A method for designing a drainage angle of a tunnel smoke exhaust cross-hole drainage structure

Abstract

This invention relates to the field of tunnel technology and provides a method for designing the diversion angle of a tunnel smoke exhaust cross passage diversion structure. The method determines the change in momentum loss with flow distance when smoke flows along the diversion plane based on the boundary layer momentum integral relationship. An adhesion margin, quantified by the boundary layer shape factor, is introduced at the end of the diversion plane. The feasibility of the diversion angle is judged by the condition that this adhesion margin is not lower than the safety lower limit calibrated based on turbulence separation experimental data. Based on this judgment condition, the diversion angle is gradually increased, and the above steps are repeated until the adhesion margin approaches the safety lower limit. The maximum allowable diversion angle is then determined as the design diversion angle. This invention directly links the diversion angle to tunnel engineering parameters, enabling quantitative prediction of flow separation risks. The final selected diversion angle effectively suppresses boundary layer separation to ensure smoke exhaust efficiency while also considering civil engineering economics. The design results are scientifically based and repeatable.

Description

Technical Field

[0001] This invention relates to the field of tunnel technology, and in particular to a method for designing the diversion angle of a tunnel smoke exhaust cross passage diversion structure. Background Technology

[0002] Currently, the design of the connection between the smoke exhaust cross passage and the main tunnel in extra-long highway tunnels mainly follows the principle of simple civil engineering structure, and generally adopts a 90° vertical connection method (such as...). Figure 3 (As shown). This right-angle connection has advantages in structural mechanics and construction surveying, but its hydrodynamic performance has serious inherent defects, which has become a bottleneck problem restricting the improvement of smoke exhaust system efficiency.

[0003] While this right-angle connection design is relatively simple in terms of structural construction, it presents significant hydrodynamic defects under fire smoke extraction conditions. When smoke enters the smoke extraction cross passage from the main tunnel, its flow direction needs to change instantaneously by 90°, resulting in severe boundary layer separation on the inner side of the corner, forming a large-scale vortex zone. This vortex zone blocks the effective flow cross-section, causing a sharp increase in local resistance. A large portion of the effective pressure head of the smoke extraction fan is consumed in overcoming vortex losses, resulting in the actual smoke capture efficiency of the smoke extraction cross passage for upstream smoke being far lower than designed.

[0004] To address this problem, existing technological improvements mainly focus on peripheral measures such as enhancing fan performance (e.g., increasing the power and air pressure of smoke exhaust fans) or optimizing the control system (e.g., adjusting fan operation strategies based on the fire location). However, these methods do not address the core issue—the inherently poor flow characteristics at the smoke exhaust cross-vent connection. While increasing power can partially compensate for resistance losses, it is economically inefficient, energy-intensive, and may introduce new problems such as noise and vibration; optimizing control strategies cannot alter the fundamental flow characteristics inherent in the given physical structure.

[0005] Therefore, optimizing the connection structure of the smoke exhaust cross passage based on the fundamental principles of fluid mechanics to fundamentally improve the flow conditions when smoke flows in is a key and yet fully resolved technical issue that aims to overcome the current bottleneck in smoke exhaust efficiency and achieve a dual improvement in tunnel fire safety and operational economy. Based on this understanding, this invention proposes a method for designing the diversion angle of the smoke exhaust cross passage diversion structure in tunnels. Summary of the Invention

[0006] The main objective of this invention is to provide a method for designing the diversion angle of a cross passage for smoke exhaust in tunnels, in order to solve the defects of low smoke exhaust efficiency caused by flow separation and eddies at the right-angle connection of existing cross passages for smoke exhaust in highway tunnels, as well as the technical problems of high energy consumption and poor economy caused by increasing the power of the fan in existing improvement methods, and the inability of the control strategy optimization to change the nature of the flow.

[0007] To achieve the above objectives, the present invention provides a method for designing the diversion angle of a tunnel smoke exhaust cross passage diversion structure. The diversion structure includes a diversion plane disposed between the upstream connection of the smoke exhaust cross passage and the main tunnel, wherein a diversion angle is formed between the diversion plane and the longitudinal axis of the main tunnel, and the method includes the following steps: S1, obtain the design longitudinal ventilation velocity in the main tunnel, the width of the main tunnel, and the kinematic viscosity of the smoke under fire conditions; S2, Based on the designed longitudinal ventilation velocity, width and flue gas kinematic viscosity, determine the process of momentum loss of flue gas close to the wall of the guide plane due to viscous hindrance as the flow distance changes when the flue gas flows along the guide plane. S3, based on the change process, when the flue gas flows to the end of the guide plane, the adhesion margin characterizes the ability of the flue gas to resist the peeling of the wall by the reverse pressure gradient, and the adhesion margin is not lower than the safety lower limit calibrated according to the turbulence separation experimental data as the evaluation condition for the feasibility of the guide angle. S4. Based on the designed longitudinal ventilation velocity, width, and flue gas kinematic viscosity, as well as the evaluation conditions, adjust the value of the diversion angle to determine the maximum value that the diversion angle can achieve under the evaluation conditions, and use the maximum value as the designed diversion angle of the diversion plane.

[0008] Preferably, step S2 includes the following steps: S21, determine the angle-related index based on the flow angle, which reflects the rate of velocity decay of flue gas as it flows along the flow plane; wherein the angle-related index increases as the flow angle increases; S22, Based on the corner correlation index, the designed longitudinal ventilation wind speed and the preset length of the diversion plane, the velocity distribution of flue gas along the diversion plane is constructed. The velocity distribution along the plane is used to reflect the trend of flue gas velocity gradually decreasing from the starting point to the end of the diversion plane. S23, the velocity distribution along the flow path is correlated with the momentum loss caused by viscous hindrance at the wall of the flow guide plane to obtain the process of the momentum loss changing with the flow distance.

