Method for identifying rotating stall region of pump-turbine under turbine operating condition

Abstract

The present invention relates to the technical fields of fluid machinery, pumped storage and fluid mechanics, and specifically to a method for identifying a rotating stall region of a pump turbine under a turbine working condition. The linearized N‑S equation group containing the disturbance amount is solved by flow field data under different working conditions to obtain the pressure disturbance amount at the runner inlet under different disturbance speeds; the pressure disturbance amount is substituted into the critical stability equation of the weak disturbance wave as the predecessor of the rotating stall determined by theoretical analysis to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, and the rotating stall starting point under each guide vane opening is determined according to the relationship, and the rotating stall region under each guide vane opening under the turbine working condition is obtained in combination with the end point of zero flow, thereby realizing the determination of the rotating stall region under the turbine working condition. Compared with the expensive model test method and the non-steady-state numerical calculation method, this method combines theoretical analysis and numerical calculation, is easy to implement, and requires low cost investment.

Description

Technical Field

[0001] The invention relates to the technical fields of fluid machinery, pumped storage and fluid mechanics, and in particular to a method for identifying a rotational stall existence region of a pump turbine under a turbine operating condition. Background Art

[0002] The core equipment of a pumped-storage power station is a pump-turbine. Unlike a general turbine that is only used for power generation, a pump-turbine needs to have the bidirectional operation capability of a pump and a turbine. According to the changes in the grid load, it is necessary to perform more frequent operating mode conversions between power generation and pumping conditions. This complex operating condition and transition process results in unstable internal flow characteristics. Under turbine conditions and pump conditions, it will face extremely unstable flow areas in the S zone and the hump zone, respectively. Taking the S zone of the turbine condition as an example, when the pump-turbine is started and shut down under the turbine condition, the same speed can correspond to more than one (3 or four) operating points on the characteristic curve, which enables the unit to operate in any condition between these points, making it difficult to stabilize. A very unstable operating characteristic in the S zone is rotating stall.

[0003] Once rotating stall occurs, the flow field near the runner and guide vanes will show obvious asymmetry in the entire circumference, with large flow rates in some flow channels and small flow rates in other flow channels. Such flow field distribution will induce strong low-frequency pressure pulsations, causing components such as the runner to be subjected to periodic alternating stress, and there is a risk of fatigue damage to important parts such as the blades, which has a great impact on the safe and stable operation of the unit.

[0004] For the analysis and research of rotating stall, the existing technology mainly utilizes unsteady numerical calculation methods or model test methods to analyze and study the designed flow channel to determine in which operating range the rotating stall phenomenon exists.

[0005] However, when using unsteady numerical calculations, it is necessary to model the entire flow path of the entire unit, including the volute, fixed guide vanes, movable guide vanes, runners, and tailwater pipes. The full flow path model is meshed, and unsteady numerical calculations are performed after boundary conditions are set. It is necessary to calculate the flow process of more than 20 runner rotation times;

[0006] When using model testing, it is necessary to manufacture a proportionally reduced pump-turbine model based on the design plan and install it on a general hydraulic machinery test platform for testing. The testing process is carried out strictly in accordance with international standards.

[0007] The above two methods for analyzing rotating stall can usually only analyze the impact of rotating stall on the operating conditions where rotating stall has occurred, including pressure pulsation, vibration and noise. However, it is difficult for the above two methods to identify and determine the characteristics of the rotating stall area. Summary of the invention

[0008] In view of this, the present invention provides a method and device for identifying the area where rotational stall exists for a pump-turbine under turbine operating conditions, so as to solve the problem that the prior art can only analyze the operating conditions where rotational stall has occurred, but cannot pre-identify the area where rotational stall exists.

[0009] In a first aspect, the present invention provides a method for identifying a region where a pump-turbine experiences rotating stall under turbine operating conditions, the method comprising: conducting a model test on the pump-turbine to be identified to obtain characteristic curves under different guide vane openings; determining an operating point for identifying rotating stall based on the characteristic curve; using computational fluid dynamics to calculate flow field data of each operating point as a background flow field; based on the background flow field, determining and solving a linearized NS equation group containing a disturbance quantity to obtain a pressure disturbance quantity at a runner inlet under different disturbance speeds; substituting the pressure disturbance quantity into a disturbance critical stability equation to obtain a relationship between a parameter for judging the stability of the disturbance wave and the disturbance speed, the disturbance critical stability equation being determined by model analysis of the pump-turbine based on disturbance theory; determining a rotating stall starting point under each guide vane opening according to the relationship, and obtaining a rotating stall existing region under each guide vane opening in combination with an end point where the flow rate is zero.

[0010] The present embodiment provides a method for identifying a rotating stall region of a pump-turbine under a turbine operating condition. The linearized NS equations containing disturbance quantities are solved by flow field data under different operating conditions to obtain pressure disturbance quantities at a runner inlet under different disturbance speeds. The pressure disturbance quantity is substituted into a disturbance critical stability equation determined by theoretical analysis to obtain a relationship between a parameter for judging the stability of the disturbance wave and the disturbance speed. The rotating stall starting point under each guide vane opening is determined based on the relationship. The rotating stall region under each guide vane opening is obtained in combination with an end point with zero flow rate. The rotating stall region under the turbine operating condition is thereby determined. Compared with expensive model test methods and non-steady-state numerical calculation methods, this method combines theoretical analysis and numerical calculation, is easy to implement, and requires relatively low cost investment.

