Active suppression method for tail water vortex strip of mixed-flow water turbine and water turbine

Abstract

The invention discloses a mixed-flow water turbine tail water vortex strip active inhibition method and a water turbine, and relates to the technical field of water turbine optimizing.According to the method, operation data are collected in real time, whether a vortex strip risk working condition is entered or not is judged, pre-judgment on the occurrence trend of a tail water vortex strip is achieved, and after it is confirmed that the vortex strip risk exists, the mixed-flow water turbine tail water vortex strip active inhibition method is provided. The basic air supply amount is determined in combination with the preset mapping database, the air supply amount is adjusted according to the pressure pulsation signal, finally, efficient and active suppression of the tail water vortex strip is achieved through the jet microbubble group, and the operation stability of the unit is remarkably improved. Adjustment can be carried out according to the change of the real-time operation working condition, and the tail water vortex strip is effectively restrained on the premise of not depending on manual experience.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water turbine optimization, and in particular to a Francis turbine tail vortex band active suppression method and a water turbine. BACKGROUND

[0002] The Francis turbine is the most widely used hydroelectric power generation equipment at present, and its operation stability is directly related to the quality of power supply of the power grid and the economic benefit of the power station. However, this type of unit has an old problem of a tail vortex band: when it operates under small flow or large flow conditions, the water flow at the outlet of the runner will have obvious rotational momentum, forming a spiral or columnar vortex band in the draft tube; the center pressure of the vortex band is very low, and cavitation phenomenon is easy to occur when it is lower than the vaporization pressure of water, and the vapor gathers to form a visible cavitation vortex band. This vortex band is not static, but periodically swings forward, producing low-frequency pressure pulsation, with a frequency generally between 0.2 and 0.4 times the rotational frequency of the unit.

[0003] This pressure pulsation transmitted to the runner will make the unit force fluctuate, and then transmitted to the generator through the shaft system, causing the output power to oscillate back and forth, and in severe cases, it may resonate with the power grid, affecting the safety of the entire system. In order to solve this problem, the industry generally supplements some air into the draft tube to break the vacuum core of the vortex band, change the fluid properties, and make it unable to exist stably, but this method has many problems: the mixed air and water flow is not sufficient, most of the air escapes along the pipe wall in the form of large bubbles, and cannot effectively penetrate into the core rotation area of the vortex band; it cannot be self-adaptively and finely adjusted according to the real-time working conditions such as water head and load; the air supplement at large flow and high flow rate, especially when the air impacts the runner blades in an unstable form, will significantly aggravate the cavitation erosion damage on the blade surface.

[0004] Therefore, the industry urgently needs a new method that can accurately attack the core of the vortex band, adjust as needed, save gas and energy, and will not damage the blades. SUMMARY

[0005] In view of the above or existing problems in the prior art, the present application is proposed.

[0006] To solve the above technical problems, the present application provides the following technical scheme: a Francis turbine tail vortex band active suppression method, comprising the following steps, real-time acquisition of operation data of the water turbine; determining whether to enter a vortex band risk working condition based on the operation data; if the vortex band risk working condition is entered, querying a preset mapping database according to the operation data to determine a basic air supplement amount; Monitoring pressure pulsation of the draft tube, adjusting the basic air supply amount according to the signal of the pressure pulsation, and generating a final air supply amount; According to the final air supply amount, a group of micro-bubbles is injected into the draft tube to suppress the draft tube vortex.

[0007] As a preferred scheme of the active suppression method of the draft tube vortex of the Francis turbine, the mapping database stores the corresponding relationship between different operating data of the turbine and the air supply amount.

[0008] By storing the mapping relationship between the required air supply amount and the operating parameters such as water head and output in the mapping database, the system can quickly match the corresponding air supply amount according to the current working condition, avoiding the problems of adjustment lag or poor effect caused by relying on artificial experience or fixed parameters in the traditional method.

