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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
Bell 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 Models
Approximate
Equations
Exact
Equations
DNS
Time
Average
Unsteady,
Spatially
Filter
LES
Use
Boussinesq
assumption
Do not use
Boussinesq
Reynolds Stress
Model
(7 new PDE’s)
Algebraic
Models
(e.g. Baldwin

Lomax)
1 Equation
Models
(Spalart

Allmaras)
2 Equation
Models
(K

& K

)
More
Physics
Less
CPU
Time
These are about as good as they are going to get

and they are not good enough for rotorcraft !!
DES
combines
these
n
dissipatio
k
j
ik
k
i
jk
production
k
i
k
j
k
j
k
i
tion
redistribu
pressure
ij
k
k
i
j
j
i
diffusion
ik
j
jk
i
k
j
i
k
advection
k
j
i
k
j
i
x
u
x
u
x
V
u
u
x
V
u
u
x
u
x
u
x
u
p
u
u
u
u
u
x
V
u
u
x
u
u
t
'
'
'
'
~
'
'
~
'
'
'
3
2
'
'
'
'
'
'
'
'
'
'
~
'
'
'
'
Reynolds
Transport
Equations
& RSM
Model
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.
RSM Solution for a 6:1 Prolate
Spheroid
Re = 6.5x10
6
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 = 6.5x10
6
, 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]
C
f
lat
Experiment
RSM 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 = 1.14x10
6
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 = 1.14x10
6
M = 0.1763
Circumferential Pressure Distribution of a Sphere
Re = 1.14x10
6
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
Experiment
RSM
Midplane Skin Friction Coefficient Distribution
Re = 1.14x10
6
, 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*sqrt(Re)
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 = 1.14x10
6
M = 0.1763
Normalized τ
xx
contours
Normalized τ
xz
contours
•
In isotropic turbulence, normalized τ
xx
and τ
xz
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 = 1.14x10
6
M = 0.1763
Cd
Experiment
(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 = 1.5x10
6
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 Mesh
BELL 214ST
y+ ~ 40
Low Angle of attack Cruise Condition
Re = 1.5x10
6
per ft M = 0.3322 (without rotors)
Dorsal Centerline Pressure Distribution
Re = 1.5x10
6
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 Solution
Experimental 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 = 1.5x10
6
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 Solution
Experimental Data
High Angle of Attack Condition
High Yaw Angle Condition
Dorsal Centerline Pressure Distribution
Re = 1.5x10
6
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 Solution
Experimental Data
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
High Angle of Attack Condition
Normalized
τ
xz
contours
Computed Using RSM
Normalized
τ
xz
contours
Computed 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 contours
without rotors
Vertical velocity contours
T = 17500 lbs., Ttr = 1104 lbs
•
Induced downwash velocities
•
Tip vortices at the edge of rotor plane
Simulation with Main and Tail Rotors
Normalized
τ
yz
contours
without rotors
Normalized
τ
yz
contours
T = 17500 lbs., T
tr
= 1104 lbs
Vortices generated by the main rotor affects downstream
turbulence structure
Bell 214ST Total Drag Predictions
Re = 1.5x10
6
per ft M = 0.3322 (without rotors)
=

2.28 and
= 0
D/q (ft
2
)
% 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 Predictions
Re = 1.5x10
6
per ft M = 0.3322 (without rotors)
=

2.28 and
= 0
D/q
(ft
2
)
%
Err
or
Wind 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% of
Total
Drag
RANS
Solution
Inaccurate
Bell 214ST Drag Predictions
Re = 1.5x10
6
per ft M = 0.3322 (without rotors)
D/q (ft
2
)
% Error
wind tunnel data
(
Oldenbuttel,1978)
(total drag)
6.521
?
RSM Simulation
(total drag)
7.159
9.7
D/q (ft
2
)
% 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
Completed
Short Term
Long Term
2003
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
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.
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