نشریه مهندسی هوانوردی
سال بیست و پنجم شماره 2 (پاییز و زمستان 1402)

In this article, the correlated free convection heat transfer in a rectangular cavity containing nanofluid and with a triangular solid area was investigated numerically.The governing equations written in terms of the primitive variables were solved numerically using the finite volume method while the velocity and pressure fields were coupled using the SIMPLER algorithm. Correlated characteristics such as the thickness of the triangular solid area (dimensions of the triangular solid area) and the ratio of the thermal conductivity coefficient of the triangular solid area to the nanofluid on the flow and free convection heat transfer cavity were investigated. Studies have been carried out for the Rayleigh number Ra  105, and constant volume fraction ϕ=0.02 for the ratio of thermal conductivity coefficients Kr = 0.1, Kr = 1 and Kr = 10,as well as for different dimensions of the triangular solid area.The results showed that with the increase in the ratio of the dimensions and thickness of the triangular solid region, as well as the ratio of the conductivity coefficient in a constant Rayleigh number, the temperature and velocity of the nanofluid increase. Also, with the increase in the ratio of the dimensions of the triangular solid area and the ratio of the conductivity coefficient, the values of the average Nusselt numbers increase along the walls, and more heat transfer passes through the solid-fluid interface.

using porous metal foams is one of the conventional methods to increase heat transfer in industrial systems, including heat exchangers. Porous media increase heat transfer and lead to an increase in pressure drop.. In this paper, the three-dimensional effects of flight altitude (1000m<H<5000m) and porous metal foam with Darcy number(0.1<Da<0.0001) in a training airplane oil cooler were investigated. The porosity coefficient was assumed to be 0.9 for all cases with porous foam.The Darcy-Brinkman-Fortheim equation was used to simulate a 20 W50 oil flow in a porous medium. The thermophysical properties of the oil including density, viscosity and thermal conductivity were extracted using laboratory data in terms of operating temperature. Hot oil with boundary condition enters the oil cooler. The boundary condition of the output oil is . The cooling wall is the boundary condition of non-slip and the heat transfer coefficient of air movement is proportional to the height. The governing equations are discrete based on the finite volume method using commercial computational fluid dynamics FLUENT. With increasing flight altitude, in pure oil mode, heat transfer, pressure drop and performance evaluation criteria increase by 0.65%, 0.45% and 0.49%, respectively. Porous metal foam with Darcy number having leads to increase of Nusselt number , increase of pressure drop and has the highest performance evaluation criterion PEC=31.75. Porous metal foam with Darcy number has the highest pressure drop and the highest heat transfer increase . According to the obtained results, Darcy's number is the most optimal performance evaluation parameter.

The performance of a Mach 6 Hypersonic nozzle designed to be installed in a reflective shock tunnel has been experimentally investigated in this paper. The purpose of nozzle performance is to create a uniform flow at the outlet and a suitable test time considering the starting flow inside the nozzle. This nozzle is designed using modern optimization methods based on a classic converging-diverging nozzle. Also, the design and construction of a total pressure rake is presented to evaluate the flow quality in the test section. The complexity of investigating hypersonic flows is the sensitivity of the flow to the existence of various types of disturbances and also fluctuations caused by acoustic waves. Therefore, in hypersonic flow, considerations related to the design of the test section as well as the geometry of the pressure rake are very important. In this paper, the dynamics of the reflected shock wave in the shock tube and the starting waves in the test section are investigated. The pressure upstream of the nozzle is in good agreement with the design values with an error of 4%. The Mach number distribution is presented by measuring the pressure distribution at the end of the nozzle. Finally, the Mach number distribution at the nozzle outlet has been compared with the numerical results which shows an error about 3%. The uniformity of the flow at the end of the nozzle, which has been observed numerically and experimentally, shows the effectiveness of the optimal design method of the ultrasonic nozzle.

