Investigation of the flow field and the pressure recovery in a gas turbine exhaust diffuser at design, part-load, and over-load conditions

Publication date
2022-03-04
Document type
Forschungsartikel
Author
Bauer, Maximilian
Hummel, Simon
Kegalj, Martin
Vogt, Damian M.
Organisational unit
DOI
URI
Publisher
ASME
Series or journal
Journal of Turbomachinery
ISSN
Periodical volume
144
Periodical issue
8
Article ID
081010
Part of the university bibliography
✅
Language
English
Abstract
The performance of axial diffusers installed downstream of heavy duty gas turbines is mainly affected by the turbine load. Thereby the outflow varies in Mach number, total pressure distribution, swirl and its tip leakage flow in particular. To investigate the performance of a diffuser at different load conditions, a generic diffuser geometry has been designed at ITSM which is representative for current heavy duty gas turbine diffusers. Results are presented for three different operating conditions, each with and without tip flow, respectively. Part-load (PL), design-load (DL) and over-load (OL) operating conditions are defined and varied at the diffuser inlet in terms of Mach number, total pressure distribution, and swirl. Each operating point is investigated experimentally and numerically and assessed based on its flow field as well as the pressure recovery. The diffuser performance shows a strong dependency on the inlet swirl and total pressure profile. A superimposed tip flow only influences the flow field significantly when the casing flow is weakened due to casing separation. In those cases, pressure recovery increases with additional tip flow. There is a reliable prediction of the computational fluid dynamics (CFD) simulations at design-load. At part-load, CFD overpredicts the strut separation, resulting in an underpredicted overall pressure recovery. At over-load, CFD underpredicts the separation extension in the annular diffuser but overpredicts the hub wake. This leads to a better flow control in CFD with the result of an overpredicted overall pressure recovery.
Version
Published version
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