Aerospace Science and Technology
Parisa Ghanooni; Mostafa Kazemi; Mahmoud Mani
Abstract
This study focuses on improving performance of a supercritical wing equipped with winglets at different cant angles. This study aims to experimentally investigate the variation of aerodynamic performance of a supercritical wing of NASA Sc (2)-0410 airfoil at lower Reynolds numbers with winglets at various ...
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This study focuses on improving performance of a supercritical wing equipped with winglets at different cant angles. This study aims to experimentally investigate the variation of aerodynamic performance of a supercritical wing of NASA Sc (2)-0410 airfoil at lower Reynolds numbers with winglets at various cant angles. The tests were performed by measuring the lift and drag force using a three-component balance within a broad range of angle of attack from -4 to 20 degrees and at three different subsonic flow velocities. Results include changes in lift, drag, and aerodynamic performance for each winglet cant angle compared to the baseline wing. The results show that winglets generally increase the lift force and decrease the drag force by decreasing the size and strength of the wingtip vortices. Moreover, the optimal winglet for each case is extracted based on the aerodynamic performance provided by each winglet. In order to better and more accurately compare the effect of different mounting angles of the winglet on the aerodynamic performance of the base wing, the impact of each winglet is shown separately. Accordingly, it is observed that the winglets with angles of 0o and 15 o, namely W0 and W15, have shown good performance in increasing the lift coefficient. Also, the winglet with 90 degrees has shown good performance in creating the least drag force.
Aerospace Science and Technology
Shayan Dehkhoda; Mohammad-Ali Amiri Atashgah
Abstract
This paper is dedicated to the optimal path-planning of a quadrotor to deliver the goods in the form of a round-trip mission. At first, quadrotor modeling is performed by the Newton-Euler method and then the problem is formulated as an optimal control effort problem. Then, by discretization of the equations ...
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This paper is dedicated to the optimal path-planning of a quadrotor to deliver the goods in the form of a round-trip mission. At first, quadrotor modeling is performed by the Newton-Euler method and then the problem is formulated as an optimal control effort problem. Then, by discretization of the equations using the direct colocation method, the problem becomes a nonlinear programming system that can be solved by available optimization methods. This discretization helps to make the derivative values in the equations of motion as simple algebraic expressions and the path optimization problem becomes a standard form of nonlinear programming problem (NLP). In this method, instead of obtaining state and control functions, state and control values are obtained at the beginning and endpoints of smaller time intervals. This method is one of the most explicit methods for the numerical solution of differential equations. It should be noted that in this research, safe areas around urban obstacles are considered fixed cylinders. Extensive simulations are evidence of the usefulness of this method, while the vehicle realizes all geometric, dynamic, and kinematic constraints.
Aerospace Science and Technology
Kamran Raissi Charmakani; Gholamreza Moradi
Abstract
Knowledge of aircraft last position and trajectory is of the utmost importance for search and rescue in aviation today. In case of an accident, this information is necessary for rapid response.The existing method of reporting the whereabouts depend upon pilot reports during flight or signals from special ...
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Knowledge of aircraft last position and trajectory is of the utmost importance for search and rescue in aviation today. In case of an accident, this information is necessary for rapid response.The existing method of reporting the whereabouts depend upon pilot reports during flight or signals from special equipment such as emergency location transmission. Future renovation to Air Traffic Control system has been planned which requires the installation of automatic Dependent Surveillances – Broadcast. However, it will take some time to implement such systems in all aircrafts and providing the necessary infrastructure. This paper proposes Geo-tagging the pilot communication using Code Division Multiple Access (CDMA) method. It is an intermediate, yet inexpensive, solution for worldwide application in aviation which can be implemented quickly. It takes advantage of the existing equipment both in the air as well as on the ground. The simulations presented show the applicability and efficiency of the proposed routine.
Aerospace Science and Technology
Ali Khoshnejad; Reza Ebrahimi; Golamhosein Pouryossefi
Abstract
Aero-engine entrance conditions are not always ideal and, for various reasons, inlet distortion may occur and cause inlet blockage and reduction of compressor performance. The aim of this study was to numerically simulate the effects of plasma actuators on the enhancement of low-speed axial compressor ...