[0009] Preferably, step S21 includes the following steps: Using formula The angle correlation index is obtained. ;in, The angle of the flow is measured in radians.

[0010] Preferably, step S22 includes the following steps: Taking the starting point of the diversion plane as the origin of the arc length coordinate, the arc length coordinate s is defined along the flue gas flow direction. The arc length coordinate s is taken as the preset length L at the end of the diversion plane. The diversion plane extends along the flue gas flow direction from the junction with the wall of the main tunnel as the starting point to the junction with the internal passage of the exhaust cross tunnel as the ending point. Construct the velocity distribution along the path as follows ;in, For the speed distribution along the path, The longitudinal ventilation velocity is defined in the design.

[0011] Preferably, step S23 includes the following steps: The speed distribution along the path As the velocity condition at the outer edge of the boundary layer, we substitute it into the momentum integral relation describing the development of momentum deficit along the boundary layer; wherein, the momentum integral relation is: Where θ is the boundary layer momentum thickness, which characterizes the momentum deficit at the boundary layer wall caused by viscous hindrance, and H is the boundary layer shape factor, defined as the ratio of the boundary layer displacement thickness to the momentum thickness. The coefficient of friction of the wall surface; Combined with the wall friction coefficient in the turbulent boundary layer The empirical correlation with the boundary layer momentum thickness θ and the velocity distribution along the path The momentum integral relationship is solved by integrating along the arc length coordinate s to obtain the momentum thickness θ of the boundary layer as the process of momentum loss changing with the flow distance.

[0012] Preferably, step S3 includes the following steps: Based on the change of momentum loss with flow distance, the boundary layer shape factor H at the end of the guiding plane is calculated, and the boundary layer shape factor H is used as the quantized value of the adhesion margin. The boundary layer shape factor H not exceeding the critical shape factor value pre-calibrated based on turbulent boundary layer separation experiments is used as the criterion for judging the feasibility of the diversion angle.

[0013] Preferably, step S4 includes the following steps: Calculate the tunnel Reynolds number based on the designed longitudinal ventilation velocity, the width, and the kinematic viscosity of the flue gas. Substituting the tunnel Reynolds number into the pre-fitted explicit angle formula, the initial drainage angle is obtained; Starting from the initial drainage angle, gradually increase the value of the drainage angle and repeat steps S2 to S3 for each value until the attachment margin approaches the safety lower limit. Take the drainage angle value at this time as the maximum value and take the maximum value as the designed drainage angle.

[0014] Preferably, the explicit angle formula is obtained through the following steps: Within the range of typical highway tunnel parameters, select multiple different tunnel Reynolds numbers. For each tunnel Reynolds number, with the diversion angle as the variable, repeat steps S2 to S3 and determine the maximum value that the diversion angle can reach under the evaluation conditions. This yields a set of discrete data points consisting of the tunnel Reynolds number and the corresponding maximum diversion angle. Using the commonly used logarithmic value of the tunnel Reynolds number as the independent variable and the maximum drainage angle as the dependent variable, linear regression fitting is performed on the discrete data points to obtain the explicit angle formula.

[0015] Preferably, the critical shape factor value is 2.4.

[0016] Preferably, the wall friction coefficient The empirical correlation between the boundary layer momentum thickness θ and the boundary layer momentum thickness θ is as follows: ;in, ;in, The local Reynolds number of the boundary layer momentum thickness θ. The kinematic viscosity of the flue gas is given.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) By obtaining the design longitudinal ventilation velocity, width and smoke kinematic viscosity of the main tunnel as input parameters, this invention establishes the correlation between the diversion angle design and the actual tunnel engineering conditions. This invention can make targeted designs for the specific ventilation conditions and fire scenarios of different tunnel sections, rather than relying on general experience values, thus ensuring that the design results match the actual engineering.

[0018] (2) This invention, by determining the change process of momentum loss with flow distance when flue gas flows along the guide plane, transforms the influence of the guide angle on the flow into a quantitatively calculable boundary layer development law, thus solving the problem in the prior art that the intrinsic relationship between the turning angle and flow separation cannot be revealed by relying solely on experience or simulation trials. By introducing an attachment margin with the boundary layer shape factor as a quantitative index at the end of the guide plane, and using the fact that this attachment margin is not lower than the safety lower limit calibrated based on turbulent separation experimental data as a criterion for the feasibility of the guide angle, a quantitative prediction of flow separation risk is achieved.

[0019] (3) This invention gradually increases the diversion angle based on the evaluation conditions and repeatedly performs momentum loss analysis and attachment margin assessment until the attachment margin approaches the safety lower limit, thereby determining the maximum allowable diversion angle under the constraint of non-separation of flow as the design diversion angle. The final selected diversion angle can effectively suppress boundary layer separation and ensure smoke exhaust efficiency, and can make the diversion plane as steep as possible to reduce the amount of civil engineering excavation. It achieves a precise balance between fluid dynamics performance and engineering economy, and solves the contradiction between smoke exhaust efficiency and engineering cost in the prior art.

[0020] (4) The design results of the present invention have scientific basis and repeatability, overcoming the problems of low efficiency and inconsistent results caused by relying on the personal experience of designers or time-consuming simulation calculations in the prior art. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart of one embodiment of the present invention; Figure 2 This is a plan view of the diversion structure applied to a smoke exhaust system in one embodiment of the present invention; Figure 3 This is a schematic diagram of a tunnel model in one embodiment of the present invention; Figure 4 The diagram shows a comparison of the smoke extraction effects of a traditional horizontal smoke extraction system and the smoke extraction system of the present invention; wherein, (a) is a schematic diagram of the smoke extraction effect of the traditional horizontal smoke extraction system, and (b) is a schematic diagram of the smoke extraction effect of the present invention. Figure 5 This is a diagram of the horizontal smoke flow field at a height of 3m above the road surface in a traditional cross-tunnel smoke exhaust system. Figure 6 This is a diagram of the horizontal smoke flow field of the smoke exhaust system of the present invention at a height of 3m above the road surface.

