S-shaped elbow low-resistance design method based on double-guide-vane combination

Abstract

The invention discloses an S-shaped elbow low-resistance design method based on a double-guide-vane combination. The problem that in the prior art, the installation positions of guide vanes are mostly determined by experience in a guide vane resistance reduction method for an S-shaped elbow is solved. The method mainly comprises the steps of visualizing a high-resistance area of fluid flowing by means of a field synergy angle, and obtaining that the high-synergy angle area is mainly distributed at the upstream turning and the downstream turning of the S-shaped elbow. Performing drag reduction rate analysis on the multiple double-guide-vane primary models, and selecting a combination of a lower guide vane model and an upper guide vane model at the optimal position according to the drag reduction rate; and then optimizing the arc angles of the upper guide vane model and the lower guide vane model. According to the invention, the internal flow distribution and resistance characteristics of the S-shaped elbow in the water system are studied by adopting a full-size experiment and numerical simulation method; the influence of the positions and angles of a single guide vane and multiple guide vanes on the drag reduction rate of the S-shaped elbow is explored; the insertion of the double guide vanes can obviously reduce the energy dissipation of the downstream of the S-shaped elbow, and effectively reduce the flow resistance and the power consumption of the pump.

Description

Technical Field

[0001] This invention relates to the field of drag reduction technology for S-shaped bends, and in particular to a method for reducing the drag of S-shaped bends based on a combination of double guide vanes. Background Technology

[0002] In building energy consumption, HVAC systems account for 40% to 60% of the total building energy consumption, with the piping system being the primary energy-consuming component. Piping components in this system (such as elbows) often exhibit significant flow resistance due to poor structural design, leading to additional energy consumption. The energy required to overcome this resistance accounts for 20% to 40% of the HVAC system's energy consumption and more than 10% of the building's total energy consumption, severely impacting building energy efficiency. High flow resistance not only reduces equipment operating efficiency and heating / cooling supply efficiency but can also cause hydraulic imbalances, thereby affecting indoor thermal comfort. Therefore, systematically studying the flow resistance mechanisms of piping components and developing optimized, standardized low-resistance designs has significant theoretical and engineering implications for improving fluid distribution efficiency and reducing operating energy consumption.

[0003] To reduce flow resistance at S-bends, traditional engineering methods mainly fall into two categories: one is optimizing the elbow's geometric parameters, such as increasing the bending radius, using non-uniform cross-sections, or variable curvature designs; the other is incorporating flow guiding devices, such as installing single guide vanes or honeycomb rectifiers. Among these, guide vanes, by guiding the fluid to smoothly change direction and suppressing secondary flow intensity, have proven to be an economical and effective passive drag reduction method. However, existing technologies have significant limitations: First, the installation position and profile design of guide vanes largely rely on empirical formulas or trial-and-error methods, lacking precise identification and quantitative characterization of high-resistance regions in the flow field, resulting in insufficient design targeting and unstable drag reduction effects; second, single guide vane structures can only locally regulate the flow in a single turning region, making it difficult to simultaneously address the coupled flow losses in the upstream and downstream turning sections of the S-bend, especially under compact layout constraints (small bending radius), where the flow separation and suppression capabilities of single guide vanes significantly decrease; third, guide vanes with fixed arc angles cannot adapt to the optimal drag reduction requirements under different operating conditions, and existing technologies rarely systematically decouple and optimize the guide vane position distribution and arc angle through parametric collaborative design.

[0004] Therefore, there is an urgent need for a new method for S-shaped elbow drag reduction design that can scientifically identify high-resistance zones, quantitatively optimize the spatial layout and profile parameters of guide vanes, and achieve upstream and downstream coupled control, so as to break through the bottleneck of traditional experience-based design and provide theoretical guidance and technical support for energy conservation and consumption reduction in pipeline systems. Summary of the Invention

[0005] To address the shortcomings in the aforementioned background technology, this invention proposes a low-resistance design method for S-shaped elbows based on a combination of dual guide vanes. This method solves the problem that in existing S-shaped elbow drag reduction methods, the guide vane installation position is often determined based on experience, and a systematic position optimization method has not been formed.

[0006] The technical solution of this invention is implemented as follows: a low-resistance design method for an S-shaped elbow based on a double guide vane combination, comprising the following steps:

[0007] S1. By visualizing the high-resistance region of fluid flow using the field coordination angle, it is found that the high coordination angle region is mainly distributed at the upstream and downstream bends of the S-shaped bend.

[0008] S2. Divide the S-shaped bend into an upstream bend and a downstream bend by the middle plane of the vertical axis. The middle plane is defined as the middle dividing plane.

[0009] S3. Set an upper position optimization point Di, i=1, 2, 3 on the upstream section of the S-shaped bend; set a lower position optimization point Cj, j=1, 2, 3 on the upstream section of the S-shaped bend; set an intermediate position optimization point Ak, k=1, 2, 3 on the intermediate equidistant surface.

[0010] S4. Draw an upper arc line with the same center as the upstream bend between Di and the corresponding Ak to form the upper guide vane model. Draw a lower arc line with the same center as the downstream bend between Cj and the corresponding Ak to form the lower guide vane model.

[0011] S5. The lower guide vane model with an arc angle of 90° is combined with the upper guide vane model with an arc angle of 90° in sequence to form a variety of primary double guide vane models.

