Method for identifying flow instability quantity of pump-turbine pump working condition

Abstract

The application discloses a method for identifying flow instability of a water pump water turbine in a water pump working condition, and specifically comprises the following steps: obtaining three-dimensional unsteady flow field data of the water pump water turbine in different flow rates in the water pump working condition, and extracting enthalpy vector of a potential rotor and coriolis force vector of a rotating coordinate system; constructing a dimensionless stability index SI based on the length of the enthalpy gradient vector of the potential rotor and the length of the coriolis force vector; extracting time series flow field data at multiple layer height sections and multiple flow direction positions of a runner flow passage, and calculating a time series of the dimensionless stability index SI; and dividing flow field stability levels according to the numerical value and time series periodicity of the SI time series, and identifying the flow instability degree. The application solves the problems of the prior art, such as the dependence on qualitative observation methods such as external characteristic curves, pressure fluctuation time-frequency analysis and velocity field cloud diagrams, the lack of a unified dimensionless quantitative index, the inability to quantitatively distinguish between stable flow, local initial instability and global complete instability, and the difficulty in horizontally comparing the instability severity of different working conditions.

Description

Technical Field

[0001] This invention belongs to the field of pump-turbine technology for pumped storage, specifically relating to a method for identifying flow instability in pump-turbine operation. Background Technology

[0002] Pumped storage is a key regulating resource supporting the safe and stable operation of new power systems. As the core energy conversion component of pumped storage units, the pump-turbine needs to operate flexibly within a wide range of operating conditions. During the transition between operating conditions, the unit inevitably passes through the high-head, low-flow operating range of the pump condition. This region is prone to inducing strong flow instability, manifested as typical instability phenomena such as rotational stall, blade backflow, and large-scale flow separation. This leads to severe pressure pulsation and blade fatigue damage, seriously restricting the safe and stable operation of the unit.

[0003] Currently, the identification of flow instability in pump turbines mainly relies on the trend judgment of external characteristic curves, time-frequency analysis of pressure pulsations, or qualitative observation of velocity field cloud maps. However, the above-mentioned existing technologies have the following defects: (1) They lack a unified dimensionless quantitative index, making it impossible to quantitatively distinguish between steady flow, local initial instability, and global complete instability; (2) It is difficult to make horizontal comparisons of the severity of instability under different operating conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying the instability of water pump turbines under pump operating conditions. This method solves the problems of existing technologies that rely on qualitative observation methods such as external characteristic curves, pressure pulsation time-frequency analysis, and velocity field cloud maps, lack unified dimensionless quantitative indicators, cannot quantitatively distinguish between stable flow, local initial instability, and global complete instability, and are difficult to compare the severity of instability under different operating conditions.

[0005] The technical solution adopted in this invention is a method for identifying flow instability in pump turbine operating conditions. Specifically, it involves: acquiring three-dimensional unsteady flow field data of the pump turbine under different flow rates, extracting the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system, constructing a dimensionless stability index SI based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector, extracting time-series flow field data at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and calculating the time series of the dimensionless stability index SI; classifying the flow field stability level according to the magnitude and time periodicity of the SI time series, and identifying the degree of flow instability.

[0006] The invention is further characterized by: The specific steps are as follows: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

[0007] In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute.

[0008] In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; Let be the flow velocity.

[0009] Step 3 specifically involves: Step 3.1: Obtain the gradient vector of the potential rotor enthalpy by calculating the gradient of the potential rotor enthalpy vector; Step 3.2: Calculate the vector magnitude of the rotor enthalpy gradient and the vector magnitude of the Coriolis force; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ; in, The enthalpy gradient vector magnitude of the potential rotor. It is the Coriolis force vector magnitude.

[0010] Step 3.1 specifically involves: using the gradient calculation function in the post-processor of the computational fluid dynamics software, and combining the radial coordinates of the flow field and the angular velocity of the rotor to solve for the potential rotor enthalpy vector. I P Then, the enthalpy vector of the potential rotor. I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector modulus is obtained; Step 3.2 specifically involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude can be obtained. ; In step 3.3, the potential rotor enthalpy gradient vector mode Dimensions and Coriolis force vector magnitude The dimensions of all are LT -2 SI is a dimensionless parameter, unaffected by unit size or operating parameters. The magnitude of SI allows for a comparative analysis of the severity of flow instability under different flow conditions and between different pumps and turbines. Potential rotor enthalpy gradient vector. Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F C It is a constraint force that affects the relative motion trajectory in a rotating coordinate system, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state.