[0011] In an optional embodiment, determining an operating point for identifying rotational stall based on the characteristic curve includes: screening a characteristic curve with a positive slope; and based on the screened characteristic curve, determining a plurality of operating points for identifying rotational stall in the operating range between the turbine operating condition and the turbine braking condition.

[0012] In this embodiment, the accuracy of rotating stall analysis is improved by screening the characteristic curve with a positive slope.

[0013] In an optional embodiment, computational fluid dynamics is used to calculate the flow field data of each operating point as the background flow field, including: using computational fluid dynamics to calculate the unsteady flow field at each operating point to obtain flow field calculation results; determining the circumferential average flow field of the impeller at each operating point based on the flow field calculation results; interpolating the circumferential average flow field to the middle surface of the blade to obtain the flow field velocity and pressure on the middle surface as the background flow field.

[0014] In this embodiment, a numerical calculation method is used to perform CFD calculation on the working conditions of the pump turbine under study, and the flow field inside the runner is averaged circumferentially. The circumferential average flow field data is interpolated on the mid-surface of the blade, which is regarded as the S2 flow surface. In this way, the background flow field is determined.

[0015] In an optional embodiment, computational fluid dynamics is used to calculate the flow field data of each operating point as the background flow field, and the method further includes: determining the rotation speed and wave number of the disturbance at each operating point, the rotation speed being a plurality of rotation speed values ​​between 0.2 and 0.7, and the wave number including one of 1, 2 or 3.

[0016] In this embodiment, by determining the rotation speed and wave number of the disturbance, a data basis is provided for solving the NS equation containing the disturbance quantity. At the same time, multiple rotation speed values ​​between 0.2 and 0.7 are determined, and the wave number includes one of 1, 2 or 3, thereby achieving accurate determination of the disturbance.

[0017] In an optional embodiment, based on the background flow field, a linearized NS equation group containing the disturbance quantity is determined and solved to obtain the pressure disturbance quantity at the impeller inlet under different disturbance speeds, including: based on multiple disturbance speeds, multiple disturbance wave numbers and the background flow field, a numerical method is used to discretize the linearized NS equation group containing the disturbance quantity to obtain a non-homogeneous linear equation group; a singular value decomposition algorithm is used to solve the non-homogeneous linear equation group to obtain the pressure disturbance quantity at the impeller inlet under different disturbance speeds.

[0018] In this embodiment, the NS equations containing the disturbance quantity are solved and the pressure disturbance quantity at the impeller inlet under different disturbance speeds is determined by solving the non-homogeneous linear equations obtained by discretizing the linearized NS equations.

[0019] In an optional embodiment, the pressure disturbance amount is substituted into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, including: substituting the pressure disturbance amount into the disturbance critical stability equation to obtain the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers; based on the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers, determining the correspondence between the disturbance speed and the parameters for judging the stability of the disturbance wave under a preset disturbance wave number, the parameters for judging the stability of the disturbance wave include a first parameter and a second parameter, and the correspondence includes a first correspondence between the disturbance speed and the first parameter and a second correspondence between the disturbance speed and the second parameter.

[0020] In an optional embodiment, the starting point of the rotating stall at each guide vane opening is determined according to the relationship, and the rotating stall existence area at each guide vane opening is obtained in combination with the end point where the flow rate is zero, including: determining the disturbance speed at which the first parameter is greater than the first threshold according to the first corresponding relationship; determining the flow rate at which the second parameter is equal to the second threshold according to the determined disturbance speed and the preset disturbance wave number and the relationship between the second parameter and the flow rate obtained based on the disturbance critical stability equation, to obtain the starting point of the rotating stall; and obtaining the rotating stall existence area at each guide vane opening according to the starting point of the rotating stall and the end point where the flow rate is zero.

[0021] In this embodiment, by analyzing the first corresponding relationship between the first parameter and the disturbance speed and the second corresponding relationship between the second parameter and the disturbance speed among the parameters for judging the stability of the disturbance wave, the flow rate at which the second parameter is equal to the second threshold value, that is, the critical stable operating condition of the disturbance wave before the rotating stall, is determined, thereby realizing the determination of the starting point of the rotating stall.

[0022] In a second aspect, the present invention provides a device for identifying a region where a pump-turbine has a rotating stall under a turbine operating condition, the device comprising: a test module, for performing a model test on the pump-turbine to be identified, and obtaining a characteristic curve under different guide vane openings; an operating point determination module, for determining an operating point for identifying a rotating stall based on the characteristic curve; a flow field calculation module, for using computational fluid dynamics to calculate flow field data of each operating point as a background flow field; a disturbance solution module, for determining and solving a linearized NS equation group containing a disturbance amount based on the background flow field, and obtaining a pressure disturbance amount at a runner inlet under different disturbance speeds; a relationship determination module, for substituting the pressure disturbance amount into a disturbance critical stability equation, and obtaining a relationship between a parameter for judging the stability of a disturbance wave and a disturbance speed, wherein the disturbance critical stability equation is determined by performing a model analysis on the pump-turbine based on disturbance theory; an identification module, for determining a rotating stall starting point under each guide vane opening according to the relationship, and obtaining a rotating stall existence region under each guide vane opening in combination with an end point where the flow rate is zero.