[0012] S6. Perform drag reduction analysis on the various primary models of the double guide vane in step S5, and select the combination of the lower guide vane model and the upper guide vane model with the best position based on the drag reduction rate.

[0013] S7. Based on the optimal combination of the lower guide vane model and the upper guide vane model in step S6, optimize the arc angle of the upper guide vane model and the lower guide vane model.

[0014] S7.1. The lower guide vane models with arc angles of 30°, 60°, and 90° are combined with the upper guide vane model with an arc angle of 90°, and the optimal lower guide vane model with the arc angle is obtained through drag reduction analysis.

[0015] S7.2 The lower guide vane model with the optimal arc angle is combined with lower guide vane models with arc angles of 30°, 60° and 90° respectively, and the upper guide vane model with the optimal arc angle is obtained through drag reduction analysis.

[0016] S8. Fit and optimize the lower guide vane model with the optimal arc angle and the upper guide vane model with the optimal arc angle to obtain the double guide vane arc surface equation, thereby obtaining the double guide vane model to reduce the resistance of the S-shaped bend.

[0017] The formula for calculating the drag reduction ratio is as follows:

[0018]

[0019] in It is the drag reduction ratio. and These are the local resistance coefficients of the traditional S-shaped bend and the new S-shaped bend, respectively.

[0020] The formula for calculating the local resistance coefficient of an S-shaped bend is:

[0021] ,

[0022] , ;

[0023] In the formula This represents the local resistance coefficient of the S-shaped bend; It is a localized pressure loss; It is the mean dynamic pressure; It is the static pressure difference between the upstream and downstream sections of the S-bend in the full-scale experimental system. It is the pressure difference in the straight pipe below the S-bend in the full-scale experimental system; The static pressure at the upstream section of the S-bend in the full-scale experimental system. The static pressure at the downstream section of the S-bend in the full-scale experimental system; The static pressure upstream of the straight pipe below the S-bend length in the full-scale experimental system. The static pressure downstream of the straight pipe at the length of the S-bend in the full-scale experimental system.

[0024] The full-scale experimental system includes a water tank and a water pump. Along the water outlet direction, a filter, water pump, butterfly valve, pressure transmitter, electromagnetic flowmeter, and the S-bend to be tested are connected sequentially. The outlet of the S-bend is connected to the inlet of the water tank. An upstream measuring point is located upstream of the S-bend, and a downstream measuring point is located downstream of the S-bend. A differential pressure pump connects the upstream and downstream measuring points. A third and fourth measuring point are located on the straight pipe below the S-bend. The distance between the third and fourth measuring points is equal to the distance between the upstream and downstream measuring points. A differential pressure pump connects the third and fourth measuring points.

[0025] Let the outer diameter of the S-shaped bend be D, the radius of curvature be R, the distance from the upstream measuring point to the upstream section of the S-shaped bend be 15D, the distance from the downstream measuring point to the downstream section of the S-shaped bend be 15D, and the distance between the third and fourth measuring points be 2×15D+0.5×2πR.

[0026] In step S3, the upper position optimization point Di, the lower position optimization point Cj, and the middle position optimization point Ak are set at equal distances. The distance between two adjacent upper position optimization points is a, the distance between two adjacent lower position optimization points is a, and the distance between two adjacent middle position optimization points is a. Therefore, a / D = 0.25.

[0027] In step S8, a spatial coordinate system is established with the center of the downstream elbow as the origin. Based on the outer diameter D and radius of curvature R of the S-shaped elbow, the equation of the double guide vane arc surface is obtained:

[0028] Equation for the lower guide vane of the S-shaped elbow: ;

[0029] Equation for the upper guide vane of the S-shaped elbow:

[0030]

[0031] Among them, the radius of curvature of the S-shaped bend is R / D < 2.0.

[0032] The low-resistance design method for S-shaped elbows based on dual-guide vane combinations also includes verification of drag reduction effectiveness under different inlet Reynolds numbers and different coupling distances. When verifying drag reduction effectiveness under different inlet Reynolds numbers, the Reynolds number is between 1.0 × 10⁻⁶. 4 ~6.0×10 5 Within the specified range, the local resistance coefficients of a traditional S-bend and an S-bend with double guide vanes are compared. To verify the effectiveness of drag reduction under different coupling distances, the local resistance characteristics of the S-bend are analyzed when the coupling distances between the upstream and downstream bends are 0D, 1D, 2D, 4D, and 8D. The drag reduction effect of the S-bend with double guide vanes under different coupling distances is also analyzed.

[0033] The low-resistance design method for S-bends based on double guide vane combination also includes energy dissipation analysis and verification. The energy dissipation distribution of traditional S-bends and S-bends with double guide vanes is compared, and the drag reduction effect of S-bends with double guide vanes is analyzed.

[0034] The beneficial effects of this invention are as follows: This invention uses full-scale experiments and numerical simulations to study the internal flow distribution and resistance characteristics of S-bends in water systems; it explores the influence of the position and angle of single and multiple guide vanes on the drag reduction rate of S-bends; based on a comparative analysis of energy dissipation, it summarizes the high resistance and high dissipation distribution of traditional S-bends and S-bends with guide vanes, and summarizes the design parameters and guide vane arc surface equations for low-resistance S-bends with different nominal diameters; the insertion of double guide vanes can significantly reduce energy dissipation downstream of the S-bend, effectively reducing flow resistance and pump power consumption.

