A.G. Burachenko, V.F. Tarasenko, I.D. Kostyrya, E.Kh. Baksht
High Current Electronics Institute of the Siberian Branch of the RAS, 634055, Tomsk, 2/3, Academichesky ave. HCEI SB RAS
Keywords: наносекундный разряд при пониженных давлениях, неоднородное электрическое поле, пучки убегающих электронов, экспериментальное моделирование высотных разрядов, nanosecond discharge at low pressures, non-uniform electric field, beams of runaway electrons, experimental simulation of sprites
Nanosecond discharges in air, SF6, and helium at pressures of units-tens of Torr are studied. Spatial heterogeneity of diffuse jets and autographs of runaway electron (RAE) beams are registered in all three gases in a non-uniform electric field. It is shown that diffuse jets in the discharge gap change their shape and their length increases and changes from pulse to pulse as the pressure decreases; as well, it is confirmed that the RAE beam amplitude increases as the pressure decreases and versus gas, decreasing with an increase in the atomic or molecular weight of the gas. It is assumed that the observed heterogeneity of diffuse jets and RAE beams can be associated with transient light phenomena in the Earth's atmosphere that have sizes of tens of kilometers and occur at high altitudes at low pressures under high thunderstorm activity.
T.D. Petukhov1,2, G.S. Evtushenko1,3, E.N. Tel'minov4
a:2:{s:4:"TYPE";s:4:"HTML";s:4:"TEXT";s:517:"1National Research Tomsk Polytechnic University, 30, Lenin Avenue, Tomsk, 634050, Russia 2Closed Joint-Stock Company Scientific Production Enterprize «Topaz» (AO NPP «Topaz»), 1, Academician Zuev square, Tomsk, 634055, Russia 3V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, 1, Academician Zuev square, Tomsk, 634021, Russia 4National Research Tomsk State University, 36, Lenin Avenue, Tomsk, 634050,Russia";}
Keywords: активная оптическая система, усиленное спонтанное излучение, щелочные металлы, натрий, оптическая накачка, active optical system, amplified spontaneous emission, alkaline metals, sodium, optical pumping
Experiments are described on the excitation of amplified spontaneous emission on the D-lines of sodium (D2 = 588.9 nm; D1 = 589.6 nm) at longitudinal optical pumping with a large detuning from the D2 line toward shorter wavelengths. The radiation spectra are measured, which proves gain on the both lines, at Na concentration of (1-5) ∙ 1014 cm-3, buffer gas (helium) pressure of 600 Torr at the working temperature, and pumping power density of more than 1.5 MW/cm2. The time characteristics show that the output radiation varies versus the concentration of sodium atoms in the active medium. The dependences of radiation absorption at the D-lines of sodium on the concentration of Na atoms and buffer gas pressure are given.
V.V. Lavrinov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, 1, Academician Zuev square, Tomsk, 634021, Russia
Keywords: датчик волнового фронта Шэка-Гартмана, параметры турбулентности, скорость ветра, алгоритм управления, Shack-Hartmann wavefront sensor, turbulence parameters, wind speed, control algorithm
It is shown that the efficiency of adaptive correction of turbulent distortions of laser radiation increases if the correcting mirror is controlled via an algorithm synthesized on the basis of prediction of Shack-Hartmann wavefront sensor measurements. The use of the predictive control algorithm makes it possible to minimize the error that associated with the time delay of the system. The prediction of the surface reproduced by the mirror is performed on the basis of an analysis of phase fluctuations in time.
H. Abdollahi1, S. Shahraki1, and M. Motahari-Nezhad2 1University of Zabol, Zabol, Iran 2Iran University of Science and Technology, Tehran, Iran
E-mail: saeid.shahraki@uoz.ac.ir
Keywords: contact heat transfer, thermal contact conductance, experimental setup, numerical solution
Pages: 499–512
In this paper, a
complete literature review for thermal contact between fixed and periodic
contacting surfaces and also thermal contact between exhaust valve and its seat
in internal combustion engines is presented. Furthermore, the effects of some parameters
such as contact pressure, contact frequency, the contacting surfaces topography
and roughness, curvature radius of surfaces, loading–unloading cycles, gas gap
conductance and properties, interface interstitial material properties,
surfaces coatings and surfaces temperature on thermal contact conductance are
investigated according to the papers presented in this field. The reviewed
papers and studies included theoretical/analytical/experimental and numerical
studies on thermal contact conductance. In studying the thermal contact between
exhaust valve and its seat, most of the experimental studies include two axial
rods as the exhaust valve, and seat and the one ends of both rods are
considered at constant and different temperatures. In the experimental methods,
the temperatures of multi-points on rods are measured in different conditions,
and thermal contact conductance is estimated using them.
