerodynamic instability is prevented or at least reduced. The aerodynamic profile of the low-pressure section rotor blade is not affected by the one or more holes.

[0068] According to a further aspect of the present disclosure, there is provided a rotor for a steam turbine comprising at least one low pressure section rotor blade as described herein.

[0069] A rotor may include a shaft and at least one row of low-pressure section rotor blades connected to the shaft. In some examples, each blade in at least one (low-pressure) row of the rotor is a low-pressure section rotor blade as described herein. That is, in these examples, each blade in at least one row includes one or more holes and is thus improved as explained herein.

[0070] In other examples, each (low-pressure) row of a rotor including the low-pressure section rotor blades may also include one or more additional low-pressure section rotor blades. Each additional low-pressure section rotor blade includes a narrower tip than the tip of the low-pressure section rotor blade. In each row, every two low-pressure section rotor blades are separated by one additional low-pressure section rotor blade.

[0071] That is, an additional low-pressure section rotor blade is arranged between the two low-pressure section rotor blades improved as explained herein. The additional blade has a tip that is narrower than the tip of the improved blade.

[0072] In some examples, a row of low pressure section rotor blades may have the same external shape (within tolerances). In other examples, the external shape may vary within the row of blades.

[0073] In some examples, at least one row may include a first group of modified blades and a second group of non-modified blades. The blades of the first group of blades in the row may include one or more first holes extending from the tip toward the root end, optionally extending to a first longitudinal position of the airfoil portion. The blades of the second group of blades in the row may not include the one or more first holes extending from the tip.

[0074] In some examples, the low pressure section rotor blade(s) of the previous aspect may belong to a first group, and the additional low pressure section rotor blade(s) may belong to a second group.

[0075] As explained previously in this disclosure, efficiency can be maximized while the risk of resonance can be minimized.

[0076] In some of these examples, the two groups of low-pressure section rotor blades may differ, within tolerance, only in that the first group of blades includes one or more first holes, while the second group of blades does not. That is, the blades of the two groups may have the same aerodynamic profile. In other examples, the blades of the two groups may have different aerodynamic profiles.

[0077] In the improved blade, the one or more first holes may extend longitudinally from the tip 4 to a first longitudinal position 12 of the airfoil portion 3.

[0078] In some examples, blades of the second group of blades (optionally, additional low-pressure blades) may include one or more second holes extending from the tip toward the root, for example, to a second longitudinal position in the airfoil portion, the second holes being different from the first holes. The one or more second holes may extend longitudinally from the tip to a different longitudinal position in the airfoil portion. Alternatively or additionally, the size and / or shape and / or position along the chord of the holes in the second group of blades may differ from the holes in the first group of blades.

[0079] The blades of the first group of blades may be interleaved with the blades of the second group of blades.

[0080] One or more first holes 11 may extend to the same first longitudinal position 12 of the wing portion 3, as shown in the example of FIG2B . In other examples, one or more first holes may extend upward to different first longitudinal positions. For example, some holes may be longer and some may be shorter. Or, in other words, one or more first holes 11 may have different depths in some examples.

[0081] The length of the one or more first holes 11 may be less than half, in particular less than one third, and more particularly less than 10% of the length of the blade 1. Since the area near the tip 4 may be particularly susceptible to vibrations, providing a hole in this area may be beneficial and sufficient to avoid or at least reduce the risk of resonance.

[0082] One or more first holes may be empty. For example, no additional material is added to the hole. In this way, for example, the tuned natural frequency of the low-pressure section rotor blade 1 can be kept in place and the vibration behavior of the blade can remain predictable.

[0083] In some examples, the first group of blades may include one or more additional holes 13 extending, for example, longitudinally from the first longitudinal position 12 to an additional longitudinal position 14, for example, in the airfoil portion 3. In some examples, the additional holes 13 may help adjust blade behavior, for example, to fine-tune the characteristic frequency of the corresponding low-pressure section rotor blade 1, and specifically the third torsional mode.

[0084] Like the same or more first holes 11, one or more additional holes 13 may extend to, for example, the same additional longitudinal locations of the airfoil portion. That is, the holes may have different lengths or depths. One or more additional holes 13 may also be empty. In some examples, one or more additional holes may reach the blade root and extend along at least a portion of the root.

[0085] The sum of the length of the longest of the one or more first holes 11 and the length of the longest of the one or more additional holes 13 may be less than half, in particular less than one third, of the length of the low-pressure section rotor blade 1. If the one or more first holes and / or the one or more additional holes have the same length, it is understood that all first holes (or additional holes) are the longest holes, and any hole length can be used for performing the sum.

[0086] The number of first holes 11 may be lower than the number of additional holes 13. This may, at least in some instances, allow the third mode of the blade to be tuned more easily.

