Diffuser Outlet Research Articles

Flow physics of a subcritical carbon dioxide jet in a multiphase ejector

Existing literature on ejectors, different researchers utilized different turbulence models by their choice, neither analyzing the physics of turbulence nor providing any sufficient optical diagnostics of the flow field. In this article, the physics captured by the Unsteady Reynolds Averaged Navier–Stokes (URANS) and Large Eddy Simulation (LES) are compared based on well-posed boundary conditions obtained experimentally from a carbon dioxide (CO2) vapor compression cycle with an error ≤2.5%. The experimental results utilized for this study are at Reynold’s number (Re) 1.2e5 at the high-pressure inlet (motive flow) maintaining CO2 in subcritical state. The low-pressure inlet (suction flow) is maintained at Re = 9.8e4 with CO2 in vapor state, providing a pressure lift ratio of 1.2 at the diffuser outlet. Comparison of flow topologies with different URANS models reveals that only standard, Shear Stress Transport (SST) k−ω, and Reynold’s Stress Model-Shear Stress Gradient (RSM-SSG) are the suitable URANS models capturing a linearly increasing anisotropy tensor component with increasing strain in the flow. LES also predicted the similar physics. However, standard k−ω overpredicted the suction pressure beyond the acceptable uncertainty limits, which made it inapplicable. For the first time, a spatio-temporal representation of the flow topology with LES revealed the actual jet morphology of a CO2 ejector. Specifically, finger-like structures are key features to entrain more surrounding warm fluid into the colder dense core fluid at the cost of destabilizing and breaking up the jet by stretching the streamwise vortices and obstructing the increase in pressure-lift ratio.

Numerical Investigation of Flow Evolution in Centrifugal Compressors During Surge

Abstract Surge can lead to violent flow fluctuations in the compression system and damage to the blade structures. In this article, a fully three-dimensional numerical model of the centrifugal compressor surge is developed, and the accurate transient flow evolutions in different components during the surge are studied in detail. The results show that in the surge initiation, the pressure distortion caused by the asymmetric geometry of the volute at the diffuser outlet transfers along blade passages to the impeller inlet, which induces two types of stall cells with different rotating speeds and sizes developing independently in two isolated circumferential positions at the impeller inlet. With the surge development, the two types of stall cells come into contact and are mixed, which causes the asymmetric local reverse flow near the casing of the impeller leading edge. Subsequently, the reverse flow extends to the full annuls at the impeller inlet, and the compressor pressure ratio falls abruptly. At the same time, several expansion waves arise in the impeller and travel downstream along the volute and the outlet pipe. As reflected by the nozzle, these expansion waves travel back upstream into the impeller. The findings of this research have great implications for the asymmetric flow control methods, which develop novel asymmetric geometries to counteract the influence of the volute and extend the compressor stable operation range.

Upgrading the Compressor Stage of the CAT250TJ Micro Gas Turbine Engine

AbstractDue to their simplicity and relative ease of manufacture, single-stage centrifugal and mixed flow micro gas turbine (MGT) engines are preferred in thrust-based remotely piloted aerial vehicles. A single-stage mixed-flow compressor upgrade for the 200 N CAT250TJ MGT engine is numerically evaluated and presented. An in-house developed mean line application and commercial CFD software is used for the design and performance evaluation of the proposed upgrade configurations. The CAT250TJ – Gen1 engine features a single-stage centrifugal compressor, annular combustor, and single stage axial turbine. Apart from an upgraded impeller, a new crossover diffuser configuration is introduced to replace the wedge-type, straight outlet diffuser configuration of the Gen1 engine. The new single vane crossover diffuser configuration provides a design point total-to-total efficiency and pressure ratio increase of 8.3% and 12.1%, respectively. A disadvantage of a single-vaned crossover diffuser compared to legacy diffusers is a narrower operating range. To alleviate this issue, various combinations of tandem and splitter vane crossover diffuser configurations are proposed. These provide an enhanced operating range, comparable with the operating range displayed by the Gen1 configuration. A turbine power matching analysis is additionally completed to ensure proper compressor integration. Gas turbine cycle software is used to evaluate the on-engine performance of the upgraded compressor configurations. It is shown that the new baseline, single vane crossover diffuser configuration provides a 10.74% increase in design point static thrust.

