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

Abstract

The invention relates to a full-streamline double-outlet air duct structure based on an NURBS curved surface. The full-streamline double-outlet air duct structure comprises an airflow inlet surface connected with a fan; the upper air outlet surface and the lower air outlet surface are arranged up and down; the streamline cavity constructed by the NURBS curved surface comprises three parameterized sections, namely a lower circulation section, an acceleration section and an upper shunting section; the lower circulation section is connected with the airflow inlet face and the lower air outlet face, and the tension coefficient is set to be 0.8 so that smooth transition can be kept. The acceleration section extends from the inlet face to the neck of the air duct, and the tension coefficient is set to be 1.8 so that streamline shrinkage can be achieved. The upper flow dividing section extends to the upper air outlet face from the air channel neck, and the tension coefficient is set to be 1.2 so as to balance airflow distribution. Compared with the prior art, the invention has the advantages of uniform air outlet, reduced energy consumption, prolonged fatigue life, increased space utilization rate of equipment and the like.

Description

Technical Field

[0001] The invention relates to the technical field of hot air drying of fabrics in the textile printing and dyeing industry, and in particular to a fully streamlined double-outlet air duct structure based on a NURBS curved surface. Background Art

[0002] The core technology of textile production mainly includes four major processes: warping, sizing, weaving and finishing. Among them, the printing and dyeing heat setting process in the finishing stage is a key quality control node, which directly affects the physical and chemical properties and appearance quality indicators of the finished fabric. As the core equipment of this process, the heat setting unit has the characteristics of complex structure and high energy consumption. Its operating efficiency is crucial to the production cost control of the enterprise. During the heat setting process of the fabric, the hot air drying system in the oven drives the high-speed airflow through the circulating fan. The airflow is heated by the steam heat exchanger to form a constant temperature hot air, which then enters the air duct system and is finally evenly blown to the surface of the wet fabric by the air spray box to complete the drying and setting of the fabric. In this process, the design of the air duct structure directly affects the uniformity of the air outlet of the heat setting machine, which in turn determines the stability of the temperature field distribution on the fabric surface and the water evaporation rate. Therefore, optimizing the design of the air duct system, ensuring uniform distribution of the airflow and reducing system resistance are of great significance to improving the efficiency of the heat setting process and reducing energy consumption.

[0003] In the field of duct system optimization research, domestic and foreign scholars have achieved a series of important results. Leqi Tong and other scholars innovatively proposed a T-joint flow guide device, which significantly improved the uniformity of the central exhaust system and reduced the system resistance through structural parameter optimization. Haoran Chen's team developed a duct parameter calculation method based on model identification algorithm. By real-time monitoring of the fan outlet and terminal pressure, the accurate prediction of duct characteristics under different working conditions was achieved. Compared with traditional calculation methods, this method has higher accuracy and stronger robustness under different working conditions. Li and other researchers used computational fluid dynamics methods to optimize the design of the arc joint structure and effectively improved the air flow distribution through flow field visualization analysis. The new low-resistance T-joint developed by Ran Gao's research group can reduce resistance by 42% through innovative arc surface structure design. However, it should be pointed out that the above research results are limited to the application scenario of a single air jet box air supply system. At present, with the rapid development of the textile printing and dyeing industry towards high efficiency and intensiveness, modern heat setting machines urgently need to adopt a new system architecture of "one air duct and multiple air jet boxes". This design can not only optimize the equipment space layout, but also improve the utilization rate of thermal energy. There is no report in the existing literature on the design of air duct structure that can provide uniform inflow parameters for multiple air jet boxes at the same time. Especially under the technical requirement of ensuring that the deviation of air uniformity of each air jet box does not exceed 5%, this key technical problem still needs to be overcome. Solving this problem will have important engineering application value in improving the quality of heat setting process and reducing energy consumption. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects existing in the above-mentioned prior art and provide a full-streamlined double-outlet air duct structure based on NURBS surface, which has uniform air outlet, reduced energy consumption, extended fatigue life, and increased space utilization rate of the equipment.

[0005] The non-uniform rational B-spline (NURBS) method is used for surface construction to strictly ensure the continuity and smoothness of the surface, reduce the friction and eddy current between the air flow and the air duct wall surface, reduce the energy loss caused by air flow and wall surface friction loss, make the air flow stable, and supply air evenly.

[0006] The present invention provides a full-streamlined double-outlet air duct structure based on NURBS surface, including:

[0007] An air flow inlet surface connected to the fan;

[0008] An upper air outlet surface and a lower air outlet surface arranged up and down;

[0009] A streamline cavity formed by NURBS surface, including three parameterized sections: a lower flow section, an acceleration section, and an upper diversion section; the lower flow section is connected to the air flow inlet surface and the lower air outlet surface, and the tension coefficient is set to 0.8 to maintain a smooth transition; the acceleration section extends from the air flow inlet surface to the air duct neck, and the tension coefficient is set to 1.8 to achieve streamline contraction; the upper diversion section extends from the air duct neck to the upper air outlet surface, and the tension coefficient is set to 1.2 to balance the air flow distribution;

[0010] There is no cross-section mutation and strong bending in the main body of the cavity, which can accurately guide the air flow direction, effectively resist the wind pressure load and turbulent impact of ≥1500Pa in the operating conditions, ensure the structural integrity and extend the service life.