[0023] In a third aspect, the present invention provides a computer device comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the method for identifying an area where rotational stall exists for a pump-turbine under turbine operating conditions according to the first aspect or any corresponding embodiment thereof by executing the computer instructions.

[0024] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the method for identifying an area where rotational stall of a pump-turbine exists under turbine operating conditions according to the first aspect or any corresponding embodiment thereof.

[0025] In a fifth aspect, the present invention provides a computer program product comprising computer instructions for causing a computer to execute the method for identifying a region where rotational stall of a pump turbine exists under turbine operating conditions according to the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is a flow chart of a method for identifying a rotating stall existing region of a pump turbine under a turbine operating condition according to an embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of a flow-speed curve according to an embodiment of the present invention;

[0029] Figure 3 is a simplified model schematic diagram of a water pump turbine according to an embodiment of the present invention;

[0030] Figure 4 is a schematic diagram of the relationship between the second parameter and the flow rate according to an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of a rotating stall existence area according to an embodiment of the present invention;

[0032] Figure 6 is a structural block diagram of a device for identifying a rotating stall existing region of a pump turbine under a turbine operating condition according to an embodiment of the present invention;

[0033] Figure 7It is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] As described in the background technology, the existing technology can only analyze the working conditions where rotating stall has occurred, and cannot pre-identify the area where rotating stall exists. At present, when the pump turbine is operating in turbine conditions, it is generally believed that the flow instability phenomenon of rotating stall occurs after the positive slope appears in the characteristic curve, that is, under the condition of dQ11 / dn11>0 in the n11-Q11 (speed-flow) characteristic curve. However, this conclusion is not accurate. Many research results have shown that rotating stall also occurs under the condition that the slope of the characteristic curve is negative. Therefore, there is currently no clear and accurate research result on the area where rotating stall occurs.

[0035] In addition, the rotational speed of rotating stall, as the most important characteristic of rotating stall, needs to be obtained through numerical calculation or model test methods. Due to the risks it poses to the safe operation of the unit, it is almost impossible to implement tests on a real machine.

[0036] In summary, the analysis of the occurrence area of ​​rotating stall and the characteristics of stall speed is still insufficient. If relevant technologies such as numerical calculation or model test are used to analyze the characteristics of the starting point of rotating stall, it requires a large amount of computing resources or test conditions and time cost, so there are great difficulties.

[0037] Among them, the existing numerical calculations are mainly aimed at the full flow channel model. It is difficult to divide the mesh in the flow channel such as the volute, runner and guide vane, and the mesh units of the entire flow channel are generally in the millions to tens of millions, which has high requirements on computer performance. In addition, rotating stall is an unsteady phenomenon with obvious dynamic characteristics. It is necessary to use unsteady calculations to obtain its starting point and frequency and other characteristics. Even with a powerful computer, it takes a long time. In addition, numerical calculations can determine the flow field characteristics of rotating stall, but it is difficult to determine the starting point of rotating stall.

[0038] Model tests can obtain more accurate information, but they require the manufacture of proportionally reduced models, and the model manufacturing cost of pump-turbine units is relatively high. During the design stage, it is impossible to test every runner designed in the design process for a certain unit. In addition, model tests also make it difficult to identify the operating point where rotating stall occurs.

[0039] In addition, the phenomenon of rotating stall will have a great impact on the unit. In order to protect the safety of the unit and ensure the life of the unit, research on rotating stall will not be conducted on the real machine.

[0040] Therefore, it is impossible to identify the area where rotating stall exists under different working conditions by using existing technologies such as numerical calculation or model test.

[0041] In view of this, the present embodiment provides a method for identifying a rotating stall existence region of a pump-turbine under a turbine operating condition, wherein the NS equation containing the disturbance quantity is solved by using a disturbance coefficient determined by flow field data under different operating conditions to obtain the pressure disturbance quantity at the runner inlet under different disturbance speeds; the pressure disturbance quantity is substituted into a disturbance critical stability equation determined by theoretical analysis to obtain the relationship between a parameter for judging the stability of the disturbance wave and the disturbance speed, and the rotating stall starting point under each guide vane opening is determined according to the relationship, and the rotating stall existence region under each guide vane opening is obtained in combination with an end point with zero flow, thereby achieving the determination of the rotating stall existence region under a turbine operating condition. Compared with the expensive model test method and the non-steady-state numerical calculation method, this method combines theoretical analysis and numerical calculation, is easy to implement, and requires a relatively low cost investment.

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0043] According to an embodiment of the present invention, there is provided an embodiment of a method for identifying an area where rotating stall of a pump turbine exists under turbine operating conditions. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0044] In this embodiment, a method for identifying a region where a pump turbine is in a rotating stall state under a turbine operating condition is provided, which can be used in electronic devices such as computers, mobile phones, tablet computers, etc. Figure 1 FIG. 4 is a flow chart of a method for identifying a rotating stall region of a pump turbine under a turbine operating condition according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps:

[0045] Step S101, conduct a model test on the pump-turbine to be identified, and obtain characteristic curves under different guide vane openings. Specifically, the pump-turbine to be identified may be a pump-turbine that needs to be subjected to rotational stall analysis. When conducting a model test on the pump-turbine to be identified, a proportionally reduced pump-turbine model can be manufactured based on the pump-turbine to be identified, and the geometric similarity and dynamic similarity of the model can be ensured. Then prepare an experimental device, including a water tank, a water supply and drainage system, force and speed measuring instruments, etc.; set the guide vane opening and gradually adjust the guide vane opening in the model to a preset series of values, and stabilize the water flow conditions after each adjustment. Under each guide vane opening setting, measure and record the flow rate (Q), speed (n) and other parameters of the turbine, and finally obtain the flow rate (Q), speed (n) and other parameters under different guide vane openings. Q 11 - n 11 (flow rate - speed) and T 11 - n 11 The curve of each guide vane opening in the test is recorded. H - Q (Head-flow) relationship curve.

