PENNSTATE1 8 5 5

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 ReviewMay 3, 2005Bell 214

Comanche

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.

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

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

Turbulence ModelsApproximate Equations

ExactEquations

DNSTimeAverage Unsteady,

SpatiallyFilter

LESUseBoussinesqassumption

Do not useBoussinesq

Reynolds Stress Model

(7 new PDE’s)

AlgebraicModels

(e.g. Baldwin-Lomax)

1 EquationModels

(Spalart-Allmaras)

2 Equation Models

(K- & K-)

MorePhysics

LessCPUTime

These are about as good as they are going to get --and they are not good enough for rotorcraft !!

DES combines

these

ndissipatio

k

jik

k

ijk

production

k

ikj

k

jki

tionredistribupressure

ijk

k

i

j

j

i

diffusion

ikjjkikjik

advection

kjik

ji

x

u

x

u

x

Vuu

x

Vuu

x

u

x

u

x

up

uuuuux

Vuux

uut

''

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~''

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3

2'''

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Reynolds Transport Equations

& RSMModel

Exact

Modelled12 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.

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

6:1 Prolate Spheroid (RSM)

Lateral Skin Friction Comparison at x/L = 0.738

Re = 6.5x106, M = 0.1322, = 30 deg

-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

90 100 110 120 130 140 150 160 170 180

[deg]

Cfla

t

ExperimentRSM Solution

•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.

6:1 Prolate Spheroid (RSM)

RSM Solution Measurement

Circumferential Location of Primary Separation [degrees]

~ 105 ~ 108

Circumferential Location of Secondary Separation [degrees]

~ 159 ~ 156

• 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

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

RSM Solution & Experiment Sphere Re = 1.14x106 M = 0.1763

Circumferential Pressure Distribution of a Sphere

Re = 1.14x106

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0 20 40 60 80 100 120 140 160 180 [deg]

Cp

ExperimentRSM

Midplane Skin Friction Coefficient Distribution

Re = 1.14x106 , M = 0.1763

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 30.00 60.00 90.00 120.00 150.00 180.00

[deg]

Cf*

sq

rt(R

e) Experiment

RSM Solution

Achenbach, E., Journal of Fluid Mechanics, Vol. 54, No. 3, 1972, pp. 565 – 575.

Alpman, E., and Long, L. N., AIAA Paper 2005-1094, January, 2005

Sphere Re = 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

Sphere Drag Prediction Re = 1.14x106 M = 0.1763

CdExperiment

(Achenbach, JFM 1972)

0.13 ± 0.01

LES

(Jindal & Long, 2004)

0.141

RSM

(Alpman & Long, 2005)

0.141

RSM Solution for a Bell 214ST Fuselage

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

Computational MeshBELL 214ST

y+ ~ 40

Low Angle of attack Cruise Condition Re = 1.5x106 per ft M = 0.3322 (without rotors)

Dorsal Centerline Pressure DistributionRe = 1.5x106 ft-1, M = 0.2322, = -2.28 deg., = 0 deg.

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0 2 4 6 8 10 12 14

x (m)

Cp

RSM SolutionExperimental Data

Surface Pressure Distribution

Good agreement with the measurements.

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.

High Angle of Attack and High Yaw Angle Conditions (without rotors)

Dorsal Centerline Pressure Distribution

Re = 1.5x106 ft-1, M = 0.2322, = -17.0 deg., = 0 deg. -2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

0 2 4 6 8 10 12 14

x (m)

Cp

RSM SolutionExperimental Data

High Angle of Attack Condition High Yaw Angle Condition

Dorsal Centerline Pressure Distribution

Re = 1.5x106 ft-1, M = 0.2322, = -1.6 deg., = 16.4 deg.

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0 2 4 6 8 10 12 14

x (m)

Cp

RSM SolutionExperimental Data

Good agreement even when the expansions are quite abrupt

Good agreement with the measurementsexcept around the tail boom.

Mainly due to differences between wind tunnel and computational geometry

High Angle of Attack Condition

Normalized τxz contoursComputed Using RSM

Normalized τxz contoursComputed Using Boussinesq Hypothesis during post

processing

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.

Simulation with Main and Tail Rotors

Vertical velocity contourswithout rotors

Vertical velocity contoursT = 17500 lbs., Ttr = 1104 lbs

• Induced downwash velocities• Tip vortices at the edge of rotor plane

Simulation with Main and Tail Rotors

Normalized τyz contourswithout rotors

Normalized τyz contoursT = 17500 lbs., Ttr = 1104 lbs

Vortices generated by the main rotor affects downstream turbulence structure

Bell 214ST Total Drag Predictions Re = 1.5x106 per ft M = 0.3322 (without rotors)

= -2.28 and = 0

D/q (ft2) % Error

Wind Tunnel Data(Oldenbuttel,1978)

4.596 ?

LES prediction(Souliez & Long, 2002)

6.225 35.4

RSM Simulation(Alpman & Long, 2005)

5.405 17.6

RSM Simulation (with rotors)(total drag)

5.547 N/A

Bell 214ST Drag PredictionsRe = 1.5x106 per ft M = 0.3322 (without rotors)

= -2.28 and = 0

D/q (ft2)

% Erro

rWind Tunnel Data

(Oldenbuttel,1978) (total drag)4.596 ?

Bell Simulations(Narramore et.al. 1992) (pressure

drag)

5.466 18.9

RSM Simulation(pressure drag)

4.356 5.22

RSM Simulation(total drag)

5.405 17.6

90% ofTotalDrag

RANSSolutionInaccurate

Bell 214ST Drag PredictionsRe = 1.5x106 per ft M = 0.3322 (without rotors)

D/q (ft2) % Error

wind tunnel data(Oldenbuttel,1978) (total drag)

6.521 ?

RSM Simulation(total drag)

7.159 9.7

D/q (ft2) % Error

wind tunnel data(Oldenbuttel,1978) (total drag)

15.058 ?

RSM Simulation(total drag)

12.886 14.4

= 17 and = 0

= -1.6 and = 16.4

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 ?

Tasks 2001 2002 2004 2005

CompletedShort TermLong Term

2003Comparisons to experimental data - Cone & 3-D CylinderGeneric Fuselage Simulations - Robin Body w & w/o NLDER. Hansen Ph.D. Thesis

Bell 214ST grid & steady solutionUnsteady loads and drag F. Souliez Ph.D. Thesis

Grid and viscous flow over ellipsoidRe-Stress Model for turbulent flow over ellipsoidS. Jindal M.S. Thesis

Steady/unsteady Comanche flows Detailed compare of RSM & LESRe-Stress Model & LES for Bell 214Helicopter drag and unsteady flowsE. Alpman Ph.D. Thesis

Schedule / Milestones

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

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)

Technology Transfer: 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

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)

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.