Wind Tunnel Validation of Computational Fluid Dynamics-Based Aero-Optics Model

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1 Wind Tunnel Validation of Computational Fluid Dynamics-Based Aero-Optics Model D. Nahrstedt & Y-C Hsia, Boeing Directed Energy Systems E. Jumper & S. Gordeyev, University of Notre Dame J. Ceniceros, Boeing SVS L. Weaver, AFRL/DE L. DeSandre, Office of Naval Research (formerly with JTO/HEL) T. McLaughlin, US Air Force Academy Jun 07

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE JUN REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Wind Tunnel Validation of Computational Fluid Dynamics-Based Aero-Optics Model 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Boeing Directed Energy Systems; AFRL/DE 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 11. SPONSOR/MONITOR S REPORT NUMBER(S) 13. SUPPLEMENTARY NOTES Third International Symposium on Integrating CFD and Experiments in Aerodynamics,, The original document contains color images. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified 18. NUMBER OF PAGES 16 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 Outline Phase II Program summary Background: Phase I summary Turret requirements & configuration CFD code, computational grid, & OPD calculation Typical CFD flow solutions & OPD maps Validation Summary & conclusions Page 2

Program Summary Need Validate CFD-based aero-optics model to analyze optical performance of larger, more realistic airborne system Objectives Validate CFD-based OPD model using wavefront sensor data

4 Program Summary Need Validate CFD-based aero-optics model to analyze optical performance of larger, more realistic airborne system Objectives Validate CFD-based OPD model using wavefront sensor data from wind tunnel experiments Exercise CFD model to assess performance of larger, more realistic configuration with conformal window Determine wavefront control system requirements CFD validation Approach Wind tunnel WFS measurements of phase over scaled turret with conformal window Compare with CFD-based model at 1:1 scale including wind tunnel boundaries & inlet flow profile Large scale analysis Assess performance of larger turret with conformal window Evaluate wavefront control requirements Status Program successfully completed Turrets designed & fabricated Wind tunnel tests conducted WFS data collected CFD-based aero model validated Large scale analysis & wavefront control requirements completed Page 3

5 Phase I Results Wind Tunnel Test 1.5 Diameter Turret with Conformal Window Successful Phase I wind tunnel tests conducted at Notre Dame Configuration: 1.5 turret with conformal window Mach number M0.36, 0.5, 0.6, & 0.68 M0.5 basis for validation Lines-of-sight Azimuth = 0 (overhead pass) Elevation = 30 to 160 Fluid measurements Steady & unsteady pressure Velocity Optical measurements Malley probe (1D phase in flow) 2D Hartmann WFS In Draft Tunnel Inlet Test Section Configuration Test Section Static Pressure Coefficient Pressure Turret Optical Turret Page 4

JTO Aero-Optics Phase I Results CFD Validation Validated Over Realistic Lines-of-Sight Resolved Horseshoe

length Time-averaged mean & standard deviation Unsteady OPD (RMS nm) Increased node density to resolve

60 (PANS) technique in k-ε 50 turbulence model Correct Shear Layer Structure CFD Code Wind Tunnel 40 30 20 10

6 JTO Aero-Optics Phase I Results CFD Validation Validated Over Realistic Lines-of-Sight Resolved Horseshoe Vortex Updated CFD-based aerooptical model Figures-of-merit Tilt-corrected OPD In-flow phase correlation length Time-averaged mean & standard deviation Unsteady OPD (RMS nm) Increased node density to resolve turbulent bdy layer, free shear layer, & necklace vortex Implemented Partially 80 Averaged Navier-Stokes (PANS) technique in k-ε 50 turbulence model Correct Shear Layer Structure CFD Code Wind Tunnel Mach 0.5, 1.5 Inch Turret Elevation Angle (Deg) Optical Path Difference 140 Phase Correlation Length Page 5

7 Phase II Turret & Lines-of-Sight 12 Diameter Turret with Conformal Window Configuration: 12 turret with conformal window Mach number M0.35, 0.4, & 0.45 M0.4 basis for validation Lines-of-sight Azimuth = 0 (overhead pass) Elevation = 45 to 130 Fluid measurements Steady & unsteady pressure Velocity Optical measurements Malley probe (200 KHz in-flow 1D phase) 2D Hartmann WFS (10 Hz) USAFA 36 Wind Tunnel Window Port Turret on Wind Tunnel Wall θ elevation = 60, 103, 130 θ elevation = 46, 76, 120 Flow Turret Location Adjusts on Side of Wind Tunnel Flow Turret Optical Turret D turret = 12 H cyl = 4.5 D beam = 5 WT Section Page 6

8 Beam Train & WFS Configuration Lenslet Array & WF Processing Phase Disturbance Tunnel Back Window Turret Tunnel Front Window Beam Steering Mirror Hartmann WFS System Flow Instruments Beam Splitter Source & BEX Laser Injected into Tunnel Optical Bench System Configuration Laser & beam expander Turret generating phase disturbance WF sensor & processing AFA Implementation Laser beam injected thru wind tunnel front window Turret on opposite vertical wall of wind tunnel Page 7

CFD Analysis Approach Grid Generation, Flow Solution, & Path

& run Node array for flow solution Varying zones & grid

flow solution Integrate density variations Interpolate flow

9 CFD Analysis Approach Grid Generation, Flow Solution, & Path Integration Generate computational grid Initialize CFD code & run Node array for flow solution Varying zones & grid density Steady-state soln from Navier-Stokes eqns Unsteady flow solution Integrate density variations Interpolate flow soln to OPD array Integrate density to yield OPD(time,LOS) Page 8

