1

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

○

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

2

Calculation results

Methodologies

3

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

4

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

5

Hybrid Method of Prescribed Wake Model/CFD (2/2)

When using the

hybrid method

6

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）

7

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.

8

・ 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

9

・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

10

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

11

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)

12

Vorticity

~ ~

Sequential AVI

13

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

14

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

15

Calculation results

Methodologies

16

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

17

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)

18

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

19

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

20

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.

21

Thank you for your attention