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ABSTRACT
Computational fluid dynamic (CFD) analysis of the
region the secondary flow path of high pressure steam
turbine was conducted. Region included two adjacent to
disc cavities and section of main flow path. The cavities
were channeled by balance holes located in the disk.
Two geometrical models were considered: single disk
cavity and both cavities with balance holes. 2D axisymmetric
and 3D analyses were conducted for the first
model, however only 3D study was performed for the
second one.
Analysis of the single disk cavity has revealed
appearance of vortexes in circumferential direction even
in case when all boundary conditions and geometry
features were close to the axi-symmetric case. The trend
of the average pressure distributions along radius was
found for 2D and 3D models.
The transient analysis of the two cavity model revealed
vortexes movement in circumferential direction with
higher than disk rotation velocity. It induces periodic
conditions at the inlet and outlet of balance hole and
periodic steam mass flow rate through the holes. The
flow pattern in the two cavities with balance holes is so
complicated that common 1D net flow representation
should be considered as significant simplification.
INTRODUCTION
Steam/gas mass flow distributions in the secondary
turbine flow path is usually treated with method
replacing real hydraulic system with equivalent graph.
Branches of such graph are 1D models of flow in
elements like tubes, annulus, valves and so on. Existing
1D models are essentially correlation dependencies of
hydraulic resistance upon various parameters.
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Mass flow rate and pressure distributions in the whole
hydraulic system of the secondary flow path are calculated
using mass conservation law at each graph node and
pressure drops on each branch.
The most of the correlations in simple cases are reliable for
the wide range of operation and geometry parameters. The
complicated flow such as flow in the disk-stator axial seals
couldn’t be treated with the same accuracy as simple ones,
and unfortunately its influence on the whole secondary flow
path is significant. In reality flow in the axial seal is
substantially 3D, especially when adjacent to seal cavities
are channeled with balance holes. In spite of that, often
such flows are treated with simple methods when whole
turbine secondary path is analyzed for the lack of more
accurate methods.
Turbine design requires development of reliable and rapid
methods of secondary flow path prediction. Such methods
must be based on deep understanding of processes in axial
disk-stator seals and should extract accurate 1D models
applicable for turbine designer needs.
An alternative way is axi-symmetric CFD modeling of the
turbine secondary flow path with several additional
assumptions related to labyrinth seals, balance holes and
others elements that induce 3D effect [1]. This approach
promises more accurate results but several assumptions
used in reduction of the problem from 3D to 2D axisymmetric
formulation need to be validated.
Flow in cavities between rotating disk and fixed stator is a
subject of many investigations [2, 3, 4, 6, 7, 8] and remains
a point of considerable interest due to a variety of disk
cavity and rim seal geometries that are explored in current
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