E. Ya. Kogan

Numerical modeling of precessing vortex core in the presence of local heat sources

Based on the results of numerical simulation of a nonstationary, nonaxisymmetric turbulent swirling gas flow in a tube with local sources of heat release, it is shown that a precessing vortex core (PVC) appears at supercritical values of the swirl parameter as a result of the development of instability of a left-handed bending mode. The dependence of the PVC frequency on the mass flow rate of the gas and the heat-source power has been studied. As the heat-source power increases, the frequency of precession grows while the amplitude of vortex core oscillations drops.

Sound waves in a nonequilibrium molecular gas

We consider relaxation processes of dynamics of a nonequilibrium vibrationally excited gas (Tv>T0). It is shown that the effective heat capacities can become negative in such a medium. This leads to anomalous effects during propagation of long-wave sound: there exist regions (in the parameter Tv/T0) of sharp enhancement and reduction of its speed, as well as regions where low-frequency sound can generally not propagate. Instability conditions are investigated for various temperature dependences of vibrational relaxation times. It is shown that in a certain region of Tv/T0 values one has amplification of sound waves, related to the formation of second viscosity in these media. In this case a change in the amount of medium nonequilibrium can vary the sound frequency corresponding to maximum amplification.

The Influence Of Vibrational Energy Relaxation On Laminar‐Turbulent Transition

The stability of vortical disturbances propagating at an angle to the main flow in a nonequilibrium compressible supersonic boundary layer has been investigated. The dependences of the critical Reynolds number on the degree of nonequilibrium and on the Mach number were defined at different angles of wave propagation. It was calculated the time of explosive instability, which realized on stage of nonlinear critical layer. The increment of secondary instability versus degree of non‐equilibrium S and amplitude of primary equilibrium solution was founded.

Heterogeneous processes affect the hydrodynamic resistance of a surface streamlined by a nonequilibrium gas flow

A mechanism responsible for a decrease in the turbulent friction of bodies moving in (or streamlined by) a vibrationally-nonequilibrium gas flow is proposed. Heating of the gas in the immediate vicinity of the surface as a result of heterogeneous relaxation may decrease the transverse velocity gradient and reduce the friction resistance coefficient.

The attenuation of shock waves in a nonequilibrium gas

The evolution of weak shock waves in nonequilibrium gas media with fluctuating parameters is investigated. Two-dimensional nonlinear, evolution equations are derived for the averaged parameters of an acoustic field induced by a body in a supersonic flow of active medium. A possible mechanism of reduction of the amplitude and broadening of the front of weak shock waves in nonequilibrium gas media is discussed.

Mechanism of breakdown development in a gas in a subthreshold HF field

The development of a breakdown wave in subthreshold HF fields is considered for the condition that the field energy density exceed the plasma energy density E2/4π > nT. It is shown that the breakdown wave propagation mechanism is controlled by HF diffusion with a coefficient μiE2/4πen. A model of breakdown development along the direction of the linear field polarization is constructed on the basis of this mechanism.