نشریه مهندسی هوانوردی
سال بیست و چهارم شماره 1 (بهار و تابستان 1401)

Increasing attention of High-Tech industries (e.g. aerospace and defense industries) to functionally graded materials (FGMs) reveals the high performance of these types of materials, which is mainly due to the unique properties of these materials. In the current study, high velocity impact on AA5083-H11 / Ti-6Al-4V FGMs is conducted numerically in ABAQUS by considering the plastic and damage models of Johnson-cook and utilizing a Python code. Influence of projectile nose (considering three different types of impactor nose), effect of type of distribution function (Power-law (P-FGM) and Sigmoid (S-FGM)), and the stacking sequence of metallic alloys in the FGM are some of the main parameters investigated in the present study. The results show that FGM samples have a better performance than the pure metallic alloys. Moreover, despite the type of distribution function, the sample with linear distribution (i.e., n=1) has the best performance against the impact. However, at a same condition, S-FGM sample has higher energy absorption than P-FGM one. Finally, it is realized that an FGM target has a higher impact resistance against a conical-shape (SCN) impactor, rather than a flat-nose (FLT) one. This behavior has been justified via formation of a petal in the impact of FLT on FGM, while in the impact of SCN on FGM, only plugging formation has been seen. As a result, it can be deduced that in the high velocity impact on FGMs, petal formation has a higher effect on the energy absorption of target, when compared to the plugging formation.

The purpose of this article is to use machine vision techniques, and to process images by the camera to identify and detect the remains of foreign objects on the runway. Recognizing the remains of foreign objects on the runway of airports is a significant issue that can cause serious damage to the aircraft and delays in the air transport system and many financial and human losses. The proposed solution is based on machine vision system and video processing. The main purpose of the proposed algorithm is to detect the remains of foreign objects, and a large number of unknown objects that can’t be categorized. The safest way to diagnose based on machine vision in the runway of airports is to monitor the area on a frame-by-frame basis and use background subtraction algorithms. Using near-realistic data in the form of video and their application to the detection algorithm. The algorithm is able to detect the remains of active and inactive foreign objects with a very small size of 0.0023 (square meters) and 79% efficiency, parts in medium dimensions with an area of 0.2201 (square meters) And 98% efficiency, detects fire, bird movements and cracks with high accuracy and the necessary warnings (high and low level) (audible (siren) and display on the air traffic controller. Fully graphical and user-friendly display, provide the exact dimensions, size and location of the foreign objects (active and inactive) to the airport inspection and firefighting teams.

Guided flying objects use various positioning systems such as GPS for airborne navigation. Unlike inertial navigation systems, GPS is a satellite-based radio navigation system that can be intentionally jammed in electronic warfare (EW). Electromagnetic interference saturates the airborne GPS receiver so that the inherent error correction cannot be performed. In the case of guided weapons, such as cruise missiles, EW increases the navigation error, which can lead to inaccurate targeting in the final impact phase. None of previous studies on GPS jamming have mathematically modeled the effect of earth on electromagnetic waves during EW operations. The main purpose of this paper is to investigate the effect of earth flat surface on the jammer performance in EW. Accordingly, a computer software is implemented to calculate the power received by the GPS antenna using the initial input parameters of the missile flight profile. Moreover, this software mathematically models the effects of the earth and the jammer altitude on the radiation of the jammer antenna.

In the present study, fluid flow around two NACA0009 airfoils in a tandem configuration with a chord length distance from each other is investigated numerically and their mutual effects are studied in case of pressure distribution. One of applications consisting tandem airfoils is a wing-canard configuration which is used in designing fighter aircrafts. In order to solve such a problem numerically, the geometry and control volume are created in the ANSYS Workbench software and results are extracted in terms of force contours and diagrams. According to the results, the point of maximum pressure occurs at the beginning of the lower surface for both airfoils which depicts the stagnation point too. Also, zones of negative and positive pressures are more pronounced for the forward airfoil which is an evidence of higher lift coefficient. Effects of the flow behind the forward airfoil and passing the second one are such that its lift coefficient will decrease. Regarding the contours of temperature, the forward airfoil has no considerable influence over the second one and just a temperature boundary layer forms on the surface meeting the free flow values not so far from the airfoil. Temperature difference between the airfoil surface and the air flow does not affect the pressure distribution and diagrams of pressure distribution are almost the same for hotter-than-air/colder-than-air airfoils. But it has been observed that the difference in temperature between the air and the airfoil surface has some influence over shear force distribution which needs further investigation.

