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The goal of the study is to study the gas-dynamic structure of a supersonic underexpanded jet in the presence of a liquid spray as applied to the topic of gas-liquid nozzles. The wave structure is detected by methods of shadowgraphy and adaptive transparency visualization. Laser Doppler anemometry is used to measure the spray velocity and also to determine its concentration and droplet size. It is found that the flow in the two-phase core is qualitatively different from the gas jet flow. The transformation of the Mach disk in a wide range of gas flow regimes and liquid flow rates is studied. A crucial role of the gradient region of the jet in the vicinity of the Mach disk in the process of liquid atomization is demonstrated.

Two diametrically opposite internal grooves were introduced in the diverging section of a supersonic nozzle. Experiments were conducted to find the effect of grooves at three different nozzle pressure ratios (NPRs), i.e., 3.6, 5.5, and 7.2 and comparisons were made with circular jet without grooves. Data reported here are for a design exit Mach number of 1.8 with an area ratio 1.44. Results are presented as pitot pressure decay along the extended geometric center-line of the nozzle and the radial distribution of pitot pressure at various axial ( x ʹ =1, 3, 5, and 8) locations. Empirical relations have been developed to identify the lengths of various regions involved in the pitot pressure decay (along X -direction). Groove effectiveness was used as a parameter to find the effect of grooves on the jet decay characteristics. The jet from grooved nozzle exhibited totally different results compared to that from plain circular nozzle. Results show that grooves played a more significant role at overexpansion condition of the nozzle than at under-expansion case. Schlieren flow visualization technique was used to capture the shock cell structure of the jets for the same NPRs and it was found that the structure of the jet emanating from the grooved nozzle was highly distorted. To understand decay characteristics, supersonic core length and the pitot pressure decay lengths for 50 % decay and 90 % decay were determined from the pitot pressure data along the extended centerline of the nozzle. A significant reduction in spatial pressure fluctuations and supersonic core length were observed at overexpansion condition of the nozzle when grooves were introduced.

The fluid dynamics of a water fluid jet with supercritical state parameters outflowing from a high-pressure vessel through a thin nozzle is investigated. The numerical modeling of the jet was carried out using a system of equations for a gas-vapor-liquid mixture which includes the conservation laws for mass, momentum and energy formulated in with one-pressure, one-velocity, and two-temperature approximation. The simulation takes into account the contact heat and mass transfer processes of evaporation and condensation under equilibrium condition using a modified solver reactingTwoPhaseEulerFoam within the OpenFOAM free open package. The process of barrel shock formation in a supersonic boiling jet with developing the Mach disk is demonstrated. It was found that the outflow process is accompanied by formation of vortex zones near the jet symmetry axis and this induces periodic pulsations in pressure and mass velocity inside the jet. Finally, this generates the acoustic pulses series preceding the main jet flow. Justification of reliability for the applied numerical method implemented through the OpenFOAM package solver is offered through comparing the numerical and analytical solutions for the Sedov problem of a strong point explosion in a two-phase gas-droplet mixture (for the planar case). The comparative analysis of simulation and the experimental photography for the supersonic nitrogen jet ejected from a cylindrical nozzle of a high-pressure reservoir is presented. The numerical results obtained using the OpenFOAM package demonstrate a satisfactory agreement with analytical solution and experimental data.

Heat exchange devices involving confined heated cylinders in crossflow require wake stability to minimize hydraulic losses, which are typically accompanied by a considerable loss in heat transfer. To address this problem, passive wake control for laminar flow past a cylinder is introduced in the form of wavy channel walls around the cylinder. The resultant effects on heat transfer and drag are investigated in detail for a range of Reynolds numbers (Re = = 20 - 200), blockage ratios ( b = 0.5 - 0.9) and Prandtl numbers (Pr = 0.25 -100). For the given range of parameters, it is shown that the wavy channel reduces cylinder drag by a minimum of ~ 36 % and a maximum of ~ 95 %, at the expense of ~ 8 % and ~ 40 % loss in heat transfer, respectively, compared to the plane channel. Thermal-hydraulic performance of the wavy channel compared to the plane channel for Pr = 0.744, is improved by ~ 14 % for b = 0.5 and ~ 160 % for b = 0.9. Therefore, the performance enhancement brought about by the wavy channel provides an appropriate trade-off between drag reduction and heat transfer loss.

