Name: wind tunnel experiments to study chaparral crown fires
Uploaded: 2017-11-14T14:00:00.000+00:00
Duration: 9 min 27 s
Description: Watch this Scientific Journal Video about Wind Tunnel Experiments to Study Chaparral Crown Fires at JoVE.com

The authors would like to acknowledge Benjamin Sommerkorn, Gabriel Dupont, Jake Eggan and Chirawat Sanpakit who assisted with the experiments presented here. Jeanette Cobian I&#241;iguez acknowledges support by NASA MUREP Institutional Research Opportunity (MIRO) grant number NNX15AP99A. This work was also funded by the USDA/USDI National Fire Plan through an agreement between USDA Forest Service, PSW Research Station and the University of California - Riverside.

Caution: As several steps in the following protocol involve activities that have the potential to cause injury, ensure that the proper personal protective equipment (PPE) is used following established safety protocols including fire resistant clothing and protective eyewear.
1. Crown Fuel Bed Load Cell Instrumentation Setup
<ol>
	<li>Modify 4 C-clamps by attaching dual spring gate carabiners (see Table of Materials) through the pin hole at the clamp&#39;s screw end (see Figure 2). Use the carabiners to suspend the crown fuel bed.</li>
	<li>Using a different set of C-clamps, affix each load strain gauge cell to the top portion of the wind tunnel frame (see Figure 2).</li>
	<li>Attach modified C-clamps to the free end of the strain gauge cells, with the carabiners hanging down. Attach chains to the platform for the crown fuel bed.</li>
	<li>To suspend the crown fuel bed platform from the wind tunnel frame, connect each of the crown fuel bed chains to a carabiner.</li>
	<li>Once each of the four load cells are fully mounted and connected to the fuel bed, connect their wires to the Wheatstone bridge which will be used for data acquisition. Cover the load cells with fire insulating material, such as the kind used for fire shelters.</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56591/56591fig2.jpg" /> 
Figure 2: Wind tunnel crown fuel bed load cell instrumentation. (a) Wind tunnel front view (b) Modified C-clamp with carabiner and crown fuel bed chain which supports the crown fuel bed. (c) Load cell attached to the wind tunnel frame using a C-clamp. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Load Cell Calibration
NOTE: The signal produced by the load cells is converted to an equivalent mass through: 
<img alt="Equation 2" src="/files/ftp_upload/56591/56591eq2.jpg" /> 
where V is the signal, typically in millivolts, A and B are constants to be determined through calibration, and m represents the mass in grams. All the parameters in equation (2) are obtained through the custom instrument control interface developed for the crown mass instrumentation in this protocol. When first using the system, precision weights are used to calibrate the load cell signal. Calibration constants A and B will be obtained based on the signal produced when measuring the load of these precision weights. The constant A is calculated from: 
<img alt="Equation 3" src="/files/ftp_upload/56591/56591eq3.jpg" /> 
where mt is a the mass of trial precision weight, aw is the signal produced with the weight loaded on the load cell, whereas aw,o corresponds to the signal produced when no weight is applied on the load cell.
<ol>
	<li>To obtain the calibration constant A, hook precision weights (a good range would be 200 - 500 g) to the first load cell. Use the mass of the precision weights as parameter mt in equation (3).</li>
	<li>Set the load cell gain to 128 using the Input # field as shown in Figure 3b, i.1. This corresponds to the maximum value allowed by the device.</li>
	<li>Read the signal output at Output 0 from the instrument interface (See Figure 3b, i2). This is parameter aw in equation (3).</li>
	<li>Unhook the weight and read the new value displayed in the instrument interface ( Figure 3b, i2). This is parameter aw,o.</li>
	<li>Calculate A based on the parameters (mt, aw, aw,o) obtained in steps 2.1 to 2.4 and the equations presented.</li>
	<li>In the controller interface, fill in the Ch 0-M value for each sensor with the A value obtained in the previous step.</li>
	<li>To find the offset value, B, remove all weights, read the value in the &#39;Outputs Calibrated (g)&#39; box (See Figure 3c, i2), multiply this value by -1. The resulting number is constant B, type this number in the &#34;Addition&#34; Ch 0-A box (See Figure 3c, i.3).</li>
	<li>Repeat steps 2.3 - 2.8 for each load cell (0, 1, 2, 3), the system is now completely calibrated; proceed to load the fuel beds with the fuels.</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56591/56591fig3.jpg" /> 
Figure 3: Instrument control interface data input steps for load cell calibration. (a) Bridge initial setup window with gain setup and enable box (b) Window for first stage of load cell calibration (c) Window for second stage of load cell calibration (d) Window for last stage of load cell calibration, file is saved here and data logging was started. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Preparation of Chaparral and Excelsior Fuel Beds
NOTE: Each experiment uses 2 kg of live chamise and 0.5 kg of excelsior (shredded aspen wood).
<ol>
	<li>From the pile of fuel collected for burning, collect several 1-pint bottles of fuel (3 - 4 bottles).
	<ol>
		<li>Follow the procedures delineated by Countryman and Dean to oven dry samples and obtain fuel moisture content30.</li>
	</ol>
	</li>
	<li>Trim individual branches from a bundle of recently harvested chamise to remove dead material and branch material greater than &#188; inch diameter. Place the remaining live fuel material in the container for weighing.</li>
