Design method for arc molded line of wall-attached flowing elbow

Abstract

The invention provides a method for designing an arc molded line of a wall-attached flow elbow. The method comprises the following steps: selecting the arc molded line of the inner and outer molded lines of the elbow; obtaining structure parameters of an inlet and an outlet of the bent pipe; and according to a calculation formula of the arc radiuses of the inner and outer molded lines of the elbow, respectively calculating the arc radiuses of the inner and outer molded lines of the elbow meeting wall-attached flow. The method has the beneficial effects that the method is proposed on the basis of the pipeline flow theory, internal flow of the designed air inlet pipeline and the designed air outlet pipeline is wall-attached flow, flow separation is not generated, the obvious low flow resistance characteristic is achieved, the method is suitable for equal-diameter and non-equal-diameter arc bent pipes, forward design of the air inlet pipeline and the air outlet pipeline is achieved, and the air exchange requirement of a high-power engine is met.

Description

Technical Field

[0001] The invention belongs to the field of engine application pipeline design, and in particular relates to a method for designing a circular arc profile of a wall-attached flow elbow. Background Art

[0002] The intake and exhaust pipes are important components of the intake and exhaust systems. The quality of their design determines the engine's charging efficiency and directly affects the engine's performance, fuel consumption and emissions. Therefore, the design of the intake and exhaust pipes is particularly important.

[0003] At present, the design research on the intake and exhaust pipes mainly combines experiments and uses CFD simulation to perform reverse optimization. However, reverse optimization lacks theoretical support and it is difficult to obtain the optimal design solution. In addition, with the increase in the flow capacity requirements of the intake and exhaust pipes, the degree of optimization is limited. Therefore, the intake and exhaust pipes need a positive theoretical guidance design method. Based on the pipeline flow theory, this paper proposes a forward design method for the arc profile of the elbow characteristics of the intake and exhaust pipes. The arc radius of the inner and outer profiles of the elbow can be directly calculated and determined according to the inlet and outlet parameters. The internal flow of the intake and exhaust pipes designed by this method is a wall-attached flow, which does not produce flow separation and has obvious low flow resistance characteristics. It is suitable for equal-diameter and non-equal-diameter arc elbows, realizing the forward design of the intake and exhaust arc elbows, and supporting the ventilation needs of high-power engines. Summary of the invention

[0004] In view of this, the present invention aims to propose a method for designing a circular arc profile of a wall-attached flow elbow to meet the design requirements of low flow resistance pipelines of an engine.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for designing a circular arc profile of a wall-coated flow elbow comprises the following steps:

[0007] S1. The inner and outer lines of the elbow are arc lines;

[0008] S2. Obtain the structural parameters of the inlet and outlet of the elbow, and determine the length d of the line connecting the intersection of the inlet and outlet outer contours and the inner and outer contour lines. in With d out ;

[0009] S3. According to the calculation formula of the arc radius of the inner and outer lines of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the inner line of the elbow that meets the wall flow;

[0010] S4. Based on the calculation formula for the arc radius of the inner and outer profiles of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the outer profile of the elbow that meets the wall-attached flow.

[0011] Furthermore, in step S3, the calculation process of the calculation formula of the arc radius of the inner and outer contour lines of the elbow includes:

[0012] S31. Determination of key focus areas for three-dimensional elbow flow separation;

[0013] S32, inner mold line flow separation;

[0014] S33, flow separation of outer mold line;

[0015] S34. Combining step S32 and step S33, a calculation formula for the arc radius of the inner and outer contour lines of the elbow is obtained.

[0016] Furthermore, in step S31, the determination of the focus area of ​​the three-dimensional elbow flow separation includes:

[0017] S311. In the axial section of the three-dimensional bent pipe, O1 and O2 are set as the centers of the arcs of the inner and outer mold lines of the bent pipe, respectively, and T1 and T2 are the intersection points of the line through O1O2 and the upper and inner mold lines, respectively;

[0018] S312, determining the maximum inner diameter of the outer mold line;

[0019] S313, determining the maximum inner diameter of the inner mold line;

[0020] In step S312, determining the maximum inner diameter of the outer mold line includes:

[0021] Take any point A2 on the arc of the outer mold line, A2O2 is perpendicular to the tangent through A2, that is, perpendicular to the velocity direction of the outer mold line. If A2O2 intersects the inner mold line at point B2, then A2B2 is the inner diameter of the outer mold line at A2;

[0022] Among them, A2B2=A2O2-B2O2, A2O2 is the radius of curvature of the outer line, which is a constant value, so when B2O2 is the smallest, A2B2 is the largest;

[0023] Among them, B2O2>B2O1-O1O2, B2O2=B2O1-O1O2 only when B2, O2, and O1 are collinear;

[0024] Among them, B2O1 is the radius of curvature of the inner line, O1O2 is the distance between the two centers of the circles, both of which are constants. When B2, O2, and O1 are collinear, B2O2 is the smallest and A2B2 is the largest. At this time, A2B2 is T1T2, so the maximum inner diameter of the outer line is T1T2.