The problems of interaction between gas dynamics and combustion are considered using the well-known database of experimental results on the boundary layer with ethanol combustion. Gas dynamics is represented by streamlines, combustion is represented by isotherms. The influence of an increased degree of air turbulence (up to 18%), acceleration in a narrowing channel, and the influence of the height of a flame stabilizing fin (3 and 6 mm) on the flow structure in individual cross-sections and in the boundary layer as a whole are studied. It is shown that immediately behind the barrier, where the signs of kinetic reaction of the gas mixture are manifested, the streamlines intersect, and during combustion in a narrowing channel with low air turbulence, the isotherms and streamlines become equidistant near the flame front, as in the case of diffusion response. Mass transfer on the liquid fuel surface remains conservative to changes in the gas-dynamic parameters of the air flow.

Based on the analysis of the wood increment dynamics in the middle-aged pine forests of the Krasnoyarsk forest-steppe of various structure, formed through thinning of different intensities and the introduction of various doses of mineral fertilizers (carbamide, 46 % of the active substance), the regularities of changes in the current annual increment were established. A model allowing assessing the trends in increment with age and density of stands growing both without and with the use of fertilizers has been proposed. Data are presented indicating that in the conditions of the Krasnoyarsk forest-steppe, due to the application of fertilizers, the current annual increment in pine plantations can be increased by 1.2-6.8 m³/ha compared to the reference site. Differences in the response of stands to fertilization in the first five years and the next three years were revealed it has been found that the current annual increment increases significantly starting from the sixth year after fertilization. The density-age optima of the productivity of pine stands, providing a multiple increase in the increment of managed stands as compared to the reference site were established. The obtained knowledge is the theoretical basis for the implementation of a model of intensive use and reproduction of forests in the best forest growing conditions, and will also be useful in creating carbon farms, which main purpose is to reduce the carbon footprint of industrial enterprises.

The dynamics of forest inventory indicators, attrition and wood growth of 35-year-old pine Рinus sylvestris L. crops with various density are analyzed, Pine crops were created in 1982 by V. N. Sukachev Institute of Forest Russian Academy of Sciences, Siberian Branch under the leadership of A. I. Buzykin on former agricultural lands in Bolshemurtinsky district of Krasnoyarsk Krai. The initial density of the stands varied in a wide range from 0.5 to 128.0 thousand trees per ha. The assessment of the stand density influence on the growth and productivity of young pine stands at the age of 2, 5, 12, 15, 20, 25, 30 and 35 years old was carried out. It has been established that since the age of five, the process of intensive self-thinning of trees has been observed, at initial planting density 90.0 thousand trees/ha the density decreased to 10 thousand trees/ha by the age of 35 years. At the initial density less than 10 thousand trees/ha the self-thinning intensity is significantly lower and the stand density has decreased by less than 2 times over the same period. It is shown that at the initial stage of stand growth there is a growth increase with the initial planting density, reaching the plateau at a density of over 70.0 thousand trees/ha. With age reaching the plateau occurs with the lower initial density. At the age of 20, the maximum increase was at the initial density from 50.0 to 70.0 thousand trees/ha, by the age of 30 it shifted to a density range from 30.0 to 50.0 thousand trees/ha. The relationship between the current annual increment, age, and the initial and actual densities of pine crops has been established. In the age range studied there is a tendency of increasing the increment with age, although for the crops with the initial density higher than 90 thousand trees per ha in the range of 15 to 22 years the decrease of annual increment is observed, which is evidently connected to the escalating of concurrent relations in cenosis. Thus, it can be suggested that high rates of carbon deposition at the initial stage of high-density stands creation can be maintained under the condition of periodic thinning, regulating the stand density.