[0023] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0024] Explanation of icon numbers: 10. Upstream tunnel; 20. Downstream tunnel; 30. Smoke exhaust cross passage; 40. Drainage plane. Detailed Implementation

[0025] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] 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 a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0028] Please see the appendix Figures 1 to 6 The present invention provides a method for designing the diversion angle of a tunnel smoke exhaust cross passage diversion structure in one embodiment. The diversion structure includes a diversion plane 40 disposed between the upstream connection of the smoke exhaust cross passage 30 and the main tunnel, wherein the diversion plane 40 and the longitudinal axis of the main tunnel form a diversion angle, comprising the following steps: S1, obtain the design longitudinal ventilation velocity inside the main tunnel, the width of the main tunnel, and the kinematic viscosity of the smoke under fire conditions; among which, the design longitudinal ventilation velocity... The value of is determined according to the provisions on critical wind speed under fire conditions in the "Detailed Rules for Ventilation Design of Highway Tunnels". As a specific example, is taken as... =2.5m / s. Design longitudinal ventilation velocity This is a key control parameter to ensure that fire smoke does not flow back and to maintain the safe evacuation of downstream personnel; the width W of the main tunnel is taken as the transverse clearance width of the tunnel at the upstream connection of the smoke exhaust transverse tunnel 30. As a specific example, the width W of the main tunnel is 10m. This width parameter directly affects the geometry of the drainage plane 40 and the channel area for smoke flow.

[0029] It is worth noting that the width of the main tunnel opening determines the lateral span that the diversion plane 40 must cover. Smoke enters from near the upstream sidewall of the tunnel and needs to be guided to the entrance of the exhaust cross passage 30; therefore, the lateral span is equal to the width W of the main tunnel opening, as detailed below. Figure 2 As shown.

[0030] flue gas kinematic viscosity The air properties are obtained from the air property table based on the design smoke temperature under fire conditions. As a specific example... =1.5×10 -5 m 2 / s. Kinematic viscosity of flue gas. It is a physical property parameter characterizing the viscous diffusion ability of flue gas, and its value directly affects the rate of momentum transfer within the boundary layer.

[0031] It should also be noted that the diversion structure described in this invention can be a prefabricated component independent of the smoke exhaust cross tunnel 30, which is fixed to the upstream connecting corner of the smoke exhaust cross tunnel 30 by post-installation; or it can be an irregularly shaped structural section integrally cast with the lining of the smoke exhaust cross tunnel 30. Regardless of the construction method used, as long as a diversion plane 40 is formed at the upstream corner of the smoke exhaust cross tunnel 30 at a diversion angle β with the longitudinal axis of the main tunnel, it falls within the scope of protection claimed by this invention.

[0032] S2, based on the designed longitudinal ventilation velocity, width and flue gas kinematic viscosity, determine the process of momentum loss of flue gas close to the wall of the guide plane 40 due to viscous hindrance as it flows along the guide plane 40, and the change process of momentum loss with flow distance. S3, based on the change process, when the flue gas flows to the end of the diversion plane 40, the adhesion margin characterizes the ability of the flue gas to resist the peeling of the wall surface by the reverse pressure gradient, and the adhesion margin is not lower than the safety lower limit calibrated according to the turbulence separation experimental data as the evaluation condition for the feasibility of the diversion angle. S4. Based on the designed longitudinal ventilation velocity, width, and flue gas kinematic viscosity, as well as the evaluation conditions, adjust the value of the diversion angle to determine the maximum value that the diversion angle can achieve under the evaluation conditions, and use the maximum value as the designed diversion angle of the diversion plane 40.

[0033] (1) By obtaining the design longitudinal ventilation velocity, width and smoke kinematic viscosity of the main tunnel as input parameters, this invention establishes the correlation between the diversion angle design and the actual tunnel engineering conditions. This invention can make targeted designs for the specific ventilation conditions and fire scenarios of different tunnel sections, rather than relying on general experience values, thus ensuring that the design results match the actual engineering.

[0034] (2) This invention, by determining the change process of momentum loss with flow distance when flue gas flows along the guide plane 40, transforms the influence of the guide angle on the flow into a quantitatively calculable boundary layer development law, solving the problem in the prior art that the intrinsic relationship between the turning angle and flow separation cannot be revealed by experience or simulation trial and error alone. By introducing an attachment margin with the boundary layer shape factor as a quantitative index at the end of the guide plane 40, and using the fact that this attachment margin is not lower than the safety lower limit calibrated according to turbulent separation experimental data as the criterion for the feasibility of the guide angle, a quantitative prediction of the flow separation risk is achieved.

[0035] (3) This invention gradually increases the diversion angle based on the evaluation conditions and repeatedly performs momentum loss analysis and attachment margin assessment until the attachment margin approaches the safety lower limit, thereby determining the maximum allowable diversion angle under the constraint of non-separation of flow as the design diversion angle. The final selected diversion angle can effectively suppress boundary layer separation and ensure smoke exhaust efficiency, and can make the diversion plane 40 as steep as possible to reduce the amount of civil engineering excavation. It achieves a precise balance between fluid dynamic performance and engineering economy, and solves the contradiction between smoke exhaust efficiency and engineering cost in the prior art.

[0036] (4) The design results of the present invention have scientific basis and repeatability, overcoming the problems of low efficiency and inconsistent results caused by relying on the personal experience of designers or time-consuming simulation calculations in the prior art.

