article info abstract

Article history:

Received 6 December 2014

Received in revised form 11 January 2015

Accepted 28 February 2015

Available online 27 June 2015

Keywords:

Mine ventilation

Computational fluid dynamics

Continuous mining face

Airflow pattern

Methane distribution

Knowledge of the airflow patterns and methane distributions at a continuous miner face under different

ventilation conditions can minimize the risks of explosion and injury to miners by accurately forecasting

potentially hazardous face methane levels. This study focused on validating a series of computational

fluid dynamics (CFD) models using full-scale ventilation gallery data that assessed how curtain setback

distance impacted airflow patterns and methane distributions at an empty mining face (no continuous

miner present). Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m (15, 25, and 35 ft) blowing

curtain setback distances were constructed and validated with experimental data collected in a full-scale

ventilation test facility. Good agreement was obtained between the CFD simulation results and this data.

Detailed airflow and methane distribution information are provided. Elevated methane zones at the

working faces were identified with the three curtain setback distances. Visualization of the setback distance impact on the face methane distribution was performed by utilizing the post-processing capability

of the CFD software.

© 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

International Journal of Mining Science and Technology 25 (2015) 635–640

Contents lists available at ScienceDirect

International Journal of Mining Science and Technology

journal homepage: www.elsevier.com/locate/ijmst

CFD modeling of methane distribution at a continuous miner face

with various curtain setback distances

Zhou Lihong a,⇑, Pritchard Christopher b, Zheng Yi a

aOffice of Mine Safety and Health Research, National Institute for Occupational Safety and Health, Pittsburgh, PA 15236, USA b Spokane Mining Research Division, National Institute for Occupational Safety and Health, Spokane, WA 99207, USA

1. Introduction

Mining is often listed one of the world’s most dangerous occupations. Many serious accidents have occurred in various parts of

the world, often with significant loss of life. Methane emissions

and accumulations at a working face in underground coal mines

can lead to a major explosion if not managed effectively. Mine

safety and health administration (MSHA) investigators determined

that an accumulation of methane gas was the initiator of a massive

explosion at the Upper Big Branch (UBB) coal mine, West Virginia,

on April 5, 2010, claiming the lives of 29 miners. Effective

ventilation is the primary approach to provide an adequate supply

of fresh air to the working areas to dilute and remove harmful

contaminants.

The distribution of ventilation airflow, as well as methane, at

continuous miner faces can be affected by several factors, such as

the method of ventilation employed (blowing or exhausting), rib

to ventilation curtain distance, curtain setback distance, volume

of air delivered at the end of the curtain, and volume of methane

released in the face area. Among these factors, the curtain setback

distance, known as the distance from the end of the ventilation

curtain to the working face, is one of the critical factors to

⇑ Corresponding author. Tel.: +1 412 3865711.

E-mail address: itn2@cdc.gov (L. Zhou).
 

http://dx.doi.org/10.1016/j.ijmst.2015.05.018

2095-2686/© 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.


 

determine if sufficient airflow can be directed to the face to effectively sweep the face of harmful gases. Luxer [1] evaluated the air

,

movement at an empty face with curtain setback distances varying

from 1.5 m (5 ft) to 6.1 m (20 ft) by observing the movement of

smoke generated with chemical tubes. Air velocities measurements were made using vane anemometers and chemical tubes

but vane anemometers can only measure flow velocity, not direction. Airflow patterns determined based this method was not effective in identifying the turbulence zone. Taylor et al. [2] replaced

vane anemometers with ultrasonic anemometers which measure

the magnitude and direction of velocity to perform measurements

at a continuous miner face with 4.6, 7.6 and 10.7 m (15, 25, and

35 ft) setback distances to investigate the impact of the setback

distance on airflow and methane distribution. However, the

methane distributions in the both research methods were determined based on methane measurements from a limited number

of sampling locations. The methane distribution map largely

depends on the sampling locations, which cannot show continuous

change in methane distribution. With the growing popularity of

computational fluid dynamics (CFD) technology in mining

research, its powerful analyzing and visualization abilities can benefit through performing studies which are impractical to conduct

in a laboratory or field test facility. Most of CFD software can provide three-dimensional visualization via its post-processing software that creates maps of velocity vectors, streamlines, iso-value
636 L. Zhou et al. / International Journal of Mining Science and Technology 25 (2015) 635–640

contours, etc. Wala et al. [3] successfully applied CFD to interpret

airflow and methane distribution at a continuous miner face,

showing that CFD has the ability to predict, evaluate and design

effective face ventilation systems. However, curtain setback distances were not varied in their study, which focused on airflow

and methane behavior at a single 10.7 m (35 ft) setback distance

in both box cut and slab cut configurations.

