Methods for obtaining the primary water droplet deposition rate and deposition location in the wet steam stage of a steam turbine.

Abstract

This invention relates to the field of steam turbine technology and addresses the problem of low accuracy and inefficiency in calculating the primary water droplet deposition rate and location within a steam turbine wet steam stage. The method involves obtaining a blade model, meshing the blade model to obtain a blade mesh diagram, and acquiring the diameter, steam humidity, mass flow rate, and temperature of the primary water droplets at the inlet of the last stage stator blade of the sixth-stage single-channel blade in the low-pressure cylinder of the steam turbine. Based on the relationship between drag velocity and slip velocity, the slip velocity of the primary water droplets within the last two stages of the low-pressure cylinder blades is calculated. Fluid simulation is performed using the slip velocity to obtain a primary water droplet deposition cloud map. The deposition location and area of ​​the primary water droplets are obtained from the cloud map, and the deposition rate of the primary water droplets is calculated based on the deposition area. This invention is applicable to obtaining the primary water droplet deposition rate and location within a steam turbine wet steam stage.

Description

Technical Field

[0001] This invention relates to the field of steam turbines. Background Technology

[0002] During turbine operation, primary water droplets in the wet steam stage significantly impact turbine efficiency and safety. The formation process of primary water droplets is complex. Steam flowing through the wet steam stage expands to the Wilson point and condenses, deviating from its original equilibrium state and resulting in wet steam condensation. Tiny droplets form at this point, and under the influence of steam flow, their diameter and number increase, forming primary water droplets. These droplets are small, typically between 0-1 μm in diameter. Most primary water droplets move with the steam, while a small portion deposits on the turbine blade surface. When the water droplets deposited on the blade surface accumulate to a certain number, they form a water film adhering to the blade. This water film, under the influence of steam flow, flows towards the blade's outlet edge. At the outlet edge, the water film is torn into larger droplets; these are called secondary water droplets. Larger secondary water droplets impact turbine blades, and prolonged impacts can cause cracks or even breakage, a phenomenon known as turbine erosion. This erosion threatens the safety of the turbine unit. Therefore, the formation of secondary water droplets is inextricably linked to that of primary water droplets, making the study of primary water droplets particularly important.

[0003] Studies on primary water droplet deposition within the wet steam stage of a steam turbine's low-pressure cylinder primarily employ experimental methods and computational programming. For experiments, some researchers utilize various probes and other experimental instruments to create an environment closely resembling the turbine's operating conditions, capturing and collecting small water droplets to approximate their movement within the wet steam stage. However, this experimental method is costly and only yields the diameter and number of primary water droplets. Other researchers first perform numerical simulations of the flow field within the wet steam stage, then extract necessary simulation parameters, import them into a programming program for calculation, and finally derive the primary water droplet deposition rate distribution. However, these methods are not only inefficient but also suffer from poor accuracy. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low accuracy and poor efficiency in calculating the primary water droplet deposition rate and deposition location in the wet steam stage of a steam turbine, and to propose a method for obtaining the primary water droplet deposition rate and deposition location in the wet steam stage of a steam turbine.

[0005] The method for obtaining the primary water droplet deposition rate and deposition location in the wet steam stage of a steam turbine according to the present invention includes:

[0006] Step 1: Perform physical modeling on the six-stage single-flow-channel blades in the low-pressure cylinder of the steam turbine to obtain the blade model, and then perform mesh generation on the blade model to obtain the blade mesh diagram;

[0007] Step 2: Discretize the blade mesh diagram and solve the flow field of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine to obtain the diameter, steam humidity, mass flow rate and temperature of the primary water droplet at the inlet of the last stage stationary blade of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine.

[0008] Step 3: Based on the relationship between dragging speed and sliding speed, and using the diameter of the water droplet, steam humidity, mass flow rate, and temperature, solve for the sliding speed of the primary water droplet in the last two stages of the low-pressure cylinder of the steam turbine.

