Ultralow specific speed unit transient pressure fluctuation suppression system and method

Abstract

The invention relates to the technical field of centrifugal pumps, in particular to an ultra-low specific speed unit transient pressure fluctuation suppression system and method.The method comprises the steps that a segmented broken line type guide vane closing rule is optimized, and decision variables are determined; determining a unit rotating speed water head ratio item in the target function of the multi-target optimization of the guide vane closing rule; according to the method, the'segmented broken line law 'of closing of guide vanes is optimized through a multi-target genetic algorithm, the'rotating speed water head ratio' is taken as a key regulation and control index, transient pressure fluctuation and runner hydraulic thrust are balanced, and the transient pressure fluctuation and the runner hydraulic thrust are controlled. The method is suitable for controlling transition processes such as starting, stopping or sudden load change of an ultralow-specific-speed unit, vibration and noise in the operation process of equipment can be reduced, the service life of the equipment is prolonged, the production efficiency is improved, equipment failures and safety accidents caused by pressure fluctuation are avoided, the production risk is reduced, meanwhile, energy waste is reduced, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of centrifugal pump technology, and in particular to a system and method for suppressing transient pressure fluctuations in ultra-low specific speed units. Background Technology

[0002] Ultra-low specific speed units typically refer to centrifugal pumps with a specific speed of less than or equal to 30. They are characterized by low flow rate and high head, and are widely used in aerospace, petrochemical and agricultural irrigation fields.

[0003] Ultra-low specific speed units are prone to transient pressure fluctuations during operation. For example, during valve-closed startup, an impact head occurs at the end of the startup process under different startup accelerations. Furthermore, the development of the internal flow field during the transient process generally lags behind that of the steady-state process. This leads to drastic changes in parameters such as flow rate, speed, and pressure, potentially causing severe impact damage to the unit equipment. Additionally, the shedding of the flow structure from the trailing edge of the blades, interacting with the volute tongue and outer casing, generates strong pressure pulsations, which are detrimental to the stable operation of the centrifugal pump.

[0004] Currently, research on medium- and high specific speed centrifugal pumps as turbines is relatively mature, but research on ultra-low specific speed centrifugal pumps as turbines is less common. The coupling mechanism between the unsteady velocity field and pressure field inside the pumps is still unclear, and the unsteady operating characteristics are still unknown. This seriously restricts the overall development of the entire series of centrifugal pumps as turbines. Therefore, it is necessary to study the transient pressure fluctuation suppression system and methods for ultra-low specific speed units. Summary of the Invention

[0005] The purpose of this invention is to provide a transient pressure fluctuation suppression system and method for ultra-low specific speed units, aiming to solve the problem of transient pressure fluctuations that easily occur in existing ultra-low specific speed units.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for suppressing transient pressure fluctuations in ultra-low specific speed units, comprising the following steps;

[0007] Optimize the closure law of the segmented polygonal guide vane and determine the decision variables;

[0008] Determine the unit speed-to-head ratio term in the objective function of multi-objective optimization for determining the guide vane closure law;

[0009] Reducing the unit's speed-to-head ratio helps control pressure pulsation and turbine thrust during the transition process of ultra-low specific speed units.

[0010] Specifically, the method for optimizing the closure law of the piecewise linear guide vane and determining the decision variables is as follows:

[0011] Clarify the form and decision variables of the guide vane closure law;

[0012] We set constraints for multi-objective optimization and solve the optimization problem based on a multi-objective genetic algorithm.

[0013] The decision variables include the inflection point coordinates, the total guide vane closing time, and the closing rate of each segment.

[0014] The constraints include pressure constraints, speed constraints, opening constraints, and time constraints.

[0015] The specific method for determining the unit speed-to-head ratio term in the objective function of the multi-objective optimization for determining the guide vane closing law is as follows:

[0016] Clarify the definition and physical meaning of the rotational speed head ratio;

[0017] The speed-to-head ratio term is incorporated into the objective function of multi-objective optimization.

