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Project Number : PS 3.1

Project Number : PS 3.1. Unsteady, Turbulent, Separated Flow Around Helicopter Fuselages. PI: Prof. Lyle N. Long tel : (814) 865-1172 Email: lnl@psu.edu Web: http://www.personal.psu.edu/lnl/ Graduate Student: Emre Alpman (PhD 2005)

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Project Number : PS 3.1

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  1. Project Number : PS 3.1 Unsteady, Turbulent, Separated Flow Around Helicopter Fuselages PI: Prof. Lyle N. Long tel : (814) 865-1172 Email: lnl@psu.edu Web: http://www.personal.psu.edu/lnl/ Graduate Student: Emre Alpman (PhD 2005) 2005 RCOE Program Review May 3, 2005 Comanche Bell 214

  2. Technical Barriers European Helifuse investigation found that turbulence models such as k-, k-, Baldwin-Lomax were not able to accurately predict lift and drag on complex helicopter geometries. RANS-based CFD methods cannot accurately predict the unsteady turbulent flow around rotorcraft fuselages.

  3. Objectives: Develop better numerical methods for flow around helicopter fuselages and for drag prediction Approach: Unstructured grid CFD methods on inexpensive parallel computers Validate code on simple shapes such as spheres and ellipsoids Make detailed comparisons between experimental data and numerical predictions for flow around helicopter fuselages Expected Research Results or Products: Better numerical algorithms and understanding of unsteady separated flows Efficient parallel CFD codes Very Complex Geometries

  4. PUMA2 Flow Solver • Finite volume ANSI C++ parallel program • Message Passing Interface (MPI) used for inter-processor communication • Unstructured grids to handle very complex geometries • Runge-Kutta for time-accurate runs • SSOR for steady-state runs • Turbulence: • Large Eddy Simulation (LES) with wall function • Reynolds Stress Model (RSM) • Runs on any Beowulf cluster or parallel computer

  5. Turbulence Models Approximate Equations Exact Equations More Physics DNS Time Average Unsteady, Spatially Filter DES combines these LES Do not use Boussinesq Use Boussinesq assumption Reynolds Stress Model (7 new PDE’s) Less CPU Time 2 Equation Models (K-e & K-w) 1 Equation Models (Spalart- Allmaras) Algebraic Models (e.g. Baldwin- Lomax) These are about as good as they are going to get --and they are not good enough for rotorcraft !!

  6. Reynolds Transport Equations& RSMModel Exact Modelled • 12 nonlinear coupled PDE’s: • 6 Re Stress eqtns • 1 Turb. Dissipation eqtn • 5 Navier-Stokes Equations Launder, B. E., Reece, G. J., Rodi W., Journal of Fluid Mechanics, vol.68, part 3, 1975. Wilcox, D. C., "Turbulence Modeling for CFD", DCW Industries Inc.

  7. RSM Solution for a 6:1 Prolate Spheroid • Re = 6.5x106 • M = 0.1322 • α = 30° • Turbulence intensity: 0.03% • Grid is composed of 5.1 million tetrahedral cells • Solution took 7 days on 30 2.4 GHz Xeon processors

  8. 6:1 Prolate Spheroid (RSM) • Qualitative agreement with experiment • Experimental data also contain some uncertainties Alpman, E., and Long, L. N., AIAA Paper 2005-1094, 2005 Experiment: Kreplin, H. P., Volmers H., Meier H. U., DFVLR Rept, IB 222-84 A 33, 1985.

  9. 6:1 Prolate Spheroid (RSM) • Vorticity contours with surface • skin friction lines • Asymptotic convergence of skin • friction lines means separation • At the upper lee side of the body • a second separation line is also • observed

  10. RSM Solution for a 6:1 Sphere • Re = 1.14x106 • M = 0.1763 • Turbulence intensity: 0.45% • Grid is composed of 3.8 million tetrahedral cells • Solution took 6 days on 30 2.4 GHz Xeon processors

  11. RSM Solution & Experiment SphereRe = 1.14x106 M = 0.1763 Alpman, E., and Long, L. N., AIAA Paper 2005-1094, January, 2005 Achenbach, E., Journal of Fluid Mechanics, Vol. 54, No. 3, 1972, pp. 565 – 575.

