Vol 24, No 6 (2017)

A coupled NS-DSMC method possessing adapted-interface and two-way coupling features is studied to simulate the plume impingement effects of space thrusters. The continuum-rarefied interface is determined by combining Kn_GL and P_tne continuum breakdown parameters. State-based coupling scheme is adopted to transfer information between continuum and particle solvers, and an overlapping grid technique is investigated to combine structured-grid NS code and Cartesian-grid DSMC code to form the coupled solver. Flow problem of a conical thruster plume impinging on a cone surface is simulated using the coupled solver, and the simulation result is compared with experimental data, which proves the validity of the proposed method. Plume flow while the ascent stage of lunar module lifting off in lunar environment is also computed by using the present coupled NS-DSMC method to demonstrate its capability. The whole flow field from combustion chamber to the vacuum environment is obtained, and the result reveals that special attention should be paid to the plume aerodynamic force at the early stage of launching process.

With the use of ANSYS Fluent software and ANSYS ICEM CFD calculation grid generator, the flows past a wing airfoil, an infinite cylinder, and 3D blunted bodies located in the open and closed test sections of low-speed wind tunnels were calculated. The mathematical model of the flows included the Reynolds equations and the SST model of turbulence. It was found that the ratios between the aerodynamic coefficients in the test section and in the free (unbounded) stream could be fairly well approximated with a piecewise-linear function of the blockage factor, whose value weakly depended on the angle of attack. The calculated data and data gained in the analysis of previously reported experimental studies proved to be in a good agreement. The impact of the extension of the closed test section on the airfoil lift force is analyzed.

Here we present the results of experimental investigation of a cross flow around a circular cylinder mounted near the wall of a channel with rectangular cross section. The experiments were carried out in the range of Reynolds numbers corresponding to the transition to turbulence in a wake of the cylinder. Flow visualization and SIV-measurements of instantaneous velocity fields were carried out. Evolution of the flow pattern behind the cylinder and formation of the regular vortex structures were analyzed. It is shown that in the case of flow around the cylinder, there is no spiral motion of fluid from the side walls of the channel towards its symmetry plane, typical of the flow around a spanwise rib located on the channel wall. The laminar-turbulent transition in the wake of the cylinder is caused by the shear layer instability.

The differential equation of heat transfer with allowance for energy dissipation and spatial and temporal nonlocality has been derived by the relaxation of heat flux and temperature gradient in the Fourier law formula for the heat flux at the use of the heat balance equation. An investigation of the numerical solution of the heat-transfer problem at a laminar fluid flow in a plane duct has shown the impossibility of an instantaneous acceptance of the boundary condition of the first kind — the process of its settling at small values of relaxation coefficients takes a finite time interval the duration of which is determined by the thermophysical and relaxation properties of the fluid. At large values of relaxation coefficients, the use of the boundary condition of the first kind is possible only at Fo → ∞. The friction heat consideration leads to the alteration of temperature profiles, which is due to the rise of the intervals of elevated temperatures in the zone of the maximal velocity gradients. With increasing relaxation coefficients, the smoothing of temperature profiles occurs, and at their certain high values, the fluid cooling occurs at a gradientless temperature variation along the transverse spatial variable and, consequently, the temperature proves to be dependent only on time and on longitudinal coordinate.

The paper describes experimental modeling of combustion of a stoichiometric propane-oxygen mixture in quasi-cylindrical bubbles with non-smooth interface using polyvinyl chloride tubes with barriers inside (multiple or single water droplets; or the balls of polystyrene and steel). The transition from combustion to detonation occurs both before and after the barrier, for any kind of barrier material.

The thermodynamic efficiencies of throttling devices and expander-generator units used for technological decompression of transported gas in gas distribution stations (GDS) and gas control points (GCP) of the gas supply system are compared. Various designs of the expander-generator units generating either electricity or electricity and cold are considered. The exergy efficiency is used as a criterion of the thermodynamic efficiency. It is shown that the replacement of the throttling device by the expander-generator unit under conditions taken for calculations leads to an increase in exergy efficiency of the station of technological decompression of the transported gas at all considered schemes of this unit inclusion: with no gas heating in the expander-generator unit, with gas heating after the expander, before the expander as well as before and after the expander.

The production of periodic oscillations in a supersonic boundary layer at the moderate and high Mach numbers (M = 2 and 5.35) is investigated within the framework of the weakly nonlinear stability theory of the second order in nonlinearity. The model includes the effects of self-action, such as the generation of stationary secondary harmonics and the disturbances of double frequencies. It is shown that for two-dimensional vortex disturbances, the character of the excitation of vortex disturbances changes from the mild one to the stiff one with the increasing Mach number, which leads to a reduction of the critical Reynolds number Re_c. For three-dimensional disturbances of low azimuthal wave numbers, a supercritical auto-oscillatory regime sets in. A complex regime realizes for two-dimensional acoustic disturbances at M = 5.35 with a stiff excitation in the region of Re_c.

In the present study, we theoretically examine the formation process of the steady-state temperature field in dielectrics under irradiation with a continuous ion beam in air with allowance for the temperature dependence of thermophysical quantities. Analytical expressions for the temperature field were obtained. An interconnected system of nonlinear algebraic equations for the steady-state temperatures at the front (irradiated) and rear surfaces of the sample, and the steady-state temperature at the interface between the ion-damaged and non-damaged region was obtained; by numerical solution of this system, a nonlinear dependence of the mentioned temperatures on the characteristics of incident ion flux was revealed.