Flanges are parts that provide the possibility of connection, change of direction, access for repairs and inspection between large and main parts of equipment and structures. In this research, due to the importance of maximum lightening while maintaining the strength of parts in aerospace structures, composite flanges and shells were made, which are used in aeronautical structures such as bossting rockets and satellite carriers. They are responsible for connecting the parts and large shells of the structure. The material of the flanges used in these structures is aluminum in the lightest state, and in this research, with the aim of lightening as much as possible, 4 flanges and 4 shells were made in 2 sets, each set includes 2 flanges and 2 shells. After connecting the flanges and shells to each other, experimental modal analysis and tensile tests were performed. Also numerical simulation of the modal and tensile test was performed with ANSYS software. The results of experimental tests and numerical analysis on the manufactured parts show that the specific frequency of the composite flange is higher than that of the steel and aluminum flange (in low frequency range). Also, the delamination factor in the composite flange blade has more effect on increasing the length of the structure due to the tensile force, rather than the failure of the matrix and fibers.

Despite the increase in competition and the need for a better understanding of the relative efficiency of an airline compared to other companies, so far, only a handful of studies have addressed the issue of airline efficiency in Iran along with taking into account the different phases of the work process and the existing uncertainties. In other words, existing researches have mostly used data envelopment analysis models in deterministic mode, despite the fact that in reality we are faced with different kinds of ambiguity and uncertainty in many issues. The purpose of this research is to evaluate Iranian Airlines by using fuzzy logic and two-stage data envelopment analysis approach in the form of presenting a new method of two-stage fuzzy data envelopment analysis (fuzzy additive analysis approach). Hence, the real data of 14 Iranian airlines have been used. The case study in question shows that Pouya, Taban, and Airtour airlines have better overall efficiency compared to other airlines with 0.1, 0.97, and 0.96 respectively, Although the only efficient airline with an efficiency of 1 is Pouya.

Thrust and specific fuel consumption are two essential parameters in a gas turbine engine. The fundamental design of various engine components is required to enhance thrust and provide optimum specific fuel consumption. This paper studies the effects of the nozzle exit area on the operating lines of fan, compressor, and turbine in a single-spool, mixed-flow, and low bypass ratio turbofan engine. The zero-dimensional modeling of the engine is examined in GasTurb, and the nozzle area is changed in 6 cases by ±5, ±10, and ±15 percent relative to design point. The inlet temperature of turbine rotor and the spool speed of the engine are limited to their maximum amount. The results show that any change in the nozzle exit area will reduce the net thrust of the engine. On the other hand, with the reduction of the nozzle area, the operating line of the fan and compressor becomes closer to the surge line, reducing the surge margin, while with the increase of the nozzle area, the surge margin of the fan and compressor increases. Also, the changes in specific fuel consumption are inversely proportional to the changes in the nozzle outlet area.

This paper introduces the schematic and new structure of a 115V AC multilevel inverter with an output frequency of 400Hz for use in the emergency power supply of aircraft and the electrical distribution system of aircraft. The input power of this converter is provided by connecting to the DC bus of the aircraft or by a pod equipped with a wind turbine and permanent magnet synchronous generator In order to stabilize the variable voltage produced by the wind turbine, an interleave boost converter has been used. In addition, the design of the desired converter has been made in such a way that compared to other conventional and novel converters, it has fewer parts. The proposed converter is able to produce a 25-level output voltage waveform with the ability to increase the input voltage. No need for a filter in the output of the converter due to the very low total harmonic distortion of this converter and its compliance with the IEEE 519-2022 standard are other noteworthy features of the converter. This feature causes a significant reduction in the weight and volume of the power supply of the aircraft compared to other available structures, which is especially important for air applications, both military and commercial types The efficiency and performance of the proposed structure under the conditions of load change and wind and aircraft speed change when connected to a wind turbine and permanent magnet synchronous generator have been checked and confirmed in MATLAB/SIMULINK simulation environment.

In the present study the aeroacoustic characteristics of an aerodynamic open circuit wind tunnel is experimentally investigated by furnishing its test section by noise absorbing panels. The objective is to evaluate the effectiveness of sound absorbing walls in reducing the wind tunnel background noise and to investigate the effect of its various parameters such as the thickness of sound absorbing materials on the background noise levels. The results showed that the presence of standing waves across the test section considerably increases the background noise levels for the frequencies higher than about 750 Hz. Using sound absorbing panels at the upstream of the test section improves the acoustic performance of the wind tunnel at mid to high-frequencies while increases the background noise at low-frequencies. The acoustic performance of the wind tunnel is improved at middle frequency range of 150-400 Hz by increasing the sound absorbing materials thickness. The existence of the air gap behind the sound absorbing materials results in a slight improvement in the wind tunnel's aeroacoustic performance at frequencies lower than 300 Hz. Finally, the results showed that using sound transmitting stretched fabric instead of sound absorbing materials results in a significant reduction of the background noise at all frequency range