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Aero-engine entrance conditions are not always ideal and, for various reasons, inlet distortion may occur and cause inlet blockage and reduction of compressor performance. The aim of this study was to numerically simulate the effects of plasma actuators on the enhancement of low-speed axial compressor rotor performance under radial inlet distortion. First, compressor performance under radial inlet distortion with 15% and 20% blockage and theirs destructive effects on stall margin was investigated. Then, the effect of plasma actuators on rotor loss subjected to inlet distortion was investigated, using an algebraic model based on the plasma actuators physics in form of body force distribution in Naiver-Stokes equations. The results show that radial inlet distortion causes decreasing stall margin of the compressor. In addition, according to the findings, applying plasma actuators boosts the flow momentum behind the distortion screen and reduces the blockage of the rotor tip region, leading to decreasing losses. Furthermore, at 15% blockage, the plasma actuators caused to increase the stall margin from -11% to -5% versus the rotor in clean condition.
Aerospace Science and Technology
Nemat Allah Ghahremani; Hassan Majed Alhassan
Abstract
This paper presents a new Modified Predictive Kalman Filter (MPKF). To solve the problem of a strap-down inertial navigation system (SINS) self-alignment process that the standard Kalman filters cannot give the optimal solution when the system model and stochastic information are unknown accurately. ...
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This paper presents a new Modified Predictive Kalman Filter (MPKF). To solve the problem of a strap-down inertial navigation system (SINS) self-alignment process that the standard Kalman filters cannot give the optimal solution when the system model and stochastic information are unknown accurately. The proposed algorithm is applied to SINS in the initial alignment process with a large misalignment heading angle. The filter is based on the idea of an accurate predictive filter applies n-steps ahead prediction of the SINS model errors to effectively enhance the corrections of the current information residual error on the system. Firstly, the formulations of a novel predictive filter and a fine alignment algorithm for SINS are presented. Secondly, the vehicle results demonstrate the superior performance of the proposed method, in which the MPKF algorithm is less sensitive to uncertainty. It performs faster and more accurate estimation of SINS' initial orientation angles compared with the conventional EKF method.
Aerospace Science and Technology
Fahimeh Barzamini; Jafar Roshanian; Mahdi Jafari-Nadoushan
Abstract
This paper aimed to utilize a Deep Neural Network (DNN) to achieve optimal path planning for a spacecraft during a landing mission on an asteroid. A minimum energy-consumption mission is evaluated in which a DNN is utilized to predict the optimal path in case of any failures or unforeseen alterations. ...
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This paper aimed to utilize a Deep Neural Network (DNN) to achieve optimal path planning for a spacecraft during a landing mission on an asteroid. A minimum energy-consumption mission is evaluated in which a DNN is utilized to predict the optimal path in case of any failures or unforeseen alterations. The paper uses a DNN and employs a polyhedral model, which is renowned as the most precise method for modelling the irregular shapes of asteroids. The DNN, is utilized for path planning and incorporates data calculated by the network into a spacecraft dynamics equations where an intelligent supporter model has been developed to handle the high computation load of the gravitational field of polyhedral models. Moreover, this study indicates that the prediction errors of final locations are less than 1 kilometer, as the training errors of networks are deemed entirely satisfactory. Eventually, the feasibility of the proposed approach is demonstrated through corresponding simulations
Mostafa Kazemi; parisa Ghanoni; Mahdi Sharifi; Mahmood Mani
Abstract
This study focuses on using rotor blade turbine winglets for the purpose of controlling the wingtip vortex in airplanes. The aim of the study is to investigate the effective geometric properties of the rotor blades that are used as winglets, as well as experimental evaluation of their effects on drag, ...
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This study focuses on using rotor blade turbine winglets for the purpose of controlling the wingtip vortex in airplanes. The aim of the study is to investigate the effective geometric properties of the rotor blades that are used as winglets, as well as experimental evaluation of their effects on drag, lift coefficient and the aerodynamic efficiency ratio of the airplane. Seven different types of rotor blades were chosen in regard of their span length, number of blades, and the shape of the blades and experimented in a wind tunnel. The drag and lift force were directly measured via a 3-axis external balance. The position and place of installment of the rotor blades were selected through the studies mentioned in the literature and their geometric properties were further investigated. A finite wing with a NACA641412 cross-sectional airfoil, two similar rotor blades with different span length, two similar rotor blades with different blade count, and three rotor blades with different aerodynamic shapes in terms of installation and twist angle were used as models in this study. All the experiments were conducted at a Reynolds Number of 100,000 and angles of attack ranging from negative 4 to positive 20. The results showed the existence of turbine winglets has increased the lift coefficient and results in a reduction in the drag coefficient. Rotor blades with larger span lengths have increased the aerodynamic efficiency, although they have increased the drag coefficient as well. The number of the blades has had different effect in different angles of attack. The results indicate that rotor blades with acceptable aerodynamic properties can increase the value of aerodynamic efficiency almost twice its base value and delay the wing stall up to the attack angles above 20 degrees.
