Flow in non-symmetric gas turbine exhaust ducts

An experimental and computational study of non-symmetric single-port gas turbine exhaust ducts has been carried out. The geometry of the exhaust duct incorporates an annular to rectangular transition with a 160° turn. The focus of the study was to determine the effect of inlet conditions and duct geometry on the flow structure and the level of overall pressure losses in the duct flow. As part of this work, the appropriateness of boundary conditions for both experimental and computational studies was investigated.; The experimental studies were carried out using a ½-scale cold flow apparatus capable of measuring the flow conditions at the inlet and outlet of the duct. Inlet conditions varied included the level of swirl and circumferential total pressure distribution. Computational fluid dynamic (CFD) studies were carried out using a commercial solver using k − &epsis; turbulence modeling and non-equilibrium wall functions. The computational solutions were benchmarked against experimental values, allowing CFD to be used to extend the range of inlet conditions beyond the range that could be obtained experimentally, to those more typical of an engine installation.; Results show that inlet conditions have a significant effect on the flow structure in the exhaust duct. Total pressure losses in the exhaust duct increase as the circumferential inlet total pressure distribution becomes more non-uniform. This results in losses measured on a standard cold-flow apparatus under-predicting those that would exist on a duct installed on a gas turbine. However, trends in the geometric variables identified experimentally using cold flow were confirmed computationally with inlet conditions more typical of an exhaust duct mounted on an engine.