The trend in the design of advanced transonic fans for aircraft engines has been toward the use of complex high-aspect-ratio blade geometries with a larger number of blades and higher loading. In addition, integrally bladed disks or blisks are being considered in fan designs for their potential to reduce manufacturing costs, weight, and complexity by eliminating attachments. With such design trends, there is an increased possibility within the operating region of part-speed stall flutter (self-excited vibrations) that is exacerbated by the reduced structural damping of blisk fans. To verify the aeroelastic soundness of the design, the NASA Glenn Research Center is developing and validating an accurate aeroelastic prediction and analysis capability. Recently, this capability was enhanced significantly as described here.
The propulsion aeroelastic analysis capability is based on a three-dimensional unsteady aerodynamic Reynolds-averaged Navier-Stokes turbo-machinery code TURBO. This code can accurately model viscous flow effects that play an important role in certain aeroelastic problems such as flutter with flow separation, flutter at high loading conditions near the stall line (stall flutter), and flutter in the presence of shock and boundary-layer interaction. Recently, a preprocessor code (named AE-prep) was developed that performs the functions of the modeshape interpolation and grid deformation. This preprocessor allows the most recent version of the TURBO code (versions 4.2) to be used for aeroelastic analysis without the long delays previously associated with the merging of the aeroelastic modifications into each new version of TURBO. Thus, the aeroelastic analysis can benefit from all the new and improved features present in the latest versions of the TURBO code: namely, improved steady and unsteady viscous flow modeling with algebraic or k-e turbulence models, improved ability to use startup solutions from other codes such as the APNASA code, real gas modeling, namelist input capability, cross-platform portability, and improved memory management with the FORTRAN 90 code. For fan flutter analysis near the stall line, the newly added capability to use a k-e turbulence model is considered to be an extremely significant enhancement.
The AE-prep aeroelastic preprocessor and the TURBO code have been and continue to be exercised for flutter analysis as part of the verification and validation efforts. Standard test configurations and actual fan designs have been used as part of the verification and validation. Researchers at Honeywell Engines and Systems have also successfully exercised the TURBO code for the flutter analysis of experimental fan designs.
University of Toledo contacts: Milind A. Bakhle, 216-433-6037, Milind.A.Bakhle@grc.nasa.gov; and Rakesh Srivastava, 216-433-6045, Rakesh.Srivastava@grc.nasa.gov
Glenn contact: George L. Stefko, 216-433-3920, George.L.Stefko@grc.nasa.gov
Authors: Milind A. Bakhle, Rakesh Srivastava, and George L. Stefko
Headquarters program office: OAT
Programs/Projects: UEET
Last updated June 25, 2001, by Nancy.L.Obryan@nasa.gov
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov
216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
Cynthia.L.Dreibelbis@nasa.gov
216-433-2912
SGT, Inc.
Web page curator:
Nancy.L.Obryan@nasa.gov
216-433-5793
Wyle Information Systems, LLC
