CN116499703A - Quantitative analysis method suitable for friction-reducing resistance effect under external flow condition - Google Patents
Quantitative analysis method suitable for friction-reducing resistance effect under external flow condition Download PDFInfo
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Abstract
The invention relates to a quantitative analysis method suitable for friction reduction resistance effect under an outflow condition. It comprises the following steps: designing a streamline test object, configuring a preset flow condition set for quantitative analysis, wherein at least one preset flow condition in the preset flow condition set is selected during quantitative analysis, and a test sample M is subjected to the selected preset flow condition s Control M d Smooth sample M 0 Making a total resistance measurement; computationally generating the smooth sample M 0 Total resistance F of smooth sample under selected preset flow conditions 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 Calculating the subtracted total resistivity DR under the selected preset flow conditions F Calculating the friction ratio a of the generated control sample d The method comprises the steps of carrying out a first treatment on the surface of the Based on the reduced total resistivity DR F Friction ratio a of control sample d Calculating test sample M s Relative control M d Is the antifriction rate DR of (2) f . The invention can effectively and accurately obtain the friction ratio, and realizes the quantitative analysis of the friction reducing effect by taking the friction components into account independently.
Description
Technical Field
The invention relates to a quantitative analysis method, in particular to a quantitative analysis method suitable for the friction reduction resistance effect under the condition of external flow.
Background
Flow resistance is directly related to power requirements, energy consumption of air and underwater vehicles, and reduction of flow resistance is a constant theme in vehicle design and application. Unlike the inner flow of pipes, open channels, etc., the flow around the aircraft is typically an outer flow wrap.
To investigate the drag and drag reduction of an aircraft in depth, the total drag of an aircraft is generally divided into different components according to the principles of fluid mechanics. For the aircraft without free liquid level influence, the main resistance components are friction resistance (friction resistance) and viscous pressure resistance; the friction coefficient is mainly related to the surface state, the wet surface area (determined by the outline dimension of the aircraft), and the Reynolds number (which is a function of the speed of the aircraft, the characteristic length and the viscosity of the fluid); when the flow state (referring to laminar/turbulent flow state, flow separation position, etc.) is unchanged, the viscous-pressure drag coefficient is only related to the appearance of the aircraft, and is irrelevant to the Reynolds number. Although the total resistance of the aircraft can be artificially divided into different resistance components, only the total resistance of the test object can be measured and obtained at present from the test measurement point of view, and each resistance component cannot be directly measured and obtained.
The friction ratio in the total drag of the aircraft is generally as high as 50% -80%. Along with the green development concepts of energy conservation, consumption reduction and the like, the antifriction technology gradually becomes a research hot spot, and various technical schemes such as surface micro grooves, surface following traveling waves, low surface energy surfaces, superhydrophobic surfaces and the like are formed at present, and the main technical thought is to change the surface state of an aircraft.
To quantitatively analyze the effect of each friction reducing scheme, a test sample having the same shape and size (same sticking resistance), containing the friction reducing scheme, and a control sample having no friction reducing scheme are generally prepared, and the total resistance of the two samples is measured and compared, respectively, in a specific comparison manner shown in fig. 1.
Essentially, the above comparison process ultimately achieves the total drag reduction effect of each friction reduction scheme for a particular test subject, rather than the friction reduction effect. Because the friction ratio of the surfaces of the test objects with different shapes and sizes is different under the same navigational speed, the same friction reducing scheme is adopted, and the consistency of the results obtained for different test objects is poor; the reason for this is that friction components cannot be considered alone, and analysis of friction reducing effect was performed.
The friction ratio of the test object is accurately obtained, which is the basis of taking the friction components into account independently and analyzing the friction reducing effect, however, on one hand, as described above, only the total resistance of the test object can be obtained by the current test measurement method, and each resistance component can not be accurately obtained, so that the friction ratio is obtained; on the other hand, as the drag reduction mechanism of the technical scheme relates to complex physical mechanisms such as micro-nano surface interface mechanics, multiple physical fields, rheology and the like, the friction ratio cannot be accurately obtained by a theoretical or numerical simulation (CFD: computational Fluid Dynamics) method at present.