[0046] Step S102, determining an operating point for identifying rotating stall based on the characteristic curve. Specifically, when determining the operating point, a determined characteristic curve, such as a flow-speed curve, is analyzed to determine an area where rotating stall may occur in the curve, and then multiple operating points with different flow rates are determined in the curve based on characteristic curves of different guide vane openings.

[0047] Step S103, using computational fluid dynamics to calculate the flow field data of each operating point as the background flow field. Specifically, when using computational fluid dynamics (CFD) to perform flow field analysis and calculation on each operating point, it can be implemented in the following way: First, a three-dimensional geometric model is constructed in the CFD software according to the actual size and structure of the pump turbine. The model includes all key components that affect the flow field, such as blades, guide vanes, and flow channels. Next, the geometric model is meshed to generate a mesh suitable for CFD calculation. The quality of the mesh directly affects the accuracy and efficiency of the calculation, and it is necessary to ensure that there is sufficient mesh density in the key area. Then, appropriate boundary conditions are set for the inlet and outlet, wall, etc. of the model. For example, the inlet flow velocity, pressure, guide vane opening angle, rotation speed, etc., these conditions should be set according to the specific operating point. Later, the non-fixed length flow field calculation can be performed on each operating point according to the set relevant model and data, and the runner flow calculation data therein is extracted, and the background flow field of different operating points is determined according to the runner flow calculation data. It should be noted that the background flow field here includes not only the correlation coefficient determined according to the runner flow calculation data, but also the rotation speed and wave number of the disturbance, so as to solve the linearized NS equations containing the disturbance.

[0048] Step S104, based on the background flow field, determine the linearized NS equations containing the disturbance quantity and solve them to obtain the pressure disturbance quantity at the runner inlet under different disturbance speeds. Among them, the full name of the NS equation is the Navier-Stokes equation, which is the basic equation describing the movement of each particle in the flow field and the basic equation of fluid mechanics. According to existing research on rotating stall, small disturbances in fluid machinery are the source of flow field instability and eventually develop into rotating stall. In a disturbed flow field, the physical quantity of each node is expressed in the form of the sum of the non-disturbance quantity and the disturbance quantity, that is: N = N a + N ', in N is the total physical quantity, N a is the non-perturbing quantity, N ' is the disturbance amount, N a >> N '. Thus, the flow field with disturbance is analyzed to determine the linearized NS equations containing the disturbance amount. Then, the relevant parameters in the background flow field can be substituted into the equation to obtain the pressure disturbance amount at the runner inlet under different disturbance speeds.

[0049] Step S105, substitute the pressure disturbance into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, wherein the disturbance critical stability equation is determined by model analysis of the pump turbine based on the disturbance theory; specifically, the disturbance critical stability equation is determined by simplifying the model of the pump turbine and according to the difference in the change of the runner head when there is a disturbance and when there is no disturbance in the model. After determining the disturbance critical stability equation, the pressure disturbance and related parameters determined at different disturbance speeds can be substituted into the equation to obtain the parameter for judging the stability of the disturbance wave at each disturbance speed, thereby obtaining the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed.

[0050] Step S106, determining the starting point of the rotating stall at each guide vane opening according to the relationship, and obtaining the rotating stall existence area at each guide vane opening in combination with the end point where the flow rate is zero. Specifically, after determining the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, the relationship can be analyzed. Since each operating point is determined based on the characteristic curve of different guide vane openings, when analyzing the relationship, the flow rate corresponding to the guide vane opening can be combined to determine the starting point of the rotating stall at each guide vane opening, and the rotating stall existence area at each guide vane opening can be obtained in combination with the end point where the flow rate is zero.

[0051] In this embodiment, a method for identifying a rotating stall region of a pump turbine under turbine operating conditions is provided, and the process includes the following steps:

[0052] Step S201, conduct a model test on the pump turbine to be identified to obtain characteristic curves under different guide vane openings. Figure 1 Step S101 of the illustrated embodiment will not be described in detail here.

[0053] Step S202: determining an operating point for identifying rotating stall based on the characteristic curve.

[0054] Specifically, the above step S202 includes:

[0055] Step S2021, screening characteristic curves with positive slopes; specifically, the obtained Q 11 - n 11 (Flow-Speed) Figure 2 As shown in the figure, for the characteristic curve of equal guide vane opening without positive slope, no rotating stall will occur and no analysis and calculation will be performed. Therefore, only the characteristic curve of equal guide vane opening with positive slope is selected, such as Figure 2 The five curves on the upper right are shown.

[0056] Step S2022, based on the screened characteristic curves, a plurality of operating condition points for identifying rotating stall are determined in the operating condition range between the turbine operating condition and the turbine braking condition. Specifically, for the screened characteristic curves, a range of operating condition changes (such as Figure 2 The curve is shown as being at the negative slope point OP1 to the positive slope point OP f Within this range, multiple operating conditions (different only in flow rate) are determined, i.e., multiple operating points.