[0011] SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, resulting in flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability.

[0012] In step 4, the multi-layer blade height cross-section includes a cross-section with a span of 0.1, an intermediate blade height cross-section with a span of 0.5, and a cross-section with a span of 0.9. The intermediate blade height cross-section with a span of 0.5 is the main observation object for instability early warning, and is not affected by the flow of the hub and rim boundary layer. The flow state represents the characteristics of the main flow region of the runner. At least 14 monitoring points are evenly arranged along the flow direction from the runner inlet to the outlet on each blade height cross-section, and at least 42 monitoring points are arranged in total on the three blade height cross-sections. The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each monitoring point are extracted within at least 3 consecutive complete rotation cycles of the runner. The instantaneous SI value is calculated for each measurement point to obtain the SI time series of each monitoring point.

[0013] In step 5, the specific criteria for determining the flow instability state of each monitoring point are as follows: when SI < 1 and the SI time series shows complete periodic fluctuations, the flow field at the monitoring point is determined to be stable and there is no obvious flow separation in the flow channel; when SI > 1 is the monitoring point only in the runner outlet area, the flow field is determined to be in a critical instability state, and the critical instability state is the initial warning signal of flow instability; when SI > 1 and the periodicity of the SI time series completely disappears, deep instability occurs at the monitoring point, and the flow separation and rotational stall persist throughout the entire domain.

[0014] When the flow field is determined to be in a critical or deep instability state, the location of the monitoring point with the earliest occurrence of SI>1 in the SI time series of each monitoring point is marked as the starting position of the flow instability. The locations of each monitoring point are connected sequentially according to the order of occurrence of SI>1 to form the spatial migration trajectory of the instability region over time. The direction of this trajectory is the propagation direction of the flow instability. When SI>1 first appears near the runner outlet, the flow instability is determined to have started in the runner outlet region. As the flow rate decreases, the monitoring point with SI>1 expands along the flow direction from the runner outlet to the runner inlet, and different degrees of flow instability are generated in the entire flow channel.

[0015] The beneficial effects of this invention are: The present invention provides a method for identifying flow instability in pump-turbine systems. Starting from the essence of the relative motion momentum equation in a rotating coordinate system, it quantifies the inherent mechanism of the mutual balance between the potential rotor enthalpy gradient driving force that induces flow instability and the Coriolis constraint force that maintains smooth flow. Therefore, it can capture early signs of backflow and separation structures in the initial stage of flow instability in pump-turbine systems. The magnitude of the dimensionless stability index (SI) directly characterizes the severity of flow instability. Its temporal evolution and spatial distribution can identify the propagation path of flow instability, achieving quantitative and dynamic diagnosis of the entire instability process. High SI value regions can accurately pinpoint the initial location of flow instability using multi-flow direction measurement points. This method is applicable to the quantitative diagnosis of unstable flow phenomena in various rotating machinery such as pumps and turbines, and the final output is a unified dimensionless scalar parameter, which can be used in existing CFD numerical simulation and hydraulic test data post-processing workflows to complete the quantitative analysis of SI values. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the method for identifying flow instability in pump operation conditions of a water pump turbine according to the present invention. Figure 2 This is a schematic diagram of the water pump turbine model in Embodiment 6 of the present invention; Figure 3 This is a schematic diagram of the different blade height plane positions of the impeller in Embodiment 6 of the present invention; Figure 4 This is a diagram showing the arrangement of SI measuring points for a cross section with a span of 0.1 in Embodiment 6 of the present invention. Figure 5 This is a diagram showing the arrangement of SI measuring points for a cross-section with a span of 0.5 in Embodiment 6 of the present invention. Figure 6 This is a diagram showing the arrangement of SI measuring points for a cross-section with a span of 0.9 in Embodiment 6 of the present invention. Figure 7 This is a graph showing the average SI variation at different flow rates in Embodiment 6 of the present invention. Figure 8 This is a schematic diagram of the stable flow curves of measuring point SI with a span of 0.5 under different working conditions in Embodiment 6 of the present invention; Figure 9 This is a schematic diagram of the critical instability curves of measuring point SI with a span of 0.5 under different working conditions in Embodiment 6 of the present invention; Figure 10 This is a schematic diagram of the depth instability curves of the measuring point SI under different working conditions with a Span of 0.5 in Embodiment 6 of the present invention.

