Pressure Loss Modeling of Non-Symmetric Gas Turbine Exhaust Ducts Using CFD

Abstract

In typical gas turbine applications, combustion gases that are discharged from the turbine are exhausted into the atmosphere in a direction that is sometimes different from that of the inlet. In such cases, the design of efficient exhaust ducts is a challenging task particularly when the exhaust gases are also swirling. A parametric Computational Fluid Dynamics (CFD) based study was carried out on non-symmetric gas turbine exhaust ducts where the effects of geometry and inlet aerodynamic conditions were examined. These exhaust ducts comprise an annular inlet, a flow splitter, an annular to rectangular transition region, and an exhaust stub. The duct geometry, which is a three-dimensional complex one, is approximated with a six-parameter model (four geometric and two aerodynamic), which was coupled with a design of experiment method to generate a relatively small number of exhaust ducts. The flow in these ducts was simulated using CFD for different values of inlet swirl and aerodynamic blockage and the numerical results were reviewed so as to assess the effects of the geometric and aerodynamic parameters on the total pressure loss in the exhaust duct. These flow simulations were used as a data base to generate a total pressure loss model that designers can use as a tool to build more efficient non-symmetric gas turbine exhaust ducts.