[0057] Step S203, using computational fluid dynamics to calculate the flow field data of each operating point as the background flow field.

[0058] Specifically, the above step S203 includes:

[0059] Step S2031, using computational fluid dynamics to calculate the unsteady flow field of each operating point to obtain a flow field calculation result; specifically, the calculation of the unsteady flow field can be performed in CFD software, which will not be described in detail here.

[0060] Step S2032, determining the circumferential average flow field of the runner at each operating point based on the flow field calculation results; wherein, when determining the circumferential average flow field, the flow field data at the guide vane outlet and the runner can be extracted from the flow field calculation results, including the coordinates, velocity, pressure and other data of each position in the flow field, and then the circumferential average flow field of the runner flow field is calculated to obtain the circumferential average flow field data including velocity and pressure.

[0061] Step S2033, interpolate the circumferential average flow field to the middle surface of the blade, and obtain the flow field velocity and pressure on the middle surface as the background flow field. Specifically, it is assumed that the circumferential flow of the non-rotating stall flow field is uniform and indifferent, that is, it satisfies the infinite blade assumption. There are infinite blades inside the entire runner, and the blades can be equivalent to the S2 flow surface in the two-dimensional blade design theory. The fluid in the runner can only flow along the blade surface, that is, along the S2 flow surface. The circumferential average flow field data determined above is used to approximate the flow field conditions under this assumption; the middle surface of the runner model is used as the blade surface under the infinite blade assumption, and the circumferential average flow field data is interpolated to the middle surface as the flow field velocity and pressure at each node on the middle surface.

[0062] Step S204, determining the speed and wave number of the disturbance at each operating point, wherein the speed is a plurality of speed values ​​between 0.2 and 0.7, and the wave number includes one of 1, 2 or 3. Specifically, for each operating point, the speed of the disturbance also needs to be f and wave number nAssumptions are made to solve the NS equations for the disturbance flow field. The wave number for each condition can be assumed to be 1, 2, and 3, which means that the disturbance wave has 1, 2, or 3 cycles in the entire circle. The disturbance wave speed can be set to 0.2, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, and 0.7, or more possible speed values ​​between 0.2 and 0.7.

[0063] Step S205, based on the background flow field, a linearized NS equation group including the disturbance quantity is determined and solved to obtain the pressure disturbance quantity at the runner inlet under different disturbance speeds.

[0064] Specifically, the above step S205 includes:

[0065] Step S2051, based on multiple disturbance speeds, multiple disturbance wave numbers and background flow field, a numerical method is used to discretize the linearized NS equations containing the disturbance quantity to obtain a non-homogeneous linear equation system. Figure 3 As shown in the figure, when analyzing the flow field containing disturbances, it is assumed that a small flow disturbance is transmitted from the upstream to the runner inlet. j , the disturbance is non-uniform in the circumferential direction, so it can be expressed as j ( θ ) has periodic circumferential rotation, and its rotation frequency is f (this frequency corresponds to the circumferential rotation frequency at which the rotating stall develops), the average flow Q The disturbance disappears at the runner outlet. At the same time, for the pump-turbine with disturbance, it is simplified to a one-dimensional model of inlet + runner flow channel + outlet for the convenience of analysis. The total pressure at the runner inlet section is p T , the outlet pressure of the outlet section is p S , runner section pressure is p E .

[0066] After determining the linearized NS equations containing the disturbance, first use the following formula to non-dimensionalize each physical quantity:

[0067] (1)

[0068] Among them, U is the circumferential velocity at the inlet of the runner blade, R1 is the radius at the inlet of the runner, F is the rotating stall rotation angular velocity, ω is the angular velocity of the runner rotation, V is the viscosity coefficient, v is the dimensionless velocity, the subscript rθz indicates the direction, radial, circumferential and axial, p is the pressure coefficient, P is the pressure, ρ is the density, rz is the dimensionless polar coordinate radius value and axial coordinate value, R is the polar coordinate radius value of the point, vis the dimensionless viscosity coefficient. Substituting the physical quantity in the NS equation of the disturbance quantity with the above form, and using dimensionless processing, ignoring the second-order infinitesimal terms in the NS equation, we get the following formula:

[0069] (2)

[0070] The nodes on the S2 flow surface are represented by polar coordinates, where θ yes r and z The function is: θ = f ( r , z ). The partial derivative in equation (2) is transformed using the following formula:

[0071] (3)

[0072] In order to discretize equation (2), it is necessary to transform the coordinates of the grid on the S2 flow surface of the complex structure. The Jacobian determinant used for the transformation is:

[0073] (4)

[0074] Using the above coordinate transformation, the node coordinate system of the S2 flow surface is changed from rzθ Converted to ξηθ Coordinate system.

[0075] Each disturbance in the NS equation (2) containing the disturbance is defined in the form of simple harmonics, n It represents the wave number of the disturbance wave in a whole circle, that is, the number of cycles, in the following form:

[0076] (5)

[0077] In the formula, R, C, A, and P are the amplitudes of the fluctuations, corresponding to the disturbance wave amplitudes of radial velocity disturbance, circumferential velocity disturbance, and pressure disturbance, respectively. The subscript R is the real part, and C is the imaginary part.