CFD uses numerical methods to solve the fundamental nonlinear differential equations that describe fluid flow (the Navier–

Stokes and allied equations) for predefined geometries and boundary conditions and has seen dramatic growth in use over the last

several decades. This technology has been widely applied to various engineering applications in the mining field starting in 1990s

[4–6]. Since then, this technique has modeled fluid flow behavior

in underground mine workings, helping engineers analyze complex airflow fields and contaminant transport to design more effective ventilation systems [3,7–13].

The major objectives of this paper are to (1) develop a CFD

model of a continuous mining machine face ventilated with a

blowing curtain at various setback distances, and (2) to validate

the base model with previously collected full-scale ventilation gallery test data. This analysis will illustrate the effects of three different curtain setback distances of 4.6, 7.6 and 10.7 m (15, 25 and

35 ft) on airflow patterns and methane distributions at the working

face, which is difficult to determine from experimental testing

alone.

2. Validation study

Some advantages of CFD over experimental approaches include

low cost, speed, and the ability to simulate both realistic and ideal

conditions. However, as a numerical solution method for complex

problems, CFD cannot avoid engineering simplifications and mathematical approximations needed to effectively perform this

research. In CFD, the conceptual model is dominated by partial differential equations (PDEs) for conservation of mass, momentum,

and energy. There is no analytical solution for the PDEs of turbulent flow. The credibility of CFD as an engineering tool depends

on the quantification of the error/uncertainty of the results. The

CFD model must then be validated against a range of relevant

experimental data before being successfully applied to parametric

studies. Only after this validation can a CFD model generate reliable numerical results.

Validation is the primary means to assess accuracy and reliability in computational simulations such as CFD, and is done by comparing the accuracy of the computational results with the

experimental data; as in this case, the experimental data from tests

conducted at the national institute for occupational safety and

health (NIOSH) full scale ventilation test gallery by Taylor et al.

[2]. Over the last few years, office of mine safety and health

research (OMSHR) researchers at NIOSH have conducted a series

of experimental tests at the full-scale ventilation gallery to investigate how different operating conditions impacted airflow patterns

and methane distributions near the face of a continuous mining

machine [2,14]. These data sets remain accurate depictions of airflow and methane levels under a number of face ventilation configurations. Some of this experimental data has been used by Wala

et al. and Kollipara et al. to validate their respective CFD models

[3,9]. Wala et al. compared their CFD simulation results with

Taylor et al.’s experimental data for both airflow and methane concentrations in an empty (containing no equipment) face area ventilated with a blowing curtain [3,14]. These authors were the first

to validate CFD simulation results for methane concentration in

the face area using full-scale, mine-related benchmark experiments. Kollipara et al. validated their model using Taylor et al.’s

airflow data but did not consider variations in methane [9]. In this

paper, CFD models of an empty continuous miner face were developed at three curtain setback distances of 4.6, 7.6 and 10.7 m (15,

25 and 35 ft) and validated using experimental airflow and

methane concentration data generated by Taylor et al. [2].

2.1. Experimental test

The NIOSH ventilation test gallery is a full-scale facility located

in an ‘‘L-shaped’’ building (Fig. 1), initially designed to conduct

deep-cut face ventilation research. Airflow and methane conditions

can be varied in the gallery to simulate a wide range of ventilation

scenarios found in face areas. A vane-axial exhaust fan draws air

through regulator doors and across the gallery face. The airflow

volume flowing through the test area is adjusted by opening and

closing the regulator doors. The test area dimensions are 2.2 m

(7 ft) high and 5 m (16.5 ft) wide, which can be narrowed by moving a mobile wall inward. Tests are conducted with either blowing

or exhausting face ventilation using curtains to direct air to the

simulated face. For blowing ventilation, the curtain is placed

0.6 m (2 ft) from the left wall, directing air toward the face area,

and the setback distance can be adjusted as needed.

The continuous miner was removed from the working face during these tests. A uniform methane gas release from the face was

simulated using a manifold consisting of four 3 m (10 ft) long horizontal copper pipes drilled on the top and bottom with 2 mm

(1/16 in) diameter holes 51 mm (2 in) apart. The four pipes were

equally spaced and located 0.1 m (4 in) on the simulated face

(Fig. 2). During evaluation of ventilation systems, it is important

to precisely know the flow rate of gas entering the gallery and to

ensure it remains constant for any given test. Gas flow rates were

set and monitored using a rotameter.

