arXiv subjects

A. Markhotok

Publications and source records attributed to A. Markhotok.

4 recordsLinked to original sources

arXiv2020

Cumulative energy effect in the shock-discontinuity interaction under real-gas conditions

A recently proposed technique for improving ignition timing is investigated for real-gas effects. A correction to the model describing the cumulative energy effect in the presence of the shock-discontinuity interaction was done by re-considering the RH-relations and the shock refraction equations. Non-dissociating gas in thermal equilibrium state, with excited translational, rotational, vibrational, and electronic degrees of freedom is considered. When applied to N2 gas at T=3000 K, 11% density increase and 17% temperature and 7% pressure jump decrease were found, compared to that in ideal gas. The derived relations are largely built on experimental data thus avoiding the complexity of careful accounting for all real gas effects and still offering satisfactory precision levels. The main result is that in real gases the effect in the interaction can be stronger than that in an ideal gas. The findings can be of interest in design of efficient combustors for hypersonic systems, detonation, space and craft design, shock-flame interaction, in astrophysics, and fusion research.

physics.flu-dyn↗

arXiv2017

A shock wave instability induced on a periodically disturbed interface

The shock wave instability induced when interacting with a small waviness on an interface was investigated analytically and numerically. The perturbation to the shock was phenomenologically treated assuming this as the consequence of the shock refraction. The instability develops in the form of wave-like stretchings into the lower density medium followed with the loss of stability in the flow behind it, and eventually evolving into an intense vortex structure. The instability mode is aperiodical and unconditional, and either a transition to another stable state or continuous development as a secondary flow is possible. Among other interesting features are: a similarity law in the spatial and temporal evolution of the perturbations with respect to the interface curvature; the instability locus independence of the gas density distribution thus identifying the interface conditions as the sole triggering factor; the role of the density gradient in the instability evolution discriminating between qualitatively different outcomes; and the possibility of decay via non-viscous dumping mechanisms. The phenomenological connection between the shock and the interface stability is discussed.

physics.flu-dyn↗

arXiv2017

A mechanism of vortex generation in a supersonic flow behind a gas-plasma interface

The origin of a vortex structure generated during the shock-plasma interaction is investigated. A two-dimensional model based on the shock refraction mechanism successfully unifies the vortex generation with major co-processes typical for the interaction and thus well fits in their cause-and-consequence relationship. Numerical simulations demonstrated the possibility of an intense vortex generation with a continuous positive dynamics as the shock crosses the interface. It was shown that while the vorticity is triggered by the shock refraction on the interface, it is the gas parameter distribution that distinctively determines the parameters of the vortex evolution. The proposed model also provides an insight into interesting aspects of the refraction effects for both, the shock wave and the flow behind it (double refraction). The results are applicable to the problems of energy deposition in a hypersonic flow, a flame-shock interaction, in combustion, in astrophysics, and in the fusion research.

physics.flu-dyn↗

arXiv2005

Precision measurement of light shifts in a single trapped Ba$^+$ ion

Using a single trapped barium ion we have developed an rf spectroscopy technique to measure the ratio of the off-resonant vector ac Stark effect (or light shift) in the 6S_{1/2} and 5D_{3/2} states to 0.1% precision. We find R = Delta_S / Delta_D = -11.494(13) at 514.531 nm where Delta_{S,D} are the light shifts of the m = +/- 1/2 splittings due to circularly polarized light. Comparison of this result with an ab initio calculation of R would yield a new test of atomic theory. By appropriately choosing an off-resonant light shift wavelength one can emphasize the contribution of one or a few dipole matrix elements and precisely determine their values.

physics.atom-ph↗