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Title: Development of the shock wave structure ahead of an impulively accelerated piston

Description: The temporal evolution of the density, velocity, and temperature field ahead of an impulively accelerated piston moving at 1000 m/s. The fluid is dense nitrogen (370 kg/m^3, 300 K, 42 MPa). The camera moves to the right together with the shock wave with velocity of 1976 m/s. It thus appears as if the piston moves to the left, whereas in fact it moves to the right into the fluid.

All quantities are normalized with respect to their pre- and post-shock values such that zero corresponds to the pre-shock state, and unity, to the post-shock state.

The piston in this Molecular Dynamics simulation is modeled as a cubic-face-centered lattice, which explains the oscillations in the density at t=0. The dashed lines show the eventual steady state profile, including the overshoot of the shock-normal temperature component. The shock thickness based on the steepest density gradient is 7.3 Angstrom. As is normal in dense fluids, this is thicker than one would expect in dilute fluids (relative to the mean free path) at the same Mach number. Likewise, the density ratio across the shock is only 2, whereas it would be 4.3 in a perfect gas.

Credits: Stefan Schlamp and Bryan C. Hathorn

References: [1] Schlamp, S., Hathorn, B. C. (2006) "Molecular orientation in shock waves," Physics of Fluids 18(9):096101.
[2] Schlamp, S., Hathorn, B. C. (2007) "Higher moments of the velocity distribution function in shock waves in dense fluids," Journal of Computational Physics 223(1):305-315.
[3] Schlamp, S., Hathorn, B. C. (2007) "Incomplete molecular chaos in shock waves," Physical Review E 76(2):026314.
[4] Schlamp, S., Hathorn, B. C. (2008) "Atomistic phenomena in dense fluid shock waves," Shock Waves, 17(6):397-407.

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Contributed By: Stefan Schlamp

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