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7/28/2019 Aerodynamics Recent Developements
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DEVELOPMENTS IN APPLIED AERODYNAMICS AND
FLIGHT MECHANICS OF UNMANNED AERIAL VEHICLESby
Dominic D. J. Chandar, Mark Leon C.S. Tan and M. Damodaran
Dr. Murali Damodaran
Associate ProfessorSchool of Mechanical and Aerospace Engineering
Nanyang Technological University
5 APRIL 2008
presented by
5- 6 April 2008,
Indian Institute of Technology, Kanpur
INDIA
2nd Joint Workshop in
Mechanical, Aerospace and Industrial
and Management Engineering
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FIXED WING
ROTARY WING/DUCTED FAN
FLAPPING WING
MORPHED CONFIGURATIONS
Unmanned Aerial Vehicles
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OVERVIEW
1. CFD Simulation of Low Reynolds NumberFlapping Wing Aerodynamics
- with Dominic
2. Integrated Computational Framework for
Aerodynamics, Flight mechanics and Control
of Fixed Wing UAVs.
- Mark Leon Tan C S
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Overture / OverBlownOverture / OverBlown
Overture Framework
Overset
Moving
grids
Overset Flow
Solver (Over-Blown)
Parallel
Computing on
Stationary
Grids A++ Framework
Faster ArrayManipulation
InterfaceWith
PETSc
DeformingBody Motion with
GCL
(Added Recently)
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LOW REYNOLDS NUMBER FLAPPING WING
AERODYNAMICS MODELING
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OVERLAPPING / COMPOSITE / OVERSET / CHIMERA MESH
Individual Component Meshes
generated independently
Ogen MeshOgen Mesh
GeneratorGenerator
LOW REYNOLDS NUMBER FLAPPING WINGAERODYNAMICS MODELING
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INTERPOLATION BETWEEN MESHES
EXPLICIT
IMPLICIT
SOLUTION AT INTERPOLATION POINTS IS OBTAINED FROM
DISCRETIZATION POINTS OF NEIGHBORING GRID
SOLUTION AT INTERPOLATION POINTS IS OBTAINED FROM
INTERPOLATION & DISCRETIZATION POINTS OF
NEIGHBORING GRID
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INTERPOLATION BETWEEN MESHES
Interpolation Weights
For 2nd order Scheme : Width of
Interpolation = 3 (Quadratic)
U(i,j)
In 1D
Width of discretization = Width of Interpolation
If Overlap ~ Constant x MeshSize : Width of Interpolation = 2pr + 1
2p = Order of PDE, 2r = Order of Discretization
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INTERPOLATION BETWEEN MESHES
Vortex On The Interpolation Boundary
Chandar and Damodaran, AIAA J, Vol 46, No2, 2008, pp 429-438
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x = G (r,t)
INTERPOLATION ON DYNAMIC MESHES
NO REMESHING
ONLY INTERPOLATION POINTS CHANGE
RIGID BODY MOTION
How About Deforming Bodies ?
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OVERLAPPING / COMPOSITE / OVERSET / CHIMERA MESH
DEFORMING WING
Hyperbolic mesh generation at each timestep.
Marching distance from the boundary
limited to a small radius
Jacobian at each deforming point follows
the Geometric Conservation Law (ONLY
for the mesh surrounding the wing)
0J
J J Jt t t t
+ + + =
J = Jacobian of the transformation x=x(,, ) ;
,, are Computational Coordinates
Deforming Wing -Video
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OVERLAPPING / COMPOSITE / OVERSET / CHIMERA MESH
DEFORMING WING
Hyperbolic mesh generation at each time
step.
Marching distance from the boundary
limited to a small radius
Jacobian at each deforming point follows
the Geometric Conservation Law (ONLY
for the mesh surrounding the wing)
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Prescribed motion (Active flight).