[0009] Step 4: Obtain a primary water droplet deposition cloud map by utilizing the sliding velocity of the primary water droplets within the last two stages of the low-pressure cylinder blades of the steam turbine.

[0010] Step 5: Based on the single-droplet deposition cloud map, obtain the deposition location and deposition area of ​​the single-droplet, and calculate the deposition rate of the single-droplet based on the deposition area of ​​the single-droplet.

[0011] Furthermore, in this invention, in step one, the blade model is meshed to obtain a blade mesh diagram using OpenFOAM software.

[0012] Furthermore, in this invention, the method for obtaining the diameter, steam humidity, mass flow rate, and temperature of the primary water droplet at the inlet of the last stage stationary blade of the sixth-stage single-channel blade in the low-pressure cylinder of the steam turbine in step one is as follows:

[0013] The flow field of the six-stage single-channel blades in the low-pressure cylinder of the steam turbine was calculated using OpenFOAM software until the convergence threshold of the average energy of the gas-liquid mixture stabilized below the energy threshold. Then, the diameter of the water droplet, the steam humidity, the mass flow rate and the temperature were obtained.

[0014] Furthermore, in this invention, the specific method for solving the sliding velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine in step three is to use OpenFOAM software to solve the relationship between the dragging speed and the sliding velocity to obtain the sliding velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine.

[0015] Furthermore, in this invention, the method for obtaining the primary water droplet deposition cloud map in step four is as follows: using Paraview software to analyze the sliding velocity results of the primary water droplets in the last two stages of the low-pressure cylinder of the steam turbine, and obtaining the primary water droplet deposition cloud map.

[0016] Furthermore, in this invention, the method for obtaining the relationship equation between the towing speed and the sliding speed in step three is as follows:

[0017] Step 3: 1. Establish the continuity equation and momentum equation of the mixture to obtain the volume fraction equation of the water droplet phase;

[0018] Step 3.2: Define the sliding speed The relationship between dragging speed and slip velocity is derived using the volume fraction equation of the water droplet phase and the volume fraction of the k-th phase.

[0019] Furthermore, in this invention, the specific process of establishing the phase continuity equation and obtaining the volume continuity equation in step three-one is as follows:

[0020] The phase continuity equation is:

[0021]

[0022] in, This represents the pressure gradient at time t; Here, m represents the gradient operator; m denotes the mixed phase.

[0023] For mixed density,

[0024] α k Let be the volume fraction of the k-th phase; Let be the density of the k-th phase; k represents the phase number.

[0025] u m For the mixing mass rate,

[0026] u k The velocity of phase k is given by n; n represents the velocity of phase n.

[0027] The momentum equation for the mixture is:

[0028]

[0029] Where τ is viscous stress; P is pressure; g is gravitational constant; T represents turbulence; and F represents volume force. It is a mixed viscous stress; This refers to the mixed viscous stress under turbulent conditions. It is a mixed viscous stress with volume forces; u d,k Let k be the towing speed of the k-th phase;

[0030]

[0031] From the momentum equation of the mixture, the volume fraction equation of the water droplet phase is derived:

[0032]

[0033] in, This represents the volume fraction of the water droplet phase. The density of the water droplet phase; The drag speed of the water droplet phase.

[0034] Furthermore, in this invention, the process of deriving the relationship between the dragging speed and the sliding speed using the volume fraction equation of the water droplet phase in step three-two is as follows:

[0035] Define slip velocity The volume fraction of the kth phase is used to deduce the relationship between the towing speed and the slip speed.

