Effects of blade count on hot streak clocking simulations using linearized and nonlinear methods

Abstract

The temperature field exiting gas turbine combustors is highly non-uniform due to streaks of fluid directly downstream of combustor fuel nozzles. These streaks have been shown to limit the life of turbine blades. Adjusting the positions of streaks with respect to inlet guide vanes, known as hot streak clocking, can be used to help control blade temperatures in gas turbines. In turbine simulations used in the design process, it is common practice to modify blade counts to decrease CPU time requirements, but the effect of this procedure on the results of the simulations has not been investigated. In the present study, results of 3-D streak clocking simulations with 1-1-1 and 3-4-3 blade counts (blades per row) are examined, and the nonlinear and linearized methods are compared. It is shown that blade count has a significant effect on predicted blade surface temperature. It is also shown that the linearized technique can be used to qualitatively capture streak clocking effects. Greek Symbols Notation Roman Symbols IGV P T inlet guide vane pressure temperature (P — Pexii)/(Ptoo — Pexii) *Sr. Scientific Programmer, Senior Member AIAA. t Graduate Student, Senior Member AIAA. * Associate Professor, Student Member AIAA. § Aerospace Engineer, Senior Member AIAA. flow angle, degrees Subscripts t oc total inlet Introduction In jet engine combustors, fuel is introduced through nozzles at a number of circumferential locations. As combustion occurs, the flow downstream of the nozzles is hotter than the surrounding fluid, l a phenomenon known as streaks. The streaks maintain their identities as the flow convects through the vanes of the highpressure turbine, and the turbine rotor blades operate in the presence of an unsteady inlet temperature field. As streaks interact with the rotor blades, they can cause localized spots on the blade surfaces, leading to diminished blade life, or in the worst case, blade failure. An early experimental investigation of streak migration was performed by Butler et al They showed that streaks cause increased temperature on rotor blade pressure surfaces and decreased temperature on suction surfaces. The temperature changes were attributed to two effects: changes in secondary flow patterns due to presence of the streaks, and circumferentially varying inlet relative flow angle as discussed by Kerrebrock and Mikolajczak. They also verified the analysis of Munk and