Home – Home – Jornals – Thermophysics and Aeromechanics 2019 number 2

Sergey A. Chaplygin, one of the outstanding mechanical engineers of our era, was among those prominent Russian researchers whose investigations paved new paths in nature sciences and served as a basis for the development of modern engineering.

Both numerically and experimentally, the possibility of using a combined method to control the incompressible turbulent boundary layer on a symmetric airfoil section of 12-% relative thickness implemented via the blow-ing/suction of air through a finely perforated section provided on the wing surface part was examined. The study was performed at Reynolds number Re_c = 0.7x10⁶ in the range of angles of attack α = -6 - 6º. The mechanism of action of this flow control method on the aerodynamic characteristics of the wing was identified. An ambiguous pattern of the effect due to blowing/suction from the viewpoint of ensuring a maximum lift, a gain in wing lift-to-drag ratio, and a reduction of wing aerodynamic drag was revealed.

The work is devoted to the use of asymptotic boundary conditions for engineering prediction of the laminar-turbulent transition position in hydrodynamic flows by the e^N -method. It is shown that the asymptotic boundary conditions can significantly reduce the total computational cost.

The peculiarities of supersonic unsteady flows forming in the processes of an impulse starting of a wind tunnel including a fore-chamber, a nozzle, a diffuser, and an exhaust tank are considered. The fore-chamber is separated from the flow duct by a thin breakable diaphragm. Before the wind tunnel starting, the gas contained in the exhaust tank is pumped out down to a very small pressure, and then the high-pressured working gas is fed into the fore-chamber. Upon reaching some value of this pressure, the diaphragm “instantaneously” ruptures, and the working gas starts exhausting through the nozzle: a rapid unsteady process of the wind tunnel starting arises. The numerical simulation of the flows forming at the impulse starting of the simplest experimental gas-dynamic facility has been carried out; the facility is arranged with a nozzle forming at its exit a two-dimensional supersonic flow with the Mach number of 2.9, and with replaceable diffusers having different relative areas of the throat. The numerical computations of two-dimensional unsteady flows have been carried out using the Reynolds-averaged Navier-Stokes equations and the SST k-w turbulence model. The flow patterns computed numerically are compared with the data of the optical visualization of the flow obtained in the experimental gas-dynamic facility in the process of its starting.

The methodology of averaging the nonuniform swirling flow in turbomachines has been developed. It is based on preserving the mass flow rate, the fluxes of total enthalpy and momentum (or entropy) with the addition of new invariant into the algorithm, i.e., the integral of the gas flow helicity. The dependence has been obtained and validated to specify the turbine stage efficiency calculation and to take into account the presence of large-scale vortex structures in the inter-blade channel of the turbomachine (the uncertainty of the influence of secondary flows on the value of losses does not exceed 0.2 %). The methods of averaging the gas flow parameters, taking into account the contribution of secondary flows to the kinetic energy loss are presented. They show a 2.4 % lower efficiency compared to the calculation previously used for the turbine stage of the Leningrad Polytechnic Institute.

A physical-mathematical model of cooling and solidification of a liquid film entrained by air along the heated surface of a streamlined body with given distribution of the heat flux density over the surface is developed. An example of model numerical testing with a set of governing parameters characteristic of experiments at an air cooling rig is presented.

It is known that introduction of the gas phase into the liquid flow leads to flow restructuring and can significantly change the key thermal-hydraulic flow parameters, for example, the heat transfer coefficient. This paper presents the results of an experimental study of an ascending bubble flow in a vertical assembly of 3´3 rods. Distilled water was used as a working liquid. The experiment was carried out at Reynolds numbers from 4000 to 11000 and volumetric gas flow rate ratio from 3 to 10 %. In the experiment, the coefficients of heat transfer from the central rod heated by electric current to the flow were determined and it was shown that gas inclusions have the maximal effect on heat transfer at low Reynolds numbers and maximal distance from the spacer grid.

The presence of bubbles exerts a strong influence on pressure drop, heat transfer, flow pattern, and many other flow characteristics. Due to the complexity of two-phase flow boiling, it is not easy to carry out experimental research. An experimental setup based on ultrasonic detection method is built up in this paper. The present study investigates bubble size distribution and vapor quality in liquid-gas two-phase flow in a vertical narrow channel with the cross section of 3×20 mm. Bubble size distribution is heavily affected by the heat power and mass flux, which means that different flow patterns show different bubble size distributions. Vapor quality is also obtained by the ultrasonic attenuation method, which is compared to the theoretical calculation. The ultrasonic detection model is mainly applied in the bubble-coalesced flow. As the vapor quality is small, the detection value is close to the theoretical value, and this detection model is suitable for nucleate boiling. As the vapor quality is increased, the deviation is larger. By comparison with the theoretical calculations, it is necessary to modify the ultrasonic detection model to fit different flow patterns, which is helpful to study the liquid entrainment mechanism in the micro-channel (especially when the inner diameter is less than 5 mm) in the future.