[0009] As a preferred scheme of the active suppression method of the draft tube vortex of the Francis turbine, the mapping database is constructed by the following method: According to the structural size of the turbine, a three-dimensional model of the turbine is established to obtain a three-dimensional model of the turbine. The least air supply amount data pairs under different combinations of water head and output conditions are obtained by full-condition numerical simulation of the three-dimensional model of the turbine. The water head and output air supply amount response surface is generated by using the data pairs.

[0010] By full-condition simulation of the three-dimensional model of the real structure of the turbine, the mapping database and the response surface constructed are highly consistent with the real unit, and the predicted least air supply amount data pairs are very reliable. As a preferred scheme of the active suppression method of the draft tube vortex of the Francis turbine, the adjustment of the basic air supply amount according to the signal of the pressure pulsation includes adjusting the air supply amount based on the PID algorithm to reduce / eliminate errors.

[0011] By using the PID algorithm to process the pressure pulsation signal, the basic air supply amount can be adjusted in real time, and the steady-state error caused by model deviation or random disturbance can be compensated.

[0012] As a preferred scheme of the active suppression method of the draft tube vortex of the Francis turbine, the group of micro-bubbles is formed by high-pressure gas through a micro-bubble jet air supply device, and the group of micro-bubbles can enter the core rotating area of the vortex.

[0013] The gas is sheared and broken into extremely fine and uniform micro-bubble groups by the micro-bubble jetting air supplementing device, the particle size is small and the distribution is uniform, the micro-bubble groups have strong water flow penetration ability, the dense micro-bubble groups effectively penetrate into the core rotating area of the vortex belt, the fluid equivalent density and viscosity of the core area of the vortex belt are changed, the energy structure and aerodynamic stability of the vortex belt are greatly destroyed, and the vortex belt is disintegrated. The problem that the traditional large bubbles float on the surface and cannot penetrate into the core rotating area of the vortex belt is solved.

[0014] As a preferred scheme of the active suppression method of the draft tube vortex belt of the mixed-flow water turbine, the method further comprises, When it is monitored that the water turbine enters a stable state, the pulse width modulation mode is switched to output air supplement, so that the vibration suppression effect is maintained while the average gas consumption is reduced.

[0015] By switching to the pulse width modulation mode after the system enters a stable state, periodic intermittent air supply is replaced by continuous air supply, the gas consumption in unit time is greatly reduced while the continuous interference effect is ensured, the operation conversion from high-intensity suppression to low-power maintenance is realized, which helps to reduce the overall energy consumption and improve the economy.

[0016] As a preferred scheme of the active suppression method of the draft tube vortex belt of the mixed-flow water turbine, the method further comprises,

[0017] By taking the condition that the pressure fluctuation amplitude is lower than the safe threshold value and lasts for a period of time as the condition for judging that the system enters a stable state, the influence of transient fluctuations can be effectively excluded, the reliability of mode switching is ensured, and the vibration suppression failure or frequent switching of control modes caused by misjudgment is prevented.

[0018] As a preferred scheme of the active suppression method of the draft tube vortex belt of the mixed-flow water turbine, the method further comprises,

[0019] By setting the pulse frequency to 5 to 10 times the characteristic frequency of the vortex belt, multiple disturbance impacts can be applied in each vortex belt precession period to form continuous interference. This high-frequency interference can continuously interrupt the energy accumulation process of the vortex belt, which is conducive to maintaining the vibration suppression effect at a lower average gas volume and improving the gas utilization efficiency.

[0020] The beneficial effects of the scheme are: The application realizes the predication of the tail water vortex belt occurrence trend by collecting the operation data in real time and judging whether the vortex belt risk working condition is entered, after confirming the vortex belt risk, the basic air supplement amount is determined in combination with the preset mapping database, and the air supplement amount is adjusted according to the pressure pulsation signal, finally the tail water vortex belt is efficiently and actively inhibited through the injection of micro bubble groups, and the stability of the unit operation is significantly improved. The application can adjust according to the change of the real-time operation condition, and effectively inhibit the tail water vortex belt without relying on artificial experience.

