Initiation of gaseous detonation in tubes with sharp U-bends (original) (raw)
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Numerical and experimental investigation of detonation initiation in profiled tubes
Combustion Science and Technology. – 2010. – V. 182, № 11 – 12. – P. 1735 – 1746., 2010
Detonation initiation in a tube with parabolic contraction and conical expansion was investigated numerically and experimentally. The optimized geometry of conical expansion with sine-shaped wall is proposed. The generalized diagram in the form of detonation curves at the contraction slope angle versus incident shock Mach number plane is presented. For solving the governing Euler equations, the numerical method based on finite volume approach with Godunov flux approximation adapted for multiprocessor systems is used. It has been shown experimentally that the parabolic contraction and conical expansion ensure shock-to-detonation transition in a stoichiometric propane-air mixture under normal conditions at a very low minimal incident shock wave velocity of 680 AE 20 m/s, which approximately corresponds to a Mach number of 2. This result is important for novel jet propulsion systems with detonative burning of fuel-pulse detonation engines.
Detonation Transition in Relatively Short Tubes
30th International Symposium on Shock Waves 1. Springer, Cham. Pages 481-485, 2017
Experimental data and numerical simulations on flame acceleration, shock-flame interaction and deflagration-to-detonation transition mechanism for stoichiometric hydrogen-oxygen mixtures at reduced pressure in relatively short tubes have been analysed. It was shown that the detonation occurs as a result of multiple reflections of precursor shock wave and its interaction with the flame. Adiabatic compression and heating of unreacted gas a front of the flame together with flame surface increase due to the Richtmyer-Meshkov instability provide preconditioning of the DDT process. Several times higher pressure, temperature and reaction rate within a preconditioning zone leads to significant decrease of run-up-distance to DDT in relatively short tubes. Results of the work will provide detailed information on multiple shock - flame interactions leading to the DDT process for numerical code validations.
Numerical simulation of detonation initiation in a contoured tube
Combustion, Explosion, and Shock Waves. – 2009. – Vol. 45, No. 6. – P. 700 – 707., 2009
The effect of the wall contours in an axisymmetric tube on the transition from the shock wave to the detonation wave is studied numerically. Qualitative features and quantitative characteristics of the detonation initiation mechanism realized in a tube with a parabolic segment of the wall contour and conical expansion are found. The calculated results are presented in the form of "detonation curves" (angle of inclination of the contoured segment versus the Mach number of the initial shock wave) for various levels of tube blockage ratio.
Initiation of detonation in a tube with parabolic contraction and conic expansion
Doklady Physics. – 2010. – Vol. 55, No. 3. – P. 150 – 154., 2010
On the basis of results of two and three dimen sional numerical simulation, we proposed for the first time to use the profiling of axisymmetric tube walls in the shape of parabolic contraction and conic expan sion for initiating the detonation by means of a rela tively weak shock wave. The detonation initiation mechanism is revealed, and its basic stages are ana lyzed. For simulating the propane-air mixture, we found the parabolic contraction shape and selected the conic expansion parameters providing the initia tion of detonation for the Mach number of an original shock wave equal to 2.65.
Initiation of heterogeneous detonation in tubes with coils and Shchelkin spiral
High Temperature, 2006
The possibilities of significant reduction of the critical energy of initiation of detonation in sprays of liquid hydrocarbon fuel in air are demonstrated experimentally. The structure developed for the purpose includes a tube of near-limiting diameter and a combination of Shchelkin spiral, tube coils, and reducing cones for transitioning a detonation wave to a tube of large diameter.
Numerical Investigation of Detonation Wave Propagation in Pulse Detonation Engine with Obstacles
SSRN Electronic Journal, 2019
The numerical investigation of Detonation wave propagation and Deflagration-to-Detonation transition is done in straight long tube of 1200 mm length and 60 mm internal circular diameter with stoichiometric (ϕ=1) mixture of hydrogen-air at ambient pressure and temperature of 0.1 MPa and 293 K respectively. The detonation tube contains obstacles having blockage ratio (BR) 0.5, 0.6 and 0.7, and having 60 mm gap among them. The computation analysis is performed firstly on simple straight tube having no obstacle (BR=0.0) and then obstructed channel. The combustion phenomena of fuel-air mixture are modeled by one-step irreversible chemical reaction model. Three-dimensional Navier-Stokes equations along with realizable k-ɛ turbulence model are solved by the commercial computation fluid dynamics software ANSYS Fluent-14 code. The performance of pulse detonation engine (PDE) depends on blockage ratio (BR) of obstacles. The simulation results show that the initiation and propagation of flame is due to exothermic expansion of hot combustion gases. The obstacles generated turbulence at obstacle wakes, which caused to increase flame surface area. Therefore, obstacles reduced the Deflagration-to-Detonation transition (DDT) run-up length. The perturbation inside the combustor increases as increased the blockage ratio of obstacle. The PDE Simulation results of with and without obstacles were analyzed and compared with adiabatic flame temperature.
Physics of Fluids, 2020
In the present work, using a high-resolution three-dimensional numerical analysis the initiation and propagation mechanism of a detonation wave is studied in a circular tube with a hot jet initiation. The reactive Euler equations with a one-step two-species chemistry model are solved based on the structured adaptive mesh refinement technique. Influences of both a single hot jet and impinging double hot jets on the formation of the detonation wave are studied. For each case, the objective is to investigate the role of the tube wall on the initiation and propagation of the detonation wave. The result for both cases shows that the hot jet-induced bow shock forms a complex reflection structure in the circular tube. The reflection effect of the circular wall strengthens the shock and facilitates the formation of the Mach stem, which leads to the formation of the detonation wave. However, when the hot jet condition and the total area of jet hole remain the same, for the case of initiation using double hot jets, the reflection strength of the bow shocks weakens when the diameters of the hot jets become smaller. When using a single hot jet, the initiated detonation is overdriven and propagates in the twoheaded mode. In this initiation mode, by increasing the inflow Mach number, a four-headed mode detonation front is formed. While in the case of impinging double hot jets, a four-headed mode detonation front is initiated directly.
Investigation of Transition of Deflagration to Detonation in Moving Mixtures of Combustible Gases
In the report the new experimental data about essential reduction of predetonation distance are presented in the case of detonation initiation with an weak electric discharge in a detonable gas flow. Experiments were done at the device, which allows modeling one cycle of pulse detonation engine operation. The experimental data are compared to the results of numerical calculations. The good consent with experiments demonstrates feasibility of the offered methods of calculations and allows to give explanation to the observed experimental effects. The results seem to be of practical application to the control of detonation process in PDE.