A small and medium scale propeller scale effect correction method based on thrust equivalence

Abstract

This invention belongs to the field of ship model testing. It discloses a method for correcting the scale effect of small-to-medium-scale propellers based on thrust equivalence. The method determines the propeller scaling ratio corresponding to the test based on test requirements and the actual size parameters of the full-scale propeller, and fabricates a small-scale propeller that meets the geometric requirements of the propeller according to the scaling ratio. The thrust coefficient of the small-scale propeller at different advance speeds is obtained through open-water tests, and thrust coefficient curves at different advance speeds are plotted. By comparing the thrust coefficient curve of the small-scale propeller with the target thrust coefficient curve of the full-scale propeller, it is determined whether a scale effect exists in the small-scale propeller. If a scale effect exists, the test results of the small-scale propeller are corrected for scale equivalence data with the target thrust of the full-scale propeller using the thrust equivalence method. Subsequent full-scale ship performance predictions are conducted based on the scale equivalence data correction of the test data points, assisting in the design and optimization of ship type and propeller matching.

Description

Technical Field

[0001] This invention relates to the field of ship model testing, and more specifically, to a method for correcting the scale effect of small- and medium-scale propellers based on thrust equivalence. Background Technology

[0002] In ship model testing, some tests, such as ship model self-propulsion tests and dynamic positioning model tests, require the installation of a propulsion system of the same scale as the ship model on the ship model. By carrying out corresponding model tests, the actual working conditions are simulated to evaluate the thrust, efficiency and other characteristics of the propeller behind the ship, so as to ensure that the propeller can generate appropriate thrust to effectively propel the ship in actual operation and assist the ship-propeller matching design.

[0003] However, in conducting ship model tests, especially self-propelled model tests, a large scale ratio is required to ensure the collection of sufficiently long stable-state data during self-propelled operation, given the limitations of the test site size. Such a scale ratio may be too large for the propeller at the stern, causing the scaled-down propeller to fail to meet the critical Reynolds number requirement. This results in a difference between the flow state on the blade cross-section of the small-scale model propeller and the actual propeller, leading to a scale effect. This causes differences in the propulsion performance and efficiency of the small-scale propeller compared to the actual propeller, thus increasing the systematic error in the self-propelled test results.

[0004] Therefore, when using experimental results obtained from small-scale propellers for real-scale forecasting, a certain method is needed to correct the scale effect of small-scale propellers. This invention provides a method for correcting the scale effect of small- and medium-scale propellers based on thrust equivalence. Summary of the Invention

[0005] To address the problem that the thrust performance of small-scale propellers with large scale ratios changes due to scale effects during self-propulsion tests, dynamic positioning tests, or other ship model tests, making it impossible to use the test results for full-scale prediction, this invention proposes a method for correcting the scale effect of small- and medium-scale propellers based on thrust equivalence.

[0006] According to one aspect of the present invention, a method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence is provided, comprising the following steps:

[0007] S1. Determine the propeller scaling ratio corresponding to the test based on the test requirements and the actual size parameters of the real-scale propeller, and manufacture a small-scale propeller that meets the geometric requirements of the propeller based on the propeller scaling ratio.

[0008] S2. Obtain the thrust coefficient of small-scale propellers at different advance speeds through open water tests, and plot the thrust coefficient curves at different advance speeds;

[0009] S3. By comparing the thrust coefficient curve of the small-scale propeller with the target thrust coefficient curve of the real-scale propeller, determine whether there is a scale effect of the small-scale propeller; if there is a scale effect, correct the test results of the small-scale propeller and the target thrust of the real-scale propeller by scale equivalent data according to the thrust equivalence method.

[0010] S4. Based on the corrected test data points from the scale equivalent data, conduct subsequent real-ship performance forecasts to assist in the design and optimization of ship type and propeller matching.

[0011] In a preferred embodiment, the thrust coefficient curve of the small-scale propeller and the target thrust coefficient curve of the full-scale propeller are compared and analyzed using a formula, wherein the formula is:

[0012]

[0013] Where J is the advance coefficient; K T K represents the thrust coefficient of a small-scale propeller at this advance speed. Tm (J i J is the advance coefficient. i The target thrust coefficient of the small-scale propeller in the model; K Ts (J i J is the advance coefficient. i The target thrust coefficient of the propeller at the real scale; P is the maximum allowable thrust coefficient error ratio.