[0018] Verify the sensitivity of the speed-to-head ratio term.

[0019] Specifically, the method for controlling pressure pulsation and turbine thrust during the transient process of ultra-low specific speed units by reducing the unit's speed-to-head ratio is as follows:

[0020] The rotational speed-to-head ratio and transient parameters are calculated based on a three-dimensional coupled simulation.

[0021] Based on the aforementioned speed-head ratio and the transient parameters, the guide vane closing mechanism is adjusted to reduce the speed-head ratio;

[0022] Verify the effect of pressure pulsation and turbine water thrust suppression.

[0023] Secondly, a transient pressure fluctuation suppression system for ultra-low specific speed units, as described in the first aspect above, is provided.

[0024] The present invention provides a method for suppressing transient pressure fluctuations in ultra-low specific speed units. This method optimizes the segmented, piecewise linear guide vane closure pattern and determines the decision variables. It also determines the unit speed-to-head ratio term in the objective function of the multi-objective optimization of the guide vane closure pattern. By reducing this unit speed-to-head ratio term, the method controls pressure pulsation and turbine thrust during the transient process of ultra-low specific speed units. This method optimizes the "segmented, piecewise linear pattern" of guide vane closure using a multi-objective genetic algorithm, with the "speed-to-head ratio" as the key control indicator. It balances transient pressure fluctuations with turbine thrust and is applicable to the control of transient processes such as startup, shutdown, or load changes in ultra-low specific speed units (e.g., centrifugal pumps and pump-turbines with a specific speed ≤30). It can reduce vibration and noise during equipment operation, extend equipment lifespan, improve production efficiency, avoid equipment failures and safety accidents caused by pressure fluctuations, reduce production risks, reduce energy waste, and lower production costs. This solves the problem of transient pressure fluctuations that easily occur in existing ultra-low specific speed units. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the method for suppressing transient pressure fluctuations in ultra-low specific speed units provided by the present invention.

[0027] Figure 2 This is a flowchart illustrating the specific methods for optimizing the closure pattern of a segmented polygonal guide vane and determining the decision variables.

[0028] Figure 3 The flowchart illustrates the specific method for determining the unit speed-to-head ratio term in the objective function of multi-objective optimization to determine the guide vane closing law.

[0029] Figure 4 This refers to a specific method for controlling pressure pulsation and turbine thrust during the transient process of ultra-low specific speed units by reducing the unit's speed-to-head ratio. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] Please see Figures 1 to 3In a first aspect, the present invention provides a method for suppressing transient pressure fluctuations in ultra-low specific speed units, comprising the following steps;

[0032] S1 optimizes the closure law of the segmented polygonal guide vane and determines the decision variables;

[0033] Specific methods:

[0034] S11 clarifies the form and decision variables of the guide vane closure law;

[0035] In this embodiment of the invention, the decision variables include the inflection point coordinates, the total guide vane closing time, and the closing rate of each segment.

[0036] Inflection point coordinates:

[0037] Using "guide vane closing time" as the x-axis (unit: seconds) and "guide vane opening" as the y-axis (unit: percentage, 100% for fully closed, 0% for fully open), the inflection point (x0, y0) represents the "rate switching point" of the closing process. For example, x0 = 5s, y0 = 60% means that the guide vane closes from 0% to 60% in the first 5 seconds, and then from 60% to 100% after 5 seconds, with different closing rates in the two segments.

[0038] Total guide vane closing time:

[0039] The total time (in seconds) for the guide vane to go from "fully open (0%)" to "fully closed (100%)" needs to be initially set within a range based on parameters such as unit inertia and pipeline length (usually 3-15 seconds; for ultra-low specific speed units, due to their high head characteristics, the total time should not be too short to avoid overpressure).

[0040] Closing rates for each segment:

[0041] The inflection point location and total time are derived. For example, if t_total = 10s and the inflection point is (5, 60%), then the rate of the first segment is (60% - 0%) / 5s = 12% / s, and the rate of the second segment is (100% - 60%) / (10 - 5)s = 8% / s. The rate of each segment can be indirectly controlled by adjusting the first two decision variables.