[0036] Define the relative slip velocity between phases Let l be the velocity of the water droplet phase relative to the gas phase g:

[0037]

[0038] in, This represents the relative slip velocity between the water droplet phase and the gas phase; u l It is the speed of the water droplet; u g It is the speed of the steam;

[0039] The mass fraction of the kth phase is c. k :

[0040]

[0041] The relationship between towing speed and slip speed is as follows:

[0042]

[0043] u lk The sliding velocity of water droplet l represents the sliding velocity of the primary water droplet within the last two stages of the low-pressure cylinder blades of a steam turbine. The method for obtaining the primary water droplet deposition rate and location within the wet steam stage of a steam turbine, as described in this invention, calculates the sliding velocity of the primary water droplets within the last two stages of the turbine. The magnitude of this sliding velocity is then used in Paraview software to reflect the relationship between water droplet deposition on the turbine blade surface, enabling accurate and rapid determination of the deposition rate and location of water droplets on the turbine blade surface. The results provide a reference for reducing the formation of secondary water droplets, thereby effectively preventing water erosion in the last stage of the steam turbine. Attached Figure Description

[0044] Figure 1 This is a flowchart of the method described in this invention;

[0045] Figure 2 This is a schematic diagram of a single-flow-channel, six-stage blade system for a low-pressure cylinder of a steam turbine.

[0046] Figure 3 It is a blade mesh diagram;

[0047] Figure 4 This is a diagram showing the deposition of water droplets on the pressure surface of the last two stages of blades in the low-pressure cylinder of a steam turbine.

[0048] Figure 5 This is a diagram showing the deposition of water droplets on the suction surface of the last two stages of the low-pressure cylinder blades of a steam turbine. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0051] Specific Implementation Method 1: The following is combined with... Figure 1 This embodiment describes a method for obtaining the primary water droplet deposition rate and deposition location within the wet steam stage of a steam turbine, comprising:

[0052] Step 1: Perform physical modeling on the six-stage single-flow-channel blades in the low-pressure cylinder of the steam turbine to obtain the blade model, and then perform mesh generation on the blade model to obtain the blade mesh diagram;

[0053] Step 2: Discretize the blade mesh diagram and solve the flow field of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine to obtain the diameter, steam humidity, mass flow rate and temperature of the primary water droplet at the inlet of the last stage stationary blade of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine.

[0054] Step 3: Based on the relationship between dragging speed and sliding speed, and using the diameter of the water droplet, steam humidity, mass flow rate, and temperature, solve for the sliding speed of the primary water droplet in the last two stages of the low-pressure cylinder of the steam turbine.

[0055] Step 4: Obtain a primary water droplet deposition cloud map by utilizing the sliding velocity of the primary water droplets within the last two stages of the low-pressure cylinder blades of the steam turbine.

[0056] Step 5: Based on the single-droplet deposition cloud map, obtain the deposition location and deposition area of ​​the single-droplet, and calculate the deposition rate of the single-droplet based on the deposition area of ​​the single-droplet.

[0057] Furthermore, in this embodiment, in step one, the blade model is meshed to obtain a blade mesh diagram using OpenFOAM software.

[0058] Furthermore, in this embodiment, the method for obtaining the diameter, steam humidity, mass flow rate, and temperature of the primary water droplet at the inlet of the last stage stationary blade of the sixth-stage single-flow-channel blade in the low-pressure cylinder of the steam turbine in step one is as follows:

[0059] The OpenFOAM software was used to calculate the flow field of the six-stage single-channel blades in the low-pressure cylinder of the steam turbine. The calculation continued until the convergence threshold of the average energy of the gas-liquid mixture stabilized below the energy threshold. Then, the diameter of the primary water droplet, steam humidity, mass flow rate, and temperature were obtained. In this embodiment, the convergence threshold stabilized at 10... -5 the following.

[0060] Furthermore, in this embodiment, the specific method for solving the sliding velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine in step three is as follows: using OpenFOAM software, the relationship between the dragging speed and the sliding velocity is solved to obtain the sliding velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine.

[0061] Furthermore, in this embodiment, the method for obtaining the primary water droplet deposition cloud map in step four is as follows: using Paraview software to analyze the sliding velocity results of the primary water droplets in the last two stages of the low-pressure cylinder of the steam turbine, and obtaining the primary water droplet deposition cloud map.