[0078] Substituting the relationship between formulas (3)-(5) into (2), and combining the inlet radial velocity disturbance, the outlet pressure disturbance, and the disturbance of the upper and lower walls of the flow channel with the impenetrable boundary, the partial differential equation is discretized, and finally the non-homogeneous linear equation system AX=B is obtained.

[0079] Step S2052, using a singular value decomposition algorithm to solve the non-homogeneous linear equations, and obtain the pressure disturbance at the rotor inlet under different disturbance speeds. Specifically, since the number of elements in the linear equation group AX=B is huge, the singular value decomposition technology is used to solve it, and a graphics processor is used to process the calculation to increase the calculation speed.

[0080] Step S206, substituting the pressure disturbance into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, wherein the disturbance critical stability equation is determined by performing model analysis on the pump turbine based on the disturbance theory.

[0081] Specifically, the above step S206 includes:

[0082] Step S2061, substitute the pressure disturbance into the disturbance critical stability equation to obtain the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers; specifically, for the simplified one-dimensional model of the inlet + runner flow channel + outlet of the pump turbine, the difference in the change of the runner head when there is a disturbance and when there is no disturbance can be analyzed based on the small disturbance theory, and it is assumed that the radial velocity disturbance at the inlet R (1) = 1, the pressure disturbance at the inlet P (1)= PR (1)+ iPM (1) PR (1) is the real part of the pressure disturbance, iPM (1) is the imaginary part of the pressure disturbance), and the critical condition for system stability (disturbance critical stability equation) is obtained as shown in the following equation, that is, the model assumes that the disturbance wave exists stably in the flow field.

[0083] (6)

[0084] Among them, the equation τ and η It is the structure and other properties of the system itself. f and n is the disturbance wave characteristic assumed in the calculation, Q is the radial velocity coefficient, V r The speed of the high pressure side of the runner U The ratio, D is the diameter of the high pressure side of the runner, n is the disturbance circumferential wave number, f is the disturbance rotation speed, H' is the derivative of the head-flow curve, that is, the slope of the tangent line of the curve at a certain point. When the above equations are established, it is believed that the weak disturbance assumed in this theory that can develop into rotating stall exists, and the operating point where the equation is established is the critical point of rotating stall, that is, the starting condition.

[0085] The pressure disturbance at the rotor inlet under different disturbance speeds is obtained PR (1) and PM (1) can be substituted into the above formula (6) to obtain the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers. Among them, the parameters for judging the stability of the disturbance wave are expressed by the following formula:

[0086] (7)

[0087] in, C rot represents the first parameter among the parameters for judging the stability of the disturbance wave, Amp Indicates the second parameter among the parameters for determining the stability of the disturbance wave.

[0088] Step S2062, based on the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers, the corresponding relationship between the disturbance speed and the parameter for judging the stability of the disturbance wave under the preset disturbance wave number is determined, the parameter for judging the stability of the disturbance wave includes a first parameter and a second parameter, and the corresponding relationship includes a first corresponding relationship between the disturbance speed and the first parameter and a second corresponding relationship between the disturbance speed and the second parameter. It should be noted that according to the above formula (7), when calculating the second parameter Amp , the disturbance speed is not used directly, but because the pressure disturbance PR (1) has a corresponding relationship with the disturbance speed, from which the corresponding relationship between the disturbance speed and the second parameter can be obtained.

[0089] Step S207, determining the rotating stall starting point at each guide vane opening according to the relationship, and obtaining the rotating stall existing area at each guide vane opening in combination with the ending point where the flow is zero.

[0090] Specifically, the above step S207 includes:

[0091] Step S2071, determining the disturbance speed when the first parameter is greater than the first threshold value according to the first corresponding relationship; specifically, when the first parameter C rot When the value is large, it means the disturbance speed is f , the wave number is n The disturbance wave energy exists, therefore, the disturbance speed corresponding to when the first parameter is greater than the first threshold can be determined from the first corresponding relationship.

[0092] Step S2072, according to the determined disturbance speed and the preset disturbance wave number, based on the relationship between the second parameter and the flow rate obtained by the disturbance critical stability equation, determine the flow rate at which the second parameter is equal to the second threshold value, and obtain the starting point of the rotating stall; specifically, after determining the disturbance speed at which the first parameter is greater than the first threshold value, the pressure disturbance amount corresponding to the disturbance speed and the preset disturbance wave number can be determined, and the pressure disturbance amount is substituted into the above formula (7) to obtain the second parameter under the disturbance speed and wave number Amp and flow Q 11 The corresponding relationship. Figure 4 As shown, it is a certain wave number nand a certain speed f Down Amp Schematic diagram of the relationship between value and flow. Figure 4 It can be seen that with Q 11 reduce, Amp It gradually decreases from close to 0 to a negative value. This law is completely consistent with the occurrence of rotating stall at low flow, so it can be determined that Amp <0, the disturbance wave will diverge unstably. This leads to a method for determining the region where rotating stall occurs, namely: C rot Has a larger value, Amp Close to 0 is the starting point of rotating stall.

[0093] Step S2073, according to the starting point of the rotating stall and the end point of the flow rate being zero, the rotating stall existence area under each guide vane opening is obtained. Specifically, after the starting point of the rotating stall is determined, the point of flow rate being zero is taken as the end point, and the area between the starting point and the end point is the rotating stall existence area. Figure 5 As shown in the figure, it is the area between the starting point of the rotating stall with different guide vane openings and the working condition with a flow rate of 0, that is, the area where the rotating stall exists under the whole turbine working condition of the pump turbine. Figure 5 , and the speed of rotating stall under different operating conditions can also be determined.

