A method for determining the friction resistance coefficient of physical air ducts used in tunnel ventilation experiments

Abstract

The present invention discloses a method for determining the frictional resistance coefficient of a physical air duct for tunnel ventilation experiments, comprising the following steps: measuring the radius of the air outlet and the wind speed at the air outlet in its initial state; then removing adjustment rings sequentially from the outside inward, measuring the radius and wind speed of the air outlet each time an adjustment ring is removed, until all adjustment rings are removed; then calculating the pressure loss of the main body of the tunnel model, and finally calculating the frictional resistance coefficient of the main body of the tunnel model. This method not only solves the problem of difficulty in varying the frictional resistance coefficient of tunnel models in the laboratory, but also enables direct calculation of the frictional resistance coefficient based on a formula.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel ventilation, and in particular relates to a method for determining a physical air duct friction resistance coefficient for a tunnel ventilation experiment. Background Art

[0002] When conducting tunnel ventilation experiments, the friction coefficient is a key variable and a crucial condition for small-scale model methods. This is primarily achieved by varying the construction material or ventilation resistance. Changing construction materials doesn't meet laboratory requirements, so the friction coefficient of laboratory model tunnels is primarily achieved by varying ventilation resistance.

[0003] Currently, the main method for changing ventilation resistance is through resistance grilles. In 2004, during model testing of the Qinling Zhongnanshan super-long highway tunnel, Xie Yongli, Wang Yaqiong, Fang Lei, and others used resistance grilles to establish tunnel ventilation physical models at scales of 1:8 and 1:24, respectively. For the Hong Kong-Zhuhai-Macao Undersea Tunnel, Xie Yongli, Wang Yaqiong, and others from Chang'an University used resistance grilles to establish large-scale 1:9 overall and local physical models. In 2009, based on the Dabie Mountain super-long highway tunnel, Xie Yongli, Wang Yaqiong, and others from Chang'an University used resistance grilles to establish a large-scale 1:10 ventilation physical model. The resistance grilles used in the construction of these three tunnel models were traditional grilles with no specific standards, and their shapes and specifications varied. Implementers had to order multiple sets of different resistance grilles and frequently replace them to meet varying ventilation resistance requirements. This method was time-consuming, labor-intensive, and increased costs.

[0004] In 2018, Han Jinping et al. published an adjustable underground tunnel resistance model. The principle is to achieve different friction resistance coefficients by installing several resistance grids of the same specifications. Compared with traditional grids, this method does not require multiple sets of different resistance grids; however, implementers have to increase or decrease the number of resistance grids to achieve different ventilation resistances, and the corresponding frames must be installed before installing the resistance grids. As can be seen in the specific implementation of this method, the frame is difficult to fit into the tunnel and is prone to detachment during experiments, making it inconvenient to operate and time-consuming.

[0005] Both traditional grilles and new adjustable grilles can change the friction resistance coefficient, but it is impossible to clearly calculate the friction resistance coefficient at a certain relative length, which affects the experimental process and data accuracy. Summary of the Invention

[0006] In order to solve the above technical problems, a method for determining the friction resistance coefficient of a physical air duct for tunnel ventilation experiments is provided, which is flexible and convenient to operate, can reduce the labor intensity of experimenters, and can realize experiments with different friction resistance coefficients by adjusting the size of the air outlet, thereby saving experimental costs.

[0007] The technical solution adopted by the present invention is: a method for determining the friction resistance coefficient of a physical air duct for a tunnel ventilation experiment, comprising a tunnel model body and an adjustment device, wherein the tunnel model body is a tubular structure, and the adjustment device is installed at the end of the tunnel model body; the adjustment device comprises a plurality of adjustment rings, the diameters of the plurality of adjustment rings are different from each other, the adjustment rings are arranged in sequence according to the size of the diameter, adjacent adjustment rings are coaxially connected, and the adjustment ring with a smaller diameter is located on the outside of the adjustment ring with a larger diameter.

