Thermophysics and Thermal Power Engineering

Effect of non-isothermality on film cooling effectiveness under partial blockage of coolant injection holes

2026-04-20T10:23:15+03:00

Modern gas turbine units (GTUs) operate at extremely high temperatures, with mainstream gas temperatures reaching 1700–1750 °C in transport and military applications, while heat-resistant blade materials are limited to approximately 1000–1100 °C. This necessitates advanced cooling techniques to ensure component durability and reliability. Film cooling, achieved by injecting coolant air through inclined holes to form a protective layer on the blade surface, is a widely adopted method. However, the effectiveness of film cooling is significantly influenced by the non-isothermality parameter Rₜ = Tf/Tc, which characterizes the temperature ratio between the mainstream and coolant flows. Real GTU operating conditions correspond to Rₜ = 2.0–2.2, while most experimental studies are conducted under low non-isothermality conditions (Rₜ ≈ 1.2), creating significant uncertainty when extrapolating laboratory data to actual turbine operating conditions.

An additional critical factor affecting cooling effectiveness is partial blockage of coolant injection holes caused by particle deposition (e.g., CaO–MgO–Al₂O₃–SiO₂) during operation in dusty or desert environments, which is particularly relevant for military GTU applications. Research shows that even after 50–200 hours of operation, sufficient deposits can accumulate to partially obstruct the hole cross-section. This study focuses on partial-load operation regimes characterized by reduced blowing ratios (m = 0.4–1.0), which are typical when the engine operates below maximum capacity. Such regimes require detailed investigation considering real temperature conditions, as reduced coolant mass flow can lead to changes in flow structure and thermal protection film redistribution.

Purpose of the Work. This study aims to numerically investigate the effect of flow non-isothermality (Rₜ = 1.8) on film cooling effectiveness of a flat surface under partial blockage of coolant injection holes in the blowing ratio range m = 0.4–1.0, characteristic of partial-load turbine operation. Particular attention is paid to comparative analysis with model conditions (Rₜ = 1.2) and assessment of transverse non-uniformity of coolant film formation in a four-hole configuration.

Research Methods. The investigation was conducted using numerical simulations in ANSYS CFX 2019 R2 with the Reynolds-Averaged Navier-Stokes (RANS) equations and SST turbulence model for closure. Three geometric configurations were created: a baseline without blockage and two configurations with partial blockage corresponding to 25% (h/d = 0.5) and 50% (h/d = 1.0) obstruction of the hole cross-sectional area. The blockage degree was characterized by the dimensionless parameter h/d, where h is the maximum transverse blockage height and d is the hole diameter (0.8 mm). Geometric dimensions were based on typical turbine blade cooling system parameters: hole diameter d = 0.8 mm, transverse pitch t = 2.4 mm (t/d = 3.0), and hole inclination angle of 30° relative to the surface. A hybrid unstructured mesh with approximately 1.1 million elements was employed, consisting of tetrahedral elements in the mainstream flow and prismatic layers near solid surfaces. Boundary conditions were set to achieve blowing ratios close to m = 0.4, 0.6, 0.8, and 1.0. The mainstream velocity was 400 m/s with a temperature of 1100 °C, while the coolant temperature was 500 °C, corresponding to Rₜ = 1.8 characteristic of real GTU operating conditions. Turbulence intensity was set to 1%, and adiabatic wall boundary conditions (δQ = 0) were applied to solid surfaces. Symmetry conditions were imposed on lateral surfaces of the computational domain. The model was verified against experimental data for the traditional configuration without blockage (h/d = 0) at m = 1.0, showing a deviation of 9.68%, which is acceptable for CFD simulations of film cooling.

Results and Conclusions. Analysis of local film cooling effectiveness distributions revealed that the character of coolant distribution maintains qualitative patterns typical of discrete film cooling with inclined holes, while absolute effectiveness values are significantly higher compared to model conditions (Rₜ = 1.2) due to the greater temperature difference between mainstream and coolant flows, providing more intensive thermal protection of the surface. The non-isothermality parameter plays a determining role in forming absolute values of film cooling effectiveness. Under high non-isothermality conditions (Rₜ = 1.8), characteristic of real operating regimes of transport and power GTUs, effectiveness is approximately twice as high as under model conditions (Rₜ = 1.2): at m = 0.4 for the baseline configuration without blockage, it increases from 16.8% to 33.6%. A similar trend is observed for all blockage configurations: at h/d = 0.5 and m = 0.4, effectiveness increases from 16.3% to 29.0%, and at h/d = 1.0 from 10.8% to 24.0%.

