Title: Influence of passive tip-injection on the excitation forces in axial turbines with shrouded blades : by Lukas Krismer
Other Titles: Einfluss passiver Einblasung auf die Spalterregung in axialen Turbinenstufen mit Deckbandbeschaufelung
Language: English
Authors: Krismer, Lukas 
Qualification level: Diploma
Advisor: Ghaffari, Pouya
Assisting Advisor: Willinger, Reinhard
Issue Date: 2017
Number of Pages: 91
Qualification level: Diploma
In turbomachinery the leakage of mass flow through the clearance between the rotor blade tips and the casing is one of the main sources of loss. In order to reduce this form of loss, the flow resistance of the blade tip clearance can be increased geometrically by winglets, squealers and shrouds or aerodynamically by a fluidic jet barrier. At the department of Fluid-Flow Machinery of the Institute for Energy Systems and Thermodynamics at the Technische Universität Wien passive tip-injection has been presented as a method of increasing the flow resistance of blade tip clearances in turbomachinery. This method extracts mass flow at the rotor blade leading edge which is then guided through the blade and injected into the blade tip clearance. Research shows, that passive tip-injection has the potential of significantly reducing the tip-leakage mass flow and improving the mixing conditions of the leakage mass flow with the main flow considerably. The term tip excitation labels aerodynamically induced cross forces acting on the rotor of turbomachinery depending on the tip-leakage mass flow. These forces have the potential of inducing an instable whirling motion of the rotor above a limiting power level of the turbomachine, which renders further operation impossible. Two effects are known to be the main reasons of tip excitation in turbomachinery: The variable tip-leakage mass flow of an eccentric rotor leading to a variation in tangential forces on the rotor blades and the pressure variation in the tip gap of an eccentric rotor under swirled flow conditions. Both result in a cross force perpendicular to the direction of displacement of the rotor. This thesis investigates the influence of passive tip-injection on the tip excitation in shrouded axial turbine stages. Therefore an analytical model for the tip-leakage mass flow and the pressure in the tip gap of a shrouded turbine rotor with passive tip-injection under swirled flow conditions is developed and evaluated numerically. Subsequently the resulting cross forces on the rotor are calculated. It is shown, that passive tip-injection has the potential of decreasing the tip excitation cross forces by reducing the tip-leakage mass flow and positively influencing the flow angles and the pressure distributions in the tip clearance.
Keywords: Axialturbine; Deckbandbeschaufelung; Labyrinthdichtung; passive Einblasung; Spalterregung
axial turbine; shrouded blades; labyrinth seal; passive tip-injection; tip excitation
URI: https://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-103058
Library ID: AC14475531
Organisation: E302 - Institut für Energietechnik und Thermodynamik 
Publication Type: Thesis
Appears in Collections:Thesis

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