	<li>Select 2 kg of the trimmed chamise and 0.5 kg of excelsior using an electronic scale. Place 0.5 kg of excelsior onto the surface fuel bed platform on the wind tunnel floor, ensuring that the bulk density is as uniform as possible. Do this by placing a known amount of excelsior over a known area depth.</li>
	<li>Pull apart (fluff) the compacted excelsior to decrease its bulk density so it will burn readily. &#160;Load 2 kg of trimmed chamise onto the platform hanging from the load cells to create the elevated fuel bed. Evenly spread the chamise branches over the entire platform to produce a uniform fuel bed.</li>
</ol>
4. Thermocouple Arrangement
NOTE: K-Type thermocouples are used to measure temperature of both fuel beds. Data is collected through a data acquisition system controlled with a custom graphical user interface (see table of materials for controller design software). The thermocouples recommended for use are 24 AWG thermocouples with a response time of 0.9 s.
<ol>
	<li>Connect an array of sixteen 24 AWG thermocouples (conductor diameter: 0.51054 mm) to a data logger (response time: 0.9 s).</li>
	<li>Insert 6 thermocouples into the crown fuel layer. Place these thermocouples 20 cm apart and avoid contact of thermocouples with branches. Insert 10 thermocouples into the surface fuel layer. Place these surface fuel thermocouples 10 cm apart and avoid contact of thermocouples with branches (See Figure 4).</li>
	<li>Activate data logging by clicking the &#34;Start&#34; button in the thermocouple control software interface.</li>
</ol>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56591/56591fig4.jpg" /> 
Figure 4: Diagram of surface and crown fuel beds with thermocouple array location. Here 6 thermocouples were inserted into the crown fuel layer 20 cm apart from each other. 10 thermocouples were inserted into the surface fuel layer 10 cm apart. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Image Acquisition Setup
<ol>
	<li>Mount the visual reference target that has red marks at 10-cm-intervals above the wind tunnel window. Use this target as a reference to determine flame height from the experiment video. 
	NOTE: Sample flame heights are presented in Figure 5.</li>
	<li>Setup photographic data collection. Focusing on the wind tunnel test area, adjust the camera focus so as to capture the entire vertical reference target as well as the fuel bed area.</li>
	<li>Setup video camera data collection. Mount the video camera with a universal camera wall mount on the wall to provide a full view of the wind tunnel test section.</li>
</ol>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56591/56591fig5.jpg" /> 
Figure 5: Photograph of sample flame heights from a typical experiment. The blue visual target with red marking serves as a reference to determine flame height from the experiment video. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
6. Flow Setup
NOTE: The wind tunnel is equipped with a variable speed fan. The air flow in the wind tunnel has been previously calibrated to the fan speed. To achieve the desired wind velocity, the fan rotational speed (in Hz) is selected. In the present experiments, no wind and 1 m/s wind flow cases were studied.
<ol>
	<li>Set the fan speed to 1 m/s on the speed controller. Turn on the fan to ensure that it is functioning properly.</li>
	<li>Turn off the fan. It is now ready for use. 
	NOTE: The burn building is designed to conduct fire experiments safely while evacuating smoke from the working space. Notify local fire authorities that experiments are being conducted to eliminate the occurrence of false alarms.</li>
	<li>Close all doors in the building to ensure that the roof vents are the only possible exit for smoke evacuation.</li>
	<li>Turn on the air supply fans to bring in fresh air from outside the building at floor level. Turn on the exhaust fans to evacuate smoke through the roof vents. 
	NOTE: This will establish a low velocity, high volume air flow from outside the building that rises vertically due to the slight pressure difference and the roof openings.</li>
	<li>Prior to each experiment, use a wet-bulb hygrometer to measure the relative humidity and temperature of the ambient air.</li>
</ol>
7. Ignition (Implement Simultaneously with Step 8)
NOTE: The ignition process should be conducted as follows by the ignition crew member. For increased safety, it is recommended that a second crew member remain near the test area during ignition.
<ol>
	<li>When instructed to &#39;ignite&#39;, soak the leading edge of the excelsior surface fuel bed with denatured ethyl alcohol. Place the alcohol bottle away from the ignition zone and using a butane torch, ignite the end of the surface fuel bed in a line parallel to leading edge of the fuel bed. Be observant as the alcohol-soaked fuel will readily ignite.</li>
	<li>Once the fuel bed has been ignited, step out of the test section and close the tunnel door. If wind is required for the experiment, turn on the wind tunnel fan.</li>
</ol>
8. Initiate Experimental Run
NOTE: Upon verifying the experiment is correctly setup, the cameras should be started.
<ol>
	<li>Turn on the video camera to record.</li>
	<li>Speak aloud the experiment number/code, the date, and experimental configuration so the microphone on the video camera records this information.</li>
	<li>Instruct the computer crew to begin data logging by ticking the &#34;Enable data logging&#34; option in the instrument control interface (see Figure 3d, i.1). Instruct the ignition person to ignite the fuel. Once the ignition crew member exits the wind tunnel, instruct the wind crew member to start the wind tunnel fan. This will be the start of the experiment where time is zero (t = 0).</li>
</ol>

