Automatic positioning method of common operating point of double-ducted fans based on Newton iteration model

Abstract

The present invention relates to an automatic positioning method for the common operating point of a dual-duct fan based on a Newton iteration model, including linear fitting of two common working lines of the inner and outer ducts of the dual-duct fan respectively; selecting the inner and outer duct outlet backpressure disturbances, and solving the inner and outer duct outlet backpressure flow fields before and after the disturbances; and then using the finite difference method to obtain the Jacobian matrix of the inner and outer duct common working line distance to the inner and outer duct outlet backpressures, thereby iterating based on the Newton method to obtain the change in the inner and outer duct outlet backpressures, and iterating with the Newton method until the distance between the updated operating point and the common working line is less than a preset error, and successfully automatically positioning the common operating point of the dual-duct fan. The present invention is a new method for quickly, accurately, and automatically positioning the common operating point of a dual-duct fan, which improves research efficiency, shortens R&D time, and reduces design costs, and strongly supports and promotes the research and design of dual-duct fans.

Description

Technical Field

[0001] The invention relates to the field of dual-duct fans of aircraft engines, and in particular to a method for positioning a common operating point of a dual-duct fan. Background Art

[0002] With the rapid development of the domestic large aircraft C919, the dream of large aircraft for Chinese people has begun to become a reality. However, the engines currently installed in C919 are still manufactured in foreign countries. Therefore, breaking the technology monopoly of foreign companies and realizing the localization of large aircraft engines is the next technological peak we need to overcome. Turbofan engines are the mainstream choice of modern large aircraft engines due to their superior performance, economy and environmental adaptability. As a key component of turbofan engines, the dual-duct fan directly affects the engine's thrust, efficiency and noise level. Therefore, the research and design of the dual-duct fan is crucial to turbofan engines.

[0003] In the research and design process of the dual-duct fan, it is first necessary to locate the common operating point of the dual-duct fan, because this point is the design point of the dual-duct fan. The dual-duct fan has two ducts, the inner duct and the outer duct, corresponding to the two performance characteristic curves of the inner duct and the outer duct, and the entire engine also has two common working lines of the inner duct and the outer duct. The common operating point of the dual-duct fan refers to a special operating point, and its inner duct performance is located at the intersection of the inner duct performance characteristic curve and the inner duct common operating point, and its outer duct performance is also located at the intersection of the outer duct performance characteristic curve and the outer duct common working line.

[0004] When using numerical calculation methods to study and design dual-duct fan engines, the current common method for locating the common operating point is the trial and error method, that is, firstly, the inner duct and outer duct outlet back pressures of the common operating point are roughly located by calculating the inner duct and outer duct performance characteristic curves; then, the outlet back pressures of the inner duct and outer duct are manually adjusted by using the characteristic that the outlet back pressure is inversely proportional to the flow rate; then, the adjusted fan flow field is calculated to obtain a new operating point; then, according to the relative position of the new operating point and the common working line, the outlet back pressures of the inner duct and outer duct are manually adjusted again, and so on and so forth, until the correct inner duct and outer duct outlet back pressures are found, so that the corresponding operating points just fall on the common working line of the inner duct and outer duct at the same time. Due to the nonlinear relationship between performance and outlet back pressure, and the intertwined influence between the inner duct and the outer duct, the current trial and error method consumes a lot of time, manpower and other resources, and is inefficient.

[0005] Therefore, it is necessary to develop a new method that can quickly, accurately and automatically locate the common operating point of dual-ducted fans, so as to strongly support and promote the research and design of dual-ducted fans. Summary of the invention

[0006] The purpose of the present invention is to avoid the shortcomings of the existing trial and error method in locating the common operating point of the dual-duct fan, and to provide a new method that can quickly, accurately and automatically locate the common operating point of the dual-duct fan, so as to achieve faster, more accurate and better positioning of the common operating point, thereby improving research efficiency, shortening R&D time, and reducing design costs, and effectively supporting and promoting the research and design of dual-duct fans.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for automatically locating the common operating point of a double-ducted fan based on a Newton iteration model, comprising the following steps:

[0008] Step 1: Linearly fit the common working lines of the inner and outer ducts of the dual-duct fan respectively to obtain a calculation formula for the distance from the working point to the two common working lines; take the inner and outer duct outlet back pressures as independent variables and the distance from the working point to the two common working lines as dependent variables to construct a Newton iteration model for converting the common working point positioning problem into a numerical root-finding problem;