[0037] In a preferred embodiment, step S2 includes the following steps: S21, determine the angle-related index based on the flow angle, which reflects the rate of velocity decay when the flue gas flows along the flow plane 40; wherein, the angle-related index increases as the flow angle increases; S22, based on the corner correlation index, the designed longitudinal ventilation wind speed and the preset length of the diversion plane 40, construct the velocity distribution of flue gas along the diversion plane 40. The velocity distribution along the diversion plane 40 is used to reflect the trend of flue gas velocity gradually decreasing from the starting point to the end of the diversion plane 40. S23, the velocity distribution along the flow path is correlated with the momentum loss caused by viscous hindrance at the wall of the flow guide plane 40 to obtain the process of the momentum loss changing with the flow distance.

[0038] Further, step S21 includes the following steps: Using formula The angle correlation index is obtained. ;in, The angle of the flow is measured in radians.

[0039] Based on potential flow theory, for the planar diffusion-type turn described in this invention, the turning angle correlation index... It can be associated with the rotation angle β (in radians) and satisfies The angle-related index *m* quantitatively describes the influence of the diversion angle on the rate of decay of flue gas velocity along the tunnel. When β=0 (i.e., the diversion plane 40° is parallel to the longitudinal axis of the main tunnel, with no turning angle), *m*=0. As discussed below, the velocity distribution along the tunnel at this time becomes... When the flue gas velocity remains constant along the path, there is no adverse pressure gradient, and the risk of boundary layer separation is lowest. When β = π / 2 (i.e., the diversion plane 40° is perpendicular to the longitudinal axis of the tunnel main shaft, making a right-angle turn), m = 1, the velocity linearly decays to zero at the end, the adverse pressure gradient is most severe, and the risk of boundary layer separation is highest. Therefore, the angle-related index... Depending on the angle of drainage The increase in the angle accurately reflects the trend of worsening flow caused by the intensified turning point.

[0040] This implementation method introduces the angle-related index m and the diversion angle. The explicit analytical relationship establishes a quantitative bridge between geometric parameters and fluid dynamics response, providing a theoretical basis for finding the maximum allowable diversion angle in step S4. At the same time, the obtained rotation angle correlation index m can be used in step S22 below to construct the velocity distribution along the path.

[0041] In a preferred embodiment, step S22 includes the following steps: Taking the starting point of the diversion plane 40 as the origin of the arc length coordinate, the arc length coordinate s is defined along the flue gas flow direction. The arc length coordinate s is taken as the preset length L at the end of the diversion plane 40. The diversion plane 40 extends along the flue gas flow direction from the junction with the wall of the main tunnel as the starting point to the junction with the internal passage of the exhaust cross tunnel 30 as the ending point. Construct the velocity distribution along the path as follows ;in, For the speed distribution along the path, The longitudinal ventilation velocity is defined in the design.

[0042] First, a spatial coordinate system is established to describe the flow of flue gas along the guide plane 40. Since the development of the boundary layer is closely related to the geometry of the surface, fluid mechanics typically uses a body-fitted coordinate system, where the surface itself is used as the coordinate axis and the arc length along the surface is used as the independent variable. In this embodiment, the guide plane 40 is a straight inclined plane structure; therefore, the arc length coordinate degenerates into a straight-line distance along the inclined plane direction.

[0043] Specifically, the origin of the arc length coordinate system is defined as the starting point of the diversion plane 40 (s=0), and the arc length coordinate s is defined along the direction of flue gas flow. The starting point of the diversion plane 40 is defined as the boundary with the tunnel main wall, that is, the position where the flue gas just enters the area of ​​the diversion plane 40 from the tunnel main. The ending point of the diversion plane 40 is defined as the boundary with the internal passage of the exhaust cross passage 30, that is, the position where the flue gas is about to leave the diversion plane 40 and complete its turn to enter the cross passage. At this ending point, the arc length coordinate s is taken as the preset length L, that is, s=L.

[0044] By converting the independent variables of the boundary layer equation from absolute spatial coordinates to relative coordinates along the object surface, the variation law of parameters such as boundary layer momentum thickness and shape factor can be directly related to the geometric dimensions of the drainage plane 40, providing a clear computational domain s∈[0,L] for the integral solution of momentum integral relationship in the subsequent step S23.

[0045] The friction velocity distribution function describes the gradual decrease in flue gas velocity at the outer edge of the boundary layer from the starting point at the guide plane 40° towards the end, and is a key input condition for subsequently solving the boundary layer momentum integral equation. The form of the friction velocity distribution function is derived from Howarth's analytical study of potential flow theory for planar diffusion-type turning flows. For flows with diffusion-type turns at planar walls, the decrease in potential velocity along the wall can be approximated by a power function, where the exponent m is proportional to the radian value of the turning angle. This embodiment adopts this classical velocity distribution model, based on the following theoretical foundation: (1) Physical rationality: When s=0 (starting point), The velocity is equal to the incoming flow velocity (i.e., the design longitudinal ventilation velocity), which meets the inlet boundary conditions; when s→L (near the end), if m<1, →0, the velocity decays to zero, reflecting the physical fact that the velocity of the flue gas decreases significantly after completing the turn.

[0046] (2) Natural introduction of the adverse pressure gradient: Taking the derivative of this velocity distribution, we can obtain When m > 0, When m < 0, the velocity decreases along the travel distance. According to Bernoulli's principle, the pressure increases along the travel distance, forming a reverse pressure gradient. When s → L, if m < 1, →-∞, meaning the terminal adverse pressure gradient tends to infinity, this mathematical characteristic accurately captures the extreme adverse pressure environment faced by flue gas at the end of a turning point due to a sharp change in flow direction, which is the dangerous section where the boundary layer is most prone to separation.

[0047] (3) Quantitative correlation with rotation angle: due to The larger the drainage angle β is, the larger m is, the more severe the velocity decay and the stronger the terminal reverse pressure gradient, which provides the theoretical conditions for controlling the separation risk by adjusting the drainage angle β in step S4.