[0011] Further, the NURBS surface knot vector is generated according to the non-uniform distribution algorithm;

[0012] Further, the surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling, and the surface tension coefficient realizes the weight distribution of normal constraint and tangential continuity by adjusting the first-order derivative of the control points.

[0013] Further, NURBS uses the DeBoor-Cox-Mansfield basis function recurrence formula.

[0014] Assume that there is a non-decreasing sequence, and the knot vector U of the control parameter is shown in Equation (1):

[0015]

[0016] In the formula, the first node u0 and the last node u n+1 are both repeated p + 1 times; u i is the i-th node.

[0017] Based on Equation (1), the expression of the B-spline basis function can be obtained, as shown in Equation (2):

[0018]

[0019] In the formula, p is the degree of the basis function. When p = 0, the expression form of the B-spline basis function is B i,0 (u); when p ≥ 1, the expression of the B-spline basis function is B i,p (u).

[0020] Assume that there exists a sequence of control vertices V i , and the degree of the B-spline is p. Based on Equation (1), the parametric equation of the p-th degree B-spline curve can be obtained as shown in Equation (3):

[0021]

[0022] To construct a B-spline curve that can pass through the existing data points, that is, to ensure that the solution of the required B-spline curve exists, its complete endpoint constraint conditions satisfy the following formula:

[0023]

[0024] In the formula, the total number of control vertices is m + 1, and the total number of data points is n + 1, satisfying m = n + p; P0, P n are the positions of the first and last endpoints respectively; represents the intermediate point interpolation equation; T0, T n are the tangent directions of the first and last endpoints respectively, and α, β are proportionality coefficients.

[0025] Compared with the B-spline curve being controlled by a single parameter, the B-spline surface is controlled by 2 parameters. Assume that V i.j is the control vertex, and the two control parameter directions of the B-spline surface are U and W respectively. Among them, the knot vector W is shown in Equation (5):

[0026]

[0027] In the formula, the first node w0 and the last node w m+1 are both repeated q + 1 times; w j is the j-th node.

[0028] When u0 = w0 = 0, u n+1 = w m+1 = 1, the definition of the two-parameter B-spline surface is shown in Equation (6):

[0029]

[0030] Wherein, B i,p (u), B j,q (w) are both basis functions of the B-spline surface; B i,p (u) takes values as shown in Equation (2); B j,q (w) is expressed as shown in Equation (7):

[0031]

[0032] The parametric equation of the NURBS surface of degree p in the u direction and degree q in the w direction is as shown in Equation (8):

[0033]

[0034] Wherein, R i,j (u, w) is the basis function of the NURBS surface of degree p in the u direction and degree q in the w direction, and the expression is:

[0035]

[0036] Therefore, the non-uniform NURBS surface of degree p in the u direction and degree q in the w direction is expressed by Equation (10):

[0037]

[0038] Furthermore, the manufacturing material of the air duct structure is galvanized steel sheet or stainless steel; it is formed by stamping, bending, and welding processes to ensure the airtightness of the cavity and the structural strength.

[0039] Furthermore, the upper air outlet surface (1) and the lower air outlet surface (2) are respectively connected to two independent air spraying boxes. When the system works, 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 spraying boxes, and finally the hot air is blown onto the surface of the wet fabric in the form of air flow through the specific outlets of the air spraying boxes, realizing an efficient heat exchange and drying process.

[0040] Furthermore, the NURBS surfaces of the lower flow section, the acceleration section, and the upper diversion section are generated by the following parameterization program:

[0041]

[0042]

[0043] Wherein: The rectangular control point array is defined using the nrbmak function; the curve is closed using the nrbclose function; the ruled surface is constructed using the nrbRuled function, and the control point coordinates are adjusted to apply the tension coefficient constraint.

[0044] Further, the parametric modeling program of the air duct structure includes:

[0045] Recursively generate NURBS surfaces using DeBoor-Cox-Mansfield basis functions; construct ruled surfaces through the nrbRuled function; adjust the control point coordinates to achieve tension coefficient constraints.

[0046] Further, the overall dimensions of the air duct are 1876 mm (y-direction) × 613 mm (x-direction) × 460 mm (z-direction), and the wall thickness is 5 mm.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] (1) Good air outlet uniformity. Precise control of the streamline profile through NURBS surfaces reduces the coefficient of variation of the air outlet velocity and the coefficient of variation of pressure at the upper and lower air outlets. The deviation of air outlet uniformity is less than 5%, improving the uniformity.