[0009] The initial back pressure at the inner and outer duct outlets is selected as the initial value of the Newton iteration model, and the iteration termination condition of the Newton iteration model is selected according to the required common operating point positioning accuracy;

[0010] Step 2: Calculate the operating point corresponding to the current back pressure at the inner and outer duct outlets, and obtain the distance from the operating point to the two common working lines according to the distance calculation formula, then select the disturbance amount, disturb the inner and outer duct outlet back pressures respectively, calculate the flow field of the inner and outer duct outlet back pressures after the disturbance, and obtain the distance from the operating point corresponding to the inner and outer duct outlet back pressures to the two common working lines according to the distance calculation formula;

[0011] Then, the finite difference method is used to obtain the Jacobian matrix of the inner and outer duct outlet back pressures before and after the disturbance and the distance between the corresponding operating point and the two common working lines, and the Newton iteration model is combined to iteratively obtain the change of the inner and outer duct outlet back pressures, and the inner and outer duct outlet back pressures are updated according to the change, and the flow field of the inner and outer duct outlet back pressures is calculated and updated to obtain the distance between the corresponding operating point and the two common working lines of the updated inner and outer duct outlet back pressures;

[0012] Step 3: If the distance between the operating point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines is less than the distance between the current actual operating point and the two common working lines, then on the basis of updating the inner and outer duct outlet back pressure, repeat step 2 to perform the next round of Newton iteration until the distance between the operating point and the two common working lines is less than the Newton iteration termination condition, that is, the automatic positioning of the common operating point of the dual duct fan is achieved;

[0013] Among them, if the distance between the updated operating point corresponding to the inner and outer duct outlet back pressure and the two common working lines is greater than the distance between the current operating point and the common working line, the change in the inner and outer duct outlet back pressure is reduced, and the inner and outer duct outlet back pressure is re-updated until the distance between the updated operating point corresponding to the inner and outer duct outlet back pressure and the common working line is less than the distance between the current operating point and the common working line.

[0014] Furthermore, in the step 1, linear fitting is performed on the common working lines of the inner and outer ducts, and the fitting equations obtained are:

[0015] ,

[0016] ,

[0017] Where: For flow, is the pressure ratio, and is the coefficient obtained by linear fitting the common working line of the connotation channel, and The coefficients obtained by linear fitting the common working line of the outer duct;

[0018] Then, the distance calculation formulas from any working point to the common working line of the inner and outer ducts are:

[0019] ,

[0020] ,

[0021] Where: is the distance from the working point to the common working line of the connotation road, It is the distance from the working point to the common working line of the outer duct;

[0022] At this time, the nonlinear vector equation based on the Newton iteration model is:

[0023] ,

[0024] Where: and are the inner and outer duct outlet back pressures respectively;

[0025] The and As the independent variable of the nonlinear vector equation, the and is the dependent variable of the nonlinear vector equation; finding the common operating point of the double duct fan is to find a pair of inner and outer duct outlet back pressures that are located on the common working line of the inner duct and the common working line of the outer duct. and The corresponding operating point corresponds to solving the nonlinear vector equation, that is, obtaining a pair of independent variables so that the dependent variables are both 0, and the relationship between the independent variables and the dependent variables is determined by the flow field of the back pressure at the inner and outer duct outlets;

[0026] Then, select the initial inner and outer duct outlet back pressure of the double duct fan and , as the initial value of the Newton iteration model, and the Newton iteration termination condition is selected according to the required common operating point positioning accuracy. and .

[0027] Furthermore, in the step 2, the current back pressure at the inner and outer duct outlets is first solved using a flow field solver. and Flow field corresponding to the operating point;

[0028] The inner and outer duct outlet back pressure before disturbance obtained by calculating the flow field is: , the external bypass flow is ; The internal pressure ratio is , the bypass pressure ratio is ;

[0029] Then, according to the distance calculation formula, the back pressure at the inner and outer duct outlets before the disturbance is obtained: and The distance from the corresponding working point to the two common working lines is and , the corresponding calculation formulas are:

[0030] ,

[0031] ,

[0032] Where: , , , is the coefficient obtained by linear fitting the common working line of the inner and outer ducts, and are the flow rate and pressure ratio of the inner channel, and are the flow rate and pressure ratio of the outer duct respectively;