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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repeatability+of+free-burning+fire+experiments+using+heterogeneous+forest+fuel+beds+in+a+combustion+wind+tunnel.">Repeatability of free-burning fire experiments using heterogeneous forest fuel beds in a combustion wind tunnel.</a> Intl J Wildl Fire. 25 (4), 445-455 (2016).</li></ol>

The authors have nothing to disclose.

The ability to measure the elevated fuel mass throughout the experiment was one of the main advantages of the technique presented here. Previous studies addressing chaparral fire have focused on either only crown fire initiation or only on surface spread, but not both. Such studies have quantified the possibility of ignition in the crown layer and have left study of spread for future work23. Our methodology allows for measurement of mass loss, temperature distribution, and flame geometry for both ...

In 2016, the state of California experienced a total of 6,986 wildland fires, consuming 564,835 acres1, costing millions of dollars in damage, and risking the wellness of hundreds of people. Because of the regional Mediterranean climate, a major fuel source for these fires are chaparral vegetation communities2. Fire spread in chaparral can be considered a crown fire since the main fuel that burns is elevated3. Co-existing with the predominantly live crown layer, is the dead surface fuel layer, which consists of cast foliage, branches, and herbaceous plants which grow under and between the individual shrubs. Fire will more easily initiate in the dead surface fuel layer. Once the surface fire ignites, the fire may transition to the crown layer where the energy released by the fire increases dramatically. While chaparral fires have typically been modelled as a fire spreading in deep surface fuels4, there has been limited study of chaparral fires as crown fires.