[0062] Furthermore, in this embodiment, the method for obtaining the relationship equation between the towing speed and the slip speed in step three is as follows:

[0063] Step 3: 1. Establish the continuity equation and momentum equation of the mixture to obtain the volume fraction equation of the water droplet phase;

[0064] Step 3.2: Define the sliding speed The relationship between dragging speed and slip velocity is derived using the volume fraction equation of the water droplet phase and the volume fraction of the k-th phase.

[0065] The deposition rate of primary water droplets is determined by their slip velocity. Assuming the turbine blades are the turbine wall, during the mixing and flow of water droplets and steam within the turbine passages, when the slip velocity increases to a certain level, the turbulence of the liquid phase is sufficiently strong to suspend the particles in the steam. However, when the slip velocity is very low, the turbulence is insufficient to prevent the downward movement of the primary water droplets. Therefore, due to their relatively low slip velocity and the influence of gravity, water droplets in the mixed phase will deposit on the surface of the turbine blades upon contact with the wall. With the continuous deposition of a large number of these water droplets, the deposition rate and location of primary water droplets on the turbine blade surface can be obtained.

[0066] Furthermore, in this embodiment, the specific process of establishing the phase continuity equation and obtaining the volume continuity equation in step three-one is as follows:

[0067] The phase continuity equation is:

[0068]

[0069] in, This represents the pressure gradient at time t; Here, m represents the gradient operator; m denotes the mixed phase.

[0070] For mixed density,

[0071] α k Let be the volume fraction of the k-th phase; Let be the density of the k-th phase; k represents the phase number.

[0072] u m For the mixing mass rate,

[0073] u k The velocity of phase k is given by n; n represents the velocity of phase n.

[0074] The momentum equation for the mixture is:

[0075]

[0076] Where τ is viscous stress; P is pressure; g is gravitational constant; T represents turbulence; and F represents volume force. It is a mixed viscous stress; This refers to the mixed viscous stress under turbulent conditions. It is a mixed viscous stress with volume forces; u d,k Let k be the towing speed of the k-th phase;

[0077]

[0078] From the momentum equation of the mixture, the volume fraction equation of the water droplet phase is derived:

[0079]

[0080] in, This represents the volume fraction of the water droplet phase. The density of the water droplet phase; The drag speed of the water droplet phase.

[0081] Furthermore, in this invention, the process of deriving the relationship between the dragging speed and the sliding speed using the volume fraction equation of the water droplet phase in step three-two is as follows:

[0082] Define slip velocity The volume fraction of the kth phase is used to deduce the relationship between the towing speed and the slip speed.

[0083] Define the relative slip velocity between phases Let l be the velocity of the water droplet phase relative to the gas phase g:

[0084]

[0085] in, This represents the relative slip velocity between the water droplet phase and the gas phase; u l It is the speed of the water droplet; u g It is the speed of the steam;

[0086] The mass fraction of the kth phase is c. k :

[0087]

[0088] The relationship between towing speed and slip speed is as follows:

[0089]

[0090] u lk Let l be the sliding velocity of the water droplet, which is the sliding velocity of a water droplet in the last two stages of the low-pressure cylinder of the steam turbine.

[0091] Example:

[0092] This invention uses the last two stages of a 600MW steam turbine single-flow-channel blade as an example to illustrate the method for obtaining the primary water droplet deposition rate and location within the last two stages of the low-pressure cylinder single-flow-channel blade of the steam turbine.

[0093] First, a physical model of the six-stage single-flow-channel blades in the low-pressure cylinder of the steam turbine is performed. A schematic diagram of the six-stage single-flow-channel blade model in the low-pressure cylinder of the steam turbine is shown below. Figure 2 As shown. Then, mesh generation is performed in the open-source software OpenFOAM. The schematic diagram of the resulting blade mesh is shown below. Figure 3 As shown, the flow field of the six-stage single-channel blades in the low-pressure cylinder of the steam turbine is finally solved and calculated in OpenFOAM. The convergence threshold of the average energy of the gas-liquid mixture stabilizes at 10... -5 The calculation ends here, and the results are automatically generated. The diameter of the primary water droplet at the inlet of the last stage stationary blade, as well as the steam humidity, mass flow rate, and temperature, are obtained. The results are shown in Table 1.

