N13A-T002 TITLE: Modeling of Integrally Bladed Rotor (IBR) Blends

TECHNOLOGY AREAS: Air Platform

ACQUISITION PROGRAM: JSF-Prop

OBJECTIVE: Develop and demonstrate an analytical means to predict the effect of large airfoil blends on integrally bladed rotors.

DESCRIPTION: Integrally bladed rotors (IBRs) are prevalent in the fan and compressor sections of the current and emerging fleet of Department of Defense (DoD) gas turbine engines such as the F119 and F135. While IBRs have inherent weight and performance benefits, they can require more man hours to repair and therefore become more costly than rotors with removable blades. When there is damage to a rotor with removable blades, the blades can simply be replaced for damage exceeding allowable blend limits. IBRs are more difficult to repair because the entire rotor must be removed from wing, blended, tuned and balanced through independent means. The ability to cost effectively and quickly repair IBRs is required to reduce acquisition life-cycle costs of the propulsion system.

Currently, foreign object damage (FOD) location and size can be measured using a boroscope through inspection ports, which mitigates the need to remove the IBR from wing. Blending, currently the only method to repair IBRs, uses specialized tooling to remove adjacent material from the damaged location to alleviate critical stress. However, blending changes the following: modal characteristics of the blade, tuning of the IBR and (if not balanced) may induce vibration to the IBR. While blends alter IBR mechanics, there can also be aerodynamic effects that adversely affect engine performance (e.g. compressor efficiency) and operability (e.g. stall). Tools currently exist to calculate each of these aspects individually, but no method exists for quickly and easily analyzing the effect of each blend and all blends as a whole. There is a need for a method to predict a blend�s effect on these mechanical and aerodynamic characteristics in a single comprehensive tool.

The development of a tool capable of conducting modal analysis of 3D airfoil shapes, with and without a variety of blend shapes, would make it possible to analyze the repair potential to highly damaged IBRs. The tool must be able to model different "types" of blends with varying aspect ratios. Specifically, the need is to quickly and iteratively minimize stress concentration ratios at the damaged location as well as percent resonant frequency shifts for different sized blends and blend shapes across multiple mode shapes. The effect these blends have on rotor balance, tuning/mistuning, performance and operability also needs to be modeled. This modeling would allow the analysis necessary to determine the optimum blending to repair the IBR, without removing it from wing. It will also provide the ability to predict the effect of multiple, larger, and more aggressive IBR airfoil blends on modal characteristics, engine performance and operability.

The new tool should leverage commercially available computer aided design and finite element analytical models and processes where available. The development of automated design procedures to build the required analytical models and execute the required process is necessary. The product should be an analytical tool to model the effect of blends and not a method to perform large blends on an IBR.

PHASE I: Develop a candidate means to assess the impact on airfoil structural dynamics from large airfoil blends. Demonstrate proof of concept of automated analytical modeling of as-measured or as-expected airfoil blends.

PHASE II: Develop and validate a prototype integrated design and analysis tool for assessing large damage and blends for compressor integrally bladed rotors on gas turbine engines.

PHASE III: Fully develop a tool to assess large blends on IBR airfoils for modal characteristics, performance and operability assessments � including the application of graphical user interfaces where appropriate. Tools and processes of these efforts can (and are expected to) interface with OEM (Original Equipment Manufacturer) tools and processes as well as COTS tool providers such as ANSYS or Siemens.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Emerging commercial fleets have also committed to the use of integrally bladed rotors in their compression systems. The analytical methodology developed under this proposed activity is directly applicable to commercial turbine engines.

REFERENCES:
1. Bladh, R., Castanier, M.P., & Pierre, C. (1999). Reduced order modeling and vibration analysis of mistuned bladed disk assemblies with shrouds. Journal of Engineering for Gas Turbines and Power, 121(3), 515-522. doi:10.1115/1.2818503

2. Castanier, M.P., Óttarsson, G., & Pierre, C. (1997). A reduced order modeling technique for mistuned bladed disks. Journal of Vibration and Acoustics, 119(3), 439-447. doi:10.1115/1.2889743

3. Hong, S., Epureanu, B.I., Castanier, M.P., & Gorsich, D.J. (2011). Parametric reduced-order models for predicting the vibration response of complex structure with component damage and uncertainties. Journal of Sound and Vibration, 330(6), 1091-1110. doi:10.1016/j.jsv.2010.09.022

4. Kruse, M., & Pierre, C. (1996). Dynamic response of an industrial turbomachinery rotor. 32nd AIAA/ASME/SAE/ASEE, Joint Propulsion Conference and Exhibit, 2820, 1-15. doi:10.2514/6.1996-2820

5. Kruse, M., & Pierre, C. (1996). Forced response of mistuned bladed disks using reduced-order modeling. 37th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference and Exhibit, 1545, 1938-1950. doi:10.2514/6.1996-1545