Some Aspects on Inlet Blockage Affecting the Performance of a Heavy Duty Gas Turbine’s Exhaust Diffuser

Abstract

Exhaust diffusers of heavy duty gas turbines significantly improve the performance of gas turbines. These diffusers typically differ from the simple and well investigated annular or conical diffusers because of the incorporated struts. The investigated model of such a typical exhaust diffuser consists of an annular duct with two rows of integrated struts and a Carnot diffuser downstream of the annular part. In this paper the influence of inlet blockage on the performance of gas turbine diffusers is numerically investigated. 3D-RANS calculations are performed applying the k-ω-SST-model. The numerical inlet conditions for the baseline are given by detailed experimental data acquired in a test rig. The results show that the impact of the inlet blockage on the diffuser flow can be split into two aspects, which both influence diffuser pressure recovery. The first aspect is the well-known reduction of effective area of the core flow leading to reduced pressure recovery feasibility. Secondly, it is observed that the inlet blockage has a significant influence on the structure of secondary flow in the vicinity of the diffuser struts affecting the diffuser pressure recovery. Using a simple correlation of the size of the secondary flow and the core flow the influence on pressure recovery is estimated. In sum, the aerodynamic performance of the annular diffuser and the first row of strut is of high importance and mainly depends on the inlet boundary conditions. Accordingly, these geometries need to be designed to their inlet conditions.