Design method of kaplan runner blade outflow edge to prevent carmen vortex, electronic device and storage medium

Abstract

The application provides a design method for preventing a Kaplan runner blade water outlet edge from being blocked by a Karman vortex, an electronic device and a storage medium, and solves the problem that a square or circular symmetric shape of an existing Kaplan runner blade water outlet edge is easy to produce a Karman vortex street and cause resonance. The application scheme comprises the following steps: segmentally measuring structure parameters of the blade water outlet edge; comparing Karman vortex frequencies of each segment with inherent frequencies of the blade, respectively; if there is a deviation that does not meet a preset frequency deviation requirement of a segment, adjusting the position of the segment on the water outlet edge or the number of segments and recalculating until all segments meet the frequency deviation requirement, and outputting final design parameters of each segment. The application can inhibit or reduce the Karman vortex, avoid blade cracks and vibration caused by resonance, reduce the overhaul frequency of a unit, and ensure long-term safe operation of a power station.

Description

Technical Field

[0001] This invention relates to the field of fluid machinery technology, and in particular to a design method and apparatus for reducing or suppressing the Karman vortex street phenomenon generated when water flows around the Kaplan impeller blades at the water outlet. Background Technology

[0002] The Kaplan runner is suitable for a head range of 5m to 70m, and typically has 3 to 7 blades. This type of runner allows for coordinated adjustment of the blade rotation angle and the opening of the turbine's guide vanes, offering significant advantages such as a wide load adjustment range and excellent operational stability. Its working principle is as follows: as water flows over the surface of the runner blades, it drives the blades to rotate around the center of rotation. Due to its structural characteristics, the working position of the Kaplan runner blades in the water changes with operating conditions, resulting in synchronous changes in the water flow pattern and the force characteristics of the blades.

[0003] Karman vortices are vortices that occur behind the tail of a flowing object and are caused by boundary layer separation when water flows over the surface of the object. When liquid flows around the streamlined blades of a turbine runner, the point where the velocity is zero is defined as the separation point. A countercurrent occurs in the water layer within the separation point, forming vortices that detach from the blades. These flowing vortices form a Karman vortex train at the blunt tail of the blades. When the size of the vortex train is appropriate and it absorbs dissolved air from the water, the vortex train becomes visible, forming Karman vortices. When the frequency of the Karman vortex is close to or coincides with the natural frequency of the turbine's flow components, it will trigger strong hydraulic elastic resonance. This not only causes abnormal vibration and noise in the unit but may also cause fatigue cracks in the blades, increasing the frequency of major overhauls, resulting in huge maintenance costs and seriously affecting the power plant's power generation efficiency.

[0004] Currently, the outlet edge of Kaplan turbine blades mostly adopts a square or circular symmetrical structure. Based on actual operating data from multiple power plants, it is known that this type of outlet edge structure is highly susceptible to inducing the Karman vortex street phenomenon when water flows through it. Regarding the Karman vortex-induced vibration problem, existing technologies still have the following shortcomings.

[0005] First, existing methods mostly employ overall homogenization, such as thinning the entire outlet edge or using symmetrical rounding, failing to consider the objective fact that the geometric parameters of each section along the span of the blade's outlet edge vary significantly, such as thickness and angle. Kaplan blades are spatially twisted surfaces, with substantial variations in thickness and angle across each section along the span of the outlet edge; using uniform grinding parameters cannot achieve optimal frequency reversal for each segment. Second, existing modification methods are mostly empirical and trial-and-error operations, lacking quantitative design basis and systematic design processes. The modification effect depends on the operator's experience level, making it difficult to guarantee the reliability and repeatability of the design. Third, existing technologies have failed to establish a quantitative relationship between the blade's outlet edge structural parameters and the thickness and rounding radius of the modified blunt edge, making precise control of the Karman vortex frequency impossible.