[0017] In the diagram, 1. tailrace pipe, 2. impeller, 3. movable guide vane, 4. fixed guide vane, 5. volute, 6. impeller rim, 7. hub, 8. blade height section with a span of 0.1, 9. intermediate blade height section with a span of 0.5, 10. blade height section with a span of 0.9, 11. SI monitoring point of section with a span of 0.1, 12. SI monitoring point of section with a span of 0.5, 13. SI monitoring point of section with a span of 0.9, 14. first impeller flow channel, 15. second impeller flow channel. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] The present invention discloses a method for identifying flow instability in a water pump turbine under pump operating conditions. Specifically, it involves: acquiring three-dimensional unsteady flow field data of the water pump turbine at different flow rates, extracting the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system, constructing a dimensionless stability index SI based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector, extracting time-series flow field data at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and calculating the time series of the dimensionless stability index SI; classifying the flow field stability level according to the magnitude and periodicity of the SI time series, and identifying the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute. Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor;p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; The velocity is the flow field velocity. Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Specifically: Step 3.1: Obtain the gradient vector of the potential rotor enthalpy by calculating the gradient of the potential rotor enthalpy vector; Specifically, the gradient calculation function in the post-processor of computational fluid dynamics software is used to solve for the potential rotor enthalpy vector by combining the radial coordinates of the flow field and the angular velocity of the rotor. I P Then, the enthalpy vector of the potential rotor. I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector modulus is obtained; Step 3.2: Calculate the vector magnitude of the rotor enthalpy gradient and the vector magnitude of the Coriolis force; Specifically, this involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude can be obtained. ; According to the momentum equation of relative motion of the runner, under the simplified assumptions of steady, inviscid, and zero blade thickness, the momentum equation of relative motion simplifies to: ; In the formula, The potential rotor enthalpy gradient vector is the active force that drives the fluid to break away from the blade profile, generate secondary flow, and separate from the flow. F C The key inertial force affecting the relative motion trajectory in a rotating coordinate system can be regarded as the key force resisting the flow from deviating from the mainstream direction and maintaining the relative stability of the flow state; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ; in, The enthalpy gradient vector magnitude of the potential rotor. The Coriolis force vector magnitude; In step 3.3, the potential rotor enthalpy gradient vector mode Dimensions and Coriolis force vector magnitude The dimensions of all are LT -2 SI is a dimensionless parameter, unaffected by unit size or operating parameters. The magnitude of SI allows for a comparative analysis of the severity of flow instability under different flow conditions and between different pumps and turbines. Potential rotor enthalpy gradient vector. Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F C The constraint force in the rotating coordinate system that affects the relative motion trajectory, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state. SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, causing flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; In step 4, the multi-layer blade height cross-section includes a cross-section with a span of 0.1, an intermediate blade height cross-section with a span of 0.5, and a cross-section with a span of 0.9. The intermediate blade height cross-section with a span of 0.5 is the main observation object for instability early warning, and is not affected by the flow of the hub and rim boundary layer. The flow state represents the characteristics of the main flow region of the runner. At least 14 monitoring points are evenly arranged along the flow direction from the runner inlet to the outlet on each blade height cross-section, and at least 42 monitoring points are arranged in total on the three blade height cross-sections. The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each monitoring point are extracted within at least 3 consecutive complete rotation cycles of the runner. The instantaneous SI value is calculated for each measurement point to obtain the SI time series of each monitoring point. Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition. In step 5, the specific criteria for determining the flow instability state at each monitoring point are as follows: when SI < 1 and the SI time series shows complete periodic fluctuations, the flow field at that monitoring point is determined to be stable, and there is no obvious flow separation in the flow channel; when SI > 1 only at the monitoring points in the runner outlet region, the flow field is determined to be in a critical instability state, and the critical instability state is the initial warning signal for flow instability; when SI > 1 and the periodicity of the SI time series completely disappears, deep instability occurs at that monitoring point, and flow separation and rotational stall persist throughout the entire region. When the flow field is determined to be in a critical or deep instability state, the location of the monitoring point with the earliest occurrence of SI>1 in the SI time series of each monitoring point is marked as the starting position of the flow instability. The locations of each monitoring point are connected sequentially according to the order of occurrence of SI>1 to form the spatial migration trajectory of the instability region over time. The direction of this trajectory is the propagation direction of the flow instability. When SI>1 first appears near the runner outlet, the flow instability is determined to have started in the runner outlet region. As the flow rate decreases, the monitoring point with SI>1 expands along the flow direction from the runner outlet to the runner inlet, and different degrees of flow instability are generated in the entire flow channel.

