Evaluation method of wall cavitation intensity and protection effect based on wall force measurement

Abstract

The present invention discloses a method for evaluating the wall cavitation intensity and protective effect based on the measurement of wall force. The present invention first uses a force sensor to measure the cavitation force of the test wall; secondly, the force data is collected to obtain the original data of the cavitation force of the test wall with protective measures applied; according to the original data, the duration and maximum negative peak of the normal force impacting the wall, as well as the duration and maximum positive peak of the normal force away from the wall are obtained; then, according to the original force data and the duration of the force in the corresponding direction, the impulse of the cavitation collapse force is calculated to evaluate the cumulative effect of the cavitation force on the wall; finally, the attenuation degree of the cavitation force peak and impulse under the protective measures is calculated by the attenuation rate. The present invention uses a force measurement system to directly measure the transient force on the wall, and introduces impulse evaluation, which can respectively show the intensity of the force on the wall in the impact direction and the departure direction.

Description

Technical Field

[0001] The invention belongs to the field of cavitation protection, and in particular relates to a method for evaluating wall cavitation intensity and protection effect. Background Art

[0002] When hydraulic machinery such as pumps, propellers, and turbines are in operation, the water velocity increases, causing a local pressure drop. When the pressure drops below the saturated vapor pressure, cavitation bubbles are formed. Cavitation bubbles go through three different stages: expansion, contraction, and collapse. During the collapse process, instantaneous high temperatures are generated and pressure waves are released. When there is a wall nearby, the cavitation bubble collapses asymmetrically, generating a high-speed jet directed toward the wall. The instantaneous high-amplitude high temperature, pressure wave, and microjet act on the wall, presenting high stress and strain, which can cause fatigue of the wall material. This is cavitation damage.

[0003] In order to prevent economic losses and safety accidents caused by cavitation, research on cavitation protection has become a key area. The research focus in this field is to regulate the jet direction and intensity of cavitation bubbles to reduce the damage of cavitation to wall materials. The current evaluation methods for cavitation protection effect mainly include the following: (1) Material damage inspection: The cavitation intensity is judged by evaluating the degree of material damage after cavitation, and the cavitation intensity is judged by weighing method. However, in the actual scene of cavitation, metal fatigue or even cracks may occur on the wall, which may not necessarily cause actual mass loss, and it is even more difficult to cause mass loss on the protected wall. This makes it difficult to quantitatively evaluate the protection effect of this method. (2) Image analysis technology: Observe the jet direction and infer the jet intensity through image analysis. This method relies on post-test image results, lacks real-time and quantification, and cannot provide accurate comparison and analysis. The final evaluation results rely on manual interpretation and have subjective bias. (3) Theoretical model establishment: A theoretical model is established based on image results to reverse the cavitation impact intensity and predict the protection effect. This method can only provide prediction results and lacks actual measured data, making it difficult to accurately evaluate the actual situation of the protection effect.

[0004] Existing technologies have certain limitations, so there is an urgent need for a more accurate and objective evaluation method to quantitatively evaluate the actual effectiveness of cavitation intensity and protection measures, so as to ensure accurate judgment of the effectiveness and durability of cavitation intensity and cavitation protection measures. Summary of the invention

[0005] In view of the problem that there is a lack of methods for quantitatively evaluating the wall cavitation intensity and cavitation protection effect in the prior art, the present invention proposes a wall cavitation protection effect evaluation method based on force measurement.

[0006] The wall cavitation intensity and protection effect evaluation method based on the wall force measurement includes the following steps:

[0007] Use a force sensor to measure the cavitation force on the test wall, including the normal force of the cavitation collapse impacting the wall and the normal force away from the wall;

[0008] Collect force data to obtain the original data of cavitation force on the test wall where protective measures are applied;

[0009] According to the original data, the duration and maximum negative peak value of the normal force impacting the wall, as well as the duration and maximum positive peak value of the normal force away from the wall are obtained;

[0010] According to the original force data and the duration of the force in the corresponding direction, the impulse of the cavitation collapse force is calculated to evaluate the cumulative effect of the cavitation force on the wall.

[0011] The attenuation degree of the peak value and impulse of the cavitation force under this protection measure is calculated by the attenuation rate formula.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The transient force on the wall is directly measured by the force measurement system, which provides a data visualization, instant feedback and high-precision cavitation protection effect evaluation method. Compared with traditional indirect evaluation methods (weighing method, image method), this method can more accurately reflect the effectiveness of protection measures and their dynamic changes in real time, intuitively and accurately, and significantly improve the repeatability and efficiency of the test.