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.
Aerospace Science and Technology
Ali Motamedi; Abolghasem Naghash
Abstract
The purpose of this paper is to present a Multi-Input Multi-Output (MIMO) linear controller based on the eigenstructure assignment method for a fixed-wing Unmanned Aerial Vehicle (UAV) in longitudinal and lateral-directional channels. To this end, a six degree-of-freedom model of the aerial vehicle is ...
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The purpose of this paper is to present a Multi-Input Multi-Output (MIMO) linear controller based on the eigenstructure assignment method for a fixed-wing Unmanned Aerial Vehicle (UAV) in longitudinal and lateral-directional channels. To this end, a six degree-of-freedom model of the aerial vehicle is considered, where dynamic modes of the system in each channel are analyzed, and the effect of each dynamic mode on state and output variables of the system is investigated. Then, the eigenvalue and eigenvector parameters of the designed controller are appropriately assigned for the system dynamic modes in each channel. In addition, the system requirements of each dynamic mode are satisfied with the proposed controller, and the adverse interaction between the system state variables is minimized. The capability and effectiveness of the designed controller in a desired maneuver are demonstrated with a nonlinear model simulation of a fixed-wing UAV. In this regard, the results in longitudinal and lateral-directional channels are presented.
Aerospace Science and Technology
Mahdi Miralam; Amir Rahni
Abstract
In multi-stage Missiles, stabilizer wings are responsible for stabilizing the Missile. The control fins located upstream of the stabilizer wings affect the flow by spinning, which influences stability as well as control. One method for resolving this problem is to design stabilizer wings with less affectability ...
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In multi-stage Missiles, stabilizer wings are responsible for stabilizing the Missile. The control fins located upstream of the stabilizer wings affect the flow by spinning, which influences stability as well as control. One method for resolving this problem is to design stabilizer wings with less affectability against the upstream flow. The present paper deals with this issue by considering multiple planar fins and grid fins. Once validation is performed, after selecting the appropriate turbulence model and choosing the planar and grid fins, the appropriate Missile model is established; then, on a model with speeds of 0.6, 0.7, and 0.8 Mach, at attack angles of 0, 2, 4, and 6 degrees, and with control fins, variation at angles of 0, 1, 3, and 6 degrees, the aerodynamic coefficients as well as the effects of the upstream stabilizer wings are investigated in pitch and roll modes at an appropriate trim angle . The obtained results indicated that the use of grid fin downstream of the control surfaces would be less affected due to its physical nature; thus, the lower capacity of the control surface would be used for control during the flight, which would significantly facilitate the process of designing.
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
Sahar Noori; Armin Sheidani; Djavad Kamari
Abstract
In this study the effect of different configurations of three plates located in an air-filled container, which included vertical, horizontal and tilted, on coupled radiation and natural convection heat transfer has been numerically investigated. The side walls of the cavity were kept a constant temperature, ...
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In this study the effect of different configurations of three plates located in an air-filled container, which included vertical, horizontal and tilted, on coupled radiation and natural convection heat transfer has been numerically investigated. The side walls of the cavity were kept a constant temperature, while the upper and the lower walls were thermally insulated. In addition, non-uniform temperature distribution was applied to each of the plates. Moreover, in this study the effect of coupled heat transfer on flow separation and local Nu number was studied. The flow separation on the heated plates due to the thermal gradients was captured and the subsequent the effects were discussed. Also, the results reveal there are two main flow patterns known as separation of the convective flow and stretching of the CW vortex which are created by combined heat transfer. It was also demonstrated that these flow patterns are the main responsible for variations in the heat transfer.
Aerospace Science and Technology
Ali Arabian Arani; S.H. Jalali Naini; Mohammad Hossein Hamidi Nejad
Abstract
This study presents the miss distance analysis of the first-order explicit guidance law due to seeker noise using the adjoint method. For this purpose, linearized equations are utillized and the adjoint model is developed. Then the first-order equations are obtained and converted into nondimensional ...
