Influence of gas compression on flame acceleration in the early stage of burning in tubes

The mechanism of finger flame acceleration at the early stage of burning in tubes was studied experimentally by Clanet and Searby [Combust. Flame 105: 225 (1996)] for slow propane-air flames, and elucidated analytically and computationally by Bychkov et al. [Combust. Flame 150: 263 (2007)] in the limit of incompressible flow. We have now analytically, experimentally and computationally studied the finger flame acceleration for fast burning flames, when the gas compressibility assumes an important role. Specifically, we have first developed a theory through small Mach number expansion up to the first-order terms, demonstrating that gas compression reduces the acceleration rate and the maximum flame tip velocity, and thereby moderates the finger flame acceleration noticeably. This is an important quantitative correction to previous theoretical analysis. We have also conducted experiments for hydrogen-oxygen mixtures with considerable initial values of the Mach number, showing finger flame acceleration with the acceleration rate much smaller than those obtained previously for hydrocarbon flames. Furthermore, we have performed numerical simulations for a wide range of initial laminar flame velocities, with the results substantiating the experiments. It is shown that the theory is in good quantitative agreement with numerical simulations for small gas compression (small initial flame velocities). Similar to previous works, the numerical simulation shows that finger flame acceleration is followed by the formation of the "tulip" flame, which indicates termination of the early acceleration process.Comment: 19 pages, 20 figure

Hydroacoustic methods and tools for fish stock assessment and fishery maintenance Part 2. Methods and tools of fishery biohydroacoustics

Studies on influence of hydroacoustic fields on behaviour of commercial species and using of hydroacoustic tools for management of fish and squids behavior to increase the fishing efficiency are overviewed. The methods and means of fisheries biohydroacoustics are considered critically and the reasons of their unsatisfactory using in fishery are analyzed. Sounds with a certain spectrum and level are still applied for influence on fish behaviour without sufficient scientific and technical substantiation, so a complex approach to development of effective hydroacoustic tools for remote control of fish movement is necessary. Results of studies on acoustic reception and acoustic activity for schooling physostomous fishes are presented. Spectral-power and temporal parameters of the sounds and their frequency differentiation by fish size are determined. Sound-generating mechanisms of fish are considered and signal significances of the sounds radiated by fish are recognized. Stereotypes of acoustic behaviour are revealed for toothed whales during their hunting upon fish: these predatory cetaceans have special acoustic manipulators able to generate signals for concentration and holding the fish, adapted for hearing system of the prey. Results of hydrobionic modelling of organs and mechanisms for sound generation of marine animals and their technical realization in hydroacoustic devices are presented. The developed devices allow to generate underwater pulse sound signals simulating biological signals of certain physostomous fish species and predatory cetaceans (dolphins and killer whales). Efficiency of these simulating signals influence on behaviour of fish is proved by behavioral experiments and fishing tests. Applications of these devices for various fisheries are discussed