1. Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics
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
12th AIAA/CEAS Aeroacoustics Conference
Cambridge, MA May 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
May 8, 2006

3. General PAA Related Effects and Features On Typical Conventional Aircraft
Jet interaction with horizontal stabilizers
Nacelle-airframe integration e.g. chines, flow distortion, relative angles
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
May 8, 2006

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
May 8, 2006

5. Numerical Tools PAB3D Jet3D 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 )
NASA Langley Research Center
May 8, 2006

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
May 8, 2006

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
NASA Langley Research Center
May 8, 2006

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 , , , , ,
NASA Langley Research Center
May 8, 2006

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
May 8, 2006

10. Jet3D SPL Predictions with LSAF
bb predicted within 1 dB for whole range
RR over 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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

15. Chevrons Add Vorticity
Pylon
Plug
Core Cowl
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
NASA Langley Research Center
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

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
May 8, 2006

22. Discussion, Extra Slides…
NASA Langley Research Center
May 8, 2006

23. Axisymmetric Nozzle Surfaces colored by temperature
NASA Langley Research Center
May 8, 2006

24. Baseline Nozzle (bb) Near surface streamlines and temperature
Fan boundary
streamline
NASA Langley Research Center
May 8, 2006

25. Reference Chevrons (RR)
Near surface streamlines
and temperature
Slight upward
movement
NASA Langley Research Center
May 8, 2006

26. PAA T-Fan Nozzle (RT) Near surface streamlines and temperature
Further upward
movement
NASA Langley Research Center
May 8, 2006

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
May 8, 2006

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 , )
PAA Experiment at Boeing LSAF 9/04
PAA Effects and Noise Reduction Technologies Studied
AIAA , ,
PAA on QTD2 – 8/05
PAA T-Fan Chevron Nozzle
PAA Effects Instrumentation
AIAA ,
NASA Langley Research Center
May 8, 2006

29. Grid Coarse in Radial Direction
NASA Langley Research Center
May 8, 2006

30. Grid Cause of Vorticity Lines
NASA Langley Research Center
May 8, 2006

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
May 8, 2006