Numerical Simulations of the
Aerodynamic Characteristics of
Circulation Control Wing Sections
A Thesis Proposal
By
YI LIU
Advisor: Dr. L.N.SANKAR
Supported by NASA
OVERVIEW
• Motivation and Objectives
• Background and Circulation Control Concept
• Mathematical and Numerical Formulation
• Solution Procedure
• Initial and Boundary Conditions
• Results and Discussion
• Code Validation for a NACA 0012 Wing
• Steady Blowing Results
• Pulsed Jet Results
• Preliminary Conclusions
• Proposed Work
Motivation and Objectives
• Noise pollution from the large aircraft has
become a major problem that needs to be
solved.
• A major source of large aircraft airframe noise
during take-off and landing is the high-lift
system - namely flaps, slats, flap-edges and
gaps.
• An
alternative to conventional high-lift
systems is the Circulation Control Wing
(CCW) technology.
Circulation Control Wing Concept
• Circulation Control Aerodynamics: In this approach a tangential jet
is blown over a highly curved aerodynamic surface (the Coanda
surface) to increase or modify the aerodynamic forces and moment
with few or no moving surfaces.
• Fig. 1 (Paper by Robert Englar) shows the traditional Circulation
Control Wing Airfoil with a rounded trailing edge.
Advanced Circulation Control
Wing Airfoil
• Use a small trailing edge flap with a large-radius arc
upper surface and a flat low surface.
• Flap can be deflected 00 < f < 900.
• During cruise, f = 00, leading to a conventional
airfoil shape with a sharp trailing edge.
Benefits of the CCW Wing
Pneumatic Airfoils Simplify Wing Complexity
(Paper by Robert Englar)
Related Research Work
• Experimental studies show that very high lift coefficient
values (as high as 8.5 at a=0) can be achieved by
CCW technology (Englar).
• Numerical studies of the dynamic stall characteristics of
the Circulation Control Wing airfoil have also been done
(Shrewsbury).
• Aeroacoustic characteristics of CCW configurations are
being studied at GTRI (Ahuja and Munro).
• Several synthetic and pulsed jet studies have also been
reported (Wygnansky, Lorber, Wake, Hassan and
Oyler). These studies have primarily focused on the
boundary layer separation control or conventional
rounded trailing edge CCW airfoils.
Mathematical and Numerical
Formulation
• Three-dimensional compressible unsteady Reynolds
Averaged Navier-Stokes equations are solved in a
strong conservation form on curvilinear coordinates.
• This solver can be used in both a 2-D mode and a 3-D
mode in this study for different applications.
• The scheme is second or fourth order accurate in space
and first order accurate in time.
• Baldwin-Lomax and Spalart-Allmaras one-equation
turbulence models have been used.
• The jet slot location, slot size, blowing velocity and
direction of blowing can easily be varied in the analysis.
Initial and Boundary Conditions
• Initial flow conditions are set to free stream
values inside the flow field.
• Boundary Conditions
• Outer Boundary
• Solid Surface Boundary
• Wake Cut Boundary
• Jet Slot Exit Boundary
Jet Slot Boundary Conditions
• The driving parameter for jet blowing is the
momentum coefficient, Cm, defined as follows:

Vjet * m
Cm 
1
2
S *   V
2
   jet Vjet * A jetis the mass flow rate of jet flow
Where m
• We specify Cm, orientation of the jet and the total
temperature of jet.
• Other quantities such as pressure and density are
found by extrapolation and /or Ideal Gas Law.
Code Validation
-3.5
-3
-3
-2.5
34% S P AN
-2.5
U pper- Exp
Low er -Exp
Low er C al
U pper C al
66% S P AN
U pper Exp
Lower Exp
-2
Lower C al
-2
U pper C al
-1.5
-1.5
-0.5
-0.5
0
0
0.5
0.5
1
1
1.5
0
0.2
0.4
0.6
0.8
1
1.5
1.2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.9
1
CHORD
CHORD
-2.5
• The figures are the Cp distribution
at three span locations of a small
aspect-ratio wing made of NACA
0012 airfoil sections.
• The results are in good agreement
with the measured data (from Bragg
and Spring) except near the tip
region where increased grid
resolution is needed.