Reduction of Disk Friction Loss by Applying a Fin to the Back of a Centrifugal Impeller

Abstract It is well known that the ratio of disk friction loss of low specific speed pumps is large. When the specific speed is 100 min−1, m3/min, m or less, the disk friction loss increases remarkably. In this study, focusing on the clearance flow from the diffuser outlet to the impeller outlet (This is called the outward flow) behind the centrifugal pump, a fin was installed on outer diameter side of the rotating wall on the back side of a centrifugal pump as a countermeasure, and the influence of changes in velocity distribution near the wall on disk friction loss was investigated by torque measurements, velocity measurement, and computational fluid dynamics (CFD) analysis. As a result, it was clarified that disk friction loss is decreasing by installing the fin in both torque measurements and CFD results, because the clearance flow is separated by fin and circumferential velocity is increased in the wake region of the fin in both measurements and CFD. In addition, it was clarified that disk friction coefficient (normalized torque) can be expressed as a function of the inlet swirl ratio and Reynolds number. Also, prediction equation is derived for each shape (with and without fin). According to the equation, it was found that disk friction loss reduction effect by installing a fin becomes larger when Reynolds number and the inlet swirl ratio are small.

Effect of Different Types of External Guide Vanes on the Performance of High-Pressure Centrifugal Compressor

In order to reduce exit swirl and obtain the desired Mach number, axial exit guide vanes (EGV) are often employed in a centrifugal compressor. NASA CC3 compressor, with wedge vane diffuser and without EGV, is considered as the base model for the analysis and validation. An axial flow domain with exit guide vane is added to this base model after the diffuser outlet to study the effect on the compressor performance. The performance of exit guide vane with different profiles: flat plate, symmetric wedge, circular arc, and airfoil vane profiles by maintaining the same chord, number of vanes, and flow angle of the vanes are studied. Numerical simulations are carried out with 60 number of exit guide vanes for all four types of vanes. Among several combinations, when the centrifugal compressor is equipped with 60 circular arc vanes as EGV, the efficiency and pressure recovery values at the design point have increased by 6.5% and 8.9%, respectively.

A numerical investigation of the effect of vaned diffuser water cooling on the internal flow field of a centrifugal compressor

Due to their high pressure rises, the gas temperature of high-speed centrifugal compressors can be very high to the detriment of compressor aerodynamic performance. A water-cooled vaned diffuser technique is proposed to alleviate this problem. Compressor housing integrated water-cooling passages are employed to introduce cooling water to the vanes through holes near the vane centre. The technique was applied to a 180 mm turbocharger compressor running at the tip speed of 452 m/s, and numerical studies with conjugate heat transfer and fluid-structure thermal interaction were carried out to find the effects of the cooling to compressor performance and the mechanical stress of diffuser vanes. The results show that compressor efficiency is improved by the cooling, and the improvement increases as compressor mass flow reduces. At modest pressure ratios around 3.3, the maximum improvement of 1.09 percentage points is achieved using 30°C inlet water temperature. The cooling is found to significantly reduce the air temperature near diffuser passage solid walls, thus lead to more uniform air temperatures at compressor exit. The reduction of 1.33°C and 2.21°C in the diffuser outlet temperature have been found at 1.68 kg/s air mass flow with 70°C and 30°C water inlet temperature respectively. Moreover, the thermal stress in diffuser vanes is shown to be lower with the cooling.

