Full streamline double-outlet air duct structure based on NURBS surface

Abstract

The application relates to a full streamline double-outlet air duct structure based on a NURBS curved surface, which comprises an air inlet surface connected with a fan, an upper air outlet surface and a lower air outlet surface arranged in an up-down mode, a streamline cavity constructed by a NURBS curved surface, and three parameterized sections including a lower flow section, an acceleration section and an upper flow distribution section; the lower flow section is connected with the air inlet surface and the lower air outlet surface, and the tension coefficient is set as 0.8 to keep a gentle transition; the acceleration section extends from the inlet surface to the neck of the air duct, and the tension coefficient is set as 1.8 to realize streamline contraction; the upper flow distribution section extends from the neck of the air duct to the upper air outlet surface, and the tension coefficient is set as 1.2 to balance air flow distribution. Compared with the prior art, the application has the advantages of uniform air outlet, reduced energy consumption, prolonged fatigue life, increased space utilization of equipment and the like.

Description

Technical Field

[0001] This invention relates to the field of hot air drying technology for textile printing and dyeing industries, and in particular to a fully streamlined dual-outlet air duct structure based on NURBS curved surfaces. Background Technology

[0002] The core processes of textile production mainly include four major steps: warping, sizing, weaving, and finishing. Among them, the dyeing and heat setting process in the finishing stage is a key quality control node, directly affecting the physicochemical properties and appearance quality of the finished fabric. The heat setting unit, as the core equipment of this process, is characterized by its complex structure and high energy consumption; its operational efficiency is crucial for controlling production costs. During the heat setting process, the hot air drying system in the oven drives a high-speed airflow through a circulating fan. The airflow is heated by a steam heat exchanger to form constant-temperature hot air, which then enters the air duct system and is finally evenly blown onto the surface of the wet fabric by the air spray box, completing the drying and setting of the fabric. In this process, the design of the air duct structure directly affects the uniformity of airflow from the heat setting machine, thus determining the stability of the fabric surface temperature field distribution and the moisture evaporation rate. Therefore, optimizing the air duct system design to ensure uniform airflow distribution and reduce system resistance is of great significance for improving the efficiency of the heat setting process and reducing energy consumption.

[0003] In the field of duct system optimization research, scholars both domestically and internationally have achieved a series of significant results. Leqi Tong et al. innovatively proposed a T-joint flow guiding device, which significantly improved the uniformity of the central exhaust system and reduced system resistance through structural parameter optimization. Haoran Chen's team developed a duct parameter calculation method based on model recognition algorithms. By monitoring the fan outlet and terminal pressure in real time, it achieved accurate prediction of duct characteristics under different operating conditions. Compared with traditional calculation methods, this method has higher accuracy and stronger robustness under different operating conditions. Li et al. used computational fluid dynamics methods to optimize the design of arc-shaped joint structures, effectively improving airflow distribution through flow field visualization analysis. RanGao's research group developed a novel low-resistance T-joint, which reduces resistance by 42% through innovative arc surface structure design. However, it should be noted that the above research results are all limited to the application scenario of a single air-jet box air supply system. Currently, with the rapid development of the textile printing and dyeing industry towards high efficiency and intensification, modern heat setting machines urgently need to adopt a new system architecture of "one duct with multiple air-jet boxes." This design can not only optimize the equipment space layout but also improve thermal energy utilization. Existing literature lacks reports on duct structure designs capable of providing uniform inflow parameters for multiple air jet boxes simultaneously. This is particularly challenging given the technical requirement of ensuring that the uniformity deviation of the airflow from each air jet box does not exceed 5%. Solving this problem will have significant engineering application value for improving the quality of heat setting processes and reducing energy consumption. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art by providing a fully streamlined dual-outlet air duct structure based on NURBS surface, which has the advantages of uniform airflow, reduced energy consumption, extended fatigue life, and increased space utilization of equipment.

[0005] The surface is constructed using the Non-Uniform Rational B-Spline (NURBS) method, which strictly ensures the continuity and smoothness of the surface, reduces friction and eddies between the airflow and the duct wall, reduces energy loss caused by airflow and wall friction, and ensures stable and uniform airflow.

[0006] This invention provides a fully streamlined dual-outlet air duct structure based on NURBS surfaces, comprising: The airflow inlet surface connected to the fan; The upper and lower air outlet surfaces are arranged vertically. The streamlined cavity constructed from NURBS surfaces comprises three parameterized sections: a lower flow section, an acceleration section, and an upper flow distribution section. The lower flow section connects the airflow inlet surface and the lower outlet surface, with a tension coefficient set to 0.8 to maintain a smooth transition. The acceleration section is located at the neck of the duct, with a tension coefficient set to 1.8 to achieve streamlined contraction. The upper flow distribution section extends from the neck of the duct to the upper outlet surface, with a tension coefficient set to 1.2 to balance airflow distribution. With no abrupt changes in cross-section and strong bending in the main body, the cavity can precisely guide the airflow direction, effectively resist wind pressure loads and turbulent impacts of ≥1500Pa in operating conditions, ensure structural integrity and extend service life.

