Improved turbine and blades to protect the root from high-temperature gases in the flow path.

Abstract

To reduce gas ingestion from a hot gas flow path passing from a low-pressure gas turbine to wheel spaces.SOLUTION: A turbine 14, particularly a low-pressure turbine, is disclosed, which comprises a plurality of rotor members 2 and spacers 7 arranged between the rotor members to prevent an ingested gas flow from a hot gas flow path channel F from reaching wheel spaces. The rotor members each include a deflector 8. The deflector is placed corresponding to each spacer and deflects purging air P pumped up from the wheel spaces by the rotor members so as to prevent the ingested gas flow from heating up roots of blades 4.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a gas turbine that can protect the rim of a wheel of a rotor assembly by sucking high-temperature gas into the wheel space during operation.

Background Art

[0002] As is well known, a gas turbine is an energy conversion plant and typically includes, among other things, a compressor for drawing in and compressing gas, a combustor (or burner) for adding fuel and heating the compressed air, a high-pressure turbine having a plurality of rotor assemblies for extracting output from a high-temperature gas flow path and driving the compressor, and a low-pressure turbine also having a plurality of rotor assemblies and mechanically connected to a load.

[0003] Particularly in low-pressure turbine designs, preventive measures are usually taken to reduce the suction of gas from the high-temperature gas flow path, which can have an adverse effect on non-high-temperature gas components such as wheels and spacers. The phenomenon of gas suction from the high-temperature gas flow path can occur when the engine is operating at part load.

[0004] More specifically, the typical low-pressure turbine described above includes a plurality of rotor members, each of which has a rotor wheel having a rim, and a plurality of blades are coupled to the rotor wheel.

[0005] Each blade has a male dovetail or root designed to fit into one corresponding groove obtained on the rim of the rotor wheel. The wheel is usually made of a material inferior to that of the blade.

[0006] Between two adjacent and opposing rotor wheels, a wheel space is individualized between the two rotor wheels of the two rotor members.

[0007] The phenomenon of gas suction from a high-temperature gas passage typically occurs when some of the high-temperature gas flows into the wheel space, resulting in the wheel rim being operated above or near its material temperature limit. This can damage wheel rims made of less noble materials, potentially reducing the wheel's lifespan. This means that this phenomenon can cause failure of the wheel's dovetail (e.g., significant deformation) and the resulting detachment of the blades.

[0008] In addition to the above, the wheel space is typically purged. For this purpose, the gas turbine is equipped with a piping system to supply purge air from the compressor to the low-pressure turbine. Specifically, the purge air is introduced into the wheel space of the low-pressure turbine. This lowers the overall temperature of the wheel space to some extent.

[0009] The intake of hot gas is typically prevented when the amount of purge air is greater than the amount of air pumped by the wheel. If the amount is less, the pumping effect compensates for the portion not provided by the purge system with hot gas air drawn in far from the wheel and discharged near the wheel (recirculation). Recirculation can occur when the engine is operating at low power, after which the compressor provides less purge air to the low-pressure turbine, but the low-pressure turbine can still operate at its high speed.

[0010] To reduce gas suction in the high-temperature gas flow path from the low-pressure gas turbine to the wheel space, several solutions can be utilized in the latest technologies.

[0011] Specifically, spacers may be added between wheels, and these spacers may have a rim that axially covers the space not covered by the wheel, and these spacer rims may also extend radially to the same outer diameter of the wheel to minimize the portion of the wheel rim above the wheel space cavity. The spacers provide a physical barrier against the inflow of hot gases, but typically the spacers do not come into contact with the rims of adjacent wheels, and therefore hot gases can flow into the gap and reach the wheel space. Spacers can protect adjacent wheels even if the wheels have different outer diameters by shaping the spacer rim into a cone shape.

[0012] Therefore, in this technology, improved turbines and blades that can reduce any possible gas inhalation from the high-temperature gas flow path are welcome. [Overview of the project]

[0013] The aforementioned spacer improvement is the provision of a near-seal flow path (NFPS) that can press against the wheel space sealing near the hot gas path. NFPS replaces more conventional spacers to better protect the wheel rim from hot gas inhalation, which can occur not only inside the wheel cavity but also through the lab seal. From a structural standpoint, an NFPS is a segment (i.e., an arm member) and not a ring (as a spacer does), and therefore causes leakage between adjacent rotor members. Moreover, an NFPS requires a multi-connection system to engage with the internally supported rotor wheel, inevitably increasing the complexity of the solution. In practice, an NFPS is a smaller component compared to a conventional spacer and therefore can be made from a more noble material.