[0014] In a preferred embodiment, the specific logic regarding whether the small-scale propeller exhibits a scale effect is as follows:

[0015] If the propulsion coefficient of the small-scale propeller does not satisfy formula (1), then the small-scale propeller has a scale effect, and the data obtained after conducting experiments using the small-scale propeller needs to be corrected.

[0016] If the propulsion coefficient of a small-scale propeller satisfies formula (1), then the small-scale propeller does not have a scale effect and does not need to be corrected.

[0017] In a preferred embodiment, the thrust equivalence method specifically includes the following logic:

[0018] S31. Perform polynomial fitting on the thrust coefficient curve of the small-scale propeller, specifically using a cubic or quadratic polynomial to obtain the fitting polynomial curve of the thrust coefficient with respect to the advance coefficient.

[0019] S32. For the advance speed and rotational speed test data points corresponding to the small-scale propeller extracted from the ship model test, calculate the first advance speed coefficient corresponding to the advance speed and rotational speed test data points, substitute the calculated first advance speed coefficient into the fitting polynomial curve in S31, calculate the first thrust coefficient of the advance speed and rotational speed test data points, and further calculate the first thrust value of the advance speed and rotational speed test data points based on the first thrust coefficient.

[0020] S33. Based on the rated thrust coefficient curve of the real-scale propeller, the first thrust value of the test data point is equivalent to the second thrust value of the real-scale propeller. Based on the relationship between thrust, thrust coefficient, and advance coefficient, the equation system with the rotational speed of the real-scale propeller as the unknown is solved to obtain the second thrust coefficient of the real-scale propeller under the same advance speed and thrust as the small-scale propeller. The advance speed and rotational speed data points corresponding to the second thrust coefficient are used as the test data points after the scale equivalent data correction.

[0021] S34. Repeat S32-S33, and substitute the remaining data points obtained from the experiment using small-scale propellers into the solution to obtain the scale effect corrected experimental data points.

[0022] In a preferred embodiment, the relationship between the advance coefficient J and the advance speed v and rotational speed n can be expressed as: J = v / nD, where D is the diameter of the experimental small-scale propeller.

[0023] In a preferred embodiment, the thrust value T and the thrust coefficient K T The relationship can be expressed as T = K T ρn 2 D 4 ρ is the density of water during the experiment.

[0024] The technical effects and advantages of the present invention regarding a method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence are as follows:

[0025] 1. This invention addresses the thrust performance variations caused by scale effects during self-propelled tests or other ship model tests of large-scale, small-scale propellers. By fitting the thrust coefficient curve of the small-scale propeller and constructing a set of equivalent thrust equations based on constant thrust conditions, the rotational speed of the full-scale propeller can be calculated. This method can correct experimental data, reducing systematic errors caused by scale effects, thereby improving the usability of experimental results and minimizing systematic errors arising from testing with large-scale, small-scale propellers.

[0026] 2. Based on the condition of equal thrust, this invention constructs a set of thrust equivalent equations and solves them to obtain the rotational speed of a real-scale propeller with the same thrust as a small-scale propeller. This allows for more efficient calculation of the rotational speed of a real-scale propeller, thereby saving calculation time and facilitating the correction of scale effects in experiments using small-scale propellers. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for correcting the scale effect of small and medium-scale propellers based on thrust equivalence in this invention.

[0028] Figure 2 This is a small-scale propeller diagram from the present invention;

[0029] Figure 3 This is a curve showing the thrust coefficient of a small-scale propeller at different advance speeds obtained from ship model tests in this invention. Detailed Implementation

[0030] 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.

[0031] To address the scale effect problem that may occur in self-propelled tests or other ship model tests of small-scale propellers with large scale ratios, and to reduce the systematic error between test results and actual scale predictions, this invention improves the test method to enhance the accuracy and applicability of scale effect correction for small- and medium-scale propellers.

