A design method for a flow channel structure with uniform cross-sectional velocity

Abstract

The present invention relates to the technical field of flow channel structure design, and in particular to a flow channel structure design method with uniform cross-sectional velocity, comprising: S1, establishing a flow channel between a flow field inlet and an outlet, setting the flow channel inlet as a velocity inlet; S2, using a finite volume method to calculate the velocity distribution of the fluid in the entire flow channel; S3, statistically analyzing the velocity distribution in the flow channel and making a judgment, comparing the maximum velocity of the flow channel section with the fluid velocity threshold, and returning to iteration when the condition is not met, modifying the outer flow channel structure; until the condition is met, outputting the outer flow channel shape; S4, calculating the velocity uniformity on different cross sections, comparing the velocity uniformity of two adjacent different cross sections, and when N cross sections all meet C i vn >C i‑1 vn The present invention forms an optimized flow channel through continuous iteration based on finite element simulation, so that no backflow vortex appears inside the flow channel and the fluid velocity inside the flow channel is evenly distributed.

Description

Technical Field

[0001] The present invention relates to the technical field of flow channel structure design, and in particular to a flow channel structure design method with uniform cross-sectional velocity. Background Art

[0002] For flow in curved channels, improper channel design can lead to uneven velocity distribution within the channel, creating backflow vortices, which can severely impact downstream flow. In the meltblown fabric production process, the desired material is typically melted and extruded through a nozzle. This filament is then guided by a drafting airflow and falls into a web-forming machine. The web curtain receives the jet melt, which is then condensed and cooled by a suction device to form the meltblown fabric. In this process, improper flow channel design can lead to uneven velocity distribution and backflow vortices. This can cause the meltblown fabric to vibrate during web formation, resulting in uneven thickness and impacting product quality. Therefore, designing a flow channel with a suitable shape and uniform internal velocity distribution is crucial. Typically, designers rely on experience to manually adjust the flow channel shape, which is inefficient and labor-intensive. The published literature, "A hybrid optimization method to design shapes of three-dimensional flow channels," describes a self-evolutionary flow channel algorithm. While this method produces a flow channel without backflow vortices, the internal fluid velocity distribution is not completely uniform. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to form an optimized flow channel through continuous iteration based on finite element simulation, so that no backflow vortex appears inside the flow channel and the fluid velocity inside the flow channel is evenly distributed.

[0004] The technical solution adopted by the present invention is: a flow channel structure design method with uniform cross-sectional velocity comprises the following steps:

[0005] S1. Establish a flow channel between the inlet and outlet of the flow field, and set the inlet of the flow channel as the velocity inlet;

[0006] Use two straight lines to connect the inlet and outlet of the flow field to establish the initial flow channel. These two straight lines are spline lines formed by sequentially connecting N equidistant spline points to establish the initial flow channel model.

[0007] S2. Use the finite volume method to find the velocity distribution of the fluid in the entire flow channel;

[0008] Input the initial flow channel model into Fluent software, set the inlet condition to velocity inlet, the inlet velocity to V, set the outlet to pressure outlet, and calculate the velocity distribution in the flow channel;

[0009] S3. Statistically analyze the velocity distribution in the flow channel and make a judgment. Compare the maximum velocity of the flow channel cross-section with the fluid velocity threshold. If the condition is not met, return for iteration, modify the outer flow channel structure until the condition is satisfied, and output the shape of the outer flow channel.

[0010] Specifically, it includes the following steps:

[0011] S31. Make projections of the spline points in the direction perpendicular to the flow channel wall, and successively connect the corresponding projection points on the two wall surfaces (the spline points and the projection points coincide in the initial state) to draw N flow channel cross-sections, and statistically analyze the velocity distribution on the N flow channel cross-sections.

[0012] S32. Modify the flow channel by moving the spline points. The moving direction of the outer wall spline points is perpendicular to the flow channel wall and outward to increase the flow channel area, and the moving direction of the inner wall spline points is perpendicular to the flow channel wall and inward to reduce the flow channel area; the moving distance of each spline point is 0%-X% of the inlet width, and different X values are set corresponding to different precisions; where 0 < X < N and N - 1 is a multiple of X.

[0013] If the X value is set smaller, the speed of modifying the flow channel will be slower, while if the X value is set larger, the speed of modifying the flow channel will be faster, but the precision will decrease.