[0049] (2) Energy consumption reduction. The fully streamlined design reduces the air duct resistance. Combined with the double-outlet structure, it improves the thermal energy utilization rate and the comprehensive energy-saving efficiency. Compared with conventional air ducts, the fully streamlined air duct can strictly ensure the continuity and smoothness of the surface, reduce the friction and eddy current between the air flow and the air duct wall surface, reduce the energy loss caused by air flow and wall surface friction loss, make the velocity gradient of the air flow in the air duct small, and can achieve high-efficiency, high-quality and uniform air supply, avoiding the phenomenon of too strong or too weak local air supply.

[0050] (3) Good structural reliability. The combination of steel plate and NURBS surface topology optimization extends the fatigue life under a wind pressure greater than 1500 Pa.

[0051] (4) Improved process adaptability and assemblability. The parametric modeling system supports rapid adjustment of the tension coefficient (adjustable range of 0.8 - 1.8), completing the design iteration of the new model air duct. The air duct designed by the present invention keeps the shapes of the air inlet surface and the two air outlet surfaces unchanged (that is, the air inlet surface of the air duct is the same as the shape of the fan outlet of the heat setting machine, and the air outlet surfaces of the air duct are the same as the shapes of the inlets of the two spray boxes arranged up and down), and the distance between the two air outlet surfaces of the air duct and the relative position of the air inlet surface of the air duct remain unchanged, thus realizing the design iteration of the new model air duct.

[0052] (5) Compared with conventional air ducts, the double-outlet air duct has two air flow outlets of the same size, improving the air supply area of the air duct and increasing the space utilization rate of the equipment. Description of the Drawings

[0053] Figure 1 It is a schematic structural diagram of the fully streamlined double-outlet air duct structure based on NURBS surface for Embodiment 1;

[0054] Figure 2 Internal flow field distribution diagram of the full streamlined double - outlet air duct based on NURBS surface for Example 1;

[0055] Figure 3 Schematic diagram of the monitoring points on the air outlet surface for Example 1;

[0056] Figure 4 Pressure and velocity values on the upper air outlet surface for Example 1;

[0057] Figure 5 Pressure and velocity values on the lower air outlet surface for Example 1;

[0058] Figure 6 Schematic structural diagram of Comparative Example 1;

[0059] Figure 7 Pressure and velocity values on the upper air outlet surface for Comparative Example 1;

[0060] Figure 8 Pressure and velocity values on the lower air outlet surface for Comparative Example 1;

[0061] Figure 9 Schematic structural diagram of Comparative Example 2;

[0062] Figure 10 Pressure and velocity data on the upper air outlet surface for Comparative Example 2;

[0063] Figure 11 Pressure and velocity data on the lower air outlet surface for Comparative Example 2;

[0064] Figure 12 Schematic structural diagram of Comparative Example 3;

[0065] Figure 13 Pressure and velocity data on the upper air outlet surface for Comparative Example 3;

[0066] Figure 14 Pressure and velocity data on the lower air outlet surface for Comparative Example 3.

[0067] Reference numerals: 1 - upper air outlet surface; 2 - lower air outlet surface; 3 - air flow inlet surface; 4 - air duct neck. Detailed implementation manners

[0068] The present invention will be described in detail below with reference to the drawings and specific embodiments. Components such as model numbers, material names, connection structures, control methods, algorithms, etc. that are not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0069] Example 1

[0070] This example provides a full - streamlined double - outlet air duct structure based on NURBS surface, including:

[0071] The air flow inlet surface 3 connected to the fan has a size of 366 mm × 348 mm;

[0072] The upper air outlet surface 1 and the lower air outlet surface 2 arranged vertically both have a size of 80 mm × 510 mm; the upper air outlet surface 1 and the lower air outlet surface 2 are respectively connected to two independent air spraying boxes. When the system works, 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 spraying boxes, and finally the hot air is blown onto the surface of the wet fabric in the form of air flow through the specific outlets of the air spraying boxes, realizing an efficient heat exchange and drying process.

[0073] The streamline-shaped cavity body constructed by NURBS surface includes three parameterized sections: the lower flow-through section, the acceleration section, and the upper splitting section; the lower flow-through section connects the air flow inlet surface 3 and the lower air outlet surface 2, and the tension coefficient is set to 0.8 to maintain a smooth transition; the acceleration section extends from the air flow inlet surface to the air duct neck 4, and the cross-sectional size of the air duct neck 4 is 150 mm × 270 mm, and the tension coefficient is set to 1.8 to achieve a streamline contraction; the upper splitting section extends from the air duct neck to the upper air outlet surface 1, and the tension coefficient is set to 1.2 to balance the air flow distribution;

[0074] The manufacturing material of the air duct structure is galvanized steel sheet or stainless steel; it is formed by stamping, bending, and welding processes to ensure the airtightness of the cavity and the structural strength. The overall size of the air duct is 1876 mm (y direction) × 613 mm (x direction) × 460 mm (z direction), and the wall thickness is 5 mm.

[0075] There is no cross-sectional mutation and strong bending in the main part of the cavity, which can accurately guide the air flow direction, effectively resist the wind pressure load and turbulent impact of ≥ 1500 Pa in the operating conditions, ensure the structural integrity and extend the service life cycle.

