Download - Numerical Simulations of the Aerodynamic Characteristics of Circulation Control Wing Sections
Numerical Simulations of the Aerodynamic Characteristics of
Circulation Control Wing Sections
A Thesis Proposal
ByYI 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)
• Experimental studies show that very high lift coefficient values (as high as 8.5 at =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.
Related Research Work
• 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.
Mathematical and Numerical Formulation
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
• The driving parameter for jet blowing is the momentum coefficient, Cdefined as follows:
Jet Slot Boundary Conditions
2
jet
V21*S
m*VC
Where jetjetjet A*Vm is the mass flow rate of jet flow
• We specify C 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 34% SPAN
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1.50 0.2 0.4 0.6 0.8 1 1.2
CHORD
Cp
Upper- ExpLower -ExpLower CalUpper Cal
66% SPAN
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CHORD
Cp
Upper ExpLower ExpLower CalUpper Cal
85% SPAN
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1.50 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
CHORD
Cp
Upper ExpLower ExpLower CalUpper Cal
• 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.
The CCW Airfoil
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Jet Slot Location
30 degree integral flap
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 ResultsComputed vs. Measured Variations of Lift Coefficient with
Momentum Coefficient
0
1
2
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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
C
Cl
Cl, Computed
Cl, Measured
Angle of Attack 0 degrees, Integral Flap at 30 degrees
Variation of Lift Coefficient with Angle of Attack
0
1
2
3
4
-2 0 2 4 6 8 10 12
Angle of Attack
Cl
Cmu=0.1657
Cmu=0.111
Cmu=0.0566
Cmu=0.0
Leading Edge Stall
Time History of Lift Coefficient for the Unblown Case
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0.72
0.74
0.76
0.78
0.8
0.82
0.84
0.86
0.88
0.9
0 1 2 3 4 5 6 7 8 9 10
Time (msec)
Clt = 1.578693 msec
t = 4.128484 msec t = 6.678274 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.
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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
Drag
Coe
ffici
ents
Multi-element Airfoil at Different Angle of Attack
30 Degree Flap CCW Airfoil, Cd not corrected
30 Degree Flap CCW Airfoil, Cd corrected by Cd+Cmu
• 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?
• Sinusoidal and Square wave form variations were considered. Sinusoidal forms were found ineffective.
• tfFCCtC ,0,0,
Momentum Coefficient Variation with Time for Pulsed Jet Square Wave Form, Frequency = 40 Hz
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0.01
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0.44 0.45 0.46 0.47 0.48 0.49 0.5
Time (sec)
C
Dt = 0.025002 (sec)
C
sec40/1t
Variations of Incremental Lift Coefficient with Time-Averaged Momentum Coefficient, CComparison of Steady Jet with Pulsed Jet
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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Time-Averaged Momentum Coefficient, C0
Cl
Steady JetPulsed Jet , f = 40HzPulsed Jet, f = 120 HzPulsed Jet, f = 400 Hz
• Cl= Clblowing- Clnonblowing
•Steady jet is continuously on, while the pulsed jet is operational only half the time during each cycle.
Variations of Incremental Lift Coefficient with Time-Averaged Mass Flow Rate
Comparison of Steady Jet with Pulsed Jet
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0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016
Time Averaged Mass Flow Rate (slugs/sec)
C
l
Steady JetPulsed Jet , f = 40 HzPulsed Jet ,f = 120 HzPulsed Jet, f = 400 Hz
jet2jet VmandVC
• The average mass flow rate of a pulsed jet is just about 70% of the steady jet at the same C0 value.
Variation of Efficiency (Cl/(Cd+C)) with Time-Averaged Momentum Coefficient, CComparison of Steady Jet with Pulsed Jet
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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Time-Averaged Momentum Coefficient, C
Cl/(C
d+C )
Steady JetPulsed Jet , f = 40 HzPulsed Jet , f = 120 HzPulsed Jet, f = 400 Hz
Average Lift Coefficient Vs. Frequency For Pulsed JetThe Time-Averaged Momentum Coefficient is 0.04
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1.6
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0 40 80 120 160 200 240 280 320 360 400Frequency (Hz)
Cl
Pulsed Jet, Ave. Cmu=0.04
Steady Jet, Cmu=0.04
0
Strouhal Number ( f * Chord / Vinf)
2.8281.414
Pulsed Jet at 400 Hz requires only 73% of the steady jet mass flow rate while achieves 95% of the steady jet lift.
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+C )) Vs. Frequency For Pulsed Jet The Time-Averaged Momentum Coefficient is 0.04
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0 40 80 120 160 200 240 280 320 360 400Frequency (Hz)
CL/
(CD
+C
Pulsed Jet, Ave. Cmu=0.04
Steady Jet, Cmu=0.04
Strouhal Number ( f * Chord / Vinf)
0 2.8281.414
• 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.
Preliminary Conclusions
Proposed Work1. 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 ?