The results of reconstructing the radial dependence of the gas density in the core of a fire tornado model based on the results of laser transillumination are presented. It is shown that the position of the energy gravity centroid of the beam passing through the flame is quite sensitive to regular spatial density variations in the tornado core. Estimates of the transverse size of the core and the temperature in the combustion region are obtained, which correspond to the results of measurements by other methods
In this work, we used the data of a laboratory experiment on registration of fluctuations in the intensity of a laser beam passing through a vortex flame (model of a fire tornado) to calculate their power spectra. The nature of the decay of the power spectra in the high-frequency region was studied. The dominance of the two-scale decay of such spectra over the single-scale decay is established. The analysis carried out makes it possible to compare the results with the well-known Kolmogorov-Obukhov theory for estimating the turbulence parameters of the free atmosphere and to assume the presence of an inertial interval in the vortex flame.
We investigated the temporal fluctuations of the intensity of a laser beam through a vortex flame - a model of a fire tornado on a laboratory scale. Three equally spaced receivers were used. The spectral functions of fluctuations of the intensity of the laser beam were calculated at several speeds of swirling of the air flow incident on a stationary flame. Several spectral functions were recorded with a feature - a spike in the high-frequency region. Quantitative estimates of the shape of such spikes have been made.
On a laboratory scale, a tornado-like flame was obtained. To study the optical inhomogeneities of such a flame, the laser transmission method was used. On different heights for 3 equally spaced horizontal sensors were digitized and signals of fluctuations in the intensity of the laser beam were recorded. When processed using FFT, the frequency spectra of intensity fluctuations were obtained. In the analysis of the spectra, sometimes occurring high-frequency peaks were distinguished. The distribution of such peaks was recorded depending on the recording time for each of the sensors.
We conducted a study of the swirling flame with a laser. A vertical tornado-like flame had a height of approximately 1 m and a width of 0.07 m. At 10 heights for 3 equally spaced sensors with an ADC frequency of 100 kHz, signals of intensity fluctuations of the laser beam passing through the flame were recorded. Using the FFT, we calculated the pulsation spectra of the intensity of laser radiation. The 2D dependences of the parameters of the temporary spectral functions were obtained: the coordinates of the maxima and the tangent in the low frequency and two slopes in the high frequency range region are determined.
Data are presented about the variations in the average power of lidar echo signals with coherent and incoherent receiving over wide range of variations of the refractive turbulence strength in the atmosphere. It is established that in the case of incoherent receiving the backscatter amplification coefficient first increases with increase of the turbulence strength, then saturates at a certain level in the regime of strong turbulence on the probing path and decreases with further refractive turbulence strength increase. The maximum value of the amplification coefficient achievable at a given distance depends on the refractive turbulence strength at the moment of measurement. The time course of the backscattering amplification coefficient is in a good agreement with the temporal changes of the structural constant of turbulent fluctuations of the air refractive index, determined from independent measurements.
On a laboratory scale, a vertical tornado-like flame with a height of up to 1 m and a diameter of the order of 0.05 m was investigated. A laser remote sensing of this flame at several altitudes was carried out. Fluctuations of the self-radiation of the flame in the visible range were recorded at these heights. We calculated the spectral functions of the intensity fluctuations for the probing laser beam and for the fluctuations of the self-radiation of the flame. For these spectral functions, the height dependences of the coordinates of the maxima and the coefficients of the tangent in the highfrequency region are determined.
We investigated the fire whirl model obtained in a laboratory scale. The results of the IR camera application are presented. The spectral function of temporal fluctuations of the thermal imaging signal was calculated. We compared the spectral maximum with the rotational speed of the impeller. We have calculated the distribution of the spectral maxima in the flame of the fire whirl model. The probability of a correct determination of the rotation frequency of the torch from the spectral maximum depends essentially on the rotational speed.
We investigated the vertical tornado flame obtained in a laboratory experiment. The results of laser sensing of the flame at several altitudes. Calculated spectral function of intensity fluctuations of a laser beam. For these functions are set depending altitude slopes in the high-frequency region.
Formation of model fire tornadoes is studied experimentally in laboratory environment. A fire vortex is formed by
swirling the gas flow coming from a burning liquid, with the help of a rotating disc under it. The conditions favoring
formation of a stable fire vortex as well as some volumetric and temperature characteristics are found.
Spectrum for smoke absorption factor over the range of 0.28 ÷ 6.5 microns is presented. Measurements were carried out in the model local forest fire at natural convection without a wind. Absorption lines of water vapor (bands of I .8 and 2.7 microns) and carbonic gas (band of 4.3 microns) were identified in the spectrum. It was shown, that the concentration in smokes at the rear of fire front increased by a factor of 1 .5 ÷ 2 for water vapor, and up by a factor of 3 for carbonic gas in comparison with initial concentration in the clean medium.
Experimental results on forest combustibles (FC) burning are treated in the paper. The relations V equals V0exp(-W2/W02) are proposed to describe the dependence of the burning front movement velocity on the humidity W (V0 equals 3 mm/s is the velocity of the burning front movement for dry FC). Maximum radiation temperature of the condensed phase burning within the range of the 3 to 12 micrometers , reconstructed by the blackbody radiation law at the radiation coefficient (epsilon) of 1, is 800 - 900 K for dry needles of pine and cedar. The higher is humidity, the lower is the maximum radiation temperature.
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