For high non-isothermality conditions (Rₜ = 1.8) at m = 0.4, partial hole blockage leads to a reduction in area-averaged effectiveness of 13.7% for h/d = 0.5 and 28.6% for h/d = 1.0 relative to the baseline configuration. The physical mechanism of this effect is complex: blockage at constant mass flow rate increases coolant exit velocity and effective blowing ratio, while also changing the jet discharge angle, causing early jet separation and intense turbulent mixing with the mainstream flow. As the blowing ratio increases to m = 1.0, characteristic of elevated partial-load regimes, effectiveness losses increase to 31.1% and 56.1%, respectively.

Importantly, the character of blockage influence is universal, but its intensity depends on temperature conditions. Comparative analysis showed that for low-temperature conditions (Rₜ = 1.2) at m = 0.4, the reduction in film cooling effectiveness was 3.0% for h/d = 0.5 and 35.7% for h/d = 1.0, whereas for real conditions (Rₜ = 1.8) it was 13.7% and 28.6%, respectively. This indicates that under high non-isothermality, the film cooling system demonstrates different sensitivity to geometric changes in holes, which must be considered when designing GTU blade cooling systems.

Analysis of spatial effectiveness distribution showed persistence of transverse non-uniformity of the coolant film for all investigated configurations and both temperature regimes. Local maxima form along hole axes corresponding to trajectories of the central portions of coolant jets, while zones with reduced effectiveness appear between holes where the surface remains inadequately protected from thermal exposure. This non-uniformity persists over a significant distance from the holes and does not disappear even with increasing blowing ratio, indicating the limited ability of discrete hole systems to provide continuous film coverage of the surface. Blockage intensifies this non-uniformity regardless of the non-isothermality level.

The obtained results emphasize the necessity of accounting for real temperature conditions when designing and optimizing film cooling systems for gas turbine blades. Extrapolation of data obtained under model conditions with low non-isothermality to real operating regimes can lead to significant errors in assessing cooling effectiveness and blade thermal state. The data obtained in this work can be used to improve calculation methods for the thermal state of turbine blades, accounting for non-isothermality effects and degradation of film cooling systems due to hole contamination.

NUMERICAL MODELING OF RADIATION-CONVECTION HEAT TRANSFER FROM A HEATED OBJECT TO THE SURROUNDING ENVIRONMENT UNDER CONDITIONS OF FREE CONVECTION

2026-04-20T10:23:13+03:00

A known method of protecting heated objects from being recognized by optoelectronic devices that detect infrared radiation is to use screens over the heated objects that reduce the intensity of this radiation. Low-emissivity coatings with low emissivity coefficients are applied to the surface of such screens. Such a coating can be copper foil. To determine the effectiveness of this method of temperature masking of heated objects, numerical simulation of radiation-convection heat transfer of a heated horizontal plate with the environment, above which a textolite screen with copper foil on the surface is located, is performed. Numerical modeling is performed by the method of numerical solution of the system of equations of hydrodynamics and heat transfer. This system is supplemented by boundary conditions of the fourth kind, which take into account the presence of radiation heat flux on the surfaces of the plate and the screen. It is determined that the radiation heat flux on the outer surface of the screen under the conditions considered can be reduced by 6.7...7.48 times due to the copper foil coating. In this case, increasing the distance between the screen and the heated object contributes to the reduction of the radiation heat flux from the screen.