Airflow velocity and methane concentration data were measured at the mid-line room level, 1.1 m (3.5 ft) from the roof. The

36 sampling locations in four columns and nine rows are shown

in Fig. 3. The first four rows of 16 sampling locations were used

to measure airflow and methane concentrations for the 4.6 m

(15 ft) curtain setback distance test, 24 sampling locations for the

7.6 m (25 ft) setback distance, and all 36 sampling locations for

the 10.7 m (35 ft) setback distance.

To maintain consistency with a series of tests performed in the

ventilation gallery, an airflow of 2.8 m3

/s (6000 ft3/min) and gas

release rate of 0.016 m3

/s (34 ft3/min) were used to validate the

CFD model in this study.

2.2. CFD model development

2.2.1. Geometry

The geometry of the continuous miner face model (Fig. 4),

including the ventilation curtain and methane gas release manifold, was developed using the ANSYS geometry model tool

Design Modeler, incorporating the same dimensions as the

Regulator doors 

Ventilation 

curtain 

Exhaust fan Face 

Fig. 1. NIOSH ventilation test gallery [2].
L. Zhou et al. / International Journal of Mining Science and Technology 25 (2015) 635–640 637

Fig. 2. Gas manifold for methane release at the ventilation test gallery face [2].

.

16'-6" 

11'-11" 

1'-6"

1'-6"

1'-6"

1'-6"

1'-0"

7'-0" 

4" 

Face 

Manifold 

ventilation gallery. The CFD gas release model was simplified by

assuming the gas was liberated from the outer surface of the tubes

instead of through multiple holes. In this experiment, three CFD

models with curtain setback distances of 4.6, 7.6 and 10.7 m (15,

25, and 35 ft) were constructed to investigate how these setback

distances might affect face airflow patterns and methane distributions. The air density 1.220 kg/m3 the same as it was measured in

the gallery test was used in the models. Three boundary conditions

were applied to the CFD models (Fig. 4):

• Velocity inlet: 2.18 m/s (430 ft/min).

• Gas inlet: 0.016 m3

/s (34 cfm).

• Pressure outlet: 0 Pa.

2.2.2. Meshing

Fig. 5 illustrates the computational mesh generated with ANSYS

Meshing 13.0 used in this study. Three separate zones with two

interfaces (Fig. 5) were used to apply hexahedral meshes to the

curtain zone and middle zone. As a comparison, a tetrahedral mesh

can be created with far fewer cells than the equivalent hexahedral

element mesh, possibly reducing computational expense. Greater

numbers of elements require more computer resources (memory/processing time). A total of 1,282,000 cells were generated in

the models.

CFD models in this paper use a second-order upwind scheme

and the SIMPLE algorithm. The Realizable k–e model was employed

to model the turbulent flow inside the face area and was solved

using the commercial CFD program ANSYS Fluent 13.0. The

Specie Transportation model was employed to simulate methane

gas transportation in the face area.

2.2.3. Comparison of CFD results and experimental tests

The airflow velocities and the methane concentrations at each

location in the mid-level plane were extracted and compared with

the gallery experimental data. A mid-level plane and corresponding

sampling locations were specified and defined in the CFD model in

the ANSYS post-processing software CFD-POST. Airflow velocities at

the sampling locations were compared point-to-point between the

experimental tests and CFD results (Fig. 6).

Fig. 6 shows the comparisons of the experimentally-measured

air velocity and the modeled air velocity at each sampling location

for the 2.8 m3

/s (6000 cfm) flow rate at the three different setback

distances. Only the first 25 sampling locations are shown in Fig. 6c

for the 10.7 m (35 ft) case due to space limitations. The simulated

air velocities and the experimental data generally show good

agreement.

Fig. 7 compares the experimentally-measured and CFDmodeled methane concentrations at each sampling location and

at each setback distance. Generally, these three figures show a reasonable match between the various data. For the 4.6 m (15 ft) setback distance case, the CFD-modeled methane concentrations are

in a good agreement with those measured at most sampling locations except for Nos.7, 8, and 10. Similarly, in Fig. 7b for the 7.6 m

(25 ft) setback distance case, the modeled methane concentrations

at sampling locations 8, 10, 12, and 16 also show poor agreement

with the measured methane data. As seen in Fig. 7c, CFD modeled

the lowest and peak methane concentrations from the fresh intake

side and return side respectively very well, but underestimated the

methane concentrations for the sampling points in the mid-face

area.

