Abstract

Turbulence can be observed in almost all the smoke videos, so turbulence parameters can be extracted as features of smoke in the video smoke detection system. A video-based turbulence parameter measuring method is proposed in this paper. Turbulence can be regarded as a series of irregular flow states with instantaneous velocity fluctuations. First, the instantaneous turbulent velocity field is obtained from the real-time video using an optical flow method, and based on the velocity field information, the turbulence kinetic energy (TKE) and dissipation rate are calculated using large eddy simulation and sub-grid scale (SGS) models. Three different methods, Smagorinsky model, gradient model, and dimensional analysis, are used to obtain the dissipation rate. The results obtained using different methods are compared. The dissipation rate estimated using the SGS models shows high consistency and that estimated by the dimensional analysis has a similar distribution, which shows that the choice of the SGS model is not important for the dissipation rate estimation. Then the TKE is calculated, and the processed images show that each plume structure has its own life cycle and the rising velocity of each plume structure is steady. This method is efficient for the plume turbulence measurement, and it provides benefits to the experimental study of fire plumes. Furthermore, the measured parameters can be analyzed for video-based fire detection. It is a useful method in both scientific research and industrial development.

Highlights

  • In the study of fire plumes, many physical parameters have been discussed and mentioned, such as temperature, velocity, flame height, air entrainment, and puffing frequency.1 In addition, the scitation.org/journal/adv turbulence behavior of fire plumes is another important aspect in the study

  • This paper presents a new method for the fire plume turbulence measurement

  • The estimation results obtained using three different methods show a high level of consistency, which demonstrates the efficiency of the video-based turbulence measurement for the experimental study of smoke movement

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Summary

INTRODUCTION

Scitation.org/journal/adv turbulence behavior of fire plumes is another important aspect in the study. The measurements and analysis were all on the sampling points so that the parameters of the subtle field distribution cannot be obtained Another notable non-intrusive measurement method, PIV (Particle Image Velocimetry), was proposed on the root of laser speckle velocimetry. With the development of digital image acquisition technology and computer vision technology, the velocity field information of a fire plume video can be obtained using the optical flow method.. A two-dimensional (2D) velocity field is obtained, and the LES method is used to estimate the TKE and turbulence dissipation rate of the smoke regions. The estimation results obtained using three different methods show a high level of consistency, which demonstrates the efficiency of the video-based turbulence measurement for the experimental study of smoke movement. With the derived relationships between the image coordination and the world coordination, the actual velocity information of the smoke turbulence can be obtained

Velocity field calculation using the optical flow algorithm
Velocity calibration in smoke videos
ESTIMATION OF THE TURBULENCE PARAMETERS
Analysis of the video velocity data
Dissipation rate estimation using the large eddy method
SGS stress calculation using the Smagorinsky model
SGS stress calculation using the gradient model
Turbulence dissipation and dimensional analysis
Turbulence kinetic energy
EXPERIMENT AND DISCUSSION
CONCLUSIONS
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