Investigations of Dust Separation in the Internal Cooling Air System of Gas Turbines

Abstract

Improvements in efficiency and performance of gas turbines require a better understanding of the internal cooling air system which provides the turbine blades with cooling air. With the increase of cooling air passing through the internal air system, a greater amount of air borne particles is transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blockage. Blockage of only a few holes could have harmful effects on the cooling film surrounding the blade. As a result, a reduced mean time between maintenance or even unexpected operation faults of the gas turbine during operation could occure. Experience showed a complex interaction of cooling air under different flow conditions and its particle load. To get more familiar with all these influences and the system itself, a test rig has been built. With this test rig, the behaviour of particles in the internal cooling air system could be studied at realistic flow conditions compared to a modern, heavy duty gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. The test rig has been designed to give information about the quantity of separated particles at various critical areas of the internal air system [1]. The operation of the test rig as well as analysis of particles in such a complex flow system bear many problems, addressed in the previous paper [1]. New measurements and analysis methods give new and more accurate results, which will be shown in this paper. Furthermore the inspection of the test rig shows dust deposits at unexpected positions of the flow path. Theoretical studies to characterize the flow behaviour of the disperse phase in a continuous fluid using Lagrangian Tracking were also performed. A comparison between the numerical solution and the measurements will be shown in the paper.