[0033] Then, the disturbance of the back pressure at the inner and outer duct outlets is selected as and ;

[0034] The back pressures at the inner and outer duct outlets are disturbed by the disturbance amount respectively. After the disturbance, the back pressures at the inner and outer duct outlets are and ;

[0035] Then, the flow field solver is used to calculate the flow field after disturbing the back pressure at the inner and outer duct outlets, and the operating point corresponding to the back pressure at the inner duct outlet is obtained. And the operating point corresponding to the disturbed outer duct outlet back pressure ;

[0036] Finally, using the distance calculation formula, the distance from the corresponding working point of the inner and outer duct outlet back pressure after disturbance to the two common working lines is obtained as follows:

[0037] ,

[0038] In the formula, and To disturb the back pressure at the inner and outer duct outlets, and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts;

[0039] At this time, the first iteration in the Newton iteration step is to set the initial inner and outer duct outlet back pressure and As the current inner and outer duct outlet back pressure and ; In the subsequent Newton iteration step, the inner and outer duct outlet back pressures updated in the previous iteration step are and As the current inner and outer duct outlet back pressure and .

[0040] Furthermore, the selected disturbance and The back pressure at the inner and outer duct outlets before disturbance and 0.1%-1%.

[0041] Furthermore, in the step 2, the finite difference method is used to obtain the Jacobian matrix of the inner and outer duct outlet back pressures before and after the disturbance and the distance between the corresponding operating point and the two common working lines: , the specific formula is:

[0042] ,

[0043] Where: and are the outlet back pressure of the inner and outer ducts in the current iteration step, and are the disturbances of the back pressure at the inner and outer duct outlets, respectively. and are the back pressures at the inner and outer duct outlets after disturbance, respectively; and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts;

[0044] Next, the Newton iteration formula is used to obtain the current independent variable inner and outer duct outlet back pressure The change in and , the specific change formula is:

[0045] ,

[0046] Where: is the inverse matrix of the Jacobi matrix, Indicates multiplication of numbers, Represents matrix and vector multiplication.

[0047] Further, based on the change and To update the current inner and outer duct outlet back pressure and , updated inner and outer duct outlet back pressure and for:

[0048] ,

[0049] In the formula, the superscript Indicates the updated inner and outer duct outlet back pressure;

[0050] Based on the updated inner and outer duct outlet back pressure and , use the flow field solver to solve the flow field corresponding to the new inner and outer duct outlet back pressure, and obtain the distance between the working point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines and .

[0051] Furthermore, if the distance and The second norm of The second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , which reduces the distance from the working point to the two common working lines;

[0052] If the distance and The second norm of Greater than the second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , it is necessary to reduce the change in the back pressure at the inner and outer duct outlets, and repeat the Newton iteration step based on the reduced change in the back pressure at the inner and outer duct outlets until the distance and The second norm of The second norm of the distance between the working point corresponding to the back pressure at the inner and outer duct outlets before the disturbance and the two common working lines .

[0053] Further, in step 3, based on updating the back pressure at the outlet of the inner and outer ducts and The distance between the operating point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines is and If the distance and Both are less than the Newton iteration termination condition and , it means that the common operating point of this dual-duct fan has been successfully found, so the Newton iteration is exited, otherwise the next round of Newton iteration is performed.

[0054] The beneficial effects of the present invention are as follows: the present invention realizes automatic positioning of the common operating point of the dual-duct fan by establishing a Newton iteration model, thereby achieving faster, more accurate and better positioning of the common operating point of the dual-duct fan, thereby improving research efficiency, shortening R&D time, and reducing design costs, and strongly supporting and promoting the research and design of dual-duct fans.