[0048] In this embodiment, by constructing a velocity distribution along the flow path, the diversion angle β and the designed longitudinal ventilation velocity are considered. Preset engineering parameters such as length L are transformed into a potential flow velocity field that can be directly used for boundary layer calculations, achieving a deterministic mapping from geometric design parameters to flow boundary conditions. Simultaneously, the friction velocity distribution function is obtained. The boundary layer momentum integral relationship can be substituted into step S23 to solve the process of momentum loss changing with flow distance.

[0049] In a preferred embodiment, step S23 includes the following steps: The speed distribution along the path As the velocity condition at the outer edge of the boundary layer, we substitute it into the momentum integral relation describing the development of momentum deficit along the boundary layer; wherein, the momentum integral relation is: Where θ is the boundary layer momentum thickness, which characterizes the momentum deficit at the boundary layer wall caused by viscous hindrance, and H is the boundary layer shape factor, defined as the ratio of the boundary layer displacement thickness to the momentum thickness. The coefficient of friction of the wall surface; Combined with the wall friction coefficient in the turbulent boundary layer The empirical correlation with the boundary layer momentum thickness θ and the velocity distribution along the path The momentum integral relationship is solved by integrating along the arc length coordinate s to obtain the edge distribution of the boundary layer momentum thickness θ as the process of momentum loss changing with the flow distance θ(s).

[0050] First, the velocity distribution along the path constructed in step S22 is... As the velocity condition at the outer edge of the boundary layer, we substitute it into the momentum integral relation describing the development of momentum deficit along the boundary layer. The momentum integral relation adopts the classic von Kármán momentum integral equation in fluid mechanics. The von Kármán momentum integral equation is derived from integrating the differential form of the momentum equation within the boundary layer along the wall normal, and is one of the fundamental governing equations in boundary layer theory.

[0051] Since the above momentum integral relationship contains three unknowns: the boundary layer momentum thickness θ, the boundary layer shape factor H, and the wall friction coefficient. However, since there is only one equation, additional empirical relations are needed to close the system of equations. For the tunnel smoke extraction condition involved in this embodiment, the Reynolds number is high when the smoke flows through the diversion plane 40°, and the boundary layer is in a fully developed turbulent state. Therefore, the wall friction coefficient is introduced into the turbulent boundary layer. Empirical correlations with boundary layer momentum thickness θ and boundary layer shape factor H.

[0052] Furthermore, using the Ludwieg-Tillmann relationship, which has been widely validated in engineering, the wall friction coefficient... The empirical correlation between the boundary layer momentum thickness θ and the boundary layer momentum thickness θ is as follows: ;in, ;in, The local Reynolds number of the boundary layer momentum thickness θ. The kinematic viscosity of the flue gas is given.

[0053] The Ludwieg-Tillmann relation is a classic empirical formula derived from extensive experimental data on turbulent boundary layers in flat and curved walls, and its applicability covers the Reynolds number range involved in this embodiment. This relation reveals the following physical law: as the boundary layer approaches separation, the boundary layer shape factor H increases. The term decreases sharply, leading to a decrease in the wall friction coefficient. Rapid decay accurately reflects the critical physical phenomenon that the boundary layer experiences a sharp decrease in wall shear force under a strong adverse pressure gradient, thereby accelerating separation.

[0054] After introducing the aforementioned empirical correlation closed equation system, the momentum integral relationship is solved by integrating along the arc length coordinate s. The velocity distribution along the path is then considered. and its derivative Wall friction coefficient Substituting the empirical expression into the momentum integral relation, we obtain a first-order ordinary differential equation with θ(s) as the unknown function.

[0055] The velocity distribution in the power function form used in this embodiment Exact analytical solutions are difficult to obtain. To obtain explicit results applicable to engineering applications, Truckenbrodt's integral approximation method for turbulent boundary layer is used. This method transforms the differential equation into an algebraic equation for approximate solution by introducing an approximate integral relationship between momentum thickness and velocity distribution. For velocity distributions with power function form... ∝(1-s / L) m The momentum thickness at the end of the flow guide plane 40 can be approximated as: Where ξ = s / L, calculate the integral term: Where ξ is a dimensionless relative position coordinate, representing the proportion of the current arc length position to the total length of the drainage plane, with a value range of 0≤ξ≤1; Combining these two formulas, we get: ; The boundary layer momentum thickness θ at any position s along the flow path can be obtained by integral or interpolation along the flow path. The boundary layer momentum thickness distribution θ(s) along the flow path reflects the cumulative process of momentum loss caused by viscous hindrance as the flue gas flows along the guide plane 40. The larger the value of θ(s), the more severe the momentum loss of the flue gas at that position.

[0056] Finally, the boundary layer momentum thickness distribution θ(s) obtained by solving is output as the process of momentum loss changing with the flow distance, and is used in step S3 to determine the attachment margin at the end of the guide plane 40.

[0057] Further, step S3 includes the following steps: Based on the change of momentum loss with flow distance, the boundary layer shape factor H at the end of the guiding plane 40 is calculated, and the boundary layer shape factor H is used as the quantized value of the adhesion margin. The boundary layer shape factor H not exceeding the critical shape factor value pre-calibrated based on turbulent boundary layer separation experiments is used as the criterion for judging the feasibility of the diversion angle.

[0058] First, based on the boundary layer momentum thickness distribution θ(s) output in step S23, the boundary layer shape factor H(L) at the end s=L of the guiding plane 40 is calculated. The boundary layer shape factor H is defined as the ratio of the boundary layer displacement thickness to the boundary layer momentum thickness, where the displacement thickness characterizes the equivalent distance by which the external potential flow is displaced outward due to the presence of the boundary layer. Its physical meaning is the thickness occupied by the mass flow loss caused by viscous hindrance within the boundary layer when converted into inviscid flow. In this embodiment, the boundary layer shape factor H(s) distribution along the path can be obtained simultaneously during the process of solving the momentum integral relationship in step S23.