[0076] In the specific implementation manner, the NURBS surface adopts a second-order basis function, and the knot vector is generated according to the non-uniform distribution algorithm; the NURBS basis function uses the DeBoor-Cox-Mansfield basis function recurrence formula.

[0077] Assume there is a non-decreasing sequence, and the knot vector U of the control parameter is shown in Equation (1):

[0078]

[0079] In the formula, the first knot u0 and the last knot u n+1 are both repeated p + 1 times; u i is the i-th knot.

[0080] Based on Equation (1), the expression of the B-spline basis function can be obtained, as shown in Equation (2):

[0081]

[0082] In the formula, p is the degree of the basis function. When p = 0, the expression form of the B-spline basis function is B i,0 (u); when p ≥ 1, the expression of the B-spline basis function is B i,p (u).

[0083] Assume that there is a sequence of control vertices V i , and the degree of the B-spline is p. Based on Equation (1), the parametric equation of the p-degree B-spline curve can be obtained as Equation (3):

[0084]

[0085] To construct a B-spline curve that can pass through the existing data points, that is, to ensure that the obtained B-spline curve has a solution, its complete endpoint constraint conditions satisfy the following formula:

[0086]

[0087] Compared with the B-spline curve being controlled by a single parameter, the B-spline surface is controlled by two parameters. Assume that V i.j is the control vertex, and the two control parameter directions of the B-spline surface are U and W respectively. Among them, the knot vector W is shown in Equation (5):

[0088]

[0089] In the formula, the first knot w0 and the last knot w m+1 are both repeated q + 1 times; w j is the jth knot.

[0090] When u0 = w0 = 0, u n+1 = w m+1 = 1, the definition of the two-parameter B-spline surface is shown in Equation (6):

[0091]

[0092] In the formula, B i,p (u), B j,q (w) are both B-spline surface basis functions. The value of B i,p (u) is shown in Equation (2), and the expression of B j,q (w) is shown in Equation (7):

[0093]

[0094] The parametric equation of the NURBS surface with p-degree in the u direction and q-degree in the w direction is as Equation (8):

[0095]

[0096] In the formula, R i,j (u, w) are the NURBS surface basis functions of degree p in the u - direction and degree q in the w - direction, and the expression is:

[0097]

[0098] Therefore, the non - uniform NURBS surface of degree p in the u - direction and degree q in the w - direction can be expressed by Equation (10):

[0099]

[0100] In the formula, α i,j is the weight parameter, which is a scalar value and corresponds one - to - one with the control vertex V i.j The greater the weight, the stronger the influence of the corresponding control vertex on the local shape of the surface, allowing for the precise representation of complex geometries such as conic curves and spherical surfaces.

[0101] In Embodiment 1, a second - order NURBS surface is adopted, and its expression can be represented by Equation (11):

[0102]

[0103] The NURBS surfaces of the downstream passage, the acceleration section, and the upper shunt section are respectively generated by the following parameterization procedures:

[0104]

[0105] Among them: The nrbmak function is used to define a rectangular control point array; 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 impose the tension coefficient constraint.

[0106] The parameterization modeling program of the air duct structure includes: using the DeBoor - Cox - Mansfield basis function to recursively generate the NURBS surface; using the nrbRuled function to construct a ruled surface; adjusting the control point coordinates to achieve the tension coefficient constraint.

[0107] The surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling. The surface tension coefficient realizes the weight distribution of normal constraint and tangential continuity by adjusting 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 and tends to a uniform relaxation state, and the surface freely transitions 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 is forced to be completely vertical at the boundary and approaches the control polygon; when the tension coefficient τ>1, small-scale out-of-range adjustment is allowed but the node spacing is exponentially compressed, and auxiliary control points need to be inserted to maintain stability. In Example 1, the tension coefficient τ of the downstream section is 0.8, indicating that 80% of the normal constraint strength is applied at the boundary, that is, 20% of the tangential freedom is allowed. This setting can not only maintain the approximate vertical geometric characteristics (80% strength) but also retain the necessary curvature transition (20% relaxation).

[0108] The commercial software Ansys Fluent 2022R1 is used for the grid division and calculation of the air duct flow field. A mixed form of honeycomb and hexahedron volume grids is adopted, and the number of grids is about 41,000; a pressure-based steady-state solver is adopted; the SST k-ω turbulence model based on the Reynolds-averaged Navier-Stokes (RANS) equation is adopted; the wall condition is described by the standard wall function. When the fan power is at 100%, the total fan pressure is 700 Pa, and the maximum air volume output can reach 7500 m 3 / h. After conversion, the air velocity at the inlet surface of the air duct is about 16.35 m / s. After the calculation is completed, the pressure and velocity distributions of the air duct are extracted, as Figure 2 shown.

