Title: Investigation of the Flow Field and the Pressure Recovery in a Gas Turbine Exhaust Diffuser at Design, Part-Load and Over-Load Condition
Authors: Bauer, Maximilian
Hummel, Simon
Schatz, Markus 
Kegalj, Martin
Vogt, Damian
Affiliation: Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM), University of Stuttgart
Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM), University of Stuttgart
Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg, Laboratory of Fluid Machinery (LSM)
Siemens AG
Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM), University of Stuttgart
Language: en
Issue Date: 2020
Publisher: American Society of Mechanical Engineers
Document Type: Conference Proceedings
Source: Proc. ASME Turbo Expo 2020, GT2020-14310
Publisher Place: New York
Conference: ASME Turbo Expo: Turbine Technical Conference and Exposition 2020 
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,
design-load and over-load 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 CFD simulations at designload.
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.
Organization Units (connected with the publication): Strömungsmaschinen in der Energietechnik 
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