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APISAT 2012
Vortex Dissipation Due to Airfoil-Vortex Interaction
Keitaroh OHSHIO (Tokyo Metropolitan University)
Masahiko SUGIURA (Aviation Program Group, JAXA)
Yasutada TANABE (Aviation Program Group, JAXA)
Hideaki SUGAWARA (Ryoyu Systems, Co., Ltd.)
Masahiro KANAZAKI (Tokyo Metropolitan University)
0148 Nov. 14, 2012 Ramada Plaza Hotel, Jeju, Korea
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Toward An Improvement of The Hybrid Method of
Prescribed Wake Model/CFD
Presentation Outline
Background
Change of vortex trajectory and circulation
Sound pressure fluctuation
Concluding remarks
Objective
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Calculation results
Methodologies
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Engine noise
Transmission noise
HSI noise
BVI noise
The simulation of BVI has to be
Tip vortex
BVI
Tail rotor noise
BVI noise has to be reduced for
next generation helicopters. Dominant parameters
・ Vertical distance between
blade and vortex center
(=miss-distance)
・ Vortex circulation high-accurate
low-cost
Development of BVI Noise Prediction Method
CFD:Computational Fluid Dynamics
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CFD
Prescribed wake model
Hybrid method
CFD
Prescribed wake model
(Estimation of the pressure distribution on blades)
(Estimation of the induced velocity)
V :Freestream velocity
αTPP :Rotor angle of attack
Ω :Rotor rotational speed
R :Rotor radius
Ψv :Vortex age
Ψb :Blade azimuth at vortex release
xv = RcosΨv + μx(Ψb-Ψv )
μx = VcosαTPP/RΩ
zv = -μz(Ψb-Ψv )+ ∫ (v/RΩ)dΨ Ψb
Ψv
μz =VsinαTPP/RΩ
yv = RsinΨv
Tip vortex geometry expressed by the prescribed wake model
Hybrid Method of Prescribed Wake Model/CFD (1/2)
B. G. van der Wall: Prediction of BVI Noise Radiation Variation Due to HHC
Using Advanced Prescribed Wake Methodology
Previous study (2012, DLR)
BVI
Δ2 [dB]
Error of prescribed wake model
influences on CFD error.
Overestimation of BVISPL
Overestimation
Error
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Hybrid Method of Prescribed Wake Model/CFD (2/2)
When using the
hybrid method
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1st BVI 2nd BVI
3rd BVI 4th BVI
Flow ・For an improvement of the
hybrid method, it is
required to estimate the
change of vortex center
and its strength due to
the sequential BVI.
When using CFD
・ Difference of vortex center
between CFD and the hybrid
method affects to the accuracy
of BVI noise prediction.
Vorticity Magnitude
Rotor
Toward An Improvement of The Hybrid Method(1/2)
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xv = RcosΨv+μx (Ψb-Ψv )
zv = -μz (Ψb-Ψv )+ ∫ (v/RΩ)dΨ Ψb
Ψv
Requirement of the modified prescribed wake model
+Δxv (Ψb-Ψv , Γ , ・ ・ ・ )
+Δzv (Ψb-Ψv , Γ , ・ ・ ・ )
yv = RsinΨv +Δyv (Ψb-Ψv , Γ , ・ ・ ・ )
Wake position to modify
Ω
Toward An Improvement of The Hybrid Method(2/2)
AVI: Airfoil-Vortex Interaction
・ It is promising approach to estimate
the change of vortex center location
and vortex circulation with 2-D AVI
simulations for development of the
modified prescribed wake model.