[0014] (2) Introducing impulse assessment. As the accumulation of force over time, impulse can show the intensity of the force acting on the wall in the impact direction and the deviation direction respectively. It can identify and quantify the performance of protective measures in two different directions, and can more comprehensively evaluate the protective effect of protective measures.

[0015] (3) A quantitative evaluation system based on the attenuation rate of force and impulse was proposed. By comparing the changes in force and impulse between the protective treatment wall and the blank control wall, an objective and quantitative evaluation standard was provided for the effectiveness of different protective measures.

[0016] (4) The evaluation method is applicable to a variety of different protective means and materials. Whether it is a coating, an additional spoiler structure, or material modification, the protective effect can be evaluated by the applied force. This method is universal and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cavitation strength test system;

[0018] Figure 2 This is a schematic diagram of the positioning of the cavitation bubble and the test wall;

[0019] Figure 3Schematic diagram of the definition of dimensionless distance of the test wall;

[0020] Figure 4 Dynamic evolution of the gas-liquid interface on the blank test wall when γ=2.36;

[0021] Figure 5 The dynamic force evolution process of the blank test wall when γ=2.36;

[0022] Figure 6 Schematic diagram for defining the structural parameters of the bubble protection wall;

[0023] Figure 7 Dynamic evolution of gas-liquid interface on bubble protection wall when γ=6.38, ξ=1.72;

[0024] Figure 8 The dynamic force evolution process of the bubble protection wall when γ=6.38 and ξ=1.72;

[0025] Fig. 9 Comparison of the peak absolute values ​​of the force acting on the bubble protection wall and the blank wall in the impact direction when γ=6.38;

[0026] Fig.10 The peak value comparison of the force on the bubble protection wall and the blank wall in the direction away from the wall when γ=6.38;

[0027] Fig.11 Comparison of the absolute value of the impulse of the bubble protection wall and the blank wall in the direction of the impact force on the wall when γ=6.38;

[0028] Fig.12 Comparison of the impulse of the force acting on the bubble protection wall and the blank wall in the direction away from the wall when γ=6.38;

[0029] Fig.13 A schematic diagram for defining the structural parameters of the cylindrical array protective wall;

[0030] Fig.14 Dynamic evolution of the gas-liquid interface on the double-cylinder array protective wall when η=0.92 and γ=1.96;

[0031] Fig.15 The dynamic force evolution process of the double cylinder array protective wall when η=0.92 and γ=1.96;

[0032] Fig.16 Comparison of the peak absolute values ​​of the impact force on the double-cylinder array protection wall and the blank wall when η=0.92;

[0033] Fig.17 The peak value comparison of the force on the double-cylinder array protection wall and the blank wall in the direction away from the wall when η=0.92;

[0034] Fig.18 Comparison of the absolute value of the impulse of the double-cylinder array protection wall and the blank wall in the direction of the impact force on the wall when η=0.92;

[0035] Fig.19 Comparison of the impulse of the force acting on the double-cylinder array protective wall and the blank wall in the direction away from the wall when η=0.92. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0037] This application provides a method for evaluating the wall cavitation intensity and protection effect based on the wall force measurement:

[0038] The force sensor is used to measure the cavitation force F(t) on the test wall, including the normal force F of the cavitation collapse impacting the wall. n (t), F n (t) is negative, which corresponds to the normal force F away from the wall. p (t), F p (t) value is positive.

[0039] Optionally, the force sensor and its fixing bracket are connected to the displacement platform, and the force measuring base is connected to the force sensor. A positioning wire is installed on the top of the base, the displacement platform is adjusted and the cavitation and the force measuring base are adjusted to the same axis using the positioning wire. After positioning, the positioning wire is removed and the test wall is installed on the force measuring base.

[0040] Optionally, the test wall substrate can be made of a rigid material such as metal, quartz glass, etc., and the substrate serves as a blank test wall.

[0041] Optionally, protective measures (coatings, flow-disrupting structures, surface modifications, etc.) are applied to the test wall substrate.

[0042] Optionally, the cavitation generation system can be configured with any cavitation fixed-point generation technology, such as laser-induced cavitation, electric spark, etc., so that the initial center of mass of the cavitation bubble is at a unique and determined position in the water tank, and the cavitation bubble size can be adjusted according to the test requirements.

[0043] Optionally, the height of the test wall is adjusted by a displacement platform to adjust the dimensionless distance between the cavitation bubble and the wall.