Industrial-scale experimental study of internal-mixing air-blast nozzle for sludge atomization

The atomization of sewage sludge is a key step in its drying process. This study conducts an industrial-scale experimental study to investigate the performance of a self-developed internal-mixing air-blast nozzle for atomizing sewage sludge. The size of atomized droplets is calculated using image processing technology. Using the specific size and characteristic size of the droplets, the droplet distribution and the droplet motion behavior in spray field are investigated at various air-to-liquid mass flow rate ratio (ALR). The larger the ALR, the smaller the atomization droplets. By installing outlet diffusers and impaction pins, the atomization angle can be increased and the distribution of droplets in the spray field can be improved. The outlet diffuser with an outlet angle of 90° and the square impaction pin exhibit optimal effect. Experiments with real scale and industrial grade have a significant reference value for industrial applications of sludge atomization.

Conditions of submarine levéed channel inception: Examination by flume experiments

ABSTRACTSubmarine levéed channels are often observed in submarine fans, although submarine fans without continuous levéed channels are also common depending on the composition of supplied sediments, particularly the proportion of muddy/sandy materials. However, parameters governing the inception of levéed channels have not yet been studied. Furthermore, depositional levéed channel topography has not been simulated in experimental flumes in any previous study conducted with dilute flows (flow concentration <10%). Herein, four experimental series were conducted (Series A, B, C and D) to simulate depositional submarine channels and to study their formative conditions. A mixture of sediment and saline water was used in the experiments, and both the width of an outlet diffuser and flow discharge rate were varied in the experimental series. A topography composed of a channel with two ridges resembling natural depositional submarine channels with levées was formed in all experiments. Comparisons between the experimental topographies and natural submarine fans revealed that two of the four experimental series produced channel levées with length to width ratios similar to those produced by natural systems. An experiment with half the outlet size produced a channel two times deeper (4.5 cm against 2.0 cm and 2.2 cm) as compared to other experiments. The flow discharge rate and outlet width were half of those observed in Series A and B. Furthermore, salt was removed from the initial mixture for one of the experiments, resulting in high natural levées with a short channel. This study demonstrated that dilute flows could form purely depositional channel levées without precursor or resultant erosive features. In addition, results revealed that the formation of submarine channels is related to two factors: channel width and muddy suspended sediment.

Оценка частот акустических колебаний в выходном диффузоре газотурбинной установки

Calculated estimation of acoustic resonances in the flow part of gas turbines in the outlet diffusers is a current problem. Its solution will improve vibration reliability of essential elements of gas turbine plant (GTP) – the rear bearing housing support and the blade apparatus. At present there are only a limited number of calculated and experimental works devoted to the study of acoustic resonance effect in the output devices of gas turbines. The objective of this paper is to estimate frequencies of acoustic oscillations in the GTP output diffuser. It allows to avoid coincidence of the indicated frequencies with the frequencies of natural oscillations of GTP structural elements. The results of the analysis of frequencies of acoustic oscillations should be confirmed in further experimental studies of the specified output device, i.e., the output diffuser. The method to solve the problem is computational. The results of numerical calculations of acoustic resonances in the GTP outlet diffuser are used for the analysis. The calculations have been performed in the Modal Acoustics ANSYS Workbench program. The model is described and the computational program to calculate the acoustic modes in the output diffuser is specified. The boundary conditions to perform the specified numerical acoustic calculations are proposed. The modes and corresponding frequencies of acoustic oscillations that are possible in the GTP outlet diffuser are considered. Justification of validity of the results of numerical calculations is their partial comparison with analytical solution for the simplest acoustic model, as well as with the preliminary result of the experimental research. The results of the acoustic calculations of the model of the GTP outlet diffuser allow to determine the modes of acoustic oscillations, and to estimate the frequency range of these modes. To substantiate the calculated estimates of frequencies of acoustic pressure pulsations, as well as to clarify the amplitudes of these pulsations, experimental aerodynamic studies of the model of the outlet diffuser with a rotating turbine stage at the inlet are necessary. Refined calculation model of acoustic resonances in the GTP outlet diffuser will contribute to the offset of frequencies of acoustic gas vibrations from the natural frequencies of vibrations of the GTP structural elements, adjacent to the diffuser. The indicated frequency offset will improve the GTP vibration reliability at the design stage.