[0008] The steps include:

[0009] 1) Measure the radius of the air outlet and the wind speed at the air outlet in the initial state;

[0010] 2) Remove the adjustment rings from the outside to the inside, and measure the radius of the air outlet and the wind speed at the air outlet after each removal until all the adjustment rings are removed; then count the radius of the air outlet from large to small as R i , i=0,1,2,3,……,n,n is the total number of adjustment rings; and the radius of the air outlet R i The anemometer is v i ;

[0011] 3) Calculate the pressure loss P of the tunnel model body f :

[0012] a) Take the air outlet radius R0 as the control group, where R0 is the original radius of the tunnel model body, and calculate the loss along the control group. The calculation formula is shown in formula (1):

[0013]

[0014] Where: P f(0) —Long-range loss when the outlet radius is R0, Pa;

[0015] λ—friction resistance coefficient, dimensionless number;

[0016] ρ—air density in the tunnel, kg / m 3 ;

[0017] D—inner diameter of the tunnel model body, D=2R0, m;

[0018] v0—wind speed when the outlet radius is R0, m / s;

[0019] L0—equivalent length of the tunnel model body when the outlet radius is R0, m;

[0020] b) Calculate the outlet radius R i , i=1, 2, 3, ..., n, the loss along the way is calculated as shown in formula (2):

[0021]

[0022] Where: P f(i) —The air outlet radius is R i Loss along the way, Pa;

[0023] L i —The air outlet radius is R i The equivalent length relative to the outlet radius R0, m;

[0024] c) Calculate the outlet radius from R0 to R i The pressure loss consumed when i=1, 2, 3, ..., n is calculated as shown in formula (3):

[0025]

[0026] Where: P f(i-0) —The air outlet radius changes from R0 to R i The pressure loss consumed when , Pa;

[0027] 4) Calculate the friction resistance coefficient λ of the tunnel model body:

[0028] a) Changes in the outlet area will cause changes in local resistance. The local loss calculation formula is shown in formula (4):

[0029]

[0030] Where: ξ is the local resistance coefficient;

[0031] b) When the outlet area suddenly decreases, the corresponding local resistance coefficient ξ is expressed as shown in formula (5):

[0032]

[0033] Where: A0—the cross-sectional area of ​​the air outlet when the main body of the tunnel model is not equipped with a regulating device, m 2 ;

[0034] A i —The air outlet radius is R i When the cross-sectional area of ​​the air outlet is m 2 ;

[0035] c) Substitute formula A0, A i Substituting the calculation formula into formula (5) yields formula (6):

[0036]

[0037] d) Substituting formula (6) into formula (4), we get formula (7)

[0038]

[0039] e) Due to P f(i-0) =P m , D=2R0, and we get formula (8):

[0040]

[0041] f) Adjust formula (8) to obtain formula (9):

[0042]

[0043] According to formula (9), the outlet wind speed and outlet radius are obtained by measurement, and L is determined according to the required equivalent length of the tunnel model body. i , the friction resistance coefficient λ of the tunnel model body at this time can be directly calculated.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] This method is easy to use. Adjustable rings of varying sizes are stacked sequentially at the end of the tunnel model to seal the tunnel exit. Once the desired length of the tunnel model is determined, the desired friction coefficient can be directly calculated. Furthermore, the correspondingly sized adjustment rings can be removed based on specific needs, and the friction coefficient can be varied by adjusting the area of ​​the air outlet. This allows for experiments with varying friction coefficient requirements, saving experimental costs. This method not only solves the problem of difficulty in varying the friction coefficient of tunnel models in the laboratory, but also allows for direct calculation of the friction coefficient based on a formula, avoiding numerical ambiguity that can affect subsequent experimental progress. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a front view of the device for determining the friction resistance coefficient of the air duct used in tunnel ventilation experiments of the present invention.

[0047] Figure 2 This is a side view of the device for determining the friction resistance coefficient of the air duct used in tunnel ventilation experiments of the present invention.

[0048] Figure 3 This is the fan characteristic curve.

[0049] Figure 4 The relationship between friction resistance coefficient and air outlet radius

[0050] In the figure: 1—adjusting ring, 2—self-tapping screw, 3—tunnel model body

[0051] R0 is the original radius of the tunnel model body; R i is the outlet radius, i = 0, 1, 2, 3, ..., n; Pf(0) is the loss along the way when the outlet radius is R0; P f(i) The radius of the air outlet is R i The loss along the way; Q (0) is the flow rate when the outlet radius is R0; Q (i) The radius of the air outlet is R i The flow rate at that time. DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the accompanying drawings and examples.

