Extensible Rectangular Nozzle Model System

Abstract

The design process for the Extensible Rectangular Nozzle (ERN) Model System is summarized. The ERN task is currently funded under the Supersonic project in NASA's Fundamental Aeronautics Program. The task supports the generation of innovative conceptual aerodynamic designs of aircraft exhaust nozzles. Reduced acoustic emissions with improved nozzle performance has been the task goal. New acoustic test rig hardware has been designed for operation at the NASA Glenn Research Center's Aero-Acoustic Propulsion Laboratory (AAPL). Testing of the new rig hardware will provide the experimental data to validate computational predictions of acoustics and performance. The design process has progressed from concept selection through to fabrication-ready three- dimensional (3D) computer solid models. Flow transition ducts have been designed to transition from round piping to a rectangular cross-section. Rectangular convergent baseline nozzle concepts with aspect ratio (AR) of 2, 4 and 8 have been designed for mounting to the flow transition ducts. Initial parametric variations on the baseline nozzles have been modeled and analyzed. Parametric nozzle concepts have included bevel, sidewall-cutback, chevron and combinations of these technologies. The structured Wind-US Reynolds- averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) code has been used throughout the design process as the main flow analysis tool. Aerodynamic design trade studies have been performed of the transition within the nozzle flow-path from a round to a rectangular cross-section in order to minimize flow non-uniformities. The definition of the nozzle external surface has been coupled to both the results from the preliminary mechanical design and supporting internal and external nozzle CFD. Finite-element based structural analyses provide the key mechanical predictions for the hardware components and assembly stack-ups, with hand calculations to help estimate factors of safety. The internal and external flow-lines for the concepts have been screened for aerodynamic performance and expected noise generation at the takeoff condition for nozzle pressure ratios (NPR) ranging from near sonic to a maximum NPR of 3.5. Jet plume predictions at NPR of 1.86 and 2.5 takeoff conditions are presented for a number of the concepts. Updates based on the CFD predictions have been implemented within the 3D computer solid models and mechanically verified throughout the design process. The detachable rectangular nozzle designs for each AR, along with the AR-specific round-to-rectangular transition ducts to which the nozzles attach, represent the key outputs of this design phase. Future acoustic spectral analyses will use the RANS CFD solutions as input during calculations of jet noise. The predictions can then be validated with the experimental test data obtained using the rig hardware. Together with the acoustic predictions, this work will help build up a database of acoustic and aerodynamic predictions to be used in systems-level trade studies of second- generation (N+2) supersonic commercial transport vehicles.