Crown characteristics in chaparral, including foliage particle shape, differ from boreal coniferous forest, where most of the research has occurred. Numerous laboratory and field scale studies have investigated various aspects of wildfire dynamics6,5,7,3,8,9,10,11,12. Within the realm of laboratory experiments, several studies have examined the influence of parameters such as wind and fuel properties on chaparral crown fire behavior. Lozano7 examined characteristics of crown fire initiation in the presence of two discrete crown fuel beds. In Tachajapong et al.3, discrete surface and crown layers were burned inside a wind tunnel and the surface fire was characterized. Only crown fire initiation was fully described leaving full analysis of spread for future work. Li et al.11 reported on the propagation of a flame though single chaparral shrubs. In related work, Cruz et al.10,9 developed a model to predict the ignition of coniferous foliage above a spreading surface fire. Burn characteristics of chaparral fuels have been explored in experimental studies of bulk fuels and individual leaves13,14,15,16. Dupuy et al.13 studied the burning characteristics of Pinus pinaster needles and excelsior by burning the fuels in cylindrical baskets. They observed that in these fuels, flame height was related to heat release rate via a two-fifths power law as has been reported previously in the literature17,18. Sun et al.14 burned chaparral fuels in similar cylindrical baskets to analyze the burning characteristics of three chaparral fuels: chamise (Adenostoma fasciculatum), ceanothus (Ceanothus crassifolius), and manzanita (Arctostaphylos glandulosa).
Motivated by results from the aforementioned laboratory studies, our purpose here is to present a methodology to characterize spread in both surface and shrub crown layers. Furthermore, we aim to clarify some of the key characteristics that dictate the degree of surface-crown layer interaction. To this purpose, we developed an experimental laboratory methodology to study the vertical transition of a fire burning in a wildland surface fuel to a fire spreading in an elevated shrub fuel. In these types of fires, translation of the fire to the shrub crown, known as crowning, may be followed by sustained spread under the right conditions. In general, chaparral fire behavior is dictated by topography, weather, and fuel19. It has been shown that wind affects energy release rate in the fuels5,3,8,20.
Fire spread in porous fuels can be viewed as a series of transitions or thresholds that must be crossed to be successful21. Energetically, a fuel particle ignites if the amount of heat that it receives results in a mixture of gases that successfully react with oxygen. The resulting flame spreads if the heat from the burning particle ignites an adjacent fuel particle. The fire spreads across the ground if it is able to cross gaps between combustible fuel elements. If the flame of a surface fire is able to propagate vertically into the crown of shrubs and trees, a significant change in fire behavior, including increased heat release rates, is often observed due to a greater availability of fuel. Thermal energy dynamics in wildland fires encompass several scales, from the very large scale, such in mega-fires which often require climatological modeling, to the small scale requiring chemical scale kinetic modeling. Here, we deal with laboratory wind tunnel scale behavior modeling; for chemical scale cellulose combustion studies, the reader is referred to works such as Sullivan et al.22
Since 2001, we have conducted a variety of experiments examining some of the laboratory scale energy thresholds23,8,24,25,26,27, with an emphasis on live fuels associated with chaparral. While outdoors measurements of fire may provide more lifelike results, the controlled environment of the wind tunnel allow for delineation of the impact of various parameters. Controlling wind, for example, is especially important for chaparral crown fires occurring in regions such as Southern California where foehn type winds, known as Santa Ana winds, are typical drivers of fire events. Because a major motivator for the methodology described here is to study the effect of wind and other controlled parameters on chaparral fire spread, this study was performed in a laboratory scale wind tunnel. The reader is directed to the work by Silvani et al.28 for field measurements of temperature in chaparral fires similar to the ones presented here. For field measurements on the effect of wind on fire spread, please see Morandi et al.29
Several parameters influencing the spread in chaparral fuels have been experimentally analyzed by quantifying the probability of fire spread success in elevated fuel beds8. The current experimental study involves a methodology developed to study chaparral crown fire spread by modeling surface fuels and crown fuels inside the test section of a low speed wind tunnel. The surface fuel is modeled with excelsior (dried shredded wood). The surface fuel bed is placed on the ground level of the wind tunnel over a standard scale (see Figure 1). Representing the crown fuel bed, a fuel bed with chamise was placed over the surface fuel bed by suspending the fuel from a platform mounted on the wind tunnel frame (see Figure 1). Both fuel beds are instrumented for temperature and mass loss measurements; flame geometry is obtained from video recordings of experiments. Parameters measured include mass loss rate, fuel moisture content and the relative humidity of the air. Parameters controlled were wind presence, distance between surface fuel bed and crown fuel bed, and the presence of surface fuel. The measured mass loss rate can be used to calculate the heat release rate, which is defined as: 
<img alt="Equation 1" src="/files/ftp_upload/56591/56591eq1.jpg" /> 
where h is the heat of fuel combustion, m is the fuel mass, and t is time.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56591/56591fig1.jpg" /> 
Figure 1: Wind tunnel experimental setup. Locations of the crown fuel bed, the surface fuel bed, and the tunnel fan have been labeled for convenience. The surface fuel bed is placed on the ground level of the wind tunnel over a standard scale. Representing the crown fuel bed, a fuel bed with chamise was placed over the surface fuel bed by suspending the fuel from a platform mounted on the wind tunnel frame. <a href="//cloudflare.jove.com/files/ftp_upload/56591/56591fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Experiments have focused on understanding the behavior of chaparral crown fires, particularly ignition, mechanisms of flame propagation and spread, flame front velocities, and fuel consumption rates.To study the interaction between a surface fire and a crown fire, six configurations of surface and crown fuel beds with and without applied wind flow, have been burned in the wind tunnel: crown fuel only with and without wind (2), crown and surface fuel beds separated by two distances with and without wind (4). Table 1 summarizes the experimental configurations with the 6 experimental classes. In the table, the surface fuel bed parameter denotes whether surface fuel was present during the experiment, the wind parameter refers to the presence of wind and crown height refers to the distance between the bottom of the crown fuel bed and the bottom of the surface fuel bed. Fuel moisture was measured for each experiment but not controlled, average fuel moisture content was 48%, whereas the minimum and maximum values were 18% to 68%, respectively.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Class</td>
			<td>Surface Fuel Bed</td>
			<td>Wind</td>
			<td>Crown Height</td>
		</tr>
		<tr>
			<td>A</td>
			<td>Absent</td>
			<td>No wind</td>
			<td>60 or 70 cm</td>
		</tr>
		<tr>
			<td>B</td>
			<td>Absent</td>
			<td>1 ms-1</td>
			<td>60 or 70 cm</td>
		</tr>
		<tr>
			<td>C</td>
			<td>Present</td>
			<td>No wind</td>
			<td>60 cm</td>
		</tr>
		<tr>
			<td>D</td>
			<td>Present</td>
			<td>No wind</td>
			<td>70 cm</td>
		</tr>
		<tr>
			<td>E</td>
			<td>Present</td>
			<td>1 ms-1</td>
			<td>60 cm</td>
		</tr>
		<tr>
			<td>F</td>
			<td>Present</td>
			<td>1 ms-1</td>
			<td>70 cm</td>
		</tr>
	</tbody>
</table>
Table 1: Experiment configurations. Here the surface fuel bed parameter denotes whether surface fuel was present during the experiment, the wind parameter refers to the presence of wind and crown height refers to the distance between the bottom of the crown fuel bed and the bottom of the surface fuel bed.
An electronic scale measured surface fuel mass and we developed a custom mass loss system for the crown layer. The system consisted of individual load cells connected to each corner of the suspended fuel bed. Consumer-grade video cameras recorded the visual flames; image processing of the visual data using a custom script generated flame characteristics including height and angle. A program was developed to convert video frames from RGB (red/green/blue) coding to black and white through a process of light intensity thresholding. The edge of the flame was obtained from the black and white video frames. Maximum flame height was defined as the highest point of the flame edge, instantaneous flame heights were also obtained. In an image, flame height was measured from the base of the fuel bed to the maximum vertical point of the flame. All processing codes as well as the instrument control interface designed for this protocol have been made available by the authors here through their software access site. Harvesting the live fuel locally and conducting the experimental burns within 24 h minimized moisture loss. A thermocouple array recorded fuel bed temperature in the wind stream-wise direction enabling the calculation of spread rate. Figure 1 shows a diagram of the fuel bed setup along with the thermocouple arrangement. Details of the experimental protocol follow.

