Том 52, № 6 (2017)

The article describes the unsteady motion of viscoelastic fluid for a Maxwell model with fractional derivatives. The flow is produced by cylinder, considering time dependent quadratic shear stress ft² on Maxwell fluid with fractional derivatives. The fractional calculus approach is used in the constitutive relationship of Maxwell model. By applying Laplace transform with respect to time t and modified Bessel functions, semianalytical solutions for velocity function and tangential shear stress are obtained. The obtained semianalytical results are presented in transform domain, satisfy both initial and boundary conditions. Our solutions particularized to Newtonian and Maxwell fluids having typical derivatives. The inverse Laplace transform has been calculated numerically. The numerical results for velocity function are shown in Table by using MATLAB program and compared them with two other algorithms in order to provide validation of obtained results. The influence of fractional parameters and material constants on the velocity field and tangential stress is analyzed by graphs.

The results of an experimental investigation of the penetration of vertical plane and round free turbulent jets through the surface of a liquid contained in a relatively narrow channel are presented. It is established that there exist the ranges of jet thicknesses, their velocities, and free region lengths, on which regular self-oscillatory regimes of the displacement of submerged jet regions and two-phase flow regions are observable. The mechanism of the generation of these regimes and the special features of the observable flows are discussed. The dependences of the self-oscillation periods on the main control parameters of the problem are established.

The fields of turbulent near-wall pressure fluctuations in the vicinities of cylindrical bodies mounted orthogonal to the surface in a flow are experimentally investigated. The considerable inhomogeneity and three-dimensionality of the pressure fluctuation field in the measurement area is shown. The dependence of the main characteristics of the inhomogeneous pressure fluctuation field on geometric parameters is presented. A weak influence of the boundary layer thickness and the obstacle height, when greater than the cylinder diameter, is demonstrated.

The effect of distributed tangential injection of heavy SF₆ gas into the wall zone of a boundary layer on the supersonic flow stability and laminar-turbulent transition is experimentally and theoretically investigated at the freestream Mach number M_∞ = 2. For the first time it is experimentally shown that in the case of this injection laminar-turbulent transition is downstream displaced.

Experiments on heat transfer in underexpanded supersonic jets of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency plasmatron at a pressure of 10.4 GPa in a compression chamber. At gas flow rates of 2.4 and 3.6 g/s and HF generator powers of 45 and 64 kW the heat fluxes to the copper, stainless steel, MPG-7 graphite, and quartz surfaces are measured at the stagnation point of a water-cooled cylindrical, flat-ended model, 20 mm in diameter. In the same regimes the stagnation pressures are measured. The effect of the surface catalyticity with respect to nitrogen atom recombination on the heat flux is demonstrated and the qualitative catalyticity scale of the studied materials is established. In the supersonic regimes nonequilibrium nitrogen plasma flow in the discharge channel of the plasmatron and the underexpanded jet flow past the model are numerically simulated for the experimental conditions. The experimental and calculated data on the stagnation pressures and the heat fluxes to cooled surfaces of the metals, graphite, and quartz are compared.

The problem of the radiative gasdynamics of the Apollo-4 command module superorbital entry in the dense terrestrial atmosphere is numerically solved in the two-dimensional formulation of flow past an aerodynamic nose shield on the entry velocity range V_∞ = 10.7−5.75 km/s and the altitude range H = 91.5−35.0 km. The specific regions of the trajectory with strongly nonequilibrium flow in the shock layer, the most high-heat areas of the trajectory, and the regions with strong radiative-gasdynamic interaction in a relatively dense and strongly rarefied oncoming flow are highlighted. The density distributions of the convective and radiative heat fluxes over the body surface are obtained. The spectral composition of the thermal radiation is studied. The results of the calculations are compared and found to be in good agreement with the experimental flight data.