Engine weight is a key design parameter for any new aircraft engine. It affects aircraft range and is a key element in fuel burn. Weight is also considered to be an indicator of engine cost. Reliable engine-weight estimation at the conceptual design stage is critical to the development of new aircraft engines. It helps to identify the best engine concept from among several candidates.

Equally important, aircraft engines must meet safety demands. Fatigue loading of turbine components associated with continuous aircraft takeoff/cruise/landing cycles is a principal source of degradation in turbomachinery. A disk burst is potentially the most catastrophic failure possible in an engine, and thus disks are designed with overspeed capability and low-cycle-fatigue life as primary objectives. The requirement for higher turbine stage work without additional stages has resulted in increased turbine blade tip speeds and higher turbine inlet temperatures in advanced commercial aircraft engines. This trend has resulted in significant increases in turbine stage disk rim loading and a more severe thermal environment, thereby making it more difficult to design turbine disks for a specific life requirement meeting current goals. The current trend indicates that both turbine blade tip speeds and turbine inlet temperatures will continue to increase in advanced commercial engines as higher turbine work levels are achieved. Advanced turbine disk concepts are required to ensure long life disks in commercial engines, without resulting in severe weight, performance, or cost penalties.

At the NASA Glenn Research Center, the Weight Analysis of Turbine Engines (WATE) computer code, originally developed by Boeing Aircraft, is being used to estimate the engine weight of various conceptual engine designs. The code was originally developed for NASA in 1979, but since then substantial improvements were made to the code to improve the weight calculations for most of the engine components. Recently, a series of efforts were performed at Glenn to enhance the capability of the WATE code. The major enhancements include the incorporation of improved weight-calculation routines for the compressor and turbine disks using the finite-difference technique. In addition, the stress distribution for various disk geometries was incorporated for a life-prediction module to calculate disk life. A material database, consisting of the material data of most of the commonly used aerospace materials was also incorporated into WATE. Collectively, these enhancements provide a more realistic and systematic way to calculate engine weight. The current effort paves the way for an integrated engine design tool, which would easily allow engine developers to perform design tradeoffs between engine weight, durability, and cost. To demonstrate the new capabilities, Glenn researchers used the improved WATE code to perform an engine weight/life tradeoff assessment on a 90,000-lb-thrust-class commercial turbofan engine.

Bibliography:
Tong, Michael T.; Ghosn, Louis J.; and Halliwell, Ian; A Computer Code for Gas Turbine Engine Weight and Disk Life Estimation. ASME Paper GT-2002-30500, 2002.

Glenn contact: Michael T. Tong, 216-433-6739, Michael.T.Tong@nasa.gov

Author:
Michael.T. Tong

Headquarters program office:
OAT

Programs/Projects:
Propulsion and Power, Propulsion Systems Research and Technology, UEET