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r 2007 49

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Paper number 

Mine face ventilation: a comparison 


of CFD results against benchmark 


experiments for the CFD code validation
 

Introduction the Mine Safety and Health Admin- A.M. WAlA, S. VytlA, The use of extended-cut (deep- istration (MSHA) and the coal in- C.D. tAylor AnD G. HuAnG cut) mining with remotely controlled dustry have conducted significant 

continuous miners is common in the studies to evaluate the performances A.M. Wala, member SME, is associate professor with the 

U.S. coal industry. Operators adopt of face ventilation systems through Department of Mining Engineering, university of Kentucky, 

this method to maximize the pro- lexington, Ky; S. Vytla is graduate student Ph. D, Department of the use of full-scale tests (underductivity of their continuous miner Mechanical and Materials Engineering, Wright State university, ground/surface) or scaled physical 

sections. The accompanying higher modeling. These studies have led to Dayton, oH; C.D. Taylor is industrial hygienist with nIoSH 

advance rates introduce the prob- Pittsburgh research laboratory, Pittsburgh, PA; G. Huang recommendations that tend to make 

lem of directing a sufficient quantity is professor and chair, with the Department of Mechanical these systems more effective. Howof air to the face when setback dis- ever, because of the aerodynamic Engineering, Wright State university, Dayton, oH. 

tances are 6 m (20 ft) and greater. complexity in the face area arising 

This can require an increase in the from the variety of ventilation arquantity of air directed behind the rangements amid limitations of the 

blowing curtain. Higher air veloci- experimental methods, doubts still 

ties are a consequence that, in turn, exist when evaluating the effectiveleads to the entrainment of more dust generated during ness of such a system. 

the coal-extraction procedure. Frequently, the increased The design of a balanced ventilation system for the 

dust entrainment is countered by the use of large-capac- scenarios described above requires consideration of the 

ity scrubbers that recirculate and filter air in the imme- system in a three-dimensional, rather than a two-dimendiate face area. These circumstances give rise to many sional, manner.Traditional theoretical and experimental 

concerns regarding the health and safety of miners. methods are available for obtaining useful results, but 

The former U.S. Bureau of Mines (currently NIOSH), the former is limited to simple geometries and experimental methods are often slow and both approaches 

are limited in the completeness, accuracy and general- Abstract ity of the results that they provide. Computational fluid Computational fluid dynamics (CFD) is a continually de- dynamics (CFD) is a promising design methodology veloping numerical technique by which complex fluid-flow by which many complicated fluid flow problems can be problems can be solved on computers.To be able to transfer solved with numerical codes. CFD embraces a variety CFD expertise to analyze and design a face-ventilation sys- of technologies, including mathematics, computer sci­ tem,a comprehensive validation study of current CFD tools ence, engineering and physics, and has the potential to against mining-related benchmark experiments is required. generate face-ventilation designs without the previously In the last four years, such studies, funded by National In- mentioned disadvantages. stitute for Occupational Safety and Health (NIOSH) under During the last four years, a validation study, funded Grant #R01 CCR415822,were conducted in the Department by NIOSH under Grant #R01 CCR415822, was carried of Mining Engineering at the University of Kentucky.A wide out in the Department of Mining Engineering at the array of ventilation schemes and mining configurations were University of Kentucky. The goal of this study was to considered. Recently, an additional study was performed in prove a CFD code’s ability to predict, evaluate and de- cooperation with the NIOSH Pittsburgh Research Labora- sign effective face-ventilation systems. To achieve this tory. This study was dedicated to the methane behavior in goal, the authors did the following: the empty (containing no equipment) face area with a blowing curtain and a 10.7-m (35-ft) setback. In this paper, the • designed and built a scaled physical model of selected authors present and discuss the computer-simulation data face-ventilation systems (Wala et al., 2003), and compare them with data collected during the laboratory • performed a series of measurements using particle studies at the NIOSH lab. image velocimetry (PIV) (Turner et al.,2002) to deter­
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1	 above, there was a need for studies 

concerning the methane behavior Ventilation test gallery. (methane distribution) in the face 

area in conjunction with ventilation. 

Recently, an effort was made to 

perform a comprehensive validation 

study of the CFD codes for simulation of the flow and methane behavior at the face area. These studies 

were the combined effort of the Department of Mining Engineering at 

the University of Kentucky and the 

NIOSH Pittsburgh Research Center. 