[0014] S33. Use the finite volume method to statistically analyze the maximum fluid velocity of each of the N cross-sections. The maximum fluid velocity of the nth flow channel cross-section is denoted as V n , where 1 <= n <= N. Set the fluid velocity threshold as V α . When max{V n}>V α , sort the fluid velocities in {V1, V n , …, V N} from large to small. The serial number corresponding to the ranking of the fluid velocity of the nth cross-section is m, where 1 <= m <= N; the spline point corresponding to the nth cross-section moves perpendicularly outward from the outer flow channel wall by the inlet width of to expand the outer wall surface and increase the flow channel area; after completing the outward movement of the outer flow channel wall this time, use the finite volume method to recalculate the velocity distribution of the fluid in the entire flow channel. When the maximum fluid velocity of the nth cross-section in the jth time satisfies max{V j n} <= V α , perform step S4, and use the expanded outer wall surface completed in the jth time as the output shape of the outer flow channel, where j >= 2; otherwise, continue to use the finite volume method to recalculate the velocity distribution of the fluid in the entire flow channel, and continue to move the spline point corresponding to the nth cross-section perpendicularly outward from the outer flow channel wall, expand the outer wall surface, and modify the structure of the outer flow channel.

[0015] S4. Compare the velocity uniformity of two adjacent flow channel sections. If the conditions are not met, return to the iteration and modify the internal flow channel structure until the conditions are met, and output the internal flow channel shape.

[0016] Specifically, after completing step S33, that is, when max{V j n}<=V α When the velocity distribution of the fluid in the entire flow channel is calculated using the finite volume method, the velocity uniformity on different cross sections is calculated: v1 ,C vn ,…,C vN , where the formula for velocity uniformity is as follows:

[0017]

[0018] Where C v is the velocity uniformity, σ v is the standard deviation of fluid velocity, is the average value of the cross-sectional fluid velocity; for {C v1 ,C vn ,…,C vN The velocity uniformity of the N sections is sorted, and the velocity uniformity of the fluid in N sections is ranked from high to low as 1, 2, ..., m, where m is the ranking number of the velocity uniformity of the nth section, where 1 <= m <= N; the spline point corresponding to the nth section is perpendicular to the inner channel wall and moves inward by the inlet width. Expand the inner wall to reduce the flow channel area; use the finite volume method to recalculate the velocity distribution of the fluid in the entire flow channel and calculate the velocity uniformity on different sections. The velocity uniformity of the N sections at the i-th time is: C i v1 , C i vn ,…,C i vN If there is C i vn >C i-1 vn When (i.e., the velocity uniformity of two adjacent sections of the same section is compared), the size of the nth section modified by the i-1th flow channel shape is taken as the final size of the nth section, where i>=3; when N sections all meet C i vn >C i-1 vn When , the inner flow channel shape is output; thus, a flow channel shape with good cross-sectional velocity uniformity is obtained.

[0019] The beneficial effects of the present invention are:

[0020] 1. In the meltblown fabric manufacturing process, the backflow vortex in the flow channel of the outlet suction device during the web forming process is eliminated to make the flow more uniform; the uneven gas velocity in the flow channel of the outlet suction device during the web forming process is solved, which leads to the uneven meltblown fabric produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the method for designing a flow channel structure with uniform cross-sectional velocity according to the present invention;

[0022] Figure 2 is a velocity distribution diagram in the initial flow channel of the present invention;

[0023] Figure 3 is a velocity distribution diagram in the flow channel after the outer wall is modified according to the present invention;

[0024] Figure 4 It is a velocity distribution diagram in the flow channel after the inner and outer walls are modified according to the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore only shows the components related to the present invention.

[0026] like Figure 1 As shown, a flow channel structure design method with uniform cross-sectional velocity includes the following steps:

[0027] S1. Establish an initial flow channel by connecting the inlet and outlet of the flow field with a straight line. In this embodiment, a spline line is formed by sequentially connecting 11 equidistant spline points between two straight lines. The inlet is set as a velocity inlet with an inlet velocity of V = 30 m / s, and the outlet is set as a pressure outlet with an outlet pressure of 1 atmosphere.