[0032] Example 1

[0033] Please see Figure 1 As shown in the figure, the method for correcting the scale effect of small and medium-scale propellers based on thrust equivalence described in this embodiment includes the following steps:

[0034] S1. Determine the propeller scaling ratio corresponding to the test based on the test type, test site size, actual ship size, and actual propeller size parameters, and manufacture a small-scale propeller that meets the propeller geometry requirements based on the propeller scaling ratio.

[0035] It should be noted that the size ratio between the full-scale propeller and the small-scale propeller is the propeller scaling ratio. The small-scale propeller that conforms to the geometry is determined based on the propeller scaling ratio.

[0036] The specific requirements for the test include, but are not limited to, the type of test, the size of the test site, and the actual dimensions of the ship.

[0037] S2. Obtain the thrust coefficient of small-scale propellers at different advance speeds through open water tests, and plot the thrust coefficient curves at different advance speeds;

[0038] It should be noted here that open-water tests can obtain the advance speed and rotational speed corresponding to small-scale propellers. During the test, the relationship between the advance speed coefficient J and the advance speed v and rotational speed n can be expressed as: J = v / nD, where D is the diameter of the small-scale propeller being tested. Thrust value T and thrust coefficient K T The relationship can be expressed as T = K T ρn 2 D 4 ρ is the density of water during the experiment;

[0039] S3. By comparing the thrust coefficient curve of the small-scale propeller with the target thrust coefficient curve of the real-scale propeller, determine whether there is a scale effect of the small-scale propeller; if there is a scale effect, correct the test results of the small-scale propeller and the target thrust of the real-scale propeller by scale equivalent data according to the thrust equivalence method.

[0040] The thrust coefficient curves of small-scale propellers and the target thrust coefficient curves of full-scale propellers are compared and analyzed using a formula, where the formula is:

[0041]

[0042] Where J is the advance coefficient; K T K represents the thrust coefficient of a small-scale propeller at this advance speed. Tm (J i J is the advance coefficient. i The target thrust coefficient of the small-scale propeller in the model; K Ts (J i J is the advance coefficient. i The target thrust coefficient of the propeller at the real scale; P is the maximum allowable thrust coefficient error ratio.

[0043] It should be noted here that: considering the impact of scale effect on the test results of small-scale propellers, the actual thrust coefficient of small-scale propellers is obtained through open-water tests. Based on the obtained thrust coefficient, the thrust of the actual-scale propellers and the small-scale propellers are made equivalent, thereby correcting the thrust difference caused by scale effect.

[0044] The specific logic regarding whether the small-scale propeller exhibits a scale effect is as follows:

[0045] If the propulsion coefficient of the small-scale propeller does not satisfy formula (1), then the small-scale propeller has a scale effect, and the data obtained after conducting experiments using the small-scale propeller needs to be corrected.

[0046] If the propulsion coefficient of a small-scale propeller satisfies formula (1), then the small-scale propeller does not have a scale effect and does not need to be corrected.

[0047] The thrust equivalence method specifically includes the following logic:

[0048] S31. Perform polynomial fitting on the thrust coefficient curve of the small-scale propeller, specifically using a cubic or quadratic polynomial to obtain the fitting polynomial curve of the thrust coefficient with respect to the advance coefficient.

[0049] S32. For the advance speed and rotational speed test data points corresponding to the small-scale propeller extracted from the ship model test, calculate the first advance speed coefficient corresponding to the advance speed and rotational speed test data points. Substitute the calculated first advance speed coefficient into the fitted polynomial curve in S31 to calculate the first thrust coefficient of the advance speed and rotational speed test data points. Based on the first thrust coefficient, further calculate the first thrust value of the advance speed and rotational speed test data points. The relationship between the advance speed coefficient J and the advance speed v and rotational speed n can be expressed as: J = v / nD, where D is the diameter of the small-scale propeller in the test. Thrust value T and thrust coefficient K... T The relationship can be expressed as T = K T ρn 2 D 4 ρ is the density of water during the experiment.

[0050] S33. Based on the rated thrust coefficient curve of the real-scale propeller, the first thrust value of the test data point is equivalent to the second thrust value of the real-scale propeller. Based on the relationship between thrust, thrust coefficient, and advance coefficient, the equation system with the rotational speed of the real-scale propeller as the unknown is solved to obtain the second thrust coefficient of the real-scale propeller under the same advance speed and thrust as the small-scale propeller. The advance speed and rotational speed data points corresponding to the second thrust coefficient are used as the test data points after the scale equivalent data correction.