[0006] In summary, existing technologies suffer from several drawbacks, including a lack of segmented differentiated design for the spatial torsion characteristics of Kaplan turbine blades, a lack of quantitative design methods for outlet side profile parameters, and difficulty in precisely controlling the Karman vortex frequency of each segment to effectively avoid the resonance range. Summary of the Invention

[0007] To address the shortcomings of existing technologies, such as the lack of segmented differentiated design for the spatial tortuous surface characteristics of Kaplan impeller blades, the inability to precisely control the Karman vortex frequency of each segment, and the lack of quantitative design basis for outlet edge modification parameters, this invention proposes a design method for preventing Karman vortices at the outlet edge of Kaplan impeller blades. The method includes: Step 1: Divide the Kaplan impeller blade into multiple segments along the outlet edge and obtain the original total thickness of the outlet edge section of each segment and the angle between the water flow outlet direction and the blade flow thickness direction at each segment. Step 2: Based on the original total thickness of each segment and the included angle, calculate the blunt edge thickness to be retained and the rounding radius of the working surface of each segment according to the preset formula; Step 3: Determine the de-flow thickness of each segment in the direction perpendicular to the water flow based on the blunt edge thickness and the included angle of each segment; Step 4: Determine the Karman vortex frequency corresponding to each segment based on the de-flow thickness of each segment, and compare the deviation of the Karman vortex frequency of each segment with the natural frequency of the blade. Step 5: If there are segments that do not meet the preset frequency error requirements, adjust the position of the segment on the outlet edge or the number of segments, and re-execute the calculation of the blunt edge thickness, determination of the flow separation thickness and determination of the Karman vortex frequency until all segments meet the preset frequency error requirements, and output the final design parameters of each segment.

[0008] Furthermore, in step one, The number of segments divided at the water outlet edge is determined based on the degree of curvature change at the water outlet edge; the original total thickness of the water outlet edge cross section of each segment and the angle between the water flow outlet direction and the blade flow thickness direction at each segment are taken from the values ​​at the middle cross section of the corresponding segment.

[0009] Furthermore, in step two, The preset relation is:

[0010]

[0011] in, For the first i Segmented retention of blunt edge thickness; For the first i Rounding radius of segmented working surfaces; For the first i The original total thickness of the sectioned blade at the water outlet edge; For the first i The angle between the working surface of the segmented blade and the thickness direction.

[0012] Furthermore, in step three, The method for calculating the de-flow thickness is as follows:

[0013] in, For the first i Segmented de-flow thickness.

[0014] Furthermore, in step four, The Karman vortex frequency is calculated as follows:

[0015] in, For the first i Segmented Karman vortex frequencies; For the first i The relative flow velocity of water at the blade outlet edge of the segment; It is a Struhar number.

[0016] Furthermore, in step four, The natural frequency of the blade is the first or second natural frequency of the blade in water.

[0017] Furthermore, in step five, The preset frequency error requirement is that the deviation between the Karman vortex frequency and the blade's natural frequency is not less than 15%.

[0018] Furthermore, After the calculation of each segment is completed, the blunt edge thickness and rounding radius of each segment are smoothed. The design parameters of each segment are used as the model value points, and spline interpolation or curve fitting methods are used to construct a continuous distribution curve along the water outlet edge.

[0019] The present invention proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described method.

[0020] The present invention proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the above-described method.

[0021] The beneficial effects of this invention are: To address the aforementioned problems, this invention proposes a design method, electronic equipment, and storage medium for preventing Karman vortices at the outlet edge of a Kaplan-type impeller blade, resulting in the following improvements: 1. This invention divides the blade's outflow edge spanwise into several segments. The original total thickness and working surface angle of each segment are measured, and the blunt edge thickness and rounding radius are calculated based on the measured geometric parameters of each segment. This allows each segment to be independently optimized according to its actual structural state. Compared to existing technologies that involve uniform thinning or symmetrical rounding, this invention fully adapts to the objective characteristics of large differences in thickness and angle across the cross-sections of the Kaplan blade's spatially twisted surface along the outflow edge, enabling each segment to achieve optimal Karman vortex frequency regulation.

[0022] 2. After calculating the design parameters for each segment, this invention further calculates the optimized Karman vortex frequency using the formula for flow separation thickness and Karman vortex street frequency, and compares the deviation with the blade's natural frequency. If the deviation of a certain segment is insufficient to meet the preset misalignment requirement, the calculation is recalculated and iterated by adjusting the segment position or increasing the number of segments until all segments meet the misalignment condition. This closed-loop verification mechanism ensures that all segments along the entire span of the outlet side can reliably avoid the resonance range.