[0025] Furthermore, in step S313, determining the maximum inner diameter of the inner mold line includes:

[0026] Take any point B1 on the arc of the inner mold line, A1 is the intersection of the line B1O1 and the outer mold line, B1O1 is perpendicular to the tangent through B1, that is, perpendicular to the velocity direction of the inner mold line, so A1B1 is the inner diameter of the inner mold line at B1;

[0027] Among them, A1B1=A1O1-B1O1, B1O1 is the inner line curvature radius, B1O1 is a constant value, when A1O1 is the maximum, A1B1 is the maximum;

[0028] Among them, A1O1<A1O2+O1O2, only when A1, O2, O1 are collinear, A1O1=A1O2+O1O2;

[0029] Among them, A1O2 is the radius of curvature of the outer line, and O1O2 is the distance between the two centers of the circles. Both are constants. Therefore, when A1, O2, and O1 are collinear, A1O1 is the largest and A1B1 is the largest. At this time, A1B1 is T1T2, so the maximum inner diameter of the inner line is also T1T2.

[0030] Further, in step S32, the inner mold line flow separation includes:

[0031] Establish a three-dimensional equal-diameter arc-shaped pipe bending model and define the curvature ratio K of the inner profile of the axial section l =r l / d;

[0032] Using pressure boundary conditions and k-ε turbulence model, the flow coefficient and pressure loss of three-dimensional equal-diameter arc-shaped elbow with different inner profile curvature ratios are calculated. The calculation conditions are inlet pressure of 100 kPa, pressure difference of 10 kPa and 50 kPa.

[0033] It can be obtained that the flow coefficient of the three-dimensional equal-diameter arc-shaped elbow with the same inner diameter first increases and then converges with the increase of the inner profile curvature ratio, and the inflection point is K l =1;

[0034] K l When <1, flow separation occurs at the inner profile of the three-dimensional equal-diameter circular arc profile elbow, generating a vortex. The effective flow area in the three-dimensional equal-diameter circular arc profile elbow is small, so the flow coefficient is small. With the increase of the inner profile curvature ratio, the separation vortex gradually decreases, the effective flow area of ​​the three-dimensional equal-diameter circular arc profile elbow increases, and the flow coefficient increases.

[0035] When K l >1, the separation phenomenon disappears, and the effective flow area reaches the maximum. After that, the flow coefficient of the three-dimensional equal-diameter arc elbow remains basically unchanged with the increase of the inner curve ratio, showing a convergence trend.

[0036] It can be obtained that when the flow coefficient does not increase with the change of the curvature ratio, the flow in the three-dimensional equal-diameter arc-shaped elbow is a wall-attached flow without separation;

[0037] Therefore, the inner line is at K l When >1, the flow in the three-dimensional equal-diameter arc-shaped elbow is wall-attached flow without flow separation.

[0038] Further, in step S33, the outer mold line flow separation includes:

[0039] Establish a three-dimensional non-uniform diameter elbow model, assuming the inlet diameter d in =40mm, because when the inner profile curve ratio K l ≥1, the inner profile does not separate; select a variety of different inner profile curvature radii, and select a different outer profile curvature radius r for each case u Modeling is performed to define the maximum diameter-to-curvature ratio K of the outer profile of the curved pipe shaft section u =d u / r u ;

[0040] The flow coefficient of the three-dimensional non-equal diameter elbow is calculated using the pressure boundary condition and the k-ε turbulence model. The calculation conditions are the intake pressure of 100 kPa, the pressure difference of 10 kPa and 50 kPa.

[0041] Under the same pressure difference and the same inner profile, the flow coefficient of three-dimensional non-equal diameter elbow increases with K u The increase of K increases first, and then u >1 and remain unchanged;

[0042] When K u >1, separation occurs at the outer line, and as K u As the separation area increases, the flow coefficient does not decrease;

[0043] It can be obtained that when the three-dimensional non-equal diameter elbow flow coefficient changes with K u When the increase of K remains unchanged, the effective flow area in the three-dimensional non-equal diameter elbow reaches the maximum. u As the pressure continues to increase, the effective flow area of ​​the three-dimensional non-equal diameter elbow remains unchanged, and flow separation occurs at the outer profile.