Fig. 3. Sampling locations for the 4.6 m (15 ft), 7.6 m (25 ft), and 10.7 m (35 ft) curtain setback distances [2]

16.5 ft 16.5 ft 16.5 ft 

9 10 11 12 9 10 11 12 9 10 11 12

1 2 3 4 1 2 3 4 1 2 3 4 

5 6 7 8 5 6 7 8 5 6 7 8 

15 ft 

13 14 15 16 

25 ft

13 14 15 16 13 14 15 16 

Blowing curtain 17 18 19 20 

35 ft 

17 18 19 20

21 22 23 24 21 22 23 24 

Blowing curtain 25 26 27 28

29 30 31 32 

33 34 35 36 

Blowing curtain 
638 L. Zhou et al. / International Journal of Mining Science and Technology 25 (2015) 635–640

Fig. 4. Geometry and boundary conditions of the CFD model (25 ft setback as an

example).

Interface 

Interface 

Gas inlet 

Velocity inlet 

Pressure 

outlet 

X

Y

0 100 200 300 400 (m) Z

Fig. 5. Isometric view of the computational mesh of the flow domain.

0 100 150 200 (m) 50 X

Y

Z

Fig. 6. Comparison of measured and modeled

locations for various setback distances.

air velocities at the sampling

Air velocity (m/s) 2.5 Air velocity (m/s) Air velocity (m/s)

1 3 5 7 9 11 13 15 

Measured 

Simulated 

Sampling location 

Sampling location 

1 3 5 7 9 11 13 15 19 21 23 17

(a) 4.6 m (15 ft) 

(b) 7.6 m (25 ft) 

1 3 5 7 9 11 13 15 17 19 21 23 25 

2.0 

1.5 

1.0 

0.5 

0 

2.5 

2.0 

1.5 

1.0 

0.5 

0 

1.6 

1.2 

0.8 

0.4 

0 

Sampling location 

(c) 10.7 m (35 ft) 

Fig. 7. Comparison of the measured and simulated gas concentration at all

sampling locations. Gas concentration (%)1.6 

1.4 

1.2 

1.0 

Gas concentration (%) Gas concentration (%) 

Sampling location 

Sampling location 

1 3 5 7 9 11 13 15 

1 3 5 7 9 11 13 15 17 19 21 23 

Measured 

Simulated 

(a) 4.6 m (15 ft) 

(b) 7.6 m (25 ft) 

0.8 

0.6 

0.4 

0.2 

0 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0 

1.0 

0.8 

0.6 

0.4 

0.2 

0 1 3 5 7 9 11 13 15 17 19 21 23 25 

Sampling location 

(c) 10.7 m (35 ft) 

Many factors can contribute to the differences between the

measured and CFD- modeled results at the above sampling locations. The authors agree with Wala et al. [3] that (1) numerical simulation was carried out with a steady-state assumption, whereas

the actual flow behavior in the tests may have been unsteady;

(2) velocity and methane concentration measurements were not

taken simultaneously, which may increase the error if the flow

was unsteady; and (3) the location and the way methane was

introduced into the face were different for the numerical and

experimental simulations.

Figs. 6 and 7 provide visual comparisons of modeled and measured air velocity and methane concentrations. However, a quantitative assessment of the degree to which the models match the

observations can provide more confidence in model performance.

Among the current model evaluation methods, the coefficient of

determination R2 is one of the most commonly and widely used.

The coefficient of determination R2 is the square of the Pearson’s

product-moment correlation coefficient and can be used to

describe how well simulated data match measured data [15,16].

R2 values range from 0 to 1, with higher values indicating less error

variance, and with values greater than 0.5 considered acceptable

[17,18]. Table 1 shows the coefficient of determination for each

simulation and indicates better agreement between modeled and

Table 1

Value of R2 for each case.

15 ft

Airflow Methane

25 ft

Airflow Methane

35 ft

Airflow Methane

R2 0.87 0.78 0.90 0.81 0.92 0.85
(m/s) 

2.3 

2.1 

1.8 

1.5 

1.3 

1.0 

0.8 

0.5 Y 0.3 

0 Z X

(a) 4.6 m (15 ft) (b) 7.6 m (25 ft) (c) 10.7 m (35 ft) 

Fig. 8. Airflow streamlines for different setback distances.

L. Zhou et al. / International Journal of Mining Science and Technology 25 (2015) 635–640 639

measured airflows than modeled and measured methane levels.

These values for airflow range from 0.87–0.92 and 0.78–0.85 for

methane.

3. Visualization of airflow pattern and methane distribution

The validation of each case provides confidence to apply CFD for

modeling airflow patterns and methane distributions at each setback distance. Model results are displayed via ANSYS CFD-Post.

Fig. 8 illustrates the airflow streamlines for 4.6, 7.6, and 10.7 m

(15, 25, and 35 ft) setback distances. These figures show that air

was directed from the curtain to the face and the majority of air

flowed back along the right side of the face. There are also minor

air currents separating from the primary airstream forming a central recirculation zone. Most importantly, the size of the recirculation zone appears to increase with setback distance.