Motion determined from the forces (Passive Flight)
Weakly Coupled Navier-Stokes- Newtons Law
x=x0sin(2ft),
=0sin(2ft)
,A i i k ki
d
F pn n dS
= ( )cmd
T r x dF
= 2
2
cmA
d xF
dt
dJ Tdt
=
= , i i iJ I e=
Ti i iI e = i ie e=
OrientationOrientation
PositionPosition
LOW REYNOLDS NUMBER FLAPPING WINGAERODYNAMICS MODELING
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Unsteady Low Reynolds NumberUnsteady Low Reynolds Number
Flow ProblemsFlow Problems Coupling With 6DOF ModelCoupling With 6DOF Model
Free Flight of a Flapping Wing
Fluttering / Tumbling of Cards
Reverse Hysteresis Effects
Numerical computations aid in analyzing
The key parameters responsible for
Flutter / Tumble of a Falling Card
The onset of Forward Flight due to Flapping
Can be determined
Can Lift drop with increase in
Angle of attack ?? Computations do reveal
This fact for pitching above certain
frequencies
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Fluttering and Tumbling of Cards
Falling Rectangular Card
Re = 630
Aspect Ratio = 2
Trajectory
Angles ~ ei . ei
e1
e2
e3
e1
e2
e3
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x
yz
Y-Vorticity X-Z Plane
Z-Vorticity Z-Vorticity
Vorticity Magnitude
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Free fall of a Rectangular card Wang, J ( 2005 )Free fall of a Rectangular card Wang, J ( 2005 )
70cm
45 cm
30 cm
L = 0.648 cm h = 0.081 cm
w = 19 cmRe = 837
Mesh ~ 512 x 256
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Trajectory
Fx
Fy
Streamlines
Vorticity
Free fall of a Rectangular card Wang, J ( 2005 )Free fall of a Rectangular card Wang, J ( 2005 )
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Autorotation / Flutter of Rectangular PlatesAutorotation / Flutter of Rectangular Plates
Pinned at the centre of mass
Inflow
( )* 21 112
b
f
I
= +Non-dimensional Moment of Inertia
Density of plate / Density of fluid
Thickness to chord ratio
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Autorotation / Flutter of Rectangular PlatesAutorotation / Flutter of Rectangular Plates
0.1= 0.5=
1.0=
log (|vorticity|)
vorticity
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Autorotation / Flutter of Rectangular PlatesAutorotation / Flutter of Rectangular Plates
A pinned card excited by aerodynamic forces will
attain any one of the three states of motion
High density and large thickness high inertia
rotates slowly
For low frequency oscillations, frequency of vortex
shedding is greater than frequency of rotation
For high frequency oscillations, frequency of vortexshedding is less than the frequency of rotation.
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Autorotation / Flutter of Rectangular PlatesAutorotation / Flutter of Rectangular Plates
0.2= 0.5=
Comparison with the numerical results of Mittal.R et al (2004)
Lift Coefficient
Not Flutter as pointed out by Mittal et.al but a state of low frequency / amplitude#oscillation
#Chandar and Damodaran, Unsteady Low Reynolds Number Aerodynamics of Flapping,
Fluttering and Tumbling, AIAA J In Review
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Autorotation / Flutter of Elliptical PlatesAutorotation / Flutter of Elliptical Plates
Comparison with the numerical results of Lugt (1981) : Forced Rotation
Moment coefficient for different Reduced frequencies (k)
K = 0.167 K = 0.25
K = 0.5 K = 1.0
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FREE-FLIGHT OF A FLAPPING WINGFREE-FLIGHT OF A FLAPPING WING
Mass = 1.207
Aspect Ratio = 2.0
Re = O(100)
t/c = 10 %
Frequency f= 1.5 Hz
0
01
sin(2 ) 0,1, 2
0
,k k kf t k
= =
=
Flap for One cycle with Centre of mass fixed then let it freeFlap for One cycle with Centre of mass fixed then let it free
x
y
z
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VORTICITY FIELDSVORTICITY FIELDS
X- Vorticity
Z- Vorticity Vorticity Magnitude
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Thrust over One CycleThrust over One Cycle
A
B
C D
E
Thrust Angular position of wing
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Trajectory and Forward SpeedTrajectory and Forward Speed
Position of centre of mass Forward speed
