N112-121 TITLE: Experimental and Analytical Techniques for the Validation of Complex Gas Turbine Engine Rotor Systems

TECHNOLOGY AREAS: Air Platform

ACQUISITION PROGRAM: F-35, Joint Strike Fighter

OBJECTIVE: Develop a low-cost, high cycle fatigue experimental and analytical capability to evaluate complex gas turbine engine rotor and airfoil systems for the purpose of component and design tool validation.

DESCRIPTION: As advanced aircraft engines continue the trend to improved thrust-to-weight, propulsion system development and validation engineers continue to wrestle with complex structural dynamics and turbine engine high cycle fatigue. Whereas much activity has been devoted to the development of advanced design tools and component technologies, advanced low-cost rotor spin test and data analysis techniques beyond the current state-of-the-art are now needed to validate both these new tools and technologies.

High cycle fatigue (HCF) is still a major factor that negatively impacts safety, operability, and readiness, while at the same time substantially increasing maintenance costs. The HCF failure of compression and turbine system components is still a major contributor to the HCF events experienced in both development and fielded weapon systems. Although much has been done over the last several years to mitigate HCF though the development, validation and transition of new physics-based HCF tools and testing protocols, escapes to the fleet or changes in operational use can result in unexpected HCF fractures of fan, compressor and turbine airfoils.

Blade to blade variations in turbine engine rotors leads to the well documented phenomenon of mistuning. Mistuning can cause an amplification of resonant response by up to 400 percent of one or more airfoils in any given stage. Mistuning has been identified as a primary factor in HCF failures, and there has been significant progress in using vibration data from bench tests to identify the properties of mistuned Integrally Bladed Rotors (IBR). This process requires that high quality frequency response data be measured for one or more points on each blade. The resulting information is then used to develop a fundamental understanding of the IBR�s vibratory response that can be used to mitigate the risk of HCF. This topic is focused on developing a comparable experimental and analytical capability for measuring the complex response of bladed disks under rotating conditions and using the information to develop a fundamental understanding of the bladed disk�s vibratory response.

A key challenge for this proposed effort is to develop a system that can both readily excite the rotor system in a manner that simulates the engine environment and measure the relatively small airfoil dynamic responses while rotating at engine-like conditions. While traditional approaches to measure full-wheel responses have employed non-contacting stress measurement systems (NSMS) that rely on measures of blade time of arrival to infer deflection and strain, these systems have significant limitations. Improved experimental capabilities are needed to reduce HCF risk in engine development programs and fielded systems, particularly for modes in the frequency range from 5 kHz to 15 kHz, although modes of both lower and higher frequency are of interest. Proposed solutions must recognize the complex system structural dynamics of compressor integrally bladed rotors and damped turbine blades. In addition, the system must provide a means for measuring vibratory responses of all airfoils within a stage at multiple airfoil locations. Although a full airfoil measurement is preferred to enable HCF mode identification, the measurement locations should be readily changed to enhance mode identification techniques. Demonstration of the capability will be required at engine relevant forcing levels given engine relevant Q�s (approximately 100 to 500), temperatures (up to 1200 degrees), and rotor speeds (up to 25,000 rpm).

Proposals should also address how the measurement system may be transitioned to development rigs or engines as part of an advanced instrumentation package for development endings and/or as part of an integrated health management system for fielded systems, recognizing airfoil line of sight through a case structure may be limited to the tip section only. To that end, upfront coordination with turbine engine original equipment manufacturers (OEMs) to identify potential rig/engine demonstration opportunities is recommended but not required. Proposed solutions should consist of advanced instrumentation, airfoil forcing systems, rotor speed control systems, and a data analysis system that uses the information to develop a fundamental understanding of the bladed disk�s vibratory response.

PHASE I: Design, develop and demonstrate technical feasibility of a system to meet the requirements listed above.

PHASE II: Validate through testing of prototype systems, including the system excitation and airfoil measurement techniques, and new data analysis and analytical capabilities at engine relevant conditions.

PHASE III: Demonstrate a fully functional analytical system on a relevant rig/engine platform if available or if the opportunity exists. Transition validated system to appropriate platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Non-contacting measurement techniques, such as laser vibrometry or holography, and rapid test article turnaround would improve the economics and viability of experimental component validation. It is expected that this experimental capability would have broad applicability to military and civilian turbine engine applications.

REFERENCES:
1. Nelson, F.C. (2007). Rotor Dynamics without Equations. International Journal of COMADEM, 10(3) July 2007, pp. 2 - 10

2. Feiner, D. M. & Griffin, J. H.( 2005). Exploring the Use of FMM ID for Engine Health Monitoring. Proceedings of NATO AVT-121 Symposium on Evaluation, Control and Prevention of High Cycle Fatigue in Gas Turbine Engines, Granada, Spain.

KEYWORDS: blisk; mistuning; integrally bladed rotors; Joint Strike Fighter (JSF) propulsion; gas turbine engine; high cycle fatigue

** TOPIC AUTHOR (TPOC) **

DoD Notice:   Between April 26 and May 25, 2011, you may talk directly with the Topic Authors to ask technical questions about the topics. Their contact information is listed above. For reasons of competitive fairness, direct communication between proposers and topic authors is not allowed starting May 26, 2011, when DoD begins accepting proposals for this solicitation.

However, proposers may still submit written questions about solicitation topics through the DoD's SBIR/STTR Interactive Topic Information System (SITIS), in which the questioner and respondent remain anonymous and all questions and answers are posted electronically for general viewing until the solicitation closes. All proposers are advised to monitor SITIS (11.2 Q&A) during the solicitation period for questions and answers, and other significant information, relevant to the SBIR 11.2 topic under which they are proposing.

If you have general questions about DoD SBIR program, please contact the DoD SBIR Help Desk at (866) 724-7457 or email weblink.