[0044] Further, in step S34, the calculation formula of the arc radius of the inner and outer profile lines of the elbow is obtained by combining step S32 and step S33, including:

[0045] Combined with the flow separation analysis of the inner and outer mold lines in step S32 and step S33, the inner mold line K is obtained. l and outer line K u All equal to 1;

[0046] The inner and outer lines and outer lines can be parameterized:

[0047] Set ABCD as the endpoints of the inner and outer lines of the elbow, O1 as the center of the inner line, and O2 as the center of the outer line; connect O1O2 and make an extension line to intersect the inner and outer lines at point T1 and point T2 respectively; make a perpendicular line through O1 to the inlet straight line segment of the outer line to intersect the inner and outer lines at point E and point F respectively; make a perpendicular line through O1 to the outlet straight line segment of the outer line to intersect the inner and outer lines at point J and point I respectively; make a perpendicular line through O2 to the inlet and outlet straight lines of the outer line to intersect the outer line at point G and point H respectively; make a perpendicular line through O2 to O1I to intersect O1I at point N; make a perpendicular line through O2 to O1F to intersect O1F at point M;

[0048] The relationship can be obtained:

[0049] T1T2=O2T2-(O1T1-O1O2);

[0050]

[0051] in:

[0052] O1M=O1F-O2G;

[0053] O2M=MH-O2H=O1I-O2H;

[0054] set up:

[0055] O1T1=O2T2=T1T2;

[0056] EF=AB=d in ;

[0057] IJ=CD=d out ;

[0058] O1E=O1J=O1T1=r l ;

[0059] O2G=O2H=O2T2=r u ;

[0060] Combining the above formulas, we can get the calculation formula of the arc radius of the inner and outer lines of the elbow:

[0061]

[0062] Among them, r l is the radius of the inner arc, r u is the arc radius of the outer profile, d in is the inlet diameter of the elbow, d out is the outlet diameter of the elbow.

[0063] Compared with the prior art, the method for designing the arc profile of a wall-coated flow elbow described in the present invention has the following advantages:

[0064] The present invention discloses a method for designing the circular arc profile of a wall-attached flow elbow. The method is proposed based on pipeline flow theory. The internal flow of the designed intake and exhaust pipes is wall-attached flow, no flow separation occurs, and the method has obvious low flow resistance characteristics. The method is suitable for equal-diameter and non-equal-diameter circular arc elbows, and realizes the forward design of the intake and exhaust circular arc elbows, supporting the ventilation needs of high-power engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0066] Figure 1 It is a schematic diagram of the inner and outer profiles of the elbow;

[0067] Figure 2 It is a schematic diagram of the inlet and outlet structural parameters of the elbow;

[0068] Figure 3 It is a schematic diagram of the two-dimensional projection of different cross sections of the three-dimensional bent pipe;

[0069] Figure 4 It is a schematic diagram of the geometric relationship between the inner and outer lines of a three-dimensional elbow;

[0070] Figure 5 Schematic diagram of arc bending pipe model with inner diameter of 40mm and different inner profile curve ratios;

[0071] Figure 6 It is a schematic diagram of the variation of the flow coefficient of the arc elbow with the curvature ratio of the inner profile;

[0072] Figure 7 Velocity cloud diagram of arc bend when the pressure difference is 10kPa;

[0073] Figure 8 It is a schematic diagram of three-dimensional non-equal diameter arc elbow with different outer line curvature radii;

[0074] Fig. 9 It is a schematic diagram of the flow coefficient of three-dimensional non-equal diameter arc elbow with different maximum diameter-to-curvature ratios of the outer profile;

[0075] Fig.10 For r l =60mm, different K when pressure difference is 50kPa u Speed ​​cloud map;

[0076] Fig.11 It is a schematic diagram of the geometric relationship of the bent pipe structure;

[0077] Fig.12 This is a schematic diagram of the shape of the original aircraft's air intake inlet. DETAILED DESCRIPTION

[0078] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0079] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0080] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0081] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0082] like Figures 1 to 12 As shown in the figure, a design method for the arc profile of a wall-attached flow elbow is mainly designed according to the following steps:

[0083] 1): The inner and outer lines of the elbow are selected as arc lines, such as Figure 1 As shown;

[0084] 2): Obtain the structural parameters of the elbow inlet and outlet, and determine the length d of the line connecting the intersection of the inlet and outlet outer contours and the inner and outer contour lines respectively in With d out ,like Figure 2 As shown;

[0085] 3): According to the calculation formula of the arc radius of the inner profile of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the inner profile of the elbow that meets the wall flow;

[0086] 4): According to the calculation formula of the arc radius of the outer profile of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the outer profile of the elbow that meets the wall-attached flow.

