MEASUREMENT OF AIRFLOW IN A SIMULATED UNDERGROUND MINE ENVIRONMENT USING AN 

ULTRASONIC ANEMOMETER 

C. D. Taylor, R. J. Timko, M. J. Senk, and A. Lusin 

National Institute for Occupational Safety and Health 

Pittsburgh, PA, USA 
ABSTRACT

 Federal regulations require that methane liberated at the 

face be diluted and removed to maintain methane gas 

concentrations below 1 pct (CFR) in working places and 

intake air courses. The delivery and distribution of intake 

air at the face is critical for effective face ventilation. 

Improved techniques for monitoring the movement of 

intake air to the face are needed. 

 A test system was developed and a computer program 

written for using a three-axis ultrasonic anemometer to 

measure airflow in a simulated mine entry. Results of 

tests conducted in the entry showed that the anemometer 

is a valuable tool for measuring mine airflow conditions 

near the face. 

BACKGROUND 

 The highest methane concentrations in coalmines are 

usually found near faces of entries where coal is being 

mined. To maintain methane concentration below 1 pct 

an adequate quantity of intake air must be supplied to the 

face. A rotating vane anemometer is routinely used to 

measure air speed at the end of the curtain or tubing. A 

pitot tube with a manometer can be used to measure 

velocity pressure, which can then be applied to a 

mathematical formula and converted to air speed. The 

quantity of intake air reaching the entry is calculated by 

multiplying the average air speed by the cross-sectional 

area of the tubing or curtain. Past studies have shown that 

these flow quantities may not be good estimates of how 

much air actually reaches the face (Thimons et al., 1999). 

 Better estimates of face airflow could be made if the 

velocities were measured closer to the face. However, it 

is difficult to get accurate readings of air velocities inby 

the tubing or brattice because the direction and magnitude 

of the flow are constantly changing in this area. 

Instruments such as the vane anemometer measure 

average speed in only one direction. Unless the 

anemometer is properly aligned with the direction of the 

airflow, the resultant air speed values will not be accurate. 

 Uultrasonic anemometers have been designed for 

measuring airflow velocities in three-dimensional space. 

With a three-axis anemometer, orientation of the 

instrument with flow direction is not necessary to measure 

speed. The anemometer can also record rapid changes in 

velocity. The instrument used for this research had a 

sampling rate of 40 Hz, and sample data was reported at 1 

Hz. 

 The ultrasonic anemometer has been used to map large 

scale flow patterns in enclosed rooms and has provided 

quantitative information concerning the amount of air 

movement and variations in flow (Yost et al., 1992). 

The objective of this work is to determine if a three-axis 

ultrasonic anemometer could be used to evaluate airflow 

movement in a test facility where underground mining 

conditions were simulated. The paper describes the 

development and use of a protocol for collecting and 

analyzing data obtained with the anemometer. 

TEST CONDITIONS 

Surface Test Facility

 Tests were conducted in the NIOSH Pittsburgh 

Research Laboratory’s Ventilation Test Gallery 

(Figure 1). One side of the gallery was designed to 

simulate a mining entry with a 2.2 m (7-ft) high roof and 

ribs 5 m (16-1⁄2 ft) apart. For half of the tests the entry 

width was reduced to 4 m (13 ft) by building a wall 1 m 

(3 1⁄2 ft) from the right rib. 

Figure 1. Ventilation Test Gallery 

 An exhaust fan draws approximately 5.9 m3

/s (12,500 

cfm) of air from the gallery. To simulate air flow in an 

underground mine, air was directed toward the entry face 

using a 2.2 m (7 ft) high brattice curtain that was 

supported by a wood frame constructed 0.6 m (2 ft) from 

the left side of the entry. The end of the blowing curtain 

was 10.7 m (35 ft) back from the face for all tests. 

Airflow between the curtain and the rib (2.8 or 4.7 m3

/s, 

6,000 or 10,000 cfm) was adjusted by opening or shutting 

regulator doors. The average air speed at the end of the 

blowing curtain was measured with a vane anemometer 

by performing a moving vertical traverse of the crosssectional area. 

EQUIPMENT 

Three-Axis Anemometer

 Air speed and direction measurements were made using 

a three-axis ultrasonic anemometer manufactured by the 
Gill Instruments, Ltd, Great Britain (References to 

specific products does not imply endorsement by NIOSH) 

(Figure 2). 

