Aerospace Science and Technology
Amir Akbari; Hossein Khaleghi
Abstract
The use of unshrouded turbine rotor blades can considerably reduce the weight of an aero engine. However, in an unshrouded high-pressure turbine, the tip leakage flow generates about 30% of the turbine total loss. Another factor which affects the loss in axial-flow turbines, is the axial distance between ...
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The use of unshrouded turbine rotor blades can considerably reduce the weight of an aero engine. However, in an unshrouded high-pressure turbine, the tip leakage flow generates about 30% of the turbine total loss. Another factor which affects the loss in axial-flow turbines, is the axial distance between the rotor and stator. The purpose of the current work is to investigate the impacts of the blade tip clearance and the axial distance between rotor and stator on the performance of a high-pressure axial turbine, by using three-dimensional numerical simulations. Comparing the numerical results to the experimental data shows that the numerical simulations can predict the turbine performance fairly accurately. Results reveal that increasing the tip clearance and the axial distance between the rotor and stator reduce the turbine efficiency. The effects of tip clearance and rotor-stator axial distance on the performance and endwall flow field of the studied turbine stage have been presented and discussed.
Aerospace Science and Technology
Hamzeh Eshraghi
Abstract
In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity ...
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In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity value, some other cases have been designed with different solidity values. Other geometrical parameters have been selected similarly in all cases. At the next stage, a three dimensional numerical model is developed to predict the characteristic performance of each tandem stage. The model is validated with the experimental results of NASA Stage and Rotor 37, and the level of the accuracy of the model is presented. Using a similar model, the performance of all cases has been derived and the effect of solidity variation on the overall performance of machine has been discussed. Lastly, the effect of solidity variation on the tip leakage flow structure near peak efficiency point is discussed for all cases.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, ...
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Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, impeller and the turbomachine itself. Surge emerges when a pump is operating with a positive slope of head and flow curve. The coincidence of the surge phenomenon with cavitation results in a damaging phenomenon called "auto-oscillation." Thus, predicting a pump's behavior outside the design points is of great importance particularly in low flow rates. In this paper, the characteristic curve of a high-speed centrifugal pump is extracted using CFD analysis to determine the stable operating range of the pump. The studied pump consists of an inducer, impeller and volute. The simulation in the pump was carried out three-dimensionally due to the asymmetry of geometry. The simulations are performed over a wide range of flow rates and the characteristic curve of the pump (head coefficient in terms of mass flow rate coefficient) is extracted. Finally, the range of stable operation of the pump is determined using its characteristic curve.
Aerospace Science and Technology
Alireza Sekhavat Benis; Reza Aghaei Togh
Abstract
The compressor blade is responsible for increasing the flow pressure. By adding a blade behind the main blade, the compressor performance can be improved by increasing the pressure ratio and reducing the weight. The tandem improves the performance and increases the compressor absorption coefficient by ...
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The compressor blade is responsible for increasing the flow pressure. By adding a blade behind the main blade, the compressor performance can be improved by increasing the pressure ratio and reducing the weight. The tandem improves the performance and increases the compressor absorption coefficient by increasing the pressure ratio, preventing flow separation and controlling the boundary layer. This has led compressor designers to seek to reduce weight, increase pressure ratio and increase efficiency by using tandem. The geometry of the compressor blade and stage along with its tandem has been obtained from previous valid sources and has been drawn in three dimensions and numerically analyzed. Then the various parameters for the blade and the tandem are examined separately and the pressure and velocity vectors are plotted to show the control of the vortices, which results in improved compressor performance. The characteristic curve of the compressor and the pressure ratio for this particular tandem are also plotted at the end. Calculations show that by using the tandem and removing the excess vortex after the main blade, we will see a 28.5% increase in total pressure, a 15% decrease in relative mach number and a 1.5% decrease in entropy.
Aerospace Science and Technology
Sarallah Abbasi; MohammadAmin Daraei
Abstract
In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, ...
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In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, the effect of these parameters on the thrust, thrust specific fuel consumption (TSFC) and engine efficiency was investigated and then in the exergy analysis, it was found that the lowest exergy efficiency with a value of 85.45% belongs to the combustion chamber; Therefore, a parametric study was conducted to improve the performance and exergy efficiency of the burner; For example, in the case of bypass ratio of 2.2 and fan pressure ratio of 2, the exergy efficiency of the burner is increased by 12.23% compared to the base case. In addition, the results of sensitivity analysis show that the burner exit temperature and the HPC pressure ratio with 21.81 and 2.2%, respectively, have the most and the least effect on the engine net thrust; Also, the burner exit temperature and the flight altitude with 4.57% and 0.11%, respectively, have the most and the least effect on the TSFC.