[0087] exist Figure 2 In the figure, subscript "0" represents the axis section parameters, subscript "1" represents the section 1 parameters, and subscript "2" represents the section 2 parameters.

[0088] In a preferred embodiment of the present invention, the calculation formula of the arc radius of the inner and outer profiles of the elbow satisfying the wall-attached flow is derived according to the following process:

[0089] For elbows, the internal flow loss includes the loss of resistance along the way, the axial separation loss and the secondary flow loss of the radial section. The loss of resistance along the way is caused by the viscosity of the fluid and the friction resistance of the pipe; the secondary flow loss is also caused by the centrifugal force that causes the fluid to accumulate on the upper boundary, resulting in a higher pressure than the lower boundary, causing the fluid to flow from top to bottom at the boundary, forming a vortex with the bottom-up flow at the center, resulting in loss; the loss of resistance along the way and the secondary flow loss are the inherent properties of the elbow flow that are inevitable. The axial separation loss is caused by the centrifugal force that causes the fluid to generate a separation vortex at the bend, thereby generating losses. From the wall effect of the fluid, it can be seen that the ratio of the inner diameter of the elbow to the radius of curvature of the profile has an important influence on the separation. Controlling the curvature of the elbow can avoid flow separation and reduce the flow loss of the elbow. Therefore, the influence of the radius of curvature of the elbow profile on the separation loss is studied.

[0090] (1) Determination of key focus areas for three-dimensional elbow flow separation

[0091] For a three-dimensional bent pipe, the two-dimensional projections of different sections parallel to the axial section are as follows: Figure 3 As shown ( Figure 3 (a) External profile geometric relationship, (b) internal profile geometric relationship). As can be seen from the figure, the inner diameter of the section d0>d1>d2, the curvature radius of the cross-sectional projection profile r0<r1<r2, so the extreme value of the ratio of the inner diameter to the profile curvature radius in the elbow occurs at the axial section, that is, the flow separation is most likely to occur at the inner profile of the entire elbow, and the inner and outer profiles of the axial section of the elbow should be focused on.

[0092] For the shaft section, first determine the point where the inner diameter of the inner and outer lines is the largest. Since the line under study is an arc line, the radius of curvature is the same everywhere, and the maximum ratio of the inner diameter to the radius of curvature of the line occurs at the point where the inner diameter is the largest. The geometric relationship between the inner and outer lines is as follows: Figure 4 shown.

[0093] O1 and O2 are the centers of the arcs of the inner and outer lines of the elbow, respectively. T1 and T2 are the intersections of the line through O1O2 with the upper and inner lines, respectively. First, determine the maximum inner diameter of the outer line. Take any point A2 on the arc of the outer line. From the properties of the circle, we know that A2O2 is perpendicular to the tangent through A2, that is, perpendicular to the velocity direction of the outer line. If A2O2 intersects the inner line at point B2, then A2B2 is the inner diameter of the outer line at A2. A2B2=A2O2-B2O2, A2O2 is the radius of curvature of the outer line, which is a constant, so when B2O2 is the smallest, A2B2 is the largest. From the triangle three-side relationship rule, we know that B2O2>B2O1-O1O2, and B2O2=B2O1-O1O2 only when B2, O2, and O1 are collinear. B2O1 is the radius of curvature of the inner mold line, O1O2 is the distance between the two centers of the circles, both of which are constants. When B2, O2, and O1 are collinear, B2O2 is the smallest and A2B2 is the largest. At this time, A2B2 is T1T2, indicating that the maximum inner diameter of the outer mold line is T1T2.

[0094] Take any point B1 on the arc of the inner line, and A1 is the intersection of the line connecting B1O1 and the outer line. From the properties of the circle, we know that B1O1 is perpendicular to the tangent through B1, that is, perpendicular to the speed direction of the inner line, so A1B1 is the inner diameter of the inner line at B1. A1B1=A1O1-B1O1, B1O1 is the radius of curvature of the inner line, which is a constant, so when A1O1 is the largest, A1B1 is the largest. From the triangle three-side relationship rule, we know that A1O1<A1O2+O1O2, and A1O1=A1O2+O1O2 only when A1, O2, and O1 are collinear. A1O2 is the radius of curvature of the outer line, and O1O2 is the distance between the two centers of the circles. Both are constants. Therefore, when A1, O2, and O1 are collinear, A1O1 is the largest and A1B1 is the largest. At this time, A1B1 is T1T2, indicating that the maximum inner diameter of the inner line is also T1T2.