[0007] Furthermore, the NURBS surface node vectors are generated using a non-uniform distribution algorithm; Furthermore, the surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling. The surface tension coefficient achieves the weight allocation of normal constraint and tangential continuity by adjusting the first derivative of the control point.

[0008] Furthermore, NURBS uses the DeBoor-Cox-Mansfield basis function recursive formula.

[0009] Assuming a non-decreasing sequence exists, the node vector of the control parameter... As shown in equation (1): In the formula, the first and second nodes Last node All repeated Second-rate; For the firsti Each node.

[0010] Based on equation (1), we can obtain B The expression for the spline basis function is shown in equation (2): In the formula, p Let the degree of the basis function be , when p= At 0 o'clock, B The spline basis function expression is of the form: ;when hour, B The expression for the spline basis function is: .

[0011] Assume there exists a sequence of control vertices. ,and B The degree of the spline is p Based on equation (1), we can obtain... p Second-rate B The parametric equation of the spline curve is given by equation (3): To construct a path that can pass through existing data points B spline curves, which guarantee the desired result B The spline curve has a solution, and its complete endpoint constraints satisfy the following equation: In the formula, the total number of control vertices is: m +1, the total number of data points is 1 n +1, to satisfy ; , These represent the positions of the first and last points, respectively. Represent the interpolation equation for the intermediate point; , These are the tangent directions at the beginning and end points, respectively. , This is the proportionality coefficient.

[0012] and B Compared to spline curves controlled by a single parameter, B Spline surfaces are controlled by two parameters. Assume... To control the vertices, and B The two control parameters of the spline surface are: direction and direction. U and W , where node vector W As shown in equation (5): In the formula, the first and second nodes Last node All repeated Second-rate; For the first j Each node.

[0013] when , When, two parameters B The definition of a spline surface is shown in equation (6): In the formula, , All B Basis functions of spline surfaces; The values ​​are shown in equation (2); The expression is shown in equation (7): u Towards p Second-rate, w Towards q The parametric equations of the NURBS surface of order 1 are given by equation (8): In the formula, for u Towards p Second-rate, w Towards q The basis functions for the NURBS surface are expressed as follows: Therefore, non-uniform u Towards p Second-rate, w Towards q The NURBS surface is represented by equation (10): Furthermore, the air duct structure is manufactured using galvanized steel sheet or stainless steel; it is formed through stamping, bending, and welding processes to ensure the airtightness and structural strength of the cavity.

[0014] Furthermore, the upper air outlet surface (1) and the lower air outlet surface (2) are respectively connected to two independent air spray boxes. When the system is working, the hot air generated by the fan is transported through the air duct, and after being split by the upper air outlet surface (1) and the lower air outlet surface (2), it enters the upper and lower air spray boxes. Finally, the hot air is blown onto the surface of the wet fabric in the form of airflow through the specific outlet of the air spray box, realizing an efficient heat exchange and drying process.

[0015] Furthermore, the NURBS surfaces of the lower flow section, acceleration section, and upper shunt section are generated using the following parametric procedure: Specifically: the nrbmak function is used to define a rectangular array of control points; the nrbclose function is used to close the curve; the nrbRuled function is used to construct a ruled surface, and the control point coordinates are adjusted to apply tension coefficient constraints.

[0016] Furthermore, the parametric modeling procedure for the air duct structure includes: The NURBS surface is generated recursively using the DeBoor-Cox-Mansfield basis function; the ruled surface is constructed using the nrbRuled function; and the tension coefficient constraint is achieved by adjusting the coordinates of the control points.

[0017] Furthermore, the overall dimensions of the air duct are 1876mm (y direction) × 613mm (x direction) × 460mm (z direction), with a wall thickness of 5mm.

[0018] Compared with the prior art, the present invention has the following advantages: (1) Good air uniformity. By precisely controlling the streamlined profile through NURBS surface, the velocity variation coefficient and pressure variation coefficient of the upper and lower air outlets are reduced, and the air uniformity deviation is less than 5%, thus improving uniformity.