Figure 2. Three-axis ultrasonic anemometer 

 The operation of this device is based on the principle 

that the speed of a sound pressure wave varies with the 

local air speed. The anemometer has a linear response 

and an absolute calibration that depends only on sensor 

spacing and transit time accuracy. 

 The anemometer uses sound pulses to determine the airvelocity vector, which is resolved into the three 

directional components (U, V and W). These orthogonal 

components correspond to flow toward and away from the 

face (U direction), right and left across the entry (V 

direction) and up and down (W direction). 

 An overhead two-dimensional traversing system was 

used to support the anemometer as it was moved to each 

sampling locations (Figure 3). The overhead system 

included a 0.6-m (2- ft) wide garage door panel that was 

attached to two roof-mounted rails. A 3.7-m (12-ft) long 

Figure 3. Support system for moving anemometer 

panel was used in the 4-m (13-ft entry) and a 4.6-m (15-

ft) long panel in the 5-m (16 1⁄2 ft) entry. A 4-wheel 

trolley moved along a rail that was attached to the front 

edge of each panel. A round aluminum rod, 25-mm (1 

inch) in diameter by 0.4-m (14-in) long, was connected to 

the bottom of the trolley. A specially designed bracket 

was used to attach the anemometer to the aluminum rod. 

The anemometer could be rotated or moved vertically in 

the bracket. The anemometer was inverted with the 

sensor head positioned 1.1 m (3.5 ft) from the floor and 

roof. All measurements were made at this elevation. 

 An arrow that was printed on one end of the sensor head 

was used to indicate the reference direction. The 

anemometer was rotated in the bracket until the arrow 

was pointed toward the face. All direction readings were 

made with respect to the arrow orientation (Figure 4). For 

example, with the arrow directed toward the face, flow 

toward the face was reported as 180 degrees and flow 

away from the face was reported as 360 degrees. The 

angle in degrees that describes the direction of flow 

increases in a clockwise direction as viewed from above 

the instrument. 

Figure 4. Reference angle directions in degrees 

 Four vertical lines, corresponding to the sampling 

distances from the left side of the entry (see Figure 5) 

were placed on the face. With the printed arrow directed 

toward the face, a beam from a laser, mounted on the 

anemometer bracket, was aligned with each of the lines. 

The alignment of the beam was checked during testing to 

assure that the anemometer had not rotated in the bracket. 

SAMPLING PROCEDURE 

 A 4 x 9 grid of sampling locations was used. Flow 

measurements were made for two entry widths, 4 and 5 m 

(13 and 16 1⁄2-ft), and two intake flows, 2.8 and 4.7 m3

/s 

(6,000 and 10,000 cfm). A repeat test was performed for 

each operating condition and results averaged for each 

location sampled (Figure 5). 

 The overhead traversing system was used to manually 

move the anemometer from one location to the next. The 
instrument was positioned at each location by aligning it 

with the distances marked on the door panel rails and on 

the front of the door panel. After positioning the 

instrument, all personnel left the gallery to avoid 

disturbing the airflow patterns during testing. Data was 

collected and recorded for three minutes. 

Figure 5. Measurement locations in gallery 

The three-minute sampling period (180 samples) was 

chosen to provide average flow magnitude and direction 

readings that would include the expected range of values. 

After data collection was completed in each row, the 

anemometer was moved either toward or away from the 

face to the next row where measurements had not been 

made. 

DATA ACQUISITION 

 The anemometer was attached to a Power 

Communication Interface (PCI) box that provided power 

and collected signals from the anemometer. The 

anemometer was configured using software 

(ANEMCOM, Version 3.04) provided by the 

manufacturer. The configuration settings used during 

these tests are given in Table 1. 

 A software program written and developed by NIOSH 

personnel, ANEMVENT 2002, facilitated the acquisition 

and analysis of data obtained with the ultrasonic 

anemometer. More information about the program is 

available in the software instruction manual. 

 The ANEMVENT 2002 program creates an EXCEL 

data spreadsheet for storing U, V, and W velocity 

components generated by the anemometer. When 

configured in the UVW Polled mode (see Table 1) one set 

of U, V, and W velocity components is recorded each 

second when the PCI is queried by the software program. 

The average value for each U, V, and W component is 

calculated for every three-minute sampling period. The 

flow angle and magnitude for the flow direction in the 

horizontal plane are calculated using the average U and V 

values. The direction and speed data are transferred to a 

second EXCEL spreadsheet that uses algorithms and 

EXCEL functions to create a chart containing vector lines 

that illustrate flow at each location sampled. 