[0020] Example 1 The method for identifying flow instability in a water pump turbine under pump operating conditions proposed in this embodiment is as follows: Three-dimensional unsteady flow field data of the water pump turbine under different flow rates are acquired, and the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system are extracted. A dimensionless stability index SI is constructed based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector. Time-series flow field data are extracted at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and the time series of the dimensionless stability index SI is calculated. Based on the magnitude and periodicity of the SI time series, the flow field stability level is classified to identify the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

[0021] Example 2 The method for identifying flow instability in a water pump turbine under pump operating conditions proposed in this embodiment is as follows: Three-dimensional unsteady flow field data of the water pump turbine under different flow rates are acquired, and the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system are extracted. A dimensionless stability index SI is constructed based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector. Time-series flow field data are extracted at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and the time series of the dimensionless stability index SI is calculated. Based on the magnitude and periodicity of the SI time series, the flow field stability level is classified to identify the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute. Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; The velocity is the flow field velocity. Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

[0022] Example 3 The method for identifying flow instability in a water pump turbine under pump operating conditions proposed in this embodiment is as follows: Three-dimensional unsteady flow field data of the water pump turbine under different flow rates are acquired, and the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system are extracted. A dimensionless stability index SI is constructed based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector. Time-series flow field data are extracted at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and the time series of the dimensionless stability index SI is calculated. Based on the magnitude and periodicity of the SI time series, the flow field stability level is classified to identify the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute. Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; The velocity is the flow field velocity. Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Specifically: Step 3.1: Obtain the gradient vector of the potential rotor enthalpy by calculating the gradient of the potential rotor enthalpy vector; Specifically, the gradient calculation function in the post-processor of computational fluid dynamics software is used to solve for the potential rotor enthalpy vector by combining the radial coordinates of the flow field and the angular velocity of the rotor. I P Then, the enthalpy vector of the potential rotor. I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector modulus is obtained; Step 3.2: Calculate the vector magnitude of the rotor enthalpy gradient and the vector magnitude of the Coriolis force; Specifically, this involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude can be obtained. ; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ; in, The enthalpy gradient vector magnitude of the potential rotor. The Coriolis force vector magnitude; In step 3.3, the potential rotor enthalpy gradient vector mode Dimensions and Coriolis force vector magnitude The dimensions of all are LT -2 SI is a dimensionless parameter, unaffected by unit size or operating parameters. The magnitude of SI allows for a comparative analysis of the severity of flow instability under different flow conditions and between different pumps and turbines. Potential rotor enthalpy gradient vector. Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F CThe constraint force in the rotating coordinate system that affects the relative motion trajectory, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state. SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, causing flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

[0023] Example 4 The method for identifying flow instability in a water pump turbine under pump operating conditions proposed in this embodiment is as follows: Three-dimensional unsteady flow field data of the water pump turbine under different flow rates are acquired, and the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system are extracted. A dimensionless stability index SI is constructed based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector. Time-series flow field data are extracted at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and the time series of the dimensionless stability index SI is calculated. Based on the magnitude and periodicity of the SI time series, the flow field stability level is classified to identify the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute. Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; The velocity is the flow field velocity. Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Specifically: Step 3.1: Obtain the gradient vector of the potential rotor enthalpy by calculating the gradient of the potential rotor enthalpy vector; Specifically, the gradient calculation function in the post-processor of computational fluid dynamics software is used to solve for the potential rotor enthalpy vector by combining the radial coordinates of the flow field and the angular velocity of the rotor. I P Then, the enthalpy vector of the potential rotor. I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector modulus is obtained; Step 3.2: Calculate the vector magnitude of the rotor enthalpy gradient and the vector magnitude of the Coriolis force; Specifically, this involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude can be obtained. ; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ; in, The enthalpy gradient vector magnitude of the potential rotor. The Coriolis force vector magnitude; In step 3.3, the potential rotor enthalpy gradient vector mode Dimensions and Coriolis force vector magnitude The dimensions of all are LT -2SI is a dimensionless parameter, unaffected by unit size or operating parameters. The magnitude of SI allows for a comparative analysis of the severity of flow instability under different flow conditions and between different pumps and turbines. Potential rotor enthalpy gradient vector. Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F C The constraint force in the rotating coordinate system that affects the relative motion trajectory, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state. SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, causing flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; In step 4, the multi-layer blade height cross-section includes a cross-section with a span of 0.1, an intermediate blade height cross-section with a span of 0.5, and a cross-section with a span of 0.9. The intermediate blade height cross-section with a span of 0.5 is the main observation object for instability early warning, and is not affected by the flow of the hub and rim boundary layer. The flow state represents the characteristics of the main flow region of the runner. At least 14 monitoring points are evenly arranged along the flow direction from the runner inlet to the outlet on each blade height cross-section, and at least 42 monitoring points are arranged in total on the three blade height cross-sections. The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each monitoring point are extracted within at least 3 consecutive complete rotation cycles of the runner. The instantaneous SI value is calculated for each measurement point to obtain the SI time series of each monitoring point. Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