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Wing in Constant Speed Rotation after a Fast StartWing in Constant Speed Rotation after a Fast Start
x
y
z
Re = 100
Aspect Ratio = 2
t/c = 0.12
0
0
0.5 (1 cos( )), 0 1
1
,
t t
t
=
= >
Lan and Sun (2001)
Dickinson et. al (1999)
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Wing in Constant Speed Rotation after a Fast StartWing in Constant Speed Rotation after a Fast Start
Volume meshes on wing tip caps
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Wing in Constant Speed Rotation after a Fast StartWing in Constant Speed Rotation after a Fast Start
+ OverBlown -102,600 points (coarse~ Wing + wing caps)
* Lan and Sun (2001) 359,055 points
CL (OverBlown) = 1.08
CL (Lan and Sun) = 1.00
CD (OverBlown) = 1.06
CD (Lan and Sun) = 1.01Steady
State
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Recent Developments - Deforming Airfoil ComputationsRecent Developments - Deforming Airfoil Computations
Development of an Interface to
Visualize Deforming Body
Problems
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Deforming Motion Class - ValidationDeforming Motion Class - Validation
( , ) ( ) sin( ) sin( )0
py x t y x Ax t kx B t = + + + +
Initial Profile Wave-like profile Rigid translation
RIGID BODY PLUNGING USING THE
DEFORMING BODY CLASS
A = 0, B = 0.4, = 2, Re = 10,000
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Deforming Airfoil ComputationsDeforming Airfoil Computations
( , ) ( ) sin( ) sin( )0
py x t y x Ax t kx B t = + + + +
A = 0.1, p =2, k =0, = /2, B =1 A = 0.3, p =2, k =0, = /2, B =1
A = 0.2, p =3, k =1, = 0, B =0
Filament-like flapping
Re = 10000
Re = 1000
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Deforming Airfoil ComputationsDeforming Airfoil Computations
Two Filaments deforming
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Integrated FlightDynamics Model of
a UAV
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Overview of Flight Dynamics and ControlOverview of Flight Dynamics and Control
Develop Integrated Computational Model to:
Address the Stability and Control Problem
Assist in Formulation of Flight Control Law
Use CFD to generate unavailable UAV aerodynamic data andto provide a basis for developing control law
Estimate unavailable UAV stability and control derivatives
Analyze impact of various flight control systems tomitigate the flight stability problem
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Integrated Computational Framework for Aerodynamics,Integrated Computational Framework for Aerodynamics,Flight Dynamics and Control ofFlight Dynamics and Control ofUAVsUAVs
Simulate Using Matlab/Simulink
drivenAerospace Blockset/AeroSim
MINDEF RSAF Air Logs
DSTA Funded Project@NTU
July 2005-July 2007
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Flight Dynamics ModelFlight Dynamics Model
Simulate Using Matlab/Simulink driven Aerospace Blockset/AeroSim
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Design of Dutch Roll Damper Dutch roll damper
Suppress the natural dynamics of the dutch roll
To desensitize the overall damping to the variation of flightparameters
Provide damping with respect to inertia space
r
a
0 +
-
u
BuAxx +=
Plant
C
ks
s
+
Aircraft
Dynamics
Dutch Roll
Damper
Open LoopAnalysis
Obtain desired
freq & damping
Close loop
analysis
Modification of
System
Design Cycle
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Design of Dutch Roll Damper
r
a
0 +
-
u
BuAxx +=
Plant
C
Need to obtain
the gain for the
feedback loop
Aircraft Dynamics
Rudder ControlSurface as the
key controller
Yaw Rate output
Dutch Roll
Damper
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Flight Dynamics ModelFlight Dynamics Model Simulation inSimulation in FlightGearFlightGear
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CONCLUDING REMARKS
CFD Simulation of Low Reynolds Number Aerodynamics of Flapping
Wing, Tumbling and Fluttering Plates etc.
Coupling of Structural Dynamics and CFD to model flexible flapping
wings the next step.
Integrated Framework to be developed to include rotary wing and
flapping wing MAVs/UAVs
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THANKTHANK
YOUYOU