The experimental part of the study, 

which was coordinated by the mining 

engineering faculty, was carried out 

by researchers at the NIOSH Pittsburgh Research Laboratory using a 

full-scale ventilation gallery. The procedures for the laboratory tests were 

designed at the University of Kentucky and were discussed with the remine the flow patterns in the scaled physical model, 

•	 developed three-dimensional numerical models of the 

physical model and performed computer simulation 

studies using CFD codes (Wala et al.,2000,2001,2003, 

2004) and 

•	 compared experimental and numerical data for the 

purpose of CFD code validation (Wala et al., 2003, 

2004, 2005). 

In all experimental and numerical studies performed 

so far, the whole attention was concentrated on understanding the airflow distribution (airflow patterns) at 

the face area. The methane gas, as the second species, 

was never introduced during the experimental study 

using scaled physical models because of the safety issue. 

Therefore, after completion of the project described 

Figure 2 

Sampling locations. 

search staff at the NIOSH laboratory 

to provide data for validation of the 

CFD simulation results. 

Experimental studies at the NIOSH laboratory 

Although the results of the experimental studies 

have been previously reported (Taylor et al., 2005), to 

make this paper easier to understand, the authors have 

included the following information from the earlier paper: 

Test facility. Tests were conducted in the NIOSH 

Pittsburgh Research Laboratory’s Ventilation Test Gallery, which is shown in Fig. 1. One side of the gallery was 

designed to simulate a mining entry with a 2.2-m- (7-ft-) 

high roof and with ribs 5 m (16.5 ft) apart. To be able to 

study the flow and methane distribution in the empty 

face area (no equipment) during two parts of the continuous mining cut sequence, i.e., box cut and slab cut, 

the 5-m (16.5-ft) total entry width was reduced to 4 m 

(13 ft) by building a wall 1 m (3.5 ft) from the right rib. 

The exhaust fan draws approximately 5.9 m3

/s 

(12,500 cfm) of air through the gallery. A part of this 

air was directed toward the entry face using a curtain 

that was constructed 0.6 m (2 ft) from the left side of 

the entry.The curtain was positioned so that the setback 

distances between the curtain and the face were 10.7 m 

(35 ft). Regulator doors were adjusted to provide intake 

flows behind the curtain of either 2.8 or 4.7 m3/s (6,000 

or 10,000 cfm). 

Airflow and methane measurements. Airflow and 

methane concentration measurements were made at the 

same sampling locations.There were a total of 36 sample 

locations, arranged in four columns and nine rows, between the curtain and the face. The sampling locations 

for the 10.7-m (35-ft) setback distance and two entry 

widths are shown in Fig. 2. 

The three-dimensional airflow measurements were 

made between the end of the curtain and the face at the 

mid-height of the entry, using “Windmaster” three-axis 

ultrasonic anemometers manufactured by Gill Instru­
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ments Ltd., Great Britain. However, Figure 3 

two-dimensional components of ve- Flow patterns: box-cut scenario (left) and slab-cut scenario (right), for 10.7-m locity in the plane of measurement (35-ft) setback with 2.8 m3

/s (6,000 cfm) airflow. are provided for comparison. The 

methane gas was released into the test 

area through four 3-m- (10-ft-) long 

horizontal copper pipes that were 

located at the mining face. The pipes 

were located 100 mm (4 in.) away 

from the face, and they were equally 

spaced horizontally to provide a relatively uniform release of gas. On the 

top and bottom of each of the 3-m- 

(10-ft-) long pipes, 2-mm- (1/16-in.-) 

diameter holes were drilled 65 mm 

(2.5 in.) apart. For the slab-cutting 

scenario, the methane flow rate was 

0.016 m3/s (34.0 cfm). However, for 

the box cut mining scenario, due to 

the flow separation phenomena that 

resulted in higher concentrations at 

the face, the methane flow into the 

gallery was reduced to 0.0032 m3

/s (6.8 

cfm) to prevent methane concentration levels in the gallery from exceeding 2 percent. 

To make methane measurements, 

four air-sampling tubes were suspended from the overhead support system. The hose inlets 

were positioned so the methane concentration measurements were made at the three entry heights; top level 

being 1.1 m (4 ft) from roof, the mid-level and bottom 

level being 1.1 m (4 ft) from the floor. 

Results — airflow patterns and methane distribution. 