Finding an absolute maximum theoretical power coefficient for ducted wind turbines

This study investigates power coefficients for ducted wind turbines to determine an absolute maximum value corresponding to a maximum ideal power output. A maximum power coefficient using the rotor area in the available kinetic energy is still an open question in the research community. Here, the available kinetic energy of a free stream uses the largest device area, diffuser outlet, funnel inlet, and virtual diffuser outlet areas in the power coefficient calculation. The virtual diffuser outlet is defined as the downstream location at which the static pressure of the fluid inside the stream tube recovers to the pressure of the free stream flow. This study performs a one-dimensional analysis based on the continuity, momentum, and energy principles and the Euler Turbomachinery equation. The results show the absolute maximum power coefficient of 0.384 using the virtual diffuser outlet area in the available kinetic energy calculation. Another finding is that both the maximum ideal power output and the cp = 0.384 happen at the same value of the rotor thrust coefficient, CT,R≈ 2/3. The power coefficient based on the rotor area is more convenient for idealized bare turbines; therefore, the power coefficient based on the virtual diffuser outlet area applies only to ducted wind turbines.

Investigation of steam ejector parameters under three optimization algorithm using ANN

Several industries have adopted Steam ejectors as promising energy-saving devices. The steam ejector is used extensively in the HVAC, refrigeration, and desalination industries because it harnesses surplus heat. Numerous computational fluid dynamics (CFD) and thermodynamic models have been addressed in the academic literature. Predictions for steam ejector parameters using these models are fairly accurate. However, considerable discrepancies between experiments and models are sometimes as high as 20 %. Contrarily, CFD simulations for an ejector are computationally expensive and necessitate careful selection and tweaking of the turbulence model. ANN-based data-driven techniques are now used for complicated mechanical system modeling. The advantages of a well-trained ANN model include low computational costs and adaptability for integration with real-time control systems. In this study, we developan artificial neural network (ANN) model of a steam ejector and analyzes how different training strategies affect the ANN model's ability to make accurate predictions. The model is trained using a sizable experimental library with various geometrical and operational conditions. Using a typology of four input factors (Nozzle Throat Diameter (Ntd), Diffuser Outlet Diameter (Dod), Ejector Area Ratio (σp), and Entrainment Ratio (ER)) that capture geometry and operating conditions characteristics, the framework predicts two output parameters: (a) Coefficient of performance (COP) and (b) Pressure reduction ratio (PRR) of the steam ejector. Among the three optimizers tested for algorithm training, the ANN model trained using the ADAM optimizer performed the best. The model's hidden layer contains 102 neurons, and a split ratio of 0.2 is used during dataset training. The average error for COP and PRR predictions made by the ANN model is ± 1.8 % and ± 2.4 %, respectively. As a result, the ANN model can be used to improve the steam ejector system's configuration and operation.

Investigations on the Splitter Structure to Improve the Aerodynamic Performance of Gas Turbine Exhaust Diffuser at Different Swirl Angles

Abstract To weaken the flow separation in the exhaust diffuser under real operating conditions and increase the static pressure recovery coefficient of the exhaust diffuser, an exhaust diffuser structure with splitters was proposed. Based on verifying the reliability of the numerical method, the paper numerically explores the influence of the height and width of the splitter on the aerodynamic performance of the exhaust diffuser under three different inlet swirl angles by solving three-dimensional Reynolds-Averaged Navier–Stokes (RANS). The results show that the introduction of the splitter structure into the exhaust diffuser can effectively suppress the separation vortex near the strut, improve the flow state at the exhaust diffuser outlet, and further increase the static pressure recovery coefficient of the exhaust diffuser. The optimal splitter structure can be obtained by comparing the effects of the splitter height and width on the static pressure recovery performance of the exhaust diffuser under different inlet swirl angles. When the inlet swirl angles are 16 degs, 28 degs, and 38 degs, compared with the original exhaust diffuser without splitters, the optimal splitter structure can increase the static pressure recovery coefficient of the exhaust diffuser by 0.036, 0.096, and 0.146, respectively, with a relative increase of 7.3%, 34.2%, and 76.2%. The introduction of the splitter structure helps to improve the aerodynamic performance of the exhaust diffuser.