[0014] However, recently, the temperature of the high-temperature gas passages has been increased in order to improve the output and efficiency of gas turbines. As a result, the flow of purge air from the compressor has decreased, increasing the risk of gas being drawn in from the high-temperature gas passages.

[0015] Furthermore, when the low-pressure turbine rotates at a low speed, the high-temperature gas passages expand less at lower speeds and pass from one stage to another, or from one rotor assembly to another, so the pressure difference decreases proportionally in the high-temperature gas passages. At the same time, as mentioned above, the pumping effect decreases when the low-pressure turbine rotates at a low speed.

[0016] Finally, wheelspace temperatures are typically monitored by appropriate thermocouples. However, the smaller layouts of turbines compared to previous designs make thermocouple installation far more complex, resulting in lower reliability. Furthermore, the placement of spacers or any other mechanical barriers between the two rotor assemblies complicates thermocouple installation. Thus, there is a tendency to reduce the number of thermocouples installed, which diminishes the control over the temperature rise of the wheel rims and the risk of their potential degradation.

[0017] Accordingly, in one embodiment, the subject matter disclosed herein relates to a turbine comprising a plurality of rotor members, which rotates by the expansion of hot combustion gas flowing into a hot gas flow channel. Each rotor member comprises a rotor wheel. A wheel space is individually separated between two adjacent rotor wheels. Each rotor member also has a protective spacer positioned between two opposing rotor members and configured to prevent the drawn-in gas flow from the hot gas flow channel to reach the wheel space. The turbine also has stator spacers. A channel is separated between each stator spacer and its associated protective spacer. The rotor members also include deflectors configured to deflect purge air pumped from the wheel space by the rotor members into the channel, where the pressure is lower than the pressure of the gas being deflected by the deflectors.

[0018] In another embodiment, the subject matter disclosed herein relates to a deflector being located on the shank of each blade.

[0019] In another embodiment, the subject matter disclosed herein relates to a deflector that is positioned on the rim of the rotor wheel of the blade and can cover the gap between the spacer and the wheel.

[0020] In another embodiment, this specification discloses a deflector having an upper surface configured to deflect any possible gas inhalation from a high-temperature gas flow channel toward the upper surface of a spacer.

[0021] In another embodiment, this specification discloses a deflector configured to redirect an inhaled gas flow toward the upper surface of a shank, while the deflector allows purge air gas to flow radially to reach a hot gas flow channel to prevent the inhalation of hot gas when the turbine is operating under base load conditions. [Brief explanation of the drawing]

[0022] Many of the embodiments of the disclosed invention and their associated advantages will become clearer as you gain a deeper understanding by referring to the embodiments for carrying out the invention described below, in relation to the accompanying drawings. [Figure 1] A schematic diagram of a gas turbine is shown as an example. [Figure 2] An example of a disassembled blade is shown. [Figure 3] A partial cross-sectional view of a low-power turbine according to the first embodiment is shown as an example. [Figure 4] A cross-sectional view of a low-power turbine section according to the first embodiment is shown as an example, illustrating the flow of purge air under normal operating conditions. [Figure 5] Figure 4 shows an example of a cross-sectional view of a low-power turbine, illustrating low gas intake. [Figure 6] Figure 4 illustrates a cross-sectional view of a low-power turbine with purge flow under so-called base load conditions. [Figure 7] A partial cross-sectional view of a low-power turbine according to the second embodiment is shown as an example.

Best Mode for Carrying Out the Invention

[0023] Improvements in gas turbines have been discovered. Gas turbines have a number of components, particularly a low-pressure turbine. Such a low-pressure turbine is formed of a number of blades radiating out from a central hub and angled to move air through the engine. Some areas of the gas turbine are very hot. Other areas are cooler. A known problem is that some of the hot gas moved by the blades flows towards the central hub under certain conditions, and can thus cause damage and reduce the service life of the turbine.