[0042] S12 sets the constraints for multi-objective optimization and solves the problem based on a multi-objective genetic algorithm.

[0043] In this embodiment of the invention, the constraints include pressure constraints, rotational speed constraints, opening degree constraints, and time constraints.

[0044] Pressure constraints: Maximum transient pressure in the pipeline ≤ 1.2 times the rated working pressure (to avoid pipeline rupture or seal failure; for ultra-low specific speed units, pressure fluctuations are more likely to exceed limits due to small flow and high head, and must be strictly controlled).

[0045] Speed ​​constraint: The maximum transient speed of the unit is ≤1.15 times the rated speed (to prevent motor overload and bearing damage. During the transition, the speed increase is positively correlated with the guide vane closing rate, and the risks of speed and speed need to be balanced).

[0046] Opening constraint: Guide vane opening change rate ≤ 20% / s (to avoid damage to the guide vane actuator (such as hydraulic cylinder) due to excessively fast action, it is necessary to match the maximum response capability of the actuator);

[0047] Time constraint: The total time for guide vane closure is greater than or equal to the unit's "round-trip time of water hammer pressure wave" (pipeline length L×2 / water velocity, usually 2-5s, to avoid the superposition of water hammer effects leading to a sudden pressure rise).

[0048] 100-200 sets of decision variables (inflection point coordinates, total time) are randomly generated, each set corresponding to a piecewise linear closure rule, and must satisfy the above constraints (invalid individuals that violate the constraints are eliminated). The fitness function is defined with "minimum transient pressure fluctuation amplitude" and "minimum transient speed increase" as the two core optimization objectives (i.e., the higher the fitness, the better the two indicators). The pressure and speed curves corresponding to each set of decision variables are calculated through a three-dimensional coupled simulation (see step 3), and the peak values ​​are extracted as the fitness evaluation basis. The top 30% of individuals (excellent closure rules) are retained. The decision variables of the excellent individuals are cross-combined to generate new individuals. The decision variables of some new individuals are slightly adjusted to avoid the algorithm getting stuck in local optima. The above operation is repeated for 50-100 generations until the change in the optimal fitness between two adjacent generations is ≤1%. At this time, the optimal individual output is the decision variable (inflection point coordinates, total time) of the "piecewise linear guide vane closure rule".

[0049] S2 determines the unit speed-to-head ratio term in the objective function of the multi-objective optimization of the guide vane closing law;

[0050] Specific methods:

[0051] S21 clarifies the definition and physical meaning of the rotational speed-head ratio;

[0052] In this embodiment of the invention, the "speed-to-head ratio (λ)" is a core parameter describing the "energy conversion characteristics" of the ultra-low specific speed unit during the transient process, defined as: λ = (n_trans / n_rated) / (H_trans / H_rated), where: n_trans: transient speed at a certain moment during the transient process (unit: r / min), n_rated: rated speed of the unit (unit: r / min), H_trans: transient head at a certain moment during the transient process (i.e., the head corresponding to the pipeline pressure, H = P / ρg, where P is pressure, ρ is fluid density, and g is gravitational acceleration, unit: m), H_rated: rated head of the unit (unit: m). Physical meaning: λ reflects the matching relationship between the "speed change range" and the "head (pressure) change range". For ultra-low specific speed units, an excessively high λ value means that "the increase in speed is much greater than the increase in head." In this case, the efficiency of the runner in doing work on the fluid decreases, which can easily lead to turbulent flow (such as the shedding of vortices at the trailing edge of the blades) and thus cause pressure pulsation. Conversely, an excessively low λ value may cause a sudden increase in head, leading to the risk of overpressure. Therefore, λ needs to be controlled within a reasonable range (usually 0.8-1.0).