[0055] Among them, in the whole process, the present invention firstly utilizes the second-order convergence characteristics of Newton's iteration method to make the whole process converge quickly and locate the common operating point more quickly; secondly, the present invention realizes the quantification of the distance between the operating point and the common working line, so that this method can locate the common operating point more accurately; finally, the whole process of the present invention is realized by an iterative algorithm, without any manual operation, so that the whole process is fully automated. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow field diagram of the method for automatically locating the common operating point of a double-ducted fan of the present invention;

[0057] Figure 2 It is a schematic diagram of the fitting effect of the connotation common working line;

[0058] Figure 3 It is a schematic diagram of the fitting effect of the external common working line;

[0059] Figure 4It is a schematic diagram of the change process of the connotation operating point in the process of automatically finding the common operating point;

[0060] Figure 5 It is a schematic diagram of the change process of the external operating point in the process of automatically finding the common operating point;

[0061] Figure 6 It is a schematic diagram of the change of the distance between the operating point and the common working line of the inner channel / outer channel during the iteration process. DETAILED DESCRIPTION

[0062] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0063] In order to achieve the above object, the present invention provides the following specific implementation methods:

[0064] Example 1: Figure 1 As shown, a method for automatically locating a common operating point of a double-ducted fan based on a Newton iteration model comprises the following steps:

[0065] S01. Linear fitting is performed on the common working lines of the inner and outer ducts of the dual duct fan, and the fitting equations obtained are:

[0066] ,

[0067]

[0068] Where: For flow, is the pressure ratio, and is the coefficient obtained by linear fitting the common working line of the connotation channel, and are the coefficients obtained by linearly fitting the common working line of the outer duct.

[0069] Then, the distance calculation formulas from any working point to the common working line of the inner and outer ducts are:

[0070] ,

[0071] ,

[0072] Where: is the distance from the working point to the common working line of the connotation road, It is the distance from the working point to the common working line of the outer duct;

[0073] At this time, the nonlinear vector equation based on the Newton iteration model is:

[0074]

[0075] Where: and They are the outlet back pressure of the inner duct and the outer duct respectively.

[0076] The and As the independent variable of the nonlinear vector equation, the and is the dependent variable of the nonlinear vector equation; finding the common operating point of the double duct fan is to find a pair of inner and outer duct outlet back pressures that are located on the common working line of the inner duct and the common working line of the outer duct. and The corresponding operating point corresponds to solving the nonlinear vector equation, that is, obtaining a pair of independent variables so that the dependent variables are both 0, and the relationship between the independent variables and the dependent variables is determined by the flow field of the back pressure at the inner and outer duct outlets;

[0077] Then, select the initial inner and outer duct outlet back pressure of the double duct fan and , as the initial value of the Newton iteration model, and the Newton iteration termination condition is selected according to the required common operating point positioning accuracy. and .

[0078] S02. Use the flow field solver to solve the current inner and outer duct outlet back pressure and The flow field corresponding to the working point; the inner and outer duct outlet back pressure before disturbance obtained by calculating the flow field is , the external bypass flow is ; The internal pressure ratio is , the bypass pressure ratio is ;

[0079] Then, according to the distance calculation formula obtained in step S01, the back pressure at the inner and outer duct outlets before the disturbance is obtained: and The distance from the corresponding working point to the two common working lines is and , the corresponding calculation formulas are:

[0080] ,

[0081] ,

[0082] Where: , , , is the coefficient obtained by linear fitting the common working line of the inner and outer ducts, and are the flow rate and pressure ratio of the inner channel, and are the flow rate and pressure ratio of the outer duct respectively;

[0083] Then, the back pressure disturbance at the inner and outer duct outlets is selected as and ;

[0084] The back pressures at the inner and outer duct outlets are disturbed by the disturbance amount respectively. After the disturbance, the back pressures at the inner and outer duct outlets are and ;

[0085] Then, the flow field solver is used to calculate the flow field after disturbing the back pressure at the inner and outer duct outlets, and the operating point corresponding to the back pressure at the inner duct outlet is obtained. And the operating point corresponding to the disturbed outer duct outlet back pressure ;

[0086] Finally, using the distance calculation formula, the distance from the corresponding working point of the inner and outer duct outlet back pressure after disturbance to the two common working lines is obtained as follows:

[0087] ,

[0088] In the formula, and To disturb the back pressure at the inner and outer duct outlets, and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts;

[0089] At this time, in the first Newton iteration step, the initial inner and outer duct outlet back pressure is and As the current inner and outer duct outlet back pressure and ; In the subsequent Newton iteration step, the inner and outer duct outlet back pressures updated in the previous iteration step are and As the current inner and outer duct outlet back pressure and .

[0090] S03. In step S02, the selected disturbance and The back pressure at the inner and outer duct outlets before disturbance and 0.1%-1%.