[0035] This invention, based on the field synergy angle theory, accurately identifies high-resistance regions at the upstream and downstream bends of S-shaped bends. By installing double guide vanes in these regions, flow separation and secondary flow are effectively suppressed, significantly reducing the local resistance coefficient. The drag reduction rate formula allows for precise calculation and evaluation of the drag reduction effects of different schemes, ensuring optimal design. A three-step process—position optimization, angle optimization, and equation fitting—gradually selects the best solution, avoiding blind design. A full-scale testing system employs a water tank-pump closed-loop system, along with pressure transmitters, electromagnetic flowmeters, and other instruments, to realistically simulate engineering conditions. In addition to comparing local resistance coefficients, energy dissipation distribution analysis is performed, verifying the drag reduction mechanism from a thermodynamic perspective, resulting in more comprehensive and reliable conclusions. This invention innovatively applies the field synergy theory to pipeline drag reduction design, providing a new theoretical guidance tool for the optimization of elbow-type pipe fittings, and possesses high academic reference value. Attached Figure Description

[0036] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the full-size experimental system of the present invention;

[0038] Figure 2 This is a schematic diagram of the test point arrangement for the S-shaped elbow of the present invention;

[0039] Figure 3 This is a schematic diagram for validating the turbulence model.

[0040] Figure 4 This is a schematic diagram for verifying grid independence.

[0041] Figure 5 This is a schematic diagram of the field coordination angle distribution of a traditional S-shaped bend;

[0042] Figure 6 A schematic diagram illustrating the optimization process of the position and angle of the dual guide vanes;

[0043] Figure 7 A schematic diagram showing the drag reduction rate of different double guide vane schemes inserted in an S-shaped bend;

[0044] Figure 8 A schematic diagram showing the distribution characteristics of the local resistance coefficient of an S-shaped bend under different inlet Reynolds numbers;

[0045] Figure 9 Schematic diagram of drag characteristics and drag reduction effect under different nominal diameters and radii of curvature;

[0046] Figure 10A schematic diagram showing the local resistance coefficient and drag reduction rate of an S-shaped bend under different coupling distances;

[0047] Figure 11 A schematic diagram comparing the energy dissipation distribution of a traditional S-shaped bend and an S-shaped bend with guide vanes;

[0048] Figure 12 A schematic diagram showing the derivation of the equation for the guide vane's arc surface. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1: A low-resistance design method for an S-shaped bend based on a double-guide vane combination, comprising the following steps: S1. Visualizing the high-resistance region of fluid flow using the field cooperation angle reveals that the high cooperation angle region is mainly distributed at the upstream and downstream bends of the S-shaped bend. Specifically, as... Figure 5 As shown, high cooperation angles are mainly distributed at S-bends and a small portion of the downstream straight pipe. The insertion of guide vanes can restructure the flow distribution and cooperation angle distribution, potentially reducing the cooperation angle. Therefore, the guide vanes should be inserted inside the S-bend to guide fluid flow and cut through the high cooperation angle in this area. For the drag reduction optimization design of inserting guide vanes inside the S-bend, a simple comparative design method is used to first optimize the guide vane position at the S-bend. Based on determining the optimal guide vane position, the guide vane angle is designed for low drag. Unlike a single 90° bend, an S-bend consists of two 90° bends, and the corresponding guide vane optimization scheme is to insert a single guide vane on each of the two 90° bend sides (two guide vanes in total). The field cooperation angle theory is used to quantitatively identify high-resistance regions, upgrading the traditional guide vane arrangement method, which relies on empirical guesswork, to a scientific decision based on the flow field energy dissipation mechanism. Visualization technology is used to intuitively locate the upstream and downstream bends as the dominant loss areas, providing a theoretical basis for the subsequent precise targeted layout of dual guide vanes and avoiding the blind placement of flow guiding devices.

[0051] S2. The S-shaped bend is divided into an upstream bend and a downstream bend by the midpoint plane of the vertical axis. The midpoint plane is defined as the midpoint dividing surface. Decomposing the complex S-shaped bend into two subdomains, the upstream and downstream bends, achieves modular dimensionality reduction processing of complex problems. The definition of the midpoint dividing surface not only establishes a geometric symmetry benchmark, but more importantly, it creates conditions for the independent design and coordinated matching of the upper and lower guide vanes, facilitating the optimization of flow control strategies for each bend segment using a divide-and-conquer approach.

[0052] S3. Set upper position optimization points Di (i=1, 2, 3) on the upstream section of the S-shaped bend, and lower position optimization points Cj (j=1, 2, 3) on the upstream section of the S-shaped bend; set middle position optimization points Ak (k=1, 2, 3) on the middle equally divided surface. By discretizing the position optimization points (Di, Ak, Cj) at the upper, middle, and lower key levels, the continuous guide vane layout space is transformed into a computable discrete parameter set. This parameterized expression retains design flexibility while providing a clear search space for subsequent combinatorial optimization, significantly improving optimization efficiency and operability.

[0053] S4. Draw an upper arc line concentric with the upstream bend between Di and the corresponding Ak to form the upper guide vane model. Draw a lower arc line concentric with the downstream bend between Cj and the corresponding Ak to form the lower guide vane model. The modeling method of concentricizing the upper guide vane with the upstream bend and the lower guide vane with the downstream bend ensures that the guide vane profile naturally matches the curvature trend of the mainstream flow, reducing the risk of adverse pressure gradient and flow separation on the guide vane surface. By optimizing the direct drawing of arc lines between points, the geometric generation method is simple and reliable, facilitating parametric automatic modeling and rapid iteration.

