Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics

1. Steven J. Massey Eagle Aeronautics, Inc. Alaa A. Elmiligui Analytical Services & Materials, Inc. Craig A. Hunter, Russell H. Thomas, S. Paul Pao NASA Langley Research Center and Vinod G. Mengle Boeing Company Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics 12th AIAA/CEAS Aeroacoustics Conference Cambridge, MAMay 8-10, 2006

2. Outline • Motivation • Objectives • Numerical Tools • Review of Generic Jet-Pylon Effect • Axi, bb, RR, RT Nozzle Configurations • Analysis Procedure • Results Chain from Noise to Geometry • Summary • Concluding Remarks NASA Langley Research Center

3. General PAA Related Effects and Features On Typical Conventional Aircraft Nacelle-airframe integration e.g. chines, flow distortion, relative angles Jet interaction with horizontal stabilizers Jet-pylon interaction of the PAA T-fan nozzle Pylon-slat cutout Jet influence on airframe sources: side edges Jet-flap trailing edge interaction Jet-flap impingement Jet and fan noise scattering from fuselage, wing, flap surfaces QTD2 partnership of Boeing, GE, Goodrich, NASA, and ANA NASA Langley Research Center

4. Objectives • To build a predictive capability to link geometry to noise for complex configurations • To identify the flow and noise source mechanisms of the PAA T-Fan (quieter at take off than the reference chevron nozzle) NASA Langley Research Center

5. Numerical Tools • PAB3D • 3D RANS upwind code • Multi-block structured with general patching • Parallel using MPI • Mesh sequencing • Two-equation k- turbulence models • Several algebraic Reynolds stress models • Jet3D • Lighthill’s Acoustic Analogy in 3D • Models the jet flow with a fictitious volume distribution of quadrupole sources radiating into a uniform ambient medium • Uses RANS CFD as input • Now implemented for structured and unstructured grids (ref AIAA 2006-2597) NASA Langley Research Center

6. Sample Grid Plane • 31 Million Cells for 180o • PAB3D solution: 33 hours on 44 Columbia CPU’s (Itanium 2) • Jet3D solution, 10 minutes on Mac NASA Langley Research Center

7. Model Scale LSAF PAA Nozzles Analyzed • Four Nozzles Chosen for Analysis: • Axisymmetric Nozzle (not an experimental nozzle) • bb conventional nozzles • RR state-of-the-art azimuthally uniform chevrons on core and fan • RT PAA T-fan azimuthally varying chevrons on fan and uniform chevrons on core • For more details see Mengle et al. AIAA 06-2467 NASA Langley Research Center

8. Generic Pylon Effect Understanding - AIAA 05-3083 • Core Flow Induced Off of Jet Axis by Coanda Effect • Pairs of Large Scale Vortices Created • TKE and Noise Sources Move Upstream • Depending on Design Details can Result in Noise Reduction or Increase with Pylon Refs: AIAA 01-2183, 01-2185, 03-3169, 03-3212, 04-2827, 05-3083 NASA Langley Research Center

9. Analysis Procedure • Start with established facts and work from derived to fundamental quantities to form connections to geometry • Measured noise data (LSAF) • SPL predictions (Jet3D) • OASPL noise source histogram (Jet3D) • Mass averaged, non-dimensional turbulence intensity (PAB3D) • OASPL noise source maps (Jet3D) • Turbulence kinetic energy (PAB3D) • Axial vorticity • Cross flow streamlines • Vertical velocity • Total temperature • Total temperature centroid • Geometry NASA Langley Research Center

10. Jet3D SPL Predictions with LSAF • bb predicted within 1 dB for whole range • RRover predicted by 1 dB for frequencies < 10 kHz, under predicted by up to 2 dB for high frequencies • RT predicted within 1 dB for whole range, under predicted high frequencies Tunnel noise * Trends predicted correctly increasing confidence of flow and noise source linkage * Axi case not thrust matched to others Observer located on a 68.1D radius from the fan nozzle exit at an inlet angle of 88.5 deg. and an azimuthal angle of 180 deg. LSAF data from Mengle et al. AIAA 2006–2467 NASA Langley Research Center

11. Noise Prediction – CFD Link Jet3D OASPL Histogram PAB3D: Mass-Avg TKE • Noise and TKE sources relative to Axi are consistent with previous pylon understanding of mixing • Mass-Avg TKE qualitatively matches noise source histogram • bb, RR, RT intersect near x/D = 10 • Axi crosses bb, RR at x/D = 12 • Axi crosses RT at x/D = 12.75 NASA Langley Research Center

12. LAA – CFD Correspondence Axi bb RR RT • Peak noise sources correspond with peak TKE • Local noise increased by chevron length • Cross flow stream lines show shear layer vorticity orientation NASA Langley Research Center