[0109] Air duct pressure field distribution Figure 2 (a) shows that the maximum static pressure appears in the area below the neck of the entire air duct. At the two air outlet positions, although there is a small range of pressure backflow phenomenon, the overall pressure distribution is relatively uniform; Air duct velocity field distribution Figure 2 (b) shows that the closer to the air duct wall surface, the smaller the velocity value. This velocity distribution characteristic can reduce the air leakage risk at the joint to a certain extent and reduce energy loss. At the same time, the velocity value inside the air duct is large, and no large-scale eddy currents are formed in the internal flow field. The velocity and pressure trace distributions of the flow field are orderly, which proves that the air duct based on NURBS surface largely avoids energy loss and has a positive effect on improving the drying efficiency of the fabric heat setting machine.

[0110] The air outflow from the two air outlet surfaces of the air duct will directly affect the fabric drying performance. From Figure 2(b) It can be seen that under the calculation conditions, the air outlet velocities of the upper and lower air outlets of the air duct are basically the same, about 30 m / s. For intuitive comparative analysis, 400 velocity monitoring points with the same interval are selected on each of the two air outlet surfaces. The specific selection method is as follows: 8 straight lines are evenly selected at 5 mm from the left and right side lines of the air outlet surface, the vertical distance between two adjacent straight lines is 10 mm, and 50 points are equally spaced on each straight line (the schematic diagram of the monitoring point positions is shown in Figure 3 ). The 50 monitoring points in each column are numbered 1 to 50 from bottom to top; the 8 columns of monitoring points are numbered 1 to 8 from left to right (numbered a1 to a8 on the upper air outlet surface; numbered b1 to b8 on the lower air outlet surface). The pressure and velocity data of the 400 monitoring points on each air outlet surface are extracted. The pressure and velocity values of the upper air outlet surface are as shown in Figure 4 , and the pressure and velocity values of the lower air outlet surface are as shown in Figure 5 .

[0111] As shown in Figure 4 and Figure 5 :

[0112] 1) Generally speaking, although the change trend curves of pressure and velocity on the upper and lower air outlet surfaces are not exactly the same, their numerical performances are quite similar: the pressure values mainly concentrate in the range of 400 - 600 Pa, and the velocity values mostly concentrate in the range of 25 - 30 m / s.

[0113] 2) On the upper air outlet surface, the pressure distribution shows a trend of "high in the middle and low on both sides". Specifically, the closer to the middle position of the air outlet surface, the greater the pressure value; on the contrary, the closer to the duct wall, the lower the pressure value. At the monitoring points with smaller numbers on the upper air outlet surface (numbered 1 to 5), the wind pressure is relatively small, and the overall lowest pressure value is the curve a8, that is, the wind pressure in the rightmost area when facing the air outlet is lower; the pressure value characteristics of the lower air outlet surface are that the pressure values corresponding to the curves b1 and b8 are the lowest, that is, the static pressure value near the wall is less than 500 Pa, and the closer to the middle area, the smaller the fluctuation range of the pressure value and the smoother the corresponding curve.

[0114] 3) On the upper air outlet surface, the velocity distribution shows a "high in the middle and low on both sides" pattern similar to the pressure change trend. On the curve a8 in the rightmost area, the pressure value is at the lowest level. If the relatively marginal parts are not considered, the velocity values of the upper air outlet mainly concentrate in the range of 25 - 32 m / s; the change trend of the velocity curve of the lower air outlet is similar to the pressure change trend of this air outlet surface. Near the duct wall, the velocity value is low and the fluctuation range is large, while in the middle area, the velocity value range is approximately 28 - 31 m / s and the distribution is relatively uniform.

[0115] The core objective of the air duct is to distribute the continuous air flow generated by the fan as evenly as possible to the two air injection boxes through the upper and lower air outlets. At the same time, it is also necessary to ensure that the air flow states at the two air outlets are consistent to the greatest extent. As a vector, velocity has three components in the x, y, and z directions in the Cartesian coordinate system. In the application scenario of the air duct, the velocity component perpendicular to the cross-section of the air outlet is the effective velocity component that plays a role.

[0116] Based on the air flow velocity data, an index - velocity coefficient of variation C is constructed to evaluate the air supply performance of the air duct. v , and its definition and calculation method are as follows:

[0117]

[0118] In the formula: σ v is the standard deviation of the velocity on the air outlet surface, indicating the degree of dispersion of the velocity; μ v is the average value of the velocity on the air outlet surface; n is the number of velocity samples on the air outlet surface (here n = 400); v i is the value of the i-th velocity sample.

[0119] The average velocity and its coefficient of variation of the air outlet surface of the air duct based on the NURBS surface are shown in Table 1.

[0120] Table 1 Air outlet surface velocity of the air duct based on the NURBS surface in Example 1

[0121]

[0122] As can be seen from Table 1, the average velocities on the upper and lower air outlet surfaces are similar, about 28 m / s, and the values of the velocity coefficient of variation are all small (by definition, the smaller the velocity coefficient of variation, the smaller the difference in the velocity distribution on the air outlet surface).