[0019] (2) Reduced energy consumption. The streamlined design reduces duct resistance, and the dual-outlet structure improves thermal efficiency and overall energy saving efficiency. Compared with conventional ducts, the streamlined duct can strictly ensure the continuity and smoothness of the curved surface, reduce friction and eddies between the airflow and the duct wall, reduce energy loss caused by airflow and wall friction, and make the airflow velocity gradient small in the duct, so as to achieve high-efficiency, high-quality and uniform air supply, and avoid the phenomenon of excessive or weak local air supply.

[0020] (3) Good structural reliability. The steel plate combined with NURBS surface topology optimization extends the fatigue life under wind pressure greater than 1500Pa.

[0021] (4) Improved process adaptability and assemblability. The parametric modeling system supports rapid adjustment of the tension coefficient (adjustable range of 0.8-1.8) to complete the design iteration of new model air ducts. The air duct designed in this invention keeps the shape of the air inlet face and the two air outlet faces unchanged (i.e., the shape of the air inlet face of the air duct is the same as the shape of the fan outlet of the heat setting machine, and the shape of the air outlet face of the air duct is the same as the shape of the inlet of the two air spray boxes arranged above and below). The distance between the two air outlet faces of the air duct and the relative position of the air inlet face of the air duct remain unchanged, so the design iteration of new model air ducts can be realized.

[0022] (5) Compared with conventional air ducts, dual-outlet air ducts have two air outlets of the same size, which increases the air delivery area of ​​the air duct and increases the space utilization of the equipment. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the fully streamlined dual-outlet air duct structure based on NURBS surface in Example 1. Figure 2 This is a flow field distribution diagram inside a fully streamlined dual-outlet air duct based on NURBS surfaces, as shown in Example 1. Figure 3 This is a schematic diagram of the monitoring points at the air outlet surface in Example 1; Figure 4 The values ​​for pressure and velocity at the air outlet surface in Example 1 are shown. Figure 5 The values ​​of air outlet surface pressure and velocity are shown in Example 1. Figure 6 This is a schematic diagram of the structure of Comparative Example 1; Figure 7 The values ​​of pressure and velocity at the air outlet surface are for comparison example 1; Figure 8 The values ​​of air outlet surface pressure and velocity are for Comparative Example 1; Figure 9 This is a schematic diagram of the structure of Comparative Example 2; Figure 10 For comparison, the air outlet surface pressure and velocity data are shown in Example 2. Figure 11 For comparison example 2, the data on the pressure and velocity at the air outlet surface are provided. Figure 12 This is a schematic diagram of the structure of Comparative Example 3; Figure 13 For comparison, the pressure and velocity data at the air outlet surface are shown in Example 3; Figure 14 The data includes the pressure and velocity at the air outlet surface for Comparative Example 3.

[0024] Attached diagram labels: 1-Upper air outlet face; 2-Lower air outlet face; 3-Airflow inlet face; 4-Neck of air duct. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0026] Example 1 This embodiment provides a fully streamlined dual-outlet air duct structure based on NURBS surfaces, including: The airflow inlet surface 3, which is connected to the fan, has dimensions of 366mm × 348mm. The upper air outlet surface 1 and lower air outlet surface 2 are arranged vertically, each measuring 80mm × 510mm. Each of these surfaces is connected to two independent air spray boxes. During system operation, hot air generated by the fan is transported through the duct, then split by the upper air outlet surface 1 and lower air outlet surface 2 before entering the upper and lower air spray boxes. Finally, the hot air is blown onto the surface of the wet fabric in the form of an airflow through specific outlets in the air spray boxes, achieving a highly efficient heat exchange and drying process.

[0027] The streamlined cavity constructed from NURBS surfaces comprises three parameterized sections: a lower flow section, an acceleration section, and an upper flow distribution section. The lower flow section connects the airflow inlet surface 3 and the lower outlet surface 2, with a tension coefficient set to 0.8 to maintain a smooth transition. The acceleration section is located at the neck of the duct 4, with a cross-sectional dimension of 150mm × 270mm, and a tension coefficient set to 1.8 to achieve streamlined contraction. The upper flow distribution section extends from the neck of the duct to the upper outlet surface 1, with a tension coefficient set to 1.2 to balance airflow distribution. The air duct structure is manufactured using galvanized steel sheet or stainless steel; it is formed through stamping, bending, and welding processes to ensure the airtightness and structural strength of the cavity. The overall dimensions of the air duct are 1876mm (y-direction) × 613mm (x-direction) × 460mm (z-direction), with a wall thickness of 5mm.

[0028] With no abrupt changes in cross-section and strong bending in the main body, the cavity can precisely guide the airflow direction, effectively resist wind pressure loads and turbulent impacts of ≥1500Pa in operating conditions, ensure structural integrity and extend service life.

