CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
highly advanced aero- and thermodynamic design principles
applicable to related turbomachinery such as gas turbines and aeroengines.
Unlike these applications, however, turbochargers are not
always operated with “clean” media. Under harsh conditions
turbochargers can ingest oil and dust laden air on the compressor
side as well as severely contaminated exhaust gases on the turbine
side. Since peak aerodynamic performance is required and the
geometries of the compressor and turbine stages are designed with
this aim, it is evident that any contamination in the flow duct or on
blade profiles will influence aerodynamics and may lead to
performance deterioration. Possible consequences for the engine of
a drop in turbocharger performance are higher exhaust gas and
valve-seat temperatures, while for the turbocharger there is the
possibility of increased rotor speed. Each of these consequences can
even lead to an undesirable reduction in engine load rating.
Additionally, fouling on the turbine side of the turbocharger can
cause the blade wear rate exceed acceptable limits. As a result
mechanical cleaning, shorter exchange intervals or premature
reconditioning may be necessary, with all their economic impacts.
Several cleaning procedures are available to counteract the build-up
of fouling on turbocharger components and thus keep performance
more or less stable. However, under certain boundary conditions,
and especially on some four-stroke HFO burning engines, these
measures often have only limited effect. As a result, an uncontrolled
downward drift in performance is possible over a turbocharger’s
operating period. Besides the drop in performance in such
circumstances, there is also the disadvantage that today’s cleaning
methods are not always well suited to the avoidance of turbine
component wear. The present paper outlines available cleaning
methods and their integration into the turbocharger design and
development process in order to narrow the gap between the
performance potential of turbocharger technology and the
performance effectively available over standard service intervals.
Current methods are described and their efficiency documented,
based on field-experience. Further, the paper provides an insight
into how wear due to contamination can be significantly reduced
and how this can have a substantial economic impact. Finally, parts
of the development process are described, showing how procedures
can be derived by adopting a systematic approach and how they
lead to performance stability in turbochargers operating on HFO.
3D-fluid-structure interaction for an axial
turbocharger turbine blade to improve the
vibrational safeguard process
A. Bornhorn, S. Mayr, T. Winter, MAN Diesel & Turbo
SE, Germany
The vibrational safeguarding of a turbine rotor blade design is still a
great challenge for today’s high performance turbochargers, in
particular thereby affected, that the turbocharger has to operate in a
very wide rotor speed range without any critical vibrational
excitation. According to the state of the art the vibrational
safeguarding is an integrated process of numerical simulation and
experimental verification. Finite Element calculations establish the
basis for experimental determination of dynamic blade load by
strain gauge measurement or non intrusive measurement techniques
e.g. tip timing. The measured blade loads again are a necessary input
for a subsequent numerical calculation of the blades fatigue safety.
As this approach is dependent on the availability of prototype
hardware results can be obtained in a very late stage of the
development process. In order to get decisive references about the
excitability of a turbine rotor blade during the development process,
a plurality of existing vibrational measurements in their critical
modes were recomputed with an unsteady CFD code. The results of
the CFD analysis are pointing to aerodynamic effects, which are
causative for an excitation. Beside the evaluation and visualisation
of the aerodynamic unsteady effects, the time depending pressure
distribution on the rotor blade surfaces is the most important result
of the CFD computation, as this distribution is impressed as a time
depending load on a FE model. Considering, that the damping
coefficient is not finally determined, the FE analysis shows
tendencies, which are comparable with the measurements. Therefore
it will be possible in the future to obtain valuable indications about
the vibration behavior of a turbine rotor blade at a very early state of
the development process.
ST27: A new generation of radial turbine
turbochargers for highest pressure ratios
R. Drozdowski, K. Buchmann, Kompressorenbau
Bannewitz GmbH, Germany
The biggest challenge to future developments of medium-size and
large diesel engines in marine applications, especially engines using
heavy fuel, will be to comply with the tougher environmental
regulations of IMO Tier II. A supercharging system offers optimum
support for these developments by providing a higher boost pressure
and better efficiencies. Since its introduction, KBB’s HPR turbocharger
range has been well accepted on the market. KBB will continue to
face up to this challenge with the new ST27 range of radial turbine
type turbochargers. Based on the successful HPR range, the new
ST27 turbochargers reach pressure ratios of up to 5.5 with a high
overall efficiency. In order to meet the new demands of engine
applications, the ST27 range has been extended by two additional
sizes over the HPR range and will be used for gas, diesel and heavy
fuel oil engines with a power output from 300 to 4800kW. However,
the outline dimensions for the ST3–ST6 are equal to those of the
HPR3000 – HPR6000. The ST2 is planned for smaller and the ST7
for higher volume flow rates. The ST27 has already been launched
onto the market. The full range will be available by the end of 2010.
This paper describes the development of the main ST27 turbocharger
features such as bearing and compressor design including
temperature measurements in the rotating impeller in preparation
for adopting a new air-cooling system. An extensive qualification
test program was successfully performed on both the turbocharger
test stand and engine test benches. The paper focuses in detail on
the development process for the radial turbine wheel. High
rotational speeds and high temperatures, but especially blade
vibration, make the turbine wheel one of the most critical parts in
the turbocharger. In contrast, less time is available for developments.
Efficient and fast design and evaluation tools help reduce prototyping
and experimental work to a minimum. Knowledge of the occurring
peak vibratory stress is essential during the design process. In this
regard, a method is presented to estimate the vibratory stress of
radial turbine blades by a simple excitation model. The effects of
mistuning induced by geometric differences in the blades result in a
further uncertainty during the design process.
The modeling and analysis of the effects of geometric-based blade
mistuning and thus the relevant effect on peak vibratory stress are
described in this paper along with the corresponding results of
blade vibration measurements.
Development of Niigata-NGT3B gas turbine
for large standby generator set
H. Kojima, S. Tarui, T. Kuribayashi, K. Takahashi,
M. Koyama, Niigata Power Systems Co., Ltd., Japan
Niigata Power Systems Co., has developed the new gas turbine
NGT3B which is installed in a large standby generator set. This gas
turbine engine meets a large capacity of important facilities in
62 Ship & Offshore | 2010 | No. 3