85% SPAN
-2
Upper
Lower
Lower
Upper
-1.5
Exp
Exp
Cal
Cal
-1
Cp
Cp
-1
Cp
-1
-0.5
0
0.5
1
1.5
0
0.1
0.2
0.3
0.4
0.5
CHORD
0.6
0.7
0.8
The CCW Airfoil
0.5
0.4
0.3
Jet Slot Location
0.2
0.1
0
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
-0.2
30 degree integral flap
-0.3
-0.4
-0.5
1
Flow Conditions
• P = 14.2 psia = 0.9324 atm
•  = 0.00225 slugs/ft3 = 1.1596 kg/m3
• V = 94.3 ft/sec = 28.743 m/s
• M = 0.0836, Re = 0.395 * 106
• Chord of the Airfoil : C = 8” = 0.20 m
• Jet Slot Height : h = 0.015” = 0.0004 m
• Jet slot is located at x/c = 88.75% on the upper side of
the airfoil.
• These values closely match the test conditions.
Steady Blowing Results
Computed vs. Measured Variations of Lift Coefficient with
Momentum Coefficient
5
4
Cl
3
2
Cl, Computed
Cl, Measured
1
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Cm
Angle of Attack 0 degrees, Integral Flap at 30 degrees
Variation of Lift Coefficient with Angle of Attack
4
Leading Edge Stall
Cmu=0.1657
3
Cmu=0.111
Cl
Cmu=0.0566
2
Cmu=0.0
1
0
-2
0
2
4
6
Angle of Attack
8
10
12
Time History of Lift Coefficient for the
Unblown Case
0.9
0.88
t = 1.578693
msec
0.86
t = 4.128484 msec
t = 6.678274 msec
0.84
Cl
0.82
0.8
0.78
0.76
0.74
0.72
0.7
0
1
2
3
4
5
6
7
8
9
10
Time (msec)
• The Vortex Shedding Frequency is about 400 Hz for this case (Strouhal No. =
2.828).
• In the acoustic experiments, two frequencies were measured (Strouhal No. =
1.67, 4.73).
Pressure Contours for the Unblown
Case
Stream Function Contours when Blowing is
Applied
Comparison with Conventional
High-lift Systems
• The figures show the high-lift systems configuration with a 300
fowler flap and the body-fitted grid.
• The results are obtained with a 2-D multi-block version of the
present method.
1
0.9
0.8
Multi-element Airfoil at Different Angle of Attack
Drag Coefficients
0.7
30 Degree Flap CCW Airfoil, Cd not corrected
0.6
30 Degree Flap CCW Airfoil, Cd corrected by Cd+Cmu
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
Lift Coefficients
• For the multi-element airfoil, high lift is achieved by changing the angle
of attack; For the CCW airfoil, high lift is achieved by changing the
blowing coefficient while the angle of attack is fixed at 0 degrees.
Pulsed Jet Results
• Pulsed jet studies were done to answer:
---- Can pulsed jets be used to achieve desired increases
in the lift coefficient at lower mass flow rates relative
to a steady jet?
----What is the optimum wave shape for the pulsed jet,
ie, how should it vary with time?
---- What are the effects of the pulsed jet frequency
on the lift coefficient?
•
Cm t   Cm ,0  Cm ,0 F  f , t 
• Sinusoidal and Square wave form variations were
considered. Sinusoidal forms were found ineffective.
Momentum Coefficient Variation with Time for Pulsed Jet
Square Wave Form, Frequency = 40 Hz
0.09
t= 0.025002
1 / 40(sec)
sec
Dt
0.08
0.07
0.06
0.05
Cm
Cm
0.04
0.03
0.02
0.01
0
0.44
0.45
0.46
0.47
Time (sec)
0.48
0.49
0.5
Variations of Incremental Lift Coefficient with
Time-Averaged Momentum Coefficient, Cm
Comparison of Steady Jet with Pulsed Jet
3
Steady Jet
Pulsed Jet , f = 40Hz
Pulsed Jet, f = 120 Hz
Pulsed Jet, f = 400 Hz
2.5
• Cl= Clblowing- Clnonblowing
•Steady jet is continuously on, while the
pulsed jet is operational only half the time
during each cycle.