[0094] The method for identifying the area where rotating stall exists for a pump-turbine under turbine operating conditions proposed in the present invention adopts a theoretical analysis method and is easy to implement. Compared with expensive model test methods and non-steady-state numerical calculation methods, the cost investment required is very low; at the same time, the method realizes the analysis of the starting point of the rotating stall, that is, it can clearly determine the starting point of the rotating stall, which is difficult to do with existing model tests and numerical calculation methods; and, the method builds a path between theory and application by analyzing different operating points; in addition, the method also provides global information on the rotating stall occurrence area and speed characteristics during the operation of the pump-turbine, provides rotating stall information for the operation process, provides a new basis for the operation and maintenance process, and can better maintain the safe operation of the unit.

[0095] In this embodiment, a device for identifying the area where a pump turbine rotates and stalls under turbine conditions is provided. The device is used to implement the above-mentioned embodiments and preferred implementation modes, and the descriptions that have been made will not be repeated. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0096] This embodiment provides a device for identifying a region where a pump turbine has a rotational stall under turbine operating conditions. Figure 6 As shown, including:

[0097] The test module 61 is used to perform a model test on the pump-turbine to be identified to obtain characteristic curves under different guide vane openings;

[0098] an operating point determination module 62, for determining an operating point for identifying rotating stall based on the characteristic curve;

[0099] A flow field calculation module 63, used to calculate the flow field data of each operating point using computational fluid dynamics as a background flow field;

[0100] The disturbance solving module 64 is used to determine and solve the linearized NS equations containing the disturbance quantity based on the background flow field, and obtain the pressure disturbance quantity at the runner inlet under different disturbance speeds;

[0101] A relationship determination module 65 is used to substitute the pressure disturbance into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, wherein the disturbance critical stability equation is determined by performing model analysis on the pump turbine based on the disturbance theory;

[0102] The identification module 66 is used to determine the starting point of the rotating stall at each guide vane opening according to the relationship, and to obtain the rotating stall existence area at each guide vane opening in combination with the end point where the flow is zero.

[0103] In an optional embodiment, the operating point determination module is specifically used to: screen characteristic curves with positive slopes; based on the screened characteristic curves, determine multiple operating points for identifying rotational stall in the operating range between the turbine operating condition and the turbine braking condition.

[0104] In an optional embodiment, the flow field calculation module is specifically used to: use computational fluid dynamics to calculate the unsteady flow field at each operating point to obtain flow field calculation results; determine the circumferential average flow field of the impeller at each operating point based on the flow field calculation results; interpolate the circumferential average flow field to the middle surface of the blade to obtain the flow field velocity and pressure on the middle surface as the background flow field.

[0105] In an optional embodiment, the device also includes: a disturbance determination module, used to determine the speed and wave number of the disturbance at each operating point, the speed is a plurality of speed values ​​between 0.2 and 0.7, and the wave number includes one of 1, 2 or 3.

[0106] In an optional embodiment, the disturbance solving module is specifically used for: based on multiple disturbance speeds, multiple disturbance wave numbers and background flow fields, using a numerical method to discretize the linearized NS equations containing the disturbance quantity to obtain a non-homogeneous linear equation group; using a singular value decomposition algorithm to solve the non-homogeneous linear equation group to obtain the pressure disturbance quantity at the impeller inlet under different disturbance speeds.

[0107] In an optional embodiment, the relationship determination module is specifically used to: substitute the pressure disturbance quantity into the disturbance critical stability equation to obtain parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers; determine the corresponding relationship between the disturbance speed and the parameters for judging the stability of the disturbance wave under a preset disturbance wave number based on the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers, the parameters for judging the stability of the disturbance wave include a first parameter and a second parameter, and the corresponding relationship includes a first corresponding relationship between the disturbance speed and the first parameter and a second corresponding relationship between the disturbance speed and the second parameter.

[0108] In an optional embodiment, the identification module is specifically used to: determine the disturbance speed at which the first parameter is greater than a first threshold value according to the first corresponding relationship; determine the flow rate at which the second parameter is equal to the second threshold value according to the determined disturbance speed and the preset disturbance wave number and the relationship between the second parameter and the flow rate obtained based on the disturbance critical stability equation, and obtain the starting point of the rotational stall; obtain the rotational stall existence area at each guide vane opening according to the starting point of the rotational stall and the ending point where the flow rate is zero.

[0109] The further functional description of each of the above modules is the same as that of the above corresponding embodiments and will not be repeated here.

[0110] The embodiment of the present invention also provides a computer device having the above Figure 6 The device shown is for identifying the area where a pump turbine experiences rotational stall under turbine operating conditions.

[0111] See also Figure 7 , Figure 7 is a schematic diagram of the structure of a computer device provided by an optional embodiment of the present invention, such as Figure 7As shown, the computer device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 7 A processor 10 is taken as an example.

[0112] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0113] The memory 20 stores instructions executable by at least one processor 10, so that at least one processor 10 executes the method shown in the above embodiment.

[0114] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created by the use of a computer device based on the presentation of a small program landing page, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0115] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0116] The computer device further comprises a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0117] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0118] A part of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the existence of the computer program instruction in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc., and accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium accessible to the computer.

