Coupling SIMPACK with Helicopter Aerodynamics€¦ · Coupling SIMPACK with Helicopter Aerodynamics...
-
Upload
truongnguyet -
Category
Documents
-
view
247 -
download
4
Transcript of Coupling SIMPACK with Helicopter Aerodynamics€¦ · Coupling SIMPACK with Helicopter Aerodynamics...
Coupling SIMPACK with Helicopter Aerodynamics
Ludwig Krause,
Johannes Hofmann,
Stefan Surrey,
Maximilian Graser
SIMPACK User Meeting,
Oct. 9th 2014, Augsburg
• Motivation
• DLRs Rotor Code S4
• Coupled SIMPACK-S4 Environment
• SIMPACK Model
• Flexible Rotor Blade
• Cross Code Verification and Differences in Modelling
• Conclusion and Outlook
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014 DLR.de • Folie 2
Outline
• Complex helicopter aerodynamics requires appropriate modelling
S4 rotor code developed at DLR Institute of Flight Systems since 1980s
• Modeling of structural dynamics in S4 doesn‘t fulfill modern requirements
o Non-moving reference frame (isolated Rotors)
o Advanced Blade design requires complex, flexible blade models
• Constrained rotor movement most naturally handled within MBS-formalism
• MBS Software like SIMPACK enables integration of flexible bodies through
interface to commercial FEM-Codes (ANSYSY, NASTRAN, ABAQUS etc.)
• Goal: Develop fully coupled aeroelastic simulation environment between
SIMPACK (structural dynamics) and S4 (aerodynamics)
DLR.de • Folie 3
Motivation
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
DLR.de • Folie 4
Rotor Modelling: Modules of S4
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• Comprehensive code very fast and accurate
• Interface for loose coupling to DLR CFD Codes Flower and Tau
• BVI (Blade-Vortex Interaction) Prediction (Noise)
Exact knowledge of blade position needed!
• Validated with wind tunnel data in several international test campaigns
DLR.de • Folie 5
S4 –Assets
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• Strong coupling: Data exchanged between both codes at every time step
• Data transferred through SIMPACK IPC Co-Simulation Interface
• Strictly speaking: No Co-Simulation!
• Equation of Motion solely solved by SODASRT 2 S4 solver discarded
• Interface programmed in C and integrated in S4 FORTRAN code
DLR.de • Folie 6
Coupled S4-SIMPACK Environment
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• 4-bladed rotor, each blade imported from NASTRAN as a beam element
• Per blade: o 20 aerodynamic marker along the c/4 line
o 20 sensors to measure blade element translational and rotational position/orientation,
velocity and acceleration
o 18x20=360 y-outputs to transfer sensor output to S4 (6 DOF per node)
o 6x20=120 u-vectors and u-inputs to import aerodynamic forces and moments
o 20 force elements at respective aerodynamic markers to apply these forces
• Further u-vectors/u-inputs for rotational speed and pitch regulation
Modell creation fully automated through QtScript
DLR.de • Folie 7
SIMPACK Model - 1
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• Additional elements/bodies incorporated to account for:
• Lag/Flap, torsion joint
• Control rods, hub, clamp, cell
• For verification purpose:
• Fixed rotor hub
• Rigid control rod
DLR.de • Folie 8
SIMPACK Model - 2
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• Beam-Element generated in NASTRAN
• Verified in NASTRAN to 3D- Volume Element w.r.t. Eigenfrequencies and –modes
• Further validated through modal testing
• To incorporate into SIMPACK, 2 calculations in NASTRAN were conducted:
DLR.de • Folie 9
The Test Blade - 1
1. Eigenvalue analysis of elastic beam
2. Static solution under initial tension to account
for geometric stiffening
0
1
2
3
4
5
6
7
8
9
10
11
12
13
0 0,2 0,4 0,6 0,8 1 1,2
ω/Ω
ref
Ω/Ωref
S4
SIMPACK
1st lag
1st torsion
3rd lag
2nd torsion
1/rev
5/rev
6/rev
4/rev
3/rev
2/rev
9/rev
8/rev
7/rev
10/rev
11/rev
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
DLR.de • Folie 10
The Test Blade - 2
-1,0
-0,5
0,0
0,5
1,0
0,0 0,4 0,8 1,2 1,6 2,0ΦFl
ap
r [m]
Simpack
S4
-1,0
-0,5
0,0
0,5
1,0
0,0 0,4 0,8 1,2 1,6 2,0
ΦLa
g
r [m]
SimpackS4
-1,0
-0,5
0,0
0,5
1,0
0,0 0,4 0,8 1,2 1,6 2,0ΦTo
rsio
n
r [m]
Simpack
S4
Lag
Flap
Torsion • SIMPACK beam imported from Nastran compared to
beam from S4-FEM-preprocessor by means of
eigenfrequencies and eigenmodes
• Eigenfrequencies and eigenmodes calculated at 100 %
rotational speed (=109 rad/s) geometrical stiffening !