[0054] S5. The lower guide vane model with a 90° arc angle is sequentially combined with the upper guide vane model with a 90° arc angle to form various primary dual guide vane models. The upper and lower guide vane models in different positions are systematically arranged and combined to comprehensively cover the possible configurations in the design space. This combination strategy can fully explore diverse solutions in the early stage, avoid getting trapped in local optima too early, and provide a rich sample of candidates for selecting the basic configuration with the greatest performance potential.

[0055] S6. Perform drag reduction analysis on the various primary dual-guide vane models from step S5, and select the optimal combination of the lower and upper guide vane models based on the drag reduction rate. Introducing drag reduction rate as an objective evaluation index, and performing quantitative evaluation through CFD simulation or experimental data, achieves a leap from empirical qualitative judgment to data-driven decision-making. This step scientifically selects the optimal upper and lower guide vane combination from numerous primary models, completing the first round of precise optimization.

[0056] S7. Based on the optimal combination of the lower and upper guide vane models from step S6, optimize the arc angles of both models. A step-by-step strategy decoupling position and angle optimization is adopted, breaking down the complex multivariate coupled problem into two controllable stages, significantly reducing the optimization difficulty. The approach of first determining the optimal position combination and then optimizing the angle ensures the independence and effectiveness of each optimization step, improving overall convergence efficiency.

[0057] S7.1. The lower guide vane models with arc angles of 30°, 60°, and 90° are combined with the upper guide vane model with an arc angle of 90°, and the optimal lower guide vane model with the arc angle is obtained through drag reduction analysis.

[0058] S7.2 The lower guide vane model with the optimal arc angle is combined with lower guide vane models with arc angles of 30°, 60° and 90° respectively, and the upper guide vane model with the optimal arc angle is obtained through drag reduction analysis.

[0059] S8. The models of the lower guide vane and the upper guide vane with the optimal arc angle are fitted and optimized to obtain the double guide vane arc surface equation, thus yielding a double guide vane model that reduces the resistance of the S-shaped bend. The optimal guide vane parameters obtained from discrete optimization are sublimated into a continuous double guide vane arc surface equation, realizing the mathematical solidification and model-based inheritance of design knowledge. This equation can be directly used for engineering manufacturing and rapid design of bends of similar specifications, avoiding redundant optimization, significantly improving the universality and engineering application value of the method, and marking the standardization and closed-loop nature of the design process.

[0060] It should be noted that this invention uses the commercial CFD software ANSYS Fluent 19.0 to calculate the flow and resistance of the S-shaped bend. The fluid is single-phase incompressible liquid water with unchanged physical properties, and heat exchange is neglected. Furthermore, the convection terms are discretized using a second-order inverse-wind scheme. The SIMPLE algorithm is used to determine the coupling between pressure and velocity. The convergence criterion is that the change in the average velocity and average pressure at the cross-section between two iterations is less than 10. -3 Normalized residual less than 10 -6 To ensure the boundary conditions in the numerical simulation are consistent with those in the experiment, the S-bend inlet is set as a velocity inlet, and the S-bend outlet is set as a pressure outlet with a static pressure of 0. The wall boundary conditions are no-slip boundaries, consistent with the roughness of the galvanized steel pipe in the experiment, with an absolute roughness of 0.15 mm.

[0061] Choosing a suitable turbulence model is crucial for accurately predicting flow distribution and pressure loss within S-bends. The local drag coefficient is a fundamental dimensionless parameter for assessing pressure loss and can be used to verify the accuracy of turbulence models. We tested the local drag coefficient of a conventional S-bend using a full-scale experimental setup and compared the experimental data with results from various turbulence models to select the most suitable model for this study. Currently, commonly used turbulence models for predicting pipe flow include realizable k-ε, standard k-ε, RNG k-ω, SST k-ω, and RSM. Figure 3The local drag coefficients of S-shaped bends obtained from various turbulence models and experimental tests at different Reynolds numbers are presented. The calculation results show that the average deviations of each turbulence model compared with the experiment are 0.7%, 2.7%, 6.7%, 8.0%, and 3.8%, respectively. Since the realizable k-ε turbulence model can accurately predict the pressure loss in the bend, the realizable k-ε turbulence model is selected for the following numerical calculations.

[0062] For mesh independence verification, a hybrid method of structured and unstructured meshes is used for mesh generation. For example... Figure 4 As shown, the mesh of the S-shaped pipe is refined. The upstream and downstream straight pipe sections are divided using a structured mesh, while the S-shaped elbow section, with its complex curved structure, can be divided using an unstructured mesh. Based on the hybrid mesh generation method, six mesh counts (0.15 million, 0.30 million, 0.60 million, 0.90 million, 1.20 million, and 1.50 million) are selected for mesh independence verification. The results of the mesh independence verification are shown in the figure. As the mesh count increases, the pressure drop of the S-shaped elbow increases until the mesh count is greater than or equal to 1.20 million, at which point the pressure drop no longer changes. Therefore, a hybrid mesh with a mesh count of 1.20 million is selected for the following numerical simulation study.