[0053] S22 incorporates the speed-to-head ratio term into the objective function of multi-objective optimization;

[0054] In this embodiment of the invention, based on the "fitness function," a third optimization objective, "minimizing the fluctuation of the speed-to-head ratio," is added, forming the final multi-objective function: MinimizeF = [ΔP_max, Δn_max, Δλ_max], where: ΔP_max: the difference between the transient pressure peak and the rated pressure (unit: MPa), the smaller the better; Δn_max: the difference between the transient speed peak and the rated speed (unit: r / min), the smaller the better; Δλ_max: the maximum fluctuation value of λ during the transient process (i.e., λ_max - λ_min), the smaller the better (ensuring that λ remains stable within the range of 0.8-1.0). The priority of each objective can be adjusted by weighting coefficients (e.g., ΔP_max weight 0.4, Δn_max weight 0.3, Δλ_max weight 0.3). Considering the characteristic of "more prominent pressure fluctuations" in ultra-low specific speed units, the weight of ΔP_max can be appropriately increased to ensure that the optimization result prioritizes suppressing pressure pulsations.

[0055] S23 verifies the sensitivity of the speed-to-head ratio term.

[0056] In this embodiment of the invention, the influence of λ on pressure fluctuations is verified using the "controlled variable method": other decision variables (such as total time t_total) are fixed, and only the inflection point position is adjusted to calculate the pressure pulsation amplitude corresponding to different λ values ​​(the peak frequency and amplitude of the pressure pulsation are extracted through spectrum analysis). If the pressure pulsation amplitude decreases by more than 30% when λ is in the range of 0.8-1.0, it indicates that the setting of the speed-head ratio is effective, and the next step of regulation can be carried out.

[0057] S3 reduces the unit's speed-to-head ratio to control pressure pulsation and turbine thrust during the transition process of ultra-low specific speed units.

[0058] Specific methods:

[0059] S31 calculates the rotational speed-head ratio and transient parameters based on a three-dimensional coupled simulation.

[0060] In this embodiment of the invention, one-dimensional calculation (pipeline system) is performed: the transient flow of the upstream inlet pipe and the downstream outlet pipe is solved using the "characteristic line method" to calculate the pressure (H_trans) distribution of the pipeline at each moment. The input parameters include pipeline diameter, length, roughness, fluid density, etc.

[0061] Three-dimensional calculation (runner flow field): The internal flow field of the runner is simulated using the "finite volume method" (software such as ANSYS CFX, FLUENT). The runner rotation speed (n_trans), blade surface pressure distribution, and flow field vortex structure (such as vortices falling off the trailing edge of the blades) are calculated at each moment. Input parameters include the number of runner blades, inlet and outlet angles, and guide vane opening.

[0062] Coupling interface: A "coupling surface" is set at the inlet and outlet of the impeller. The one-dimensional calculated pipeline pressure is used as the boundary condition of the three-dimensional flow field, and the three-dimensional calculated impeller flow rate is used as the flow boundary condition of the one-dimensional pipeline. This achieves dynamic coupling of "pressure-flow-speed". The parameters are updated every 0.1s to ensure simulation accuracy.

[0063] S32 adjusts the guide vane closing law to reduce the speed-head ratio based on the speed-head ratio and the transient parameters;

[0064] In this embodiment of the invention, based on the speed-head ratio and the transient parameters, if the value of λ exceeds the range of 0.8-1.0 (e.g., λ = 1.2, the speed increases too quickly), the guide vane closing pattern needs to be adjusted in the following ways to reduce λ: If λ is too high (the speed increase is too large): appropriately reduce the rate in the early stage of guide vane closing (e.g., reduce the first stage rate from 12% / s to 10% / s), extend the early closing time (this can be achieved by increasing the inflection point x0, e.g., adjusting it from 5s to 6s), reduce the speed increase rate, and make λ approach 0.9; if If λ is too low (the head rise is too large): appropriately increase the rate in the later stage of guide vane closure (e.g., increase the second stage rate from 8% / s to 10% / s), shorten the later closure time (this can be achieved by reducing the inflection point y0, e.g., adjusting it from 60% to 50%), control the head rise, and make λ approach 0.9; after each adjustment of the decision variables, perform a three-dimensional coupled simulation again until λ stabilizes at 0.8-1.0, and ΔP_max and Δn_max satisfy the constraints. The guide vane closure law at this time is the "optimal control law".

