Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-12-16
2002-05-21
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S104000, C700S117000, C703S001000
Reexamination Certificate
active
06393331
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to computer-based methods of designing products, and more particularly to a computer-based method of designing an outer air seal for the turbine blades of a gas turbine engine.
BACKGROUND ART
An aircraft gas turbine engine generally comprises a compression section, a combustion section and a turbine section. Each section operates on the working fluid in a well-known manner to generate thrust. The compressor and turbine both comprise a plurality of airfoil blades attached to rotating disks to form rotor assemblies. The outermost radial surfaces or tips of the blades in each turbine and compressor rotor are designed to be in close proximity to a corresponding outer air seal. The air seal is part of a shroud assembly attached to the inside of the engine casing and disposed in a radial manner outward from the corresponding turbine or compressor rotor.
The clearance between the blade tips and the outer air seal is sized to reduce the performance penalty that results from air that may leak from the pressure side to the suction side of the blade. As the blade tip clearance increases, an increasing amount of air can leak over the blade tips, causing the compressor and turbine to lose efficiency. Also, the compressor can approach a stall condition, which may be catastrophic for the engine. On the other hand, it is undesirable for the blade tips be in physical contact with the outer air seal, since this could damage the blades and seal. In an effort to reduce these problems, there exist numerous embodiments of active and passive tip clearance controls.
As is well known, a relatively small yet adequate and constant amount of tip clearance must be maintained at every engine operating condition. The tip clearance can vary due to the thermal expansion of the rotors and engine casing as well as the rotational loading applied to the blades and casing. Because of the relatively greater mass of the compressor and turbine rotors compared to the engine casing, the casing experiences larger physical thermal expansion and contraction relative to the rotors, especially during transient engine operating conditions. Maintaining tip clearance is more of a problem with turbine blades than with compressor blades because of the higher turbine operating temperatures. Also, maintaining tip clearance is more of a problem for military engines than with commercial engines. This is due to the more varied and extreme engine transient operating conditions encountered by military aircraft engines.
The outer air seal typically comprises a circular ring made of a plurality of individual segments connected together. Each segment contains a number of primary physical structural features, including means for sealing between adjacent segments (“inter-segment sealing”), means for attaching each segment to the engine casing, and means for cooling each segment using, e.g., air bled from the compressor. The inter-segment sealing means typically comprises a ship lap joint that mates with a similar joint on an adjacent segment. The means for attaching each segment to the engine casing typically comprises one or more L-shaped hooks that mate with corresponding grooves in the shroud assembly. The means for cooling each segment typically comprises one or more cooling channels formed within the segment body. Outer air seals typically include other well-known structural features. Examples of outer air seals are given in U.S. Pat. Nos. 5,609,469, 5,374,161 and 5,373,973. All of these patents are assigned to the assignee of the present invention and are incorporated herein by reference.
It is known to design various products using a computer-aided design (“CAD”) system, a computer-aided manufacturing (“CAM”) system, and/or a computer-aided engineering (“CAE”) system. For sake of convenience, each of these similar types of systems is referred to hereinafter as a CAD system. A CAD system is a computer-based product design system implemented in software executing on a workstation. A CAD system allows the user to develop a product design or definition through development of a corresponding product model. The model is then typically used throughout the product development and manufacturing process. An example is the popular Unigraphics system commercially available from Unigraphics Solutions, Inc. (hereinafter “Unigraphics”).
In addition to CAD systems, there is another type of computer-based product design system which is known as a “Knowledge-Based Engineering” (“KBE”) system. A KBE system is a software tool that enables an organization to develop product model software, typically object-oriented, that can automate engineering definitions of products. The KBE system product model requires a set of engineering rules related to design and manufacturing, a thorough description of all relevant possible product configurations, and a product definition consisting of geometric and non-geometric parameters which unambiguously define a product. An example is the popular ICAD system commercially available from Knowledge Technologies, Inc. KBE systems are a complement to, rather than a replacement for, CAD systems.
An ICAD-developed program is object-oriented in the sense that the overall product model is decomposed into its constituent components or features whose parameters are individually defined. The ICAD-developed programs harness the knowledge base of an organization's resident experts in the form of design and manufacturing rules and best practices relating to the product to be designed. An ICAD product model software program facilitates rapid automated engineering product design, thereby allowing high quality products to get to market quicker.
The ICAD system allows the software engineer to develop product model software programs that create parametric, three-dimensional, geometric models of products to be manufactured. The software engineer utilizes a proprietary ICAD object-oriented programming language, which is based on the industry standard LISP language, to develop a product model software program that designs and manipulates desired geometric features of the product model. The product model software program enables the capturing of the engineering expertise of each product development discipline throughout the entire product design process. Included are not only the product geometry but also the product non-geometry, which includes product configuration, development processes, standard engineering methods and manufacturing rules. The resulting model configuration and parameter data, which typically satisfy the model design requirements, comprise the output of the product model software program in ICAD from which the actual product may be manufactured. This output comprises a file containing data (e.g., dimensions) defining the various parameters and configuration features associated with each component or element of the product.
Also, the product model software program typically performs a “what if” analysis on the model by allowing the user to change model configuration and/or parameter values and then assess the resulting product design. Other analyses (e.g., a fatigue life analysis) may be run to assess various model features with regard to such functional characteristics as performance, durability and manufacturability. These characteristics generally relate to the manufacturing and operation of a product designed by the product model software program. They are typically defined in terms of boundaries or limits on the various physical parameters of each product feature. The limits have been developed over time based on knowledge accumulated through past design, manufacturing, performance, and durability experience. Essentially, these parameters comprise rules against which the proposed product model design is measured. The rules generally comprise numbers that define physical design limits or constraints for each physical product parameter. Use of these historically developed parameters, analyses, and design procedures in this way is typically referred to as product “rule-
Chetta Gregory E.
Ellis Charles A.
Hayes Joey C.
Kane Daniel E.
Neff William D.
Grant William
Rodriguez Paul
United Technologies Corporation
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