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This study presents the miss distance analysis of the first-order explicit guidance law due to seeker noise using the adjoint method. For this purpose, linearized equations are utillized and the adjoint model is developed. Then the first-order equations are obtained and converted into nondimensional ones. The analysis is carried out for different values of the power of the alpha function, defined as the time decrease rate of the zero-effort miss distance to unit control input. The unity power gives the first-order optimal guidance strategy, minimizing the integral of the square of the commanded acceleration during the total flight time.The seeker and control system is assumed as a fifth-order binomial transfer function. Due to computational error and stability consideration, the effective navigation ratio is kept constant for very small time-to-go until intercept, which its effect on the miss distance is also investigated. Finally, approximate formulas are obtained using curve fitting method for rms miss distance due to seeker noise.
Aerospace Science and Technology
Amir reza Kosari; Alireza Akbar Attar; Peyman Nikpey
Abstract
In this study, the performance requirements influencing the orbital and attitude control system of a geostationary satellite in the station-keeping flight mode considering the coupling effect of both attitude and orbital motion is determined. Controlling and keeping the satellite in its orbital window ...
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In this study, the performance requirements influencing the orbital and attitude control system of a geostationary satellite in the station-keeping flight mode considering the coupling effect of both attitude and orbital motion is determined. Controlling and keeping the satellite in its orbital window have been done using a set of four thrusters located on one side of the satellite body, with considering the coupling effect of the attitude motion on orbital motion. The satellite’s orbital motion could be disturbed by the attitude motion in the allowable orbital window. The main factors conducting this behavior are derived utilizing the satellite attitude and orbital dynamic equations of motion. In the mathematical analysis of this study, the effects of environmental perturbations originating from the oblateness of Earth, third mass gravity like sun and moon, and solar radiation pressure on the satellite dynamic behavior are also considered. Afterward, the condition of using four installed thrusters on one side of the satellite and the reaction wheels in order to control the satellite orbital and attitude motion is investigated. To reduce the satellite attitude’s error, a proportional-derivative controller is employed to activate the reaction wheels properly. The satellite positions in north-south and east-west directions are controlled by a specific array of thrusters in order to maintain in its predefined orbital window. The required amount of velocity variations for a duration of one year via some simulation may demonstrate the effectiveness of the proposed approach in enhancing the orbital maintenance procedure of the satellite.
Reza Jamilnieya
Abstract
In this paper, a new method for optimal guidance in the atmospheric return phase is proposed. This guidance method is based on instantaneous and online trajectory optimization in which optimal guidance commands are obtained from sequential solving of optimal control problems. In order to solve optimal ...
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In this paper, a new method for optimal guidance in the atmospheric return phase is proposed. This guidance method is based on instantaneous and online trajectory optimization in which optimal guidance commands are obtained from sequential solving of optimal control problems. In order to solve optimal control problems quickly and online, a combined approach including the concepts of differential flatness, B-spline curves, direct collocation, and non-linear programming is used. By performing the trajectory optimization process in the form of closed-loop control and implementing the receding horizon control, the open-loop responses of optimal control can be dependent on the instantaneous conditions of the object and the target. In this case, guidance commands can be generated based on various objective functions and constraints, and model uncertainties can be considered by entering the vehicle conditions into the trajectory optimizer. In order to show the capabilities of the proposed guidance method, a numerical example of the guidance of a reentry vehicle in the presence of model uncertainties is presented.
Aerospace Science and Technology
Amir reza Kosari; Masoud Mirzaei Tashenizi
Abstract
This article is aimed to investigate the interference elimination between multiple aircraft using game theory. A differential game is used to eliminate the interference if all the interfering aircraft cooperate to eliminate the interference or if each makes a rational decision based on their own interests. ...
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This article is aimed to investigate the interference elimination between multiple aircraft using game theory. A differential game is used to eliminate the interference if all the interfering aircraft cooperate to eliminate the interference or if each makes a rational decision based on their own interests. All interfering aircraft calculate the interference elimination route in cooperative mode by defining the flight priority. In the non-cooperative state, the problem of eliminating the interference is investigated using the Nash equilibrium, and then the new path is calculated. A point mass model has been used to implement this problem, which is converted into a linear model by changing the control variable. The above problem is solved using the quasi-spectral numerical solution method. In order to validate the presented method, the problem of eliminating the interference between several aircraft in two-dimensional space has been studied, and the results show the appropriate performance of the presented method.