10 Zone & Node Density About Turret Grid Development Zones & Nodes Define Computational Boundaries 52 Zones 2.7M Nodes CFD model includes turret, wind tunnel walls, & inlet flow profile Conformal window flow symmetry allows single grid for all Mach numbers & LOS angles Structured grid Grid density increased in boundary & shear layers Extends 45 upstream to 150 downstream 52 zones 2.7 million nodes Page 9

time-accurate calculations Partially Averaged Navier-Stokes (PANS) k-ε model Values 5 μsec time step Solution saved at

11 Flow Solver & Conditions Time Iterative Density/pressure-based Algorithm (TIDAL) Code features Generalized 3D flow solver Finite 3D volume with multi-zone method Structured grid Steady & unsteady flow Dual time stepping for time-accurate calculations Partially Averaged Navier-Stokes (PANS) k-ε model Values 5 μsec time step Solution saved at Δt = 50 μsec 300 frames saved (15 msec) for wavefront analysis ftk = 0.4 ~ 1.0 Freestream: ftk = 0.5 Wall: ftk = 1.0 Variable ftk Page 10

flow density to beam grid Integrate density or index along beam direction (grid

12 OPD Calculation N X N Beamlet Array Generate beam grid 25 x 25 mesh ~ 12.7 x 12.7 x 120 cm 3 Beam grid extends from turret window to tunnel wall Interpolate flow density to beam grid Integrate density or index along beam direction (grid line) to obtain OPL Use ambient density inside turret & outside of tunnel Page 11

of necklace vortex Instability in shear layer rolls into vortices Pressure within vortices shows oscillatory

13 Typical Flow Solutions Solution Shows Required Features Instantaneous realizations of central plane & shoulder plane sections Low pressure aft result of wake Low pressure, circular area forward at base is core of necklace vortex Instability in shear layer rolls into vortices Pressure within vortices shows oscillatory behavior as in PIV Resolution of shear layer vortices is critical to accurate simulation of aero-optical effect Page 12

Fluid Mechanical Validation First Match Fluid Properties 2.0 Location 1 Location 3 Location 5 2.0 2.0 Locations of unsteady pressure sensors Z/H 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 CFD, M=0.

14 Fluid Mechanical Validation First Match Fluid Properties 2.0 Location 1 Location 3 Location Locations of unsteady pressure sensors Z/H CFD, M=0.4, Case 1 CFD, M=0.4, Case 2 Test, M= U_mean/U_in Z/H CFD, M=0.4, Case 1 CFD, M=0.4, Case 2 Test, M= U_mean/U_in Z/H CFD, M=0.4, Case 1 CFD, M=0.4, Case 2 Test, M= U_mean/U_in CFD-based & measured velocity profiles (Case 1 is selected model) CFD & measured C P over elevation angle Locations of velocity profile sensors Page 13

15 OPD Maps in Time Piston & Tilt Removed OPD at 60, 90, 120 & 132 Elevation Page 14

16 JTO Aero-Optics Optical Validation FOM: RMS Wavefront Error & Phase Correlation Length Mean RMS OPD Bin (nm) OPD WT(M0.4,120 Deg) Phase Correlation Length Mean RMS OPD Bin (nm) Measured & CFD-based PDF for RMS OPD at each elevation CFD Code 80 Wind Tunnel OPD CFD(M0.4,132 Deg) 0.4 OPD WT(M0.4,132 Deg) Correl_WT(M0.4,90 Deg) Mean RMS OPD Bin (nm) Correlation Length Bin (mm) 16 Measured & CFD-based PDF for phase correlation length at each elevation Mach 0.4, 12-Inch Turret CFD Code 9 Wind Tunnel Mach 0.4, 12-Inch Turret Correlation Length Bin (mm) Correl_WT(M0.4,132 Deg) Phase Corr Length (cm; Along Flo Dir) 90 Correl N170CFD(M0.4,90 Deg) Correl CFD(M0.4,132 Deg) 0.6 Normalized Freq of Occurrence 0.1 Normalized Freq of Occurrence OPD CFD(M0.4,120 Deg) Normalized Freq of Occurrence 0.3 Unsteady OPD (RMS nm) Normalized Freq of Occurrence OPD WT(M0.4,60 Deg) Normalized Freq of Occurrence Wavefront Error OPD CFD(M0.4,60 Deg) Elevation Angle (Deg) Elevation Angle (Deg) Page 15

17 Summary & Conclusions Successful Model Validation Aero-optical effects beyond separation point can be a significant performance degrader in airborne systems Wind tunnel testing is expensive, time-consuming, & subject to scaling limitations; exercising CFD is cost effective JTO program successfully validated CFD-based aero-optical model based on fluid & optical FOMs Good agreement using reasonable turret & window configurations over practical range of LOS angles Lessons learned: Grid generation (resolution vs CPU time), turbulence model, & scaling limits WFS data useful for validation in future CFD development Page 16

Wind Tunnel Validation of Computational Fluid Dynamics-Based Aero-Optics Model

Wind Tunnel Validation of Computational Fluid Dynamics-Based Aero-Optics Model D. Nahrstedt & Y-C Hsia, Boeing Directed Energy Systems E. Jumper & S. Gordeyev, University of Notre Dame J. Ceniceros, Boeing