[0119] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for identifying a rotating stall region of a pump turbine under turbine operating conditions, characterized in that: The method comprises: A model test was conducted on the pump turbine to be identified, and the characteristic curves under different guide vane openings were obtained; determining an operating point for identifying rotating stall based on the characteristic curve; Computational fluid dynamics is used to calculate the flow field data of each operating point as the background flow field; Based on the background flow field, the linearized NS equations containing the disturbance are determined and solved to obtain the pressure disturbance at the runner inlet under different disturbance speeds. Substituting the pressure disturbance into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, wherein the disturbance critical stability equation is determined by performing model analysis on the pump turbine based on the disturbance theory; The rotating stall starting point at each guide vane opening is determined according to the relationship, and the rotating stall existence area at each guide vane opening is obtained in combination with the end point where the flow rate is zero.

2. The method according to claim 1, characterized in that Determining an operating point for identifying rotating stall based on the characteristic curve includes: Screening characteristic curves with positive slopes; Based on the screened characteristic curve, a plurality of operating points for identifying rotating stall are determined in the operating range between the turbine operating condition and the turbine braking condition.

3. The method according to claim 1, characterized in that Computational fluid dynamics is used to calculate the flow field data of each operating point as the background flow field, including: Computational fluid dynamics is used to calculate the unsteady flow field at each operating point and the flow field calculation results are obtained; Determine the circumferential average flow field of the runner at each operating point according to the flow field calculation result; The circumferential average flow field is interpolated to the middle surface of the blade to obtain the flow field velocity and pressure on the middle surface as the background flow field.

4. The method according to claim 1, characterized in that: After calculating the flow field data of each operating point using computational fluid dynamics as the background flow field, the method further includes: The rotation speed and wave number of the disturbance at each operating point are determined, wherein the rotation speed is a plurality of rotation speed values ​​between 0.2 and 0.7, and the wave number includes one of 1, 2 or 3.

5. The method according to claim 4, characterized in that Based on the background flow field, the linearized NS equations containing the disturbance are determined and solved to obtain the pressure disturbance at the runner inlet under different disturbance speeds, including: Based on multiple disturbance speeds, multiple disturbance wave numbers and background flow field, a numerical method is used to discretize the linearized NS equations containing disturbance quantities to obtain a non-homogeneous linear equation system. The non-homogeneous linear equations are solved using a singular value decomposition algorithm to obtain the pressure disturbance at the impeller inlet under different disturbance speeds.

6. The method according to claim 5, characterized in that Substituting the pressure disturbance into the disturbance critical stability equation, the relationship between the parameters for judging the stability of the disturbance wave and the disturbance speed is obtained, including: Substituting the pressure disturbance into the disturbance critical stability equation, obtaining parameters for judging the stability of disturbance waves corresponding to different disturbance rotation speeds and different disturbance wave numbers; Based on the parameters for judging the stability of the disturbance wave corresponding to different disturbance speeds and different disturbance wave numbers, the corresponding relationship between the disturbance speed and the parameters for judging the stability of the disturbance wave is determined under a preset disturbance wave number, the parameters for judging the stability of the disturbance wave include a first parameter and a second parameter, and the corresponding relationship includes a first corresponding relationship between the disturbance speed and the first parameter and a second corresponding relationship between the disturbance speed and the second parameter.

7. The method according to claim 6, characterized in that The rotating stall starting point at each guide vane opening is determined according to the relationship, and the rotating stall existence area at each guide vane opening is obtained in combination with the end point where the flow rate is zero, including: Determine, according to the first corresponding relationship, a disturbance speed at which the first parameter is greater than a first threshold; According to the determined disturbance speed and the preset disturbance wave number, based on the relationship between the second parameter and the flow rate obtained by the disturbance critical stability equation, the flow rate at which the second parameter is equal to the second threshold value is determined to obtain the starting point of the rotating stall; The rotating stall existence area under each guide vane opening is obtained according to the starting point of the rotating stall and the ending point where the flow rate is zero.

8. A device for identifying the area where a pump turbine has a rotating stall under turbine operation, characterized in that: The device comprises: The test module is used to conduct model tests on the pump-turbine to be identified and obtain characteristic curves under different guide vane openings; an operating point determination module, configured to determine an operating point for identifying rotating stall based on the characteristic curve; A flow field calculation module is used to calculate the flow field data of each operating point using computational fluid dynamics as the background flow field; The disturbance solving module is used to determine and solve the linearized NS equations containing the disturbance quantity based on the background flow field, and obtain the pressure disturbance quantity at the runner inlet under different disturbance speeds; A relationship determination module is used to substitute the pressure disturbance into the disturbance critical stability equation to obtain the relationship between the parameter for judging the stability of the disturbance wave and the disturbance speed, wherein the disturbance critical stability equation is determined by performing model analysis on the pump turbine based on the disturbance theory; The identification module is used to determine the starting point of the rotating stall at each guide vane opening according to the relationship, and obtain the rotating stall existence area at each guide vane opening in combination with the end point where the flow is zero.

9. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the method for identifying a rotational stall area of ​​a pump turbine under turbine operating conditions according to any one of claims 1 to 7 by executing the computer instructions.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the method for identifying a rotating stall region of a pump-turbine under a turbine operating condition according to any one of claims 1 to 7.

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