[0053] like Figures 1 and 2 As shown, the device for determining the friction resistance coefficient of the air duct used in tunnel ventilation experiments used in the present invention includes a tunnel model body 3 and an adjustment device. The tunnel model body 3 is a tubular structure, and the adjustment device is installed at the end of the tunnel model body 3. The adjustment device can adjust the size of the opening at the end of the tunnel. The adjustment device includes two adjustment rings 1 (the number of adjustment rings 1 can be more than two) and a self-tapping screw 2. The two adjustment rings 1 have different diameters. The adjustment rings are arranged in sequence according to the size of the diameter. Adjacent adjustment rings are coaxially connected by self-tapping screws 2, and the adjustment ring with the smaller diameter is located outside the adjustment ring with the larger diameter. The adjustment ring with the largest diameter is fixed to the end of the tunnel model body 3 by self-tapping screws, thereby fixing the adjustment device to the end of the tunnel model body 3.

[0054] Remove the adjustment rings from small to large, and measure the wind speed and air outlet radius each time you remove an adjustment ring until all the adjustment rings are removed. The air outlet radius from large to small is R i (i=0,1,2,3,……,n,n is the total number of adjustment rings), air outlet radius R i The wind speed at time v i Then, calculate the different outlet diameters R according to the pressure loss formula i The pressure loss under the condition of λ is calculated, and the pressure loss formula is reasonably deduced to obtain the friction resistance coefficient λ of the tunnel model body.

[0055] The specific implementation steps of the present invention are as follows:

[0056] 1) Measure the radius of the air outlet and the wind speed at the air outlet in the initial state;

[0057] 2) Remove the adjustment rings from the outside to the inside, and measure the radius of the air outlet and the wind speed at the air outlet after each removal until all the adjustment rings are removed; then count the radius of the air outlet from large to small as R i , i=0,1,2,3,……,n,n is the total number of adjustment rings; and the radius of the air outlet R i The anemometer is v i ;

[0058] 3) Calculate the pressure loss P of the tunnel model body f :

[0059] a) Take the air outlet radius R0 as the control group, where R0 is the original radius of the tunnel model body, and calculate the loss along the control group. The calculation formula is shown in formula (1):

[0060]

[0061] Where: P f(0) —Long-range loss when the outlet radius is R0, Pa;

[0062] λ—friction resistance coefficient, dimensionless number;

[0063] ρ—air density in the tunnel, kg / m 3 ;

[0064] D—inner diameter of the tunnel model body, D=2R0, m;

[0065] v0—wind speed when the outlet radius is R0, m / s;

[0066] L0—equivalent length of the tunnel model body when the outlet radius is R0, m;

[0067] b) Calculate the outlet radius R i , i=1, 2, 3, ..., n, the loss along the way is calculated as shown in formula (2):

[0068]

[0069] Where: P f(i) —The air outlet radius is R i Loss along the way, Pa;

[0070] L i —The air outlet radius is R i The equivalent length relative to the outlet radius R0, m;

[0071] c) Calculate the outlet radius from R0 to R i The pressure loss consumed when i=1, 2, 3, ..., n is calculated as shown in formula (3):

[0072]

[0073] Where: P f(i-0) —The air outlet radius changes from R0 to R i The pressure loss consumed when , Pa;

[0074] 4) Calculate the friction resistance coefficient λ of the tunnel model body:

[0075] a) Changes in the outlet area will cause changes in local resistance. The local loss calculation formula is shown in formula (4):

[0076]

[0077] Where: ξ is the local resistance coefficient;

[0078] b) When the outlet area suddenly decreases, the corresponding local resistance coefficient ξ is expressed as shown in formula (5):

[0079]

[0080] Where: A0—the cross-sectional area of ​​the air outlet when the main body of the tunnel model is not equipped with a regulating device, m 2 ;

[0081] A i —The air outlet radius is R i When the cross-sectional area of ​​the air outlet is m 2 ;

[0082] c) Replace the formula A0, A i Substituting the calculation formula into formula (5) yields formula (6):

[0083]

[0084] d) Substituting formula (6) into formula (4), we get formula (7)

[0085]

[0086] e) Due to P f(i-0) =P m , D=2R0, and we get formula (8):

[0087]

[0088] f) Adjust formula (8) to obtain formula (9):

[0089]

[0090] According to formula (9), the outlet wind speed and outlet radius are obtained by measurement, and L is determined according to the required equivalent length of the tunnel model body. i , the friction resistance coefficient λ of the tunnel model body can be directly calculated at this time. The following is a specific embodiment:

[0091] The following data is an experimental measurement of a tunnel model in a laboratory.

