Home – Home – Jornals – Thermophysics and Aeromechanics 2003 number 2

Investigation results on unsteady vortex breakdown obtained simultaneously using two diagnostics methods: a) determination of a velocity field by particle tracks (particle image velocimetry – PIV), b) determination of velocity field by Laser Doppler Anemometry (LDA), are presented. The experiments data are in some regimes supplemented by the 3D computations of the incompressible Navier – Stokes equations in cylindrical coordinates. Perfect agreements between calculation and experiment reveal efficiency of both suggested diagnostics method for pulsating vortex breakdown and numerical method for solution to 3D un-steady Navier – Stokes equations.

The equation of convective diffusion of particles is considered, and the problem is formulated on the separation of dust particles from a turbulent gas flow in a parallel flow cyclone. The equations of pulsation motion of particles in the field of the action of the centrifugal and Coriolis forces are analyzed, and an analytic dependence is obtained for their diffusion coefficient.

The structure of nonstationary vortical wakes of the rotor was studied experimentally in the system of rows stator – rotor – stator of the axial compressor. It was established that besides deceleration of relative flow velocity in the zone of turbulent vortical wake of the blades, a layer of free vortices develops at the wake axis. The free vortices pulsate with the frequency of passing of blades between neighbor rows, causing pulsation in velocity, pressure; and due to mixing process the total pressure loss becomes higher.

The transonic regime of the flow around the airfoil is modelled in conditions of an pulse periodic energy. The objective of the present work is to study the effect of energy release on flow structure: decay and generation of shock waves, change of their position and strength as well as other effects caused by the flow reconstruction. The computed results are presented for the ideal gas flow around the airfoil NACA 0012 with the freestream Mach number of 0.8 for different locations of energy zones and values of the energy released. The flow was modelled on the basis of two-dimensional nonstationary gas dynamics equations. The stationary flow around the airfoil without the energy release was used as the initial condition. The explicit finite volume method diminishing the total variation (the TVD reconstruction) was used to find the numerical solution. The nonstationary problem was solved from the moment of time when the energy release is started up to obtaining a periodic regime. The possibilities are shown to control both the local and integral characteristics of airfoils at transonic flow regimes. A periodic character of the forming flow is established, which may be implemented at cruise flight speeds. The examples of both global and local flow reconstruction are presented.

Results of experimental investigations of a flow around airfoils in the subsonic wind tunnels are presented. The investigation objective is to compare flows above the upper surfaces of a smooth unswept wing and a waved one imitating a wing of a paraplan. Three-dimensionality of the flow structure in the zone of laminar separation bubbles is revealed, and their formation peculiarities on the smooth and waved wings are shown. Normal and tangential components of an aerodynamic force affecting the wing are measured, and the advantages of the paraplan over the planar wing are shown.

Onset of powerful resonant acoustic oscillations caused by coincidence of eigen acoustic frequency and coher-ent structures shedding frequency (a source of excitation of oscillations) is experimentally investigated in regions near 2D and 3D spa-tial configurations of rectangular, swept, and round plates mounted in a channel in parallel to its walls. Some new phenomena were revealed, in particular, an interrelation of several systems of the coherent structures, and, respectively, simultaneous  excitation of several resonance frequencies under transient conditions, arising of 3D coherent structures,  and formation of complex standing sound waves near the bodies. The results obtained are considered as different ways to control the aeroacoustic resonance and the flow on the whole.

A linear problem for the perturbations of a compressible laminar boundary layer caused by a small sinusoidal roughness of the plate surface is formulated and solved with the use of parabolized equations of stability. The peculiarities of the disturbances behaviour are studied for the angles between the front of the roughness wave and flow direction, which are equal to the Mach angle. The parameters of sound emitted by the rough plate are calculated at a supersonic flow (M = 2).

Experimental data are reported on convective heat transfer and hydraulic resistance in air flows through an annular gap whose inner tube was shaped with staggered spherical recesses-cavities and through a pipe with spherical bulges. The experiments were carried out in the following ranges of flow and geometric parameters: Re_f,°d = 2^.10³ 8^.10³

Thermal conductivity of gaseous and liquid 1, 1, 1, 2, 3, 3-hexafluoropropane (HFC-236ea) was studied over the temperature range from 307 to 434 K at pressures from 0.18 up to 2.8 MPa. Measurements were carried out by a steady-state coaxial-cylinder method. The purity of samples used in the measurements are 99.4 mole %. Measurement error does not exceed 2 % within the measurement errors. The low-density thermal conductivity of HFC-236ea does not differ from thermal conductivity of HFC-227ea and octafluoropropane, but it is significantly lower than thermal conductivity of propane. A dependence of thermal conductivity of HFC-236ea on the temperature and pressure was approximated by a fourthpower polynomial (in pressure). Thermal conductivities of gaseous and liquid HFC-236ea at the saturation line were calculated.

Formation of temperature fields and radiation fluxes during melting of a semitransparent gray medium with differ-ent absorption factors was studied numerically. Evolution of the temperature growth at the left opaque boundary and propagation dy-namics of the phase transition front were considered at different reflection coefficients of the layer boundaries.

Formation of vacancy-gaseous pores in crystalline lattice of metal is simulated using the method of stochastic analog; this method reduces the blistering phenomena to a random Markov

The All-Russian seminar

The results of experimental simulation in the vacuum chamber of processes of the International Space Station sur-face contamination by plumes of orientation thrusters are reported. Problems of modelling of orientation thruster plumes are considered, descriptions of experimental setup, methods, and results of measurements of angular distribution of a droplet phase with a co-current supersonic gas flow are given. It was shown that the mounting of the gas-dynamic protectors on the orientation thruster allows essential reduction of the droplet (contaminating) phase backflow.

The photophoretic motion of atmospheric aerosol particles in the field of solar radiation and in the field of outgo-ing thermal radiation of the Earth is examined. The problem statement and the technique for computing the basic characteristics of phenomenon are presented. A tentative analysis of the obtained results is conducted. The soot particles as well as other light and low heat conductivity aerosols in the stratosphere are shown to be highly sensitive to the photophoretic effects. In particular, the levitation and even vertical lifting against gravity for soot particles with sizes of about 0.1 0.8 m in the solar radiation field and for particles with sizes of 1 2 m in the thermal radiation field of the Earth are predicted. At the same time, the radiometric photophoresis of particles in the thermal radiation field appears to be no significant mechanism in maintaining a stable existence of known aerosol layers in stratosphere and mesosphere.

Gas mixtures with internal degrees of freedom and any chemical reactions including dissociation and recombina-tion are considered. Along with the atoms and the molecules (Boltzmann