In this study, due to the importance of controlling the thrust vector of beveled nozzles, the effects of secondary injection on the output flow deviation from the convergent-divergent beveled nozzle have been investigated experimentally. For this purpose, three beveled nozzles with beveled angles of 25, 45, and 65 degrees have been used. Also, to control the direction of the output flow from the nozzle, a convergent injector has been installed to discharge the secondary flow perpendicular to the center direction of the nozzle at 0.8 divergent nozzle length. The main parameters studied in this research are the effects of changing the stagnation pressure of the main nozzle and the secondary flow and changing the beveled nozzle angle. The output flow deviation from the nozzle in different conditions is extracted from the shadowgraph images, and the results are presented. The results show that the performance of beveled nozzles with a low beveled angle with secondary injection is very good and the flow control in beveled nozzles up to 45 angle is much more favorable than high beveled angle nozzles. As the beveled angle increases, the nozzle performance decreases Strongly, So that the rate of reduction of flow deflection in 45 beveled nozzle compared to the 25, was close to 3%. While this deflection in the 65 beveled nozzle is reduced to 83%.

In the past decade, flow separation control on the compressor cascade surface has been of interest for scientists to increase efficiency and total pressure loss reduction. One method of active flow control is using a Dielectric Barrier Discharge (DBD) plasma actuator. In this research, DBD plasma actuator on flow separation control was stimulated on the blade surface and the of axial compressor cascade. Navier-Stokes equations are considered steady compressible and three-dimensional. The kw SST Turbulent model is used to simulate the turbulent flow. After validating the simulation results, effect of plasma actuators in three positions were investigated for application of the plasma actuator on the end wall, the suction surface of the blade or simultaneously at both locations at variable inflow angles. The results show that the use of plasma actuator on the end wall has a greater effect on decreasing the total pressure loss comparing suction surface. Also, plasma actuator on the suction surface proved to be more effective for corner separation than the two other types, at positive inflow angles as well as the design point.

In this study, a biodegradable composite by ML506 as matrix and kenaf fibers as reinforcement was designed, manufactured, and finally, its mechanical properties were investigated. The test samples were manufactured by the Vacuum-assisted resin transfer molding (VARTM) method. To determine the mechanical properties, a tensile test and three-point bending test were performed. Young modulus, yield stress, ultimate stress, maximum elongation, and toughness were obtained from the tensile test. Flexural strength and flexural chord modulus of elasticity were obtained from the three-point bending test. To determine the electrical properties, a dielectric constant test in X-band was performed. The loss tangent, as well as composite products, were obtained. The maximum tensile strength and tensile modulus were achieved in this research respectively equal to 62.42 Mpa and 4.43 Gpa. The flexural strength and flexural modulus were achieved in this research respectively equal to 99.19 Mpa and 5.619 Gpa. The dielectric constant and loss tangent of the samples produced in the X -band were 4.74 and 0.053, respectively. Finally, to validate the results in this research, the result of the tests were compared with the result of the other similar studies.

The aim of present study is to delay stall and increase the aerodynamic performance of NASA GAW- (2) supercritical airfoil by using a synthetic jet actuator. In this research, the diaphragm movement and the generated jet flow of the actuator are numerically simulated using Fluent software. The flow simulation was performed by solving the Navier-Stokes equations under turbulent and unsteady flow conditions in the subsonic flow. Before simulating the actuator, the flow around the based airfoil is first numerically simulated and aerodynamic properties of the airfoil are compared and validated with existing experimental results. In the next step, the effect of the synthetic jet actuator in delaying separation in stall region and increasing aerodynamic performance is numerically simulated. The location of the actuator on the airfoil has been studied. In this study, synthetic jet simulations were performed in three locations of 12, 20 and 30% of the airfoil chord length to identify the optimal location for actuation. The location of 30% of airfoil chord length at all angles of attack was able to provide a higher CL than the maximum CL in the based airfoil. The highest value of the lift can be seen by using the flow control at an angle of attack of 18 degrees with a 6% lift increment compared to the based airfoil. Also, the drag coefficient in the position of 30% of the chord length and the angle of attack of 20 degrees decreased by 26% compared to the based airfoil.