[0051] S34. Repeat S32-S33, and substitute the remaining data points obtained from the experiment using small-scale propellers into the solution to obtain the scale effect corrected experimental data points.

[0052] It should be noted that: based on the fitted small-scale propeller thrust coefficient curve, the thrust magnitude of the test data points is calculated and equivalent to the thrust of the real-scale propeller. The equation system is then solved to obtain the propeller thrust coefficient that conforms to the real-scale propeller thrust coefficient at the same advance speed with the same thrust as the small-scale propeller, which is the propeller speed that conforms to the hydrodynamic characteristics of the real-scale propeller. Based on the test data points, the corrected test data points can be easily calculated, reducing the systematic error of the test using a large-scale propeller with a large scale ratio.

[0053] S4. Based on the corrected test data points from the scale equivalent data, conduct subsequent real-ship performance forecasts to assist in the design and optimization of ship type and propeller matching.

[0054] Example 2

[0055] This embodiment mainly uses specific examples to explain the method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence, including the following steps:

[0056] S1: Based on the dimensions of the test tank and the actual ship dimensions, the propeller scaling ratio is determined to be 50. Figure 2 A small-scale model of a certain type of propeller with a 50 scale reduction ratio, its diameter is 75mm, which is relatively small.

[0057] S2: Obtain the thrust of the small-scale propeller at different advance speeds through open water tests. Calculate the thrust coefficient of the small-scale propeller based on the test results and plot the thrust coefficient curves at different advance speeds. Figure 3 The thrust coefficient curves of the small-scale propeller at different advance speeds obtained from the experiment are shown; where the experimental value is the thrust coefficient measured in the experiment of the small-scale propeller, and the target value is the thrust coefficient of the corresponding real-scale propeller.

[0058] S3: By comparing the thrust coefficient curve test results of the small-scale propeller with the target thrust coefficient curve of the full-scale propeller, determine whether there is a scale effect for this type of propeller at this scale. According to the formula, MAX(p) = 0.27 > 0.05, indicating that a scale effect exists, and the data obtained after conducting tests using the small-scale propeller needs to be corrected.

[0059] S31: A cubic polynomial was used to fit the small-scale propeller thrust coefficient curve obtained from the open-water test to obtain the thrust coefficient K. T The fitted polynomial curve for the advance coefficient J is as follows:

[0060] K T =0.23326J 3 -0.3439J 2 -0.2847J +0.3393

[0061] S32: Based on the specific small-scale propeller advance speed of 0.31 m / s and rotational speed of 17 rps obtained in the ship self-propelled model test, the advance coefficient at this point is calculated to be 0.243. Substituting this calculated advance coefficient value into the polynomial curve fitted in S4, the thrust coefficient at this point is calculated to be 0.253. Based on the thrust coefficient, the first thrust value at this data point is further calculated to be 2.373 kg.

[0062] S33: Based on the thrust coefficient curve of a real-scale propeller, the first thrust value at the experimental data point is equivalent to the second thrust value of the real-scale propeller. Based on the relationship between thrust, thrust coefficient, and advance coefficient, the system of equations with the rotational speed n of the real-scale propeller as the unknown is solved:

[0063]

[0064] Where f(J) is the thrust coefficient of the real-scale propeller as a function of the advance coefficient, and T1 is the thrust value calculated in step S32;

[0065] The thrust coefficient of a real-scale propeller, which corresponds to the thrust of a small-scale propeller at the same advance speed, was obtained as 13.3 rps, indicating that the propeller speed conforms to the hydrodynamic characteristics of a real-scale propeller. The advance speed and rotational speed data points of this real-scale propeller were used as the corrected experimental data points.

[0066] S34: Repeat S32-S33, substituting the remaining data points obtained from the experiment using small-scale propellers into the solution to obtain the scale-effect corrected experimental data points. A set of experimental data points obtained during the experiment is shown in Table 1. The scale-effect corrected data points obtained from steps 5 and 6 are shown in Table 2.

