جستجوی مقالات مرتبط با کلیدواژه "تحلیل سه بعدی" در نشریات گروه "مکانیک"

In the high-pressure gas-turbines, with hot-flowing gas through the stator channels with a high mass-flow rate, even slight variation in the blade geometry will have significant effects on the downstream flow-field. These minor changes can be compared to corrosion rates. The first occurrence of this corrosion is the non-uniformity of flow in the stator-rotor axial distance. This non-uniform flow, due to the complex pattern of vortices, prevents the complete transfer of fluid energy to the rotor and greatly reduces the turbine performance. In this research, a high-pressure turbine is considered to be at high risk of corrosion. The main goal is to predict these variations due to corrosion. Firstly, a 3D numerical analysis of the turbine initial model was conducted to accurately observe the flow field and the results were validated by the existing experimental results. Then, in order to investigate the effects of corrosion on the turbin performance, the blades geometrical changes were applied in stator blade profile and the flow distribution was analyzed. Results show that the highest corrosion risk is at the trailing-edge of the blades. Due to reduction in the stator inlet-outlet area ratio, the axial-velocity is reduced. But simultaneously, with increasing the stator channels outlet area, the mass-flow rate is increased by 7.31%. Therefore, the turbine undergoes to an off-design condition. The flow pattern will be more complicated in the rotor's entrance, and corrosion will develop rapidly due to temperature rise as the flow separates from the rotor blades.

In this work, the modeling and utter and nonlinear dynamical behaviors of uid-conveying pipes in three dimensions are undertaken. All equations of motion are derived assuming an appropriate displacement in nonlinear form using Lagrange principle to circumvent the complex modeling approach given in mentioned references. In previous works on modeling three-dimensional motion of pipe, a complex approach based on inextensibility of pipe was used for derivation of equation of motion. This assumption resulted in nonlinear complex equation of motion and boundary condition. But, here, a simple method is used to obtain equation of motion. Due to three-dimensional motions of pipe, double bending and in-plane displacement eld are assumed. Governing partial dierential equations are discretized by Rayleigh- Ritz's method, and dimensionless form of equation is derived with dening appropriate parameters. The nonlinear equations are solved numerically and its vibration behavior is examined. Due to uid ow, detrimental utter phenomenon occurs, which make system unstable. Dierent types of bifurcations are observed, and the eect of varying parameters on utter is accurately examined. Discussion of how utter occurs and dierent modes of utter are presented. Finally, the eect of design parameters on the system instability and its type is presented. With varying ow velocity, dierent types of nonlinear vibrations are occurred. These behaviors include simple limit cycle oscillations, period doubling, intermittency, and chaos. Also, in some ow velocities, locking motion in a special plane is occurred. The eects of dierent parameters on these nonlinear behaviors are examined. Some new results are presented, which are not previously reported. Obtained results and their comparison with appropriate references show the accuracy of modeling according to the assumed eld displacement. Obtained results show the ecacy of the proposed modeling in capturing all nonlinear behavior phenomenon reported in literature. It is simple to extend the proposed modeling for dierent boundary conditions.

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.

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.