[0029] In a specific implementation, the NURBS surface uses second-order basis functions, and the node vectors are generated using a non-uniform distribution algorithm; the NURBS basis functions use the DeBoor-Cox-Mansfield basis function recursive formula.

[0030] Assuming a non-decreasing sequence exists, the node vector of the control parameter... As shown in equation (1): In the formula, the first and second nodes Last node All repeated Second-rate; For the first i Each node.

[0031] Based on equation (1), we can obtain B The expression for the spline basis function is shown in equation (2): In the formula, p Let the degree of the basis function be , when p= At 0 o'clock,B The spline basis function expression is of the form: ;when hour, B The expression for the spline basis function is: .

[0032] Assume there exists a sequence of control vertices. ,and B The degree of the spline is p Based on equation (1), we can obtain... p Second-rate B The parametric equation of the spline curve is given by equation (3): To construct a path that can pass through existing data points B spline curves, which guarantee the desired result B The spline curve has a solution, and its complete endpoint constraints satisfy the following equation: and B Compared to spline curves controlled by a single parameter, B Spline surfaces are controlled by two parameters. Assume... To control the vertices, and B The two control parameters of the spline surface are: direction and direction. U and W , where node vector W As shown in equation (5): In the formula, the first and second nodes Last node All repeated Second-rate; For the first j Each node.

[0033] when , When, two parameters B The definition of a spline surface is shown in equation (6): In the formula, , All B Basis functions of spline surfaces, The values ​​are shown in equation (2). The expression is shown in equation (7): u Towards p Second-rate, w Towards qThe parametric equations of the NURBS surface of order 1 are given by equation (8): In the formula, for u Towards p Second-rate, w Towards q The basis functions for the NURBS surface are expressed as follows: Therefore, non-uniform u Towards p Second-rate, w Towards q The NURBS surface can be represented by equation (10): In the formula, These are weight parameters, which are scalar values, and are related to the control vertices. One-to-one correspondence; the greater the weight, the stronger the influence of the corresponding control vertex on the local shape of the surface, allowing for precise representation of complex geometries such as conic sections and spheres.

[0034] In Example 1, a second-order NURBS surface is used, and its expression can be represented by equation (11): The NURBS surfaces of the lower flow section, acceleration section, and upper flow branch section are generated using the following parametric procedures: Specifically: the nrbmak function is used to define a rectangular array of control points; the nrbclose function is used to close the curve; the nrbRuled function is used to construct a ruled surface, and the control point coordinates are adjusted to apply tension coefficient constraints.

[0035] The parametric modeling procedure for the air duct structure includes: recursively generating NURBS surfaces using DeBoor-Cox-Mansfield basis functions; constructing ruled surfaces using the nrbRuled function; and adjusting the coordinates of control points to achieve tension coefficient constraints.

[0036] The surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling. It adjusts the weight distribution of normal constraints and tangential continuity by modifying the first derivative of the control points. The mathematical essence of the tension coefficient can be expressed as follows: when the tension coefficient τ→0, the surface releases the vertical constraint, tending towards a uniformly relaxed state, and the surface transitions freely at the boundary; when the tension coefficient τ∈(0,1), partial constraints are applied by linear interpolation; when the tension coefficient τ→1, the surface has a forced boundary that is completely vertical, approaching a controlled polygon; when the tension coefficient τ>1, small-scale over-range adjustments are allowed, but the node spacing is exponentially compressed, requiring the insertion of auxiliary control points to maintain stability. In Example 1, the tension coefficient τ=0.8 for the lower flow section, indicating that 80% of the normal constraint strength is applied at the boundary, i.e., 20% of the tangential degree of freedom is allowed. This setting maintains approximately vertical geometric features (80% strength) while retaining necessary curvature transition (20% relaxation).

[0037] The flow field meshing and calculation of the duct were performed using the commercial software Ansys Fluent 2022R1, employing a volume mesh with a hybrid honeycomb and hexahedral structure, resulting in approximately 41,000 meshes. A pressure-based steady-state solver was used. The SST k-ω turbulence model based on the Reynolds-averaged Navier-Stokes (RANS) equations was employed. Wall conditions were described using standard wall functions. With the fan power at 100%, the total fan pressure was 700 Pa, and the maximum output airflow reached 7500 m³ / h. 3 / h, after conversion, the airflow inlet velocity of the duct is approximately 16.35 m / s. After the calculation is completed, the pressure and velocity distribution of the duct are extracted, such as... Figure 2 As shown.