[0023] 3. The above design avoids forced vibration and fatigue cracks in the blades caused by Karman vortex resonance, reduces the number of unit overhauls, lowers operation and maintenance costs, and provides a guarantee for the long-term safe and stable operation of the power plant unit. Attached Figure Description

[0024] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 A schematic diagram of Karman vortices forming around a cylinder in liquid flow; Figure 2 A side view of a Kaplan rotor blade; Figure 3 This is a schematic diagram of the Kaplan-type impeller blade's anti-Kaman vortex structure at the water outlet. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Combination Figures 1-3This invention proposes a design method for preventing Karman vortices at the water outlet edge of a Kaplan-type turbine runner, the method comprising: Step 1: Divide the water outlet edge of the Kaplan impeller blade into several segments, and obtain the original total thickness of the water outlet edge section of each segment and the angle between the water outlet direction and the blade flow thickness direction at each segment. Furthermore, in step one, The number of segments divided at the water outlet edge is determined based on the degree of curvature change at the water outlet edge; the original total thickness of the water outlet edge cross section of each segment and the angle between the water flow outlet direction and the blade flow thickness direction at each segment are taken from the values ​​at the middle cross section of the corresponding segment.

[0028] Step one is as follows: Based on the blade's exit edge profile and overall dimensions, the exit edge is divided into several segments. The number of segments is determined based on the degree of curvature change at the outlet edge. The structural parameters (original thickness) of the outlet edge section of each segment are measured separately. The angle between the direction of the water flow outlet at the water outlet and the direction of the flow around the blade thickness. To ensure data accuracy during measurement, each segment... and The value should be taken at the middle section of the segment.

[0029] Step 2: Based on the original total thickness of each segment and the included angle, calculate the blunt edge thickness to be retained and the rounding radius of the working surface of each segment according to the preset formula; Furthermore, in step two, The preset relation is:

[0030]

[0031] in, For the first i Segmented retention of blunt edge thickness; For the first i Rounding radius of segmented working surfaces; For the first i The original total thickness of the sectioned blade at the water outlet edge; For the first i The angle between the working surface of the segmented blade and the thickness direction.

[0032] Step two is as follows: This invention proposes a method for optimizing and adjusting the water outlet edge, and summarizes the relationship between structural parameters and water outlet edge design parameters. The core of this invention lies in: by grinding the water outlet edge of the blade, retaining a blunt edge of a specific thickness on the back of the blade, and machining a rounded edge of a specific radius at the corner of the working surface, the flow separation thickness of the water outlet edge is changed, thereby adjusting the Karman vortex frequency away from the blade's natural frequency, and adjusting the blunt edge thickness... and fillet radius From the original structural parameters and It is determined by the following two relationships.

[0033] Blunt edge thickness The relationship is as follows:

[0034] In the formula, For the first Segmented retention of blunt edge thickness; For the first Rounding radius of segmented working surfaces; For the first The original total thickness of the sectioned blade at the water outlet edge; For the first The angle between the working surface of the segmented blade and the thickness direction; Rounding radius The relationship is as follows:

[0035] Establish a quantitative relationship between structural parameters and outlet design parameters, and calculate the parameters for each segment using this relationship. Design parameters.

[0036] Step 3: Determine the de-flow thickness of each segment in the direction perpendicular to the water flow based on the blunt edge thickness and the included angle of each segment; Furthermore, in step three, The method for calculating the de-flow thickness is as follows:

[0037] in, For the first i Segmented de-flow thickness.

[0038] Step 4: Determine the Karman vortex frequency corresponding to each segment based on the de-flow thickness of each segment, and compare the deviation of the Karman vortex frequency of each segment with the natural frequency of the blade. Furthermore, in step four, The Karman vortex frequency is calculated as follows:

[0039] in, For the first i Segmented Karman vortex frequencies; For the first i The relative flow velocity of water at the blade outlet edge of the segment; It is a Struhar number.

[0040] Furthermore, in step four, The natural frequency of the blade is the first or second natural frequency of the blade in water.

[0041] Step 5: If there are segments that do not meet the preset frequency error requirements, adjust the position of the segment on the outlet edge or the number of segments, and re-execute the calculation of the blunt edge thickness, determination of the flow separation thickness and determination of the Karman vortex frequency until all segments meet the preset frequency error requirements, and output the final design parameters of each segment.

[0042] Furthermore, in step five, The preset frequency error requirement is that the deviation between the Karman vortex frequency and the blade's natural frequency is not less than 15%.