  12. SphereRe = 1.14x106 M = 0.1763 Normalized τxx contours Normalized τxz contours • In isotropic turbulence, normalized τxx and τxz take the values of 2/3 and 0 • respectively • Flow is highly anisotropic • Anisotropic models (e.g. RSM) necessary for 3-D separated flows

  13. Sphere Drag PredictionRe = 1.14x106 M = 0.1763

  14. Re = 1.5x106 per ft M = 0.3322 α = -2.28°, ψ=0° (low angle of attack cruise condition) α = 17.04°, ψ=0° (high angle of attack condition) α = -1.6°, ψ=16.4° (high yaw angle condition) α = -2.28°, ψ=0° (low angle of attack cruise condition with rotors modeled using momentum theory with linear loading) Turbulence intensity: 1% Grid is composed of 2.9 million tetrahedral cells Solution took 7 days on 30 2.4 GHz Xeon processors RSM Solution for a Bell 214ST Fuselage

  15. Computational MeshBELL 214ST y+ ~ 40

  16. Low Angle of attack Cruise Condition Re = 1.5x106 per ft M = 0.3322 (without rotors) Good agreement with the measurements. Surface Pressure Distribution Alpman, E., and Long, L. N., AHS International 61st Annual Forum and Display, June, 2005 Experiment: Oldenbuttel, R. H., Report No. LSWT 554, Vought Corporation, 1978.

  17. High Angle of Attack and High Yaw Angle Conditions (without rotors) High Angle of Attack Condition High Yaw Angle Condition Good agreement even when the expansions are quite abrupt Good agreement with the measurements except around the tail boom. Mainly due to differences between wind tunnel and computational geometry

  18. High Angle of Attack Condition Normalized τxz contours Computed Using Boussinesq Hypothesis during post processing Normalized τxz contours Computed Using RSM Reynolds stresses and mean strain rates are grossly misaligned. Turbulence models based on the Boussinesq approximation might perform poorly for this flow and warrants the use of RSM.

  19. Simulation with Main and Tail Rotors Vertical velocity contours without rotors Vertical velocity contours T = 17500 lbs., Ttr = 1104 lbs • Induced downwash velocities • Tip vortices at the edge of rotor plane

  20. Simulation with Main and Tail Rotors Normalized τyz contours T = 17500 lbs., Ttr = 1104 lbs Normalized τyz contours without rotors Vortices generated by the main rotor affects downstream turbulence structure

  21. Bell 214ST Total Drag PredictionsRe = 1.5x106 per ft M = 0.3322 (without rotors)  = -2.28 and  = 0

  22. Bell 214ST Drag PredictionsRe = 1.5x106 per ft M = 0.3322 (without rotors)  = -2.28 and  = 0 RANS Solution Inaccurate 90% of Total Drag

  23. Bell 214ST Drag PredictionsRe = 1.5x106 per ft M = 0.3322 (without rotors)  = 17 and  = 0  = -1.6 and  = 16.4

  24. Accomplishments • CY 2002 Accomplishments: • Drag of Bell 214 compared to experiment • Unsteady tail loadings predicted on Bell 214 ST • Steady Comanche fan-in-fin simulations compared to experiment • CY 2003 Accomplishments • Comanche Fan-in-fin Simulations: Unsteady, rapid maneuvers • LES Wall function implemented on unstructured grids • RSM implemented on unstructured grids • LES & RSM Sphere Simulations: • LES & RSM Ellipsoid simulations: • CY 2004 Accomplishments • Detailed comparisons between LES & RSM • Bell 214ST RSM & LES simulations • French fuselage simulations ?