[0024] Example 5 The method for identifying flow instability in a water pump turbine under pump operating conditions proposed in this embodiment is as follows: Three-dimensional unsteady flow field data of the water pump turbine under different flow rates are acquired, and the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system are extracted. A dimensionless stability index SI is constructed based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector. Time-series flow field data are extracted at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and the time series of the dimensionless stability index SI is calculated. Based on the magnitude and periodicity of the SI time series, the flow field stability level is classified to identify the degree of flow instability. Specifically, follow these steps: Figure 1 As shown: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used to conduct unsteady transient calculations based on steady-state calculation results as the initial field, selecting multiple flow rate target conditions under the pump condition of the pump-turbine to output the flow field data at each time step. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The entire flow path of a water pump turbine includes the tailrace, runner, movable guide vanes, fixed guide vanes, and volute. Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; In step 2, the expression for the potential rotor enthalpy vector is: ; in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ; in, F C The Coriolis force vector; The velocity is the flow field velocity. Step 3: Obtain the gradient of the potential rotor enthalpy vector and construct the dimensionless stability index SI. Specifically: Step 3.1: Obtain the gradient vector of the potential rotor enthalpy by calculating the gradient of the potential rotor enthalpy vector; Specifically, the gradient calculation function in the post-processor of computational fluid dynamics software is used to solve for the potential rotor enthalpy vector by combining the radial coordinates of the flow field and the angular velocity of the rotor. I P Then, the enthalpy vector of the potential rotor. I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector modulus is obtained; Step 3.2: Calculate the vector magnitude of the rotor enthalpy gradient and the vector magnitude of the Coriolis force; Specifically, this involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude can be obtained. ; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ; in, The enthalpy gradient vector magnitude of the potential rotor. The Coriolis force vector magnitude; In step 3.3, the potential rotor enthalpy gradient vector mode Dimensions and Coriolis force vector magnitude The dimensions of all are LT -2 SI is a dimensionless parameter, unaffected by unit size or operating parameters. The magnitude of SI allows for a comparative analysis of the severity of flow instability under different flow conditions and between different pumps and turbines. Potential rotor enthalpy gradient vector. Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F C The constraint force in the rotating coordinate system that affects the relative motion trajectory, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state. SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, causing flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability. Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; In step 4, the multi-layer blade height cross-section includes a cross-section with a span of 0.1, an intermediate blade height cross-section with a span of 0.5, and a cross-section with a span of 0.9. The intermediate blade height cross-section with a span of 0.5 is the main observation object for instability early warning, and is not affected by the flow of the hub and rim boundary layer. The flow state represents the characteristics of the main flow region of the runner. At least 14 monitoring points are evenly arranged along the flow direction from the runner inlet to the outlet on each blade height cross-section, and at least 42 monitoring points are arranged in total on the three blade height cross-sections. The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each monitoring point are extracted within at least 3 consecutive complete rotation cycles of the runner. The instantaneous SI value is calculated for each measurement point to obtain the SI time series of each monitoring point. Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition. In step 5, the specific criteria for determining the flow instability state at each monitoring point are as follows: when SI < 1 and the SI time series shows complete periodic fluctuations, the flow field at that monitoring point is determined to be stable, and there is no obvious flow separation in the flow channel; when SI > 1 only at the monitoring points in the runner outlet region, the flow field is determined to be in a critical instability state, and the critical instability state is the initial warning signal for flow instability; when SI > 1 and the periodicity of the SI time series completely disappears, deep instability occurs at that monitoring point, and flow separation and rotational stall persist throughout the entire region. When the flow field is determined to be in a critical or deep instability state, the location of the monitoring point with the earliest occurrence of SI>1 in the SI time series of each monitoring point is marked as the starting position of the flow instability. The locations of each monitoring point are connected sequentially according to the order of occurrence of SI>1 to form the spatial migration trajectory of the instability region over time. The direction of this trajectory is the propagation direction of the flow instability. When SI>1 first appears near the runner outlet, the flow instability is determined to have started in the runner outlet region. As the flow rate decreases, the monitoring point with SI>1 expands along the flow direction from the runner outlet to the runner inlet, and different degrees of flow instability are generated in the entire flow channel.

