Gas turbine tip shroud blade cavity

The invention relates to a cavity constituted by a casing of a gas turbine and a moving blade with a tip shroud, by which a cavity space is made to a necessary minimum size, a main flow gas is prevented from being entrained and a pressure loss is reduced. A tip shroud (6) is mounted on a tip end portion of a moving blade (4), a fin (7) is mounted thereon, a recess-like cavity (15) narrower than the conventional one is formed by portions (12a) and (12b) of a casing (12) and the fin (7), and further a projecting portion (16) is provided to an upstream end portion of the tip shroud (6). The projecting portion (16) is at a position (13a) at a time of a cold start and is at a position (13b) at a time of a hot start run, even if a thermal expansion occurs, thus the projecting portion (16) is not in contact with the recess portion, a main flow gas (1) is less entrained within the cavity (15), and a pressure loss is reduced because of no swirl, so that a performance of the gas turbine is enhanced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cavity surrounded by a turbine casing 
for a gas turbine and a moving blade with a tip shroud. 
2. Description of the Related Art 
FIG. 3 is a cross sectional view which schematically shows a conventional 
gas turbine. In the drawing, reference numeral 1 denotes a main flow gas 
flowing from a combustor (not shown), reference numeral 2 denotes a casing 
for a turbine, reference numeral 3 denotes a disc, reference numeral 4 
denotes a moving blade mounted to a periphery of the disc and arranged in 
several stages in an axial direction of the disc, and reference numeral 8 
denotes a stationary blade disposed in the axial direction in an alternate 
manner with the moving blade 4. 
In the gas turbine having the above structure, the main flow gas 1 of a 
high temperature supplied from the combustor (not shown) flows between the 
moving blade 4 and the stationary blade 8 in the axial direction. The 
moving blade 4 mounted to the disc 3 is rotated at a high speed so as to 
drive a rotor,thereby rotating a generator (not shown) connected to the 
rotor, so that power generation is performed. 
FIG. 2 is a cross sectional view which shows a cavity of a tip shroud blade 
in a conventional gas turbine. In the drawing, reference numerals 3 to 4 
denote the elements explained in FIG. 1 mentioned above, reference numeral 
5 denotes a cavity, reference numeral 6 denotes a tip shroud for the 
moving blade 4, and reference numeral 7 denotes a fin disposed on the tip 
shroud. As shown in the drawing, the cavity 5 is constituted by a portion 
surrounded by the turbine casing 2, the tip shroud 6 and the fin 7. The 
volume of this cavity 5 is set to be large enough so as to prevent the 
rotating portion and the stationary portion from being in contact with 
each other due to a displacement caused by difference in a thermal 
expansion. As a result, the main flow gas 1 of a high temperature is 
entrained into the cavity 5, as shown by an arrow 1a, and a very large 
swirl 1b is produced. 
As mentioned above, in the tip shroud blade cavity for the conventional gas 
turbine, since the cavity 5 is large, the main flow gas 1 of a high 
temperature is entrained and a very large swirl 1b is produced within the 
cavity 5, so that a large pressure loss is produced. 
The pressure loss due to the production of the swirl 1b causes the lowering 
of a performance of the gas turbine. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a tip shroud blade cavity 
which prevents a main flow gas of a high temperature from being entrained 
within a cavity and makes a swirl produced within the cavity smaller. The 
object is attained by improving the shape of the cavity formed by a casing 
of a gas turbine, a tip shroud and a fin, and a shape of an end portion of 
the tip shroud, thereby making the pressure loss caused thereby smaller so 
as to improve turbine performance. 
The invention provides the following in order to achieve the object 
mentioned above. 
A tip shroud blade cavity is surrounded by a casing and a moving blade with 
a tip shroud, in which a recess portion having substantially a U shape is 
formed on a casing side opposite to an upstream end portion of the tip 
shroud. A projecting portion projecting in a tongue-like manner from the 
upstream end portion of the tip shround is provided so as to neither be in 
contact with the recess portion at a time of a cold start nor to be in 
contact with the recess portion with thermal expansion at the time of a 
heat run. 
In the tip shroud blade cavity in accordance with the present invention, 
since the recess portion disposed on the casing side and the projecting 
portion of the tip shroud entering the inside thereof without making 
contact therewith are provided, the cavity can be made to a minimum size 
in comparison with the conventional cavity. The minimum size means a 
minimum size necessary for the purpose that the recess portion of the 
casing and the tip shroud are not in contact with each other in any and 
all operating conditions of the gas turbine. In this structure, the main 
flow gas flows into the tip shroud portion of the moving blade. However, 
since the space of the cavity is small and the projecting portion enters 
the inside of the cavity so as not to be in contact with the recess 
portion even in the case of elongation due to a thermal expansion, the 
main flow gas of a high temperature is prevented from being entrained 
within the cavity and the swirl produced within the cavity can be made 
small. Accordingly, a pressure loss caused thereby can be reduced and the 
performance of the gas turbine can be enhanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment in accordance with the present invention will be concretely 
described below with reference to the drawings. FIG. 1 is a cross 
sectional view which shows a tip shroud blade cavity in accordance with an 
embodiment of the invention. In FIG. 1, reference numeral 1 denotes a main 
flow gas of a high temperature and reference numeral 4 denotes a moving 
blade which has a tip shroud 6 on its tip end, and a fin 7 being provided 
on the tip shroud 6. 
Reference numeral 12 denotes a casing in which an improvement is added to 
the shape of the conventional casing 2, and as shown in the drawing, a 
recess portion is provided by a portion 12a and a portion 12b so as to 
form a cavity 15 in such a manner as to make the cavity a necessary 
minimum cavity. Further, an upstream end surface of the tip shroud is 
improved so that a tongue-like projecting portion 16 is provided. 
The tongue-like projecting portion 16 projects toward the cavity 15 within 
the recess portion, and the cavity 15 is designed so that at time of a 
cold start, the projecting portion 16 of the tip shroud 6 is received in 
the cavity 15 without contact therewith as shown by a chain a line 13a in 
the drawing. At the time of a heat run, the improved cavity 15 and the tip 
shroud 6 are not in contact with each other, even if displacement of the 
tip shround portion is caused by a difference of a thermal expansion, as 
shown by a chain line 13b in the drawing. 
In accordance with the embodiment mentioned above, the cavity 15 is made to 
a necessary minimum space by the portions 12a and 12b of the casing 12. 
Further, the projecting portion 16 is provided to the tip shroud 6 so that 
the main flow gas 1 can be prevented from being entrained, and the swirl 
produced within the cavity 15 can be made smaller, thereby reducing 
pressure loss. 
While the preferred form of the present invention has been described, 
variations thereto will occur to those skilled in the art within the scope 
of the present inventive concepts which are delineated by the following 
claim.