[0095] In summary, for three-dimensional bent pipes, the maximum inner diameter of the inner profile is T1T2, so it should be paid special attention to.

[0096] (2) Inner mold line flow separation

[0097] Through the 90° three-dimensional equal-diameter arc-shaped pipe bending with different inner line radius (hereinafter referred to as arc bending pipe), Figure 5 Steady-state CFD simulation is performed to study the changing law of inner mold line separation loss.

[0098] The inner diameters of the elbows are 40 and 20 mm respectively. In order to ensure the same resistance loss along the way as much as possible, the lengths of the different elbows are set to be equal by changing the length of the straight line segment and the radius of curvature. Define the curvature ratio of the inner profile of the shaft section (the ratio of the inner profile radius of curvature to the inner diameter of the elbow) K l =r l / d.

[0099] Using the pressure boundary condition and k-ε turbulence model, the flow coefficient and pressure loss of the arc elbow under different inner profile curve ratios are calculated. The calculation conditions are the intake pressure of 100kPa, the pressure difference of 10kPa and 50kPa. The calculation results are as follows: Figure 6 shown.

[0100] It can be seen that the flow coefficient of the arc elbow with the same inner diameter first increases and then converges with the increase of the inner profile curve ratio, and the inflection point is approximately K l = 1. Take the velocity cloud diagram of a circular curved pipe with a pressure difference of 10 kPa and an inner diameter of 40 mm as an example. Figure 7 shown.

[0101] Visible K l When K is less than 1, there is obvious flow separation at the inner profile of the elbow, generating vortices, and the effective flow area in the elbow is small, so the flow coefficient is small. As the inner profile curve ratio increases, the separation vortex gradually decreases, the effective flow area of ​​the elbow increases, and the flow coefficient increases. l >1, the separation phenomenon disappears, the effective flow area reaches the maximum, and then the elbow flow coefficient remains basically unchanged with the increase of the inner profile curve ratio, showing a convergence trend. Combined with the velocity cloud map, it can be inferred that when the flow coefficient does not increase with the change of the curve ratio, the flow in the elbow is wall-attached flow without separation.

[0102] In summary, the inner line is K l When >1, the flow in the curved pipe adheres to the wall without flow separation.

[0103] (3) Flow separation of outer mold line

[0104] A three-dimensional non-uniform pipe bending model was established (such as Figure 8 As shown), assume the inlet diameter d in =40mm, because when the inner profile curve ratio K l ≥1, the inner mold line does not separate, so the inner mold line curvature radius is selected as 40, 60 and 80 mm, a total of 3 cases, each case selects a different outer mold line curvature radius r u Modeling is performed to define the maximum diameter-to-curvature ratio K of the outer profile of the curved pipe shaft section u =d u / r u .

[0105] Using the pressure boundary condition and k-ε turbulence model, the flow coefficients of all elbows are calculated. The calculation conditions are as follows: intake pressure 100 kPa, pressure difference 10 kPa and 50 kPa. Fig. 9 shown.

[0106] Under the same pressure difference and the same inner profile conditions, the elbow flow coefficient increases with K u The increase of increases first, and then both in Ku >1 and remain basically unchanged. l = 60mm elbow model as an example, the velocity cloud diagram when the pressure difference is 50kPa is as follows Fig.10 shown.

[0107] When K u >1, obvious separation occurs at the outer line, and as K u As the flow coefficient does not decrease, the separation area increases. This is because the separation of the outer line occurs in the outer direction of the fluid, and the size of the separation area does not affect the effective flow area in the elbow. Therefore, it can be inferred that when the flow coefficient of the non-equal diameter elbow increases with K u When the increase of K remains unchanged, the effective flow area in the elbow reaches the maximum. u As the pressure continues to increase, the effective flow area of ​​the elbow remains unchanged, and flow separation occurs at the outer profile.