[0038] Pressure field distribution in air duct Figure 2 (a) shows that the maximum static pressure occurs in the area below the neck of the entire duct. Although there is a small-scale pressure backflow at both outlet locations, the overall pressure distribution is relatively uniform; the duct velocity field distribution... Figure 2 (b) shows that the velocity value decreases closer to the duct wall. This velocity distribution characteristic can reduce the risk of air leakage at the joint and reduce energy loss to a certain extent. At the same time, the velocity value inside the duct is relatively large, and no large-scale eddies are formed in the internal flow field. The velocity and pressure traces of the flow field are distributed in an orderly manner, which proves that the duct based on the NURBS surface largely avoids energy loss and has a positive effect on improving the drying efficiency of the fabric heat setting machine.

[0039] The outflow from the two air outlets of the air duct directly affects the drying performance of the fabric. Figure 2(b) As can be seen, under the calculated operating conditions, the air velocity at the upper and lower air outlets of the duct is basically the same, approximately 30 m / s. For a more intuitive comparative analysis, 400 velocity monitoring points were selected at equal intervals on each of the two air outlet surfaces. Specifically, eight straight lines were evenly selected 5 mm from the left and right sides of the air outlet surface, with a vertical distance of 10 mm between each pair of lines. Then, 50 points were selected at equal intervals on each straight line (see diagram for monitoring point locations). Figure 3 Number the 50 monitoring points in each column from bottom to top as 1 to 50; number the 8 monitoring points from left to right as 1 to 8 (a1 to a8 on the upper air outlet surface; b1 to b8 on the lower air outlet surface). Extract the pressure and velocity data from 400 monitoring points on each air outlet surface. The pressure and velocity values ​​on the upper air outlet surface are as follows: Figure 4 As shown, the pressure and velocity values ​​at the lower air outlet are as follows: Figure 5 As shown.

[0040] like Figure 4 , Figure 5 As shown: 1) Overall, although the pressure and velocity trend curves on the upper and lower air outlets are not completely consistent, their numerical values ​​are quite similar: the pressure values ​​are mainly concentrated in the range of 400~600Pa, while the velocity values ​​are mostly concentrated in the range of 25~30m / s.

[0041] 2) On the upper air outlet surface, the pressure distribution exhibits a "high in the middle, low on both sides" pattern. Specifically, the closer to the center of the air outlet surface, the higher the pressure value; conversely, the closer to the duct wall, the lower the pressure value. At the monitoring points with smaller numbers (numbered 1 to 5) on the upper air outlet surface, the air pressure is relatively low. The lowest overall pressure value is found at curve a8, indicating that the air pressure is lower in the rightmost area when facing the air outlet. The pressure characteristics of the lower air outlet surface are that the pressure values ​​corresponding to curves b1 and b8 are the lowest, meaning that the static pressure value near the wall is lower, below 500 Pa. Furthermore, the closer to the middle area, the smaller the pressure fluctuation range, and the more stable the corresponding curve.

[0042] 3) On the upper air outlet surface, the velocity distribution exhibits a similar "high in the middle, low on both sides" pattern to the pressure change trend. The pressure value is at its lowest level on curve a8 in the rightmost region. If the more peripheral parts are not considered, the velocity value at the upper air outlet is mainly concentrated in the range of 25~32 m / s. The velocity curve change trend at the lower air outlet is similar to the pressure change trend at the air outlet surface. Near the duct wall, the velocity value is lower and fluctuates more, while in the middle region, the velocity value ranges from approximately 28~31 m / s and is relatively evenly distributed.

[0043] The core objective of an air duct is to distribute the continuous airflow generated by the fan as evenly as possible through the upper and lower air outlets to the two air jet boxes. Simultaneously, it's crucial to ensure the airflow conditions at both outlets are as consistent as possible. Velocity, as a vector, has three components in the Cartesian coordinate system: x, y, and z. In air duct applications, the velocity component perpendicular to the outlet cross-section is the effective velocity component.

[0044] Based on airflow velocity data, an index for evaluating the air supply performance of ducts—the velocity variation coefficient—is constructed. Its definition and calculation method are as follows: In the formula: The standard deviation of the velocity at the air outlet surface represents the degree of velocity dispersion. This represents the average velocity on the surface of the air outlet. n The number of velocity samples on the air outlet surface (here) ); For the first One speed sample value.

[0045] The mean velocity and singularity coefficients of the air outlet surface of the air duct based on the NURBS surface are shown in Table 1.

[0046] Table 1. Velocity of air outlet surface in duct based on NURBS surface in Example 1 As shown in Table 1, the average velocity values ​​on the upper and lower air outlet surfaces are similar, approximately 28 m / s, and the velocity singularity coefficients are relatively small (by definition, the smaller the velocity singularity coefficient, the smaller the difference in velocity distribution on the air outlet surface).