[0059] Specifically, when using the Truckenbrodt integral approximation method to solve the momentum integral relationship, the boundary layer shape factor H can be correlated with the boundary layer momentum thickness θ and external flow conditions based on an empirical model of the velocity profile within the boundary layer (such as a power-law profile). For the adverse pressure gradient turbulent boundary layer involved in this embodiment, the shape factor gradually increases along the flow path, reaching a maximum value H(L) at the end of the flow plane 40 s=L. This end shape factor H(L) serves as a quantitative indicator of the adhesion margin.

[0060] The critical condition for boundary layer separation in turbulent flow is typically determined by the boundary layer shape factor. When the boundary layer shape factor H exceeds a certain critical threshold, flow separation is considered to have occurred. This criterion is validated through extensive experiments. ; ( (This is the critical value for turbulent boundary layer separation).

[0061] To allow for flexibility in the design and incorporate a safety factor, the design objective is set to meet the following at the 40° end of the drainage plane: . ( (Design value for turbulent boundary layer separation).

[0062] As a better example, the critical shape factor value is 2.4.

[0063] In a preferred embodiment, step S4 includes the following steps: Calculate the tunnel Reynolds number based on the designed longitudinal ventilation velocity, the width, and the kinematic viscosity of the flue gas; Tunnel Reynolds Number It is a dimensionless parameter characterizing the relative importance of inertial and viscous forces in the flow of smoke within the main tunnel, expressed by the formula... ; This refers to the width of the main tunnel opening.

[0064] Substituting the tunnel Reynolds number into the pre-fitted explicit angle formula, the initial drainage angle is obtained; Preferably, an explicit angle formula The expression is: Scope of application: 1×10 5 ≤Re W ≤1×10 7 .

[0065] Starting from the initial drainage angle, gradually increase the value of the drainage angle and repeat steps S2 to S3 for each value until the attachment margin approaches the safety lower limit. Take the drainage angle value at this time as the maximum value and take the maximum value as the designed drainage angle.

[0066] Starting from the initial drainage angle, gradually increase the value of the drainage angle, and repeat steps S2 to S3 for each value until the attachment margin approaches the safety lower limit. Record the drainage angle value at this time as the maximum value.

[0067] If the drainage angle is less than the safety lower limit, it indicates that there is still a margin of attachment at the current drainage angle. The drainage angle can be further increased by setting an angle increment step of 0.5°. Steps S2 to S3 are repeated until the attachment margin approaches the safety lower limit. The drainage angle at this time is taken as the maximum value, and the maximum value is taken as the designed drainage angle.

[0068] If the drainage angle is approximately equal to the lower safety limit (i.e., the difference between the two is less than the preset engineering allowable error, for example, 0.01), it indicates that the attachment margin has approached the lower safety limit. The current angle is the maximum allowable angle that meets the evaluation conditions, and the iteration stops. The drainage angle at this time is taken as the maximum value. If the drainage angle is greater than the lower safety limit, it indicates that boundary layer separation has occurred at the current angle. The angle needs to be reduced by setting an angle increment of 0.5°. Repeat steps S2 to S3 until the attachment margin approaches the lower safety limit. The drainage angle at this time is taken as the maximum value and the maximum value is taken as the designed drainage angle.

[0069] The design diversion angle obtained in this embodiment can be directly used to guide the construction layout and civil engineering excavation of the diversion plane 40.

[0070] In a preferred embodiment, the explicit angle formula is obtained through the following steps: Within the range of typical highway tunnel parameters, select multiple different tunnel Reynolds numbers. For each tunnel Reynolds number, with the diversion angle as the variable, repeat steps S2 to S3 and determine the maximum value that the diversion angle can reach under the evaluation conditions. This yields a set of discrete data points consisting of the tunnel Reynolds number and the corresponding maximum diversion angle. Using the commonly used logarithmic value of the tunnel Reynolds number as the independent variable and the maximum drainage angle as the dependent variable, linear regression fitting is performed on the discrete data points to obtain the explicit angle formula.

[0071] First, several different Reynolds numbers were selected as sample points within the typical highway tunnel parameter range. The typical highway tunnel parameter range refers to: a design longitudinal ventilation velocity between 1.5 m / s and 3.5 m / s, a main tunnel width between 8 m and 12 m, and a smoke kinematic viscosity of 1.5 × 10⁻⁶ under fire conditions. -5 m² / s. The Reynolds number range covers the actual flow conditions of most highway tunnels in my country under fire smoke extraction conditions, and has sufficient engineering representativeness.

[0072] Within the Reynolds number interval, multiple tunnel Reynolds number values ​​are selected as sample points at appropriate intervals (e.g., equal intervals in logarithmic coordinates). The number of sample points should be sufficient to ensure fitting accuracy; typically, 10 to 20 sample points are sufficient to meet engineering design requirements.

[0073] For each selected tunnel Reynolds number, steps S2 to S3 are repeated, using the drainage angle as a variable, to determine the maximum value that the drainage angle can achieve under the aforementioned evaluation conditions. Specifically, for a fixed tunnel Reynolds number, starting from a smaller initial angle (e.g., 10°), the drainage angle is gradually increased. Each time the drainage angle is changed, steps S2 to S3 are performed to calculate the corresponding end shape factor until the attachment margin first approaches the safety lower limit. The drainage angle value at this point is taken as the maximum value, and the maximum value is taken as the design drainage angle.

[0074] Therefore, for each sample tunnel Reynolds number, a corresponding maximum value is obtained, forming a set of discrete data points consisting of the tunnel Reynolds number and the corresponding maximum drainage angle. Linear regression fitting is performed on the discrete data points to establish an explicit functional relationship between the tunnel Reynolds number and the maximum drainage angle.