[0108] Combining (2) and (3), we can see that in order to enable wall-attached flow in the elbow, it is only necessary to ensure that the inner profile Kl and the outer profile Ku are both equal to 1. In this way, the inner and outer profiles can be parameterized. The geometric relationship of the elbow structure is as follows: Fig.11 As shown, ABCD are the endpoints of the inner and outer lines of the elbow, O1 is the center of the inner line, and O2 is the center of the outer line. Connect O1O2 and make an extension line that intersects the inner and outer lines at points T1 and T2 respectively; make a perpendicular line through O1 to the inlet straight line segment of the outer line that intersects the inner and outer lines at points E and F respectively; make a perpendicular line through O1 to the outlet straight line segment of the outer line that intersects the inner and outer lines at points J and I respectively; make a perpendicular line through O2 to the inlet and outlet straight lines that intersect the outer line at points G and H respectively; make a perpendicular line through O2 to O1I that intersects O1I at point N; make a perpendicular line through O2 to O1F that intersects O1F at point M. Based on geometric relationships and design criteria, the relationship can be obtained:

[0109] T1T2=O2T2-(O1T1-O1O2);

[0110]

[0111] in:

[0112] O1M=O1F-O2G;

[0113] O2M=MH-O2H=O1I-O2H;

[0114] The design criteria are:

[0115] O1T1=O2T2=T1T2;

[0116] in addition:

[0117] EF=AB=d in ;

[0118] IJ=CD=d out ;

[0119] O1E=O1J=O1T1=r l ;

[0120] O2G=O2H=O2T2=r u ;

[0121] Combining the above formulas, we can get the calculation formula for the curvature radius of the inner and outer lines of the curved pipe arc profile (i.e. the calculation formula for the radius of the curved pipe inner and outer lines):

[0122]

[0123] Among them, r l is the radius of the inner arc, r u is the arc radius of the outer profile, d in is the inlet diameter of the elbow, d out is the outlet diameter of the elbow.

[0124] Advantages of the present invention: This method is proposed based on pipeline flow theory. The internal flow of the designed intake and exhaust pipelines is wall-attached flow, which does not produce flow separation and has obvious low flow resistance characteristics. It is suitable for equal-diameter and non-equal-diameter arc bends, and realizes the forward design of intake and exhaust arc bends, supporting the ventilation needs of high-power engines.

[0125] Example 1

[0126] The present invention provides a method for designing the arc profile of a wall-attached flow elbow. The design process includes: in Determination of size, elbow outlet d out Determination of dimensions, determination of characteristic parameter design range, determination of inner and outer profile parameters of curved pipe arc. Taking the intake duct of a certain type of engine as an example, the specific implementation method of the curved pipe arc profile design method for wall flow is explained.

[0127] 1. Determine the elbow inlet d in size

[0128] The inlet shape and parameters of the original engine intake duct are as follows: Fig.12 As shown, the inlet is a slot type, consisting of straight line segments and arc segments, which can determine the inlet d in =2R=50mm.

[0129] 2. Determine the elbow outlet d out size

[0130] The throat diameter of the intake valve seat is 40mm. The intake valve seat is the outlet of the intake duct, i.e. d out =40mm.

[0131] 3. Determine the length and height of the air intake duct (determine the design range of characteristic parameters)

[0132] According to the outer contour dimensions of the original cylinder head, the length of the inner mold line of the intake duct can be determined to be L = 113.5 mm. In order to make the inner mold line curvature radius meet the characteristics of the wall flow, the height of the inner mold line of the intake duct must meet H ≥ r l According to the principle of structural compactness, the height of the inner profile of the inlet duct is finally determined as H = r l .

[0133] 4. Determine the parameters of the inner and outer profiles of the curved pipe

[0134] The d determined in steps 1 and 2 is in and d out Substitute the following relationship for calculation:

[0135]

[0136] First, we can get r l ≥64.03mm, due to the limited design space of the engine, r l Take the minimum value of 64.03 mm that satisfies the wall-attachment flow characteristics, and then use the obtained r l Substituting back into the relationship, we can get r u =64.02mm.

[0137] The non-bending parts of the inlet duct all use straight line transitions, the tangents at the starting points of the inner and outer lines are perpendicular to the inlet cross-section, while the tangents at the end points of the inner and outer lines are perpendicular to the outlet cross-section, and the inner and outer lines are continuous everywhere.

[0138] Combining the above steps, the inner and outer contours of the only air intake duct can be determined.

[0139] The air intake duct is manufactured according to the above-mentioned design method, and the flow capacity of the air intake duct is verified by a steady-flow air duct test.

[0140] The test tested the intake duct flow resistance under the same intake flow rate and different intake pressure conditions. The intake flow rate was 0.1kg / s, and the intake pressures were 100kPa, 110kPa and 115kPa respectively. The test results are shown in the following table.