In conclusion, the existing outflow friction-reducing effect analysis method has the problems that the friction ratio cannot be accurately obtained, friction components cannot be considered independently, and friction-reducing effect analysis cannot be performed, so that the consistency of results obtained by different test objects is poor, and a large improvement and improvement space is provided.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a quantitative analysis method suitable for the friction reducing resistance effect under the outflow condition, which can effectively and accurately obtain the friction ratio, realize the independent consideration of friction components and the quantitative analysis of the friction reducing effect, and improve the consistency and reliability of the analysis of the friction reducing effect on different test objects.
According to the technical scheme provided by the invention, the quantitative analysis method suitable for the friction reduction resistance effect under the external flow condition comprises the following steps:
designing a streamline test object, wherein the designed streamline test object comprises a test sample M with a friction reducing scheme s Control M without friction-reducing protocol d Smooth sample M with hydraulically smooth surface 0 Test sample M s Control M d Smooth sample M 0 At least have the same external dimensions;
configuring a preset flow condition set for quantitative analysis, wherein at least one preset flow condition in the preset flow condition set is selected during quantitative analysis, and the test sample M is subjected to the selected preset flow condition s Control M d Smooth sample M 0 Measuring total resistance to obtain test samples M s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 ；
Based on smooth sample M 0 Total resistance F of (2) 0 Calculating to generate the smooth sample M 0 Total resistance F of smooth sample under selected preset flow conditions 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 ；
Based on test sample M s Total resistance F of (2) s Control M d Total resistance F of (2) d Calculating the subtracted total resistivity DR at selected preset flow conditions F ；
Based on control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Smooth sample friction ratio a 0 Calculating and generating a friction ratio a of the control sample d ；
Based on the reduced total resistivity DR F Friction ratio a of control sample d Calculating test sample M s Relative control M d Is the antifriction rate DR of (2) f 。
For designing streamline test objects, designing and forming based on flow conditions, wherein,
the flow conditions include a flow rate and a reynolds number.
Measuring to obtain smooth sample M 0 Total resistance F of (2) 0 After that, through a CFD meterCalculating and generating corresponding total resistance F of smooth sample 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 Wherein, the method comprises the steps of, wherein,
when CFD calculation is adopted, the configured calculation conditions include CFD method type, turbulence model and grid division strategy.
Friction ratio a for smooth sample 0 The following steps are:
for a reduced total resistivity DR at selected preset flow conditions F The following steps are:
generating a comparative friction ratio a for calculation d The following steps are:
for test sample M s Relative control M d Is the antifriction rate DR of (2) f The following steps are:
the invention has the advantages that: including a smooth sample M in designing a streamlined test object 0 By using test samples M under the same preset flow conditions s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Can finally calculate the friction-reducing rate DR f The friction ratio of the test object can be accurately obtained, friction components are considered independently, analysis of friction reducing effect is carried out, and consistency of analysis of friction reducing scheme effect is improved.
Drawings
FIG. 1 is a schematic diagram of a conventional outflow drag reduction effect analysis method.
FIG. 2 is a schematic diagram of a quantitative analysis method for the effect of outflow friction reduction in the present invention.
Detailed Description
The invention will be further described with reference to the following specific drawings and examples.