[0065] S33 verifies the effect of suppressing pressure pulsation and turbine water thrust.

[0066] In this embodiment of the invention, the control effect is verified through both simulation and experimentation to ensure the engineering applicability of the method:

[0067] Pressure pulsation verification: Virtual pressure sensors (simulation) or actual pressure transmitters (experiment) are set up at key locations in the pipeline (such as the impeller outlet and the volute tongue). The pressure curves during the transient process are collected, and the peak-to-peak value (maximum value - minimum value) of the pressure pulsation is calculated. If the peak-to-peak value of the pressure pulsation is reduced by more than 40% after adjustment, and there is no obvious high-frequency pulsation (such as the harmonic component of the blade passage frequency), it indicates that the pressure fluctuation suppression is effective.

[0068] Runner water thrust verification: Runner water thrust is a key factor causing unit vibration and bearing wear. The axial water thrust of the runner (integrated blade surface pressure distribution) is calculated through three-dimensional simulation, or the axial vibration acceleration of the bearing housing is measured experimentally. If the peak water thrust is reduced by more than 25% after adjustment, and the vibration acceleration is ≤0.1g (g is the acceleration due to gravity), it indicates that the water thrust control meets the standard.

[0069] Engineering experiment verification: Apply the optimal guide vane closing law to the prototype unit, simulate the start-up, shutdown or load change process (such as sudden valve closure), and record parameters such as pressure, speed, and vibration. If the deviation between the experimental results and the simulation results is ≤10%, it indicates that the method can be applied in practice.

[0070] The above-disclosed embodiments are merely preferred embodiments of the transient pressure fluctuation suppression system and method for ultra-low specific speed units of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art can understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method of suppressing transient pressure fluctuations in an ultra-low specific speed machine train, characterized by, The method comprises the following steps: optimizing the segmented broken-line guide vane closing law to determine the decision variables; determining the unit speed-head ratio term in the objective function of the multi-objective optimization of the guide vane closing law; reducing the unit speed-head ratio term to control the pressure pulsation and water thrust of the runner during the transient process of the ultra-low specific speed unit.

2. The method according to claim 1, wherein: the specific way of optimizing the segmented broken-line guide vane closing law to determine the decision variables is: defining the form of the guide vane closing law and the decision variables; setting the constraint conditions of the multi-objective optimization and performing optimization and solution based on the multi-objective genetic algorithm.

3. The method of claim 2, wherein ； the decision variables include the coordinates of the folding point position, the total closing time of the guide vane and the closing speed of each segment.

4. The method of claim 2, wherein ； the constraint conditions include the pressure constraint, the speed constraint, the opening constraint and the time constraint.

5. The ultra-low specific speed machine transient pressure surge suppression method of claim 1, wherein: the specific way of determining the unit speed-head ratio term in the objective function of the multi-objective optimization of the guide vane closing law is: defining the definition and physical meaning of the unit speed-head ratio; integrating the unit speed-head ratio term into the objective function of the multi-objective optimization; verifying the sensitivity of the unit speed-head ratio term.

6. The ultra-low specific speed machine transient pressure surge suppression method of claim 1, wherein: the specific way of reducing the unit speed-head ratio term to control the pressure pulsation and water thrust of the runner during the transient process of the ultra-low specific speed unit is: calculating the unit speed-head ratio and the transient parameters based on a three-dimensional coupling simulation; adjusting the guide vane closing law based on the unit speed-head ratio and the transient parameters to reduce the unit speed-head ratio; verifying the suppression effect of the pressure pulsation and the water thrust of the runner.

7. A system for suppressing transient pressure fluctuation of an ultra-low specific speed unit, which is configured to perform the method according to any one of claims 1-6.

Images