Table 1. - Configuration and Tabular Options using Windmaster Anemometer 

Output mode ASCII, UVW, polled 

Output units m/s 

Measurement average Off 

Sample period 1 Hz (1 sample per second) 

Baud rate 36,400 

Parity 8 Data, No parity 

 

 
RESULTS, DISCUSSION AND FUTURE 

RESEARCH 

Qualitative Flow, Profiles

 The flow profiles in Figures 6 and 7 are drawings 

adapted from vector lines created with the EXCEL charts. 

For each location, the direction of the line indicates flow 

direction, and the length of the line is proportional to the 

magnitude. 

Figure 6 Flow profiles in 13ft entry 

 Figure 7. Flow profiles in 16-1⁄2 ft entry 

 A comparison of the profiles provided two specific 

results. First, increasing the intake flow quantity from 2.8 

to 4.7m3

/s (6,000 cfm to 10,000) cfm increased air 

velocities for both entry widths but did not significantly 

change the direction of flow. 

 Second, airflow directions in the 4- and 5- m (13 and 16 

1⁄2-ft) entries were significantly different. In the 4-m (13-

ft) wide entry the flow profile formed a pattern 

approximating the shape of a “figure 8." Air moved from 

the curtain along the left rib for about 4-m (13-ft) before 

turning right, flowing toward the right rib, and paralleling 

the right rib to the face. Air moved from right to left 

across the face, back toward the curtain along the left rib 

before turning again to the right rib. Airflow in the 5-m 

(16 1⁄2-ft) entry traveled in a simpler pattern. It moved 

from the curtain up the left rib to the face, left to right 

across the face and back along the right rib. 

QUANTITATIVE FLOW, U AND V COMPONENTS 

 The U and V components of the airflow were used to 

compare velocity profiles for air moving toward and 

parallel to the face. The U values were measured at 

sampling locations 0.6-m (2-ft) from the left rib and the V 

values at locations 0.6-m (2-ft) from the face. Air 

velocity measurements in the U direction are shown in 

Figures 8 and 9. Figures 10 and 11 show flow velocities 

in the V direction. 

Figure 8. Air speed toward face in 13 ft entry, 2 ft from 

the left side 
Figure 9. Air speed toward face in 16-1⁄2 ft entry, 2 ft 

from the left side 

Figure 10. Air speed across face in 13 ft entry, 2 ft from 

face 

Figure 11. Air speed across face in 16-1⁄2 ft entry, 2 ft 

from face 

 The velocities in the U and V directions varied for 

different entry widths and intake quantities. As expected, 

velocities measured in the U and V directions increased 

when the intake air quantity was increased from 2.8 to 4.7 

m3

/s (6,000 to 10,000 cfm). In the 4-m (13-ft) wide entry 

the reversal in velocity in the U direction was the result of 

the figure 8 flow pattern (Figure 9). In the 5-m (161⁄2- ft) 

entry velocity readings in the U direction generally 

increased as the air moved toward the face. 

 For the same intake quantity, velocities across the face 

were higher in the 16 1⁄2- ft entry. Air velocities 

increased as the air moved across the 5-m (16 1⁄2-ft) face 

and decreased across the 4-m (13-ft) face. 

QUANTITATIVE FLOW, TURBULENCE 

 The flow profiles described above were drawn using 

time averaged velocity and direction data. The individual 

(one second) readings for flow direction and speed were 

plotted versus time to show how much the readings varied 

during each 3-minute test. The scatter plots in Figure 12 

show how the direction readings varied at two adjacent 

locations (21 and 22) in the 5-m (16 1⁄2 ft) entry when the 

intake flow was 4.7 m3

/s (10,000 cfm). The average flow 

direction at both locations was approximately 180 degrees 

(i.e. toward the face), but the flow direction varied much 

more at location 22. Scatter plots showing the changes in 

speed with time are shown in Figure 13. Airspeed varied 

much more at location 21 where the average magnitude 

was much higher. 

Figure 12. Flow direction at two locations 
Figure 13. Speed measurements at two locations 

FUTURE RESEARCH 

 To measure airflow at a simulated mining face, 

researchers adapted a three-axis ultrasonic anemometer 

and developed a computer program. The ultrasonic 

anemometer provided airflow information that could not 

be obtained with instruments normally used for measuring 

airflow, such as a vane-type anemometer. The resulting 

data showed how entry geometry and intake flow 

quantities affected airflow profiles. 