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・ N u m e r i c a l s i m u l a t i o n o f AV I f o r
i mp rovemen t o f t he hyb r i d me thod
E s t i m a t i o n o f t h e c h a n g e o f v o r t e x
c e n t e r l o c a t i o n a n d v o r t e x
c i r c u l a t i o n d u e t o s e q u e n t i a l A V I
2 - D C F D s i m u l a t i o n c o m p o s e d o f
a s i n g l e v o r t e x a n d t w o a i r f o i l s
Objective
AVI
Airfoil
Vortex
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・Numerical flux evaluation:
SLAU(Simple Low-dissipative Advection Upstream Splitting Method)
・Governing equations:2-D compressible Euler equations
Methodologies(1/2)
・Temporal scheme:
Dual-time stepping implicit method solved with LU-SGS
(Lower-Upper Symmetric-Gauss-Seidel) method
・Spatial reconstruction:
FCMT(Fourth-order Compact MUSCL TVD) method
・Grid construction:Overset grids platform
Background grid
Airfoil grid
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0.626M Zv
c(=1.0)
NACA0012 (#1) x
23c
Z
~
~
NACA0012 (#2)
~
~
10c
Scully Vortex ※
Caradonna, F. X. et al., “An Experimental Study of Blade-Vortex Interaction Aerodynamics
and Acoustics Utilizing an Independently Generated Vortex,” NASA TM 199208790, 1999 ※
AoA=0.0, 5.0[deg] Miss-distance Zv=0.0~1.5
・Investigation of the correlation between miss-distance and vortex trajectory
(Vertical distance between airfoil and vortex)
2
ˆ
2
0
2
2
rr
r
rU
v
ˆcU
Scully vortex
cr 162.00Core radius
Swirl velocity
Non-dimensional circulation 2536.0ˆ (equivalent to Cl=-0.50)
Methodologies(2/2)
r0 r 0 Vθ
Presentation Outline
Background
Change of vortex trajectory and circulation
Sound pressure fluctuation
Concluding remarks
Objective
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Calculation results
Methodologies
・ 1st airfoil divides the clockwise vortex into two vortices.
・ Counter-clockwise vortices are induced due to 1st AVI.
Zv=0.05 (AoA=0.0) Zv=0.05 (AoA=0.0)
2nd AVI (#2) 1st AVI (#1)
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Vorticity
~ ~
Sequential AVI
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Original vortex
Flow
Δz
Δx Before 2nd AVI
Before 2nd AVI
Change of the vortex center location
⊿ x : In case of AoA=0.0, the
original vortex is decelerated
by counter-clockwise vortex
x
z ⊿ z : In both cases, the original
vortex moves upward due to
the induced velocity of
counter-clockwise vortex
Two cases are compared: AoA=0.0, 5.0
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Zv=0.05 (AoA=0.0)
Flow
Original vortex
Zv=0.25 (AoA=0.0)
Before 2nd AVI
^
z z
x
x
Change of the vortex circulation
Original vortex Since the total vorticity is conserved,
it is promising to capture the change of
vortex center by considering the several
vortices as a single vortex
Presentation Outline
Background
Change of vortex trajectory and circulation
Sound pressure fluctuation
Concluding remarks
Objective
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Calculation results
Methodologies
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Pressure fluctuation coef. Observation points
Estimation of the difference between Lavi1 and Lavi2
Since the miss-distance increases after 1st AVI,
Lavi2 is lower than Lavi1.
Lavi
Sound pressure fluctuation(1/2)
2aρ
ΔpLavi
AoA=0.0
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Lavi2/Lavi1
0.05
0.25 0.414
0.355
Zv
When the initial miss-distance is long (Zv=0.25),
AoA=0.0
the intensities of both AVIs are lower than those of AoA=0.0
larger miss-distance provides lower Lavi2
・ Investigation of the effect of miss-distance
Sound pressure fluctuation(2/2)
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According to the previous study,
the following regression between
miss-distance and Lavi is introduced
by using the calculation results
※
※ Yasutada, T., Saito, S., Takasaki K., and Fujita H., “A Parametric Study on Parallel Blade-Vortex Interaction
for Helicopter Rotor,” JAXA RR-07-051E, 2008
Lavi0 :Sound pressure fluctuation in case of Zv=0.0
Correlation between miss-distance and pressure fluctuation
AoA=0.0
1Z2
1
avi0
avi1.2
vL
L
caLL
bvZ
d
avi0
avi
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By using regression line and initial miss-distance, corrected
miss-distance is estimated to modify the area where vortex
dissipates.
The variation of miss-distance for modification of the hybrid
method is obtained from right-hand figure by considering that
total vorticity is conserved.
Identification of corrected miss-distance
AoA=0.0
Investigation of the ratio of
Lavi1 and Lavi2 with CFD results
Modification of miss-distance
in case of AoA=0.0
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After 1st AVI, several vortices are induced
and complex vortex wake flow exists.
When considering several vortices as the single
vortex, it is required to modify the vortex center
location and vortex circulation in the hybrid method.
Fundamental insights necessary to modify
the hybrid method are obtained.
Concluding remarks
・ N u m e r i c a l s i m u l a t i o n o f AV I f o r
i mp rovemen t o f t he hyb r i d me thod
Parametric study for validating the modified
hybrid method is performed for future work.
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Thank you for your attention