[0025] Example 6 The method for identifying flow instability in pump turbine operating conditions proposed in this embodiment includes step 1, which uses numerical simulation to analyze, for example... Figure 2 , 3 Numerical calculations were performed on the entire flow path of the pump-turbine shown to obtain transient flow field data under different operating conditions, including flow field data such as pressure, velocity, radial radius and rotational angular velocity of fluid micro-elements; In this invention, simulation data of the pump turbine's operating conditions are obtained. The data at the operating point includes the corresponding rotational speed, flow rate, and head parameters of the pump turbine during operation. This data is then processed using 3D modeling software. Figure 2, 3 The pump-turbine full flow channel model shown is used to establish an accurate 3D model. The 3D modeling software includes, but is not limited to, SolidWorks, UG, and Pro / E. The pump-turbine full flow channel model includes the tailrace pipe 1, runner 2, movable guide vane 3, fixed guide vane 4, volute 5, rim 6, and hub 7. Finite element mesh generation technology is used for Figure 2 , 3 The 3D model of the pump-turbine shown was subjected to structured / unstructured mesh generation, and mesh independence was verified. Steady-state calculations were performed on the 3D fluid mesh obtained from the pump-turbine mesh generation using computational fluid dynamics software under different operating conditions. Unsteady transient calculations were then performed using the steady-state calculation results as the initial field basis. Through transient calculations, 3D unsteady flow field data of the pump-turbine under multiple flow rate target operating conditions were obtained, including pressure... P ,speed u Radial radius of fluid micro-element r and rotational angular velocity ω Flow field data; In step 2, based on the transient flow field data obtained from numerical simulation, commercial computational fluid dynamics software (including but not limited to ANSYS CFX, Fluent, STAR) is used. The gradient calculation function in the post-processor of the CCM (Continuous Computational Machine) combines the radial coordinates of the flow field and the angular velocity of the rotor to solve for the potential rotor enthalpy. Then, the gradient of the potential rotor enthalpy is calculated to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Simultaneously, the Coriolis force vector is calculated based on the relative velocity field and the angular velocity of the rotor. F C ; In step 3, the two types of core forces are separated based on the relative motion momentum equation of the rotating coordinate system. Dimensionless parameters are constructed using the ratio of vector magnitudes, and interference from operating conditions and geometric dimensions is eliminated; potential rotor enthalpy gradient. Coriolis force is the instability driving force that drives fluid to detach from the blades and induces backflow and flow separation. F C To determine the stabilizing constraint force that ensures smooth fluid flow along the blades, the vector magnitude of the potential rotor enthalpy gradient is calculated. Coriolis force vector model The dimensionless stability index SI is constructed by the ratio of the two. The larger the SI value, the higher the risk of flow field instability. SI=1 is set as the critical threshold for flow field stability. ; Both types of vectors have a magnitude of LT. -2With a unified dimension, the ratio of the two is 1, which can uniformly represent the strength of the balance between driving force and constraint force. In step 4, a three-dimensional time-series monitoring network is constructed in the impeller flow channel. Three layers of blade height sections are selected: section 1 with a span of 0.1, section 9 with a span of 0.5, and section 10 with a span of 0.9. Seven monitoring points are evenly distributed along the impeller inlet to outlet direction (i.e., from the first impeller flow channel 14 to the second impeller flow channel 15) at each blade height section, for a total of 42 time-series monitoring points. Figure 4 , 5 As shown in Figure 6, SI monitoring points include point 11 (span 0.1), point 12 (span 0.5), and point 13 (span 0.9). The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each measuring point are extracted within three consecutive complete rotor rotation cycles. The instantaneous SI time series is calculated for each measuring point, as shown below. Figure 7 As shown; In step 5, the section at Span=0.5 (intermediate blade height) is selected as the primary observation target for instability early warning. The intermediate blade height is unaffected by the flow in the hub and rim boundary layers, and its flow state represents the characteristics of the main flow region of the runner, making it the optimal observation section for capturing early signs of flow instability. Combining the SI values ​​and periodicity of the measuring points at Span=0.5, the following flow field stability criteria are established: 1) Flow stability: SI at the monitoring point < 1, the SI time series periodicity is complete and without distortion, and there is no obvious flow separation in the flow channel. Figure 8 As shown; 2) Critical instability: Only the measuring point SI > 1 in the runner outlet area is a preliminary warning signal of flow instability, such as Figure 9 As shown; 3) Deep instability: SI at the measuring point of the impeller flow channel > 1, the time-series periodicity of SI completely disappears, and global flow separation and rotational stall persist, as shown. Figure 10 As shown; Meanwhile, based on the spatial migration trajectory of high SI measurement points over time, the starting position of flow instability can be marked. SI>1 first appears near the runner outlet, and then as the flow rate decreases, different degrees of flow instability occur throughout the flow channel.