• Max. deviation for eigenfrequencies at 1. Torsion (6.55 %)
• Deviation in eigenmodes negligible
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• Test Case: o 1 Blade
o Hover flight
o Thrust 1200 N
Still considerable deviations in lag and
torsion!
Still differences in modelling between S4
and SIMPACK:
DLR.de • Folie 11
First Results for Hover
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
flap
lag
torsion
SIMPACK S4 Verification
Fully coupled motions Structurally uncoupled motions Coupled motions implemented in S4 (simplified)
Blade is structurally pitched Only forces are transformed Fixed structural pitch in SIMPACK
Centrifugal terms depend on deformation Centrifugal terms depend only on RPM No compensation (deviation <2%)
No propeller moment in SIMPACK Formulation for a flat plate Additional force-element in SIMPACK
DLR.de • Folie 12
Differences in Modelling – Secondary Components
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
flap
lag
torsion
• Offsets between mass and elastic axes + pretwist lead
to coupled motions
No pure flap, lag or torsion motion
• S4 used only dominant mode shapes so far
Sufficient assumption for most cases so far
Secondary components added to dynamic response
calculation in S4 (simplified)
Discrepancy in lag deflection almost completely
disappeared
DLR.de • Folie 13
Differences in Modelling – Propeller Moment
SIMPACK S4 Verification
Fully coupled motions Structurally uncoupled motions Coupled motions implemented in S4 (simplified)
Blade is structurally pitched Only forces are transformed Fixed structural pitch in SIMPACK
Centrifugal terms depend on deformation Centrifugal terms depend only on RPM No compensation (deviation <2%)
No propeller moment in SIMPACK Formulation for a flat plate Additional force-element in SIMPACK
With Propellermoment Without Propellermoment
Including propeller moment into SIMPACK using an additional force element
deviation in torsion eigenmodes disappears
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
DLR.de • Folie 14
Verification in Hover
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
• After implementing secondary components
and propeller moment deviations negligible
• 2 explanations for slight deviation in flapping:
1. Centrifugal terms in SIMPACK depend on
deformation
2. Simplified approach for secondary mode
components in S4
• Accuracy of results largely independent of
load case
• Coupling chain verified for hover flight
• Tight fluid-structure coupling between comprehensive rotor code S4 and
SIMPACK has been established
• Using 1D-beam elements for the flexible rotor blades leads to underestimation
of torsional deflection additional force elements needed
• Further complex test cases have to be investigated
o Forward flight
o Advanced blade design
• Still a lot of verification needed until SIMPACK-S4 can be used to simulate the
complex aeroelastics of helicopter rotors
• Coupling environment can be extended to overall helicopter simulation to take
full advantage of SIMPACKs MBS formalism
DLR.de • Folie 15
Conclusion and outlook
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014
DLR.de • Folie 16
Thank you for your attention!
> SIMPACK UM `14 > Ludwig Krause• Coupling S4 and SIMPACK > 09.10 2014