[0021] It is another object of the application to provide a water turbine runner, comprising a spiral case, fixed guide vanes arranged on one side of the spiral case, movable guide vanes arranged on one side of the fixed guide vanes, a runner arranged on one side of the movable guide vanes, and a draft tube arranged on one side of the runner, wherein a micro-bubble jet air supplement device is arranged on the draft tube, one side of the micro-bubble jet air supplement device is connected with an air inlet pipe, and the air inlet pipe is connected with an external air path through a control valve.

[0022] The application has the following beneficial effects: The application adds a micro-bubble jet air supplement device on the draft tube, so that the micro-bubble jet air supplement device becomes part of the water turbine body, the air supplement function is integrated with the main machine structure, the air supplement amount is controlled through the control valve, the micro-bubbles are injected in the vortex belt prone area in a directional manner, the response speed is fast, the installation is convenient, and the original hydraulic performance is not affected, which provides a hardware basis for active inhibition. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 It is a flowchart of a Francis turbine tail water vortex belt active inhibition method.

[0025] Figure 2 It is a PID algorithm diagram of a Francis turbine tail water vortex belt active inhibition method.

[0026] Figure 3 It is a schematic diagram of the overall structure of a water turbine.

[0027] Wherein: 1, spiral case; 2, fixed guide vanes; 3, movable guide vanes; 4, runner; 5, draft tube; 6, micro-bubble jet air supplement device; 61, air inlet pipe; 62, control valve; 63, mounting seat. DETAILED DESCRIPTION

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0031] Reference Figures 1-3 This embodiment provides an active suppression method for the vortex zone in the tailrace of a mixed-flow turbine, which includes the following steps: Real-time acquisition of turbine operating data; Determine whether the system has entered a risky operating condition based on operational data; If the system enters a vortex risk condition, the basic gas supply volume is determined by querying the preset mapping database based on the operating data. Monitor the pressure pulsation in the tailwater pipe, adjust the basic air supply volume based on the pressure pulsation signal, and generate the final air supply volume; Based on the final air supply volume, microbubble clusters are injected into the tailwater pipe to suppress the tailwater vortex.

[0032] Reference Figures 1-3 As one embodiment of the present invention, The mapping database stores the correspondence between different operating data of the water turbine and the amount of air supplied.

[0033] Furthermore, the mapping database is constructed using the following methods: Based on the structural dimensions of the water turbine, the structure of the water turbine is modeled to obtain a three-dimensional model of the water turbine runner; Numerical simulation of the turbine under all operating conditions was performed using a three-dimensional model to obtain the minimum air supply data pairs under different combinations of head and output conditions. Using the data pairs, a response surface for the head output and air replenishment was generated.

[0034] In this embodiment, a mixed-flow turbine is used as the object for design optimization. The specific basic parameters are shown in Table 1: Table 1 Parameters of Mixed-Flow Turbine

[0035] Numerical simulation of the entire turbine flow path is performed by selecting points (Hi,Pj) covering the boundary and central region on the head-output (HP) working plane. This yields a series of discrete optimal (Hi,Pj,Q(i,j)) data pairs, representing the minimum air supply data pairs where a small increase in air supply significantly reduces pressure pulsation until saturation, meaning further increases in air supply have no significant improvement in suppression effect. Using these data pairs, the contour of the vortex zone with severe intensity is initially outlined on the head-output working plane. Local radial basis function interpolation is then performed in areas with large gradient changes in model prediction to densify the measurement points until the error between the newly added measurement points and the model prediction is less than 5%. This generates a continuous head-output-air supply response surface covering the entire operating range, thus forming a mathematical model for the mapping database.

[0036] Reference Figures 1-3 As one embodiment of the present invention, Adjusting the basic air supply based on pressure pulsation signals, including adjusting the air supply based on PID algorithms, can reduce / eliminate errors.