Cl
2
1.5
1
0.5
0
0
0.02
0.04
0.06
0.08
0.1
Time-Averaged Momentum Coefficient, Cm0
0.12
0.14
Variations of Incremental Lift Coefficient with
Time-Averaged Mass Flow Rate
Comparison of Steady Jet with Pulsed Jet
3
• The average mass flow
rate of a pulsed jet is just
about 70% of the steady jet
at the same Cm0 value.
2.5
2
Cl
2
  V jet
C m  V jet
and m
1.5
1
Steady Jet
Pulsed Jet , f = 40 Hz
Pulsed Jet ,f = 120 Hz
Pulsed Jet, f = 400 Hz
0.5
0
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
Time Averaged Mass Flow Rate (slugs/sec)
0.0014
0.0016
Variation of Efficiency (Cl/(Cd+Cm)) with
Time-Averaged Momentum Coefficient, Cm
Comparison of Steady Jet with Pulsed Jet
25
Steady Jet
Pulsed Jet , f = 40 Hz
Pulsed Jet , f = 120 Hz
Pulsed Jet, f = 400 Hz
Cl/(Cd+Cm)
20
15
10
5
0
0
0.02
0.04
0.06
0.08
0.1
Time-Averaged Momentum Coefficient, Cm
0.12
0.14
Average Lift Coefficient Vs. Frequency For Pulsed Jet
The Time-Averaged Momentum Coefficient is 0.04
2
1.6
Pulsed Jet at 400 Hz requires only
73% of the steady jet mass flow
rate while achieves 95% of the
steady jet lift.
Cl
1.2
0.8
0.4
Pulsed Jet, Ave. Cmu=0.04
Steady Jet, Cmu=0.04
0
0
40
80
120
160
200
240
280
320
360
400
Frequency (Hz)
0
1.414
Strouhal Number ( f * Chord / Vinf)
2.828
Effect of Pulsed Jet Frequency
• High Frequencies were more effective.
• This is explained as follows:
• When the jet is turned off, the beneficial Coanda
effect persists for several chord lengths of travel.
• If a new cycle starts soon, the Coanda effect quickly
reestablishes itself.
Stream Lines around the Airfoil Trailing Edge
Pulsed Jet Frequency = 120 Hz
Stream Lines around the Airfoil Trailing Edge
Pulsed Jet Frequency = 400 Hz
Average L/D (Efficiency CL/(CD+Cm)) Vs. Frequency For Pulsed Jet
The Time-Averaged Momentum Coefficient is 0.04
20
18
16
CL/(CD+Cm
14
12
10
8
6
4
Pulsed Jet, Ave. Cmu=0.04
2
Steady Jet, Cmu=0.04
0
0
0
40
80
120
160
200
240
Frequency (Hz)
280
1.414
Strouhal Number ( f * Chord / Vinf)
320
360
400
2.828
Preliminary Conclusions
• CCW concept is an extremely effective way of
achieving high CLmax, without the drawbacks of
conventional high-lift systems.
• The steady jet calculations are in good agreement
with the measurements. It is seen that blowing can
successfully eliminate the vortex shedding, a
potential noise source.
• The pulsed jet configuration can give larger
increments in lift coefficient compared to the steady
jet at the same mass flow rate.
• The pulsed jet performance improved at higher pulse
frequencies.
Proposed Work
1. Effects of Tangential Blowing on Leading Edge Stall
• Slats are often used as a way of suppressing
leading edge stall at high angles of attack; the use of
slats creates new noise sources and wing
complexities; leading edge tangential blowing is an
effective way of eliminating leading edge stall without
using of slats.
Leading Edge Blowing
Trailing Edge Blowing
Proposed Work (cont’d)
2. Effects of Tangential Blowing for Flap Edge Vortex
Reduction (Three Dimensional Application)
The Lift Distribution along Span for Traditional Wing-Flap Configurations
The Lift Distribution along Span for CCW Wing-Flap Configurations
• Circulation Control Jets are used on the main wing and on the flap
edge to reduce the flap edge vortex strength.
Questions ?