<table><tbody><tr><td>&lt;strong&gt;Wind Tunnel Instrumentation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>cDAQ-9178 CompactDAQ Chassis</td><td>National Instruments</td><td>781156-01</td><td></td></tr><tr><td>NI-9213 C Series Temperature Input Module</td><td>National Instruments</td><td>785185-01</td><td></td></tr><tr><td>NI SignalExpress for Windows</td><td>National Instruments</td><td>779037-35&amp;nbsp;</td><td>Newest version, older version used for experiment</td></tr><tr><td>High Temperature Nextel Insulated Thermocouple Elements</td><td>Omega</td><td>XC-24-K-18</td><td></td></tr><tr><td>Thermocouple Extension Wire with Polyvinyl Coated Wire and Tinned Copper Overbraid</td><td>Omega</td><td>EXPP-K-24S-TCB-P</td><td></td></tr><tr><td>Ultra High Temperature Miniature Connectors</td><td>Omega</td><td>SHX-K-M</td><td></td></tr><tr><td>CompuTrac MAX 2000XL&amp;nbsp;</td><td>Arizona Instruments</td><td>MAX-2000XL</td><td>Discontinued, Newer Model Out</td></tr><tr><td>Kestrel 3000 Pocket Weather Meter</td><td>Nielsen-Kellerman</td><td>0830</td><td></td></tr><tr><td>Satorius CPA 34001S&amp;nbsp;</td><td>Sartorius</td><td>25850314</td><td>Discontinued Model</td></tr><tr><td>5 Kg Micro Load Cell (X4)</td><td>Robotshop.com</td><td>RB-Phi-118</td><td>Strain Gauge Load Cell</td></tr><tr><td>Phidget PhidgetBridge Wheatstone Bridge Sensor Interface</td><td>Robotshop.com</td><td>RB-Phi-107</td><td>Interfaces with 4 load cells, performs signal amplification</td></tr><tr><td>#2 Stainless S-Biner (X4)</td><td>Home Depot</td><td>SB2-03-11</td><td>Dual spring gate carabiners used to mount load cells</td></tr><tr><td>2 in. Malleable Iron C-Clamp</td><td>Home Depot</td><td># 4011</td><td>Used to mount load cells</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Personal Protective Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Wildland Firefighter Nomex Shirt</td><td>GSA Advantage</td><td>SH35-5648</td><td></td></tr><tr><td>Fireline 6 oz Wildland Fire Pants</td><td>GSA Advantage</td><td>139702MR SEV16</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Fuels&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Chamise</td><td>Collected in situ</td><td>N/A</td><td></td></tr><tr><td>Natural Shredded Wood Excelsior &amp;ndash; Natural Coarse 50 lbs bail</td><td>Paper Mart</td><td>21-711-88</td><td></td></tr><tr><td>Bernzomatic UL100 Basic Propane Torch Kit</td><td>Home Depot</td><td>UL100KC</td><td></td></tr><tr><td>Isopropyl alcohol</td><td>Convenience store</td><td>N/A</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Video and Photography&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Nikon D3000 10.2-MP DSLR camera with DX-format sensor and 3x 18x55mm Zoon-NIKKOR VR Image Stabilization Lens</td><td></td><td></td><td></td></tr><tr><td>Sony Handycam Camcorder DCR-SX85</td><td>Amazon.com</td><td>DCR-SX85</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Software&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>NI LabView</td><td>National Instruments</td><td>Student Version</td><td>Used for instrument control and interfacing</td></tr><tr><td>MATLAB Student Version (MATLAB_R2014a)</td><td>Mathworks</td><td>Student Version&amp;nbsp;</td><td>Used for data post-processing including image processing</td></tr></tbody></table>

