Ilya Semenov

Numerical and Experimental Investigation of Detonation Initiation in Profiled Tubes

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 ± 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.

Towards understanding the physics of supersonic jet screech

Jet flows have been a subject of intensive theoretical, numerical, and experimental investigations during last several decades. Many fluid dynamicists and specialists in computer simulations have endeavored to learn more about very complicated structures in jet flows. This interest have been in the first turn feeding by the desire to understand basic mechanisms of strong noise generated by high-speed jets, in particular very intense tones known as jet screech.

Initiation of detonation in a tube with parabolic contraction and conic expansion

On the basis of results of two and threedimensional numerical simulation, we proposed for the firsttime to use the profiling of axisymmetrictube walls inthe shape of parabolic contraction and conic expansion for initiating the detonation by means of a relatively weak shock wave. The detonation initiationmechanism is revealed, and its basic stages are analyzed. For simulating the propane–air mixture, wefound the paraboliccontraction shape and selectedthe conicexpansion parameters providing the initiation of detonation for the Mach number of an originalshock wave equal to 2.65.According to the theoretical results of V.P. Korobeіnikov, V.A. Levin, and V.V. Markov, the externaldisturbance of a reacting flow can become the cause offormation of a selfsustained detonation [1, 2]. Thesedisturbances can result in substantially nonlinearoscillatory processes due to the instability of the exothermicreaction front. Apparently, only detailednumerical experiments can provide the solution of theproblem under consideration on detonation initiationand indicate ways of its practical realization.Two processes at which the detonation wave can begenerated are wellknown and used in practice; theseare the direct initiation [1] and deflagrationtodetonation transition [3]. In [4] we proposed, investigated,and justified an original approach to shock detonationinitiation with the help of a regular shaped obstacles inplanar channel in which the leading shock wave(LSW) propagates. On the basis of numerical investigations and experiments, we showed that the regularparabolic structure of walls of the channel makes itpossible to reduce considerably the time and the distance before detonation initiation in comparison withthe wall structure in the shape of rectangular irregularities. The subsequent numerical investigation of theshocktodetonation transition (SDT) in an axisymmetric tube with the geometry of the walls investigatedin [4] for the planar case showed that for the Machnumbers in the initiating shock wave (ISW) importantfrom the viewpoint of practical applications, the process differs from that in the planar channel. It provedto be that the local explosion occurs in the region offocus of already the first parabolic element of thestructure instead of in the vicinity of the fifth one asoccurred in [4] for