DESIGN AND FABRICATION OF OPTIMISED AEROSTATIC DRY GAS SEALS USING ADVANCED NUMERICAL MODELS AND NEXT GENERATION PRODUCTION TECHNOLOGY

Sažetak

To avoid pollution of the environment, it is
necessary to separate the oil of the oil- lubricated
bearings of a turbomachine from the atmosphere.
For this purpose, gas driven sealing systems
which operate with a non- toxic gas are used.
These sealing systems must be robust and
reliable but also should have a low consumption
of the operating gas to meet economic criteria.
Furthermore, the seals should be tight without
any operating medium when the turbomachine
is at a standstill “blocked situation”. All these
requirements are combined in the so- called
aerostatic seals which are used in the industry
already. The robust aerostatic seals are
manufactured conventionally by drilling a defined
number of holes with fixed diameter in the seal
sliding ring to ensure the permeability. The
characteristic of the seals can be influenced in a
certain spectrum by varying the number and the
diameter of the holes. This effect has already been
demonstrated by Gerke (1991), Schulz (1999)
or Dormann (2002), among others. Actually,
the possibilities of conventional manufacturing
processes restrict the use of the complete potential
of such seal types. An approach to increase the
performance of this seals is the application of
Additive Manufacturing (AM) processes directly
during the design. It is widely accepted, that
AM processes offer a great potential in terms
of geometrical freedom and thus for optimised
functionality. One of the main advantages of these
AM processes is that exposure strategies which
contain the typic process parameters can be set
for each part separately. Furthermore, the technic
offers a great potential for production of filigree
structures.
With these structures it is possible to manufacture
a seal with the necessary permeability as well as
dense material which serves as a mounting device.
As shown in a previous publication from Schoar
et al. (2019), a numerical model which is
required to support the design process of seals
with undefined as well as defined distributed
permeabilities has been derived and validated
using a test bench. In this work, the AM process
of laser-based powder bed fusion of metals is
used to generate coaxial gas seals with defined
permeability distributions according to the
calculations of the numerical model. It is shown
that the fabrication of AM dry gas seals with the
required permeability distributions is possible. A
comprehension of the results from the numerical
model and the experiment proves, that the
validated numerical model can be used for the
design of seals with different permeabilities and
thus for the aerostatic dry gas seals (ADGS).