wind tunnel experiments to study chaparral crown fires

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low velocity fire wind tunnel where two distinct layers of fuel were constructed to represent surface and crown fuels in chaparral. Chamise, a common chaparral shrub, comprised the live crown layer. The dead fuel surface layer was constructed with excelsior (shredded wood). We developed a methodology to measure mass loss, temperature, and flame height for both fuel layers. Thermocouples placed in each layer estimated temperature. A video camera captured the visible flame. Post-processing of digital imagery yielded flame characteristics including height and flame tilt. A custom crown mass loss instrument developed in-house measured the evolution of the mass of the crown layer during the burn. Mass loss and temperature trends obtained using the technique matched theory and other empirical studies. In this study, we present detailed experimental procedures and information about the instrumentation used. The representative results for the fuel mass loss rate and temperature filed within the fuel bed are also included and discussed.

Crown and surface flame height data were obtained from the video data. Typical flame height trends for experiments is presented in Figure 6. Flame height behavior followed that found in Sun et al.14
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56591/56591fig6.jpg" /> 
Figure 6: Estimated crown flame height. Here U = 1 m/s,...

Watch this Scientific Journal Video about Wind Tunnel Experiments to Study Chaparral Crown Fires at JoVE.com

Wind Tunnel Experiments to Study Chaparral Crown Fires

This protocol describes wind tunnel experiments designed to study the transition of a fire from the ground to the canopy of chaparral shrubs.

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low ...

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9.6K Views.  University of California, Riverside. This protocol describes wind tunnel experiments designed to study the transition of a fire from the ground to the canopy of chaparral shrubs.

Video: Wind Tunnel Experiments to Study Chaparral Crown Fires

Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface

Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study evaporation under various surface boundary conditions to improve our current understanding and characterization of this multiphase phenomenon as well as to validate numerical heat and mass transfer theories that couple Navier-Stokes flow in the atmosphere and Darcian flow in the porous media. Experimental data were collected using a unique soil tank apparatus interfaced with a small climate controlled wind tunnel. The experimental apparatus was instrumented with a suite of state of the art sensor technologies for the continuous and autonomous collection of soil moisture, soil thermal properties, soil and air temperature, relative humidity, and wind speed. This experimental apparatus can be used to generate data under well controlled boundary conditions, allowing for better control and gathering of accurate data at scales of interest not feasible in the field. Induced airflow at several distinct wind speeds over the soil surface resulted in unique behavior of heat and mass transfer during the different evaporative stages.

A protocol for the design and construction of a soil tank interfaced to a small climate controlled wind tunnel to study the effects of atmospheric forcings on evaporation is presented. Both the soil tank and wind tunnel are instrumented with sensor technologies for the continuous in situ measurement of environmental conditions.

Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study ...

Environment

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power ...

Using Tree-Rings to Reconstruct Fire History Information from Forested Areas

Annual tree-ring patterns are a source of ecological and environmental information including the history of fires in forested areas. Tree-ring based fire histories include three fundamental phases: field collection, laboratory methods (preparation and dating), and data analysis. Here we provide step-by-step instructions and issues to consider, including the process for selecting the study area, sampling sites, plus how and which fire-scarred trees to sample. In addition, we describe fire-scar sample preparation and dating which are done in the laboratory. Finally, we describe basic analysis and relevant results, including examples from studies that have reconstructed fire history patterns. These studies allow us to understand the historical fire frequency, changes in those frequencies related to anthropogenic factors, and analyzes of how climate influences fire occurrence over time. The description of these methods and techniques should provide a greater understanding of fire history studies that will benefit researchers, educators, technicians, and students interested in this field. These detailed methods will allow new researchers to this field, a resource to start their own work and achieve greater success. This resource will provide a greater integration of tree-ring aspects within other studies and lead to a better understanding of natural processes with forested ecosystems.