[0123] Similarly, an index for evaluating the uniformity of the pressure at the test points is established, that is, the pressure coefficient of variation C p , and its calculation method is:

[0124]

[0125] In the formula, σ p is the standard deviation of the pressure on the air outlet surface, indicating the degree of dispersion of the pressure; μ p is the average value of the pressure on the air outlet surface; p i is the i-th pressure sample value on the air outlet surface.

[0126] The average pressure and its coefficient of variation of the air outlet surface of the air duct based on the NURBS surface are shown in Table 2.

[0127] Table 2 Air outlet surface pressure of the air duct based on the NURBS surface in Example 1

[0128]

[0129] Table 2 shows that the average pressures on the upper and lower air outlet surfaces are close, approximately 514 Pa, and the pressure singularity coefficient values are also close and both are low, indicating good pressure uniformity on the air outlet surface (by definition, the smaller the pressure singularity coefficient, the smaller the difference in the pressure distribution on the air outlet surface).

[0130] Combined with Figure 4 、 Figure 5 and Tables 1 and 2, it can be seen that for the fully streamlined double - outlet air duct designed based on NURBS surface parameterization, the outflow velocity and pressure are uniform and stable, the deviation of the air outlet uniformity is extremely small, which can provide excellent pressure and velocity inlet conditions for the subsequent air - spraying box, and it is very likely that the deviation of the air outlet uniformity of each air - spraying box meets the technical requirement of not exceeding 5%, which is very conducive to achieving high - efficiency and high - quality drying of fabrics.

[0131] Comparative Example 1

[0132] As Figure 6 shown, for the streamlined double - outlet air duct based on NURBS surface, the node vector adopts a non - uniform distribution algorithm, the appearance structure is similar to that of Embodiment 1, the air - flow inlet section, the two air - outlet sections and the air - duct neck section are the same as those of Embodiment 1, and the relative positions of the two air - outlet surfaces and the air - duct air - flow inlet surface remain unchanged. Compared with Embodiment 1, Comparative Example 1 only changes the NURBS tension parameters:

[0133] Lower flow - through section: Connecting the air - flow inlet surface and the lower air - outlet surface, the tension coefficient is set to 1.1;

[0134] Acceleration section: From the inlet surface to the air - duct neck, the tension coefficient is set to 1.0;

[0135] Upper shunt section: Extending from the neck to the upper air - outlet surface, the tension coefficient is set to 1.1.

[0136] Carry out simulation calculations on the streamlined air duct of Comparative Example 1. The working conditions and boundary conditions are the same as those of Embodiment 1, and the extraction positions of the monitoring points are also the same as those of Embodiment 1. The pressure and velocity distribution curves of the upper and lower air - outlet surfaces of Comparative Example 1 are as Figure 7 、 8 shown.

[0137] Figure 7 、 Figure 8 show that compared with Embodiment 1, there are no significant differences in the distribution ranges and change trends of the velocity and pressure values on the upper and lower air - outlet surfaces of Comparative Example 1.

[0138] The average velocity and its singularity coefficient of the air - outlet surface of the air duct in Comparative Example 1 are shown in Table 3; the average pressure and its singularity coefficient of the air - outlet surface of the air duct in Comparative Example 1 are shown in Table 4.

[0139] Table 3 Face velocity at the air outlet of Comparative Example 1

[0140]

[0141] Table 4 Face pressure at the air outlet of Comparative Example 1

[0142]

[0143] By comparing the statistical results of Comparative Example 1 (i.e., Table 3 and Table 4) with those of Example 1 (i.e., Table 1 and Table 2), it can be seen that:

[0144] 1) The face velocities at the upper and lower air outlets of Example 1 are both 28 m / s, while the average difference in the face velocities of the two air outlets in Comparative Example 1 is about 3 m / s; in terms of the velocity singularity coefficient values, the velocity singularity coefficients of the two air outlet faces in Comparative Example 1 are both greater than those in Example 1, indicating that the velocity uniformity of Example 1 is better.

[0145] 2) The average face pressure at the upper air outlet of Comparative Example 1 is about 544 Pa, while the average pressure on the lower surface is about 520 Pa, with a pressure difference of about 22 Pa; while the average face pressures at the upper and lower air outlets of Example 1 are similar, both around 514 Pa. In addition, the pressure singularity coefficients of the upper and lower air outlet faces in Comparative Example 1 are also greater than those in Example 1, indicating that the outflow pressure uniformity of Comparative Example 1 is inferior to that of Example 1.

[0146] In summary, by comparing the pressure and velocity uniformity indexes of the air outlet faces of Comparative Example 1 and Example 1, Comparative Example 1 is inferior to Example 1. Thus, it can be seen that even when using NURBS surface parametric modeling, different tension coefficients will affect the air outlet performance of the air duct.

