1. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 1 Modeling of Rotorcraft Noise in Maneuvering Flight PI: Kenneth S. Brentner (814)865-6433, ksbrentner@psu.edu Graduate Students: Hsuan-Nien Chen (started Dec 2002 – PhD) 2005 RCOE Program Review May 3, 2005 Kenneth S. Brentner, Dept. of Aerospace Engineering Project: PS 4.1

2. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 2 Overview of Work  Project Overview (Ken Brentner)  Acoustic Analysis (Sam Chen)  Summary (Ken Brentner )

3. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 3 Background/Problem Statement:  Current rotor aerodynamics and noise prediction primarily for steady flight conditions  Noise of maneuvering rotorcraft can be significantly higher than for a similar steady flight condition  A tool is needed that is able to predict noise generated by rotorcraft in maneuver — including the transient aircraft motion and blade loading. Technical Barriers or Physical Mechanisms to Solve:  Acoustics  Very complex source motion and time dependence  Complicated time-dependent noise directivity  Transient blade loading and motion are an “additional” noise source  Aeromechanics  Nonperiodic blade loading and motion is unique to each blade  Rotor-wake interaction extremely challenging problem

4. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 4 Task Objectives:  Develop a noise prediction capability for rotors in steady AND transient maneuvers (including multiple rotors)  Gain better understanding of noise directivity in maneuvering flight—especially the components (thickness, loading, transients, etc.) of maneuver noise  Quantify the importance of transients  Assess the requirements for wake fidelity and airloads accuracy in the context of maneuver noise-prediction  Improve maneuver noise prediction through the utilization and/or development of maneuvering wake

5. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 5 Approach:  Develop acoustics code with full rotor-blade motion and complete aircraft motion  Utilize best available comprehensive analysis tools for initial developmental work, accepting known weaknesses  Incorporate advanced maneuver airloads/wake modeling as it becomes available Emphasis is on approaching the problem from the acoustics point of view, then working to provide required input data Expected Research Results or Products:  A new rotorcraft noise prediction code—much more useful and general purpose than the current generation of codes  Understanding of the extra noise generated in maneuvers  Guidance for the development of maneuver aerodynamics and flight dynamics (acoustic requirements)

6. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 6 Overview of Work  Project Overview  Acoustic Analysis  Summary

7. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 7 Maneuver Noise Analyzed  Several maneuvers were analyzed:  Arrested descent  Left turn entry (with three different roll rates)  Right turn entry (with three different roll rates)  Left-right-left roll reversal maneuver  Right-left-right roll reversal maneuver  Quick stop maneuver  Level acceleration maneuver  Climb maneuver  Focus of this presentation on maneuvers with roll motion

8. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 8 Code Validation – BVI Condition  Compared predictions with DNW acoustic measurement  Contemporary design 4-bladed rotor for utility helicopter  μ = 0.2 and C T =0.0056 and zero shaft tilt angle (wind tunnel conditions not fully reported)  Two mic positions, Mic 9: Ψ=150º and 25º below; Mic 7: Ψ=150º in-plane.  Aerodynamic calculation was performed by RCAS free vortex-wake model Mic 7 Mic 9 Predicted levels lowered by 20 Pa for clarity

9. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 9 Transient Maneuver Noise Identified Rotor Normal Force Ratio* OASPL (dB) Observer Location : (800, - 400, 0) m * Rotor Normal Force / Gross Weight Fixed Observer Location Observer Location: 30R form rotor hub, 45º below rotor and 120º azimuth angle Moving Observer Location

10. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 10 Turn-Entry Maneuvering Flight  Both right and left turn-entry maneuvering flights.  Three different turn transient duration settings: 0.5, 1 and 5 seconds.  Focus on the helicopter roll maneuver. Left Turn Right Turn 0.5 sec duration 1 sec duration 5 sec duration

11. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 11  OASPL “spike” amplitude is a strong function of transient duration 0.5 sec duration 1 sec duration 5 sec duration Observer locations:  45º below rotor tip path plane  30 R from rotor hub  Upstream ±60º from centerline Acoustic Signature with Different Roll Rates Thickness noise Loading noise

12. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 12 Disk Loading in Right Turn-Entry Maneuver 0.5s duration1.0s duration5.0s duration

13. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 13 Rotor Wake Geometry for Right Turn  Wake bundling effect starts from Rev 27  Interaction of wake bundle and blade result in a “Super BVI”  occurs in both Revs 28 and 29  Helicopter roll overshoot during maneuver is partially responsible

14. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 14 BVISPL Prediction in Right Turn-Entry Maneuver 1.0s duration0.5s duration5.0s duration

15. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 15 Disk Loading in Left Turn-Entry Maneuver 0.5s duration1.0s duration5.0s duration

16. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 16 Rotor Wake Geometry for Left Turn  The wake bundling effect observed in the retreating side.  The wake bundling effect also occurred in the advancing side but less interaction with rotor blades.  The strength of the “super BVI” is less than what we observe in the right turn.

17. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 17 BVISPL Prediction in Left Turn-Entry Maneuver 0.5s duration1.0s duration5.0s duration

18. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 18 Summary for Turn Maneuvers  Both right and left turns experienced vortex bundling in the transient maneuver condition. Right turn maneuver has stronger bundling and interaction in the aggressive turn.  The overshoot in roll attitude results in strong BVI during the right turn maneuver. It is like a mini roll-reversal maneuver.  A more aggressive maneuver triggers a stronger wake bundling condition. As this bundled tip vortices encounter the rotor during the maneuver has the potential to generate very high level of impulsive loading and BVI noise.  Right turn maneuver generated higher noise level than the left turn.

19. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 19 A More Complex Example: LRL Roll Reversal Maneuver  The LRL roll reversal maneuver consists of three components within 6 sec:  A -50º left roll over approximately 2 sec.  A 100º right roll over approximately 2 sec.  A second left to zero roll angle over approximately 2 sec.  The advance ratio for maneuver was relatively low, μ=0.093

20. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 20 Disk Loading in the LRL Roll Reversal Maneuver

21. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 21 LRL Roll Reversal Maneuver  The high level BVISPL concentrated in the forward area at beginning of the right roll (t =7.24 s)  The very large BVISPL levels ahead of the rotor at t = 8.25 s and t = 8.65 s are primarily caused by BVI loading during Revs 36 and 37  As helicopter returns to level flight, both advancing and retreating side BVI are present (t = 10.66 s)

22. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 22 Summary for Roll Reversal Maneuver  In these maneuvers, BVI noise dominates  BVI noise during a transient maneuver is different than in steady flight  Vortex bundling  Dynamic state of vortex system (not steady after start of maneuver)  The formation of the vortex bundle and its subsequent interaction with the rotor blades was strongly influenced by the pilot overshoots in the turn-entry maneuver  Due to the short duration of maneuver duration, the helicopter is constantly in the transient maneuver state and the noise generated in this condition can be considered as transient maneuver noise

23. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 23 Accomplishments  2004 Accomplishments  Limited noise prediction system validation against wind tunnel measurement for both thickness and loading noise  Systematically unraveling the source of maneuver noise  Transient maneuver noise for climb, acceleration maneuver flights.  Compute maneuver noise with BVI using UMD maneuver wake  Rotor wake interaction analyzed for elemental maneuvers  Roll maneuver, quick stop, roll reversal maneuvers  2005 Planned Accomplishments  Investigate issues of signal processing for aperiodic conditions  RCAS maneuver model with free vortex-wake model

24. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 24 Milestones 20012002 2004 2005 CODE DEVELOPMENT: Initial aircraft motions and complete rotor motions Validate with WOPWOP Self-scheduling parallel implementation Coordinate transformation enhancements Acoustic analysis of non-periodic time history data “Flight-test” modeling (GENHEL coupling) Efficiency enhancements (real-time?) ANALYSIS Determine spatial regions where noise depends strongly on wake. Simple maneuvers analysis Simple flight path and attitude determination Validation (with data – flight or wind tunnel) Advanced wake modeling (RCAS or UMD maneuver wake) 2003 Schedule and Milestones Complete In Progress / Near Term Long Term Moved from last year’s schedule

25. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 25 Technology Transfer Activities  Papers:  AHS Specialists’ Meeting, San Francisco, Jan 2004  AIAA Aerospace Science Meeting and Exhibit, Jan 2004  AIAA/CEAS Aeroacoustics Conference, May 2005  AHS Annual Forum, Grapevine, TX, June 2005  Other Interactions:  Collaboration with Gordon Leishman, University of Maryland  Work with Professor Horn: GENHEL coupling and work toward acoustic prediction capability in new flight simulator

26. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 26  Recommendations at the last review (2004)  It is recommended to pick concrete physical problems and a firm plan is needed to solve physics or physical mechanisms, such as effects of roll or Lock number on noise. And also validation of analysis is needed for steady flight first, before deeply involved with maneuvering flight conditions.  Actions Taken (2004)  Some validation for steady flight performed  Focus on physical mechanisms of associated with aircraft roll, including BVI noise in maneuver  Gaining understanding of role of BVI and nonimpulsive noise in maneuver  Leveraging or Attracting Other Resources or Programs  DURIP equipment funding for RCOE  124 processor RCOE parallel cluster  Rotorcraft flight simulator with acoustic simulation capability  NASA LaRC contract for high-speed maneuver noise prediction modifications to PSU-WOPWOP (Burley/Boyd)  Teamed with Georgia Tech for DARPA “Helicopter Quieting” Project  Phase I SBIR with Continuum Dynamics for real-time rotor noise prediction (NASA LaRC) Other Impact

27. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 27 Any Questions … ?

28. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 28 Auxiliary Presentation Material

29. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 29 Validation of GENHEL/PSU-WOPWOP: Comparison with Wind Tunnel Data Microphone 1, M AT =0.796 Microphone 7, M AT =0.796 Microphone 1, M AT =0.690 Microphone 7, M AT =0.690 Side View Microphone 7 30 Deg. 1. 5 D Microphone 1 Top View 1.5 D In-plane Microphones measured (Visintainer et al., 1993) Predicted (GENHEL/PSU-WOPWOP)

30. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 30 80-Second Maneuver Flight Simulation  Helicopter gross weight: 74800N  4-bladed articulated main rotor and tail rotor  Main rotor radius: 8.18 m ManeuverStart TimeEnd Time Levelt = 0 sect = 1 sec Climbt = 1 sect = 14 sec Accelerationt = 1 sect = 18 sec Levelt = 14 sect = 22 sec Coordinated Turnt = 22 sect = 56 sec Levelt = 56 sect = 80 sec Pilot controlsAircraft response

31. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 31 Arrested Descent Wake (From UMD, Ananthan & Leishman)

32. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 32 PSU-WOPWOP Validation Comparison with WOPWOP  Thickness and loading noise predictions validated Operating conditions: UH-1H model scale untwisted rotor M H =0.88 Observer at 3.09 R in plane Rotation only (hover)

33. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 33 Main rotor blade description Lower surface Upper surface Tip  Permeable surface formulation  Coupling with CFD for high-speed- impulsive noise  Object oriented approach  Modularity and flexibility for complex rotor configuration PSU-WOPWOP Features

34. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 34 Arrested Descent Maneuver  Starts from 6º flight path angle and μ=0.186.  A half-doublet collective pitch input applied between t = 5 and t = 6 s.  At the end of the maneuver, the helicopter is pitched up by over 20º.

35. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 35 Acoustic Pressure Prediction    Free Vortex-Wake Model – ● – Pitt-Peters Inflow Model Observer location Ψ=135º, 22º below the helicopter and 7R away.

36. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 36 Summary For Arrested Descent  This arrested descent maneuver is a simple maneuver by applying collective pitch input.  In the steady descent condition, BVI is not dominant source of noise due to steep flight path angle.  In this maneuver, the primary effect of the maneuver is that the rotor wake goes through the rotor disk resulting in several BVIs in the rear of the disk that are nearly parallel to the rotor blade during the interactions.  Less BVIs were observed after the maneuver due to helicopter attitude.

37. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 37 height deceleration Arrested Descent Case Description –Initial condition: 3 degree steady descent –Total time: 2 sec –Flight speed: 40 m/s Descent arrested by collective pulse

38. Kenneth S. Brentner, Dept. of Aerospace EngineeringRCOE Review, May 3, 2005 38 Sound Pressure Level Computation Discrete Fourier Transform Compute sound pressure level Move slice of data Frequency analysis issues – Non-periodic signal – Noise widely fluctuating in amplitude and frequency Extract slice of data Apply Hanning Window