[0091] S04. Apply the finite difference method to obtain the Jacobian matrix of the inner and outer duct outlet back pressure before and after the disturbance and the distance between the corresponding operating point and the two common working lines. , the specific calculation formula is:

[0092] ,

[0093] Where: and are the outlet back pressure of the inner and outer ducts in the current iteration step, and are the disturbances of the back pressure at the inner and outer duct outlets, respectively. and are the back pressures at the inner and outer duct outlets after disturbance, respectively; and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts;

[0094] Next, the Newton iteration formula is used to obtain the current independent variable inner and outer duct outlet back pressure The change in and , the specific change formula is:

[0095] ,

[0096] Where: is the inverse matrix of the Jacobi matrix, Indicates multiplication of numbers, Represents matrix and vector multiplication.

[0097] S05, based on the amount of change and To update the current inner and outer duct outlet back pressure and , updated inner and outer duct outlet back pressure and for:

[0098] ,

[0099] In the formula, the superscript Indicates the updated inner and outer duct outlet back pressure;

[0100] Based on the updated inner and outer duct outlet back pressure and , use the flow field solver to solve the flow field corresponding to the new inner and outer duct outlet back pressure, and obtain the distance between the working point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines and .

[0101] S06. Analyze and judge the results in step S05.

[0102] If the distance and The second norm of The second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , which reduces the distance from the working point to the two common working lines;

[0103] If the distance and The second norm of Greater than the second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , it is necessary to reduce the change in the back pressure at the inner and outer duct outlets, and repeat the Newton iteration step based on the reduced change in the back pressure at the inner and outer duct outlets until the distance and The second norm of The second norm of the distance between the working point corresponding to the back pressure at the inner and outer duct outlets before the disturbance and the two common working lines .

[0104] S08, based on the updated inner and outer duct outlet back pressure and The distance between the operating point corresponding to the back pressure of the inner and outer duct outlets after the update and the two common working lines and , if the distance and Both are less than the Newton iteration termination condition and , it means that the common operating point of this dual-duct fan has been successfully found, so the Newton iteration is exited, otherwise the next round of Newton iteration is performed.

[0105] In order to explain the purpose, technical solution and advantages of the present invention in more detail, a double duct fan is used as an example for further detailed description:

[0106] Example: Figures 2 to 6 As shown, this example uses a self-programmed method to develop a program for automatically locating the common operating point of a dual-duct fan. The programming language is Python. The flow field solver in the example uses the self-developed program NutsCFD. Among them, all data are scaled to the corresponding integer power of 10. The specific steps used in this example are:

[0107] S01. Linear fitting is performed on the two common working lines of the inner and outer ducts of the double duct fan, and the obtained fitting equations are:

[0108]

[0109] Where: For flow, is the pressure ratio.

[0110] The fitting effects of the common working line of the inner channel and the common working line of the outer channel are as follows: Figure 2 , Figure 3 As shown; it can be seen that the linear fitting effect captures the trend and changes of the original data of the working line of the inner channel and the outer channel very well.

[0111] After completing the linear fitting, the distance calculation formula from the working point to the common working line of the inner channel / outer channel can be obtained according to the distance formula from the point to the straight line:

[0112] ,

[0113] Where: is the distance from the working point to the common working line of the connotation road, It is the distance from the working point to the common working line of the external duct.

[0114] At this point, the Newton iteration model can be introduced to convert the physical problem of locating the common operating point of the dual-ducted fan into the mathematical problem of finding the roots of a nonlinear vector equation. The corresponding nonlinear vector equation is:

[0115] ,

[0116] Where: and They are the outlet back pressure of the inner duct and the outer duct respectively.

[0117] In the mathematical problem of finding the roots of this vector equation, the distance between the inner channel and the outer channel working line and is the dependent variable of the nonlinear vector equation, and and is the independent variable of the nonlinear vector equation.

[0118] The physical definition of the common operating point is: the operating point that falls on the common working line of the inner channel and the outer channel at the same time. Numerically locating the common operating point is to find a pair of inner channel and outer channel outlet back pressure and This operating point is located on the common working line of the inner channel on the inner channel performance characteristic diagram, and on the outer channel performance characteristic diagram. This corresponds to solving this nonlinear vector equation and obtaining a pair of independent variables inner channel / outer channel outlet back pressure and , so that the distance between the dependent variable inner channel and outer channel common working line and Both are 0.