Investigation of high-speed deep well pump performance with different outlet setting angle of space diffuser

As one of the important equipment for pumping groundwater, how to improve the operation performance of deep well pump has been a research hotspot. At present, most of the deep well pump hydraulic design research mainly focuses on the low speed condition, and there is still a lack of systematic research on the internal flow theory and design method of the high speed deep well pump. In this paper, numerical simulation is used to investigate the performance change law of high speed deep well pump under different space diffuser blade outlet setting angles, and the performance test of the design scheme model is used to verify the accuracy of numerical simulation. The hydraulic loss inside the space diffuser and the velocity moment at the outlet are quantitatively analyzed. The results shown that the outlet setting angle of 90° is a relatively optimal solution. Under the designed outlet setting angle, the hydraulic loss in the first-stage space diffuser decreases with the increase of the flow rate, and the average hydraulic loss in the space diffuser at all levels fluctuates between 16% and 20%. With the increase of the number of stages, the velocity moment at the outlet of the space diffuser also increases gradually, and the change trend of the velocity moment at the outlet of the first-stage space diffuser under different outlet setting angles is relatively consistent. This research can provide reference for the optimal design and application of high speed deep well pump.

Расходные характеристики инжекционных водовыпусков-регуляторов

In cases where the supply of energy sources to hydraulic structures located on irrigation canals is economically unjustified, hydraulic automation means are widely used in Russia and abroad. The purpose of the research is to derive design dependencies to determine the flow rate of the injected and injected flows, taking into account hydraulic losses within the flow path of the structure, to construct the flow characteristic of the regulator with a nozzle and an output section of a constant area with its subsequent verification by the data of the hydraulic experiment. Injection flow regulators have several modifications: with a diffuser outlet section without restricting the outlet pipe with a nozzle, with a nozzle and diffuser, with a nozzle and an outlet section of a constant area. For regulators with a nozzle, dependences for hydraulic calculations have now been obtained, which can be considered conditionally “ideal”, since they do not take into account a number of local resistances and frictional resistances along the length that arise when flows merge with subsequent movement in the mixing chamber. As a result of the research, the authors for the first time obtained calculated dependencies for determining the flow rate of the injected and injected flows, taking into account hydraulic losses within the flow path of the structure, and constructed the flow characteristic of a regulator with a nozzle and an outlet section of a constant area. The flow characteristic is verified using available hydraulic experiment data. An analysis of the shape of the flow characteristics of the injection regulator was carried out by comparison with the generalized characteristics of hydraulic jet pumps. The practical significance of the research lies in the possibility of using the dimensionless characteristics of the injection water outlet to link it to specific operating conditions, as is customary when selecting pumps. To determine the flow rates in the regulator, a computer program has been registered.