[0063] The formula for calculating the drag reduction rate in this invention is as follows:

[0064]

[0065] in It is the drag reduction ratio. and These are the local resistance coefficients of the traditional S-shaped bend and the new S-shaped bend, respectively; the formula for calculating the local resistance coefficient of the S-shaped bend is:

[0066] ,

[0067] , ;

[0068] In the formula This represents the local resistance coefficient of the S-shaped bend; It is a localized pressure loss; It is the mean dynamic pressure; It is the static pressure difference between the upstream and downstream sections of the S-bend in the full-scale experimental system. It is the pressure difference in the straight pipe below the S-bend in the full-scale experimental system; The static pressure at the upstream section of the S-bend in the full-scale experimental system. The static pressure at the downstream section of the S-bend in the full-scale experimental system; The static pressure upstream of the straight pipe below the S-bend length in the full-scale experimental system. The static pressure downstream of the straight pipe at the length of the S-bend in the full-scale experimental system.

[0069] Example 2: A low-resistance design method for S-shaped elbows based on a double-guide vane combination, further optimized from Example 1, such as... Figure 1 As shown, the full-scale experimental system in this embodiment includes a water tank and a water pump. Along the water outlet direction, a filter, water pump, butterfly valve, pressure transmitter, electromagnetic flowmeter, and the S-bend to be tested are connected sequentially. The outlet of the S-bend is connected to the inlet of the water tank. An upstream measuring point is located upstream of the S-bend, and a downstream measuring point is located downstream of the S-bend. A differential pressure pump is connected between the upstream and downstream measuring points. A third and fourth measuring point are located on the straight pipe below the S-bend, with the distance between the third and fourth measuring points equal to the distance between the upstream and downstream measuring points. A differential pressure pump is also connected between the third and fourth measuring points. Both the inlet and outlet of the pump are connected to flexible rubber joints to prevent pipe vibration during pump operation. A filter is installed at the water tank outlet to filter impurities. After the water pump is turned on, the flow rate and pressure in the pipeline can be changed by adjusting the frequency converter and butterfly valve. The pressure difference between measuring points 1 and 2 upstream and downstream of the S-bend can be measured using a Rosemount 3051DP differential pressure transmitter. Friction resistance can be obtained by measuring the pressure difference between measuring points along a straight pipe section of equal length. An electromagnetic flowmeter is installed downstream of the water pump to obtain the flow rate in the pipe. Each measuring instrument is connected to a paperless recorder to collect and record its measurement data.

[0070] Specifically, the pipe material is galvanized steel with a surface roughness of 0.15 mm. Let the outer diameter of the S-bend be D, the radius of curvature be R, the distance from the upstream measuring point to the upstream section of the S-bend be 15D, the distance from the downstream measuring point to the downstream section of the S-bend be 15D, and the distance between the third and fourth measuring points be 2 × 15D + 0.5 × 2πR. Figure 2 As shown.

[0071] In step S3, the upper position optimization point Di, the lower position optimization point Cj, and the middle position optimization point Ak are set at equal distances. The distance between two adjacent upper position optimization points is a, the distance between two adjacent lower position optimization points is a, and the distance between two adjacent middle position optimization points is a. Therefore, a / D = 0.25.

[0072] like Figure 12 As shown, in step S8, a spatial coordinate system is established with the center of the downstream elbow as the origin. Based on the outer diameter D and radius of curvature R of the S-shaped elbow, the equation of the double guide vane arc surface is obtained:

[0073] Equation for the lower guide vane of the S-shaped elbow: ;

[0074] Equation for the upper guide vane of the S-shaped elbow:

[0075]

[0076] Among them, the radius of curvature of the S-shaped bend is R / D < 2.0.

[0077] This invention employs full-scale experiments and numerical simulations to study the internal flow distribution and resistance characteristics of S-bends in water systems. The influence of the position and angle of the double guide vanes on the drag reduction rate of the S-bend was investigated. Based on a comparative analysis of energy dissipation, the distribution of high resistance and high dissipation in traditional S-bends and S-bends with guide vanes was analyzed, and the design parameters and guide vane arc surface equations for low-resistance S-bends with different nominal diameters were summarized. The insertion of double guide vanes can significantly reduce energy dissipation downstream of the S-bend, effectively reducing flow resistance and pump power consumption.

[0078] Example 3: The low-resistance design method for S-shaped elbows based on double guide vane combination of the present invention also includes verification of drag reduction effectiveness under different inlet Reynolds numbers and different coupling distances. When verifying the drag reduction effectiveness under different inlet Reynolds numbers, the Reynolds number is between 1.0 × 10⁻⁶. 4 ~6.0×10 5 Within a certain range, the local resistance coefficients of a traditional S-bend and an S-bend with double guide vanes are compared. Specifically, the inlet Reynolds number has a significant impact on the local resistance coefficient of the S-bend. For example... Figure 8 As shown in the figure, from the overall trend, as the inlet Reynolds number increases, the local resistance coefficient of traditional S-bends and S-bends with guide vanes gradually increases until Re = 2.0 × 10⁻⁶. 5 The local drag coefficients of both no longer change. Observing the drag reduction rate of the S-shaped elbow with guide vanes, it can be seen that as the inlet Reynolds number increases, the drag reduction first gradually decreases until Re > 2.0 × 10⁻⁶. 5 The drag reduction ratio remains constant. The Reynolds number is at 1.0 × 10⁻⁶. 4 ~6.0×10 5 Within this range, the drag reduction rate of the S-shaped elbow with guide vanes is 34.0%~38.0%. Therefore, the S-shaped elbow with guide vanes can effectively reduce the local resistance coefficient and has a good drag reduction and energy consumption reduction effect.