[0147] Comparative Example 2

[0148] As Figure 9 shown, for the streamlined double - outlet air duct based on NURBS surface, the node vector adopts a non - uniform distribution algorithm, the appearance structure is similar to that of Example 1, the air flow inlet section, the two air outlet sections, and the air duct neck section are the same as those in Example 1, and the relative positions of the two air outlet faces and the air duct air flow inlet face remain unchanged. Compared with Example 1, Comparative Example 2 only changes the NURBS tension parameters:

[0149] Lower flow - through section: Connecting the air flow inlet face and the lower air outlet face, the tension coefficient is set to 1.2;

[0150] Acceleration section: From the inlet face to the air duct neck, the tension coefficient is set to 1.8;

[0151] Upper shunt section: Extending from the neck to the upper air outlet face, the tension coefficient is set to 0.8.

[0152] Perform a simulation calculation on the streamline air duct of Comparative Example 2. The working conditions and boundary conditions are the same as those in Example 1, and the extraction positions of the monitoring points are also the same as those in Example 1. The pressure and velocity distribution curves of the upper and lower air outlet surfaces of Comparative Example 2 are as shown in Figure 10 , 11 .

[0153] Figure 10 , 11 show that, compared with Example 1, there are no significant differences in the distribution ranges and change trends of the velocity and pressure values on the upper and lower air outlet surfaces of Comparative Example 2.

[0154] The mean velocity and its singular coefficient of the air outlet surface of the air duct in Comparative Example 2 are shown in Table 5; the mean pressure and its singular coefficient of the air outlet surface of the air duct in Comparative Example 2 are shown in Table 6.

[0155] Table 5 Mean velocity of the air outlet surface of Comparative Example 2

[0156]

[0157] Table 6 Mean pressure of the air outlet surface of Comparative Example 2

[0158]

[0159] Comparing the statistical results of Comparative Example 2 (i.e., Table 5 and Table 6) with the statistical results of Example 1 (i.e., Table 1 and Table 2), it can be seen that:

[0160] 1) The velocities of the upper and lower air outlet surfaces of Comparative Example 2 and Example 1 are both 28 m / s, but the singular coefficient values of the velocity in Comparative Example 2 are all greater than those in Example 1, indicating that the velocity uniformity of Example 1 is better.

[0161] 2) The mean pressure of the upper air outlet surface of Comparative Example 2 is about 494 Pa, and the mean pressure of the lower surface is about 514 Pa, with a pressure difference of about 20 Pa; while the mean pressures of the upper and lower air outlet surfaces of Example 1 are similar, both around 514 Pa. In addition, the pressure singular coefficients of the upper and lower air outlet surfaces of Comparative Example 2 are also greater than those in Example 1, indicating that the outflow pressure uniformity of Comparative Example 2 is inferior to that of Example 1.

[0162] In summary, comparing the pressure and velocity uniformity indexes of the air outlet surfaces of Comparative Example 2 and Example 1, Comparative Example 2 is inferior to Example 1. Thus, it can be seen that even if NURBS surface parametric modeling is used, different tension coefficients will affect the air outlet performance of the air duct.

[0163] Comparative Example 3

[0164] As shown in Figure 12As shown, for the double - outlet air duct, the shapes, dimensions and spatial positions of the air - flow inlet section, the two outlet sections and the air - duct neck section are the same as those in Embodiment 1. Compared with Embodiment 1, in Comparative Example 3, parametric modeling based on NUBRS surfaces is not adopted, and its appearance is not streamlined, and the outlet surface is perpendicular to the inlet surface.

[0165] The structure of Comparative Example 3 has the following characteristics:

[0166] 1) Comparative Example 3 also keeps the air - flow inlet section, the two outlet sections and the air - duct neck section unchanged. However, Comparative Example 3 does not adopt the modeling method based on NURBS, and the overall air duct is not streamlined, and the pipe between the two outlet surfaces is bent twice.

[0167] 2) In terms of structure, Comparative Example 3 can be regarded as composed of multiple sections of pipes spliced together.

[0168] 3) Since the air - duct inlet and outlet planes are perpendicular to each other in space, there are multiple bends and cross - section mutations in Comparative Example 3.

[0169] Perform a simulation calculation on the air duct of Comparative Example 3. The working conditions and boundary conditions are the same as those in Embodiment 1, and the extraction positions of the monitoring points are also the same as those in Embodiment 1. The pressure and velocity distribution curves of the upper and lower outlet surfaces of Comparative Example 3 are as shown in Figure 13 、 Figure 14 .

[0170] From Figure 13 、 Figure 14 it can be seen that:

[0171] 1) The trends of the 8 curves (a1 - a8) of the pressure on the upper outlet surface of Comparative Example 3 are not similar, and there is no regularity between the lines, indicating that there are large differences between the data, and the maximum pressure difference is greater than 2000 Pa. Moreover, the pressure value of the monitoring point close to No. 50 is the highest, and there is a small pressure peak at the monitoring points of some curves near No. 10.