[0047] Similarly, an index for evaluating the uniformity of pressure at test points, namely the pressure singularity coefficient, is established. The calculation method is as follows: In the formula, The standard deviation of pressure at the air outlet surface represents the degree of pressure dispersion. This represents the average pressure on the air outlet surface. The first one on the surface of the air outlet i Each pressure sample value.

[0048] The mean pressure and singularity coefficients of the air outlet surface of the air duct based on the NURBS surface are shown in Table 2.

[0049] Table 2. Air outlet surface pressure of the duct based on NURBS surface in Example 1. Table 2 shows that the average pressure on the upper and lower air outlet surfaces is close, approximately 514 Pa, and the pressure singularity coefficients are also close and low, indicating good pressure uniformity on the air outlet surfaces (by definition, the smaller the pressure singularity coefficient, the smaller the difference in pressure distribution on the air outlet surface).

[0050] Combination Figure 4 , Figure 5 As shown in Tables 1 and 2, the streamlined dual-outlet air duct based on NURBS surface parametric design exhibits uniform and stable outflow velocity and pressure with minimal deviation in airflow uniformity. This provides excellent pressure and velocity inlet conditions for subsequent air supply to the air jet boxes and makes it entirely possible to ensure that the airflow uniformity deviation of each air jet box meets the technical requirement of no more than 5%. This is highly beneficial for achieving high-efficiency and high-quality drying of fabrics.

[0051] Comparative Example 1 like Figure 6 As shown, a streamlined dual-outlet air duct based on a NURBS surface uses a non-uniform distribution algorithm for node vectors. Its appearance and structure are similar to Example 1, with the same airflow inlet cross-section, two outlet cross-sections, and duct neck cross-section. The relative positions of the two outlet surfaces and the airflow inlet surface remain unchanged. Compared to Example 1, Comparative Example 1 only changes the NURBS tension parameters: Lower flow section: connects the airflow inlet surface and the lower air outlet surface, with a tension coefficient set to 1.1; Acceleration section: located at the neck of the duct, with a tension coefficient set to 1.0; Upper flow segment: extends from the neck to the upper air outlet surface, with a tension coefficient set to 1.1.

[0052] Simulation calculations were performed on the streamlined air duct of Comparative Example 1. The operating conditions and boundary conditions were the same as in Example 1, and the monitoring point extraction locations were also consistent with Example 1. The pressure and velocity distribution curves of the upper and lower air outlet surfaces of Comparative Example 1 are shown below. Figure 7 , 8 As shown.

[0053] Figure 7 , Figure 8 The results show that, compared with Example 1, there is no significant difference in the distribution range and trend of velocity and pressure values ​​on the upper and lower air outlet surfaces in Comparative Example 1.

[0054] The mean velocity and singularity coefficients of the air outlet surface of Comparative Example 1 are shown in Table 3; the mean pressure and singularity coefficients of the air outlet surface of Comparative Example 1 are shown in Table 4.

[0055] Table 3 Comparative Example 1: Outlet surface velocity Table 4 Comparative Example 1: Air Outlet Surface Pressure Comparing the statistical results of Comparative Example 1 (i.e., Tables 3 and 4) with the statistical results of Example 1 (i.e., Tables 1 and 2), we can see that: 1) The velocity of the upper and lower air outlet surfaces in Example 1 is 28 m / s, while the average velocity of the two air outlet surfaces in Comparative Example 1 differs by about 3 m / s. From the perspective of velocity singularity coefficient values, the velocity singularity coefficients of the two air outlet surfaces in Comparative Example 1 are greater than those in Example 1, indicating that the velocity uniformity of Example 1 is better.

[0056] 2) The average pressure at the upper outlet surface of Comparative Example 1 is approximately 544 Pa, while the average pressure at the lower surface is approximately 520 Pa, with a pressure difference of approximately 22 Pa. In contrast, the average pressures at the upper and lower outlet surfaces of Example 1 are similar, both around 514 Pa. Furthermore, the pressure singularity coefficients at the upper and lower outlet surfaces of Comparative Example 1 are also greater than those of Example 1, indicating that the uniformity of the outflow pressure in Comparative Example 1 is not as good as that in Example 1.

[0057] In summary, comparing the pressure and velocity uniformity at the air outlet surface of Comparative Example 1 and Example 1, Comparative Example 1 is inferior to Example 1. This demonstrates that even when using NURBS surface parametric modeling, different tension coefficients can affect the air outlet performance of the duct.