[0044] Optionally, an ultra-high-speed image acquisition system is also included to capture the changes in the gas-liquid wall of the cavitation bubble to determine the dimensionless distance of the cavitation bubble and the parameters of the protective structure. The dimensionless distance and structural parameters are test variables.

[0045] The force data is collected by a data acquisition card to obtain the original data F(t) of the cavitation force on the test wall where the protective measures are applied.

[0046] According to F(t), we can get the normal force F acting on the impact wall: n (t) Duration t n With the maximum negative peak F nmax , and the normal force F away from the wall p (t) Duration t p With the maximum forward peak F pmax .

[0047] According to the force data and the duration in the corresponding direction, the cavitation collapse force impulse I is calculated, and the normal force impulse I of the impact wall is calculated respectively. n The normal force I away from the wall p Impulse is used to evaluate the cumulative effect of cavitation force on the wall. The impulse calculation formula is as follows:

[0048]

[0049] The attenuation degree of the peak value and impulse of the cavitation force under this protection measure is calculated by the attenuation rate formula. The attenuation rate calculation formula is as follows:

[0050]

[0051] where σ f is the peak force attenuation rate, which is used to evaluate the peak force attenuation rate in the direction of impacting the wall and away from the wall, F 0max is the peak value of the blank test wall force, F max It is the peak force under the same test conditions with protective measures applied.

[0052]

[0053] where σ i is the impulse attenuation rate, which is used to evaluate the impulse attenuation rate in the direction of impacting the wall and away from the wall. I0 is the impulse of the force acting on the wall in the blank test, and I is the impulse of the force acting on the wall under the same test conditions with protective measures applied.

[0054] Furthermore, in the attenuation rate calculation process, the interpolation algorithm is used to process the data to achieve variable correspondence and predict the measured values, thereby improving the accuracy and reliability of the assessment.

[0055] The present invention is further described below with reference to the accompanying drawings and examples.

[0056] like Figure 1 , 2 As shown, the devices involved in this embodiment include a delay trigger 1, a high-speed camera 2, a high-precision three-dimensional displacement platform 3, a sensor bracket 4, a flicker-free LED light source 5, a data acquisition card 6, a computer 7, a charge amplifier 8, a quartz water tank 9, a cavitation bubble 10, a test wall 11, a force measuring base 12, a force sensor 13, and a positioning wire 14.

[0057] like Figure 1 , 2 As shown, the sensor bracket 4 is fixed to the three-dimensional displacement platform 3, the force sensor 13 is installed through the bracket thread, and the force measuring base 12 is fixed through the force sensor 13 thread. The positioning wire 14 is installed on the central axis of the force measuring base 12 through the thread. After the installation is completed, the force sensor 13, the force measuring base 12, and the positioning wire 14 are coaxial.

[0058] After the positioning device is installed, a cavitation generating device is used to generate cavitation 10, and the three-dimensional displacement platform is used in conjunction with a high-speed camera to adjust the position of the positioning wire, and the positioning wire is adjusted to be above the cavitation bubble and coaxial, and the positioning is completed. After the positioning is completed, the positioning wire 14 is removed, and the test wall 11 is installed on the force measuring base 12 to make it fit tightly.

[0059] During the test, cavitation bubbles are generated by a cavitation bubble generating device to cause a collapse force on the test wall 11. The interface timing of the delay trigger 1 is adjusted to synchronize the force sensor 13, the high-speed camera 2, and the data acquisition card 6, and the image and force information of the cavitation effect are recorded and stored in the computer 7. The charge amplifier 8 adjusts the range of the force sensor 13.

[0060] The dimensionless distance and the structural parameters of the protective measures are used as test variables. The displacement platform 3 is used to adjust the distance between the test wall 11 and the cavitation bubble to adjust the dimensionless distance. The protective measures are set on the test wall to adjust the structural parameters according to the test requirements. The test wall base is used as a blank test wall for comparison. The cavitation bubble size is adjusted by the cavitation generation device.

[0061] like Figure 3 In this example, the dimensionless near-wall distance γ is defined as: the distance L between the center of the cavitation bubble and the test wall and the maximum radius R of the cavitation bubble max Ratio:

[0062]

[0063] After the cavitation is generated, it will go through a life cycle of expansion, contraction, and collapse to produce pressure waves and jets, which will repeat many times. Figure 4 This is the evolution process of cavitation bubbles generated by laser induced cavitation technology near the stainless steel wall without any protection measures when γ=2.36. The substrate size is 76mm×25mm×1mm.