Claims

1. A method for identifying flow instability in pump-turbine pump operating conditions, characterized in that, Specifically, the process involves: acquiring three-dimensional unsteady flow field data of the water pump turbine under different flow rates, extracting the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system, constructing a dimensionless stability index SI based on the magnitude of the potential rotor enthalpy gradient vector and the magnitude of the Coriolis force vector, extracting time-series flow field data at multiple blade height sections and multiple flow direction positions in the turbine flow channel, and calculating the time series of the dimensionless stability index SI; classifying the flow field stability level based on the magnitude and time periodicity of the SI time series, and identifying the degree of flow instability.

2. The method for identifying the flow instability of a water pump turbine under operating conditions according to claim 1, characterized in that, The specific steps are as follows: Step 1: Obtain three-dimensional unsteady flow field data of the pump turbine under pump operating conditions; Step 2: Calculate the potential rotor enthalpy vector and the Coriolis force vector in the rotating coordinate system based on the flow field data; Step 3: Calculate the gradient of the potential rotor enthalpy vector to obtain the potential rotor enthalpy gradient vector, and construct the dimensionless stability index SI; Step 4: On the multi-layer blade height section of the runner flow channel, arrange multiple monitoring points along the flow direction from the runner inlet to the outlet, extract the time-series flow field data of each monitoring point, and calculate the time series of SI for each monitoring point; Step 5: Based on the magnitude of the SI values ​​at each monitoring point and whether the periodicity of the SI time series is complete, determine the flow instability state at each monitoring point and complete the identification of flow instability quantities in the pump turbine operating condition.

3. The method for identifying the flow instability of a water pump turbine under operating conditions according to claim 2, characterized in that, In step 1, the three-dimensional unsteady flow field data is obtained through numerical calculation or experimental measurement. When obtained through numerical calculation, a three-dimensional model of the entire flow channel of the pump-turbine is established, and structured or unstructured mesh generation is performed. Mesh independence verification is completed, and computational fluid dynamics software is used with steady-state calculation results as the initial field basis. Unsteady transient calculations are carried out under multiple flow rate target conditions of the pump-turbine pump operation, and the flow field data at each time step is output. The flow field data includes the static pressure of the flow field. p Fluid density ρ Flow field velocity Radial radius of the flow field element r and the rotational angular velocity of the wheel ω The water pump turbine flow path includes a tailrace pipe, a runner, movable guide vanes, fixed guide vanes, and a volute.

4. The method for identifying the flow instability of a water pump turbine under operating conditions according to claim 2, characterized in that, In step 2, the expression for the potential rotor enthalpy vector is: ； in, I P The enthalpy vector of the potential rotor; p For static pressure in the flow field, ρ For fluid density, ω The angular velocity of the rotating wheel. r Let be the radial radius of the flow field element; In step 2, the expression for the Coriolis force vector is: ； in, F C The Coriolis force vector; Let be the flow velocity.

5. The method for identifying flow instability in water pump turbine operating conditions according to claim 2, characterized in that, Step 3 specifically involves: Step 3.1: Obtain the potential rotor enthalpy gradient vector by calculating the gradient of the potential rotor enthalpy vector; Step 3.2: Calculate the potential rotor enthalpy gradient vector magnitude and the Coriolis force vector magnitude; Step 3.3: Construct the dimensionless stability index SI using the ratio of the potential rotor enthalpy gradient vector magnitude to the potential rotor enthalpy gradient vector magnitude; the formula for the dimensionless stability index SI is: ； in, The enthalpy gradient vector magnitude of the potential rotor. It is the Coriolis force vector magnitude.