[0094] Then, the last two stages of the low-pressure cylinder blades of this 600MW steam turbine were taken as the research object. Figure 2 This is a physical model of the last two stages of blades in the low-pressure cylinder of a steam turbine. Figure 3The image shows the mesh diagram of the last two stages of blades. These steps were performed using the open-source software OpenFOAM. The diameter of the primary water droplets at the inlet of the last stage stator blades, along with parameters such as steam humidity, mass flow rate, and temperature obtained in Step 1, and the turbine exhaust pressure obtained from the power plant's thermal characteristics specification, were used as the boundary conditions for the solution in Step 2. In Step 2, before the software solution calculation, these parameter values ​​were set as boundary conditions. Then, the algebraic slip model equations were programmed and imported into the open-source software OpenFOAM to begin the solution calculation. The calculation continued until the energy convergence threshold stabilized at 10... -5 The calculation stops at this point, and a results file is generated.

[0095] The results file is then imported into the open-source fluid simulation post-processing software Paraview to obtain deposition cloud images of water droplets on the pressure and suction surfaces of the last two stages of the low-pressure cylinder blades of the steam turbine, as shown below. Figure 4 and 5 express.

[0096] from Figure 4 and 5 It can be seen that the area with the largest value indicates the most severe deposition. The most severe deposition occurs in the turbine's moving blades, with a maximum value of 4 × 10⁻⁶. -4 kg / (m 2 •s); The suction surface of the turbine stator blades has almost no deposits, with a minimum deposition rate of 0 kg / (m²). 2 (·s). It can also be seen that the deposition severity on the pressure surface is higher than on the suction surface, with the most severe deposition occurring at the trailing edge of the stationary blade. This is because although the primary water droplets formed by condensation nucleation are small and most can flow well with the steam, a small portion still deposits at the stationary blade. With the flow of steam and the accumulation of deposits, these small droplets slowly move towards the stationary blade, forming a water film or stream at its trailing edge. Therefore, areas with severe primary water droplet deposition are the main source of secondary water droplet formation.

[0097] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for obtaining the primary water droplet deposition rate and deposition location within a steam turbine wet stage, characterized in that, It includes: Step 1: Perform physical modeling on the six-stage single-flow-channel blades in the low-pressure cylinder of the steam turbine to obtain the blade model, and then perform mesh generation on the blade model to obtain the blade mesh diagram; Step 2: Discretize the blade mesh diagram and solve the flow field of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine to obtain the diameter, steam humidity, mass flow rate and temperature of the primary water droplet at the inlet of the last stage stationary blade of the six-stage single-channel blade in the low-pressure cylinder of the steam turbine. Step 3: Based on the relationship between dragging speed and sliding speed, and using the diameter of the water droplet, steam humidity, mass flow rate, and temperature, solve for the sliding speed of the primary water droplet in the last two stages of the low-pressure cylinder of the steam turbine. Step 4: Obtain a primary water droplet deposition cloud map by utilizing the sliding velocity of the primary water droplets within the last two stages of the low-pressure cylinder blades of the steam turbine. Step 5: Based on the single-droplet deposition cloud map, obtain the deposition location and deposition area of ​​the single-droplet, and calculate the deposition rate of the single-droplet based on the deposition area of ​​the single-droplet; The specific process is as follows: Taking the last two stages of the low-pressure cylinder blades of the steam turbine as the research object, the diameter of the primary water droplet at the inlet of the second-to-last stage stator blade obtained in step two, the steam humidity, mass flow rate, temperature, and the steam turbine exhaust pressure value obtained from the power plant's thermal characteristic specification are used as the boundary conditions for the solution calculation. Then, the algebraic slip model equations are imported into the open-source software OpenFOAM, and the solution calculation begins under the stated boundary conditions. When the energy convergence threshold stabilizes at 10... -5 The calculation stops and a results file is generated at the following time. The resulting file is then imported into Paraview, an open-source software for fluid simulation post-processing, to obtain deposition cloud maps of water droplets on the pressure and suction surfaces of the last two stages of the low-pressure cylinder blades of a steam turbine.