Designing of non circular air intakes for subsonic gas-turbine engines

The subject matter of the article is the process of subsonic air intake shaping for gas-turbine engines at the airplane preliminarily design stage. The goal is to develop a mathematical model for non-circular air intake shaping for gas-turbine engines on the base of V. I. Polikovskii method of subsonic air intake shaping for high-bypass ratio turbofan. The tasks to be solved are: to consider the possibility of non-circular shape of the external outline of the engine nacelle; to take into account the possibility of non-circular shape of the internal air intake duct (in the first approximation, the shape of internal air intake duct cross-section is defined in the form of a rectangular with possible four different radiuses in its corners); to consider the engine inlet spinner presence. The methods used are: analytical and digital mathematical methods, implemented in MathCAD and Microsoft Visual Studio systems. The following results were obtained: On the base of the proposed method, new calculation module for the Power Unit software version 11.8 has been developed (С-language Win32 UNICODE application) having a friendly user interface. Conclusions. The scientific novelty of the results obtained is as follows: 1) mathematical model (algorithm and its program implementation) for non-circular air intake shaping for gas-turbine engines has been developed considering non-circular shape of the external outline of the engine nacelle, non-circular shape of the air intake duct internal outline, presence of engine inlet spinner, and zero expansion angle in the diffuser outlet cross-section; 2) adequacy of calculation results by the developed mathematical model is shown by means of comparison with the shape of real air intake, developed by the Antonov Company. For the following improvement of the mathematical model, it is desirable to add the possibility of considering S‑shape of the air intake duct, defining its length from designer’s considerations, defining a bigger radius of curvature of the air intake lip, and considering the presence of boundary layer bleeding devices in front of the air intake.

Design of circular air intakes for subsonic turbofans

The subject matter of this article is the process of subsonic air intake shaping for high-bypass ratio turbofan at the airplane preliminarily designing stage. The goal was to improve a mathematical model of V. I. Polikovskii method of subsonic air intake shaping for high-bypass ratio turbofan. The tasks are to consider the presence of cant of inlet cross-section, required to perform effective operation at airplane cruising angle-of-attacks; to increase the radius of curvature of the air intake lip to provide air flow near it without flow separation, which was definitely determined and could not be increased in the existing method; to improve constant length velocity gradient law (used in this method) so that too large duct expansion angles near the air intake outlet cross-section can be avoided; to consider the engine inlet spinner presence. The methods used are analytical and digital mathematical methods, implemented in MathCAD and Microsoft Visual Studio systems. The following results were obtained: based on the proposed method, new calculation module for the Power Unit software version 11.8 has been developed (С-language Win32 UNICODE application) with a friendly user interface. Conclusions. The scientific novelty of the results obtained is as follows: 1) mathematical model (algorithm and its program implementation) for circular turbofan air intake shaping has been improved considering cant of the inlet cross-section, air intake lip rounding with two radiuses, presence of engine inlet spinner, and zero expansion angles in the diffuser outlet cross-section; 2) adequacy of calculation results using the improved mathematical model is shown using comparison with shapes of circular turbofan air intakes, developed by the leading aviation companies.

Influence of mixing section inlet and diffuser outlet velocities on the performance of ejector-expansion refrigeration system using zeotropic mixture

• Theoretical analysis of an ejector expansion refrigeration cycle . • Effects of mixing section inlet and diffuser outlet velocities on the system. • Effects of zeotropic mixture mass ratio on system performance. It is known that the performance of vapor compression cooling systems can be increased thanks to the ejector. In the literature, there are many studies on the subject, in which mathematical models of ejector-expansion cooling systems are developed. However, the refrigerant velocities at the mixing section inlet for the secondary flow (suction stream) and diffuser outlet were neglected in these studies. In the mathematical model used in this study, the velocities in both sections are considered and the system performance is calculated. The performance assessment of an ejector-expansion refrigeration system was realized in the case of using the R600a/R290 refrigerant mixture as a working fluid. Thus, the effect of zeotropic refrigerant mixtures on the system performance is also investigated, considering the refrigerant velocities at the mixing section inlet and diffuser outlet. According to the obtained results, it has been found that the cooling performance of the system that uses R600a/R290 mixture as a refrigerant is 5.8%-7% higher when the velocities at the mixing section inlet and diffuser outlet are considered compared to the neglected one. The exergy efficiency is also calculated to be around 4.6% lower when the ejector mixing section inlet and diffuser outlet velocities are neglected.