[0037] Real-time data (H, P, Q) is collected based on the actual operating conditions of the unit. Whether Q is positive is used to determine if the unit has entered a vortex risk condition. The optimal data pair (Hi, Pj, Q(i,j)) is matched to the mapping database to output the basic air supply. The air supply is then fine-tuned based on the actual pressure pulsation value using a PID algorithm. A schematic diagram of the PID algorithm is shown below. Figure 2 As shown; The expression for the local radial basis function is: in, ,j=1...k; (r)= ,r>0; The optimal air supply amount of the optimal data pair (Hi,Pj,Q(i,j)) under different working conditions is found in the mapping database and used as its basic air supply amount Qe. The PID algorithm is used to adjust the air supply to eliminate steady-state errors, and to provide fine compensation for unpredictable, random, and slowly varying disturbances, as detailed below: Frequency domain analysis was performed using real-time Fast Fourier Transform (FFT) to screen out signal components in the wake eddy band ranging from 0.2fn to 0.4fn (1 to 2 Hz) and calculate the safe vibration amplitude A. s The error e(t) between the pressure pulsation amplitude A0 before air replenishment and the actual air replenishment is -170μm. This error e(t) is calculated using a proportional (P), integral (I), and derivative (D) process to ultimately output the air replenishment correction value ΔQ(t). The formula for calculating the frequency corresponding to the rated speed of the hydro-generator unit is: Where n is the rated speed of the unit, 300 r / min. The formula for calculating the error e(t) is: e(t) = A s -A0=50-220=-170μm The formula for calculating the gas replenishment correction value is: The formulas for calculating the proportional coefficient Kp, integral coefficient Ki, and differential coefficient Kd are as follows: m³ / (h・μm) (m³ / h) / (μm・s) (m³ / h)・s / μm in, To find the basic gas replenishment volume of 670 under the mapping database based on operating conditions , The integration time constant is taken as 16s here. is the differential time constant, which is taken as 2.5s here.

[0038] Reference Figures 1-3 As one embodiment of the present invention, Microbubble clusters are formed by high-pressure gas through a microbubble jet gas replenishment device, and the microbubble clusters can enter the core rotating region of the vortex. The supplementary gas is a high-pressure gas with a pressure 0.5-1 MPa higher than that inside the tailrace pipe. After the external high-pressure gas is controlled by a precise control valve to limit the final supplementary gas volume, it is sheared and broken into extremely fine and uniform microbubble clusters at the nozzle outlet of the microbubble jet supplementary gas device. These microbubble clusters are then ejected at high speed towards the vortex formation zone at the center of the tailrace pipe. The dense microbubble clusters effectively penetrate to the core rotation zone of the vortex. By altering the fluid equivalent density and viscosity of the vortex core region, the microbubble clusters significantly disrupt the energy structure and aerodynamic stability of the vortex, thus causing it to disintegrate. The principle is that when sufficient energy is injected into a gas jet, it causes instability and fracture, ultimately overcoming the surface tension of the liquid and contracting into a spherical shape, thus breaking into tiny bubbles. These tiny bubbles are then used to disrupt the vortex structure.

[0039] Reference Figures 1-3 As one embodiment of the present invention, Once the turbine is detected to have entered a stable state, the output is switched to pulse width modulation mode to replenish air, maintaining the vibration suppression effect while reducing average air consumption.

[0040] Furthermore, a stable state is defined as a period of time during which the monitored pressure pulsation amplitude is lower than the safe vibration amplitude.

[0041] Furthermore, the pulse frequency of the pulse width modulation mode is 5 to 10 times the characteristic frequency of the wake vortex.

[0042] When the system enters a stable state, i.e., the monitored pressure pulsation amplitude is lower than the safe vibration amplitude for 3-5 minutes, the pulse width modulation mode is activated. After the power oscillation subsides, i.e., the power fluctuation amplitude caused by the power oscillation of the tailrace vortex does not exceed ±0.1% of the rated power, the data of this air replenishment is collected and recorded into the historical data of the mapping database for reference in the next round of air replenishment. The safe vibration amplitude is a fixed 50, which is written in the parameters of the mixed-flow turbine mentioned above and is determined by the key parameters of the turbine.