 To simplify the flow patterns this study was conducted 

with an empty entry. During future studies airflow 

measurement will be taken with equipment, such as a 

model-mining machine, at the face. Tests with the modelmining machine will include the operation of machinemounted sprays and a simulated scrubber. Past research 

has shown that the machine-mounted water sprays and 

scrubber have a large effect on methane dilution at the 

face. The three-axis anemometer will be used to 

characterize how airflow at the face is affected by spray 

and scrubber operation. 

 Practical considerations of test time and available 

equipment limited the number of sampling locations to 

36. The locations were evenly distributed throughout the 

test area. When drawing the flow profiles it was assumed 

that the flow patterns remained uniform between 

sampling locations, especially between locations near the 

center of the entry. However, it is more difficult to 

estimate flow speeds and directions between the sampling 

locations and the face or ribs. 

 Differences in velocity profiles between 2 and 1 ft of 

the left rib of the entry were noted using measurements 

taken with a vane anemometer. For a 5-m (16 1⁄2 ft) entry 

with an air quantity of 4.7 m3

/s (10,000 cfm), velocity 

measurements were taken 0.6 and 0.3 m (2 ft and 1 ft) 

from the left rib with a hand-held vane anemometer. 

Figure 14 shows that, while velocities 0.3 m (1 ft) from 

the left rib decreased as one moved away from the 

curtain, velocities measured 0.6 m (2 ft) from the left rib 

tended to increase while moving toward the face from the 

curtain. A similar increase in velocity was seen with the 

ultrasonic measurements. Additional locations will be 

sampled closer to the entry face and ribs with the threeaxis anemometer to better identify differences in speed 

and direction in these border areas. 

Figure 14. Speeds 2 ft and 1 ft from the left rib 

 Measurements will also be taken at different heights in 

the gallery. No vertical velocity profiling took place 

during these tests since all data were collected in a single 

plane, midway between the floor and roof. The W 

(vertical) component of flow was measured, and, although 

always smaller than the U and V components, it varied in 

magnitude and direction. Measurements in multiple 

vertical planes will provide data for plotting flow in the 

UV (horizontal) and UW (vertical) planes. 

 As part of a cooperative study with the University of 

Kentucky Department of Mining Engineering, data 

obtained in these studies will be compared with the results 

from small-scale airflow studies, which used Particle 

Imaging Velocimetry (PIV) to measure airflow patterns 

(Wala, et. al., 2002). If there is good correlation between 

the full-scale and small-scale study flow measurements, 

PIV data may provide the information needed to 

interpolate air speed and direction data in areas not 

sampled during the gallery studies. 

 The flow velocity and flow direction measurements 

made with the ultrasonic anemometer was constantly 

changing during the three minutes that data were 

collected. The amount these readings varied depended on 

the sampling location and the test operating conditions. 

The flow direction and speed data collected each second 

were plotted versus the test elapsed time to compare the 

relative variation in readings. The variation in the 

velocity readings can be related to the flow turbulence. 

Flow turbulence will be calculated during future tests and 
its impact on methane dilution and removal will be 

evaluated. 

 During future studies, a three-axis anemometer will be 

used to evaluate the effects of other factors, such as 

exhaust ventilation and curtain setback distance, on face 

air direction and speed. For the same operating 

conditions, methane will be released at the face of the 

mining entry and methane concentrations measured at the 

same locations used to measure airflow. The airflow and 

methane profiles will be compared to determine the 

relationship between the airflow and methane 

concentrations. 

REFERENCES 

 Code of Federal Regulations (CFR-30) 75.323, (b)(ii). 

 Thimons, E. D., Taylor, C. D., Zimmer, J. .A., 1999, 

“Evaluating the Ventilation of a 40-Foot Two-Pass 

Extended Cut,” NIOSH Report of Investigations (RI 

9648). 

 Yost, M.G., and Spear, R.C., 1992, “ Measuring Indoor 

Airflow Patterns by Using a Sonic Vector Anemometer, 

American Industrial Hygienist Association Journal, Vol. 

53, November, pp. 677-680. 

 Wala. A., Tuner, D., and Jacob, J, 2002, “Experimental 

Study for Mine Face Ventilation System for Validation of 

Numerical Models,” Proceedings of the North 

American/Ninth U.S. Mine Ventilation Symposium, pp. 

191-196.