[0087] The size of the one or more first holes 11 along the direction of the arc 10 can be larger than the size of the one or more additional holes 12 along the direction of the arc 10. That is, in some examples, the one or more first holes 11 can be thicker or wider than the one or more additional holes 12. This can be beneficial for properly adjusting blade behavior, for example, for properly tuning the high eigenfrequency of the low-pressure section rotor blades.

[0088] The blade row may be a final row. That is, one or more low-pressure section rotor blades may be final blades. Because final blades may be longer and may be negatively impacted by aerodynamic instabilities and vibrations, improving one or more low-pressure section rotor blades as described herein may reduce the risk of damage due to aerodynamic instabilities, vibrations, and resonances.

[0089] In some examples, all blades in a rotor row can be made of the same material. For example, the low-pressure section rotor blades can be metal. Making blades from a single type of material, rather than, for example, including metal and composite parts, can facilitate blade manufacturing. Manufacturing the blades can also be easier and less expensive.

[0090] One or more low pressure section rotor blades may be unshrouded.

[0091] In some examples, the low pressure section rotor blades may have a pitch to chord ratio lower than 0.9, in particular lower than 0.87, for example equal to 0.86.

[0092] The explanations provided with respect to one or more low-pressure section rotor blades 1 and holes are also applicable to the method 30 described above.

[0093] According to a further aspect of the present disclosure, there is provided a steam turbine comprising a rotor as described herein, for example in relation to the previous aspects.

[0094] Also provided is a thermal power plant, a renewable energy power plant, a waste-to-energy power plant, a combined cycle power plant, or a nuclear power plant comprising the steam turbine described herein or the rotor described herein.

[0095] According to a further aspect, a low-pressure section rotor blade for a steam turbine is provided, optionally a shrouded low-pressure section rotor blade. The low-pressure section rotor blade includes a root 2, an airfoil portion 3, and one or more first holes 11 extending, for example, longitudinally from a tip 4 of the airfoil portion 3 to a first longitudinal position 12 of the airfoil portion 3. The airfoil portion 3 further includes one or more additional holes 13 extending, for example, longitudinally from the first longitudinal position 12 to an additional longitudinal position 14 of the airfoil portion 3. The features and explanations described with respect to the low-pressure section rotor blade including the first hole 11 and the additional hole 13 with respect to the previous aspect also apply to this aspect.

[0096] According to a further aspect of the present disclosure, an unshrouded low-pressure section rotor blade 1 for a steam turbine is provided. The low-pressure section rotor blade includes a root and an airfoil portion. The airfoil includes a plurality of holes that tune a third mode of the torsional frequency of the low-pressure section rotor blade. At least a portion of the holes extend longitudinally from the tip of the low-pressure section rotor blade.

[0097] This written description uses examples to disclose the present teachings (including the preferred embodiments) and also to enable one skilled in the art to practice the teachings, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims and may include other examples that occur to one skilled in the art. Such other examples are intended to be within the scope of the claims if they do not have structural elements that differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. According to the principles of this application, which are part of this disclosure, anyone skilled in the art can mix and match elements of the various embodiments, aspects, and examples described, as well as other known equivalents of each such aspect, to construct additional embodiments, aspects, and examples. If reference numerals in the drawings are placed in parentheses within the claims, these are intended solely to aid in understanding the claims and should not be construed as limiting the scope of the claims.

[0098] 1: Blade 2: root or root end; leaf root 3: Wing-shaped part 4: Tip or point 5: Leading edge 6: trailing edge 7: Pressure side 8: Suction side 9: Imaginary Line 10: Arc 11: first hole; hole 12: First longitudinal position; longitudinal position 13: Extra hole 14: Additional vertical position 30: Method 31,32: Block AB: Line

Claims

1. A method for improving the performance of one or more low-pressure section rotor blades for a steam turbine, the method comprising: determining at least one of vibration and aerodynamic instability of the one or more low-pressure section rotor blades, wherein the low-pressure section rotor blades have a root end, a tip, and an airfoil portion between the root end and the tip, the root end for attaching the low-pressure section rotor blades to a rotor of the steam turbine; and providing one or more orifices in the tip of the one or more low-pressure section rotor blades while the one or more low-pressure section rotor blades are attached to the rotor, thereby reducing at least one of the determined vibration and the determined aerodynamic instability; wherein the one or more orifices extend from the tip toward the root end, and the aerodynamic profile of one or more low-pressure section rotor blades remains unchanged.

2. The method of claim 1, wherein the aerodynamic instabilities include at least one of fluttering, rotating stall, and buffeting.

3. The method of claim 1, wherein the vibrations include at least one of a first mode, a second mode, and a third mode of blade resonant vibration.