6. The method for identifying flow instability in pump-turbine pump operating conditions according to claim 5, characterized in that, Step 3.1 specifically involves: using the gradient calculation function in the post-processor of the computational fluid dynamics software, and combining the radial coordinates of the flow field and the angular velocity of the rotor to solve for the potential rotor enthalpy vector. I P Then, the potential rotor enthalpy vector I P Calculate the gradient to obtain three components. , , Together they constitute the potential rotor enthalpy gradient vector field Then, the potential rotor enthalpy gradient vector magnitude is obtained; Step 3.2 specifically involves calculating the Coriolis force vector based on the relative velocity field and the angular velocity of the rotor. F C Then, the Coriolis force vector magnitude is obtained. ; In step 3.3, the potential rotor enthalpy gradient vector mode The dimensions of the Coriolis force vector modulus The dimensions of all are LT -2 SI is a dimensionless parameter, unaffected by unit size and operating parameters. The magnitude of SI allows for a lateral comparison of the severity of flow instability under different flow conditions and between different pump-turbine systems. The potential rotor enthalpy gradient vector... The Coriolis force is the active force that drives the fluid away from the blade profile and generates secondary flow and flow separation. F C It is a constraint force that affects the relative motion trajectory in a rotating coordinate system, resists the flow from deviating from the mainstream direction, and maintains the relative stability of the flow state.

7. The method for identifying flow instability in water pump turbine operating conditions according to claim 6, characterized in that, SI=1 is set as the critical threshold for flow stability. When SI<1, it indicates that the Coriolis constraint force is dominant and the fluid moves smoothly along the blade profile. When SI>1, it indicates that the potential rotor enthalpy gradient is dominant and the flow is prone to deviate from the blade profile, causing flow instability. The value of SI directly indicates the severity of flow instability. The larger the SI value, the higher the risk of flow instability.

8. The method for identifying the flow instability of a water pump turbine under operating conditions according to claim 2, characterized in that, In step 4, the multi-layer blade height cross section includes a section with a span of 0.1, an intermediate blade height cross section with a span of 0.5, and a section with a span of 0.

9. The intermediate blade height cross section with a span of 0.5 is the main observation object for instability early warning, and is not affected by the flow of the hub and rim boundary layer. The flow state represents the characteristics of the main flow region of the runner. At least 14 monitoring points are evenly arranged along the flow direction from the runner inlet to the outlet on each blade height cross section, and at least 42 monitoring points are arranged in total on the three blade height cross sections. The static pressure, velocity, radial coordinate, and angular velocity time-series flow field data of each monitoring point are extracted within at least 3 consecutive complete rotation cycles of the runner, and the instantaneous SI value is calculated for each measurement point to obtain the SI time series of each monitoring point.

9. The method for identifying the flow instability of a water pump turbine under operating conditions according to claim 2, characterized in that, In step 5, the specific criteria for determining the flow instability state of each monitoring point are as follows: when SI < 1 and the SI time series shows a complete periodic fluctuation, the flow field at the monitoring point is determined to be stable and there is no obvious flow separation in the flow channel; when SI > 1 is the monitoring point only in the runner outlet area, the flow field is determined to be in a critical instability state, and the critical instability state is the initial warning signal of flow instability; when SI > 1 and the periodicity of the SI time series completely disappears, deep instability occurs at the monitoring point, and the flow separation and rotational stall persist throughout the entire domain.

10. The method for identifying flow instability in pump-turbine pump operating conditions according to claim 9, characterized in that, When the flow field is determined to be in a critical or deep instability state, the location of the monitoring point with the earliest occurrence of SI>1 in the SI time series of each monitoring point is marked as the starting position of the flow instability. The locations of each monitoring point are connected sequentially according to the order of occurrence of SI>1 to form the spatial migration trajectory of the instability region over time. The direction of this trajectory is the propagation direction of the flow instability. When SI>1 first appears near the runner outlet, the flow instability is determined to have started in the runner outlet region. As the flow rate decreases, the monitoring point with SI>1 expands along the flow direction from the runner outlet to the runner inlet, and different degrees of flow instability are generated in the entire flow channel.

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