13. Beginning Fan/Core Shear Merger Axi bb RR RT • Noise and TKE peak as layers merge • RR levels slightly lower than bb • RT merger delayed, much lower levels • Axi noise asymmetry due to LAA observer location. TKE is symmetric • Axial velocity 20 times stronger than cross flow, thus strongest vortex would take about 60D for one revolution NASA Langley Research Center

14. Peak Noise From Shear Merger Axi bb RR RT • bb, RR peak shown; RT peaks 0.5D later, one contour lower than bb and RR • Unmerged Axi with lower noise and TKE, but will persist more downstream NASA Langley Research Center

15. Chevrons Add Vorticity • Axi cross flow is symmetric, so axial vorticity = zero • bb shows boundary layer vorticity shifted off axis by pylon • RT longer chevrons show increased vorticity over RR and shorter chevrons on bottom show decreases Pylon Plug Core Cowl NASA Langley Research Center

16. Pylon, Plug, Chevron Interaction • RT fan vortices more defined on top, less on bottom due to chevron length • Vertical velocity component shows effect of pylon on cross flow: • Axi shows Coanda effect on plug • Pylon cases have expanded downward flow region to get around pylon to fill in plug • Less downward movement in fan flow for RT NASA Langley Research Center

17. Consolidation and Entrainment • Core and fan shear layer vorticity consolidates to form vortex pair • RR vortex pair slightly stronger than bb • RT vortex pair significantly weaker than bb and RR NASA Langley Research Center

18. T-Fan Reduces Overall Mixing • RT local mixing proportional to chevron length • RT decreases net mixing, extends core by ~ 1/2 D • RR negligible mixing over bb NASA Langley Research Center

19. Overall Jet Trajectory Total Temperature Centroid • bb and RR equivalent – symmetric chevron does not interact with pylon effect • RT showing less downward movement – favorable interaction of asymmetric chevron with pylon effect NASA Langley Research Center

20. Summary • Overall mixing does not vary much between bb, RR and RT and is not indicative of noise in this study The T-Fan effect: • Varies the strength azimuthally of the localized chevron vorticity • Reduces the downstream large scale vorticies introduced by the pylon • Delays the merger of the fan and core shear layers • Reduces peak noise and shifts it downstream • There is the possibility of a more favorable design for shear layer merger, which can now be found computationally NASA Langley Research Center

21. Concluding Remarks • A predictive capability linking geometry to noise has been demonstrated • The T-Fan benefits from a favorable interaction between asymmetric chevrons and the pylon effect NASA Langley Research Center

22. Discussion, Extra Slides… NASA Langley Research Center

23. Axisymmetric Nozzle Surfaces colored by temperature NASA Langley Research Center

24. Baseline Nozzle (bb) Near surface streamlines and temperature Fan boundary streamline NASA Langley Research Center

25. Reference Chevrons (RR) Near surface streamlines and temperature Slight upward movement NASA Langley Research Center

26. PAA T-Fan Nozzle (RT) Near surface streamlines and temperature Further upward movement NASA Langley Research Center

27. Motivation Propulsion Airframe Aeroacoustics (PAA) • Definition: Aeroacoustic effects associated with the integration of the propulsion and airframe systems. • Includes: • Integration effects on inlet and exhaust systems • Flow interaction and acoustic propagation effects • Configurations from conventional to revolutionary • PAA goal is to reduce interaction effects directly or use integration to reduce net radiated noise. NASA Langley Research Center

28. PAA on QTD2: Concept to Flight in Two Years Exploration of Possible PAA Concepts with QTD2 Partners (5/03 – 4/04) Extensive PAA CFD/Prediction Work (10/03 – 8/05) (AIAA 05-3083, 06-2436) PAA Experiment at Boeing LSAF 9/04 PAA Effects and Noise Reduction Technologies Studied AIAA 06-2467, 06-2434, 06-2435 • PAA on QTD2 – 8/05 • PAA T-Fan Chevron Nozzle • PAA Effects Instrumentation • AIAA 06-2438, 06-2439 NASA Langley Research Center

29. Grid Coarse in Radial Direction NASA Langley Research Center

30. Grid Cause of Vorticity Lines NASA Langley Research Center

31. PAA Analysis Process to Develop Understanding of PAA T-fan Nozzle’s Flow/Noise Source Mechanisms Begin with Highly Complex LSAF Jet-Pylon Nozzle Geometries JET3D Validation of Spectra Trend at 90 degrees Detailed PAA Flow Analysis • Three major effects to understand: • Pylon effect • Chevron effect • PAA T-fan effect • and their interaction JET3D Noise Source Map Trends Validated with LSAF Phased Array Measurements Develop Linkages of complex flow and noise source interactions NASA Langley Research Center