[0141] Table 1 Flow resistance results before and after intake duct optimization

[0142]

[0143]

[0144] Note:

[0145] Compared with the original engine, the optimized intake duct flow resistance is significantly reduced, with a maximum reduction of 13.64%, indicating that the elbow designed by the design method proposed in this patent can effectively reduce the flow resistance.

[0146] 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 designing the arc profile of a wall-coated flow elbow, characterized in that: The following steps are involved: S1. The inner and outer lines of the elbow are arc lines; S2. Obtain the structural parameters of the inlet and outlet of the elbow, and determine the length d of the line connecting the intersection of the inlet and outlet outer contours and the inner and outer contour lines. in With d out ; S3. According to the calculation formula of the arc radius of the inner and outer lines of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the inner line of the elbow that meets the wall flow; S4. Based on the calculation formula for the arc radius of the inner and outer profiles of the elbow, combined with the inlet and outlet structural parameters, calculate the arc radius of the outer profile of the elbow that meets the wall-attached flow.

2. A method for designing a circular arc profile of a wall-coanda flow elbow according to claim 1, characterized in that: In step S3, the calculation process of the arc radius calculation formula of the inner and outer contour lines of the elbow includes: S31. Determination of key focus areas for three-dimensional elbow flow separation; S32, inner mold line flow separation; S33, flow separation of outer mold line; S34. Combining step S32 and step S33, a calculation formula for the arc radius of the inner and outer contour lines of the elbow is obtained.

3. A method for designing a circular arc profile of a wall-coanda flow elbow according to claim 2, characterized in that: In step S31, the determination of the focus area of ​​the three-dimensional curved pipe flow separation includes: S311. In the axial section of the three-dimensional bent pipe, O1 and O2 are set as the centers of the arcs of the inner and outer mold lines of the bent pipe, respectively, and T1 and T2 are the intersection points of the line through O1O2 and the upper and inner mold lines, respectively; S312, determining the maximum inner diameter of the outer mold line; S313, determine the maximum inner diameter of the inner mold line.

4. A method for designing a circular arc profile of a wall-coanda flow elbow according to claim 3, characterized in that: In step S312, determining the maximum inner diameter of the outer mold line includes: Take any point A2 on the arc of the outer mold line, A2O2 is perpendicular to the tangent through A2, that is, perpendicular to the velocity direction of the outer mold line. If A2O2 intersects the inner mold line at point B2, then A2B2 is the inner diameter of the outer mold line at A2; Among them, A2B2=A2O2-B2O2, A2O2 is the radius of curvature of the outer profile, which is a constant value, so when B2O2 is the smallest, A2B2 is the largest; Among them, B2O2>B2O1-O1O2, B2O2=B2O1-O1O2 only when B2, O2, and O1 are collinear; Among them, B2O1 is the radius of curvature of the inner line, O1O2 is the distance between the two centers of the circles, both of which are constants. When B2, O2, and O1 are collinear, B2O2 is the smallest and A2B2 is the largest. At this time, A2B2 is T1T2, so the maximum inner diameter of the outer line is T1T2.

5. The method for designing the arc profile of a wall-coanda flow elbow according to claim 3, characterized in that: In step S313, determining the maximum inner diameter of the inner mold line includes: Take any point B1 on the arc of the inner mold line, A1 is the intersection of the line B1O1 and the outer mold line, B1O1 is perpendicular to the tangent through B1, that is, perpendicular to the velocity direction of the inner mold line, so A1B1 is the inner diameter of the inner mold line at B1; Among them, A1B1=A1O1-B1O1, B1O1 is the inner line curvature radius, B1O1 is a constant value, when A1O1 is the maximum, A1B1 is the maximum; Among them, A1O1<A1O2+O1O2, only when A1, O2, O1 are collinear, A1O1=A1O2+O1O2; Among them, A1O2 is the radius of curvature of the outer line, and O1O2 is the distance between the two centers of the circles. Both are constants. Therefore, when A1, O2, and O1 are collinear, A1O1 is the largest and A1B1 is the largest. At this time, A1B1 is T1T2, so the maximum inner diameter of the inner line is also T1T2.

