Air-cooled cylinder with piston ring labyrinth

A turbine cylinder is in contact at its outer surface with split rings which are held in place in annular slots in a cylindrically extending ring holder. The rings, while remaining in contact with the outer surface of the cylinder, are allowed to expand and contract within their respective slots. Notches are constructed at the inner circumference of the rings to form a labyrinth type cooling passage in conjunction with the outer surface of the turbine cylinder.

BACKGROUND OF THE INVENTION 
One of the most difficult areas to design in a gas turbine engine is the 
interface between the turbine blade and its surrounding shroud. It is 
required, for maximum efficiency, that the clearance between the blade tip 
and the shroud be as close as possible. This is a distinct problem in that 
these cooperating parts of the engine have different thermal and 
centrifugal expansion characteristics and if tip clearance is not 
maintained at least at a minimum level, rubbing could occur with a 
potentially destructive result. On the other hand, if a large gap is 
present a significant loss of power may occur. Cooling is generally 
necessary to further minimize the differential transient growth rates, for 
example, between radial growth of the shroud and thermal and centrifugal 
growth of the blades. 
It is, therefore, necessary to design a shroud assembly which can 
accommodate the differential thermal growth, but which can maintain a tip 
clearance at a relatively constant and minimum level. 
It is, therefore, the purpose of this invention to provide a structure 
which provides cooling to the turbine shroud and can react dynamically as 
differential thermal expansion occurs to maintain a minimum tip clearance. 
SUMMARY OF THE INVENTION 
An air cooled turbine cylinder assembly is constructed having a floating 
arrangement which allows unrestrained movement between the parts of the 
assembly. This assembly consists of a cylindrical ring holder constructed 
with a plurality of annular slots at its radially innermost surface. These 
slots accomodate a series of axially spaced split rings which extend 
radially inward to engage the outer surface of the turbine shroud. The 
rings are allowed to slide radially within the slots when thermal growth 
occurs, which provide the floating aspect of the design. An optional 
spring device may be employed to maintain the ring in contact with the 
outer surface of the shroud. The inner circumference of each ring is 
notched to allow the entrance of cooling air into the annular passage 
formed by the axial spacing of the slots. By staggering the position of 
each ring, a labyrinth type cooling passage is formed in conjunction with 
the outer surface of the turbine shroud.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The tip clearance area of the turbine section of a gas turbine engine is 
shown in FIG. 1 as it relates to this invention. The major elements 
consist of turbine blade 1, inner cylindrical shroud 2, and outer 
cylindrical shroud 3. The blade 1 is mounted for rotation on the turbine 
shaft (not shown), while shrouds 2 and 3 are fixed to appropriate engine 
structure. In modular type engines it is recommended that the shrouds 2 
and 3 be fixed to different modules. For example, the forward portion of 
outer shroud 3 is fixed to the gas producer module and the rear portion of 
inner shroud 2 is fixed to the power turbine module. This can provide an 
axial freedom of movement between the shrouds. 
Outer shroud 3 includes a cylindrical ring holder 4 having several annular 
slots 5 axially spaced on its inner surface. 
The ring holder 4 and shroud 2 are separated by split rings 6 which are 
mounted for radial sliding motion in slots 5. The rings 6 extend radially 
inward to engage the outer surface 7 of shroud 2 and contact the shroud 2 
in a manner which accommodates the dynamics of this assembly during 
thermal growth. The axial spacing of the slots creates a channel 14 
between each ring in conjunction with surface 7. 
As best shown in FIG. 3, ring 6 is split at 8 to allow expansion and 
contraction with the thermal loading which occurs during engine operation. 
An optional spring device 17 may be installed in the residual space 16 
surrounding rings 6 in slots 5 to bias the ring 6 radially inward. The 
purpose of the spring device 17 is to assure contact of the ring 6 with 
surface 7 of shroud 2. The rings 6 are also constructed with notches 9 on 
the inner surface 10 which forms the interface with surface 7 of shroud 2. 
The notches communicate with channels 14 between rings 6 to form a 
labyrinth chamber 13 for cooling air 15 as shown in FIG. 2. 
Cooling air 15 may be compressor bleed air or ambient air forced forward 
through the labyrinth to cool surface 7. As best seen in FIG. 1, by 
exhausting the air forward of shroud 2, film cooling of its inner surface 
can be achieved. 
Each of the rings 6 may be constructed identically and include an index tab 
11 extending from the outer circumference of ring 6. A positioning hole 12 
is constructed in the ring holder adjacent slot 5 to receive tab 11. The 
positioning holes 12 are circumferentially spaced about the annular slots 
5 so that the rings 6 are angularly displaced from each other thereby 
offsetting the relative position of the notches to form the labyrinth 
cooling chamber 13 as shown in FIG. 2. 
In this manner a very simple air cooled turbine shroud assembly is 
constructed which provides the flexibility needed to accommodate the 
movement caused by the thermal characteristics of the system. Cooling is 
accomplished with a minimum of air flow because of the high flow per unit 
area created in the circumferential passages between the rings.