In order to realize the quantitative analysis of friction resistance effect by taking friction resistance components into account independently and improving the consistency and reliability of friction resistance effect analysis on different test objects, and a quantitative analysis method of friction resistance effect applicable to an outflow condition, in one embodiment of the invention, the quantitative analysis method comprises the following steps:
designing a streamline test object, wherein the designed streamline test object comprises a test sample M with a friction reducing scheme s Control M without friction-reducing protocol d Smooth sample M with hydraulically smooth surface 0 Test sample M s Control M d Smooth sample M 0 At least have the same external dimensions;
configuring a preset flow condition set for quantitative analysis, wherein at least one preset flow condition in the preset flow condition set is selected during quantitative analysis, and the test sample M is subjected to the selected preset flow condition s Control M d Smooth sample M 0 Measuring total resistance to obtain test samples M s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 ；
Based on smooth sample M 0 Total resistance F of (2) 0 Calculating to generate the smooth sample M 0 Total resistance F of smooth sample under selected preset flow conditions 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 ；
Based on test sample M s Total resistance F of (2) s Control M d Total resistance F of (2) d Calculating the subtracted total resistivity DR at selected preset flow conditions F ；
Based on control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Smooth sample friction ratio a 0 Calculating and generating a friction ratio a of the control sample d ；
Based on the reduced total resistivity DR F Friction ratio a of control sample d Calculating test sample M s Relative control M d Is the antifriction rate DR of (2) f 。
As can be seen from the above description, when analyzing the friction-reducing resistance effect under the external flow condition, it is necessary to design a streamline test object, where the design of the streamline test object mainly means determining the shape and main dimension of the test object; the shape comprises a flat plate type, a rotary body type and the like, and the selection standard of the shape is generally closer to a real object to be simulated, such as a drag reduction coating for simulating the bottom surface of a ship with smaller curvature, and the flat plate is selected for testing more properly/reasonably; the drag reduction coating used on the surface of the torpedo with larger curvature is simulated, and the test is more proper/reasonable by selecting the revolving body.
The main dimensions refer to major dimensions such as length, width, thickness, etc., and when testing, it is generally required to achieve a certain test water velocity (U) and reynolds number (Re), since re=u×l/v, L is the main dimension, and v is the fluid viscosity (generally, the change is not large). Therefore, in order to achieve a certain Re, a mode of a large-size model with a lower test water speed may be adopted, or a mode of a small-size model with a higher test water speed may be adopted, which is also required to be determined according to specific situations (such as a maximum water speed which can be achieved by a water hole, a maximum model size which can be adopted, and the like) and requirements.
In addition, the streamline object refers to an object which has no obvious flow separation on the whole surface and is approximately a front circle and a rear tip, but the degrees of the front circle and the rear tip are different according to different flow rates, fluid media, reynolds numbers and the like, and the streamline object is designed according to specific situations; the main design methods of streamline objects include experimentation and CFD.
In one embodiment of the invention, the designed streamline test object needs to simultaneously comprise a test sample M with a friction reducing scheme s Control M without friction-reducing protocol d Smooth sample M with hydraulically smooth surface 0 For test samples with antifriction schemeM s Generally, in the test sample M s A coating for reducing friction resistance is arranged on the coating; control M without friction-reducing protocol d In particular to a coating which is not provided with friction-reducing resistance on a test object and is a smooth sample M 0 In particular to test subjects with smooth surfaces and without a friction-reducing resistance coating. From the above description, test sample M s Control M d Smooth sample M 0 At least the same external dimensions, which are provided to ensure the reliability of the quantitative analysis.
As is clear from the above description, the design of the streamline test object is based on the flow conditions including the flow velocity and the reynolds number, and the specific conditions of the flow velocity and the reynolds number are related to the test object, specifically, the streamline test object required for the design can be satisfied.
During analysis, a preset flow condition set is generally required to be configured, the preset flow condition set at least comprises one preset flow condition, and the number of the preset flow conditions in the preset flow condition set can be selected according to requirements. The preset flow conditions specifically refer to test requirements such as test water velocity and Reynolds number, and are determined according to actual analysis requirements and the related content of the main scale.
In the analysis, at least one preset flow condition is generally selected, and after the preset flow condition is selected, a resistance measuring device commonly used in the technical field is adopted for the test sample M s Control M d Smooth sample M 0 The total resistance is measured to obtain test samples M after measurement s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Wherein, test sample M s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 I.e. measured by a resistance measuring device under the same preset flow condition.
