Flow Analysis around a Dimpled Cylinder Using Detached

Transcription

Flow Analysis around a Dimpled Cylinder
Using Detached-Eddy Simulation
Symposium on Hybrid RANS-LES Methods
Rica City Hotel, Stockholm, 14-15 July,
2005
Hyoung-Chol KIM, Kazuhiro NAKAHASHI,
Hyoung-Jin KIM
Dept. of Aerospace Eng., Tohoku Univ.
Masaya TSUNODA
SRI Research and Development LTD.
Takuma KATO
Inst. of Fluid Science, Tohoku University
Hyoung-Chol KIM, Dep’t of Aerospace Engineering, Tohoku Univ., Japan
Contents
I. Background
II. Objectives
III. Numerical Method
IV. Results
V. Conclusions
Background : DES
9
Computational Fluid Dynamics (CFD) can be applied to the
complicated flow fields.
9
However, analysis of complicated flow fields with massive
separation such as blunt body problems at high Reynolds number
is still challenging.
9
One of the reasons is difficulty in adequate consideration of
turbulence effects.
9
To deal with these problems, recently, Detached-Eddy Simulation
(DES) based on Spalart-Allmaras one equation turbulence model
is proposed by Spalart et al.
Background : Gold ball
1.2
smooth cylinder (Wieselsberg)
smooth sphere (Achenbach, 1974)
golf ball (Bearman and Harvey, 1976)
1
9
Flow around a sphere has a
very complicated and
interesting physics.
9
A golf ball flies at about
M=0.2 and the Reynolds
Number of 105, but the drag
coefficient is about half of
the smooth sphere.
CD
0.8
0.6
0.4
0.2
0 4
10
105
106
107
Re
Background : Gold ball
9
Dimples on the golf ball surface play an important role to trigger the
boundary layer transition and reduce the drag.
9
However, the mechanism of the boundary layer transition by
dimples has not been fully understood and the design of the dimples
around a golf ball still highly depends on the experiences and
experiments.
9
The CFD application to the golf ball is still challenging, but is
becoming a powerful tool to investigate the effect of the geometry
of dimples to the flows and the drag reduction.
Objectives
9
Main objective is to understand the effectiveness of the dimple shape on
the turbulent flow around a dimpled sphere.
9
As a first step, flows around dimpled cylinders rather than dimpled
spheres are simulated for simplicity and reduced computational cost.
9
This talk mainly focuses on the effectiveness of the DES for simulations
of dimpled cylinders.
<3-D view>
<top view>
On the cylinder surface, there are three lines of dimples, each line having
thirty dimples in the circumferential direction.
Numerical Method ： Flow solver & Conditions
TAS code (Tohoku univ. Aerodynamic Simulation code)
i.
ii.
Governing Eq.
： Compressible Navier-Stokes Eq.
Spatial Discritization
： Cell-Vertex, Finite Volume
Method
iii. Numerical Flux Evaluation ： HLLEW Riemann Solver
iv. Time Integration
： LU-SGS Implicit Method
Flow conditions (shot off)
i.
ii.
iii.
iv.
v.
vi.
vii.
Ma. Number
Re. Number
Far boundary
Wall boundary
Side boundary
Time step
Newton subiterations
： 0.17
： 1.65 x 105
： Uniform Flow
： No slip condition
： Symmetry
： UΔt=D/500
： 4 times
Numerical Method ： Turbulence models
Applied turbulence models
i.
Without turbulence model (LAMINAR)
ii.
Goldberg-Ramakrishnan one equation model (G-R)
iii. Spalart-Allmaras one equation model (S-A)
iv. Detached-Eddy Simulation based on S-A model (DES)
Assumption of fully turbulent boundary layer
Numerical Method ： Grid
9
Hybrid volume grid information
1) nodes
:
1,045,951
2) edges
:
4,695,576
3) tetrahedra :
1,132,589
4) prisms
:
1,620,868
5) pyramids :
8,817
9
Grid density in the boundary layer region
is increased by prismatic grid layer.
(# of prism layers = 30,
minimum spacing = 2.2 x 10-5)
9
Outer boundary is located at 50D from
the cylinder surface (D is the cylinder
diameter).
Result ：
Separation regions (time averaged)
(U_velocity contours )
LAMINAR
S-A
G-R
DES
In turbulent flows, separation regions move downward resulting in drag reduction.
Result ：