Pressure distribution on a flat plate in the context of the phenomenon of the Coanda effect hysteresis

As a result of the Coanda effect, a symmetrical free jet will flow as an asymmetrical wall jet. At the same time, at the obstacle along which the flow is observed, the wall jet generates pressure distribution. In this study, the obstacle located at the diffuser outlet is a flat plate with a variable inclination angle. The article presents results of the study on pressure distributions on a flat plate with a variable angle of inclination. In the experiment, the Reynolds number ranged from 16,192 to 42,240. A fixed geometry diffuser (Witoszyński nozzle) with a height of 0.60 m, width of 0.02 m and outlet velocity of 11.33–29.57 m/s was used. A plate with a length of 1.00 m and a variable inclination angle was installed at the diffuser outlet. What is new, however, is that the presented results of the experimental research include the influence of the Coanda effect hysteresis on the pressure distribution on the plate. The article shows how pressure distributions change on the plate depending on whether the initial angle of inclination was 0° and was increased gradually in the course of the experiment until a detachment of the jet flowing from the plate was observed, or the initial angle of inclination was close to 90° in the primal state and as the angle of the plate inclination was decreased, the jet flowing towards the plate reached the state of attachment to the plate surface. The study demonstrated that for a turbulent jet, pressure distribution on a flat plate is determined not only by the plate’s inclination angle, but also by the direction of its rotation.

Numerical modeling of the dynamic unsteadiness with global mode decomposition approach in a high-speed compressor with abnormal diffuser vane

Adjustable vane diffuser is addressed as one of the main techniques in centrifugal compressor in seeking of wider stability margin. Flow instabilities, however, may be driven by the three-dimensional flow separation induced by the abnormal vane in the diffuser. In the present work, a numerical investigation of the radial vaned diffuser with abnormal vane was applied to identify the correlation between stall inception and asymmetric flow distribution. Unsteady numerical simulations of the centrifugal compressor with vaned diffuser was carried out and validated against experimental data. Then, the aerodynamic characteristics and evolution process of the flow instabilities in vaned diffuser was analyzed with the compressed dynamic mode decomposition in term of perturbation frequency and dominating flow mode. Finally, concerning the relative position of the volute tongue and abnormal vane, the influence of the abnormal vane on the matching between the diffuser and volute regarding the stall mechanism was summarized. The results indicate that the abnormal vane needs to be altered large enough, which is above 10°, to trigger the flow instability of vaned diffuser before the spike stall in impeller. With the increase of stagger angle alternation, the stall mechanism turns from a global flow separation in multiple passages into a regional and abrupt phenomenon in limited passages. With the mode composition approach, the flow separation near diffuser outlet and the tornado-type vortices at the leading edge of the abnormal vane are responsible for the flow instability of the case with 15° vane alternation. When combined with the volute, the case with abnormal vane close to the volute tongue tends to be more unstable than that 180° away from volute tongue. The tornado-type vortices are also moved to the trailing edge rather than the leading edge under the influence of the asymmetric volute.

Application of numerical simulation for the modernization of the exhaust system of gas turbine engines

Objective. The aim of the study is to modernize the design of the exhaust system of gas turbine engines (GTE) in order to reduce aerodynamic losses using numerical methods (CFD methods) for simulating the flow of exhaust gases.Method. The directions of modernization were chosen by considering the pattern of the flow of exhaust gases (separated flow zones and vortex flows) in the exhaust system during numerical modeling (Computational Fluid Dynamics). The modernization of the exhaust system consists in profiling the axial diffuser and changing the design of the gas collector.Result. The profiling of the axial diffuser was performed using numerical simulation methods. The design of the gas collector was changed based on the technical solution proposed by V.B. Yavkin. Numerical simulation of the flow of exhaust gases in the modernized exhaust device was performed. To evaluate the results of modernization in numerical models of the modernized design and prototype, the values of aerodynamic losses at the outlet of the axial diffuser and gas collector were determined.Conclusion. CFD modeling made it possible to obtain data on the structure of the exhaust gas flow in the upgraded exhaust system, to see the pattern of the distribution of velocities and pressures. The results of the numerical experiment showed a decrease in pressure losses in the exhaust system by 11% relative to the prototype.