[0058] Comparative Example 2 like Figure 9 As shown, a streamlined dual-outlet air duct based on a NURBS surface uses a non-uniform distribution algorithm for node vectors. Its appearance and structure are similar to Example 1, with the same airflow inlet cross-section, two outlet cross-sections, and duct neck cross-section. The relative positions of the two outlet surfaces and the airflow inlet surface remain unchanged. Compared to Example 1, Comparative Example 2 only changes the NURBS tension parameters: Lower flow section: connects the airflow inlet surface and the lower air outlet surface, with a tension coefficient set to 1.2; Acceleration section: located at the neck of the duct, with a tension coefficient set to 1.8; Upper flow segment: extends from the neck to the upper air outlet surface, with a tension coefficient set to 0.8.

[0059] Simulation calculations were performed on the streamlined air duct of Comparative Example 2. The operating conditions and boundary conditions were the same as in Example 1, and the monitoring point extraction locations were also consistent with those in Example 1. The pressure and velocity distribution curves of the upper and lower air outlet surfaces of Comparative Example 2 are shown below. Figure 10 , 11 As shown.

[0060] Figure 10 , 11 The results show that, compared with Example 1, Comparative Example 2 has no significant difference in the distribution range and trend of velocity and pressure values ​​on the upper and lower air outlet surfaces.

[0061] The mean velocity and singularity coefficients of the air outlet surface of Comparative Example 2 are shown in Table 5; the mean pressure and singularity coefficients of the air outlet surface of Comparative Example 2 are shown in Table 6.

[0062] Table 5 Comparative Example 2: Outlet surface velocity Table 6 Comparative Example 2: Air Outlet Surface Pressure Comparing the statistical results of Comparative Example 2 (i.e., Tables 5 and 6) with the statistical results of Example 1 (i.e., Tables 1 and 2), we can see that: 1) The velocity at the upper and lower air outlet surfaces of Comparative Example 2 and Example 1 is 28 m / s, but the velocity singularity coefficient value of Comparative Example 2 is greater than that of Example 1, indicating that the velocity uniformity of Example 1 is better.

[0063] 2) The average pressure at the upper outlet surface of Comparative Example 2 is approximately 494 Pa, while the average pressure at the lower surface is approximately 514 Pa, with a pressure difference of approximately 20 Pa. In contrast, the average pressures at the upper and lower outlet surfaces of Example 1 are similar, both around 514 Pa. Furthermore, the pressure singularity coefficients at the upper and lower outlet surfaces of Comparative Example 2 are also greater than those of Example 1, indicating that the uniformity of the outflow pressure in Comparative Example 2 is not as good as that in Example 1.

[0064] In summary, comparing the pressure and velocity uniformity at the air outlet surface of Comparative Example 2 and Example 1, Comparative Example 2 is inferior to Example 1. This demonstrates that even when using NURBS surface parametric modeling, different tension coefficients can affect the air outlet performance of the duct.

[0065] Comparative Example 3 like Figure 12 As shown, the dual-outlet duct has the same shape, size, and spatial position as Example 1 for the airflow inlet cross-section, the two outlet cross-sections, and the duct neck cross-section. Compared to Example 1, Comparative Example 3 does not use parametric modeling based on NUBRS surfaces, and is not streamlined in appearance; its outlet surface is perpendicular to the inlet surface.

[0066] The structure of Comparative Example 3 has the following characteristics: 1) Comparative Example 3 also keeps the airflow inlet section, the two outlet sections and the duct neck section unchanged, but Comparative Example 3 does not use the NURBS-based modeling method, the overall duct does not present a streamline shape, and the pipe between the two outlet surfaces undergoes two bends.

[0067] 2) Comparative Example 3 can be structurally considered as being composed of multiple pipe segments spliced ​​together.

[0068] 3) Because the air inlet and outlet planes of the air duct are perpendicular to each other in space, Comparative Example 3 has many bends and abrupt changes in cross-section.

[0069] Simulation calculations were performed on the air duct of Comparative Example 3. The operating conditions and boundary conditions were the same as in Example 1, and the monitoring point extraction locations were also consistent with those in Example 1. The pressure and velocity distribution curves at the upper and lower air outlet surfaces of Comparative Example 3 are shown below. Figure 13 , Figure 14 .

[0070] Depend on Figure 13 , Figure 14 It can be known that: 1) The eight curves (a1~a8) of the outlet surface pressure in Comparative Example 3 show dissimilar trends and irregular lines, reflecting significant differences between the data, with the maximum pressure difference exceeding 2000 Pa. Furthermore, the pressure value is highest at monitoring points numbered close to 50, and some curves show a small pressure peak near monitoring point number 10.

[0071] 2) In Comparative Example 3, the velocity fluctuation trend at the air outlet surface is similar to the pressure fluctuation trend. For monitoring points numbered less than 30, the velocity values ​​are unstable, fluctuating wildly. However, for monitoring points numbered greater than 30, the pressure values ​​remain stable on some curves and show an increasing trend on others. The maximum velocity difference exceeds 50 m / s. This suggests that vortices may exist in the lower half of the upper air outlet surface, causing numerical turbulence.