The measured airflow patterns in the face area (area 

between the end of the blowing curtain and the face) of 

the ventilation gallery are shown in Fig. 3 for both boxcut and slab-cut scenarios and a curtain flow of 2.8 m3

/s 

(6,000 cfm). 

The contours in Fig. 4 show the distribution of the 

methane concentration at the face area when the amount 

of air delivered for ventilation behind the curtain was 2.8 

m3/s (6,000 cfm). 

Computer simulation study for the CFD code

validation 

There are three major steps in any CFD solution process: 

•	 preprocessing (mesh generation), 

Table	1 

Data	used	to	calculate	the	boundary	condition. 

•	 processing (CFD simulation and refinement/adaptation of grid) and 

•	 post-processing (visualization and analysis of results). 

FLUENT 6.X, a commercially available CFD solver, 

together with the GAMBIT mesh generator (preprocessor), which comes as a package along with FLUENT, 

was used to simulate the methane and flow behaviors 

for the same scenarios used during the laboratory tests. 

The results of these simulations are visualized using the 

post-processing capabilities of FLUENT and are graphically shown using the Excel plots capability. The results 

of these simulations were tested (compared) against the 

experimental data for CFD code validation. For validation purposes, the CFD simulation data were extracted 

at the same locations as the experimental data were collected. 

Preprocessing. The model’s geometry, shown in Fig. 

5, includes: 

•	 the flow path between the rib and brattice from the velocity inlet (air) to the discharge 

location at the end of the blowing 

curtain, 

• flow through the	 interface 

	 	 	 	 	 	 										Methane	flow	 

	 	 	 Airflow,		 	 Measured	 Corrected 

SI	No.	 Scenario	 m3

/s	 (cfm)	 	 m3/s	 (cfm)	 m3/s	 (cfm) 

1	 Box	cut	 	 2.8	 (6,000)	 	 0.0032	(6.8)		 0.0025			(5.27) 

2	 Box	cut	 	 4.7	 (10,000)		 0.0032	(6.8)	 0.0025		(5.27) 

3	 Slab	cut		 2.8	 (6,000)	 	 0.016		(34.0)	 0.016				(34.0) 

4	 Slab	cut		 4.7	 (10,000)		 0.016		(34.0)	 0.016				(34.0) 

zone, 

• flow in the face area, 

• flow return toward the outlet 

and 

• velocity inlet (methane). 

Two ventilation arrangements 

for box cut and slab cut scenarios, with a 10.7-m (35-ft) setback, 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4 due to the temperature fluctuations. 

Methane concentration: box-cut scenario (left) and slab-cut scenario (right), The computational mesh of the 

for 10.7-m (35-ft) setback with 2.8 m3/s (6,000 cfm) airflow.	 test box cut configuration is shown in 

Fig. 6.The mesh with around 1,190,000 

cells was accepted based on previously 

performed studies concerning the grid 

independence results. 

Processing. A three-dimensional, 

steady state incompressible solution 

for Navier-Stokes equations with species transport without chemical reactions was performed using FLUENT. 

FLUENT solves the Reynolds averaged form of Navier-Stokes equations 

considering the conservation of mass, 

momentum, energy and species transport.The analysis was performed using 

different turbulence models to identify 

the model that can best predict both 

the flow and the methane distribution. In this study, only the analysis rewere considered. The configuration of the model for the 

box-cut scenario is shown in Fig. 5. 

The computational mesh (grid) was generated using 

the GAMBIT 2.1 mesh generator. In the CFD model, 

the methane boundary condition represents 192 nozzles 

that bring the methane into the face area. These nozzles 

are evenly distributed on the face surface. The most important zone in this study is the area between the end of 

blowing curtain and the face. To have enough grid resolution in the area of importance, the entire flow region 

was divided into two zones. First, the zone of the face 

area and second, the interface zone.The mesh generation 

for each zone was performed independently. These two 

zones are connected by an interface boundary condition. 

The velocity inlet boundary condition was applied 

at the air and methane inlet sites. The outlet boundary 

condition was applied at the outflow site. All the other 

surfaces are treated as adiabatic walls with a no-slip 

boundary condition. Table 1 shows the experimental 

values used to calculate the boundary conditions. Correction was applied to the methane density calculations 

Figure 5 

Boundary conditions (box-cut scenario). 

sults using two turbulence models, i.e., 

shear-stress transport and Spalart-Allmaras (SA) models, are discussed. Pressure velocity coupling of momentum and continuity equations is obtained 

using the SIMPLE algorithm.The outflow boundary condition is applied at the outlet. Buoyancy is introduced 

into the model by switching on gravity.To adjust for this, 

the default value for the turbulence Schmidt number 

is adjusted to be 0.5 instead of 0.7. Further details are 

discussed in the results section.As mentioned above, the 

test was carried out in the beginning of the analysis to 

identify the mesh size that gives grid independence and 

the same mesh is used for further analysis. 