This work explains the most appropriate techniques and methods for conducting a fire history study from beginning site selection to final analysis of fire-climate relationship.

Annual tree-ring patterns are a source of ecological and environmental information including the history of fires in forested areas. Tree-ring based fire ...

Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is not well understood. The flow visualization technique is a promising non-intrusive method to illustrate the complex flow field spatially and temporally. A basic flow visualization setup consists of a high-powered laser and optic lenses to generate the laser sheet, a camera, a tracer particle generator, and a data processor. The wind tunnel setup, the specifications of devices involved, and the corresponding parameter settings are dependent on the flow features to be obtained.
Normal smoke wire flow visualization uses a smoke wire to demonstrate the flow streaklines. However, the performance of this method is limited by poor spatial resolution when it is conducted in a complex flow field. Therefore, an improved smoke flow visualization technique has been developed. This technique illustrates the large-scale global LEV flow field and the small-scale shear layer flow structure at the same time, providing a valuable reference for later detailed particle image velocimetry (PIV) measurement.
In this paper, the application of the improved smoke flow visualization and PIV measurement to study the unsteady flow phenomena over a delta wing is demonstrated. The procedure and cautions for conducting the experiment are listed, including wind tunnel setup, data acquisition, and data processing. The representative results show that these two flow visualization methods are effective techniques for investigating the three-dimensional flow field qualitatively and quantitatively.

Here, we present a protocol to observe unsteady vortical flows over a delta wing using a modified smoke flow visualization technique and investigate the mechanism responsible for the oscillations of the leading-edge vortex breakdown locations.

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is ...

Air Curtain Burners and Biochar &#8211; Advancing Forest Health and Carbon Capture

Continuous In-woods Production of Biochar Using a Trailer-Mounted Air Curtain Burner

Fuel treatments and other forest restoration thinning practices aim to reduce wildfire risk while building forest resilience to drought, insects, and diseases and increasing aboveground carbon (C) sequestration. However, fuel treatments generate large amounts of unmerchantable woody biomass residues that are often burned in open piles, releasing significant quantities of greenhouse gases and particulates, and potentially damaging the soil beneath the pile. Air curtain burners offer a solution to mitigate these issues, helping to reduce smoke and particulates from burning operations, more fully burn biomass residues compared to pile burning, and eliminate the direct and intense fire contact that can harm soil beneath the slash pile. In an air curtain burner, burning takes place in a controlled environment. Smoke is contained and recirculated by the air curtain, and therefore burning can be conducted under a variety of climatic conditions (e.g.,&#160;wind, rain, snow), lengthening the burning season for disposal of slash material. The mobile pyrolysis unit that continuously creates biochar was specifically designed to dispose of residual woody biomass at log landings, green wood at landfills, or salvaged logged materials and create biochar in the process. This high-carbon biochar output can be used to enhance soil resilience by improving its chemical, physical, and biological properties and has potential applications in remediating contaminated soils, including those at abandoned mine sites. Here, we describe the general use of this equipment, appropriate siting, loading methods, quenching requirements, and lessons learned about operating this new technology.

Author Spotlight: Advancing Place-Based Biochar Production for Ecosystem Restoration and Soil Health

We describe the use of a place-based mobile pyrolysis unit equipped with an air curtain to continuously create biochar. The technology reduces the need for open slash pile burning, which results in lower emissions and fewer soil impacts. The protocol includes guidelines for site selection, loading, and quenching.

Fuel treatments and other forest restoration thinning practices aim to reduce wildfire risk while building forest resilience to drought, insects, and ...

Turbulence Sphere Method: Evaluating Wind Tunnel Flow Quality

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful in the design of vehicles and structures that are subjected to airflow during their use. Wind tunnel data are generated by applying a controlled air flow to a model of the object being studied. The test model usually has a similar geometry but is a smaller scale compared to the full-sized object. To ensure accurate and useful data is collected during low speed wind tunnel tests, there must be a dynamic similarity of the Reynolds number between the tunnel flow field over the testing model and the actual flow field over the full-sized object.
In this demonstration, wind tunnel flow over a smooth sphere with well-defined flow characteristics will be analyzed. Because the sphere has well-defined flow characteristics, the turbulence factor for the wind tunnel, which correlates the effective Reynolds number to the test Reynolds number, can be determined, as well as the free-stream turbulence intensity of the wind tunnel.

Turbulence Measurements at Varying Air Speeds

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful ...