When the resistance measuring device is selected/designed, the resistance measuring device mainly comprises a structural form (considering strength and rigidity), a balance measuring range (considering measuring precision) and a shape (needing to form a streamline assembly with the test object).
In specific implementation, the resistance measuring device can adopt a resistance measuring form disclosed in publication No. CN114964706A, in particular to meet the requirement of the test sample M s Control M d Smooth sample M 0 The total resistance measurement is performed, and a test sample M is obtained by specific measurement s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 For the procedure of (1), reference may be made to the description of publication No. CN114964706A, test sample M s Control M d Smooth sample M 0 When combined with the resistance measuring device of publication No. CN114964706A, the device can form a streamline assembly shape as a whole. In addition, it is also possible to select all preset flow conditions within the set of preset flow conditions and measure the corresponding total resistance under each preset flow condition.
In one embodiment of the invention, a smooth sample M is measured 0 Total resistance F of (2) 0 Then, the corresponding smooth sample total resistance F is generated through CFD calculation 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 Wherein, the method comprises the steps of, wherein,
when CFD calculation is adopted, the configured calculation conditions include CFD method type, turbulence model and grid division strategy.
Specifically, during CFD calculation, the main configuration conditions include, besides basic conditions such as fluid medium, water velocity and test object, a CFD method type, a turbulence model, a grid division strategy, etc., where the main purposes of the basic conditions, the methods, the models, the strategies, etc. of the above configuration are to make the CFD simulation situation as similar as possible to the actual situation, the simulation result as consistent as possible to the actual situation, and the calculation conditions of the specific configuration may be selected according to the needs, for example, the CFD method type may be "Reynolds Average (RANS) method", the turbulence model may be "RNG k-epsilon turbulence model", the grid division strategy may be "adopting boundary layer grid near the near wall surface, 12 layers altogether, the first layer grid height y+ is set to 30, and the grid growth rate is set to 1.1".
In particular, to measure the obtained smooth sample M 0 Total resistance F of (2) 0 For verifying data, turbulence model, calculation grid, etc. are preferable, and the high-precision resistance CFD method is established, and common CFD commercial software can be adopted to calculate and obtain total resistance F of smooth sample 0c Smooth sample friction f 0c 。
Calculating to obtain the friction resistance f of the smooth sample 0c After that, the friction ratio a of the smooth sample can be obtained 0 Specifically, for a smooth sample friction ratio a 0 The following steps are:
in one embodiment of the invention, the total resistance DR is reduced at selected preset flow conditions F The following steps are:
generating a comparative friction ratio a for calculation d The following steps are:
for test sample M s Relative control M d Is the antifriction rate DR of (2) f The following steps are:
specifically, through test sample M s Relative control M d Is the antifriction rate DR of (2) f The quantitative analysis of the friction reducing resistance effect under the condition of external flow can be realized.
The process of quantitative analysis is specifically illustrated below.
Example 1
In this embodiment, it is required to reach a maximum Reynolds number of 1×10 in the water tunnel 7 Test sample M was run under turbulent conditions of (2) s Coating relative to control M d Quantitative determination of the outflow antifriction effect of a coatingAnd (5) analyzing. The water tunnel test section is cuboid, the main scale is 1600×225×225mm (length×width×height), and the coating thickness is negligible. The quantitative analysis mainly comprises the following steps:
step 1: design streamline test object
According to the required Reynolds number range and the actual condition of the water tunnel, determining that the water speed range is 6 m/s-14 m/s, adopting a test object with the length of 0.8m, and the actual Reynolds number can reach 4.6X10 6 ～1.1×10 7 (viscosity coefficient of water is 1.036X10) -6 m 2 S) far greater than the generally considered critical Reynolds number for laminar flow (5X 10 5 ) The surface of the model can be regarded as a fully developed turbulence state under all test working conditions, and the flow condition requirements are met.