[0043] Step five is as follows: Using the formula for calculating the von Kármán vortex street, the values ​​of each segment along the water's edge are determined. Karman vortex frequency in its original state Comparison of Karman vortex frequencies and the natural frequency of the blade in water The step involves determining the frequency misalignment values ​​between these values. This step aims to identify any resonance risk in the original blade structure and to mark segments with higher risks, providing a target for subsequent optimization.

[0044] Specifically as follows: Regarding the first Segmentation, original state of de-fluxing thickness Calculated based on the effective projected thickness perpendicular to the water flow direction and the outlet edge:

[0045] Will Substitute into the Karman vortex calculation formula

[0046] In the formula, This indicates the thickness of the flow separation layer as water flows past the blade outlet. This indicates the relative flow velocity as water flows past the outlet edge of the blade. This represents the Struh number, which typically ranges from 0.2 to 0.23.

[0047] The natural frequency of the blade in water The natural frequencies of a Kaplan turbine blade are obtained through finite element modal analysis or experimental modal testing. For Kaplan turbine blades, the natural frequencies in water vary depending on the blade material, geometry, and the added mass effect in the water. Usually, the first or second natural frequency of the blade is taken as the calibration benchmark.

[0048] If a certain Segmentation satisfies the frequency misalignment condition:

[0049] It is then assumed that the original state of this segment has met the requirement of avoiding the resonance interval; If the above-mentioned frequency misalignment conditions are not met, the segment is marked as a segment to be optimized, and the parameters for the water outlet edge grinding are designed.

[0050] If all segments meet the above frequency misalignment conditions, the current design parameters are acceptable. If any segment does not meet the frequency misalignment conditions, adjust the position of that segment on the outlet edge or increase the number of segments at that location, changing the local thickness and angle values, and recalculate until the frequency misalignment conditions are met. Repeat the above optimization iteration process until all segments on the outlet edge meet the frequency misalignment requirements.

[0051] Furthermore, After the calculation of each segment is completed, the blunt edge thickness and rounding radius of each segment are smoothed. The design parameters of each segment are used as the model value points, and spline interpolation or curve fitting methods are used to construct a continuous distribution curve along the water outlet edge.

[0052] After the calculations for each segment are completed, the blunt edge thickness of each segment is... and fillet radius All values ​​are discrete. Since the blade's exit edge is a continuous spatial curved surface, directly using discrete segmented parameters for manufacturing would result in sharp edges and steps on the blade surface due to abrupt parameter changes between adjacent segments. This would not only affect the continuity of the water flow pattern but also generate additional stress concentrations and flow disturbances at the abrupt changes. Therefore, the design parameters for each segment must be smoothly transitioned to ensure overall geometric harmony of the exit edge until the entire curve is smooth, continuous, and without abrupt changes.

[0053] The blunt edge thickness of each segment as determined by the above smoothing process. and fillet radius The working surface and the side of the blade exiting the water are ground and polished. After the processing is completed, the anti-jamming vortex design of the blade exiting the water is finished.

[0054] The present invention proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described method.

[0055] The present invention proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the above-described method.

[0056] This invention proposes a design method for preventing Karman vortex at the outlet edge of a Kaplan runner blade. By adjusting the geometric parameters of the outlet edge section of the Kaplan runner blade, the separation thickness of the water flow when it leaves the blade is changed, thereby causing the Karman vortex frequency to deviate from the blade's natural frequency.

[0057] The water outlet edge is divided into several segments, and the thickness of the water outlet edge section of each segment is measured separately. The angle between the direction of the water flow outlet at the water outlet and the direction of the flow around the blade thickness. ,according to and The blunt edge thickness of each segment is calculated using a preset formula. and fillet radius The water outlet edge is processed according to the design parameters.

[0058] After the calculations for each segment are completed, the design parameters obtained for each segment will be... and A smooth transition process is performed, which involves using this value as the model point and constructing a continuous distribution curve along the water outlet edge using spline interpolation or curve fitting methods, so that the parameter changes are uniform between adjacent segments and the overall surface of the water outlet edge is smooth.

[0059] The calculated blunt edge thickness Substitute into the formula for calculating the de-flow thickness Then substitute it into the Kármán vortex street frequency formula If the deviation between the Karman vortex frequency and the natural frequency of the blade in a certain segment is less than 15%, the coefficient is adjusted and the calculation is repeated until all segments meet the frequency misalignment requirement.