  25. Completed Short Term Long Term Schedule / Milestones 2001 2002 2005 2003 2004 Tasks Comparisons to experimental data - Cone & 3-D Cylinder Generic Fuselage Simulations - Robin Body w & w/o NLDE R. Hansen Ph.D. Thesis Bell 214ST grid & steady solution Unsteady loads and drag F. Souliez Ph.D. Thesis Grid and viscous flow over ellipsoid Re-Stress Model for turbulent flow over ellipsoid S. Jindal M.S. Thesis Steady/unsteady Comanche flows Detailed compare of RSM & LES Re-Stress Model & LES for Bell 214 Helicopter drag and unsteady flows E. Alpman Ph.D. Thesis    

  26. Publications & Theses • 2005: • Alpman, Long, “Separated Flow Simulations,” AIAA-2005-1094, January, 2005 • Alpman Long, “Bell 214ST RSM Simulations”, AHS Annual Forum, June 2005. • Lee, Sezer-Uzol, Horn, and Long, “Ship Airwakes,” Jnl of Aircraft, 2005 • Sezer-Uzol, PhD Thesis, 2005 • Alpman, PhD Thesis, 2005 • 2004: • Corfeld, Strawn, and Long, “Martian Rotor,” AHS Journal, 2004 • Jindal, Long, Plassmann, and Sezer-Uzol, “LES,” AIAA 2004-2228, 2004 • Modi, Sezer-Uzol, Long, Plassmann, “Visualization,” Jnl of Aircraft, 2004 • Alpman, Long, and Kothmann, “Comanche (steady),” Jnl. of Aircraft, 2004 • Alpman, Long, and Kothmann, “Comanche (unsteady),” Jnl. of Aircraft, 2004 • Jindal, MS Thesis, 2004

  27. Publications & Theses (cont.) • 2003: • Alpman, Long, and Kothmann, “Comanche,” AHS Forum, 2003 • Lee, Sezer-Uzol, Horn, and Long, “Ship Airwakes,” AHS Forum, 2003 • Alpman and Long, “Comanche,” AIAA-2003-4231, CFD Conf., June, 2003. • 2002: • Souliez, Long, Sharma, and Morris, Intl. Jnl. of Aeroacoustics, • Corfeld, Long and Strawn, AIAA Paper, St. Louis Mtg., June, 2002 • Souliez, Long, Morris, and Sharma, AIAA 2002-0799, Reno, Jan., 2002 • Hansen and Long, AIAA 2002-0982, Reno, Jan., 2002 • Fred Souliez, Ph.D. Thesis (Unsteady CFD for Helicopter Fuselages) (at BMW) • Anirudh Modi, Ph.D. Thesis (Computational Steering and Wake Vortices) (at Intel) • Kelly Corfeld, M.S. Thesis (CFD for Martian Rotorcraft) (at Lockheed) • 2001: • L. Long, P. Plassmann, and A. Modi, “Airport Capacity,” London, Sept., 2001 • Long and Modi, NCSA Linux Revolution Conference, Illinois, June, 2001. • LTC Bob Hansen, Ph.D. Thesis (Unsteady CFD using unstructured grids) • Nilay Sezer-Uzol, M.S. Thesis (CFD simulations of rotors) • Anupam Sharma, M.S. Thesis (ship airwake simulations)

  28. Worked with Bruce Kothmann at Boeing Helicopter on Comanche fan-in-fin Got Bell 214ST data from Jim Narramore Working with Georgia Tech (joint DARPA project) Very good relationship with West Point (USMA) Graduate student (Kelly Corfeld) was in Co-op program with NASA Ames Rotorcraft worked on Martian Rotorcraft with Dr. Roger Strawn (she is now at Lockheed) Working with Dr. Earl Duque who is using different CFD approaches Technology Transfer:

  29. Leveraging or Attracting Other Resources or Programs • DARPA quiet helicopter project (joint Penn State, GATech, & NAU effort) • NSF Center for Particle Methods (Monte Carlo, Molecular Dynamics, & Vortices) • Army DURIP grant for computer hardware • 120 processor Beowulf for RCOE center (with Prof. Brentner) • Institute for Computational Science and Engineering (2004), wide-spread financial support across Penn State • Grant from National Renewable Energy Lab for Wind Turbine Aeroacoustics (with Morris and Brentner)

  30. 2005 Recommendations: • The task work is excellent. It is suggested to compare various turbulence modelings and to contact Langley for Comanche tail buffett data. • Response: • Have compared LES and RSM for same geometry. Have also post processed results to see what 2-equation model might yield. With cancellation of Comanche we decided to focus on Bell 214ST and simple shapes with good experimental data.

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