Aerospace Science and Technology
Hamed Arhami; Mohammad Mazidi Sharfabadi
Abstract
In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. ...
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In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. The non-premixed combustion model is used to simulate combustion and the K-ω method is used to simulate turbulent flow. This study investigated how the combustion phenomenon occurs, the internal temperature distribution, the outlet, and the wall of the combustion tube, for which comprehensive three-dimensional data were not previously available. These simulations have identified the weaknesses of the combustion tube and by eliminating these weaknesses, the problem of reducing the efficiency of several gas turbine engines has been solved. Comparison of the results of the present study with a similar numerical analysis showed that the results of this study are more in line with laboratory results. The results of the simulation of combustion pipe defects show that the combustion liner that had a welding line near the outlet had a 25% higher pressure drop than a typical combustion liner and the effective cross-sectional area of the fluid flow was reduced by 11%. The output of a repaired combustion tube is different from a typical type.
Aerospace Science and Technology
Mohammad Reza Salimi; Mohsen Rostami; Amir Hamzeh Farajolahi; Morteza Ghanbari
Abstract
In this paper, flow and heat transfer inside a helicopter shell and tube heat exchanger is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are ...
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In this paper, flow and heat transfer inside a helicopter shell and tube heat exchanger is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are produced longitudinally and integrally with the tube body. The current flowing in the shell is MIL-PRF 23699 oil and the flowing fluid in the tubes is JP-4 fuel. These two fluids flow in opposite directions and exchange heat with each other. Using Aspen software, the design is done in such a way that the heat exchanger has minimum length and weight to have a better and higher effect on the efficiency of the helicopter. To investigate the effect of tube geometry and oil mass flow on the heat transfer between fuel and oil, simulation has been performed in ANSYS Fluent program. In this simulation, a part of the whole heat exchanger is selected as the geometry and the effect of changing the geometry of the tubes, mass flow of fuel and oil on the heat transfer coefficient, Colburn coefficient, coefficient of friction and their ratio, and outlet temperature changes are investigated. The results of this simulation show that the heat transfer rate between fuel and oil for a heat exchanger with finned tubes is about 11% higher than without a fin. Also, reducing the mass flow of oil entering the shell increases the efficiency of the heat exchanger.
Aerospace Science and Technology
Omid Habibi; Reza Ebrahimi; Hassan Karimi Mazraeh Shahi
Volume 14, Issue 2 , October 2021, , Pages 141-151
Abstract
The nozzle, an end-element of the propulsive process Cycle, represents a critical part of any aerospace vehicle. The task of accelerating and efficiently exhausting combusted and reactive gases according to the delivered thrust represents the main objective of the propulsion system design. Flow separation ...
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The nozzle, an end-element of the propulsive process Cycle, represents a critical part of any aerospace vehicle. The task of accelerating and efficiently exhausting combusted and reactive gases according to the delivered thrust represents the main objective of the propulsion system design. Flow separation in supersonic convergent–divergent nozzles has been the subject of several experimental and numerical studies in the past. Now, with the renewed interest in supersonic flights and space vehicles, the subject has become increasingly important, especially for aerospace applications (rockets, missiles, supersonic aircrafts, etc). Flow separation in supersonic nozzles is a basic fluid dynamics phenomenon that occurs at a certain pressure ratio of chamber to ambient pressure, resulting in shock formation and shock/turbulent-boundary layer interaction inside the nozzle. From purely gas-dynamics point of view, this problem involves basic structure of shock interactions with separation shock, which consists of incident shock, Mach reflections, reflected shock, triple point and slip lines. In this article A Review on Flow Separation Phenomenon for Supersonic Convergent–Divergent Nozzles has been investigated.
Aerospace Science and Technology
Amin Sarabchi; Mojtaba Heydarian Shahri; Ali Madadi
Abstract
Compared to the enormous costs of laboratory experiments, numerical approaches to improving the performance of turbomachines are less costly and more practical. In the present study, by using the Taguchi method and orthogonal arrays while doing a limited number of simulations (according to the Taguchi ...