[0060] Because the thickness of the blade at the water outlet edge is not equal to the geometric thickness of the water outlet edge, but rather equal to the effective projected width of the retained blunt edge thickness in the direction perpendicular to the water flow, i.e. Based on this, the present invention proposes: adjusting the geometric parameters of the blade's outlet section. and fillet radius It can precisely control the thickness of the dewatering process. This, in turn, shifts the Karman vortex frequency away from the blade's natural frequency.

[0061] By combining the structural parameters of the blade's exit edge and employing a multi-dimensional optimization strategy, the design is optimized to improve the frequency misalignment between the blade's natural frequency and the Karman vortex junction frequency. This achieves the effect of suppressing or reducing Karman vortices. Theoretical calculations and simulations can be used in the early stages of product development to avoid resonance problems and prevent increased costs later on.

[0062] This invention relates to a design method for reducing or suppressing the Karman vortex street phenomenon that occurs when water flows around the exit edge of a Kaplan turbine runner blade. Based on derived formulas, the thickness of the blunt edge and the radius of the rounding are calculated. On the working surface of the blade, anti-Karman vortex design is implemented according to the calculated values. Using this invention, the frequency misalignment between the blade's natural frequency and the Karman vortex junction frequency is increased, thereby suppressing or reducing Karman vortices. This avoids resonance caused by Karman vortices, reduces the frequency of unit overhauls, and provides a guarantee for the long-term safe operation of the power plant unit.

[0063] The design method, device, electronic equipment, and storage medium for preventing Karman vortices at the water outlet of the Kaplan-type impeller blade proposed in this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A design method for preventing Karman vortices at the outlet edge of a Kaplan-type impeller blade, characterized in that, Includes the following steps: Step 1: Divide the Kaplan impeller blade into multiple segments along the outlet edge and obtain the original total thickness of the outlet edge section of each segment and the angle between the water flow outlet direction and the blade flow thickness direction at each segment. Step 2: Based on the original total thickness of each segment and the included angle, calculate the blunt edge thickness to be retained and the rounding radius of the working surface of each segment according to the preset formula; Step 3: Determine the de-flow thickness of each segment in the direction perpendicular to the water flow based on the blunt edge thickness and the included angle of each segment; Step 4: Determine the Karman vortex frequency corresponding to each segment based on the de-flow thickness of each segment, and compare the deviation of the Karman vortex frequency of each segment with the natural frequency of the blade. Step 5: If there are segments that do not meet the preset frequency error requirements, adjust the position of the segment on the outlet edge or the number of segments, and re-calculate the blunt edge thickness, determine the flow separation thickness and determine the Karman vortex frequency until all segments meet the preset frequency error requirements, and output the final design parameters of each segment.

2. The method according to claim 1, characterized in that, In step one, The number of segments divided at the water outlet edge is determined based on the degree of curvature change at the water outlet edge; the original total thickness of the water outlet edge cross section of each segment and the angle between the water flow outlet direction and the blade flow thickness direction at each segment are taken from the values ​​at the middle cross section of the corresponding segment.

3. The method according to claim 1, characterized in that, In step two, The preset relation is: in, For the first i Segmented retention of blunt edge thickness; For the first i Rounding radius of segmented working surfaces; For the first i The original total thickness of the sectioned blade at the water outlet edge; For the first i The angle between the working surface of the segmented blade and the thickness direction.

4. The method according to claim 1, characterized in that, In step three, The method for calculating the de-flow thickness is as follows: in, For the first i Segmented de-flow thickness.

5. The method according to claim 1, characterized in that, In step four, The Karman vortex frequency is calculated as follows: in, For the first i Segmented Karman vortex frequencies; For the first i The relative flow velocity of water at the blade outlet edge of the segment; It is a Struhar number.

6. The method according to claim 1, characterized in that, In step four, The natural frequency of the blade is the first or second natural frequency of the blade in water.

7. The method according to claim 1, characterized in that, In step five, The preset frequency error requirement is that the deviation between the Karman vortex frequency and the blade's natural frequency is not less than 15%.

8. The method according to any one of claims 1-7, characterized in that, After the calculation of each segment is completed, the blunt edge thickness and rounding radius of each segment are smoothed. The design parameters of each segment are used as the model value points, and spline interpolation or curve fitting methods are used to construct a continuous distribution curve along the water outlet edge.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium for storing computer instructions, characterized in that, When the computer instructions are executed by the processor, they implement the steps of the method according to any one of claims 1-8.

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