Date of Award

2010

Degree Type

Dissertation

Department

Mechanical Engineering

First Advisor

Ibrahim, Mounir

Subject Headings

film cooling, airfoil, Jets, Vortex generators, CFD, Flow control, Film cooling, LES, Airfoil, Separation, Vortex generator jets

Abstract

Jets have been utilized in various turbomachinery applications in order to improve gas turbines performance. Jet pulsation is a promising technique because of the reduction in the amount of air removed from compressor, which helps to increase turbine efficiency. In this work two areas of pulsed jets applications were investigated, first one is film cooling of High Pressure Turbine (HPT) blades and second one is flow separation control over Low Pressure Turbine (LPT) airfoil using Vortex Generator Jets (VGJ) The inlet temperature to the HPT significantly affects the performance of the gas turbine. Film cooling is one of the most efficient methods for cooling turbine blades. This technique is simply employing cool air discharged from rows of holes into the hot stream. Using pulsed jets for film cooling purposes can help to improve the effectiveness and thus allow higher turbine inlet temperature without affecting the blade's life. Engine cost will thus be reduced by providing the same capacity from smaller, lighter engines. Fuel consumption will be lowered, resulting in lower fuel cost. Effects of the film hole geometry, blowing ratio and density ratio of the jet, pulsation frequency and duty cycle of blowing on the film cooling effectiveness were investigated in the present work. As for the low-pressure turbine (LPT) stages, the boundary layer separation on the suction side of airfoils can occur due to strong adverse pressure gradients. The problem is exacerbated as airfoil loading is increased. If the boundary layer separates, the lift from the airfoil decreases and the aerodynamic loss increases, resulting in a drop in an overall engine efficiency. A significant increase in efficiency could be achieved if separation could be prevented, or minimized. Active flow control could provide a means for minimizing separation under conditions where it is most severe (low Re), without causing additional losses under other conditions (high Re). Minimizing separation will allow improved designs with fewer stages and fewer a

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