Effect of Unsteady Wakes on Turbine Tip Gap Leakage.

摘要

Gas turbines are found in military and civilian aircraft, ships, and power plants. Because of this widespread use, relatively small improvements in efficiency can have a large cumulative impact on energy use. The most significant source of loss and inefficiency in a gas turbine engine is tip gap leakage. Tip gap leakage occurs when flow travels across the top of the turbine blade through the small clearance space between the blade tips and the turbine casing, instead of along the length of the turbine blades. Tip gap leakage reduces the amount of force on the turbine blades, and the flow that is leaked across the tip gaps is wasted. Additionally, tip gap leakage leads to vortices that result in dissipated rotational kinetic energy and can disrupt the flow in the next stage of the turbine. In this project, experimental methods were used to study the effects of unsteadiness on gas turbine tip gap leakage. A case with steady flow and no tip gap was used as a baseline to compare to the results of the other cases. The flow patterns were studied for each of the cases and compared to see the effects of unsteadiness on tip gap vortices and end wall flows. Particle Image Velocimetry, PIV, was used to collect velocity fields upstream of the blades, inside the blade passage and in planes perpendicular to the flow downstream of the blades. These data will be used to help limit the negative effects of tip gap leakage and make gas turbine engines more efficient.