1 s2.0 S2214157X18300649 Main
1 s2.0 S2214157X18300649 Main
1 s2.0 S2214157X18300649 Main
www.elsevier.com/locate/csite
PII: S2214-157X(18)30064-9
DOI: https://doi.org/10.1016/j.csite.2018.03.007
Reference: CSITE268
To appear in: Case Studies in Thermal Engineering
Received date: 9 March 2018
Revised date: 16 March 2018
Accepted date: 16 March 2018
Cite this article as: Du Cuifeng and Bian Menglong, Numerical simulation of
fluid solid coupling heat transfer in tunnel, Case Studies in Thermal Engineering,
https://doi.org/10.1016/j.csite.2018.03.007
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Numerical simulation of fluid solid coupling heat transfer in tunnel
Abstract
In order to obtain the fluid solid coupling heat transfer law of the roadway, the
coupled heat transfer between rock and air is analyzed through Fluent, Steady-State
Thermal and Static Structural module in ANSYS. The heat flux and thermal strain of
rock and the influence of air which under different wind speed and inlet temperature are
obtained. The heat flux in the rock is approximately uniformly distributed in the circular
ring shape, and the distribution of the heat flux from high to low is as follows: the
roadway wall > rock mass > air. The heat flux of the rock near the wall is greater than
that in the far side wall. The maximum is located at the wall, and the value is 160 W·m-2.
The thermal strain of rock is greatly influenced by local heat source, and the maximum
value is 5.1×10-5m·m-1. Compared with the loader, the hydrothermal water which has
greater influence on the temperature of rock and wind can be regarded as the focus on
Keywords: tunnel; fluid solid coupling; heat transfer; temperature; numerical simulation
1. Introduction
As mining moves deeper, more and more heat problems are faced.[1] Heat damage is
generated by the surrounding rock, mechanical and electrical equipment, hot water or
other heat sources. [2-3] Obtaining heat transfer is the premise of heat treatment, a
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variety of heat sources will affect each other in ventilation tunnels. [4-5] The rocks
surrounded the roadway are continuously cooled because of heat generating equipment
and hot water, and continuous humidity changes occur in the air, so the heat transfer in
Fluid-solid coupled heat transfer problem is mainly studied through CFD. There are
many cases in this area, and a variety of CFD software including Multiflux, COMSOL,
LS-DYNA are applied to the heat transfer in mines.[8-10] The heat damage in mines is
mainly caused by hot rock masses. Von et al. simulated the heat flow of rocks under
conductivity and geothermal gradients, a heat transfer simulation model was developed
to determine the amount of heat needed to heat the intake air in winter. [12] When the
mine rock mass is subjected to high thermal stress, the thermal damage caused by inter-
particle cracks and intra-particle cracks in the rock mass increases, which will affect the
stability of the rock mass. [13-14] Zhang et al. establish differential equations of heat
transfer and seepage to describe the distribution of temperature and seepage fields in
fractured rock masses. Combining the boundary conditions and parameters, a numerical
solution is obtained by numerical solution. [15] Sidney et al. study the geometric
parameters of heat exchange in a complex broken rock combination. [16] The presence
of hot gushing water in the mines causes damage to the walls of the roadway and
increases heat damage. Through the numerical simulation of water inrush from confined
formations in the strata, the change of water pressure and permeability in the formation
can be analyzed to effectively predict the potential water inrush. [17-18] Wang and You
study the influence of multi-parameters such as ventilation parameters, cracks and hot
water in rock mass on thermal conductivity of rock mass from the perspective of fluid-
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solid coupling heat transfer. [19-20] Gui studied the effect of groundwater flow on the
improve thermal convection by increasing the percolation velocity so that the heat
transfer in porous media is improved. [21] In addition, various physical field coupling
variable density flow - transport coupling are also numerically simulated in the mine.
[22-24] Simulation studies have shown that underground mine structures can be suitable
systems for heating because of their thermal stability.[25-26] Through the coupled heat
transfer simulation, the change of mine water temperature is relatively small, and the
flooded mine can be used as heat pump water source even in low temperature.[27-28]
More research cases are also related to tunnel heat transfer in cold region, human
Under the influence of mixing of rock mass, roadway, vehicle and hot water heat
source, there are few research cases on the distribution of thermal physical field of mine
roadway and rock mass. In this paper, the steady-state heat transfer model of ventilation
tunnel and the surrounding rock is considered, the mathematical model of steady-state
Static Structural modules in ANSYS are used for thermal-fluid-structure coupled heat
transfer analysis, and the temperature field distribution under different conditions was
obtained.