[0024] The inventors have discovered that this problem can be mitigated and / or addressed by placing a new deflector element corresponding to the shank of each blade and intervening between the blade itself and a spacer disposed between two adjacent wheels. The deflector deflects purge air towards the low-pressure channel 74 between two adjacent rotor members, particularly towards the upper surface of the spacer, and is shaped to subsequently deflect any possible suction of hot gas upwards. In this way, the deflector protects the components inside the turbine and prevents an average increase in temperature therein.

[0025] FIG. 1 schematically illustrates a gas turbine generally designated by reference numeral 1. The gas turbine 1 includes, inter alia, a compressor 11 for drawing in and compressing gas supplied to a combustion chamber or burner (not shown) for adding fuel and heating compressed air, a plurality of rotor assemblies, a high-pressure turbine 12 for extracting output from the hot gas flow path and driving the compressor 11, a shaft 13 connecting the compressor 11 and the high-pressure turbine 12, and a low-pressure turbine 14 also having a plurality of rotor assemblies and driving, by means of a further shaft 15, for example, a gearbox and a centrifugal compressor, or any other load.

[0026] In addition, the gas turbine 1 includes a purge system 16 for supplying purge air to the low-pressure turbine 14. The purge system generally comprises an extraction extractor 161 connected to a cooler 163 by a connecting pipe 162, which then connects to the low-pressure turbine 14 by a purge pipe 164 to purge the wheel space between the rotor assemblies (see below). This has the effect and function of reducing the overall temperature of the wheel space to some extent.

[0027] Referring here to Figures 2 and 3, the low-pressure turbine 14 comprises several rotor members, typically shown herein by reference no. 2, that rotate around a rotation axis R and are coupled to a shaft 15.

[0028] More specifically, each rotor member 2 is coupled to a shaft 15 and comprises a rotor wheel 3 having a rim 31 and a plurality of circumferentially spaced female dovetail-shaped slots or grooves 32 around the rim 31. In this embodiment, each groove 32 has a fir tree shape. However, in some embodiments, the grooves may have different shapes.

[0029] Each rotor member 2 also comprises a plurality of blades 4, each blade having a male-shaped dovetail or root 41 designed to fit into one corresponding groove 32 of the rotor wheel 31 along the insertion direction. Thus, each root 41 has substantially the same shape as the corresponding groove 32.

[0030] The base 41 of the blade 4 has only a mechanical function to firmly connect the blade 4 to the rotor wheel 3, and in particular to the groove 32 of the rotor wheel 31.

[0031] Each blade 4 also comprises a platform or shank 42 to which the root 41 is connected, and an airfoil 43 coupled to the shank 42. Since the airfoil 43 is subjected to significant thermal and mechanical stress, the airfoil 43 is made of a noble material. An airfoil shroud 44 is also present at the top of the airfoil 43 for connecting each blade 4 to a neighboring one.

[0032] As described above, between the two adjacent and opposing rotor wheels, a wheel space 5 is individually located between the two rotor wheels 3 of the two rotor members 2.

[0033] Figure 3 also illustrates the stator spacer 6 of the turbine 14 (not shown) and the nozzle 6', which are interposed between the two rotor members 2.

[0034] The high-temperature gas flow path is indicated by arrow F and, naturally, flows through the high-temperature gas flow channel, passing through the airfoil 43 of blade 4.

[0035] Between two adjacent rotor wheels 3, a protective spacer 7 is positioned, which functions to provide a barrier to prevent gas from being drawn in from the high-temperature gas flow channel F into the wheel space 5. Gas ingestion can raise the temperature on the upper side of the wheel space 5, and consequently, raise the temperature of the root 41 of the blades 4. As described above, excessive thermal stress on the root 41 adversely affects the operation of the root. In this embodiment, the protective spacer 7 is conical. However, in some embodiments, the protective spacer 7 can be cylindrical or have other shapes, and always functions to define the wheel space 5 and provide protection for the wheel space 5. Also, on the upper surface 71 of each spacer 7 facing the stator spacer 6, there is a labyrinth seal 72 (typically called a diaphragm) to minimize the amount of purge flow P required to prevent high-temperature gas from being drawn in through the gap between the spacer 7 and the stator spacer 6.