[0075] According to boundary layer theory, the boundary layer shape factor H is related to the dimensionless pressure gradient parameter Λ=(θ). 2 / ν)(du e The relationship is closely related to / ds). Near the separation point, an approximate relationship exists. For simplification, a widely used engineering separation correlation is adopted: the flow is in a critical state when the following equation is satisfied: ; The left-hand side represents dimensionless parameters that take into account the strong adverse pressure gradient at the end, with subscripts... This represents the value of the physical quantity or expression under the critical state of flow separation. Using equations... In s→L - The expression for time and the above equation To make the equation more specific: ; Note that here is du e / ds represents the average effective gradient associated with the terminal limit, and its dimensions have been adjusted. Substituting L=W / sinβ and m=2β / π into the equation and rearranging, we obtain the implicit equation for the optimal β angle: ; This equation requires numerical iteration for solution. For ease of engineering application, the typical tunnel parameter range is assumed to be (U0 = 1.5~3.5 m / s, W = 8~12 m, ν = 1.5 × 10⁻⁶). -5 m 2 Numerical calculations and fitting are performed using / s to obtain the explicit design formula: .

[0076] To verify the effectiveness of the smoke exhaust system (smoke exhaust cross passage 30 + diversion structure) of the present invention, two tunnel fire numerical simulation conditions were established: Condition (a): traditional smoke exhaust cross passage 30 smoke exhaust system condition (right angle connection, no diversion structure); Condition (b): smoke exhaust system of the present invention with diversion structure condition (the angle between the diversion plane 40 and the longitudinal axis of the tunnel is 55°).

[0077] The tunnel model is 1500m long, with a reinforced concrete structure. The upstream tunnel 10 is 500m long, and the downstream tunnel 20 is 1000m long. The smoke exhaust cross passage 30 is located 500m from the tunnel entrance, and the fire source is 250m from the entrance. The fire source power is set at 20MW. The tunnel employs longitudinal ventilation combined with centralized smoke exhaust through the cross passage 30 for fire smoke extraction. According to highway tunnel industry standards, for a 20MW tunnel fire, the longitudinal airflow is taken as 2.5m / s, and the smoke exhaust volume of the cross passage 30 is taken as 174m³ / s. 3 / s. A schematic diagram of the tunnel model is shown below. Figure 3 As shown, the red area represents a schematic diagram of a fire source.

[0078] Figure 4 This is a schematic diagram comparing the smoke extraction effects of a traditional horizontal smoke extraction system (right-angle connection, no drainage structure) and the smoke extraction system of this invention (300 seconds after the fire starts, i.e., the golden five minutes for fire escape).

[0079] from Figure 4As can be seen, in the case of the traditional smoke exhaust cross passage 30, a large amount of smoke failed to be effectively discharged from the smoke exhaust cross passage 30 within 300 seconds of the fire starting, and spread to the downstream tunnel 20, endangering the safety of downstream evacuation. However, in the case of the smoke exhaust system of this invention, within 300 seconds of the fire starting, most of the smoke entered the smoke exhaust cross passage 30 and was discharged from the tunnel, with only a small portion entering the downstream tunnel 20. Moreover, the distance of spread to the downstream tunnel 20 was much shorter than that of the traditional case, demonstrating a better smoke exhaust effect.

[0080] Figure 5 This is a horizontal flow field diagram at a height of 3m above the road surface for the traditional smoke exhaust system of tunnel 30 (right-angle connection, no diversion structure). It can be seen that in the traditional right-angle connection structure, when the smoke flows from the upstream of the tunnel through the tunnel entrance, a significant large-scale separation vortex forms inside the right-angle turn. This vortex is strong and wide (accounting for 30% of the tunnel width). The fluid within the vortex zone exhibits periodic swirling motion, with some smoke stagnating or even flowing out in the opposite direction, forming a distinct "cavity area," similar to a "barrier effect." This causes a large amount of smoke on the left side to be compressed and spread downstream to tunnel 20. Figure 5 and Figure 6 The horizontal axis represents the X-axis coordinate scale, and the vertical axis represents the Y-axis coordinate scale.

[0081] Figure 6 This is a diagram of the flue gas flow field at a height of 3m above the road surface in the smoke exhaust system of this invention. It can be seen that, under the influence of the guiding plane 40, the streamlines show that the flue gas smoothly changes direction while adhering to the wall surface. The separation vortex near the inlet of the exhaust transverse tunnel 30 is effectively controlled, allowing the flue gas to enter the exhaust transverse tunnel 30 earlier and more smoothly (attached flow). After entering the transverse tunnel, the flue gas quickly forms a stable pipe flow velocity distribution. This invention successfully weakens the inherent flow separation and vortex phenomena of traditional structures, achieving attached flow, which is the fundamental reason for the improved smoke exhaust effect.

[0082] To further illustrate the technical solution of this invention, the inventors also provide the following embodiments: The main tunnel of a certain tunnel has a width W = 10m, a designed longitudinal ventilation velocity U0 = 2.5m / s, and a flue gas kinematic viscosity ν = 1.5 × 10⁻⁶ m / s. -5 m 2 / s.

[0083] Calculate the tunnel Reynolds number: Re W =(2.5×10) / 1.5×10 -5 ≈1.67×10 6 .

[0084] Apply the explicit angle formula: ; ; Considering the safety margin of the model and the convenience of construction, the value is rounded to β=55°.

[0085] Design and Implementation: At the upstream corner of the smoke exhaust tunnel 30, construct a drainage plane 40 at a 55° angle to the longitudinal axis of the tunnel.