[0079] To verify the drag reduction effectiveness under different coupling distances, the local resistance characteristics of S-shaped bends were analyzed when the coupling distances between the upstream and downstream bends were 0D, 1D, 2D, 4D, and 8D. The drag reduction effect of S-shaped bends with double guide vanes under different coupling distances was also analyzed. Specifically, different coupling distances between the two bends may cause changes in the internal flow regime and alter the local resistance characteristics, thus affecting the drag reduction effect of the guide vanes. Therefore, the local resistance characteristics of S-shaped bends with distances of 0D, 1D, 2D, 4D, and 8D between the two bends were investigated, and the drag reduction effect of S-shaped bends with guide vanes under different adjacent distances was analyzed. Figure 10 As shown, unlike the results for U-shaped bends, the local resistance coefficients of both traditional S-shaped bends and S-shaped bends with guide vanes fluctuate with increasing distance between the two bends, while the drag reduction rate of the S-shaped bend with guide vanes decreases. At different coupling distances, the S-shaped bend with guide vanes exhibits good drag reduction effects.

[0080] The low-resistance design method for S-bends based on double-guide vane combinations also includes energy dissipation analysis and verification. It compares the energy dissipation distribution of traditional S-bends and S-bends with double guide vanes, analyzing the drag reduction effect of the S-bend with double guide vanes. Specifically, when fluid passes through an S-bend, the sudden change in flow path causes flow separation and vortices, resulting in energy dissipation. For example... Figure 11 As shown, the energy dissipation distribution of a traditional S-bend and an S-bend with guide vanes are compared. When the fluid enters the S-bend, there is relatively little energy dissipation in the straight section. However, after passing through the S-bend, due to continuous collisions and flow separation between the fluid and the wall, higher energy dissipation occurs near the wall and in some downstream areas. Compared to a traditional S-bend, the downstream straight section of the S-bend with guide vanes exhibits significantly lower energy dissipation, and the high-energy-dissipation area is considerably reduced. Therefore, the S-bend with guide vanes can effectively reduce fluid energy dissipation, achieving energy saving and consumption reduction.

[0081] In addition, such as Figure 9 As shown, the local resistance coefficients and corresponding drag reduction rates of traditional S-bends and S-bends with guide vanes were compared under different nominal diameters (DN32~DN200) and radius-of-curvature ratios (0.8~2.0). For traditional S-bends with different nominal diameters, the local resistance coefficient decreases with increasing radius-of-curvature ratio. When the radius-of-curvature ratio of the traditional S-bend remains constant, the local resistance coefficient decreases with increasing nominal diameter. Under different nominal diameters and radii of curvature, the drag reduction rate of the low-resistance S-bend with guide vanes ranges from 0% to 34.2%. Therefore, under different nominal diameters and radius-of-curvature ratios, S-bends with guide vanes can effectively reduce local resistance losses.

[0082] Example 4: A low-resistance design method for an S-shaped bend based on a double guide vane combination. This example elaborates on steps S3 to S7. Due to the special structure of the S-shaped bend, guide vanes can be inserted into the two 90° bends respectively for drag reduction design. During the optimization process, the inlet velocity of the S-shaped bend is kept constant at 1 m / s, and the inlet Reynolds number is 3.2 × 10⁻⁶. 4 The specific parameters for each double-guide vane optimization scheme are shown in Table 1, and the specific optimization process is as follows: Figure 6 As shown in the figure. First, the position of the double guide vanes was optimized for low drag, resulting in nine possible positions: C1-D1, C1-D2, C1-D3, C2-D1, C2-D2, C2-D3, C3-D1, C3-D2, and C3-D3. The dimensionless distance between two adjacent guide vanes was a / D = 0.25. The optimization results for the double guide vane position are shown below. Figure 9As shown, for guide vane combinations of type C1-D, the combination with the best drag reduction effect is C1-D2, with a drag reduction rate of 9.7%. For guide vane combinations of type C2-D, the combination with the best drag reduction effect is C2-D3, with a drag reduction rate of 28.3%. For guide vane combinations of type C3-D, the combination with the best drag reduction effect is C3-D2, with a drag reduction rate of 24.2%. Therefore, for the above 9 different double guide vane position schemes, the combination with the highest drag reduction rate is C2-D3; that is, the double guide vane formed by the arc where C2-A2 is located (corresponding to the right guide vane) and the arc where A3-D3 is located (corresponding to the left guide vane). In this case, the distance from the arc where A3-D3 is located to the bend is a / D=0.25, and the distance from the arc where C2-A2 is located to the bend is 2a / D=0.5. Then, based on the obtained double guide vane position scheme C2-D3, its angle is optimized. There are six angle schemes for the dual guide vanes. For ease of description, the upstream guide vane is defined as the right guide vane, and the downstream guide vane as the left guide vane. First, the position and angle of the right guide vane are kept constant. The angle of the left guide vane is then changed to obtain a better angle. The angle of the right guide vane is designed according to the same optimization logic. The angle schemes are D3-E1, D3-E2, D3-E3, E2-F1, E2-F2, and E2-F3. D3 represents the right guide vane (A3-D3) with an angle of 90°. E1, E2, and E3 represent the left guide vane with angles of 30°, 60°, and 90°, respectively. F1, F2, and F3 represent the right guide vane with angles of 30°, 60°, and 90°, respectively. For the D3-E type guide vane combination, the D3-D2 combination has the best drag reduction effect, with a drag reduction rate of 28.6%. For the E2-F type guide vane combination, the E2-F2 combination has the best drag reduction effect, with a drag reduction rate of 35.1%. Therefore, the position and angle of the double guide vanes were optimized using a simple comparative design method. The resulting optimal double guide vane combination was E2-F2. Compared with the 17.5% drag reduction rate of inserting a single guide vane in the S-bend, the 35.1% drag reduction effect of the double guide vanes is significantly greater than that of the single guide vane. Figure 7 As shown in Table 1, the final results show that double guide vanes with positions a / D=0.25 and 2a / D=0.50, both at an angle of 60°, achieve excellent drag reduction.