[0172] 2) The velocity fluctuation trend on the upper outlet surface of Comparative Example 3 is similar to the pressure fluctuation trend. The velocity values of some monitoring points with numbers less than 30 are unstable, fluctuating up and down numerically. While for the monitoring points with numbers greater than 30, the pressure values are stable on some curves and show an increasing trend on some curves. The maximum velocity difference is greater than 50 m / s. This reflects that there may be eddy currents in the lower half of the upper outlet surface, resulting in numerical disorder.

[0173] 3) The change trends of the pressure and velocity curves on the lower outlet surface of Comparative Example 3 are also similar. The velocity at the end with numbers 0 - 20 is close to 0 m / s, and the pressure is close to 0 Pa. It can be seen that there may be no air flow blowing out from the lower half of the lower outlet surface.

[0174] 4) For Comparative Example 3, the pressure differences at the monitoring points numbered 20 - 50 on the lower air outlet surface are large, approaching 2250 Pa, and the velocity differences are also large, approaching 60 m / s.

[0175] The average velocity and its singular coefficient of the air duct outlet surface in Comparative Example 3 are shown in Table 7; the average pressure and its singular coefficient of the air duct outlet surface in Comparative Example 3 are shown in Table 8.

[0176] Table 7 Velocity of the Outlet Surface in Comparative Example 3

[0177]

[0178] Table 8 Pressure of the Outlet Surface in Comparative Example 3

[0179]

[0180] Comparing the statistical results of Comparative Example 3 (i.e., Table 7 and Table 8) with those of Example 1 (i.e., Table 1 and Table 2), it can be seen that:

[0181] 1) The velocity differences between the upper and lower air outlet surfaces in Comparative Example 3 are very large, approximately 45 m / s and 28 m / s respectively, while the velocities of the upper and lower air outlet surfaces in Example 1 are both 28 m / s. Moreover, the singular coefficient values of the velocity in Comparative Example 3 are much larger than those in Example 1, indicating that the velocity uniformity in Example 1 is significantly better than that in Comparative Example 3.

[0182] 2) The average pressure of the upper air outlet surface in Comparative Example 3 is approximately 1353 Pa, and the average pressure of the lower air outlet surface is approximately 842 Pa, with a pressure difference reaching 511 Pa; while the average pressures of the upper and lower air outlet surfaces in Example 1 are similar, both around 514 Pa. In addition, the pressure singular coefficients of the upper and lower air outlet surfaces in Comparative Example 3 are also much larger than those in Example 1, indicating that the outflow pressure uniformity in Comparative Example 3 is much worse than that in Example 1.

[0183] The components not elaborated in this embodiment are all existing components that can be purchased through public channels.

[0184] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A full streamline double - outlet air duct structure based on NURBS surface, characterized in that, Comprising: An air inlet surface (3) connected to a fan; An upper air outlet surface (1) and a lower air outlet surface (2) arranged vertically; A streamline cavity formed by NURBS surfaces, including three parametric sections: a lower flow section, an acceleration section, and an upper diversion section; the lower flow section connects the air inlet surface (3) and the lower air outlet surface (2), with a tension coefficient set to 0.8; the acceleration section extends from the air inlet surface to the duct neck (4), with a tension coefficient set to 1.8; the upper diversion section extends from the duct neck (4) to the upper air outlet surface (1), with a tension coefficient set to 1.

2.

2. The all-streamlined double-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The NURBS surface knot vector is generated according to the non-uniform distribution algorithm.

3. The all-streamlined double-outlet air duct structure based on NURBS surface according to claim 2, wherein, The surface tension coefficient is the vertical constraint strength factor in NURBS surface modeling. The surface tension coefficient realizes the weight distribution of normal constraint and tangential continuity by adjusting the first derivative of the control points.

4. A full-streamlined double-outlet air duct structure based on NURBS surface according to claim 2, characterized in that, The NURBS surface uses the DeBoor-Cox-Mansfield basis function recurrence formula.

5. A full-streamlined double-outlet air duct structure based on NURBS surface according to claim 2, characterized in that The non-uniform knot vector is defined as: where u i and w i are nodes. The first and last nodes of the non-uniform node vectors (vectors) U and V are repeated p + 1 and q + 1 times respectively to ensure that the surface passes through the first and last control points.

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

7. A full-streamlined double-outlet air duct structure based on NURBS surface according to claim 1, characterized in that The upper air outlet surface (1) and the lower air outlet surface (2) are respectively connected to two independent air spraying boxes.

8. A full-streamlined double-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The NURBS surfaces of the lower flow section, the acceleration section, and the upper diversion section are respectively generated by a parametric program: using the nrbmak function to define a rectangular control point array; closing the curve by the nrbclose function; using the nrbRuled function to construct a ruled surface, and adjusting the control point coordinates to apply the tension coefficient constraint.

9. A full-streamlined double-outlet air duct structure based on NURBS surface according to claim 1, characterized in that, The parametric modeling program of the duct structure includes: Using the DeBoor-Cox-Mansfield basis function recurrence to generate the NURBS surface; constructing a ruled surface by the nrbRuled function; adjusting the control point coordinates to achieve the tension coefficient constraint.

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

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