[0092] Close all other air outlets, leaving only the outlets required for the experiment. Turn on the fan at a frequency of 20.8 Hz, leaving all other data unchanged. Open the control loops one by one and measure the control loop radius. The tunnel model's main length, L0, is 10 m. Without the adjustment device, the tunnel model's main outlet radius, R0, is 10 m. At this point, the outlet wind speed, v0, is 6.11 m / s. Substituting these values ​​into formula (9), the results are shown in Table 1.

[0093] Table 1

[0094]

[0095] Select the relative length L required for different experiments and substitute it into Table 1 in turn to obtain the specific numerical values ​​in Table 2. The results are as follows Figure 4 shown.

[0096] Table 2

[0097]

Claims

1. A method for determining the friction coefficient of a physical air duct used in tunnel ventilation experiments, implemented using a device for determining the friction coefficient of a physical air duct used in tunnel ventilation experiments. The device comprises a tunnel model body and an adjustment device. The tunnel model body is a tubular structure, and the adjustment device is mounted at the end of the tunnel model body. The adjustment device comprises a plurality of adjustment rings having different diameters. The adjustment rings are arranged sequentially according to their diameters, with adjacent adjustment rings coaxially connected, and the smaller diameter adjustment ring is positioned outside the larger diameter adjustment ring. The steps include: 1) Measure the radius of the air outlet and the wind speed at the air outlet in the initial state; 2) Remove the adjustment rings from the outside to the inside, and measure the radius of the air outlet and the wind speed at the air outlet after each removal until all the adjustment rings are removed; then count the radius of the air outlet from large to small as R i , i=0,1,2,3,……,n,n is the total number of adjustment rings; and the radius of the air outlet R i The anemometer is v i ; 3) Calculate the pressure loss P of the tunnel model body f : a) Take the air outlet radius R0 as the control group, where R0 is the original radius of the tunnel model body, and calculate the loss along the control group. The calculation formula is shown in formula (1): Where: P f(0) —Long-range loss when the outlet radius is R0, Pa; λ—friction resistance coefficient, dimensionless number; ρ—air density in the tunnel, kg / m 3 ; D—inner diameter of the tunnel model body, D=2R0, m; v0—wind speed when the outlet radius is R0, m / s; L0—equivalent length of the tunnel model body when the outlet radius is R0, m; b) Calculate the outlet radius R i , i=1, 2, 3, ..., n, the loss along the way is calculated as shown in formula (2): Where: P f(i) —The air outlet radius is R i Loss along the way, Pa; L i —The air outlet radius is R i The equivalent length relative to the outlet radius R0, m; c) Calculate the outlet radius from R0 to R i The pressure loss consumed when i=1, 2, 3, ..., n is calculated as shown in formula (3): Where: P f(i-0) —The air outlet radius changes from R0 to R i The pressure loss consumed when , Pa; 4) Calculate the friction resistance coefficient λ of the tunnel model body: a) Changes in the outlet area will cause changes in local resistance. The local loss calculation formula is shown in formula (4): Where: ξ is the local resistance coefficient; b) When the outlet area suddenly decreases, the corresponding local resistance coefficient ξ is expressed as shown in formula (5): Where: A0—the cross-sectional area of ​​the air outlet when the main body of the tunnel model is not equipped with a regulating device, m 2 ; A i —The air outlet radius is R i When the cross-sectional area of ​​the air outlet is m 2 ; c) Replace the formula A0, A i Substituting the calculation formula into formula (5) yields formula (6): d) Substituting formula (6) into formula (4), we get formula (7) e) Due to P f(i-0) =P m , D=2R0, and we get formula (8): f) Adjust formula (8) to obtain formula (9): According to formula (9), the outlet wind speed and outlet radius are obtained by measurement, and L is determined according to the required equivalent length of the tunnel model body. i , the friction resistance coefficient λ of the tunnel model body at this time can be directly calculated.

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