[0083]

[0084] Next, we will study the resistance characteristics and analyze the drag reduction effect of the S-shaped elbow with double guide vanes.

[0085] Effectiveness of drag reduction under different inlet Reynolds numbers: The inlet Reynolds number has a significant impact on the local resistance coefficient of S-shaped bends. For example... Figure 8As shown in the figure, from the overall trend, as the inlet Reynolds number increases, the local resistance coefficient of traditional S-bends and S-bends with guide vanes gradually increases until Re = 2.0 × 10⁻⁶. 5 The local drag coefficients of both no longer change. Observing the drag reduction rate of the S-shaped elbow with guide vanes, it can be seen that as the inlet Reynolds number increases, the drag reduction first gradually decreases until Re > 2.0 × 10⁻⁶. 5 The drag reduction ratio remains constant. The Reynolds number is at 1.0 × 10⁻⁶. 4 ~6.0×10 5 Within this range, the drag reduction rate of the S-shaped elbow with guide vanes is 34.0%~38.0%. Therefore, the S-shaped elbow with guide vanes can effectively reduce the local resistance coefficient and has a good drag reduction and energy consumption reduction effect.

[0086] Drag reduction effectiveness under different nominal diameter and radius of curvature ratios: such as Figure 9 As shown, the local resistance coefficients and corresponding drag reduction rates of traditional S-bends and S-bends with guide vanes were compared under different nominal diameters (DN32~DN200) and radius-of-curvature ratios (0.8~2.0). For traditional S-bends with different nominal diameters, the local resistance coefficient decreases with increasing radius-of-curvature ratio. When the radius-of-curvature ratio of the traditional S-bend remains constant, the local resistance coefficient decreases with increasing nominal diameter. Under different nominal diameters and radii of curvature, the drag reduction rate of the low-resistance S-bend with guide vanes ranges from 0% to 34.2%. Therefore, under different nominal diameters and radius-of-curvature ratios, S-bends with guide vanes can effectively reduce local resistance losses.

[0087] Drag Reduction Effect of Two Elbows with Different Coupling Distances: When there are different coupling distances between two elbows, it may cause changes in the internal flow pattern and alter the local resistance characteristics, thus affecting the drag reduction effect of the guide vanes. Therefore, this section explores the local resistance characteristics of S-shaped elbows with guide vanes when the distance between the two elbows is 0D, 1D, 2D, 4D, and 8D, and analyzes the drag reduction effect of S-shaped elbows with guide vanes under different adjacent distances. Figure 10 As shown, unlike the results for U-shaped bends, the local resistance coefficients of both traditional S-shaped bends and S-shaped bends with guide vanes fluctuate with increasing distance between the two bends, while the drag reduction rate of the S-shaped bend with guide vanes decreases. At different coupling distances, the S-shaped bend with guide vanes exhibits good drag reduction effects.

[0088] Energy dissipation analysis: When fluid passes through an S-shaped bend, the sudden change in flow direction causes flow separation and vortices, resulting in energy dissipation. For example... Figure 11As shown, the energy dissipation distribution of a traditional S-bend and an S-bend with guide vanes are compared. When the fluid enters the S-bend, there is relatively little energy dissipation in the straight section. However, after passing through the S-bend, due to continuous collisions and flow separation between the fluid and the wall, higher energy dissipation occurs near the wall and in some downstream areas. Compared to a traditional S-bend, the downstream straight section of the S-bend with guide vanes exhibits significantly lower energy dissipation, and the high-energy-dissipation area is considerably reduced. Therefore, the S-bend with guide vanes can effectively reduce fluid energy dissipation, achieving energy saving and consumption reduction.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-resistance design method for S-shaped elbows based on a double-guide vane combination, characterized in that: The steps are as follows: S1. By visualizing the high resistance region of fluid flow using the field coordination angle, it is found that the high coordination angle region is mainly distributed at the upstream and downstream bends of the S-shaped bend. S2. Divide the S-shaped bend into an upstream bend and a downstream bend by the middle plane of the vertical axis. The middle plane is defined as the middle dividing plane. S3. Set an upper position optimization point Di on the upstream section of the S-shaped bend, i=1, 2, 3, and set a lower position optimization point Cj on the upstream section of the S-shaped bend, j=1, 2, 3. Set an optimization point Ak at the middle position on the equally divided surface, where k=1, 2, 3; S4. Draw an upper arc line with the same center as the upstream bend between Di and the corresponding Ak to form the upper guide vane model. Draw a lower arc line with the same center as the downstream bend between Cj and the corresponding Ak to form the lower guide vane model. S5. The lower guide vane model with an arc angle of 90° is combined with the upper guide vane model with an arc angle of 90° in sequence to form a variety of primary double guide vane models. S6. Perform drag reduction analysis on the various primary models of the double guide vane in step S5, and select the combination of the lower guide vane model and the upper guide vane model with the best position based on the drag reduction rate. S7. Based on the optimal combination of the lower guide vane model and the upper guide vane model in step S6, optimize the arc angle of the upper guide vane model and the lower guide vane model. S7.