4. The method of any one of claims 1 to 3, wherein the one or more low-pressure section rotor blades are unshielded low-pressure section rotor blades.

5. The method of any one of claims 1 to 3, wherein the step of determining at least one of the vibration and aerodynamic instability of the one or more low-pressure section rotor blades is performed simultaneously with the connection of the one or more low-pressure section rotor blades to the rotor.

6. The method of any one of claims 1 to 3, wherein the step of determining at least one of the vibration and aerodynamic instability of the one or more low-pressure section rotor blades comprises rotating the rotor at a speed within a range between a design speed of the steam turbine and a speed equal to 150% of the design speed of the steam turbine.

7. The method of any one of claims 1 to 3, wherein the one or more low-pressure section rotor blades contain a pitch-to-chord ratio of less than 0.

9.

8. The method of request item 7, wherein the pitch-to-chord ratio is equal to 0.

86.

9. The method of any one of claims 1 to 3, wherein at least one of the one or more holes extends at least partially through the airfoil portion or to the root end.

10. The method of any one of claims 1 to 3, wherein the one or more holes are empty.

11. The method of any one of claims 1 to 3, wherein at least one of the distribution, depth, and size of the holes is determined based on at least one of excitation measurement and calculation.

12. The method of any one of claims 1 to 3, wherein the aerodynamic profile includes the pressure side and suction side of the low-pressure section rotor blade or is composed of the pressure side and suction side of the low-pressure section rotor blade, or wherein the aerodynamic profile includes the outer shape of the airfoil portion or is composed of the outer shape of the airfoil portion, or wherein the aerodynamic profile includes the outer shape of the airfoil portion and the outer shape of the root end or is composed of the outer shape of the airfoil portion and the outer shape of the root end.

13. A rotor blade for a low-pressure section of a steam turbine, wherein the low-pressure section rotor blade includes a root end, a tip, and an airfoil portion between the root end and the tip, the root end for attaching the low-pressure section rotor blade to a rotor, and one or more orifices provided in the tip based on a determination of at least one of vibration and aerodynamic instability of the low-pressure section rotor blade at the time of attachment to the rotor, for reducing at least one of the vibration and the aerodynamic instability, the orifices extending from the tip toward the root end, and an aerodynamic profile of the low-pressure section rotor blade unaffected by the orifices.

14. The low-pressure section rotor blades of claim 13, wherein the aerodynamic instabilities include at least one of fluttering, rotating stall, and buffeting.

15. The low-pressure section rotor blade of claim 13, wherein the vibrations include at least one of a first mode, a second mode, and a third mode of blade resonant vibration.

16. The low-pressure section rotor blade of any one of claims 13 to 15, wherein the low-pressure section rotor blade is an unshielded low-pressure section rotor blade.

17. The low-pressure section rotor blade of any one of claims 13 to 15, wherein the low-pressure section rotor blade has a pitch-to-chord ratio of less than 0.

9.

18. The low-pressure section rotor blades of request item 17, wherein the pitch-to-chord ratio is equal to 0.

86.

19. The low-pressure section rotor blade of any of claims 13 to 15, wherein at least one of the one or more holes extends at least partially through the airfoil portion or to the root end.

20. The low-pressure section rotor blade of any of claims 13 to 15, wherein the one or more holes are empty.

21. The low-pressure section rotor blade of any of claims 13 to 15, wherein at least one of the distribution, depth, and size of the holes is determined based on at least one of excitation measurement and calculation.

22. The low-pressure section rotor blade of any one of claims 13 to 15, wherein the aerodynamic profile includes or is composed of the pressure side and suction side of the low-pressure section rotor blade, or wherein the aerodynamic profile includes or is composed of the outer shape of the airfoil portion, or wherein the aerodynamic profile includes or is composed of the outer shape of the airfoil portion and the outer shape of the root end.

23. A rotor comprising at least one low-pressure section rotor blade as claimed in any one of claims 13 to 22.

24. The rotor of claim 23, wherein each blade in at least one column of the rotor is a low-pressure section rotor blade of any one of claims 13 to 22.

25. The rotor of claim 23, including the low-pressure section rotor blades, wherein each column of the rotor also includes additional low-pressure section rotor blades, wherein each additional low-pressure section rotor blade includes a narrower tip compared to the tip of the low-pressure section rotor blade, and wherein in each column, every two low-pressure section rotor blades are separated by an additional low-pressure section rotor blade.

26. A steam turbine comprising a rotor as claimed in any one of claims 23 to 25.

27. A fossil power plant, a renewable energy power plant, a waste-to-energy power plant, a combined cycle power plant, or a nuclear power plant comprising a steam turbine as claimed in claim 26 or a rotor as claimed in any of claims 23 to 25.

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