Mahya Ramezani; Nima Assadian
Abstract
The purpose of this paper is to propose a method for the dual space tether system to continue its mission in the event of a failure by using fault-tolerant control. To accomplish this, a new and accurate model of a space tether with two tethers has been introduced, which can demonstrate the effects of ...
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The purpose of this paper is to propose a method for the dual space tether system to continue its mission in the event of a failure by using fault-tolerant control. To accomplish this, a new and accurate model of a space tether with two tethers has been introduced, which can demonstrate the effects of the tensile force more precisely in the model. One of the features of this model is the ability to modify the junction of the tethers to the subsatellite, which can be included as a control parameter in the problem. As a result, the fuel required to control the mission can be decreased. To mitigate the effects of tether failure, a fault-tolerant control strategy based on model predictive control (MPC) has been developed for the nonlinear space tether system. This control method has the advantage of being both optimal and capable of controlling the system in the event of a failure. The simulation results demonstrate that the proposed control method is capable of controlling the dual spatial tether system despite thruster and tether failure.
Aerospace Science and Technology
Seyed Sam Saham; Saeed Karimian Aliabadi
Abstract
The use of urban and rural scale wind turbines that in addition to generating power can play the role of old wind turbines in arid areas will be very attractive. In this research it has been tried to first evaluate the wind energy potential in Zahedan city and then to evaluate a sample of vertical axis ...
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The use of urban and rural scale wind turbines that in addition to generating power can play the role of old wind turbines in arid areas will be very attractive. In this research it has been tried to first evaluate the wind energy potential in Zahedan city and then to evaluate a sample of vertical axis wind turbine. First, a three-dimensional semi-analytic code based on the DMST method was developed, the validation of which was studied and presented. Using this tool, the performance of the turbine in terms of power and ventilation has been investigated and in the results of this parametric study, the effect of the cone angle on the power and ventilation coefficient has been explained in detail. Based on the results of this study, it can be seen that increasing the cone angle to 20 degrees, although it reduces the power of the turbine, but does not have a significant effect on the power coefficient and at the same time causes a ventilation coefficient of about 1.6 percent. It was also observed that at a conical angle of 10 degrees and at the working point of the turbine, the output power will be 30 kW and the ventilation flow will be 30,000 m^3⁄h.
Aerospace Science and Technology
Morteza Bayati
Abstract
Minimizing the computational cost and improving the convergence speed is the main goal of any computational design. In this regard, due to the low convergence speed of the traditional iterative method of fluid flow solution, a new method to improve the traditional iterative method is applied. In this ...
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Minimizing the computational cost and improving the convergence speed is the main goal of any computational design. In this regard, due to the low convergence speed of the traditional iterative method of fluid flow solution, a new method to improve the traditional iterative method is applied. In this paper, two-dimensional fluid flow in a channel with an aspect ratio of 10, uniform inlet velocity, constant outlet pressure, and no-slip conditions at the walls is studied using the Lattice-Boltzmann Method. The speed of convergence of the solution is increased by verifying that the mass flux is conserved between the inlet and each channel section. The solution time of channel flow obtained by Lattice-Boltzmann Method for Reynolds number of 100 and three types of grids 40x400, 60x600 and 80x80 are 261, 1039 and 4264 s, respectively. Based on the results, by introducing a flow rate control in each channel section of these three types of grids, the solution time is reduced by 35, 266, and 1590 seconds. This method can be implemented not only for normal but also for channel with an obstacle. According to the results, the speed of convergence increases by at least 2 times using this method
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
Alireza Sekhavat Benis; Reza Aghaei Togh
Volume 16, Issue 1 , June 2023, , Pages 146-158
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
Amir reza Kosari; Ehsan Abbasali; Majid Bakhtiyari; Hamed Golpour
Abstract
The main purpose of this article is to examine the periodic coupled orbit-attitude of a satellite at restricted three body problem considering both primaries oblateness perturbations. The proposed model was based on a simplified coupled model meaning that the time evolution of the orbital state variables ...