6. A method for designing a circular arc profile of a wall-coanda flow elbow according to claim 2, characterized in that: In step S32, the inner mold line flow separation includes: Establish a three-dimensional equal-diameter arc-shaped pipe bending model and define the curvature ratio K of the inner profile of the axial section l =r l / d; Using pressure boundary conditions and k-ε turbulence model, the flow coefficient and pressure loss of three-dimensional equal-diameter circular arc elbow with different inner profile curvature ratios are calculated. The calculation conditions are inlet pressure of 100 kPa, pressure difference of 10 kPa and 50 kPa. It can be obtained that the flow coefficient of the three-dimensional equal-diameter arc-shaped elbow with the same inner diameter first increases and then converges with the increase of the inner profile curvature ratio, and the inflection point is K l =1; K l When <1, flow separation occurs at the inner profile of the three-dimensional equal-diameter circular arc profile elbow, generating a vortex. The effective flow area in the three-dimensional equal-diameter circular arc profile elbow is small, so the flow coefficient is small. With the increase of the inner profile curvature ratio, the separation vortex gradually decreases, the effective flow area of ​​the three-dimensional equal-diameter circular arc profile elbow increases, and the flow coefficient increases. When K l >1, the separation phenomenon disappears, and the effective flow area reaches the maximum. After that, the flow coefficient of the three-dimensional equal-diameter arc elbow remains basically unchanged with the increase of the inner curve ratio, showing a convergence trend. It can be obtained that when the flow coefficient does not increase with the change of the curvature ratio, the flow in the three-dimensional equal-diameter arc-shaped elbow is a wall-attached flow without separation; Therefore, the inner line is at K l When >1, the flow in the three-dimensional equal-diameter arc-shaped elbow is wall-attached flow without flow separation.

7. A method for designing a circular arc profile of a wall-coanda flow elbow according to claim 6, characterized in that: In step S33, the outer mold line flow separation includes: Establish a three-dimensional non-uniform diameter elbow model, assuming the inlet diameter d in =40mm, because when the inner profile curve ratio K l ≥1, the inner profile does not separate; select a variety of different inner profile curvature radii, and select a different outer profile curvature radius r for each case u Modeling is performed to define the maximum diameter-to-curvature ratio K of the outer profile of the curved pipe shaft section u =d u / r u ; The flow coefficient of the three-dimensional non-equal diameter elbow is calculated using the pressure boundary condition and the k-ε turbulence model. The calculation conditions are as follows: the inlet pressure is 100 kPa, and the pressure difference is 10 kPa and 50 kPa. Under the same pressure difference and the same inner profile, the flow coefficient of three-dimensional non-equal diameter elbow increases with K u The increase of K increases first, and then u >1 and remain unchanged; When K u >1, separation occurs at the outer line, and as K u As the separation area increases, the flow coefficient does not decrease; It can be obtained that when the three-dimensional non-equal diameter elbow flow coefficient changes with K u When the increase of K remains unchanged, the effective flow area in the three-dimensional non-equal diameter elbow reaches the maximum. u As the pressure continues to increase, the effective flow area of ​​the three-dimensional non-equal diameter elbow remains unchanged, and flow separation occurs at the outer profile.

8. The method for designing the arc profile of a wall-coanda flow elbow according to claim 7, characterized in that: In step S34, the calculation formula of the arc radius of the inner and outer profile lines of the elbow is obtained by combining step S32 and step S33, including: Combined with the flow separation analysis of the inner and outer mold lines in step S32 and step S33, the inner mold line K is obtained. l and outer line K u All equal to 1; The inner and outer lines and outer lines can be parameterized: Set ABCD as the endpoints of the inner and outer lines of the elbow, O1 as the center of the inner line, and O2 as the center of the outer line; connect O1O2 and make an extension line to intersect the inner and outer lines at point T1 and point T2 respectively; make a perpendicular line through O1 to the inlet straight line segment of the outer line to intersect the inner and outer lines at point E and point F respectively; make a perpendicular line through O1 to the outlet straight line segment of the outer line to intersect the inner and outer lines at point J and point I respectively; make a perpendicular line through O2 to the inlet and outlet straight lines of the outer line to intersect the outer line at point G and point H respectively; make a perpendicular line through O2 to O1I to intersect O1I at point N; make a perpendicular line through O2 to O1F to intersect O1F at point M; The relationship can be obtained: T1T2=O2T2-(O1T1-O1O2); in: O1M=O1F-O2G; O2M=MH-O2H=O1I-O2H; set up: O1T1=O2T2=T1T2; EF=AB=d in ; IJ=CD=d out ; O1E=O1J=O1T1=r l ; O2G=O2H=O2T2=r u ; Combining the above formulas, we can get the calculation formula of the arc radius of the inner and outer lines of the elbow: Among them, r l is the radius of the inner arc, r u is the arc radius of the outer profile, d in is the inlet diameter of the elbow, d out is the outlet diameter of the elbow.

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