In this research, the aim is to find the shortest path, without encountering the existing obstacles, to guide a missile in a linear way through fixed and moving obstacles towards a moving target. The movements of the obstacles and the target are unknown in the first place, but after discovering and finding the target and obstacles, the method proposed in this article can generate commands for the missile to track the target until it is reached. The proposed algorithm of this article is designed in such a way that it can be ensured that the missile finds the shortest possible path and approaches the target by avoiding the obstacles completely. On the other hand, considering that the presented algorithm does not use all the information available in the environment and in order to control the volume of calculations in the next cycles, corrective operations are used in the algorithm, so it is expected that the proposed algorithm will reach the optimal solution in a very short time. Also, we have simulated some complex scenarios to test the algorithm in MATLAB software, the results of which show the convergence of the algorithm in finding the optimal path leading to the moving or stationary target while avoiding moving or stationary obstacles in the appropriate time frame.

In this paper, Analysis variations of volume fraction continuous functionally graded materials on the vibration of reinforced cylindrical shell under axial loads with asymmetric boundary conditions are studied. The functionally graded plates shell is made in accordance to the volume fraction plates from two constituents namely stainless steel and nickel. These constituents are graded through the thickness direction, from one surface of the shell to the other and are controlled by volume fraction plates distribution. The reinforced functionally graded shell equations with axial loads are established based on first order shear deformation theory. The governing equations were employed with energy functional by applying Ritz method. The asymmetric boundary conditions represented by end conditions of the functionally graded shell are clamped-free, clamped-simply support and free-sliding. For validity and accuracy of the present methodology, the results obtained are compared with those available in the literature. Effects of volume fractional variations of functionally graded, axial loads, reinforced and asymmetric boundary condition on vibration of reinforced functionally graded cylindrical shell model are studied.

Flight crew management is an important factor in flight in order to ensure operational safety and reduce flight errors. In order to monitor all threats and errors managed or not by flight pilots, considering flight safety factors that will have a direct impact on pilots' errors is one of the basic and important issues to maintain an airline at an acceptable level of safety performance. In accordance with literature review study on the subject in airline companies, it is observed that there is a gap in the comprehensive consideration of the identification and evaluation of the basic factors of flight safety which are affected on the pilot’s errors during flight. Therefore, in this paper, an evaluation method of the pilot’s performance management is proposed by providing criteria and sub-criteria and also the pilot’s error assessment in order to increase the level of flight safety. The statistical population of this research is active airline pilots in Airbus fleets of wide-body and narrow-body aircrafts. Simple random sampling has been used to collect the data which are needed for the research and also to analyze them. In this research, the method of data discovery and content validity has been used in order to identify the criteria which are affected the pilot’s error. The most important achievement of the paper are the identification of the types of errors which affecting the pilot’s error and how to evaluate them, as well as the discovery of the effective safety factors.

In this paper, a CRLH-TL antenna is presented to cover multiple frequency bands and improve bandwidth. Antennas designed as ultra-wide bands can cover different frequency bands with small dimensions, all-directional radiation pattern and appropriate gain. Antennas designed as ultra-wide bands can cover different frequency bands with small sizes, all-directional radiation pattern and appropriate gain. Considering the basic application of antennas in Flight communication systems and control navigation, optimizing and controlling their performance in navigation is of particular importance. For this purpose, in this paper, the desired antenna structure with magnetic metamaterials has been investigated. Finally, two combination methods have been proposed to improve antenna control performance. The first method, a circuit-based model with combined CRLH structure is proposed for effective miniaturization and versatility. Then, by using incomplete terrain (via) and FSS frequency selector levels, the antenna is designed with optimal gain and bandwidth. In the proposed antenna, miniaturization is provided through metamaterial transmission line and feed by electromagnetic coupler and CRLH element. The Right- Hand part consists of 35 Micron copper metal patch and Left side of the effective transmission line of homogeneous. The FR-4 antenna bed is the characteristic impedance of 50 ohms and the frequency range is 2 to 7 GHz.removing the system design disruption by symmetrical polarization and improving the quality of bandwidth through the slotted ground. The proposed antenna is a compact microstrip antenna that improves the frequency of resonance, increases gain, bandwidth and impedance matching and ultimately an improved control system.