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High temperatures and different properties of entering gas into the turbine of a gas turbine cycle can decrease its performance. Considering the complexity of the flow distribution inside the turbine, three-dimensional analysis to find out the flow and temperature field in the turbine stages is very important. As time passing the increasing of the roughness of blades is unavoidable. The aim of this paper is investigation of the blades roughness effects on flow field and efficiency of gas turbine with numerical calculations. In this research, a two-stage turbine is modeled in the form of three-dimensional and the results are validated with experimental data. Then the effects of blades roughness on flow field and performance of turbine in five pressure ratios is investigated. Also, in order to determine the role of stators and rotors in decreasing the turbine efficiency, in a special roughness, the first and second stators and then corresponding rotors have separately been examined and then this phenomenon affected on blades simultaneously. Results showed that the efficiency drop by applying all together on the turbine stage is approximately equal to summation of efficiency drops by applying separately.

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With respect to special conditions apply to the gas turbine, its blades are affected by many different factors such as, hot corrosion, oxidation, wear, impact of external particles, and etc. and are destroyed. Due to the reduction of their working life time, the turbine efficiency reduces and ultimately the heavy costs of periodic repairs are needed, and also new replacements of their blades are unavoidable. The aim of this study is investigation of the effects of corrosion and blade damage on flow field and gas turbine performance, by numerical simulation. In this research, a two stage turbine is modeled in the form of three dimensional and the results are validated with experimental data. To analyze of the behavior of entire flow, conservation of mass, momentum, and energy equations are solved. The numerical simulation of the turbine is done with ANSYS CFX software. Then the increased rotors tip clearance effects with decreasing thickness due to corrosion in both nozzles and blade leading edge and trailing edge were separately studied on turbine flow field and its performance in five actual different pressure ratios. The results showed that the most important factor in reducing the efficiency of gas turbine is due to rotor tip clearance increasing. Also corrosion of the blade edge respect to the trailing edge damage is a little more affected on reducing efficiency and increasing loss coefficients.

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Cemented carbides are the most common cutting tool materials. To improve machining process, the surface of the cutting tools must be wear resitance with high hardness and chemical inertness. In recent years, several coatings have been developed for tungsten carbide. In this paper, the effect of TiN/TiCN/Al2O3 multicoatings on the performance of drilling process of spherodized cast iron was studied. The external layer is Al2O3 which has high resitance to wear and TiN was chosen as internal layer because of it excellent adhesion to the tungsten carbide surface. The intermediate layer was TiCN because of its compatibility with the other layers. At first, drills were prepared by machining process and then the triple layer coating was applied on the surface of tungsten carbide drills by chemical vapor deposition method. The coating process was performed under usual industrial condition. The thickness of the coatings was 10 micrometers. The wear of drills, the surface roughness and the hole diameter tolerance were investigated. The structure of coating and wear surface was studied by scanning electron microscopy. It was found that the multiple coating significantly improved the wear resistance of the drill compared to uncoated tolls. In addition, it was found that the surface roughness and hole diameter tolerances improved by drilling with coated tools. The reason of this would be the lower wear rate and resulting dimension stability of the coated tools. In addition, according ot wear surface structure, it was concluded that the mechanism of wear was abrasion.

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Sedimentations and hard cakes formation of magnetic particles restrict magnetorheological fluid response to magnetic field and can cause the MR fluid containing device to collapse. Therefore, researches on MR fluids sedimentation reduction procedures and its effective factors are in great deal of interest to improve magnetorheological applications. In this study, the effects of some parameters on typical MRF stability were investigated. For this purpose, at first, MRF samples were constructed and the effects of various factors including carrier fluid type, particles concentrations and MRF mixing methods on its stability were investigated and the importance of each factor were determined by Taguchi algorithm and the stable MRF sample for application of magnetorheological dampers was chosen. Next, by investigation of the most stable MRF sample, based on the combination of stability and off- state viscosity factors, the relation for yield stress in various magnetic fields was presented. This relation was derived based on fitting the Herschel- Bulkley model with experimental data in conjunction with the existing relations of yield stress. As the results shown, after 168 hours, sedimentation for the most stable sample is 7%. This sample consists of silicon oil and 70%wt iron powder which prepared with mechanical stirrer. Adding 3%wt stearic acid to carrier fluid for increasing the stability, results to increasing the viscosity of carrier fluid up to 39 times. In spite of this, an acceptable MR effect is presented so that, in magnetic field of 146KA/m the sample yield stress is 15KPa.