Vorticity magnitude contours (time averaged)
LAMINAR
S-A
G-R
DES
The difference with the high vorticity magnitude regions in the wake.
Result ：
Vorticity magnitude contours (time averaged)
LAMINAR
S-A edges.
The vortices take place at dimple
G-R
DES
Result
：
Vorticity magnitude contours (instantaneous, CL=0)
LAMINAR
S-A
G-R
DES
The difference in vortex structure at wake.
Result
：
LAMINAR
Velocity vectors (time averaged)
S-A
Secondary vortex
G-R
DES
Result
：
Section CP distributions (I)
y=0 section
2
2
LAMINAR
G-R
Experiment
1
S-A
DES
Experiment
1
0
-1
-1
CP
CP
0
-2
-2
-3
-3
dimple geometry
-4
-5
0
30
60
90
degree
120
150
180
dimple geometry
-4
-5
0
30
60
90
120
150
180
degree
Peaky CP occurs between dimples
Experiments : Institute of Fluid Science, Tohoku Univ. Japan (2004).
In the front of the cylinder, CP distributions show good agreement with numerical
and experimental results.
Result
：
Section CP distributions (II)
y=0.4 section
2
2
LAMINAR
G-R
Experiment
1
S-A
DES
Experiment
1
0
CP
CP
0
-1
-1
-2
-2
-3
0
30
60
90
degree
120
150
180
-3
0
30
60
90
120
150
180
degree
Result
：
Velocity gradients distributions (I)
y=0 section
1200
1200
LAMINAR
G-R
600
300
Separation
pointpoint
Separation
0
-600
30
60
90
degree
120
300
G-R
-300
97.0°
S-A
-600
96.4°
150
DES
180
Separation point
(y=0 section)
73.0°
dimple geometry
0
600
0
LAMI
-300
S-A
DES
900
(du/dy)y=surface
(du/dy)y=surface
900
0
30
85.0°
dimple geometry
60
90
120
150
180
degree
At between dimples, the velocity gradients have a sudden peak, due to the
dimpled surface geometry. This corresponds to the lower peak of CP.
Result
：
Velocity gradients distributions (II)
y=0.4 section
500
500
LAMINAR
G-R
400
(du/dy)y=surface
(du/dy)y=surface
400
300
200
300
200
Separation point (y=0.4
100 section)
Separation
point
83.7°
LAMI
100
0
-100
S-A
DES
0
G-R
0
30
60
90
degree
120
S-A
150
DES
Separation point
106.1°
180
-100105.4°
0
30
106.1°
60
90
120
150
180
degree
In the smooth region of the dimpled cylinder, the separation takes place
around 106°from the foremost stagnation point.
RESULT
：
CD history
2
2
LAMINAR
G-R
1.8
S-A
DES
1.8
1.6
1.4
1.4
CD
CD
1.6
1.2
1.2
Time averaged
CD
1
1.298
LAMI
1
0.8
0.6
40
G-R
50
60
70
80
tU/D
90
100
S-A120
110
DES
0.8
0.6
40
0.942
0.763
50
60
0.903
70
80
90
100
110
120
tU/D
In only S-A model, the CD history shows the periodic oscillation manner.
Result
1.6
Comparisons of CD
smooth cylinder (Wieselsberg)
smooth sphere (Achenbach, 1974)
golf ball
cd-comparison
(Bearman and Harvey, 1976)
LAMINAR
G-R
S-A
DES
1.5
1.4
1.2
1.3
1
1.2
CD
CD
1.4
：
0.8
1.1
0.6
1
0.4
0.9
0.2
0.8
0 4
10
105
106
Re
107
Experiment (Tohoku Univ.)
LAMINAR
G-R
S-A
DES
0.7
2 104
4 104
6 104 8 104 105
Re
At this flow conditions and grid, S-A model predicted the most accurate CD
with experimental results
Conclusions
i.
Turbulence effects around a dimpled cylinder using DES were numerically
simulated.
ii.
For the comparison with DES, G-R and S-A one equation turbulence models
and without turbulence model were applied.
iii. The results plotted with the time averaged vorticity magnitude and velocity
vectors showed the difference in the high vorticity regions in the wake of
cylinder.
iv. The time averaged section CP and velocity gradients distributions show the
sudden peaks, due to the dimpled surface geometry.
v.
For drag comparisons, S-A model predicted the most accurate results with
experimental data.
Thank you for your attention.

Flow Analysis around a Dimpled Cylinder Using Detached

Transcription

Similar documents

Place des Arts

A mechanically driven form of Kirigami as a route to 3D

From the HOTEL DES LICES (Lices square) to the Bus lines at

Lubawa 9

are you interested in a career in aerospace?

2015 Coldwater Creek Presentation

Stuttgart, Germany June 7

MEMS hands-on access fab.

What we learn - Kanazawa University, Institute for Theoretical Physics

Better Than Stock – Bike Feature