A two-dimensional contraction channel with a theoretically designed concave-oblique-convex wall profile is proposed to obtain a smooth planar-to-planar shock transition with shock intensity amplification that can easily overcome the limitations of a conventional shock tube. The concave segment of the wall profile, which is carefully determined based on shock dynamics theory, transforms the shock shape from an initial plane into a cylindrical arc. Then the level of shock enhancement is mainly contributed by the cylindrical shock convergence within the following oblique segment, after which the cylindrical shock is again "bent" back into a planar shape through the third section of the shock dynamically designed convex segment. A typical example is presented with a combination of experimental and numerical methods, where the shape of transmitted shock is almost planar and the post-shock flow has no obvious reflected waves. A quantitative investigation shows that the difference between the designed and experimental transmitted shock intensities is merely 1.4%. Thanks to its advantage that the wall profile design is insensitive to initial shock strength variations and high-temperature gas effects, this method exhibits attractive potential as an efficient approach to a certain, controllable, extreme condition of a strong shock wave with relatively uniform flow behind.

A convergent channel method is applied to create an imploding arc shock as a partial representative of an overall cylindrical shock. The self-ignition phenomenon induced by such an imploding shock is investigated experimentally and numerically. Agreements between experimental and numerical results are widely reached not only for the shock imploding process but also for shock reflection and features of self-ignition, which approves the validity of the method. The induced self-ignition is found to lag behind the incident shock front and experience a shockless spontaneous process before the onset of detonation. The mechanisms are briefly addressed.

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