STUDY OF THE INFLUENCE OF GAINER LIQUID COMPOSITION ON THEIR DRYING KINETICS IN THE “DROPLET–VAPOR–GAS MEDIUM” SYSTEM

2026-04-20T10:23:12+03:00

Considering today’s wartime conditions in Ukraine, dry concentrates of sports nutrition (gainers) with a powerful protein–carbohydrate complex are advisable to use in the general therapy of severely wounded servicemen to increase the effectiveness of their treatment and accelerate recovery. Obtaining them by spray drying makes it possible to minimize thermal effects on thermolabile biologically active substances, particularly those derived from fresh fruit raw materials. The proteins and carbohydrates used in the proposed formulations, including pumpkin puree, represent insufficiently studied multicomponent heterogeneous systems, which should be additionally investigated as objects of spray drying.

The aim of the study was to examine the kinetic regularities of drying in the “droplet–steam–gas medium” system for liquid gainer compositions in order to determine the rational heat-technology parameters of their spray drying.

Research methods. The study used liquid gainer compositions that included proteins, fats, and carbohydrates in different proportions. The required consistency, containing particles of insoluble fractions ≤150–180 μm from pumpkin puree (30% content in the compositions), was achieved by processing in a cylindrical-type rotary-pulsation apparatus. The drying kinetics of single droplets of the compositions were studied in the “droplet–steam–gas medium” system using an experimental setup in a heat-carrier flow heated to 150 °C, 165 °C, and 185 °C. Based on experimental drying data (critical points and thermogram patterns), the corresponding kinetic dependences were constructed.

Results. The dehydration process of all three compositions occurred in the high-temperature drying period, which included the stages of crust formation, boiling, and final drying. According to the kinetic dependences of droplet heating rate: during crust formation, the heat–moisture transfer process in droplets of samples No. 2 and No. 1 proceeded under milder conditions, while during the final drying stage, sample No. 1 was able to dry at an accelerated rate. Shortening of the crust formation and boiling stages reduced the relative duration of dehydration up to the critical point cr.3 to values of 0.35–0.45 and significantly extended the final drying stage to 0.55–0.65, which is typical for colloidal systems. Rapidly formed dense shells on the droplet surface resisted moisture transfer, leading to the formation of hollow, thin-walled particles of enlarged size, especially at temperatures ≥180 °C, with a high probability of elevated moisture content and increased adhesiveness in the hot state.

Conclusions. The study showed that, as with typical colloidal systems, the proposed compositions are characterized by the low diffusion capacity of poorly permeable surface shells of drying droplets, which hinders moisture transfer and increases the risk of obtaining powder with elevated moisture content and adhesiveness in the hot state. The hollow structure of enlarged particles reduces the bulk density of the powder.

It was experimentally established that, among all the tested compositions, composition No. 1 was the most suitable for obtaining high-quality powder by spray drying. According to its kinetic characteristics, its structural protein–carbohydrate potential ensured reduced deformation of the particle shape during drying and smaller final particle size at 165–175 °C, while structural strengthening and the disappearance of adhesiveness were achieved after cooling due to the vitrification of sugary substances.

ENCHANCEMENT OF TRAY EFFICIENCY IN COLUMN MASS-EXCHANGE APPARATUS

2026-04-20T10:23:11+03:00

Technological calculations of the column mass–exchange apparatus assume instantaneous transfer of volatile components of vapour and liquid phases, without considering the residence time the liquid on the trays. There is a threshold below which the contact time between the phases is insufficient to reach equilibrium, and as a result, the efficiency of commonly used tray types does not exceed 0.4-0.6.

The aim of the work was to study the phase equilibrium between liquid and vapour in the ethanol-water system under subatmospheric pressure; to select appropriate methods for thermodynamic thermodynamic validation of experimental data; to develop approaches for modeling mass transfer between liquid and vapour in cyclic column apparatuses in order to increase tray efficiency; and to evaluate their effectiveness in processing of ethanol–containing fractions under industrial conditions.

Research methods included analytical, computational, physicochemical and chromatographic techniques using instruments and methodologies applied in the production of rectified ethanol. The custom-designed experimental apparatus was developed, which allowed to increase the accuracy measurements and reduced the time required to achieve phase equilibrium to 30–40 min. Experimental data on phase equilibrium in the ethanol-water system were obtained in the pressure range of 103 to 50.6 kPa specifically in the low ethanol concentration region (below 3.0 mоl. %), which corresponds to the operation conditions in the lower sections of distillation and rectification columns. Based on the experimental data, phase equilibrium modeling was performed for the specified pressure. The Tsuboko-Katayama equation was used for modeling. Thermodynamic validation of the results demonstrated a satisfactory level of agreement between calculated and experimental data. Phase equilibrium curves were constructed, the relationship between ethanol evaporation coefficients and pressure was established, and the inversion of equilibrium curves was identified.