[0028] S2. Use the finite volume method to find the velocity distribution of the fluid in the entire flow channel; Figure 2 The figure shows how the Fluent simulation software simulates the initial flow channel model and obtains the velocity distribution in the initial flow channel;

[0029] S3: Count the velocity distribution in the flow channel and make a judgment, compare the maximum velocity of the flow channel section with the initial threshold, return to iteration if the condition is not met, modify the outer flow channel structure until the condition is met, and output the outer flow channel shape; including the following steps:

[0030] S31, projecting the spline points perpendicular to the channel wall, sequentially connecting the corresponding projection points on the two walls (in the initial state, the spline points and the projection points coincide) to draw a channel cross section. In this embodiment, N=11, and the velocity distribution on 11 channel cross sections is calculated;

[0031] S32. Modify the flow channel by moving spline points. The outer wall spline points move outward perpendicular to the flow channel wall to increase the flow channel area. The inner wall spline points move inward perpendicular to the flow channel wall to reduce the flow channel area. In this embodiment, X is set to 5, and the distance moved by each spline point is in the range of 0%-5% of the inlet width.

[0032] S33. Count the maximum fluid velocities on 11 sections and record them as V1, V2, ..., V 11 , set the speed threshold to V α =36m / s, in this embodiment, the first measurement {V1, V2, ..., V 11} is {118,108,98,91,83,75,66,60,54,50,47}, where max{V1,V2,…,V 11}=118m / s, 118m / s corresponds to m=1, for {V1,V2,…,V 11}, the fluid velocity ranking order is {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, then the spline points corresponding to the cross sections are moved perpendicular to the outer channel wall outward by 5%, 4.5%, 4%, 3.5, 3, 2.5, 2, 1.5, 1, 0.5, 0% of the inlet width to expand the outer wall; the finite volume method is used to recalculate the velocity distribution of the fluid in the entire channel, and the second measurement {V1, V2, …, V 11} is {104,107,98,91,81,70,62,55,50,45,41}, because max{V1,V2,…,V 11}=107, that is, V2>V α The outer wall is expanded to increase the flow channel area. The corresponding speed ranking is {2, 1, 3, 4, 5, 6, 7, 8, 9, 10, 11}. The spline points corresponding to the cross-section are moved perpendicular to the outer flow channel wall outward by 4.5%, 5%, 4%, 3.5, 3, 2.5, 2, 1.5, 1, 0.5, 0% of the inlet width respectively; the cycle continues until max{V j n}<=V α If , proceed to step S4, otherwise repeat the above steps; Figure 3 The figure shows the velocity distribution in the flow channel after the final outer wall modification is completed;

[0033] S4. After completing step S33, the velocity distribution of the fluid in the entire flow channel is recalculated using the finite volume method, and then the velocity uniformity on different sections is calculated using the formula: C v1 , C v2 ,…,C v11 , the first measurement of velocity uniformity is:

[0034] {75.52%, 96.54%, 106.67%, 103.56%, 99.79%, 90.47%, 82.38%, 73.82%, 65.53%, 62.37%, 49.07%}, the velocity uniformity ranking from large to small (larger values indicate worse uniformity, smaller values indicate better uniformity) is 7, 4, 1, 2, 3, 5, 6, 8, 9, 10, 11. In this example, the velocity uniformity corresponding to different sections is from high to low, and the moving distance of each section is: 2%, 3.5%, 5%, 4.5%, 4%, 3%, 2.5%, 1.5%, 1%, 0.5%, 0%, completing the first inward movement of the inner channel wall; using the finite volume method to calculate the velocity distribution of the fluid in the entire channel for the second time, the second measured velocity uniformity is:

[0035] {71.31%, 92.64%, 100.17%, 99.85%, 95.34%, 88.87%, 80.41%, 68.42%, 61.33%, 59.89%, 47.31%}. Since the velocity uniformity of the 11 sections measured in the second time is less than that in the first measurement, the order of velocity uniformity from high to low is 7, 4, 1, 2, 3, 5, 6, 8, 9, 10, 11. The moving distance of each section is 2%, 3.5%, 5%, 4.5%, 4%, 3%, 2.5%, 1.5%, 1%, 0.5%, 0% of the inlet width, completing the second inward movement of the inner channel wall. The measurement is repeated continuously. The 27th and 28th calculated fluid velocities in the entire channel are:

[0036] {40.66%,41.73%,44.21%,44.67%,41.34%,38.96%,36.62%,35.11%,33.24%,29.76%,24.81%},{39.59%,40.73%,42.19%,41.62%,39.34%,37.67%,35.47%,33.87%,32.69%,27.84%,26.36%}, due to C 28 v11 >C 27 v11 , then the size of the 27th flow channel shape modification is used as the final size of the 11th section, and the number of sections involved in the adjustment will also change from 11 to 10; when the number of sections involved in the adjustment is reduced to 0, the expansion of the inner wall surface is stopped and the modification of the flow channel is completed. At this time, a flow channel structure with better cross-sectional velocity uniformity is obtained; Figure 4 As shown in the figure, it can be seen that the maximum velocity in the figure drops from 118m / s to 33.5m / s, and the velocity distribution of the fluid in the entire flow channel is Figure 2More uniform in.