Comparison of the experimental and simulation

data 

The study involves the analysis of both 2.8 and 4.7 m3/s 

(6,000 and 10,000 cfm) airflow rates. In this section, the 

simulation results are compared with the experimental 

results. Only the results for the 2.8 m3/s (6,000 cfm) airflow rates are shown and discussed in this section. Figure 

7 shows the flow pattern for both box and slab cut test 

scenarios. It can be observed that the flow pattern is highly 

complicated in the box cut case and is highly three dimensional in nature, whereas in the case of 

the slab cut case it is less complex.The 

experimental data provided for velocity vectors are two dimensional in nature, so the authors decided to extract 

the corresponding two components of 

velocity from the simulation results 

for point-to-point comparison. Similarly, the methane concentration at the 

sample locations is extracted from the 

simulated results for comparison. 

Figure 8 shows the comparison of 

the flow pattern and methane concentration for the box-cut scenario. It can 

be seen that the flow separation location predicted by the SA turbulence 

model is in good agreement with the 

experimental results. However, the 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

magnitude of the velocities is not exactly the same because of the threedimensional nature of the flow. The 

methane concentrations predicted by 

both the turbulence models are also 

in good agreement with experimental results. In this plot, the maximum 

methane concentration is observed to 

be at the left top corner region, which 

is close to the face.This is the result of 

the flow pattern observed in the recirculation region. Figures 9a, 9b and 9c 

show comparisons of the methane concentration at each sample locations at 

three different heights. It is observed 

that even though the qualitative comparison is in good agreement with the 

experimental data, the quantitative 

comparison shows that the simulation 

results predict a high concentration 

at certain locations especially in the 

area near the separation region. The 

reasons for this might be one of the 

following: 

•	 numerical simulation is carried out 

with a steady-state assumption, 

whereas the actual flow behavior 

in this scenario might be unsteady; 

•	 velocity and the methane concentration measurements were not 

taken simultaneously, which might 

intensify the error if the flow were 

unsteady; and 

•	 the location and the way that methane was introduced into the systems 

were different for the numerical and 

experimental simulations. 

Figure 6 

Computational mesh: (a) top view and (b) side view of the mesh in the boxed 

area. 

Figure 7 

Path lines colored by particle numbers: box-cut scenario (left) and slab-cut 

scenario (right), for 10.7-m (35 -t) setback and 2.8 m3/s (6,000 cfm) airflow. 

Figure 8 

Box-cut scenario results comparison. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9a 

Methane concentration comparison at plane 1 m (3.5 ft) 

from the ground, for 2.8 m3/s (6,000 cfm) airflow. 

Figure 9B 

Methane concentration comparison at plane 0.6 m (2 ft) 

from the ground, for 2.8 m3/s (6,000 cfm) airflow. 

Figure 9c 

Methane concentration comparison at plane 1.5 m (5 ft) 

from the ground, for 2.8 m3/s (6,000 cfm) airflow. 

For the laboratory experiments, methane was introduced through pipes that are 100 mm (4 in.) away from 

the wall and the holes on the top and bottom of the pipes, 

making the methane entry direction normal to the main 

flow direction. However, in the computer simulation, the 

methane was introduced normal to the face.The authors 

noted similar results when comparing data from the 2.8- 

and 4.7-m3/s (6,000- and 10,000-cfm) tests (not shown in 

this paper). 

Figure 10 shows the comparison of the flow pattern 

and methane concentration for the slab-cut scenario. 

It can be seen that the flow patterns predicted by the 

SA turbulence model are in good agreement with the 

experimental results with one exception. The exception is that the turbulence model predicted the point 

of highest methane concentration to be at the left top 

corner of the face area, whereas in the experiments 

it was observed at the right top corner. Results from 

the simulations using the SST turbulence model show 

that, in the region along the right hand-side wall, there 

is higher cross-flow in the z-direction than that of the 

SA of model. This three-dimensional effect may lead 

to a different concentration profile in the mid-plane 

of face area. Figures 11a and 11b show comparisons of 

methane concentration at each sample location for the 

slab cut scenario and 2.8- and 4.7-m3/s (6,000 or 10,000 

cfm) airflow at the end of the blowing curtain. It can be 

seen that both qualitative and quantitative simulation 

results are in good agreement with the experimental 

data, except at the first location. 

