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Numerical investigations of missles acceleration by hydrogen explosion

Efimenko A.A., Denkevits A.V., Dorofeev S.B., Breitung W.

Archivum Combustionis

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1998

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Vol. 18 nr 1-4

47-73

EN

Combustion, deflagration, and detonation of combustible gas mixtures are possible in the course of industrial accident. This leads to generation of intense gas flows. Equipment and some parts of construction can be accelerated by these flows and form hazardable missiles. Interaction of the missle with the gas flow was studied numerically by means of three-dimensional gas-dynamic computer code. aerodynamic tube was modelled in which missles of different schape were inserted in supersonic gas flow. Mach number and specific heat ratio of the flow as well as missile's orientation with respect to the flow were varied. Dependences of drag coefficient of missiles on Mach number and specific heat ratio under conditions typical for industrial accidents were evaluated. They are presented together with distributions of parameters of the gas flow around missile. It was shown that dependence of drag coefficient on specific heat ratio of the gas is not steep and may be omitted in evaluation of missile hazard. the method which is used in evaluation of drag coefficients is based on direct numerical simulation of hydrodynamics of the gaseous flow. it can be applied to obtain the extact values of drag coefficients under various conditions. The data on drag coefficient values give way to application of the computer code, in which drag coefficient model of missile-flow interaction was implemented. This code is capable to model gas flows, subsequent pressure loads, and missiles' motion in case of detonation or explosion of combustible gas mixture. Drag coefficient model used in the code assumes that missiles are much smaller than characteristics size of the flow. Hence it limits applicability of this code to the case of large scle detonations. However, hazardable missiles can be expected in case of smaller scale, i.e. local detonations. Direct simulations of missile acceleration were performed under the following conditions. Compartment of 8 by 6 2.2 m size was filled with stoichiometric hydrogen - air mixture. Detonation was ignited at the centre of the shorter wall. A part of the opposite wall (2.2 by 1.2 m) could move freely under the pressure stress from detonation wave and form the missile. In five tests the wall thickness, missile thickness and its mass were varied. Resulting missiles' velocities, distributions of gas flow parameters, and pressure loads are presented. Results of these numerical tests give the data on the missile velocities and momenta in some typical cases. Scaling relationships are proposed. The results of numerical tests and scaling relationships provide the estimation of velocities and momenta of missiles that are possible under accidental conditions.

2

Influence of initial temperature, dilution and scale on DDT conditions in hydrogen - air mixtures

Sidorov V.P., Dorofeev S.B.

Archivum Combustionis

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1998

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Vol. 18 nr 1-4

87-103

EN

Results of large scale experiments on deflagration to detonation transition (DDT) in hydrogen - air - stream mixtures at elevated temperature are presented. The objectives of the tests were (1) study of conditions for DDT at large scale, (2) evaluation of DDT scaling criteria for steam diluted hydrogen - air mixtures at elevated initial temperatures. Experiments were carried out in the RUT facility, Russia. Total volume of mixture was about 480 m3. Inner volume of the facility was preheated by specially designed heating system in tests with steam. Initial gas temperature inside the facility was 370-380 K. Ignition was made by weak electric spark. The combustion modes observed include shock-less (slow) deflagration, fast turbulent deflagration, and DDT. Onset of detonations was observed either in the obstructed channel, or in the largest compartment of the enclosure. Results of the present tests were comapred with tests carried out in the same facility at normal initial temperature (285 K) with hydrogen - air mixtures. Critical conditions for DDT were analysed in terms of the detonation cell size as a measure of mixture sensitivity to detonation initiation. Avaible measured data on detonation sell sizes for different initial conditions and hydrogen - air - steam mixture compositions have been approximated by an analytical function. This function was used to estimate detonation sell size for mixtures within composition range where the measured data are not avaible. It was shown that the compositions with the cell size close to 1 m are the critical compositions for DDT in the RUT facility. The critical compositions expressed in terms of detonation cell size appeared to be very similar in hydrogen - air DDT experiments at 285 K, and in hydrogen - air - steam tests at 375 K in the same facility.

3

Blast wave interactions with burning cloud of fuel sprays

Kuznetsov M.S., Dorofeev S.B., Alekseev V.I., Abyzov M.M.

Archivum Combustionis

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1998

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Vol. 18 nr 1-4

7-20

EN

Experimental results on the interaction between blast wave and burning cloud of fuel spray in air are presented. The objective of the work was to study evoluation of blast wave parameters as a result of pressure wave interaction with burning heterogeneous fuel-air cloud. Experiments have been performed with gasoline (B 70), kerosene (Jet A), and diesel fuel. Unconfined clouds were produced by the liquid fuel dispersing through split nozzles mounted on the horizontal tube. Amount of a fuel was about 100-110 kg in the testes. Aerosol clouds had semi cylindrical shape and their volume was about 1000 m3 (up to 7.5 m in radius, 15-20 m in length). Spray clouds were ignited by a distributed ignition source (an elastic HE charge of 16 m in length) located along the cloud on the height of 1.5 m above the ground. Blast wave was generated by a HE charge (0.35-10 kg), located outside the cloud. Time delay between the cloud ignition moment and the external blast wave initiation was varied from 0.02 to 1.0 s. Piezoelectric pressure transducers were used to record shock propagation. Pressure transducers were placed along two perpendicular directions from the HE charge. Blast wave overpressure and impulse as functions of distance from explosion origin were studied in cases with and without influence of burning cloud. It was found out that interaction of the air blast wave with the burning cloud is able to change parameters of the blast wave significantly. In addition to decreased decay rate of blast intensity with distance, amplification of intensity of the blast wave inside the clouds was observed. The effect of amplification was found to be very sensitive to the time delay between cloud ignition and blast-cloud interaction, and to the fuel type. Possibility of blast wave parameters changes due to interactions with burning clouds may be important for analyses of the blast effect of accidental explosions.