[0036] Referring further to Figure 3, arrow P indicates the purge air path coming from the purge system 16. In addition to lowering the temperature of the wheel space 5, the purge air pressure provides a pressure barrier against the injection of gas from the high-temperature gas flow channel F. The shank 42 of each blade 4 has a deflector 8, which is located on the shank 42 of each blade 4 and positioned on the protective spacer 7, particularly corresponding to its edge, to cover the gap 73 between each protective spacer 7 and the rotor member 2, and in particular, referring to the embodiment of Figure 3, between the protective spacer 7 and the rim 31 of the rotor wheel 3.

[0037] The pressure in channel 74 is lower than the pressure of the gas deflected by the deflector 8. More specifically, the pressure along channel 74 is lower along the direction of the high-temperature gas flow channel F. In fact, in a field considering several adjacent rotor members, the rotor member 2 upstream of the high-temperature gas flow channel F is called the forward rotor member, and the purge air or gas surrounding such a forward rotor member 2 has a higher pressure than that of a subsequent one called the rear roto member, and then the deflector is located in the forward rotor member 2 and necessarily has a higher pressure than channel 74.

[0038] In other words, in some embodiments, the deflector 8, which is actually ring-shaped, has a projecting edge facing forward of the edge of the protective spacer 7 to correspond to the deflector in order to close the gap between the protective spacer 7 and the rotor wheel 3. In practice, the protective spacer 7 is also ring-shaped, with its edge facing the rotor wheel 3. The surface of the deflector 8 is such that it can deflect hot gas, as will be better described below.

[0039] In the embodiment shown in Figure 3, and particularly with reference to the magnified window shown in the same figure, the deflector 8 is molded to have an upper surface 81 intended to deflect any possible gas inhalation back from the high-temperature gas flow channel F to the main flow path shown in Figure 5, and a lower surface 82 intended to allow purge air or gas coming from the wheel space 5 to pass through the gap 73 between each protective spacer 7 and the rotor member 2.

[0040] In some embodiments, the deflector 8 can be positioned in different locations, more specifically, on the rotor wheel 3, roughly corresponding to the rim 31 (see Figure 7, which is discussed below).

[0041] In general, it is necessary that the deflector 8 can deflect any possible gas inhalation from the hot gas flow channel F whenever the purge air pressure P from the wheel spacer 5 is generally insufficient to prevent hot gas from entering the wheel space 5, so that it can overcome the mechanical barrier of the protective spacer 7.

[0042] The low-pressure turbine 14 and deflector 8 operate as follows:

[0043] As the low-pressure turbine 14 operates and the rotor member 2 rotates, purge air P from the compressor 163 and transported by the purge pipe 164 cools the wheel space 5. Simultaneously, the combined effect of the pumping effect due to the rotational speed of the low-pressure turbine 14, i.e., the rotor member 2, along with the barrier provided by the protective spacer 7, prevents gas from being drawn into the wheel space 5 from the high-temperature gas flow channel F. Furthermore, any possible gas suction, even if localized, is further prevented by the action of the deflector 8, which, on the one hand, is positioned in correspondence with the protective spacer 7 and deflects any possible localized gas suction away from the high-temperature gas flow channel F by its first surface 81, while on the other hand, it also allows the purge air P to pass through the gap 73. Localized gas suction can also occur due to the fact that the pressure field generated by the high-temperature gas flow in the high-temperature gas flow channel F is not necessarily uniform in the circumferential direction. Referring to the deflector 8, its positioning in correspondence with the protective spacer 7 means that, in some embodiments, it can deflect the hot gas toward the shank 42 of the blade 4 and return it upward.

[0044] The deflector's operation has a specific effect when the rotational speed of the low-pressure gas turbine 14 decreases, for example, when the low-pressure gas turbine 14 is operating at 50% of its nominal operating speed. In this case, the protective effect of the pumping effect decreases in proportion to the decrease in speed.

[0045] In particular, to better illustrate the operation of the deflector 8, Figures 4, 5, and 6 illustrate several operating conditions of the low-pressure turbine 14. In Figure 4, a typical flow path for purge air P is shown, with no gas inhalation expected. In this case, the purge air P coming from the compressor 11 passes through the wheel space 5 to the hot gas flow channel F, protecting the wheel space 5 from the high temperature of the hot gas. Under these operating conditions, element 8 does not cover the protective spacer 7 and therefore does not act as a deflector. Rather, it is an element that reduces the gap 73.