Conclusions 

•	 As far as the authors know,this was the first validation 

test of the CFD simulation results for both flow and 

methane concentration in the face area against the 

full-scale, mine-related benchmark experiments. 

•	 Because this was the first test at this scale,the arrangement at the face area was simplified by removing the 

equipment at the face to minimize the sources for flow 

interruption. 

•	 During this study, it was shown that two turbulence 

models,namely,the Shear-StressTransport model and 

the Spalart-Allmaras model,could be used to simulate 

the three-dimensional methane concentration along 

with the airflow distributions. 

•	 In the box-cut scenario of the face ventilation system, 

the simulation results using the SST model show that 

the flow and the methane concentration are in good 

agreement with the experimental results. 

•	 In the slab-cut scenario of the face ventilation system, 

the simulation results using the SA model show that 

the flow and the methane concentration are in good 

agreement with the experimental results. 

•	 Based on these studies,it can be seen that there is a lot 

of potential for the FLUENT CFD software package 

for developing mine face-ventilation system designs 

•	 It was observed in the experiments that the methane 

concentrations were oscillating at some frequency.This 

could be caused by the unsteady flow of methane,which 

was delivered by the commercial natural gas pipeline, 

or by air quantity, which was delivered by the gallery 

fan. To verify the source of these unstable behaviors, 

the authors suggest repeating one of the laboratory 

tests. During this test, all the measured (monitored) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

parameters, Figure 10 

i.e., airflow, Comparison of results from simulations using different turbulence model (slab-cut scenario). a m o u n t o f 

methane, air 

velocities and 

methane concentrations,at 

each location 

of the face 

area must be 

measured and 

recorded simultaneously 

•	 To f i n a l l y 

prove that the 

CFD code is 

the proper 

tool for the 

face-ventilation system 

analysis and 

the designs, 

similar studi e s w i t h 

e q u i p m e n t 


must be performed. n
 

References 

Taylor, C.D., Timko, R.J., Thimons, E.D., and Mal, T., 2005, “Using 

ultrasonic anemometers to evaluate factors affecting face ventilation 

effectiveness,” Paper number 05-080, presented at the 2005 SME Annual Meeting, Salt Lake City, UT. 

Wala, M.A., Jacob, J., and Turner, D., 2002,“Experimental study of 

mine face ventilation system for validation of numerical models,” Proceedings of the North American/9th U.S. Mine Ventilation Symposium, 

Kingston, Ontario, Canada, June. 

Wala, M.A., Jacob, J., Huang, P.G., and Brown, J.T., 2002, “A new 

approach to evaluate mine face ventilation,” Paper number 02-177, 

presented at the 2002 SME Annual Meeting, Phoenix, AZ. 

Wala, M.A., Jacob, J., Huang, P.G., and Brown, J.T., 2003, “A new 

approach to evaluate mine face ventilation,” Mining Engineering, Vol. 

Figure 11a 

Methane concentration comparison at plane 1 m (3.5 ft) 

from the ground, for 2.8 m3

/s (6,000 cfm) airflow.combination (Decanter, 2002; Falcon, 2002). 

55, No. 3, March. 

Wala, M.A., Jacob, J., Huang, P.G., and Rangubhotla, L., 2004, 

“How scrubbers help ventilate the face during deep cut mining with a 

blowing curtain,” Proceedings of the 10th U.S. Mine Ventilation Symposium, Anchorage, AK, May. 

Wala, M.A., Stoltz, J.R., and Hassan, M.I., 2000, “Scaled modeling 

of a mine face ventilation system for CFD code validation,” Proceedings of the Third International Symposium on Scale Modeling, Nagoya, 

Japan, September. 

Wala, M.A., Stoltz, J.R., and Jacob, J., 2001,“Numerical and experimental study of a mine face ventilation system for CFD code validation,” Proceedings of the 7th International Mine Ventilation Congress, 

Krakow, Poland, June. 

Figure 11B 

Methane concentration comparison at plane 1 m (3.5 ft) 

from the ground, for 4.7 m3

/s (10,000 cfm) airflow.