Sharif Digital Repository

Rotor contact with a stationary element of a rotating machine and the subsequent rubbing at the contact area is a serious malfunction that may lead to the machine’s catastrophic failure. In the past decades, many studies have been done on the rubbing phenomena, its different regimes and its various consequences on the machine performance and safety. However, most of them have used a simple model to investigate the rubbing interaction between the rotor and the stator. This simple model consists of the Jeffcott rotor, as a model for the real rotors, and a rigid annular block surrounding the rotor, as a model for the real stators. The objective of this thesis is to build an algorithm to... 

Nowadays, reaching higher speed in marine crafts and underwater vehicles mostly requires a modern propulsor with high efficiency and enhanced cavitation performance. Because of these requirements, numerous researches for developing the existing propulsion systems and invention of new systems have been conducted in recent years. One of the most sophisticated and developed propulsion systems that have high hydrodynamic efficiency and high cavitation performance and low acoustic signature is pumpjet. This propulsor contains a rotor, stator and a duct that surrounds two other parts. Stator reduces the swirl of flow coming from rotor and thereby reduces the loss of energy. High cavitation... 

Prediction techniques of axial flow turbine performance for different operating conditions are always developing due to high costs and lack of reliable empirical data. In axial gas turbines, fluid flow is three-dimensional, viscous, and highly turbulent. Nowadays, although flow field specifications are predicted accurately well using computational and numerical tools, the appropriate loss models are required for one-dimensional modeling and optimization in early design phases. In this research, an accurate and a complete investigation of aerodynamic losses in axial flow turbines will be discussed. Some suggested models for calculating losses in axial gas turbines, are considered and... 

In this thesis, a one-dimensional simulation, developed in previous studies, is utilized to study the stability phenomenon in axial compressors of gas turbine engines. The transient and dynamic operation of the axial compressor is determined by solving the conservation equations, expressed as one dimensional and time dependent Euler equations with related turbomachinery source terms. As known, stall and surge are one of the most destructive dynamic phenomenon in gas turbine engine compression systems starting with a flow separation. This occurrence is investigated in detail. In general, while choking phenomenon may occur during engine startup in the first stages, stall... 

In this thesis, the rear part of a turbo-jet engine consisting of a one stage axial turbine and its exhaust nozzle are optimized numerically and experimentally. The decrease of total pressure loss of the flow in the stator and rotor blade cascades is investigated by change of two-dimensional profiles. The three-dimensional blade shape optimization is employed to study the effects of the axial turbine stator and rotor lean and sweep angles as well as radial distributions of stagger angle on the turbine performance. In adition, the effect of the turbo-jet engine exhaust nozzle on its performance is explored. Geometry candidates for the three-dimensional optimization algorithm of the axial...