[0043] Pulse width modulation (PWM) is an advanced energy-saving and efficiency-enhancing strategy that uses intermittent pulsed air columns with a frequency of 5-10 times that of the vortex band to replace continuous, stable airflow, achieving better vibration suppression with lower average air consumption. Calculate the basic gas supply Q(t). With the correction value of the replenishment volume The sum of the values ​​is processed and the final replenishment volume Q is output after amplitude limiting. The formulas for calculating the replenishment volume Q(t) and the final replenishment volume Q are as follows: The switching frequency of the pulse is selected to be 5-10 times or more than the eddy band frequency of 0.2fn~0.4fn (1~2Hz), which ensures that the pulse will be subjected to multiple pulse impacts in each eddy band cycle, forming continuous interference. The model was simulated using CFD, and the maximum head and full opening conditions were selected as verification conditions. After no less than three calculations, the experimental data results of efficiency and stress are shown in Table 2. Table 2 Comparison of efficiency and vortex vibration amplitude before and after air injection

[0044] It can be seen that, compared with before air replenishment, microbubble jet air replenishment achieves the effect of suppressing the wake vortex while maintaining efficiency.

[0045] Reference Figures 1-3 This embodiment provides a water turbine, including a volute 1, a fixed guide vane 2 disposed on one side of the volute 1, a movable guide vane 3 disposed on one side of the fixed guide vane 2, a runner 4 disposed on one side of the movable guide vane 3, and a tailrace pipe 5 disposed on one side of the runner 4. A microbubble jet air supply device 6 is disposed on the tailrace pipe 5, and an air inlet pipe 61 is connected to one side of the microbubble jet air supply device 6. The air inlet pipe 61 is connected to an external air circuit through a control valve 62.

[0046] The microbubble jet air supply device 6 uses the LJW-5 micro-nano bubble generator from Nanjing Lanjiang Water Treatment Equipment Co., Ltd. When the system is working, compressed air with a pressure 0.5~1.0MPa higher than the pressure inside the tailwater pipe 5 is delivered to the generator after the flow rate is limited by a precision control valve 62.

[0047] The precision control valve 62 uses an electric regulating valve from Wuzhong Instrument, with a nominal valve body diameter of DN50 and a nominal pressure of PN1.6MPa. It is equipped with a Tianjin Bernard SD series intelligent electronic actuator, specifically model SD-60-1.6-0-SMMMA-4-20. This actuator has a built-in microprocessor, a full stroke time of no more than 3 seconds, and can automatically switch control modes according to the instructions of the intelligent controller: in continuous regulation mode, it receives 4-20mA analog signals to achieve continuous and precise proportional adjustment of the valve opening; in PWM energy-saving mode, it directly receives 10-25Hz PWM square wave digital signals, analyzes them into the target opening degree through internal algorithms, and drives the valve motor to perform high-frequency opening and closing.

[0048] The LJW-5 generator, based on its unique pressurized dissolved gas decompression principle, efficiently breaks down the delivered high-pressure gas, generating an extremely dense and uniform cluster of microbubbles with an average diameter between 50 and 300 micrometers. This microbubble cluster is then propelled at high speed towards the vortex zone forming area at the center of the tailrace pipe 5. The resulting dense cluster of microbubbles effectively penetrates to the core rotating region of the vortex zone. By altering the fluid equivalent density and viscosity of the vortex core region, the microbubble cluster significantly disrupts the energy structure and aerodynamic stability of the vortex zone, ultimately causing its disintegration.