As the ventilation goes on, the radius of the heating circle of the roadway increases
conductivity and the surface heat transfer coefficient of the rock are only a function of
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temperature, and the variation range is small, which can be considered as the fixed value.
After experiencing ventilation for a long enough time, the thermo-physics field of the
surrounding rock heat ring and ventilation tunnel is stable under the same ventilation
parameters. The steady-state thermal conductivity model can solve the problem of fluid-
solid coupling thermal conductivity of the ventilation tunnel. Figure 1 shows the
schematic diagram of ventilation tunnel heat transfer, the dark part of the figure is the
rock heat circle, and the white part is the ventilation tunnel.
In the Figure 1, r1 is the characteristic length; r2 is the radius of the heating circle; t0
is the original rock temperature; tw is the rock wall temperature; tf is the air temperature;
qy and qh are the heat flux. Under the condition of steady heat conduction, the heat
transfer form in the heat transfer circle of the rock mass is heat conduction, and the heat
transfer form of the roadway wall to the air is thermal convection. The heat flux from
the original rock to the rock wall is equal to that produced from the rock wall to the air,
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(t0 tw )
qy (1)
r2 r1
qh h(tw tf ) (2)
Where: qy and qh are the heat flux density (W·m-2); λ is the thermal conductivity of
rock (W·m-1·K-1); t0, tw and tf are the temperature (℃); r2 and r1 is the radius (m); h is
Q hS(tw tf ) Q J (3)
Where: S is the area of heat transfer (m2); QJ is the heat production from the local
h Nu 0.023 Re0.8 Prn (4)
D D
Where: λ—the thermal conductivity of air, 0.025 W/(M·K); D—the feature length, m;
Nu—Nusselt number; Pr—Prandtl number, 0.7; n—the number is 0.4 when the air is
Under steady-state heat conduction there is a relation: qy=qh, which gives the value of
tw by solving equations (1) and (2), and tw can be substituted into equation (3):
ht (r r1 ) t0
Q hS f 2 tf Q J (5)
h(r2 r1 )
Navier-Stokes was used to establish the flow control equations in the numerical
simulation of fluid flow. The standard k-ε two-equation model was used to calculate the
flow characteristics. The fluid is a continuous medium model, and both speed and
5
density are continuous and differentiable functions of spatial coordinates and time. The
(ui ) 0
xi (6)
The momentum theorem states that the magnitude of the external force acting on an
object is equal to the rate of change of momentum of the object in the direction of force.
p u j ui
(uiu j ) ( t )( )
xi xi xi x i x j (7)
k
(ui k ) ( ) G k
xi xi k xi (8)
k C 1 2
(ui ) ( ) G C
xi
k 2
xi xi k k (9)
and:
k2
t C
(10)
u j u j ui
G k t ( )
xi xi x j (11)
Where: xi and xj are the coordinates of name; ρ is the air density (kg·m-3); P is the
turbulence effective pressure; ui and uj are the fluid velocity (m·s-1); μ is the laminar
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turbulent kinetic energy (m2·s-2); ε is the turbulent dissipation (m2·s-3); Gk is the
influence coefficient (kg·s-3·m-1); Cε1, Cε2, Cp, Cε, Ck are 1.43, 1.91, 0.09, 1.20, 1,
respectively.
chosen as the experimental subject, and the tunnel is 692 m deep. The cross-sectional
area of the tunnel is 8.34 m2, and the perimeter is 11 m; the experimental lane length is
100 m. The original rock temperature is 31 ℃; the radius of heating circle is 10-20m;
the wind speed is 1 m·s-1; the inlet air temperature is 25 ℃; and the air relative humidity
is 100%. There are a loader whose power is 92KW in the tunnel. Some hydrothermal
water whose area has a length of about 20 m and a depth of about 0.2 m exist in the
The interval between each test point is 10 m, and the point is located at the center of
the roadway. The ventilation multi-parameter detector for each measuring point is used
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Fig. 2. Geometric model
In Figure 2, the part (a) is the overall model; the part (b) is the roadway model; the
part (c) is the loader model, and the area designated by the dotted line is the heat
producing area; the part (d) is the hydrothermal model. The loader is located 20-30 m
away from the inlet and the hydrothermal water is located 40-60 m away from the inlet.