[0046] Referring to Figure 5 below, an example is shown of preventing gas suction during low-power operation of a gas turbine. In this case, a portion of the hot gas in the hot gas flow channel F (see arrow F') does not reach the protective spacer 7, in particular the channel 74, the top surface 71, and the labyrinth seal 72. In practice, the deflector 8 deflects the purge air P pumped from the wheel space 5 by the rotor member 2. The purge air P is deflected by the deflector 8 into the channel 74, and since the channel 74 is at a lower pressure than the purge air P, it is drawn in by the channel itself.

[0047] Furthermore, the gas intake flow F is redirected radially upward thanks to the shape of the upper surface 81 of the deflector 8. In other words, the deflector 8 reverses the direction of the intake gas flow F'. Specifically, the intake gas flow F' is redirected toward the upper surface of the shank 42. In this case, gas intake into the wheel space 5 is blocked by either the deflector 8 or, in particular, by the purge air P coming from the compressor 163. The deflector 8 also helps prevent the rim 31 from being heated by any possible high-temperature intake gas F' coming from the high-temperature gas flow in the high-temperature gas flow channel F leaking into the wheel space 5.

[0048] Figure 6 shows the operation of the deflector 8 when the gas turbine 1 is operating under base load conditions, i.e., when the rotor member 2 is rotating at nominal speed. As illustrated in Figure 6, the purge air P coming from the wheel space 5 is divided into two flows, P' and P''. One (P') is moved by the deflector 8, specifically the lower surface 82, due to the pressure difference in the channel 74 (the pressure along the channel 74 is lower than the pressure of the purge gas P), while the other flow P'' into which the purge air P is divided is moved towards the airfoil 43 by the pumping effect. As can be seen, in this case, the deflector 8 does not interfere with the pumping effect of the rotor member 2 and allows the flow of purge air P to avoid reaching the flow path F and being sucked in.

[0049] Referring to Figure 7, a second embodiment of the improved low-pressure turbine 14 is shown. In the figures referred to, the same reference numerals represent the same or corresponding parts, elements, or components already illustrated in Figure 3 and described above, and will not be described again here. However, in this case, the protective spacer 7 is cylindrical rather than conical. Also in this case, the deflector 8 is disposed on the shank 7 or on the rim 31 of the rotor wheel 3, corresponding to the spacer 7.

[0050] Figure 7 also illustrates several paths for the purge air P coming from the compressor 11 through the purge pipe 164.

[0051] In this case, the operation of the low-power turbine 14 is the same as that disclosed in the previous figure.

[0052] While the present invention has been described in relation to various specific embodiments, it will be apparent to those skilled in the art that many modifications, changes, and omissions are possible without departing from the spirit and scope of the claims. In addition, unless otherwise specified herein, the order or arrangement of any process or method step may be changed or rearranged according to alternative embodiments.

[0053] Detailed references are made to embodiments of this disclosure, and one or more of these examples are illustrated in the drawings. Each example is provided for illustrative purposes only and does not limit the disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to this disclosure, as long as they do not deviate from the scope or spirit of this disclosure. Throughout this specification, any reference to “a certain embodiment,” “one embodiment,” or “several embodiments” means that a particular feature, structure, or characteristic described in relation to one embodiment is included in at least one embodiment of the subject matter of the disclosure. Thus, where the phrases “in a certain embodiment,” “one embodiment,” or “several embodiments” appear in various places throughout this specification, they do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics can be combined in any preferred manner in one or more embodiments.

[0054] When presenting elements of various embodiments, the articles "a," "an," "the," and "said" are intended to indicate that there is one or more of the elements. The terms "comprising," "including," and "having" are intended to be non-exclusive, meaning that additional elements other than those listed may exist.

