Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Irregular – flanged or channel forming blade surface
Reexamination Certificate
2002-01-29
2003-05-20
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Irregular, flanged or channel forming blade surface
C416S228000, C415S191000
Reexamination Certificate
active
06565324
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a turbine blade having a bracket arranged in the tip region of the blade and projecting beyond the blade profile.
BACKGROUND OF THE INVENTION
In particular in smaller turbomachines, the gap losses occurring in the tip region of the turbine blades, i.e. between the blade tip and the blade shroud, may assume considerable proportions and thus may lead to a distinct loss of efficiency. These gap losses are caused by the pressure difference between the pressure side and the suction side in the tip region of the blade, as a result of which there is an overflow of the working fluid. This overflow can be reduced by increasing the friction losses between the blade tip and the blade shroud, a factor which leads to a reduction in the gap losses and thus to an increase in the efficiency.
A known measure aimed at reducing the gap losses and increasing the reliability of the turbine blade is the arrangement of a rib or bracket (so-called minishroud or winglet) projecting laterally beyond the blade profile in the tip region of the blade (Ü. Okapuu, presentation “Aerodynamic design of first stage turbines for small aero engines”, held as part of the lecture series 1987-07 of the Karman Institute for Fluid Dynamics, on the topic “Small High Pressure Ratio Turbines”, Jun. 15-18, 1987, pages 1-4 and FIGS. 1-4). GB-A-2 153 447 and GB-A-2 050 530 also disclose blade bodies having brackets projecting onto the suction side and onto the pressure side. GB-A-2 050 530 also indicates a blade body having a bracket which is arranged on the suction side and above which the blade body rises on all sides.
However, all these solutions result in an increase in both the leading and trailing wedge angles of the blade and thus in corresponding efficiency losses.
SUMMARY OF THE INVENTION
The object of the invention, in attempting to avoid all these disadvantages, is to achieve a further improvement in efficiency for a turbine blade which is provided with a bracket arranged in the tip region of the blade and projecting beyond the blade profile.
According to the invention, this is achieved in that, the bracket is formed on the pressure side of the blade and only in a section of a defined surface region of this pressure side. In this case, this defined surface region constitutes that region of the pressure side which is enclosed by an imaginary chord bearing against the pressure side of the blade body both in the region of the leading edge and in the region of the trailing edge.
The pressure-side section having the bracket is formed between and at a distance from two points lying on the pressure side of the blade body, the first point being arranged in the region of the leading edge and the second point being arranged in the region of the trailing edge, and the imaginary chord bearing against both points. It has proved to be especially expedient to form a distance a
1
, a
2
between the first point and the bracket and between the second point and the bracket, and this distance a
1
, a
2
in each case corresponds approximately to a blade thickness d
1
, d
2
in the corresponding region of the blade body.
Since the bracket therefore extends only over part of the pressure side, both wedge angles of the blade body, i.e. the leading angle and the trailing angle, can be kept small. The wedge angles can be reduced further through selection of the defined distances a
1
, a
2
. This results in an acute blade geometry, which ensures that high Mach numbers in the leading-edge region and wake zones in the trailing-edge region of the blade body are avoided. Ultimately, a further improvement in efficiency is achieved while a reduction in the gap losses continues to be ensured.
Starting from the leading edge, the bracket has a maximum height h
max
above the pressure side in a region of 30 to 40% of the chord length l of the blade body. In this case, the height of the bracket continuously decreases both in the direction of the leading edge and in the direction of the trailing edge of the blade body. The maximum height h
max
of the bracket corresponds approximately to a blade thickness d
3
as formed in a region of the blade body which is adjacent to the bracket and remote from the blade tip. Furthermore, it is advantageous if the bracket is of wavelike design.
It has been found that, in particular with such a design of the bracket, optimum flow guidance can be achieved.
REFERENCES:
patent: 3706512 (1972-12-01), Strelshik
patent: 4108573 (1978-08-01), Wagner
patent: 5137426 (1992-08-01), Rhoda
patent: 5151014 (1992-09-01), Greenwald et al.
patent: 5282721 (1994-02-01), Kildea
patent: 6318961 (2001-11-01), Phillipsen
patent: 216224 (1957-07-01), None
patent: 560589 (1932-10-01), None
patent: 2405050 (1975-08-01), None
patent: 2050530 (1981-01-01), None
patent: 2153447 (1985-08-01), None
“Aerodynamic Design of First Stage Turbines for Small Aero Engines”, U. OKAPUU, Pratt & Whitney, Canada, von Karman Institute for Fluid Dynamics Lecture Series Jul. 1987, Small High Pressure Ratio Turbines Jun. 15-18, 1987.
Mamaev Boris
Phillipsen Bent
Ryabov Evgeny
ABB Turbo Systems AG
Burns Doane Swecker & Mathis L.L.P.
Verdier Christopher
LandOfFree
Turbine blade with bracket in tip region does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Turbine blade with bracket in tip region, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Turbine blade with bracket in tip region will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3024373