A new fundamental
low-parametric equation of state in the form of reduced Helmholtz function for
describing thermodynamic properties of normal substances was obtained using the
methods and approaches developed earlier by the authors. It allows us to
describe the thermal properties of gas, liquid, and fluid in the range from the
density in ideal-gas state to the density at a triple point (except the
critical region) with sufficiently high accuracy close to the ac-curacy of
experiment. The caloric properties and sound velocity of argon, nitrogen, and
carbon dioxide are calculated without involving any caloric data, except the
ideal gas enthalpy. The obtained values of isochoric heat capacity, sound
velocity, and other thermodynamic properties are in good agreement with
experimental (reliable tabular) data.
A semi-empirical model based on
the linear kinetic theory was developed for intense evaporation. The
extrapolated drops for pressure and temperature at the condensed phase surface
were calculated through summing of linear and squared terms. The analytical
dependencies were obtained for gas parameters in gas-dynamic zone as functions
of Mach number, condensation coefficient, and the number of degrees of freedom
for molecules of ideal gas. The calculations from semi-empirical model are in
agreement with results from known analytical and numerical studies.
Results of experimental
studies on dynamics of explosive boiling and third heat transfer crisis under
the conditions of liquid subcooling are presented for the vertical
arrangement of the heat-transfer surface. Acetone was used in experiments at
the pressure in the working volume from 20 to 46 kPa and subcooling from 0 to
20 K. The studied processes were recorded. Data on the velocity of
evaporation front propagation at liquid subcooling were obtained. These data
are compared with the results of calculations according to the models available
in the literature. The effect of liquid subcooling on the regions of regime
parameters corresponding to explosive boiling and third heat transfer crisis is
studied.
The efficiency of a pair
of wind turbines is experimentally investigated for the case when the model of
the second rotor is coaxially located in the wake of the first one. This
configuration implies the maximum level of losses in wind farms, as in the
rotor wakes, the deceleration of the freestream is maximum. As a result of
strain gauge measurements, the dependences of dimensionless power
characteristics of both rotors on the distances between them were determined
for different modes at different tip speed ratios. The obtained results are of interest
for further development of aerodynamics of wind turbines, for optimizing the
work of existing wind farms and reducing their power losses due to interactions
with wakes of other wind turbines during design and calculation.
The
paper presents the numerical simulation results of the surface roughness influence
on gas-dynamic processes inside flow parts of
a supersonic ejector. These simulations are performed using two commercial CFD
solvers (Star-CCM+ and Fluent). The results are compared to each other and
verified by a full-scale experiment in terms of global flow parameters (the
entrainment ratio: the ratio between secondary to primary mass flow rate - ER
hereafter) and local flow parameters distribution (the static pressure distribution
along the mixing chamber and diffuser walls). A detailed comparative study of
the employed methods and approaches in both CFD packages is carried out in
order to estimate the roughness effect on the logarithmic law velocity
distribution inside the boundary layer. Influence of the surface roughness is
compared with the influence of the backpressure (static pressure at the ejector
outlet). It has been found out that
increasing either the ejector backpressure or the surface roughness height, the
shock position displaces upstream. Moreover, the numerical simulation results
of an ejector with rough walls in the both CFD solvers are well quantitatively
agreed with each other in terms of the mean ER and well qualitatively agree in
terms of the local flow parameters distribution. It is found out that in the
case of exceeding the “critical roughness height” for the given boundary
conditions and ejector’s geometry, the ejector switches to the “off-design”
mode and its performance decreases considerably.
In the present paper, we
analyze emergency situations typical of short-duration wind tunnels with
electric-arc or combined test-gas heating in the presence of stabilization and
diaphragm-rupturing systems, which occur in the case of no discharge initiation
in the settling chamber, with the capacitor battery having remained charged during
the start of wind-tunnel systems. For avoiding such emergency situations, some
additional changes based on using feedback elements are introduced into the
wind-tunnel design: the piston of the fast-response valve is made hollow for
increasing the volume of the shutoff cavity and for making the release of
pressure from this cavity unnecessary; the high-pressure channel, which
connects the piston and the piston rod with the settling-chamber cavity, is
filled with a liquid and is closed from the side of the settling chamber with a
piston; the device for controlled diaphragm breakdown is provided with an
external electric circuit intended to control the diaphragm-rupturing process.
Those modifications allow subsequent functioning of the wind-tunnel systems
only in the presence of heat-supply-induced pressure growth in the settling
chamber of the wind tunnel.