The air transport industry is considered as a forerunner and influential industry in the progress and development of any country and its status is one of the main and important indicators of development. Hegemony to the cost structure of airlines can manage the aircraft operating system on a systematic basis.The purpose of this research is to study and scrutiny the cost of aircraft maintenance in the airline and provide practical solutions to reduce these costs.To achieve this purpose, first, cost reduction methods were identified by studying documents and libraries and research background.Then a questionnaire was developed by Delphi method with a range of 5 Likert options and was distributed in 3 stages among 20 experts of airlines and cost reduction strategies were identified using SPSS software.Then, in order to prioritize the identified solutions, a hierarchical analysis questionnaire was prepared and distributed among the skilled staff of an airline.The results of the questionnaires were analyzed in Expert Choice software and the strategies were prioritized in four dimensions: structure, manpower, technology and budgeting.Finally, according to the research results, applicable solutions were presented based on 4 dimensions.

Due to the lack of proper planning and the integrity of the information command in the event of an accident & incident, as well as the lack of a clear and codified model for crisis communication, the air transport industry in Iran has always unsuccessful to use media capacity to accidents Manage. The main goal of this paper is to develop a media strategy to manage the air accident crisis. The grounded theory of Strauss and Corbin has been used in the interpretive paradigm which was based on qualitative methodology. In the pre-crisis period, reviewing the method of content production and distribution, formulating a comprehensive communication and educational program, and the crisis are predicted and simulated with the emphasis on the time. The crisis will be further enhanced by the unity of media command, media engagement, transparency, honesty, confidence-building, overlapping traditional and modern media, preparedness to deal with the crisis, by assessing the probability and vulnerability, as well as reducing the damage and negative consequences of air accidents.Using this strategy, and through assessing the probability and vulnerability, as well as reducing the damage and negative consequences of air accidents, the planned programs and media actions in times of crisis and preparedness to deal with it will be much more effortless and straightforward. Finally, local, national and international media coverage will be investigated. Also, by examining the strengths and weaknesses of the crisis management system, we gain experiences that will help us prevent the repetition of possible mistakes in the future.

The study of turbulent boundary layer trailing-edge noise is a fundamental issue in design and production of flying vehicles with minimum noise. Over the past decades, to reduce trailing-edge noise, various passive methods have been proposed, and the most recent strategy is the use of noise-reducing finlets. In the present study, to investigate the effect of noise reduction finlets on the turbulent flow field in the vicinity of the model trailing edge, a flat-plate model equipped with unsteady surface pressure transducers has been designed and built. Then, by installing a set of finlets with different lateral spacing on it, their effects on the flow field downstream of the finlets have been experimentally studied. Results show that the flow behavior downstream of the finlets is strongly affected by the spacing between the finlets. While the use of coarse finlets leads to a reduction in the mean velocity, turbulence intensity, and energy contents of low-frequency turbulent structures in the near-wall regions downstream of finlets, the flow behavior downstream of fine finlets are somewhat similar to the flow behind a backward-step. For fine finlets, the energy contents of turbulent structures in the near-wall regions are significantly reduced over the whole frequency range. he results of cross-correlation and coherence between surface pressure fluctuations and velocity field also showed that while the most important mechanism affecting surface pressure fluctuations for the coarse finlets is the exit low-momentum flow, for the fine finlets, vortical structures formed by flow separation have the most impact.

ACHEON nozzle is a thrust vectoring control device in which interaction of two jet flows under the influence of Coanda effects is implemented. The effects of inlet mass flow rate and the position of septum (relative to nozzle outlet) on flow structure, thrust vectoring, and shock formation have not been paid enough attention in previous studies. However, in this study, different mass flow rates and various positions of the septum were investigated. Flow was considered turbulent, two-dimensional, stationary, and compressible and RANS approach with standard k-ε model was implemented. The equations were solved using a pressure-based finite volume method on a structured computational grid. Using different Mach and Reynolds numbers and also various positions of the septum, thrust vectoring angle, flow structure, and nozzle shock position were studied. Our results show that with increasing inlet mass flow rate, thrust vectoring angle increases. It is noted that at a certain mass flow rate, a normal shock wave is formed in the nozzle. Also, except at this special mass flow rate (with shock wave), increasing inlet mass flow rate leads to increasing thrust vectoring angle. In addition, reducing the distance between the septum tip and the nozzle outlet increases thrust vectoring angle.