[0049] The jet nozzle of the LJW-5 micro-nano bubble generator is fixed to the maintenance access door reinforcement cover plate of the tailwater pipe 5 cone section through the adjustable angle mounting base 63; the mounting base 63 includes the QJB-50 / 16-FF ball joint produced by Hebei Weiye Corrugated Pipe Manufacturing Co., Ltd. and the matching SO-50-16RF flange mounting base. During installation, firstly, weld and fix the SO-50-16RF type flange mounting base to the access door cover. Then, fasten the lower end of the QJB-50 / 16-FF type ball joint to the base flange using 8 sets of M16×70-8.8 grade hexagonal head bolts with M16-8 grade hexagonal nuts. The upper end of the ball joint is directly connected and fastened to the SO-50-16RF interface flange of the micro-nano bubble generator jet nozzle using another set of 8 sets of M16×70-8.8 grade hexagonal head bolts with M16-8 grade hexagonal nuts. The ball joint can achieve universal adjustment within a range of not less than ±12° in one direction, so that the spray direction of the jet nozzle can be precisely adjusted to point towards the central axis area of ​​the tailwater pipe 5. After adjustment, use the locking mechanism of the ball joint itself to rigidly lock it.

[0050] The main unit of the micro / nano bubble generator is placed outside the tailwater pipe 5 and connected to the jet nozzle via a metal hose with a pressure resistance rating of not less than PN2.0MPa. Figure 3 The hose was stretched out to show the position of the nozzle and mounting base 63.

[0051] Importantly, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A Francis turbine draft tube vortex band active suppression method, characterized in that: The method comprises the following steps: Real-time acquisition of operation data of the water turbine; Judgment of whether to enter the vortex band risk working condition based on the operation data; If the vortex band risk working condition is entered, the basic air supplement amount is determined according to the operation data and the preset mapping database; The pressure pulsation of the draft tube is monitored, and the basic air supplement amount is adjusted according to the signal of the pressure pulsation to generate a final air supplement amount; According to the final air supplement amount, micro-bubble groups are injected into the draft tube to suppress the draft tube vortex band.

2. The method according to claim 1, wherein: The mapping database stores the corresponding relationship between different operation data of the water turbine and air supplement amounts.

3. The Francis turbine draft tube vortex band active suppression method of claim 2, wherein: The mapping database is constructed by the following method: According to the structural size of the water turbine, a three-dimensional model of the water turbine is obtained by modeling the structure of the water turbine; Through the three-dimensional model of the water turbine, a full-condition numerical simulation is performed to obtain a minimum air supplement amount data pair under different combinations of water head and output conditions. Using the data pair, a water head-output-air supplement amount response surface is generated.

4. The method according to claim 1, wherein: The adjustment of the basic air supplement amount according to the signal of the pressure pulsation includes adjustment of the air supplement amount based on a PID algorithm to reduce / eliminate errors.

5. The method according to claim 1, wherein: The micro-bubble groups are formed by high-pressure gas through a micro-bubble jet air supplement device, and the micro-bubble groups can enter the core rotating area of the vortex band.

6. A Francis turbine draft tube vortex band active suppression method according to claim 1, characterized in that: Further comprising, When it is monitored that the water turbine enters a stable state, switching to a pulse width modulation mode to output air supplement, maintaining the vibration suppression effect while reducing the average air consumption.

7. A Francis turbine draft tube vortex band active suppression method according to claim 6, characterized in that: The stable state is that the monitored pressure pulsation amplitude is lower than the safe vibration amplitude for a period of time.

8. The method according to claim 6, wherein: The pulse frequency of the pulse width modulation mode is 5 to 10 times the characteristic frequency of the draft tube vortex band.

9. A hydraulic turbine comprising a spiral case (1), fixed vanes (2) arranged on one side of the spiral case (1), movable vanes (3) arranged on one side of the fixed vanes (2), a runner (4) arranged on one side of the movable vanes (3), and a draft tube (5) arranged on one side of the runner (4), characterized in that: The draft tube (5) is provided with a micro-bubble jet air supplement device (6), one side of the micro-bubble jet air supplement device (6) is connected with an air inlet pipe (61), and the air inlet pipe (61) is connected with an external air path through a control valve (62).

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