Claims

1. It is a turbine, A downstream rotor member and an upstream rotor member configured to rotate by the expansion of high-temperature gas flowing into a high-temperature gas flow channel, wherein each of the downstream rotor member and the upstream rotor member is equipped with a rotor wheel, and the rotor wheels of the upstream rotor member and the downstream rotor member form a wheel space, A protective spacer is positioned between the downstream rotor member and the upstream rotor member and configured to prevent the gas flow drawn in from the high-temperature gas flow channel from reaching the wheel space, A stator spacer is positioned between the downstream rotor member and the upstream rotor member, spaced apart from the protective spacer so as to form a channel between it and the protective spacer, The downstream rotor member and the deflector positioned on one of the upstream rotor members, A purge system having a cooler for cooling purge air and being fluidly connected to the wheel space, configured to supply the purge air that has passed through the cooler to the wheel space, Equipped with, The deflector has an upper surface configured to deflect the incoming gas flow in order to reverse its direction, and a lower surface that deflects the purge air flowing from the wheel space into the channel. The channel is at a pressure lower than the pressure of the purge air deflected by the deflector. The protective spacer has an upper part that is inclined with respect to the columnar portion of the protective spacer. When the direction from one of the upstream rotor member and the downstream rotor member toward the other is defined as the first direction, and the direction from the protective spacer toward the stator spacer is defined as the second direction, The upper part of the protective spacer and the upper surface of the deflector are inclined in the second direction as they move toward the first direction, The lower surface of the deflector is tilted in the opposite direction to the second direction as it approaches the first direction, in a turbine.

2. The turbine according to claim 1, wherein the deflector is arranged in correspondence with the protective spacer.

3. Each of the rotor wheels of the downstream rotor member and the upstream rotor member has an outer rim, The turbine according to claim 1 or 2, wherein the deflector is disposed on the outer rim of the rotor wheel of the upstream rotor member.

4. The turbine according to any one of claims 1 to 3, wherein the deflector covers a portion of the gap between the protective spacer and the rotor wheel of the upstream rotor member.

5. Each of the downstream rotor member and the upstream rotor member is A rotor wheel configured to rotate around a rotation axis, having an outer rim and a plurality of grooves spaced circumferentially around the outer rim of the rotor wheel, A plurality of blades, each blade comprising a shank, a root coupled to the shank and designed to fit into one corresponding groove of the rotor wheel, and an airfoil for rotating the rotor member by receiving hot gas from the hot gas flow channel, The deflector is positioned on the shank of the upstream rotor member, The turbine according to claim 1 or 2, wherein the deflector covers a portion of the gap between the protective spacer and the rotor wheel of the upstream rotor member.

6. The turbine according to claim 5, wherein the deflector is configured to reverse the direction of the inhaled gas flow toward the upper surface of the shank.

7. The turbine according to any one of claims 1 to 6, wherein when the turbine is operating under base load conditions, the deflector allows purge air to flow radially to the hot gas flow channel to prevent the inhalation of hot gas.

8. The turbine according to any one of claims 1 to 7, wherein the deflector has a lower surface configured to move a portion of the purge air into the high-temperature gas flow channel through which the high-temperature gas flows.

9. The turbine according to any one of claims 1 to 8, wherein a labyrinth seal is interposed between the stator spacer and the protective spacer.

10. The turbine according to any one of claims 5 or 6, wherein the deflector is integrated with the shank.

11. The turbine according to any one of claims 1 to 10, wherein the turbine is a low-pressure turbine.

12. It is a turbine, A blade comprising a shank, a base connected to the shank, an airfoil configured to capture a high-temperature gas flow path, and a deflector configured to deflect the high-temperature gas flow, The first spacer and A second spacer is positioned opposite the first spacer, spaced apart from the first spacer to form a channel between them, A purge system equipped with a cooler to cool the purge air, Equipped with, The deflector has an upper surface configured to deflect any gas suction that may occur from the high-temperature gas flow path, and a lower surface that deflects the purge air from the cooler of the purge system into the channel. The upper part of the second spacer is inclined with respect to the columnar portion of the second spacer. When the direction from the second spacer to the first spacer is defined as the second direction, and the direction intersecting the second direction is defined as the first direction, The upper part of the second spacer and the upper surface of the deflector are inclined in the second direction as they move toward the first direction, The lower surface of the deflector is tilted in the opposite direction to the second direction as it approaches the first direction, in a turbine.

13. Equipped with a rotor wheel, The turbine according to claim 12, wherein the deflector covers the gap between the second spacer and the rotor wheel.

14. The turbine according to any one of claims 12 or 13, wherein the deflector has a lower surface configured to allow purge air to flow into the high-temperature gas flow path through which the high-temperature gas flows.

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