[0064] Figure 5 for Figure 4 The dynamic force F0(t) generated by the cavitation bubble on the blank test wall. Under this connection mode, the cavitation bubble collapse will have a duration of t n The negative force during the impact is F 0n (t), the peak force is F 0nmax After the impact process, due to the change of fluid flow and static pressure, the test wall will be subjected to a force F in the direction away from the wall. 0p (t), peak value F 0pmax , duration t p The impact force starts at t1, the force in the direction of the impact wall changes to the direction away from the wall at t2, and the force in the direction away from the wall ends at t3.

[0065] According to F 0n (t) and F 0p (t) and its corresponding duration, the impulse I in the direction of the impact wall can be calculated n The force impulse I in the direction away from the wall p The calculation formula is as follows:

[0066]

[0067]

[0068] The blank test wall results are used as a control for the wall test results with protective measures applied, and the effectiveness of the protective measures is judged by comparing the changes in the peak force and impulse.

[0069] Figures 6 to 12 This is an example of bubble protection wall. This protection measure reduces the impact strength of the wall by attaching bubbles to the wall surface.

[0070] Figure 6 Schematic diagram of the definition of bubble protection wall structure parameters. The dimensionless radius ratio ξ is the bubble radius R b The maximum radius of the cavitation bubble R max Ratio.

[0071]

[0072] Figure 7This is the time sequence diagram of the laser-induced cavitation collapse on the bubble protection wall, where γ=6.38, ξ=1.72. The substrate is glass with a substrate size of 76mm×25mm×1mm. The bubbles are attached through the patterned superhydrophobic coating.

[0073] Figure 8 for Figure 7 Dynamic evolution of cavitation bubble collapse force, and the peak impact force F is obtained bnmax , the impact force on the wall F bn (t), peak force F in the direction away from the wall bpmax , the force F away from the wall bp (t), as well as the duration of the force and the start and end times of the force.

[0074] Fig. 9 When γ=6.38, the absolute value of the peak impact force changes as ξ changes. The peak absolute value of the blank test wall force corresponding to this condition is 2.80N.

[0075] According to the test results, the maximum absolute value of the peak force is 0.98N when ξ=1.61, and the minimum absolute value of the peak force is 0.84N when ξ=2.25. Calculated according to the attenuation rate:

[0076]

[0077]

[0078] Under test conditions, the force attenuation rate of this protective measure in the impact direction is 65%-70%.

[0079] Fig.10 When γ=6.38, the force changes in the direction opposite to the wall when ξ changes. This condition corresponds to a peak value of 3.36N for the blank test wall force.

[0080] According to the test results, the maximum peak force is 1.91N when ξ=1.61, and the minimum peak force is 1.65N when ξ=2.25. Calculated according to the attenuation rate

[0081]

[0082]

[0083] Under the test conditions, the force attenuation rate of this protective measure in the impact direction is 43.15%-50.89%.

[0084] Fig.11 When γ=6.38, the absolute value of the impulse of the force acting on the wall changes with the change of ξ. Under this condition, the absolute value of the impulse of the force acting on the wall in the blank test is 1.35×10 -4 N·s.

[0085] According to the test results, when ξ=1.61, the maximum absolute value of the force impulse is 1.30×10 -4 N·s, when ξ=2.25, the minimum peak value of the force impulse is 1.12×10 -4 N·s. Calculated based on the decay rate

[0086]

[0087]

[0088] Fig.12 When γ=6.38, the impulse of the force acting in the direction away from the wall changes when ξ changes. Under this condition, the impulse of the force acting on the wall in the blank test is 2.54×10 -4 N·s.

[0089] According to the test results, when ξ=1.61, the maximum absolute value of the force impulse is 3.58×10 -4 N·s, when ξ=2.25, the minimum peak value of the force impulse is 3.08×10 -4 N·s. This indicates that under this test condition, the bubble protection wall cannot attenuate the impulse of the force acting in the direction away from the wall.

[0090] Fig.13 to- Fig.19 This is an example of a double micro-column array protective wall. This type of fluid disturbance protection measure is to apply a micro-column installed vertically on the wall, and induce cavitation to generate a jet directed toward the micro-column, thereby weakening the jet of cavitation collapse to the wall. The double micro-column array protective wall in the embodiment is a special case where the cavitation on the micro-column array wall is generated in the center of the two micro-columns.