Experimental and theoretical study was conducted on liquid evaporation from free interface when the liquid is placed into an enclosed tank and subjected to vacuum and sonic exposure. A mathematical model was developed describing the influence of sonic exposure and gas pressure on the liquid temperature and evaporation rate. The experimental program and methods were designed; experimental setup was constructed, the test jobs were accomplished. The experiments were based on a piezoceramic transmitter with assigned frequency and amplitude of sonic oscillations. Distilled water was chosen as working fluid. The paper presents experimental dependency of the liquid temperature variation and calculated evaporation rate for situations of composite sonic and vacuum exposure or separate influence of every factor. Comparison of calculated and experimental value of liquid temperature while evaporation demonstrated the compliance with 10 % accuracy. The research presents the regression analysis for the factor impacting the liquid evaporation rate: pressure inside the vacuum chamber and power of sonic exposure. The regression equation was derived for estimating the impact of sonic and vacuum exposure on the liquid evaporation rate during experiments at different pressures and liquid mass. The suggestions for further studies were formulated as well.

An experimental investigation of coinstantaneous heat and mass transfer phenomena between water and air in a counter flow wet cooling tower filled with a new type packing named “FCP-08” is presented in this paper. The packing consisted of foamed ceramic corrugated board with sine waves and surface retention groove is 1.0 m high and have a cross sectional test area of 0.68x0.68 m². The present investigation is focused mainly on the effect of the water/air mass flow ratio on the heat and mass transfer characteristics of the cooling tower, for different inlet water temperatures. The results show that the cooling water range R and the cooling tower efficiency e decrease with the increase of water/air mass flow ratio L/G . Meanwhile, the cooling characteristic coefficient KαV/L slightly decreases with the increase of water/air mass flow ratio and the value is obviously higher than that of other packing investigated before. The expression of cooling characteristic coefficient related to water/air mass flow ratio and inlet water temperature is obtained by linear fitting. The comparison between the obtained results and those found in the literature for other types of packing indicates that cooling performance of the tower with foam ceramic packing is better.

The article presents a methodology of comprehensive study of thermal radiation emitted by furnace gases during solid fuel combustion. The characteristics of initial fuel and chemical composition of flyash are described. The absorption coefficients of the gaseous phase in relation to the wavelength, temperature, and concentration of the main gas components are measured. The gas composition was determined by calculation of the total combustion products, as well as experimentally (through a gas analyzer). The experimental results on the particle shapes and sizes, the distribution function of flyash particles, the fusibility of mineral part were used to calculate the radiation characteristics of the condensed phase. Calculations of emission characteristics of furnace gases (spectral and integral flux densities and emissivity factors) depending on the influence of each phase at different operating temperatures are presented. The method efficiency is estimated through comparing with calculated and experimental data on the emission characteristics for homogeneous and heterogeneous combustion products. Spectral ranges were chosen to determine the temperature for furnace gases, a plume, and the surface of flyash deposits on the furnace walls. Experimental dependences of the emissivity factors for flyash deposits on temperature are presented. The findings can be used to calculate heat fluxes, for the purposes of furnace gases pyrometry, and to determine the temperature level in the compilation of operational maps for the boiler.

The processes of heat and mass transfer occurring in real furnaces of the industrial TPS’s have been investigated with the aid of advanced methods of the three-dimensional computer modeling. The computational experiments have been done on the study of the aerodynamics of high-temperature flows and heat transfer characteristics at a combustion of a low-grade Karaganda coal of the KR200 brand in the combustion chamber of the BKZ-75 boiler of the Shakhtinsk TPS. As a result of the execution of numerical experiments, the aerodynamic pattern of high-temperature flows as well as the temperature distribution in the main cross sections of the furnace chamber and along its height have been obtained. The radiation heat flux on the combustion chamber walls has been computed by the methods of numerical modeling, which has enabled the determination of the regions of its maximum action on furnace shields. The obtained pattern of the distribution in the furnace space of the heat release intensity at combustion determines the regions of the maximum interaction of the fuel and oxidizer.