[0119] First, the initial outlet back pressure is selected according to the known inner channel / outer channel common working line and the inner channel / outer channel performance characteristic curve. and , and select the Newton iteration method termination condition according to the required common operating point positioning accuracy and .

[0120] S02. Calculate the current outlet back pressure (this is the first step of iteration, and the current outlet back pressure is the initial outlet back pressure) and The flow field is obtained by looking at the inner channel and the outer channel flow rate and pressure ratio. , internal pressure ratio , bypass flow , bypass pressure ratio .

[0121] According to the distance calculation formula obtained in S01, the distance between the operating point corresponding to the current outlet back pressure and the common working line of the inner channel / outer channel can be calculated:

[0122] ,

[0123] Then, select the back pressure disturbance at the inner channel / outer channel outlet and , select , .

[0124] The back pressures at the inner and outer duct outlets are disturbed by the disturbance amount respectively. After the disturbance, the back pressures at the inner and outer duct outlets are and .

[0125] Next, the flow field solver NutsCFD is used to calculate the flow field after disturbing the back pressure at the inner and outer duct outlets. Specifically, the operating point corresponding to the back pressure at the inner duct outlet is (hereinafter referred to as operating condition A) and the operating point corresponding to the disturbed outer duct outlet back pressure (hereinafter referred to as working condition B) flow field.

[0126] The internal flow rate of working condition A , internal pressure ratio , bypass flow , bypass pressure ratio The distance between working condition A and the common working line of the inner channel can be calculated , the distance from the common working line of the outer duct .

[0127] The internal flow rate of working condition B , internal pressure ratio , bypass flow , bypass pressure ratio The distance between working condition B and the common working line of the inner channel can be calculated , the distance from the common working line of the outer duct .

[0128] S03, using the finite difference method, based on the current outlet back pressure and The distance from the corresponding operating point to the common working line of the inner and outer ducts and the distance from the operating point (operating condition A and operating condition B) to the common working line of the inner and outer ducts obtained after the perturbation of the outlet back pressure obtained in step S02, calculate the Jacobian matrix of the inner and outer duct outlet back pressure and the distance between the corresponding operating point and the two common working lines , the specific calculation results are:

[0129] ,

[0130] Then, using the Newton iteration formula, we can get the independent variable inner and outer duct outlet back pressure The amount of change , the specific change formula is:

[0131] ,

[0132] Where: is the inverse matrix of the Jacobi matrix, Indicates multiplication of numbers, Represents matrix and vector multiplication.

[0133] According to this formula, the current Newton iteration step independent variable inner channel / outer channel outlet back pressure can be obtained and The changes in and .

[0134] S04. Based on the obtained change and To update the current inner and outer duct outlet back pressure and , the updated connotation road exit back pressure , updated duct outlet back pressure .

[0135] Based on the updated inner and outer duct outlet back pressure and , the flow field corresponding to the new outlet back pressure is solved by using the flow field solver NutsCFD, and the flow rate and pressure ratio of the operating point corresponding to the updated inner and outer duct outlet back pressure are obtained. , internal pressure ratio , bypass flow , bypass pressure ratio .

[0136] According to the distance calculation formula obtained in step S01, the distance between the operating point corresponding to the new outlet back pressure and the common working line of the inner and outer ducts can be calculated:

[0137] ,

[0138] S05. Analyze and judge the results in step S04.

[0139] In step S02, the distance from the working point corresponding to the current outlet back pressure to the common working line of the inner channel / outer channel has been obtained, and the corresponding second norm is In step S04, the distance between the working point corresponding to the new outlet back pressure and the common working line of the inner channel / outer channel is obtained, and the corresponding second norm is .

[0140] It can be found that after updating the outlet back pressure, the second norm of the distance changes from Down to , which means that the distance from the working point to the common working line of the inner and outer ducts has been successfully reduced. The current Newton iteration step is completed and enters step S06.

[0141] S06, distance from the working point corresponding to the new outlet back pressure to the common working line of the inner duct / outer duct and No less than the preset error and , so it is necessary to repeat steps S02 to S05 to proceed to the next round of Newton iteration.