[0067] Vmi(m / s) 0.31 0.2 0.31 0.4 0.51 0.61 Nmi(rps) 17 17.5 17.9 12 19 19.6

[0068] Table 1. Test data points for small-scale propellers

[0069]

[0070]

[0071] Table 2 shows the data points after scale effect correction.

[0072] S34: Based on the scale effect-corrected test data points, conduct subsequent real-ship performance forecasts to assist in the design and optimization of ship type and propeller matching.

[0073] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters and thresholds in the formulas are set by those skilled in the art according to the actual situation.

[0074] In the several embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only one method, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0075] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0076] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0078] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence, characterized in that, Includes the following steps: S1. Determine the propeller scaling ratio corresponding to the test based on the test requirements and the actual size parameters of the real-scale propeller, and manufacture a small-scale propeller that meets the geometric requirements of the propeller based on the propeller scaling ratio. S2. Obtain the thrust coefficient of small-scale propellers at different advance speeds through open water tests, and plot the thrust coefficient curves at different advance speeds; S3. By comparing the thrust coefficient curve of the small-scale propeller with the target thrust coefficient curve of the real-scale propeller, determine whether there is a scale effect of the small-scale propeller; if there is a scale effect, correct the test results of the small-scale propeller and the target thrust of the real-scale propeller by scale equivalent data according to the thrust equivalence method. S4. Based on the corrected test data points from the scale equivalent data, conduct subsequent real-ship performance forecasts to assist in the design and optimization of ship type and propeller matching. The thrust equivalence method specifically includes the following logic: S31. Perform polynomial fitting on the thrust coefficient curve of the small-scale propeller, specifically using a cubic or quadratic polynomial to obtain the fitting polynomial curve of the thrust coefficient with respect to the advance coefficient. S32. For the test data points of advance speed v and rotational speed n corresponding to the small-scale propeller extracted from the ship model test, calculate the first advance speed coefficient corresponding to the advance speed and rotational speed test data points, substitute the calculated first advance speed coefficient into the fitting polynomial curve in S31, calculate the first thrust coefficient of the advance speed and rotational speed test data points, and further calculate the first thrust value of the advance speed and rotational speed test data points based on the first thrust coefficient. S33. Based on the rated thrust coefficient curve of the real-scale propeller, the first thrust value of the test data point is equivalent to the second thrust value of the real-scale propeller. Based on the relationship between thrust, thrust coefficient, and advance coefficient, the equation system with the rotational speed of the real-scale propeller as the unknown is solved to obtain the second thrust coefficient of the real-scale propeller under the same advance speed and thrust as the small-scale propeller. The advance speed and rotational speed data points corresponding to the second thrust coefficient are used as the test data points after the scale equivalent data correction. S34. Repeat S32-S33, and substitute the remaining data points obtained from the experiment using small-scale propellers into the solution to obtain the scale effect corrected experimental data points.

2. The method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence according to claim 1, characterized in that, The thrust coefficient curves of small-scale propellers and the target thrust coefficient curves of full-scale propellers are compared and analyzed using a formula, where the formula is: （1） in, This is the advance coefficient; This represents the thrust coefficient of a small-scale propeller at this advance rate; Precession coefficient The target thrust coefficient of the small-scale propeller in the lower model; Precession coefficient Target thrust coefficient of a propeller with actual dimensions; This represents the maximum permissible thrust coefficient error ratio.

3. The method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence according to claim 2, characterized in that, The specific logic regarding whether the small-scale propeller exhibits a scale effect is as follows: If the propulsion coefficient of the small-scale propeller does not satisfy formula (1), then the small-scale propeller has a scale effect and the data obtained after the experiment using the small-scale propeller needs to be corrected. If the propulsion coefficient of a small-scale propeller satisfies formula (1), then the small-scale propeller does not have a scale effect and does not need to be corrected.

4. The method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence according to claim 3, characterized in that, Precession coefficient With advance Rotation speed The specific calculation formula is as follows: ； Among them, the advance coefficient With advance Rotation speed Relationship, To test the diameter of a small-scale propeller.

5. The method for correcting the scale effect of small-to-medium scale propellers based on thrust equivalence according to claim 4, characterized in that, Thrust value With thrust coefficient The specific calculation formula is as follows: ， in, This represents the density of water during the experiment.

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