Since the tunnel heating circle is 10-20 m, the rock mass within 20 m around the tunnel
The grid generation plays a vital role in any analysis. The grid independence test is
executed to obtain the most suitable mesh faces size for particular geometry. In this
paper, the number of grids in the fluid region is tested at 635899, 1040328, 1459987,
2095887, 2568485, respectively. When the number of grids reaches 1040328, the
parameters of the fluid region are basically unchanged. Considering the accuracy and
time of the calculation, the number of grids in the fluid area is set to 1040328. In
In the experiment, Fluent, Steady-State Thermal and Static Structural modules are
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respectively coupled. After the solution of Fluent is completed, the results of the flow
field are respectively imported into Steady-State Thermal and Static Structural modules
to calculate the temperature field in the solid region and the thermal strain. The Fluent
parameter is set as table 1. The temperature of each surface of the heat generating zone
(Fig. 2. c) is set to 40 ℃. Since the hydrothermal water comes from the interior of the
rock mass and its initial temperature is close to the original rock temperature, so the
Hydraulic diameter 3m
After reaching the state of steady heat conduction through ventilation, the
temperature field of rock mass and air is basically stable, but the heat transfer in
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different areas is different due to the influence of local heat source. The heat flux is the
heat transfer per unit time and unit cross-sectional area, which reflects the strength of
the heat transfer capacity. When the inlet air temperature is 25 ℃ and the wind speed is
As can be seen from the upper left part of Figure 3, the heat flux in the rock mass is
distributed approximately in a uniform and continuous state. It can be also seen from the
upper right part of the figure that the heat flux in the rock mass is distributed in an
approximately circular ring shape and the heat flux is low at 35 W·m-2 and below. The
heat flux near the wall of the roadway is higher than other locations, with the value
above 71 W·m-2 and the highest value is 160 W·m-2. The isosurface distribution near the
loader is complicated, and the values of heat flux are basically distributed below 35
W·m-2. In summary, the heat flux density near the wall of the roadway is more than
twice that of other areas. As the value of heat flux reflects the strength of heat transfer,
the heat transfer capacity at the wall of the roadway should be weakened in order to
control the heat damage. For example, one of the methods is to install the heat
10
insulation material on the wall of the roadway.
Compared with Figure 3 and Figure 4, it can be seen that the overall heat flux values
in the ventilation tunnel are very low, and the heat flux values are mostly distributed
between 0 and 17 W·m-2. In the presence of the loaders and hydrothermal water, the
Comparing the heat flux density between the rock mass and the tunnel, it can be seen
that the heat flux density in most areas is relatively low in steady-state heat transfer
conditions, and the heat flux density distribution is descending order: wall > rock mass>
air. In addition, the heat flux of the near-wall rock mass is greater than the heat flux
density of the far-wall rock mass, and some higher heat flux values exist at the local
Since the temperature of the rock mass decreases with the continuous ventilation, the
micro-shape or size change of the rock mass is affected by the temperature stress, which
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is the thermal strain. During the long time ventilation in the roadway, the temperature
stress always exists in the rock mass. Long-term thermal stress will lead to thermal
fatigue of the rock, and even lead to rock cracks and damage. The thermal strain of rock
mass is shown in Figure 5 under the conditions of an inlet air temperature of 25 ℃ and
It can be seen from the upper left part of Figure 5 that the thermal strain of the rock
mass is at a relatively low value as a whole, and the values are between 4.46×10-5 and
4.57×10-5 m/m. From the upper right part of the figure, it can be seen that the thermal
strain values in the rock mass near the roadway are between 4.57×10-5 and 4.68×10-5
m/m. The thermal strain distribution is affected by the loader and hot water. There is a
significant change about thermal strain in the rock mass surrounding the tunnel and the
area is a continuous thin wall. The maximum value of thermal strain exists on the wall
surface of 5.1×10-5 m/m near the hydrothermal water, and the lowest value is 4.1×10-5
m/m near the loader. The hydrothermal water in the roadway has a natural heat
preservation function, which makes the nearby wall suffer from hot water and cold air at
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the same time, so that the maximum value of thermal strain is generated. The loader
blocks the wind, which reduced the wind profile and increased the wind speed. The heat
transfer is enhanced so that the wall temperature decreases, and the minimum value of
On the whole, the larger value of thermal strain is on the roadway wall, which is