Mass transfer methods between liquid and vapor under controlled cycles of liquid holdup and overflow have been developed, along with designs of mass-exchange apparatus for their implementation. The hydrodynamic operating modes of trays under cyclic conditions have been determined. Experimental results have shown that the extending the contact time between phases on the trays to 30-60 seconds significantly increases the efficiency and reduces steam consumption up to 40%.

HEAT AND MASS EXCHANGE IN PROTEIN PRODUCTION DEVICES BASED ON HYDROGEN OXIDIZING BACTERIA

2026-04-20T10:23:09+03:00

Global economic development trends urgently require the transition of agricultural food production to industrial scale.

Numerous patents recently obtained confirm that many countries are interested in protein production processes, particularly those based on hydrogen-oxidizing bacteria.

Research into this process is currently in the laboratory experimentation and preliminary design stages for pilot plants.

This paper examines the current state of development in protein production using hydrogen-oxidizing bacteria. To identify deficiencies in the biomass cultivation process, a pilot plant was created and a series of studies were conducted. The results were compared with existing data.

Based on the experimental results, the key principles of the biomass production process were clarified, and the reliability of individual components of the laboratory setup was verified.

A comprehensive analysis of the resulting biomass, conducted in I. Mechnikov Institute of Microbiology and Immunology (Kharkiv, Ukraine) established that, during continuous cultivation, protein synthesis by the Alkaligenes eutropha Z1 bacterium is stable, accounting for 72-74 % of the resulting biomass, consistent with published data. The content of lipid, carbohydrate components, and nucleic acids is within normal limits. The presence of other species in the biomass does not exceed permissible levels.

Thus, it has been proven that the individual components and the entire system operate reliably.

Based on the results of experimental studies of the process, it was recommended to change the equipment design of the stand – to dissolve hydrogen in the cultural liquid before feeding it to the fermenter, and to use film devices as fermenters with stirrers.

A calculation sequence for heat and mass transfer in a film fermenter was developed.

It has been shown that the conversion of protein production from agricultural methods to industrial ones will yield significant economic benefits and improve the environment by reducing harmful emissions into the atmosphere.

A RESEARCH ON INFLUENCE OF NOZZLE GEOMETRY ON THERMODYNAMIC AND FLUID DYNAMIC EXHAUST PROPERTIES OF A SMALL-SCALE JET ENGINE

2026-04-20T10:23:07+03:00

The purpose of this study is to evaluate the effectiveness of nozzle profiling of a small turbojet engine with an ejector as a method of reducing the thermal signature of an aircraft by CFD modeling of the original and modified engine nozzle ducts and by analyzing the resulting flow parameters.

The main task of the research is to conduct a qualitative analysis of the intensification of mixing of ejector and nozzle flows in a small turbojet engine using CFD simulation of a modified design in order to reduce the thermal signature of the engine.

During the simulation, a number of factors were identified that influence the studied effects of interaction between the ejector flow and the nozzle: aircraft speed, aerodynamic drag of the ejector, parameters characterizing flow turbulence in the mixing zone, etc. The results of the simulation include contours of dynamic pressure, temperature, flow velocity, and all the main thermal and fluid dynamic parameters of the flow in the three-dimensional calculation domain.

It has been shown that profiling the nozzle of a small turbojet engine in combination with the use of an ejector allows the formation of vortex flows that intensify the mixing of the secondary flow of the ejector with the primary flow of the nozzle and can be used to improve heat transfer and, according to similar studies, reduce the thermal signature of engine exhaust.

The described method will be further improved for a detailed quantitative analysis of the influence of the geometric profile parameters of the ejector nozzle on the mixing intensification and thermal visibility of a small turbojet engine.