Large-eddy Simulation of Variable Density Flows

A fully compressible direct numerical simulation flow and combustion solver (S3D) is modified and turned into a Large-eddy simulation (LES) solver. In this study, Favre-averaged governing equations are formulated first, supplemented with the classical Smagorinsky model and the dynamic procedure. To simulate low-Mach number flows, the speed of sound is artificially reduced while preserving the zero-Mach number physics. This pseudo-compressibility method is called Acoustic Speed Reduction (ASR). With ASR, the code has the capability to compute low-Mach number flows in an efficient way. The boundary conditions in S3DLES are based on a one-dimensional characteristic analysis. To stabilize the solution, a buffer layer treatment is introduced at outflow boundaries to reduce acoustic reflections. The resulting flow is stable and produces results that compare well with a reference study. The implementation of the Smagorinsky model and other sub-models are validated using published plane jet simulation results with well-defined flow and perturbation conditions. A second test case is the simulation of a round thermal plume. The ASR method is adopted to increase the computational efficiency by a factor of at least 10, thus making the computation of a 3-D round plume feasible on a small-scale cluster. A third configuration is the simulation of a saltwater plume that was studied experimentally at UMD and is analog to a gaseous thermal plume. A comparison methodology between saltwater and gaseous plumes is developed. It is found that the computational requirement of a configuration that includes both the near- and far-field remains large and grid-resolution in our simulations remains marginal. The fourth and last simulation takes advantages of the compressible flow formulation and considers flow-acoustic-interactions as a part of a thermoacoustic study. Three streams of different densities and momentums are introduced into a wall-confined domain. The flow is acoustically excited by an acoustic driver. The amplitude and phase of the driver are controlled. The high frequency modal response of the chamber compares well with experimental results. A variety of numerical tests in 1D, 2D and 3D configurations reveal the mechanism of transverse resonance and the resulting flow-acoustic interactions. This suggests that S3DLES will be a good prediction tool for future combustion noise and combustion instability studies. Overall, the series of tests presented in this work serve to document the strengths and weaknesses of the current version of S3DLES

Burning Rate of Liquid Fuel on Carpet (Porous Media)

Research paper published in the journal Fire Technology 2004The occurrence of a liquid fuel burning on carpet has been involved in many incendiary and accidental fires. While the research on a liquid fuel fire on carpet is still limited, much work on porous media has been performed using sand or glass beads soaked with liquid fuel. In this study, a heat and mass transfer theory was first developed to analyze the burning process of liquid on carpet, and then several small-scale tests were performed to validate the theory. This analysis is valid for pool fires intermediate in size (5-20 cm. in diameter). The experimental apparatus consisted of a circular pan (105mm) and a load cell. Varying amounts of fuels (heptane, kerosene and methanol) were spilled onto the carpet, which was allowed to burn in a quiescent environment. It was found that due to the different controlling mechanisms, the liquid burning rate could be less or more than that of a similarly spilled free-burning pool fire. For the worst-case scenario in fires, the maximum enhancement of the burning rate due to the porous media is predictable through the physical properties of the fuel. This analysis is valid for both combustion and evaporation. Several similar results in the scientific literature are analyzed to further describe the trend. This work explains the role of carpet in liquid pool fires and also helps to explain special risks related to the presence of carpet involved in arsons and will be useful in reconstruction of the early development of an incendiary or accidental fire

Ignitability and explosibility of gases and vapors

The book provides a systematic view on flammability and a collection of solved engineering problems in the fields of dilution and purge, mine gas safety, clean burning safety and gas suppression modeling. For the first time, fundamental principles of energy conservation are used to develop theoretical flammability diagrams and are then explored to understand various safety-related mixing problems. This provides the basis for a fully-analytical solution to any flammability problem. Instead of the traditional view that flammability is a fundamental material property, here flammability is discovered to be a result of the explosibility of air and the ignitability of fuel, or a process property. By exploring the more fundamental concepts of explosibility and ignitability, the safety targets of dilution and purge can be better defined and utilized for guiding safe operations in process safety. This book provides various engineering approaches to mixture flammability, benefiting not only the safety students, but also field operators, as a useful resource for the safe handling of flammable gases and liquids. It will be useful to anyone who worries about the ignition potential of a flammable mixture

The Behavior of Liquid Fuel on Carpet (Porous Media): A Case for the Inclusion of Science in Fire Investigation

Flammable liquid fuel spills on flooring including carpets and other porous materials have long been a subject of interest to the fire investigation community. Early understanding in this community about the indicators of a liquid fuel fire, such as holes in flooring material or heavy burning in this area, have been shown to be incomplete. Research from the past two decades have enabled fire investigators to identify burn patterns from liquid fuel pours, estimate the evaporation and mass burning rates of the liquid fuel on the carpet, and be able to test the carpet forensically to determine if the fuel was present during the fire or was introduced by post-fire contamination. These science-based tools have enabled fire investigators to tackle a seemingly simple fire problem and have aided in fire origin and cause determination. The authors believe that the type of work that has been undertaken on liquid fuels on carpet and flooring should be conducted for many other problems in fire investigation to give fire investigators as many scientific tools as possible. These tools should be taught in the framework of education instead of as simple rule of thumb training. As this is done, the fire investigation industry will advance as a whole