similar to the heat flux density distribution. This shows that rock mass near the tunnel
wall is not only a strong heat transfer area, but also a thermal damage prone area. The
heat flux and thermal strain near the hydrothermal water are both high, which shows
that the heat transfer capacity in this area is strong and the thermal damage is easy to
occur. From the diagram of the heat flux and the thermal strain, the influence of the
loader in the roadway on the thermal environment is much less than that of the
hydrothermal water, so the hydrothermal water can be used as the focus of thermal
pollution prevention and control. When the inlet air temperature or the wind speed
change, the values of heat flux and thermal strain will change, but the distribution will
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Fig. 6. Temperature distribution of wind flow at different inlet temperatures
The loader is located 20 to 30 meters from the entrance of the roadway in the figure,
and the hydrothermal water is in the position of 40 to 60 meters. It can be seen from
Figure 6 that the temperature of the airflow remains basically constant at a distance of 0
Comparing the temperature difference of the different inlet air temperature, the higher
the air temperature, the closer to the temperature of the original rock or the heat source,
the smoother the curve of the air temperature. When the inlet air temperatures are 10 ℃,
respectively 14.3 ℃, 18.3 ℃, 22.2 ℃ and 26.2 ℃. The lower the airflow temperature,
the greater the temperature curve changes. From the wind temperature curve in the
changing the temperature of inlet air can greatly change the temperature field of the
overall airflow, and the heat damage can be effectively prevented by lowering the inlet
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air temperature.
The temperature distribution of the air in the roadway under different wind speeds is
shown in Figure 7.
to that in Figure 6 as a whole. When the wind temperature is 25 ℃ and the wind speeds
are 0.5 m/s, 1 m/s, 2 m/s, 3 m/s, 4 m/s and 5 m/s respectively, the outlet airflow
temperatures of the roadway are 26.9 ℃, 26.2 ℃, 25.8 ℃, 25.6 ℃, 25.5 ℃, 25.4 ℃
respectively, the maximum difference in the outlet air temperatures is 1.5 ℃. Compared
the curves in the figure, with the wind speed increases, the vertical difference between
the curves gradually decreases, it can be seen that the way of increasing wind speed
Comparing Figure 6 and Figure 7, the change of air temperature in the hydrothermal
section when the inlet temperature changes is much larger than that when the inlet air
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velocity changes. Therefore, by reducing the inlet air temperature can get better cooling
effect. The presence of hydrofacies in the roadway has a significant impact on the
When the air temperature is 25 ℃ and the wind speed is 1m/s, the simulation data
The temperature values at the points of the experiment (sorted from the inlet) are
27 ℃, and the simulated temperature values corresponding to the measuring points are
26.2 ℃. In addition to the starting point of the temperature difference is 1 ℃ and the
outlet temperature difference is 0.8 ℃, the other points’ difference is between 0.1 ~
0.6 ℃. The experimental data is expressed as fe, the simulated experimental data is
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fe fs
ei 100%
fs (12)
The relative errors are 3.85%, 3.79%, 0.76%, 0.77%, 0.75%, 2.38%, 1.49%, 0.38%,
1.13%, 0.75%, and 3.05%, respectively. All the relative errors are less than 4%. The
difference between the simulated and experimental values are small, so the errors are
5. Conclusion
A detailed analysis of thermal fluid solid coupling case is presented in the present
study. The heat transfer analysis of Fluent, Steady-State Thermal and Static Structural
module in ANSYS is conducted, and the interaction relationship between the loader,
According to the simulation results, there is a rule in the rock mass around a
ventilated tunnel. The heat flux is approximately uniformly distributed in a ring shape,
and its values from high to low rankings: wall> rock mass> air. The heat flux of the
rock near the wall is greater than that in the far side wall, and the value of heat flux on
The thermal strain in the rock mass is a very small change in physical size, which
reflects the possibility of thermal fatigue. From the simulation results, the thermal strain
has a high value in the tunnel wall position, but it is more affected by the local heat
source. The highest value is 5.1×10-5m/m at the wall of the tunnel near the hydrothermal
water and the lowest value is at the wall of the roadway near the loader with a value of
4.1×10-5m/m.
The influence of local heat sources which include the hydrothermal water and loader,
can not be ignored on the environment. The hydrothermal water have a significant
17
impact on the temperature field of rock mass and wind flow, and the influence on the
thermal environment is much greater than that of the loader. Therefore, the
Finally, compared with the increase of wind speed, reducing the inlet temperature has
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