[0072] 3) The pressure and velocity curves on the lower air outlet surface in Comparative Example 3 also show similar trends. The velocity at the 0~20 numbered end is close to 0 m / s, and the pressure is close to 0 Pa. It can be seen that there may be no airflow blowing out from the lower half of the lower air outlet surface.

[0073] 4) In Comparative Example 3, the pressure difference at monitoring points numbered 20-50 on the air outlet surface is large, close to 2250Pa, and the velocity difference is also large, close to 60m / s.

[0074] The mean velocity and singularity coefficients of the air outlet surface of Comparative Example 3 are shown in Table 7; the mean pressure and singularity coefficients of the air outlet surface of Comparative Example 3 are shown in Table 8.

[0075] Table 7 Comparative Example 3: Outlet surface velocity Table 8 Comparative Example 3: Air Outlet Surface Pressure Comparing the statistical results of Comparative Example 3 (i.e., Tables 7 and 8) with the statistical results of Example 1 (i.e., Tables 1 and 2), we can see that: 1) The velocities of the upper and lower air outlets in Comparative Example 3 are very different, approximately 45 m / s and 28 m / s respectively, while the velocities of the upper and lower air outlets in Example 1 are both 28 m / s. Furthermore, the velocity singularity coefficients of Comparative Example 3 are much larger than those of Example 1, indicating that the velocity uniformity of Example 1 is significantly better than that of Comparative Example 3.

[0076] 2) The average pressure at the upper outlet of Comparative Example 3 was approximately 1353 Pa, and the average pressure at the lower outlet was approximately 842 Pa, resulting in a pressure difference of 511 Pa. In contrast, the average pressures at the upper and lower outlets of Example 1 were similar, both around 514 Pa. Furthermore, the pressure singularity coefficients at the upper and lower outlets of Comparative Example 3 were significantly greater than those of Example 1, indicating that the uniformity of the outflow pressure in Comparative Example 3 was far inferior to that in Example 1.

[0077] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0078] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A fully streamlined dual-outlet air duct structure based on NURBS surfaces, characterized in that, include: (3) airflow inlet surface connected to the fan; The upper air outlet surface (1) and the lower air outlet surface (2) are arranged vertically; the upper air outlet surface (1) and the lower air outlet surface (2) are respectively connected to two independent air spray boxes, and the hot air generated by the fan blows the hot air to the surface of the wet fabric in the form of airflow through the air spray boxes. The streamlined cavity constructed by the NURBS surface includes three parameterized sections: a lower flow section, an acceleration section, and an upper flow splitting section. The lower flow section connects the airflow inlet surface (3) and the lower outlet surface (2), with a tension coefficient of 0.

8. The acceleration section is located at the neck of the air duct (4), with a tension coefficient of 1.

8. The upper flow splitting section extends from the neck of the air duct (4) to the upper outlet surface (1), with a tension coefficient of 1.

2.

2. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, NURBS surface node vectors are generated using a non-uniform distribution algorithm.

3. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 2, characterized in that, The surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling. The surface tension coefficient achieves the weight allocation of normal constraint and tangential continuity by adjusting the first derivative of the control point.

4. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 2, characterized in that, NURBS surfaces use the DeBoor-Cox-Mansfield basis function recursive formula.

5. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 2, characterized in that, The non-uniform node vector of a NURBS surface is defined as: ， In the formula, , For nodes, non-uniform node vectors U , V The first and last nodes are repeated respectively , This is done to ensure that the curved surface passes through the beginning and end control points.

6. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The air duct structure is made of galvanized steel sheet or stainless steel; it is formed by stamping, bending and welding processes to ensure the airtightness and structural strength of the cavity.

7. The streamlined dual-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The NURBS surfaces of the lower flow section, acceleration section, and upper flow branch section are generated by a parametric program: a rectangular control point array is defined using the nrbmak function; the curve is closed using the nrbclose function; a ruled surface is constructed using the nrbRuled function, and tension coefficient constraints are applied by adjusting the coordinates of the control points.

8. The fully streamlined dual-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The parametric modeling procedure for air duct structures includes: The NURBS surface is generated recursively using the DeBoor-Cox-Mansfield basis function; the ruled surface is constructed using the nrbRuled function; and the tension coefficient constraint is achieved by adjusting the coordinates of the control points.

9. The fully streamlined dual-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The overall dimensions of the air duct structure are 1876mm×613mm×460mm, and the wall thickness is 5mm.

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