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The main purpose of this article is to examine the periodic coupled orbit-attitude of a satellite at restricted three body problem considering both primaries oblateness perturbations. The proposed model was based on a simplified coupled model meaning that the time evolution of the orbital state variables was not a function of the attitude state variables. Since, the problem has no closed-formed solution, and the numerical methods must be used, so the problem can have different periodic or non-periodic responses to the initial conditions. The initial guess vector of the coupled model’s states was introduced to achieve the optimal initial conditions leading to the periodic responses, and then the P-CR3BP coupled orbit-attitude correction algorithm was proposed to correct this initial guess. Since, the number of periodic solutions is restricted; the suitable initial guess vector as the inputs of the coupled orbit-attitude correction algorithm increases the chances of achieving more accurate initial conditions. The initial guess of orbital states close to the initial conditions of the P-CR3BP periodic orbit, along with initial guess vector of attitude dynamics states with Poincaré mapping was suggested as the suitable initial guess vector of the coupled model.
Ehsan Roohi
Abstract
In this paper simulation of cavitating flow over a disk cavitator is reported using computational fluid dynamics (CFD) technique. To apply the cavitation model, the flow has been considered as a single fluid, two-phase mixture. A transport equation model for the local volume fraction of vapor is solved ...
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In this paper simulation of cavitating flow over a disk cavitator is reported using computational fluid dynamics (CFD) technique. To apply the cavitation model, the flow has been considered as a single fluid, two-phase mixture. A transport equation model for the local volume fraction of vapor is solved and a finite rate mass transfer model is used for the vaporization and condensation processes based on the Kunz model. The volume of fluid (VOF) method is applied to track the interface of liquid and vapor phases. Our simulation is performed using a two phase solver available in the framework of the OpenFOAM package, namely “interPhaseChangeFoam”. The solver is based on finite volume method. Two different turbulence model, i.e., k-w SST and large eddy simulation (LES) are employed. Simulation is performed for the supercavitation regime. The results of our simulation are compared with the experimental data and analytical expressions and suitable accuracy has been investigated.
Mohamad Palizvan; Mohammad Tahaie Abadi; Mohammad Homayoun Sadr
Volume 11.1, Issue 2 , October 2018, , Pages 1-7
Abstract
This paper investigates the micromechanical damage behavior of composite materials on the transverse tensile response of representative volume elements (RVEs) with various fiber volume fractions. A new algorithm is developed to generate the random distribution of fibers in the RVE, and it is possible ...
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This paper investigates the micromechanical damage behavior of composite materials on the transverse tensile response of representative volume elements (RVEs) with various fiber volume fractions. A new algorithm is developed to generate the random distribution of fibers in the RVE, and it is possible to create a fiber distribution with high fiber volume fraction. The fibers and matrix are considered linear elastic and elastoplastic with Drucker–Prager's criterion, respectively. The fiber-matrix debonding is modeled by cohesive elements which lead to matrix cracking. To achieve a more realistic microstructure, the normal cohesive properties distribution is applied for interfaces between fibers and the matrix. To investigate the effect of the position of fibers with the weakest cohesive strength, sensitivity analysis concerning the different arrangements of specific normal cohesive properties on the RVE’s strength are performed. Moreover, the effects of different damage parameters such as fiber random distributions and various cohesive strengths on the overall damage behavior of the RVE are described in detail. It is revealed that the application of a normal cohesive distribution strongly reduces the maximum strength of the RVE and shifts the strain of damage initiation point and crack propagation path.
Shahrokh Shams; َA.R. Torabi; Mahdi Fathi Narab
Abstract
In this paper, damage in composite wings is introduced, firstly, then using Euler- Bernoulli equations with including flexural and torsional coupling, governing equations on cantilevered composite wing is derived. By applying separation method damaged beam is converted to two interconnected intact beams ...
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In this paper, damage in composite wings is introduced, firstly, then using Euler- Bernoulli equations with including flexural and torsional coupling, governing equations on cantilevered composite wing is derived. By applying separation method damaged beam is converted to two interconnected intact beams and using boundary conditions and continues conditions in damage location, the dynamic stiffness matrix is composed and modal analysis of damaged wing is done. Composite type is fiber-reinforced and damage type is edge crack with various locations and depths. Also effects crack depths and locations on modal properties in various fiber angle are examined. Results showed that existence a crack even with small depth in root of large span wing can reduce natural frequencies, seriously.