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Compared to the enormous costs of laboratory experiments, numerical approaches to improving the performance of turbomachines are less costly and more practical. In the present study, by using the Taguchi method and orthogonal arrays while doing a limited number of simulations (according to the Taguchi method), the sensitivity level of objective functions have been investigated to optimization variables in a fan of a high-bypass ratio turbofan engine (JT9D-7 Engine). a mathematical parameterized algorithm coupled to a computational fluid dynamic solution is employed to modify the geometry and calculate the objective functions. 15 optimization variables are defined by varying:The radial distribution of the chord length from the hub to the tip of the blade and alsoeach profile's lean and sweep in five control points compared to hub profile.The lean, sweep and chord length are parameterized by a spline algorithm. The objective functions included the pressure ratio, isentropic efficiency and mass flow rate of the fan in the design point. The results showed that the lean angle affects the isentropic efficiency, and the sweep angle affects the mass flow rate of the fan. The pressure ratio was sensitive to both variables. Concerning the design variables, 2-level L16 and L32 arrays of the Taguchi method were used for running the sensitivity analysis. Assuming a fixed number of blades, a fixed angle of incidence, and a fixed camber angle, distributing the chord length did not significantly affect the objective functions compared to the lean and sweep distribution.
Aerospace Science and Technology
Ali Cheraqi; Reza Ebrahimi
Abstract
This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation ...
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This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation number was calculated based on the cavitation breakdown characteristic curve. Two-phase flow inside the pump was simulated using the homogenous mixture method and the Rayleigh-Plesset model. The SST turbulence model and MRF rotating model were used to simulate turbulence and rotation of the flow throgh the pump, respecively. The critical cavitation number that was the outcome of numerical analysis results was compared to the experimental data. This comparison implied the necessity of considering the safety factor for determining the critical cavitation number and inlet pressure required to uninterrupted operation of the pump cavitation, using the results of numerical analysis.
Aerospace Science and Technology
Rahman Amiri; Ali Madadi; Abolghasem Mesgarpour Tousi
Abstract
Designing and manufacturing turbine engines have many complexities and challenges that need time and cost. Therefore, reputable companies producing gas turbines have always sought to shorten the design and construction processes, one of which is to use the core of aerial gas turbines in industrial gas ...
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Designing and manufacturing turbine engines have many complexities and challenges that need time and cost. Therefore, reputable companies producing gas turbines have always sought to shorten the design and construction processes, one of which is to use the core of aerial gas turbines in industrial gas turbines. This category of industrial gas turbines is called aero-derivative gas turbines. Aerial gas turbines can be used as industrial gas turbines due to their particular characteristics such as lightweight, relatively small dimensional size, high efficiency, and performance. These characteristics can shorten the design and manufacturing process. In the present work, ALF 502 aero gas turbine has been studied to convert its application to the derived industrial gas turbine. GasTurb software has been used to model this gas turbine for industrial applications. In this study, six different scenarios have been studied for converting aero engines to industrial engines, and results have been discussed. Finally, three scenarios were selected to be implemented on this engine among the studied scenarios.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
One of the most effective ways of high-speed motion in water is the motion in the supercavitation regime. This way provides the possibility to avoid considerable viscose resistance of boundary layer and consequently reach to very small drag coefficient which can be several times smaller than, that ...
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One of the most effective ways of high-speed motion in water is the motion in the supercavitation regime. This way provides the possibility to avoid considerable viscose resistance of boundary layer and consequently reach to very small drag coefficient which can be several times smaller than, that of the continuous flow. In this study the numerical simulation of developed and supercavitating flow is performed. The CFX code which served as a platform for the present work is a three-dimensional code that solves the Reynolds-Averaged Navier-Stokes equations with a finite volume method. The cavitation model is implemented based on the use of Rayleigh-Plesset equation to estimate the rate of vapor production. A high Reynolds number form ĸ-ε model is implemented to provide turbulence closure. For steady state flows and poor mesh resolution near the wall (using log-law wall functions), there is a priori no difference between the two equations formulations. For the different case studies, multi-block structured meshes were generated and the numerical simulation is performed in a wide range of cavitation numbers. Results are presented for steady state flows with natural cavitation about various bodies. Comparisons are made with available measurement of surface pressure distribution, cavitation bubble geometry (cavity length and cavity width) and drag coefficient. The simulated results are in a good agreement with the experimental data. Finally, the three-dimensional results are presented for a submerged body running at several angles of attack.
Aerospace Science and Technology
Gholamreza Rashed
Abstract
In this paper, using the Abaqus finite element software, the torsional hysteresis of X52, X60, X65 steels under loadings with different torsion values, has been numerically investigated and they are compared to each other. The shear stress, effective stress, residual stress and elastic and plastic ...