The results of the formation of overstocked 15-year pine stands (with initial density of trees 35.6 thousand per ha) in the Krasnoyarsk forest-steppe the thinning aimed at reducing their density with keeping only the trees of a certain cenotic position (dominant, co-dominant and suppressed) in order to obtain information about the possible equalization of their forest inventory indicators in the process of their growth are presented. It was found that after thinning the dominant trees stand had density of 4.3 thousand per ha, had the best growth characteristics (mean height and mean diameter) and upheld that tendency through the whole observation period. After 7 years mean diameter of dominant trees increased from 4.8 ± 0.1 to 9.4 ± 0.2 cm, mean height increased from 4.8 ± 0.1 до 8.1 ± 0.1 m. Stem timber volume increased 5.0 times to the value of 141.63 m³ per ha, relative density - from 0.51 to 1.27. Stand density for co-dominant trees decreased to 6.6 thousand per ha after the thinning. The mean diameter of co-dominant trees increased 2.6 times and amounted 6.1 ± 0.1 cm, the mean height increased from 3.4 ± 0.1 to 5.7 ± 0.1 m. Stem timber volume increased from 7.92 to 60.06 m³/ha, relative density increased 3.7 times (1.00). After the thinning the suppressed trees underwent a long (1-2 years) adaptation period, had disproportional growth in height and decreased growth in diameter (relative height 244). Stand density for suppressed trees pine Pinus sylvestris L. decreased to 6.3 thousand per ha after the thinning. The mean diameter of the suppressed trees after 7 years after the thinning changed from 0.9 ± 0.1 to 4.2 ± 0.1 cm, the mean height - from 2.3 ± 0.1 to 3.8 ± 0.1 m. Timber volume increased from 1.09 to 17.23 m³ per ha, relative density increased from 0.07 to 0.69.

A simulation model of the growth of pine stands is proposed. The model, taking into account the competition for the available resource, allows to calculate the increase in trunk diameter for each tree in the simulated area, as well as to derive the taxation characteristics: stand density, completeness, stock of stem wood and make monitoring the dynamics of all these indicators in increments of one year. The model takes into account the relative location of trees in the tree stand, their size and the amount of available resource for each tree. The verification of the model was carried out using the materials of long-term research on permanent research plots of young, middle-aged and ripe stands. Several scenarios for the growing of pine stands are considered. The influence of cutting on the dynamics of a number of taxation characteristics is studied. These are the average diameter the average diameter of the trunk and the increase in diameter, the value of the average annual increase; the density of the stand; the stock of stem wood. The proposed simulation model is an effective tool for studying the growing of stands and serves as an alternative to time-consuming field studies, which are difficult to implement over long time intervals. Modeling allows studying the impact of logging in forests for various destinations. It is possible to choose such a system of forest care activities using the analysis of the dynamics of the main taxation indicators, which provides the most complete implementation of the tasks of intensive reforestation by varying the intensity and frequency of cutting during modeling.

The basis for forecasting the growth of forest stands is the site index scales. Expansion of knowledge about the processes of functioning of forest ecosystems, the nature of changes in the process of growth of morphological indicators of trees and stands, their interconnections and interdependencies, and the creation of a more suitable mathematical apparatus and appropriate software for describing biological processes form the prerequisites for formulating and solving the problem of forecasting the growth of stands on higher methodological level. The aim of this work is to assess the predictive ability of the growth equations obtained using the generalized algebraic difference approach (GADA) to describe the course of growth of tree stands at the average height and to construct a site index scale. The data for the study were general tables of the course of growth of complete (normal) pine stands North Eurasian. A total of 25 equations obtained using the GADA approach are analyzed. Comparative analysis showed that the best quality of data alignment is provided by an equation based on the Mitscherlich function (also known as Drakin-Vuevsky, Chapman-Richards) with the replacement of parameters responsible for the limiting values of the height and the shape of the curve. This model is polymorphic, has the shape of a sigmoid curve and variable asymptotes, i.e. takes into account most of the properties imposed on the growth rate models in height. Model errors are distributed depending on the selected forecasting interval and the site index of the stand. With an increase in the forecasting period, an increase in the error occurs. For all intervals of the forecast range, the value of the mean absolute error is not exceeding 2.01 %. The highest average absolute forecast error (1.1-2.2 %) is characteristic of the extreme site index classes (I^b, V, V^a and V^b). The methodology considered in the study can be applied to develop models of the growth rate of stand inventory variables of other forest-forming species in Russia.