Fig. 9 shows the face area methane distributions for the various

setback distances. Data collected from the ventilation gallery are

not sufficient to create the entire picture of the methane cloud.

Fortunately, ANSYS CFD-Post, an ANSYS post-processor, displays

a three dimensional methane cloud based on the discrete methane

concentration data set obtained from the simulation. Fig. 9 confirms previous work showing the highest methane level exists at

the off-curtain side face corner and accumulations of gas increase

in size with setback distance.

4. Integration of CFD modeling with experimental tests

This paper delivers a clear concept for integrating CFD modeling

with experimentation, in addition to investigating the impact of

setback distance on the airflow profile and methane distribution

at a continuous miner face. A well-designed full-scale experiment

is reliable but can be time consuming and costly. In contrast, CFD

provides powerful visualization capabilities that can evaluate the

performance of a wide range of system configurations without

the time, expense, and disruption required to make actual changes

in test facilities. However, its credibility is often questioned due to

discretization error, round-off error, and algorithm error associated

with this approach. The practical strategy applied in this study validated the CFD model against experimental test data to more accurately interpret the results and also to extend the validated results

for work that could not be done in a laboratory setting.

One of the significant advantages of CFD analyses over experimental approaches is the improved visualization and interpretation of the results. CFD can provide three-dimensional

visualization via its post-processing software that creates maps

of velocity vectors, streamlines, iso-value contours, etc. The

methane distributions are well interpreted in the CFD modeling

with a three-dimensional methane cloud clearly displayed at

the face. More specifically, the methane distributions can be displayed at any user-specified location within the simulation

domain, including lines, planes or volumes. Research could be

significantly enhanced if the CFD simulation and full scale experiments could be integrated, as has been done in this study.

Through CFD, the design and reliability of experiments can be

significantly enhanced, the scope of experimental measurements

extended and the credibility of the simulation results enhanced

by the availability of suitable measurements from experimentation. CFD provided researchers with improved visualization of

the methane distribution over the entire face and with insight

into the dynamic behavior of a physical system that would

otherwise be very difficult, time-consuming, and expensive to

achieve using experimental methods.

Methane 

concentration (%) 

1.625 

1.500 

1.375 

1.125 

1.000 

0.870 

0.750 

0.500 

0.375 Y 0.250 

Z X

(a) 15 ft (4.6 m) (b) 25 ft (7.6 m) (c) 35 ft (10.7 m) 

Fig. 9. Visualization of the face methane cloud for different setback distances.
640 L. Zhou et al. / International Journal of Mining Science and Technology 25 (2015) 635–640

5. Conclusions and discussions

ANSYS Fluent has the ability to present a comprehensive picture

of a methane cloud at a continuous miner face which is difficult to

obtain using gallery experimental data alone. The successful integration of experimentation with CFD modeling has shown potential to solve complicated test scenarios. A proven, practical

strategy is to validate the CFD model with experimental test data

and then use the CFD model for analyses that cannot be conducted

practically in the lab.

A validated CFD model can improve the fundamental understanding of airflow and methane distribution in an underground

mine working face. Three CFD models of a continuous miner face

with setback distances of 4.6, 7.6 and 10.7 m (15, 25, and 35 ft)

were constructed and validated with experimental ventilation gallery test data. Good agreement in both airflow and methane levels

were achieved for each case. This work found that a zone of recirculation existed and increased in size with curtain setback distance. This distance also impacted the extent of the methane

cloud at the face, with the size of the methane cloud increasing

with setback distance, confirming previous research done by

Taylor et al. [2].

A study limitation is the simplification of the CFD gas release

model. In gallery tests, the gas enters the face from hundreds of

small holes drilled at the top and bottom of each pipe. Due to computer resource limitations, the CFD model utilized the surfaces of

the gas pipes as the release source, in lieu of specifying each hole

individually. To maintain the same total gas release rate as the

experiments, the CFD model release velocity was modified to be

much smaller than that used in the gallery tests. This study only

takes into account the empty working face. Adding the presence

of a continuous miner would have considerable impact on face airflow and methane distribution.

Disclaimer

The findings and conclusions in this report are those of the

authors and do not necessarily represent the views of the

National Institute for Occupational Safety and Health. Mention of

any company or product does not constitute endorsement by

NIOSH.

Acknowledgments

The authors sincerely thank Chuck Taylor, retired NIOSH

OMSHR mine ventilation researcher, for his valuable assistance in

interpreting the experimental test data. The authors are grateful

to Yuan Liming for his assistance on CFD modeling.

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