The designed test object is an airfoil flat plate, the main scale is 800 multiplied by 200 multiplied by 14mm (length multiplied by width multiplied by thickness), the head part is 1:5 (short axis: long axis) semi-ellipse, and the tail part is 1:5 (short axis: long axis) wedge-shaped. The resistance measuring device disclosed by the publication No. CN114964706A comprises an upper connecting plate, a force measuring balance, a supporting rod and a lower connecting plate, wherein 1 lower connecting plate is arranged flush with the bottom surface of a water tunnel test section; the support rod 2 pieces are 108 multiplied by 28 multiplied by 113mm (length multiplied by width multiplied by height), the head part is semicircular, the tail part is 1:2 (short axis: long axis) semi-elliptical, and the support rod 2 pieces are fixedly connected with the lower connecting plate and serve as a fixed base and a guide cover of the force measuring balance; the force measuring balance 2 pieces are respectively arranged in the 2 support rods; the upper connecting plate 1 has dimensions of 441×20×10mm (length×width×thickness), and the head and tail parts are 1:4 (short axis: long axis) semi-ellipse, and can be used for fixedly connecting a test object with a force measuring balance.
In general, the streamline test subject and the resistance measuring device are streamlined. Subsequent analysis (see step 3) showed that smooth sample M 0 Numerical simulation at the time of direct navigation has higher accuracy.
Step 2: for smooth sample M 0 Measuring total resistance F 0 ；
According to the appearance and the size of the test object, a smooth sample M with a hydraulically smooth surface is manufactured 0 Measuring the total resistance F under different flow conditions 0 As shown in table 1.
Table 1 total resistance measurement for each test piece
Step 3: CFD calculation of the total resistance F of the smooth sample 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 ；
Specifically, smooth sample M obtained by experimental measurement 0 Total resistance F of (2) 0 To validate the data, calculations were performed in a commercial CFD software STAR-CCM using the Reynolds Average (RANS) method in combination with the RNG k- ε turbulence model. In the aspect of calculating grids, boundary layer grids are adopted near the near wall surface, 12 layers are adopted, and the height y of the first layer of grids is + Let 30 be the grid growth rate 1.1. Calculating to obtain total resistance F of smooth sample 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 As shown in Table 2
TABLE 2 smooth sample CFD calculation results
| Water velocity V (m/s) | Total resistance F 0c (N) | Difference from the test value | Friction resistance f 0c (N) | Friction ratio a 0 |
| 6 | 35.9 | 3.5％ | 21.9 | 61.1％ |
| 8 | 59.1 | 3.1％ | 36.4 | 61.5％ |
| 10 | 85.8 | 0.5％ | 53.0 | 61.8％ |
| 12 | 116.2 | -1.0％ | 71.5 | 61.5％ |
| 14 | 156.8 | -1.8％ | 97.2 | 62.0％ |
As is clear from Table 2, the smooth sample M was in the range of 6 to 14M/s 0 The numerical simulation precision in direct navigation is high, and the deviation between the numerical simulation result of the total resistance and the test result is less than 3.5%. For differences from the test values, the test values are given in Table 1, e.g., 34.7N, and the total resistance F of the smooth sample calculated by CFD is given in Table 2 0c Such as 35.9N, where 35.9/34.7-1=3.5%, other calculations for differences from the test values are referred to herein and are not illustrated.
Step 4: control M d Test sample M s Respectively measuring and obtaining total resistance F d 、F s And calculate the reduced total resistivity DR F ；
According to the appearance and the size of the test object, a control sample M without antifriction scheme is prepared d And test sample M containing antifriction and resistance protocol s Respectively measuring and obtaining the total resistance F of the two d 、F s As shown in Table 1, a test sample relative control M was calculated as described above d Is the reduced total resistivity DR of (2) F As shown in table 3.
TABLE 3 test sample vs. control sample M d Is to be used as a damping effect of (a)
Step 5: calculating the friction ratio a of the control sample d ；
According to the control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Friction ratio a of smooth sample 0 The friction ratio a of the control sample is calculated in the above manner d As shown in table 4.
