An explicit algebraic
model of Reynolds stresses and the turbulent heat flux vector for the planetary
boundary layer in a neutrally stratified boundary layer of the atmosphere above
a homogeneous rough surface is tested. The version of the algebraic model
under consideration is constructed on the physical principles of the RANS (Reynolds-averaged Navier-Stokes)
approximation for describing stratified turbulence, it employs three forecasting equations, and a correct reproduction of the main characteristics of a neutral
atmospheric boundary layer ¾ the components of the mean wind velocity, the wind turn angle, and the turbulent statistics is shown. Test computations show that the proposed model may be used for
goal-oriented investigations of the atmospheric boundary layer.
In the present paper, we
report on the results of an experimental study of the process of gravity
sedimentation of a cloud of monodispersed solid spherical particles with
initial volume concentration C >
0.03, which was performed in a wide range of Reynolds numbers. An
analytical estimate of the settling regimes of spherical particle clouds is presented.
A new method for creating a spherical particle cloud with a high concentration
of particles is proposed. A qualitative picture of the settling process of
a highly concentrated particle cloud under gravity is revealed. A criterial
dependence for the drag coefficient of a sedimenting spherical particle cloud
as an entity is obtained.
Results of a film
cooling numerical simulation over a flat plate with coolant supply into
indentations of different shape are reported. The calculations were performed for the blowing-ratio changed from 0.5
to 2.0. For comparison, data for traditional film cooling scheme with one row
of discrete cylindrical inclined holes were used. At small value of blowing ratio (m = 0.5), the average film-cooling efficiency is roughly
identical for all indentations tested. With blowing ratio growth, the scheme
with a coolant supply into the transverse trench demonstrates the best results.
The conditions of
formation of a three-dimensional thermocapillary structure on the surface of a
liquid film flowing along a heater with the constant temperature were studied
numerically based on the derived system of equations. Formation of the
thermocapillary structure was modeled by periodic perturbations in the
transverse direction superimposed on the two-dimensional flow. It is shown in
calculations that transversal perturbations can develop into periodic rivulet
structures on the film surface if the Marangoni number exceeds some threshold
value. It is revealed that the rivulet structure develops when the period
belongs to a certain range, which is determined by the value of Marangoni
number. The results of calculations are in a good agreement with experimental
data.
An evaporation of
kerosene and water was investigated based on convective heat transfer in the
experimental setup simulating a typical volume of the fuel tank of the launch
vehicle. Basic criteria of similarity used in choosing the design parameters of
the setup, parameters of the coolant and model liquids, were numbers of
Reynolds, Prandtl, Biot, and Nusselt. The used coolants were gases, including
air and nitrogen; in addition, at the stage of preliminary experiments,
products of combustion of hydroxyl-terminated polybutadiene (HTPB) were
considered. Boundary conditions were taken for the liquid located on the plate
in the form of "drop" and at its uniform film spread in the experimental
model setup. On the basis of experimental investigations, the temperature
values were obtained for the system "gas-liquid-wall", and areas of
mass transfer surface and heat transfer coefficients of “gas-liquid” and “gas-
plate” were determined for coolants (air and nitrogen) and for liquids (water
and kerosene). The comparative analysis of the obtained results and the known
data was carried out. Proposals for experiments using coolants based on HTPB
combustion products have been formulated.
This study presents
dual-temperature two-phase model for liquid-vapor mixture with account for
evaporation and inter-phase heat transfer (taken in single-velocity
single-pressure approximation). Simulation was performed using the
shock-capturing method and moving Lagrangian grids. Analysis was performed for
simulated and experimental values of nucleation frequency (for refining the
initial number and radius of microbubbles) which affect the evaporation rate.
Validity of 2D and 1D simulation was examined through comparison with
experimental data. The peculiarities of the water-steam formation at the
initial stage of outflow through a thin nozzle were studied for different initial equilibrium states of water for the
conditions close to chosen experimental conditions.
Interdiffusion in
lithium-lead melts containing 10.0, 15.0, 18.1, 20.0, 25.1, 30.2, 38.2, 40.1,
43.1, 46.7, 50.2, 60.2, and 70.0 at. % Pb was investigated using gamma-ray
attenuation technique in the temperature range from 720 to 1030 K. It has
been found that the concentration dependence of the interdiffusion coefficient
has a maximum in the vicinity of 20 at. % Pb. This phenomenon is
shown to relate to a tendency of formation of short-range order in liquid
alloys of lithium-lead.
Numerical evaluation of
the laser-pulse modification of a metal layer with refractory nano-size
particles was done. The modes of the laser-pulse action promoting creation of
the flows for homogeneous distribution of modifying particles in the melt were
determined for various amounts of the surface-active admixture in the metal.
The paper describes
the developed method for analyzing technological schemes of thermal power
plants based on solving problems of auxiliary linear programming. This method
involves solving the linear programming problems to evaluate the effect of
supply and removal of heat or material flows of various sizes at different
points of the technological scheme of a thermal power plant (TPP). The method
effectiveness is demonstrated by the example of the coal-dust steam turbine
unit with nominal electrical output of 660 MW. As a result of its application,
the change of the technological scheme of the unit was found to provide
reduction in electricity cost by 0.3%.
Simulation
is presented for the case of water coolant outflow with initial supercritical
parameters after high pressure pipeline breaking. The nonequilibrium relaxation
model of phase transition was developed and validated. The model describes
both boiling and condensation processes.