[0086] Technical effects: Comparative CFD simulations show that after optimizing the flow plane to 40°, the local resistance coefficient at the entrance of the transverse tunnel is reduced by more than 40% compared to the right angle case, the flow separation vortex basically disappears, and the flue gas capture efficiency is expected to be improved by 20%-30%.

[0087] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention’s specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for designing the diversion angle of a tunnel smoke exhaust cross passage diversion structure, the diversion structure comprising a diversion plane disposed between the upstream connection of the smoke exhaust cross passage and the main tunnel, wherein the diversion plane and the longitudinal axis of the main tunnel form a diversion angle, characterized in that, Includes the following steps: S1, obtain the design longitudinal ventilation velocity in the main tunnel, the width of the main tunnel, and the kinematic viscosity of the smoke under fire conditions; S2, Based on the designed longitudinal ventilation velocity, width and flue gas kinematic viscosity, determine the process of momentum loss of flue gas close to the wall of the guide plane due to viscous hindrance as the flow distance changes when the flue gas flows along the guide plane. S3, based on the change process, when the flue gas flows to the end of the guide plane, the adhesion margin characterizes the ability of the flue gas to resist the peeling of the wall by the reverse pressure gradient, and the adhesion margin is not lower than the safety lower limit calibrated according to the turbulence separation experimental data as the evaluation condition for the feasibility of the guide angle. S4. Based on the designed longitudinal ventilation velocity, width, and flue gas kinematic viscosity, as well as the evaluation conditions, adjust the value of the diversion angle to determine the maximum value that the diversion angle can achieve under the evaluation conditions, and use the maximum value as the designed diversion angle of the diversion plane.

2. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 1, characterized in that, Step S2 includes the following steps: S21, determine the angle-related index based on the flow angle, which reflects the rate of velocity decay of flue gas as it flows along the flow plane; wherein the angle-related index increases as the flow angle increases; S22, Based on the corner correlation index, the designed longitudinal ventilation wind speed and the preset length of the diversion plane, the velocity distribution of flue gas along the diversion plane is constructed. The velocity distribution along the plane is used to reflect the trend of flue gas velocity gradually decreasing from the starting point to the end of the diversion plane. S23, the velocity distribution along the flow path is correlated with the momentum loss caused by viscous hindrance at the wall of the flow guide plane to obtain the process of the momentum loss changing with the flow distance.

3. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 2, characterized in that, Step S21 includes the following steps: Using formula The angle correlation index is obtained. ;in, The angle of the flow is measured in radians.

4. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 3, characterized in that, Step S22 includes the following steps: Taking the starting point of the diversion plane as the origin of the arc length coordinate, the arc length coordinate s is defined along the flue gas flow direction. The arc length coordinate s is taken as the preset length L at the end of the diversion plane. The diversion plane extends along the flue gas flow direction from the junction with the wall of the main tunnel as the starting point to the junction with the internal passage of the exhaust cross tunnel as the ending point. Construct the velocity distribution along the path as follows ;in, For the speed distribution along the path, The longitudinal ventilation velocity is defined in the design.

5. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 4, characterized in that, Step S23 includes the following steps: The speed distribution along the path As the velocity condition at the outer edge of the boundary layer, we substitute it into the momentum integral relation describing the development of momentum deficit along the boundary layer; wherein, the momentum integral relation is: Where θ is the boundary layer momentum thickness, which characterizes the momentum deficit at the boundary layer wall caused by viscous hindrance, and H is the boundary layer shape factor, defined as the ratio of the boundary layer displacement thickness to the momentum thickness. The coefficient of friction of the wall surface; Combined with the wall friction coefficient in the turbulent boundary layer The empirical correlation with the boundary layer momentum thickness θ and the velocity distribution along the path The momentum integral relationship is solved by integrating along the arc length coordinate s to obtain the momentum thickness θ of the boundary layer as the process of momentum loss changing with the flow distance.

6. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 5, characterized in that, Step S3 includes the following steps: Based on the change of momentum loss with flow distance, the boundary layer shape factor H at the end of the guiding plane is calculated, and the boundary layer shape factor H is used as the quantized value of the adhesion margin. The boundary layer shape factor H not exceeding the critical shape factor value pre-calibrated based on turbulent boundary layer separation experiments is used as the criterion for judging the feasibility of the diversion angle.

7. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 5, characterized in that, Step S4 includes the following steps: Calculate the tunnel Reynolds number based on the designed longitudinal ventilation velocity, the width, and the kinematic viscosity of the flue gas. Substituting the tunnel Reynolds number into the pre-fitted explicit angle formula, the initial drainage angle is obtained; Starting from the initial drainage angle, gradually increase the value of the drainage angle and repeat steps S2 to S3 for each value until the attachment margin approaches the safety lower limit. Take the drainage angle value at this time as the maximum value and take the maximum value as the designed drainage angle.

8. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 7, characterized in that, The explicit angle formula is obtained through the following steps: Within the range of typical highway tunnel parameters, select multiple different tunnel Reynolds numbers. For each tunnel Reynolds number, with the diversion angle as the variable, repeat steps S2 to S3 and determine the maximum value that the diversion angle can reach under the evaluation conditions. This yields a set of discrete data points consisting of the tunnel Reynolds number and the corresponding maximum diversion angle. Using the commonly used logarithmic value of the tunnel Reynolds number as the independent variable and the maximum drainage angle as the dependent variable, linear regression fitting is performed on the discrete data points to obtain the explicit angle formula.

9. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 7, characterized in that, The critical shape factor is 2.

4.

10. The method for designing the diversion angle of the tunnel smoke exhaust cross passage diversion structure according to claim 5, characterized in that, Wall friction coefficient The empirical correlation between the boundary layer momentum thickness θ and the boundary layer momentum thickness θ is as follows: ;in, ;in, The local Reynolds number of the boundary layer momentum thickness θ. The kinematic viscosity of the flue gas is given.

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