[0091] Fig.13 Schematic diagram of double micropillar array wall structure parameter definition. H is the length from the center of the cavitation bubble to the edge of the micropillar, and D is the diameter of the micropillar. The dimensionless spacing is defined as η:

[0092]

[0093] Fig.14 The time sequence diagram of laser-induced cavitation collapse on the wall of double micropillar array when η=0.92 and γ=1.96. The substrate is made of stainless steel, with a substrate size of 76mm×25mm×1mm and D=1.15mm.

[0094] Fig.15 for Fig.14 Time evolution of the dynamic force exerted by cavitation collapse on the wall of a double micropillar array.

[0095] The force acting on the double micropillar array is set to F d(t), the force F acting in the direction of the impact wall dn (t), the force F away from the wall dp (t).

[0096] Fig.16 The peak absolute value of the force acting on the double micropillar array in the direction of impacting the wall varies with γ. By comparing it with the peak absolute value of the impact force on the blank test wall, the peak impact force attenuates significantly.

[0097] Fig.17 This is the variation law of the peak force of the double micropillar array away from the wall as a function of γ. Compared with the peak force in the blank test wall, the peak force in the direction away from the wall is obviously attenuated.

[0098] according to Fig.18 and Fig.19 , the impulses of the force both impacting the wall and away from the wall show significant attenuation.

[0099] The interpolation algorithm can be used to Figure 16-Figure 19 By processing the data in the test, the complete correspondence of the test variable γ can be achieved, the peak force and impulse value can be predicted, and the change law of the attenuation rate can be obtained through the attenuation rate formula.

[0100] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A method for evaluating the wall cavitation intensity and protection effect based on the measurement of wall force, characterized in that The method comprises the following steps: Use a force sensor to measure the cavitation force on the test wall, including the normal force of the cavitation collapse impacting the wall and the normal force away from the wall; Collect force data to obtain the original data of cavitation force on the test wall where protective measures are applied; According to the original data, the duration and maximum negative peak value of the normal force impacting the wall, as well as the duration and maximum positive peak value of the normal force away from the wall are obtained; According to the original force data and the duration of the force in the corresponding direction, the impulse of the cavitation collapse force is calculated to evaluate the cumulative effect of the cavitation force on the wall. The attenuation degree of the peak value and impulse of the cavitation force under this protection measure is calculated by the attenuation rate formula; The method also includes connecting a force sensor and a fixing bracket thereof to a displacement platform, connecting a force measuring base to the force sensor, installing a test wall surface to the force measuring base so that the test wall surface fits tightly thereto; and utilizing a cavitation bubble generating device to generate cavitation bubbles to cause a collapse force on the test wall surface.

2. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 1 is characterized in that: Before measurement, there is also a positioning step, which is: A positioning steel wire is installed on the top of the force measuring base, and the displacement platform is adjusted and the cavitation bubble and the force measuring base are adjusted to the same axis by using the positioning steel wire. After the positioning is completed, the positioning steel wire is removed.

3. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 2, characterized in that: The test wall substrate is made of metal or quartz glass, and the test wall substrate serves as a blank test wall.

4. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 1, characterized in that: The cavitation generation system is configured to generate cavitation at any fixed point, so that the initial center of mass of the cavitation bubble is at a unique and determined position in the water tank, and the size of the cavitation bubble is adjusted according to the test requirements.

5. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 4 is characterized in that: It also includes an ultra-high-speed image acquisition system for capturing the changes in the gas-liquid wall of the cavitation bubble to determine the dimensionless distance of the cavitation bubble and the parameters of the protective structure, wherein the dimensionless distance and the structural parameters are test variables.

6. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 5, characterized in that: The height of the test wall is adjusted by the displacement platform, thereby adjusting the dimensionless distance between the cavitation bubble and the wall.

7. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 1, characterized in that: In the process of attenuation rate calculation, the interpolation algorithm is used to process the data to achieve variable correspondence and predict the measured values, thereby improving the accuracy and reliability of the assessment.

8. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 1 or 7, characterized in that: Peak force attenuation rate σ f The calculation is as follows: ； in The peak force attenuation rate is used to evaluate the peak force attenuation rate in the direction of impacting the wall and away from the wall. F 0max is the peak value of the wall force in the blank test, F max It is the peak force under the same test conditions with protective measures applied.

9. The method for evaluating wall cavitation intensity and protection effect based on wall force measurement according to claim 1 or 7, characterized in that: Impulse decay rate σ i The calculation is as follows: ； The impulse attenuation rate is used to evaluate the impulse attenuation rate in the direction of impacting the wall and away from the wall. I 0 is the blank test wall force impulse, I It is the force impulse under the same test conditions when protective measures are applied.

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