[0037] The beneficial effects of the present invention are: in the meltblown cloth manufacturing process, the backflow vortex in the internal flow channel of the outlet suction device during the web forming process is eliminated, making the flow more uniform; and solving the problem of uneven meltblown cloth produced due to uneven gas velocity in the flow channel of the outlet suction device during the web forming process.

[0038] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for designing a flow channel structure with uniform cross-sectional velocity, characterized in that: The following steps are involved: S1. Establish a flow channel between the flow field inlet and outlet, set the flow channel inlet as the velocity inlet, and establish an initial flow channel model; S2. Use the finite volume method to find the velocity distribution of the fluid in the entire flow channel; S3. Compare the maximum velocity of the flow channel section with the fluid velocity threshold. If the condition is not met, return to the iteration and modify the outer flow channel structure until the condition is met, and output the outer flow channel shape. Comparing the maximum velocity of the flow channel section with a fluid velocity threshold comprises the following steps: S31, projecting the spline points perpendicular to the channel wall, sequentially connecting the corresponding projection points on the two walls to draw N channel sections, and calculating the velocity distribution on the N channel sections; S32. Modify the external flow channel by moving spline points. The outer wall spline points move outward perpendicular to the flow channel wall to expand the outer wall surface to increase the flow channel area. The inner wall spline points move inward perpendicular to the flow channel wall to expand the inner wall surface to reduce the flow channel area. Each spline point movement distance is 0% - X% of the inlet width, where N-1 is a multiple of X. S33. Statistically calculate the maximum fluid velocity at the cross-section of the nth flow channel and denote it as V n , where 1 <= n <= N. Set the fluid velocity threshold as V α . When max{V n} > V α , sort the fluid velocities in {V1, V n , …, V N} from largest to smallest. The serial number corresponding to the ranking of the fluid velocity at the nth cross-section is m, where 1 <= m <= N. The spline point at the nth cross-section moves perpendicularly outward from the outer wall of the outflow channel by the inlet width: The expanded outer wall surface; after completing the expanded outer wall surface, recalculate the velocity distribution of the fluid in the entire flow channel. When the maximum fluid velocity at the nth cross-section in the jth iteration satisfies max{V j n} <= V α , perform step S4 and take the expanded outer wall surface completed in the jth iteration as the output outflow channel shape; otherwise, recalculate the velocity distribution of the fluid in the entire flow channel and continue to expand the outer wall surface; S4. Compare the velocity uniformity of two adjacent flow channel sections. If the conditions are not met, return to the iteration and modify the internal flow channel structure until the conditions are met, and output the internal flow channel shape.

2. The method for designing a flow channel structure with uniform cross-sectional velocity according to claim 1, wherein: Comparing the velocity uniformity of adjacent two flow channel cross-sections includes: after completing step S33, statistically analyzing the velocity distribution of the fluid in the entire flow channel, and calculating the velocity uniformity at the nth cross-section as C vn , where 1 <= n <= N, and the formula for velocity uniformity is as follows: Where C v is the velocity uniformity, σ v is the standard deviation of fluid velocity, is the average value of the cross-sectional fluid velocity; for {C v1 ,C vn ,…,C vN The velocity uniformity of the n-th section is sorted from large to small, and the sequence number corresponding to the velocity uniformity ranking of the fluid in the n-th section is m, where 1<=m<=N; the spline point of the n-th section is perpendicular to the inner flow channel wall and moves inward by the inlet width. Expand the inner wall surface; calculate the velocity uniformity of the fluid in the entire flow channel at the i-th and n-th sections as C i vn , when the i-th n-th section satisfies C i vn >C i-1 vn When the inner channel wall moves inwards for i-1 times, the inner channel shape of the nth section is taken as the inner channel shape; then the remaining N-1 sections are measured repeatedly. When all sections meet C i vn >C i-1 vn When , the inner flow channel shape is output.

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