1. The lower guide vane models with arc angles of 30°, 60°, and 90° are combined with the upper guide vane model with an arc angle of 90°, and the optimal lower guide vane model with the arc angle is obtained through drag reduction analysis. S7.2 The lower guide vane model with the optimal arc angle is combined with lower guide vane models with arc angles of 30°, 60° and 90° respectively, and the upper guide vane model with the optimal arc angle is obtained through drag reduction analysis. S8. Fit and optimize the lower guide vane model with the optimal arc angle and the upper guide vane model with the optimal arc angle to obtain the double guide vane arc surface equation, thereby obtaining the double guide vane model to reduce the resistance of the S-shaped bend.

2. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 1, characterized in that: The formula for calculating the drag reduction ratio is as follows: in It is the drag reduction ratio. and These are the local resistance coefficients of the traditional S-shaped bend and the new S-shaped bend, respectively. The formula for calculating the local resistance coefficient of an S-shaped bend is: ， ， ； In the formula This represents the local resistance coefficient of the S-shaped bend; It is a localized pressure loss; It is the mean dynamic pressure; It is the static pressure difference between the upstream and downstream sections of the S-bend in the full-scale experimental system. It is the pressure difference in the straight pipe below the S-bend in the full-scale experimental system; The static pressure at the upstream section of the S-bend in the full-scale experimental system. The static pressure at the downstream section of the S-bend in the full-scale experimental system; The static pressure upstream of the straight pipe below the S-bend length in the full-scale experimental system. The static pressure downstream of the straight pipe at the length of the S-bend in the full-scale experimental system.

3. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 2, characterized in that: The full-scale experimental system includes a water tank and a water pump. Along the water outlet direction, a filter, water pump, butterfly valve, pressure transmitter, electromagnetic flowmeter, and the S-bend to be tested are connected sequentially. The outlet of the S-bend is connected to the inlet of the water tank. An upstream measuring point is located upstream of the S-bend, and a downstream measuring point is located downstream of the S-bend. A differential pressure pump connects the upstream and downstream measuring points. A third and fourth measuring point are located on the straight pipe below the S-bend. The distance between the third and fourth measuring points is equal to the distance between the upstream and downstream measuring points. A differential pressure pump connects the third and fourth measuring points.

4. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 3, characterized in that: Let the outer diameter of the S-shaped bend be D, the radius of curvature be R, the distance from the upstream measuring point to the upstream section of the S-shaped bend be 15D, the distance from the downstream measuring point to the downstream section of the S-shaped bend be 15D, and the distance between the third and fourth measuring points be 2×15D+0.5×2πR.

5. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 4, characterized in that: In step S3, the upper position optimization point Di, the lower position optimization point Cj, and the middle position optimization point Ak are set at equal distances. The distance between two adjacent upper position optimization points is a, the distance between two adjacent lower position optimization points is a, and the distance between two adjacent middle position optimization points is a. Therefore, a / D = 0.

25.

6. The low-resistance design method for S-shaped elbows based on double guide vane combination according to any one of claims 1 to 5, characterized in that: In step S8, a spatial coordinate system is established with the center of the downstream elbow as the origin. Based on the outer diameter D and radius of curvature R of the S-shaped elbow, the equation of the double guide vane arc surface is obtained: Equation for the lower guide vane of the S-shaped elbow: ; Equation for the upper guide vane of the S-shaped elbow: Among them, the radius of curvature of the S-shaped bend is R / D < 2.

0.

7. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 6, characterized in that: It also includes verification of drag reduction effectiveness under different inlet Reynolds numbers and different coupling distances.

8. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 7, characterized in that: When verifying the drag reduction effectiveness at different import Reynolds numbers, the Reynolds number was 1.0 × 10⁻⁶. 4 ~6.0×10 5 Within the specified range, the local resistance coefficients of a traditional S-bend and an S-bend with double guide vanes are compared.

9. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 7 or 8, characterized in that: To verify the effectiveness of drag reduction under different coupling distances, the local resistance characteristics of the S-shaped bend were analyzed when the coupling distances between the upstream and downstream bends were 0D, 1D, 2D, 4D, and 8D, and the drag reduction effect of the S-shaped bend with double guide vanes under different coupling distances was also analyzed.

10. The low-resistance design method for S-shaped elbows based on double guide vane combination according to claim 9, characterized in that: It also includes energy dissipation analysis and verification, comparing the energy dissipation distribution of traditional S-bends and S-bends with double guide vanes, and analyzing the drag reduction effect of S-bends with double guide vanes.

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