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In this paper, using the Abaqus finite element software, the torsional hysteresis of X52, X60, X65 steels under loadings with different torsion values, has been numerically investigated and they are compared to each other. The shear stress, effective stress, residual stress and elastic and plastic shear strain distribution are presented in the numerical results. In this analysis, the “chaboche” kinematic hardening theory has been used to predict the behavior of the material in the plastic region. By comparing the difference percentage graphs of the steels under the same load, it has been concluded that the hysteresis loops in X65 steel will become stable sooner than X60 and in X60 steel they become stable sooner than X52.
Aerospace Science and Technology
alireza moradi; fathollah ommi; Zoheir Saboohi
Abstract
In the course of all-round advancement of engineering science, space research can be considered as the drivers of this forward movement. In the field of space propulsion, this trend can be seen as a backward trend, not in the sense of regression, but in the sense of optimizing the original designs used ...
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In the course of all-round advancement of engineering science, space research can be considered as the drivers of this forward movement. In the field of space propulsion, this trend can be seen as a backward trend, not in the sense of regression, but in the sense of optimizing the original designs used for space systems, which not only lead to the re-invention of these systems based on the acquisition of specific modern manufacturing technologies, but also strengthened the link between sciences such as Materials science and Mechanics science. In this research, according to the space propulsion system roadmap and also the review of old and reference designs, an attempt has been made to study some of the optimizations made in recent years and to express the weaknesses and challenges ahead. One of the ideas that optimizes, minimizes and increases the reliability of the space propulsion system is the injection of fuel through the porous media. The study of a type of showerhead injector expresses the formation path of the idea of using porous materials in the injection system and then the efficiency of these two types of injections is compared in a design that connects the porous material with the coaxial injector design.
Aerospace Science and Technology
Mahyar Naderi; Liang Guozhu; Hassan Karimi; Sara Pourdaraei
Abstract
In order to reduce cost and time along with enhancing the safety issues, numerical computer modelling and simulations are widely used for analyzing complex systems such as launch vehicle or spacecraft propulsion system. The objective of this research is to obtain an algorithm for simulation of ...
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In order to reduce cost and time along with enhancing the safety issues, numerical computer modelling and simulations are widely used for analyzing complex systems such as launch vehicle or spacecraft propulsion system. The objective of this research is to obtain an algorithm for simulation of staged combustion cycle liquid propellant engines. For this purpose the space shuttle main engine (SSME), as one of the world’s most complicated engines, is selected as a case study. A total of 34 elements is taken into account and using more than 100 linear/non-linear equations, the engine’s steady state system model has been established in MATLAB SIMULINK software. The simulation method uses eleven nested loops for iteration. The algorithm is based on the known parameters at the inlet of engine main feed lines namely mass flow rate and pressure, similar to the known conditions during hot test of engine on test stand. The simulation is capable of predicting the engine’s operation in wide range of thrust throttling levels from 69 percent to 109 percent of the nominal thrust. In order to validate the suggested method, SSME main component parameters, operating at 109 percent of rated thrust is presented. Simulation result mean error is less than 5 percent.
Aerospace Science and Technology
Azadeh Kebriaee; Ali Nouri -Borujerdi; Ali Darvan
Abstract
The weaknesses of liquid propellants have led to special attention to gelled propellants in the last two decades as a way to overcome the weaknesses of these propellants. Previous studies have shown that the addition of gel-forming agents to liquid propellants converts these propellants, mainly Newtonian ...
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The weaknesses of liquid propellants have led to special attention to gelled propellants in the last two decades as a way to overcome the weaknesses of these propellants. Previous studies have shown that the addition of gel-forming agents to liquid propellants converts these propellants, mainly Newtonian fluids, into non-Newtonian fluids, which greatly affects the physical properties of these propellants. In order to better understand the changes occurred in the physical properties of liquid propellants due to their gelled structure, on factors such as spraying and atomization, in this study, impinging jet injectors have been used to spray and atomize a non-Newtonian gelled fluid with rheological properties similar to gelled propellants. Analysis of the results of the present study shows that the use of impinging jet injectors causes different regimes of spraying and atomization (due to the jets’ high Reynolds number) for non-Newtonian gelled fluids, some of which being fundamentally different from the regimes formed for Newtonian fluids. In general, 4 regimes including stable closed rim, unstable closed rim with the formation of vermicular ligaments, open rim with successive formation of bow-shaped ligaments and a turbulent regime have been identified in this study. The properties of each of these regimes and their details will be explained in this paper.