[0142] In the current example, Figure 4 and Figure 5 As shown in the figure, during the entire iteration process, the operating point is constantly approaching the intrinsic characteristic line and the extrinsic characteristic line, and finally falls on both the intrinsic and extrinsic characteristic lines. Figure 6 The change process of the distance from the working point to the inner and outer characteristic lines during the iteration process is further given. It can be seen that after three rounds of Newton iteration, the distance between the inner and outer common working lines is achieved. , less than the preset error , external duct , less than the preset error , successfully meets the convergence criteria, and then exits the Newton iteration.

[0143] S07. After the entire Newton iteration step is completed, the common operating point of this double-duct fan is successfully found, and the corresponding duct outlet back pressure , back pressure at the duct outlet .

[0144] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for automatically locating the common operating point of a double-ducted fan based on a Newton iteration model, characterized in that: The steps include: Step 1: Linearly fit the common working lines of the inner and outer ducts of the dual-duct fan respectively to obtain a calculation formula for the distance from the working point to the two common working lines; take the inner and outer duct outlet back pressures as independent variables and the distance from the working point to the two common working lines as dependent variables to construct a Newton iteration model for converting the common working point positioning problem into a numerical root-finding problem; The initial back pressure at the inner and outer duct outlets is selected as the initial value of the Newton iteration model, and the iteration termination condition of the Newton iteration model is selected according to the required common operating point positioning accuracy; Step 2: Calculate the operating point corresponding to the current back pressure at the inner and outer duct outlets, and obtain the distance from the operating point to the two common working lines according to the distance calculation formula, then select the disturbance amount, disturb the inner and outer duct outlet back pressures respectively, calculate the flow field of the inner and outer duct outlet back pressures after the disturbance, and obtain the distance from the operating point corresponding to the inner and outer duct outlet back pressures to the two common working lines according to the distance calculation formula; Then, the finite difference method is used to obtain the Jacobian matrix of the inner and outer duct outlet back pressures before and after the disturbance and the distance between the corresponding operating point and the two common working lines, and the Newton iteration model is combined to iteratively obtain the change of the inner and outer duct outlet back pressures, and the inner and outer duct outlet back pressures are updated according to the change, and the flow field of the inner and outer duct outlet back pressures is calculated and updated to obtain the distance between the corresponding operating point and the two common working lines of the updated inner and outer duct outlet back pressures; Step 3: If the distance between the operating point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines is less than the distance between the current actual operating point and the two common working lines, then on the basis of updating the inner and outer duct outlet back pressure, repeat step 2 to perform the next round of Newton iteration until the distance between the operating point and the two common working lines is less than the Newton iteration termination condition, that is, the automatic positioning of the common operating point of the dual duct fan is achieved; Among them, if the distance between the updated operating point corresponding to the inner and outer duct outlet back pressure and the two common working lines is greater than the distance between the current operating point and the common working line, the change in the inner and outer duct outlet back pressure is reduced, and the inner and outer duct outlet back pressure is re-updated until the distance between the updated operating point corresponding to the inner and outer duct outlet back pressure and the common working line is less than the distance between the current operating point and the common working line.

2. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model according to claim 1, characterized in that: In the step 1, linear fitting is performed on the common working lines of the inner and outer ducts, and the obtained fitting equations are: ， ， Where: For flow, is the pressure ratio, and is the coefficient obtained by linear fitting the common working line of the connotation channel, and The coefficients obtained by linear fitting the common working line of the outer duct; Then, the distance calculation formulas from any working point to the common working line of the inner and outer ducts are: ， ， Where: is the distance from the working point to the common working line of the connotation road, It is the distance from the working point to the common working line of the outer duct; At this time, the nonlinear vector equation based on the Newton iteration model is: ， Where: and are the inner and outer duct outlet back pressures respectively; The and As the independent variable of the nonlinear vector equation, the and is the dependent variable of the nonlinear vector equation; finding the common operating point of the double duct fan is to find a pair of inner and outer duct outlet back pressures that are located on the common working line of the inner duct and the common working line of the outer duct. and The corresponding operating point corresponds to solving the nonlinear vector equation, that is, obtaining a pair of independent variables so that the dependent variables are both 0, and the relationship between the independent variables and the dependent variables is determined by the flow field of the back pressure at the inner and outer duct outlets; Then, select the initial inner and outer duct outlet back pressure of the double duct fan and , as the initial value of the Newton iteration model, and the Newton iteration termination condition is selected according to the required common operating point positioning accuracy. and .

3. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model according to claim 1, characterized in that: In the second step, the flow field solver is first used to solve the current inner and outer duct outlet back pressure and Flow field corresponding to the operating point; The inner and outer duct outlet back pressure before disturbance obtained by calculating the flow field is: , the external bypass flow is ; The internal pressure ratio is , the bypass pressure ratio is ; Then, according to the distance calculation formula, the back pressure at the inner and outer duct outlets before the disturbance is obtained: and The distance from the corresponding working point to the two common working lines is and , the corresponding calculation formulas are: ， ， Where: , , , is the coefficient obtained by linear fitting the common working line of the inner and outer ducts, and are the flow rate and pressure ratio of the inner channel, and are the flow rate and pressure ratio of the outer duct respectively; Then, the disturbance of the back pressure at the inner and outer duct outlets is selected as and ; The back pressures at the inner and outer duct outlets are disturbed by the disturbance amount respectively. After the disturbance, the back pressures at the inner and outer duct outlets are and ; Then, the flow field solver is used to calculate the flow field after disturbing the back pressure at the inner and outer duct outlets, and the operating point corresponding to the back pressure at the inner duct outlet is obtained. And the operating point corresponding to the disturbed outer duct outlet back pressure ; Finally, using the distance calculation formula, the distance from the corresponding working point of the inner and outer duct outlet back pressure after disturbance to the two common working lines is obtained as follows: ， In the formula, and To disturb the back pressure at the inner and outer duct outlets, and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts; At this time, the first iteration in the Newton iteration step is to set the initial inner and outer duct outlet back pressure and As the current inner and outer duct outlet back pressure and ; In the subsequent Newton iteration step, the inner and outer duct outlet back pressures updated in the previous iteration step are and As the current inner and outer duct outlet back pressure and .

4. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model as claimed in claim 3, characterized in that: The selected disturbance and The back pressure at the inner and outer duct outlets before disturbance and 0.1%-1%.

5. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model according to claim 1, characterized in that: In the second step, the finite difference method is used to obtain the Jacobian matrix of the inner and outer duct outlet back pressures before and after the disturbance and the distance between the corresponding operating point and the two common working lines. , the specific formula is: ， Where: and are the outlet back pressure of the inner and outer ducts in the current iteration step, and are the disturbances of the back pressure at the inner and outer duct outlets, respectively. and are the back pressures at the inner and outer duct outlets after disturbance, respectively; and The internal outlet back pressure is , the back pressure at the culvert outlet is The distance from the working point to the common working line of the inner and outer ducts; Next, the Newton iteration formula is used to obtain the current independent variable inner and outer duct outlet back pressure The change in and , the specific change formula is: ， Where: is the inverse matrix of the Jacobi matrix, Indicates multiplication of numbers, Represents matrix and vector multiplication.

6. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model according to claim 5, characterized in that: Based on the change and To update the current inner and outer duct outlet back pressure and , updated inner and outer duct outlet back pressure and for: ， In the formula, the superscript Indicates the updated inner and outer duct outlet back pressure; Based on the updated inner and outer duct outlet back pressure and , use the flow field solver to solve the flow field corresponding to the new inner and outer duct outlet back pressure, and obtain the distance between the working point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines and .

7. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model as claimed in claim 6, characterized in that: If the distance and The second norm of The second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , which reduces the distance from the working point to the two common working lines; If the distance and The second norm of Greater than the second norm of the distance between the working point corresponding to the current actual inner and outer duct outlet back pressure and the two common working lines , it is necessary to reduce the change in the back pressure at the inner and outer duct outlets, and repeat the Newton iteration step based on the reduced change in the back pressure at the inner and outer duct outlets until the distance and The second norm of The second norm of the distance between the working point corresponding to the back pressure at the inner and outer duct outlets before the disturbance and the two common working lines .

8. The method for automatically locating the common operating point of a dual-ducted fan based on a Newton iteration model according to any one of claims 1 to 7, characterized in that: In the step 3, based on updating the inner and outer duct outlet back pressure and The distance between the operating point corresponding to the updated inner and outer duct outlet back pressure and the two common working lines is and If the distance and Both are less than the Newton iteration termination condition and , it means that the common operating point of this dual-duct fan has been successfully found, so the Newton iteration is exited, otherwise the next round of Newton iteration is performed.

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