2. The method of claim 1, wherein the method further comprises: In step one, the blade model is meshed to obtain the blade mesh diagram using OpenFOAM software.

3. The method for obtaining the primary water droplet deposition rate and deposition location in the wet steam stage of a steam turbine according to claim 1, characterized in that, In step one, the method for obtaining the diameter, steam humidity, mass flow rate, and temperature of the primary water droplets at the inlet of the last stage stator blade of the sixth-stage single-flow-channel blade in the low-pressure cylinder of the steam turbine is as follows: The flow field of the six-stage single-channel blades in the low-pressure cylinder of the steam turbine was calculated using OpenFOAM software until the convergence threshold of the average energy of the gas-liquid mixture stabilized below the energy threshold. Then, the diameter of the water droplet, the steam humidity, the mass flow rate and the temperature were obtained.

4. The method of claim 1, wherein the method further comprises: In step three, the specific method for solving the slip velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine is as follows: using OpenFOAM software, the relationship between the drag speed and the slip velocity is solved to obtain the slip velocity of the primary water droplet in the last two stages of the low-pressure cylinder blades of the steam turbine.

5. The method of claim 4, wherein the method further comprises: In step four, the method for obtaining the primary water droplet deposition cloud map is as follows: Paraview software is used to analyze the sliding velocity of the primary water droplets in the last two stages of the low-pressure cylinder blades of the steam turbine to obtain the primary water droplet deposition cloud map.

6. The method of claim 1, wherein the method further comprises: In step three, the method for obtaining the equation relating to towing speed and slip speed is as follows: Step 3:

1. Establish the continuity equation and momentum equation of the mixture to obtain the volume fraction equation of the water droplet phase; Step three two, define slip velocity And the volume fraction of the k phase, the relationship between drag velocity and slip velocity is derived using the volume fraction equation of the water droplet phase.

7. The method for obtaining the primary water droplet deposition rate and deposition location in a steam turbine wet steam stage according to claim 6, characterized in that, In step 3.1, the specific process of establishing the phase continuity equation and obtaining the volume continuity equation is as follows: The phase continuity equation is: in, This represents the pressure gradient at time t; For gradient operators; m represents the mixed phase. For mixed density, α k Let be the volume fraction of the k-th phase; The density of the k-th phase; k represents the phase number; u m For the mixing mass rate, u k V is the velocity of the kth phase; n denotes the nth phase; the momentum equation for the mixture is: Where τ is viscous stress; P is pressure; g is gravitational constant; T represents turbulence; and F represents volume force. It is a mixed viscous stress; This refers to the mixed viscous stress under turbulent conditions. It is a mixed viscous stress with volume forces; u d,k Let be the drag speed of the k-th phase; From the momentum equation of the mixture, the volume fraction equation of the water droplet phase is derived: in, This represents the volume fraction of the water droplet phase. The density of the water droplet phase; The drag velocity of the water droplet phase.

8. The method of claim 7, wherein the method further comprises: In step 3.2, the process of deriving the relationship between the dragging speed and the slip velocity using the volume fraction equation of the water droplet phase is as follows: Defining the slip velocity and the volume fraction of the kth phase, from which the relationship between the drag velocity and the slip velocity is derived; Defining the interfacial relative slip velocity Vig is the velocity of the water droplets phase l with respect to the gas phase g: in, This represents the relative slip velocity between the water droplet phase and the gas phase; u l It is the speed of the water droplet; u g It is the speed of the steam; The mass fraction of the kth phase is c k : The relationship between towing speed and slip speed is as follows: u lk Let l be the sliding velocity of the water droplet, which is the sliding velocity of a water droplet in the last two stages of the low-pressure cylinder of the steam turbine.

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