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Flow Visualization in a Water Tunnel: Observing the Leading-edge Vortex Over a Delta Wing

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The delta wing, shown in Figure 1D, is a popular design in high-speed airplanes due to its superb performance in transonic and supersonic flight regimes. This type of wing has a small aspect ratio and high sweep angle, which reduces drag at high subsonic, transonic and supersonic flight regimes. The aspect ratio is defined as the wing span divided by the average chord <img align="middle" src="/files/ftp_upload/10459/10459eq1a.jpg" />.
An important advantage of the delta wing is its high stall angle. The stall of a delta wing is delayed compared to the stall of a high aspect ratio wing. This is because the lift of a delta wing is enhanced by the leading-edge vortex over the wing.
An effective way to observe this vortex flow phenomenon and study the vortex breakdown in a delta wing is by visualizing the flow in a water tunnel. By injecting dye in the flow surrounding a model from dye ports on the leading-edge, the vortex development and breakdown can be observed and its position measured. The data can also be used to estimate the stall angle.
<img src="/files/ftp_upload/10459/10459fig1.jpg" />
Figure 1. Typical wing planform shapes: A) Rectangular, with constant chord along span, B) elliptical, C) tapered, with variable chord along the span, and D) delta wing, an aft-swept wing with zero taper ratio.

Flow in a Water Tunnel: Leading-edge Vortex over a Delta Wing

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The ...

Measuring Turbulent Flows

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows exhibit very high frequency fluctuations that require instruments with high time-resolution for their appropriate characterization. Hot-wire anemometers have a short enough time-response to fulfill this requirement. The purpose of this experiment is to demonstrate the use of hot-wire anemometry to characterize a turbulent jet.
In this experiment, a previously calibrated hot-wire probe will be used to obtain velocity measurements at different positions within the jet. Finally, we will demonstrate a basic statistical analysis of the data to characterize the turbulent field.

Measuring Turbulent Flows Using Hot-Wire Anemometers

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows ...

Mechanical Engineering

Constant Temperature Anemometry: A Tool to Study Turbulent Boundary Layer Flow

Source: Xiaofeng Liu, Jose Roberto Moreto, and Jaime Dorado, Department of Aerospace Engineering, San Diego State University, San Diego, California
A boundary layer is a thin flow region immediately adjacent to the surface of a solid body immersed in flow field. In this region, viscous effects, such as the viscous shear stress, dominate, and the flow is retarded due to the influence of friction between the fluid and the solid surface. Outside of the boundary layer, the flow is inviscid, i.e., there is no dissipative effects due to friction, thermal conduction or mass diffusion.
The boundary layer concept was introduced by Ludwig Prandtl in 1904, which enables significant simplification to the Navier-Stokes (NS) equation for the treatment of flow over a solid body. Inside the boundary layer, the NS equation is reduced to the boundary layer equation, while outside of the boundary layer, the flow can be described by the Euler equation, which is a simplified version of the NS equation.
<img src="/files/ftp_upload/10455/10455fig1a.jpg" />
Figure 1. Boundary layer development over a flat plate.
The simplest case for boundary layer development occurs on a flat plate at zero angle of incidence. When considering boundary layer development on a flat plate, the velocity outside of the boundary layer is constant so that the pressure gradient along the wall is considered to be zero.
The boundary layer, which naturally develops on a solid body surface, typically undergoes the following stages: first, the laminar boundary layer state; second, the transition state, and third, the turbulent boundary layer state. Each state has its own law(s) describing the flow structure of the boundary layer.
The research into the development and structure of boundary layer is of great importance for both theoretical study and practical applications. For example, boundary layer theory is the basis for calculating the skin friction drag on ships, aircraft and the blades of turbomachines. Skin friction drag is created on the body surface within the boundary layer and is due to the viscous shear stress exerted on the surface through fluid particles in direct contact with it. The skin friction is proportional to the fluid viscosity and the local velocity gradient on the surface in the surface normal direction. Skin friction drag is present on the entire surface, thus it becomes significant over large areas, such as an airplane wing. Additionally, turbulent fluid flow creates more skin friction drag. The macro-turbulent fluid motion enhances the momentum transfer within the boundary layer by bringing fluid particles with high momentum down to the surface.
This demonstration focuses on the turbulent boundary layer over a flat plate, in which the flow is irregular, such as in mixing or eddying, and the fluctuations are superimposed on the mean flow. Thus, the velocity at any point in a turbulent boundary layer is a function of time. In this demonstration, constant temperature hot-wire anemometry, or CTA, will be used to conduct a boundary layer survey. Then, the Clauser chart method will be used to calculate the skin friction coefficient in a turbulent boundary layer.

Constant Temperature Anemometry: Turbulent Boundary Layer Flow Study

Source: Xiaofeng Liu, Jose Roberto Moreto, and Jaime Dorado, Department of Aerospace Engineering, San Diego State University, San Diego, California
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