TABLE 4 friction ratio of control sample
| Water velocity V (m/s) | Friction ratio a d |
| 6 | 63.4％ |
| 8 | 66.0％ |
| 10 | 68.1％ |
| 12 | 69.8％ |
| 14 | 71.1％ |
Step 6: calculating the friction-reducing resistance DR f 。
According to the reduced total resistivity DR F Friction ratio a of the control sample d The test sample relative control M was calculated as described above d Is the antifriction rate DR of (2) f As shown in table 3.
In summary, when the test object and the resistance measuring device form a combined streamline object, the smooth sample M can be obtained through CFD calculation 0 Is a smooth sample of friction resistance f 0c Smooth sample friction ratio a 0 And reference sample M d And smooth sample M 0 The external dimensions (and thus the viscous pressure resistance) are the same, and the control sample M can be calculated d Friction ratio a of control sample of (2) d Further based on the friction ratio a of the control sample d Analysis of test sample M s Relative control M d The friction reducing effect of (1) can be determined f 。
It should be noted that the above description is illustrative of the invention and not limiting the invention, and the scope of the invention is defined by the claims, and any modification can be made within the scope of the invention.
Claims (7)
1. The quantitative analysis method suitable for the friction reducing resistance effect under the external flow condition is characterized by comprising the following steps:
designing a streamline test object, wherein the designed streamline test object comprises a test sample M with a friction reducing scheme s Not involving friction reductionControl M of resistance scheme d Smooth sample M with hydraulically smooth surface 0 Test sample M s Control M d Smooth sample M 0 At least have the same external dimensions;
configuring a preset flow condition set for quantitative analysis, wherein at least one preset flow condition in the preset flow condition set is selected during quantitative analysis, and the test sample M is subjected to the selected preset flow condition s Control M d Smooth sample M 0 Measuring total resistance to obtain test samples M s Total resistance F of (2) s Control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 ；
Based on smooth sample M 0 Total resistance F of (2) 0 Calculating to generate the smooth sample M 0 Total resistance F of smooth sample under selected preset flow conditions 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 ；
Based on test sample M s Total resistance F of (2) s Control M d Total resistance F of (2) d Calculating the subtracted total resistivity DR at selected preset flow conditions F ；
Based on control M d Total resistance F of (2) d Smooth sample M 0 Total resistance F of (2) 0 Smooth sample friction ratio a 0 Calculating and generating a friction ratio a of the control sample d ；
Based on the reduced total resistivity DR F Friction ratio a of control sample d Calculating test sample M s Relative control M d Is the antifriction rate DR of (2) f 。
2. A method for quantitative analysis of the effect of friction-reducing resistance under outflow conditions according to claim 1, wherein the design of streamline test objects is based on flow conditions, wherein,
the flow conditions include a flow rate and a reynolds number.
3. The adaptation of claim 1A quantitative analysis method for the effect of friction reduction resistance under outflow condition is characterized by measuring smooth sample M 0 Total resistance F of (2) 0 Then, the corresponding smooth sample total resistance F is generated through CFD calculation 0c Friction resistance f of smooth sample 0c Smooth sample friction ratio a 0 Wherein, the method comprises the steps of, wherein,
when CFD calculation is adopted, the configured calculation conditions include CFD method type, turbulence model and grid division strategy.
4. A method for quantitative analysis of the effect of friction reduction resistance under an outflow condition as claimed in claim 3, wherein the friction ratio of the smooth sample is a 0 The following steps are:
5. a method for quantitative analysis of the effect of friction-reducing resistance under external flow conditions according to any one of claims 1 to 4, characterized by the fact that, for the total resistance DR reduced under selected preset flow conditions F The following steps are:
6. a quantitative analysis method for a friction reducing resistance effect under an outflow condition according to claim 5, wherein a reference friction ratio a is calculated d The following steps are:
7. a method for quantitative analysis of the effect of friction reduction resistance under an outflow condition according to claim 5, wherein the test sample M s Relative control M d Is the antifriction rate DR of (2) f The following steps are:
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