نشریه مهندسی هوانوردی
سال چهاردهم شماره 2 (پاییز 1391)

In this research, An investigation is done to understand the effects of blades surface roughness on the Transonic 4-stageAxial compressor performance parameters. A CFD code, which solves the Reynolds-averaged Navier–Stokes equations, was used to simulate the complicated 3D flow field of the Axial compressor. Numerical results was validated against experimental data of the Axial compressor performance curves. Numerical data showed good agreement with experimental data. Then, the effects of blades surface roughness on the Axial compressor performance parameters at design point was analyzed. Results show that blades surface roughness leads to increase boundary layers and pressure loss and decrease the efficiency and pressure ratio. So efficiency reduction goes up comparing with pressure ratio in the compressor.

The elastic properties and breaking strength do not remain constant and vary nonlinearly under cyclic thermal loading. The variation is larger and indeed more important in the case of composites as compared to isotropic materials. The variations of strength and elasticity modulus may be represented as a function of the number of thermal shocks, i.e. the difference among the temperatures exerted in these cycles and a reference temperature; which are measured experimentally. A new experimental device is designed and manufactured which can be conveniently used to apply thermal loads with different temperature on composite laminates. Subsequently, orthotropic glass-epoxy composites made by hand lay-up are tested under cyclic thermal loading using this apparatus. The variation of the elasticity modulus and breaking stress of the samples are measured before and after exerting defined number of thermal load cycles. As a result a convenient mathematical model is proposed whose predictions are in agreement with the experimental measurement. Finally, the obtained equations are used as the representative of material behavior in an analytical study of laminate fracture. The result show that nonlinear behavior of the composite under the thermal shock affects the breaking strength.

While an aircraft experiences a damage, system parameters severely change depending on the damage location and quantity. The autopilot is not able to maintain the airplane control in case of considerable damage. A preliminary requirement for recoverability and survivability of an aircraft after the damage is a better understanding of its performance and flight envelope. In this paper, wing damaged airplane maneuvering flight envelope and stability properties inside the maneuvering flight envelope are investigated for different wing damages and at different altitudes. In addition, eigenvector analysis is utilized to demonstrate the effect of damage on motion modes, handling quality, and longitudinal and lateral-directional coupling. The overall above analysis provides a comprehensive understanding of the wing damage effect on airplane performance and dynamics that is essential for flight durability and safe landing.

Today, most of the organizations due to their environmental conditions and also for increasing their competitiveness power have turned to outsourcing. Outsourcing strategy means to exploit the resources of other companies to improve business process both inland and overseas, internally and externally. Indeed, the process of the selection for this approach, specifically in the current situation is very crucial for airline organizations. Therefore, the present study aimed to select the best and the most efficient methods for maintenance checks in and out of the country. The best way has been sought to answer questions such as, what is the most efficient method for aircraft maintenance checks. What are the selected indexes of maintenance checks for aircraft inside the country and how important are they? should these checks be done inside or outside? Consequently, to achieve the research objectives and answer the above mentioned questions, and also to compare the efficient method we have dealt with Iran Air Tour aircraft maintenance check inside and outside the country, and deciding on inside or outside outsourcing maintenance check by the assistance of experts. In this study, the maintenance check selected criteria, includes trained human resource, time-saving tools and equipment’s, financial condition, management changing, facilities, the expense of all services and method of choice to choose the proper maintenance check of combined AHP technique with TOPSIS multi-criteria decision making and Electre.The survey shows that trained human resources have the most effective influence on the useful maintenance check of aircraft and there is a significant difference between maintenance check inside and outside. The results suggested that in 300 hours maintenance checks, the performance of the foreign organization was better while in 1200 hours maintenance checks the performance of the inner was better.It is worth noting that in the present survey, all of the experts in the field of aircraft maintenance outsourcing were in the Iran Air tour-Airline and the other similar companies. Due to the limitations 51 experts were selected as a sample population.

In this article, the effects of unsteady parameters including mean angle of attack, oscillation amplitude, reduced frequency and pitching axis position on aerodynamic coefficients of a pitching airfoil are studied. The numerical method is described as Coarse Grid CFD (CGCFD) in which the Euler equations are solved using a coarse grid and no slip boundary conditions with compressible surface vorticity confinement technique. The required unsteady time for this method is significantly lower compared to that of the full Navier-Stokes equations with even a simple one equation turbulence model. It is found that the computational time for one oscillation loop is reduced more than fifty times. In addition, a multi zone adaptive spring network is applied to simulate the moving boundary which further reduces the computational time. The obtained numerical predictions are in good agreement with experimental data. In this paper, first, the results are compared with the experiments in two mean angles of attack with specific oscillation amplitude and reduced frequency. Then, the effect of these parameters and pitching axis positions on aerodynamic coefficients of pitching NACA0015 airfoil is investigated. It is observed that moving the pitching axis position to the right or left outside and distancing from trailing edge or leading edge have inverse effects on thickness of the hysteresis loops, the maximum, minimum, and average lift and drag coefficients. Further, increasing the reduced frequency results in a reduction of the lift hysteresis loop slope and the maximum lift and drag coefficients.

An octagonal to square diffuser is an important section of the vertical wind tunnel, which has been designed for sky-diving operations. To determine the actual pressure drop of the diffuser, the velocity distribution should be measured. In addition, flow separation can be investigated by velocity distribution. In this research, a 7.8 % model of the original diffuser has been constructed, and velocity distribution and turbulence intensity of airflow have been measured using hot-wire Anemometer. The results of velocity distribution and turbulence intensity showed no flow separation in the tested diffuser. The error associated with pressure drop estimation is significant in the absence of the velocity distribution effects.

Aviation industry in accordance with its development and use of sophisticated techniques and technology has faced many repeated air accidents. Any event that happened in the past can be used as a historical experience in order to prevent similar disasters in the future. In other word, evaluating and analyzing the past events can be used to identify the potential factors which cause the air accidents. In addition, exact investigation of these factors could be a solution for reducing these accidents. In order to be much closer to this goal, comprehensive database should be designed and also be accessible for administrators, technical managers and the strategic and operational levels to maintain the readiness and minimize damage to the aviation industry. This study is a theoretical research in the field of air accidents to present a comprehensive model of flight database and operation in order to prevent the ocurrance of similar accidents. The population of the research consists of aviation accident experts in aviation industry. Non probability sampling method is used to determine the sample of this research. Data collection is done by in-person questionnaire and archival data. The research method is field- descriptive. The results show the importance of database design to increase the flights’ safety factors of aviation industry.