PHD thetis
Analysis of Vortex Structures Induced by the Synthetic Jet for the Control of Separated Flows
Journals
(1) International Journal of Aerospace and Engineering
Computational Study on Effect of Synthetic Jet Design Parameters, Koichi Okada, Akira Oyama, Kozo Fujii, and Koji Miyaji
Volume 2010 (2010), Article ID 364859, 11 pages
Abstract
Effects of amplitude and frequency of synthetic jet on the characteristics of induced jet are investigated. To estimate effects of
the parameters, flow inside the synthetic jet cavity and orifice and the outer flow is simultaneously simulated using large-eddy
simulation (LES). Comparison of the present LES result with the experimental data shows that three-dimensional LES of the flow
inside the cavity is essential for accurate estimation of the velocity and velocity fluctuation of the synthetic jet. Comparison of the
present results under various flow conditions shows that amplitude and frequency can control profiles of time-averaged vertical
velocity and fluctuation of the vertical velocity as well as damping rate of the induced velocity and fluctuation.
(2) Transaction of JSASS
Computational Study of Effects of Nondimensional Parameters on Synthetic Jets, Koichi Okada, Akira Oyama, Kozo Fujii, and Koji Miyaji
Vol. 55 (2012) , No. 1 p.1-11
http://www.jstage.jst.go.jp/article/tjsass/55/1/55_1/_article/-char/ja/
International Conferences
(1) Okada, K.; Fujii, K. and Miyaji, K., "Effect of Internal Flows in Synthetic Jet Cavity", Proceedings of the ICCFD 5 - International Conference on Computational Fluid Dynamics, Seoul, (2008).
Abstract
Three-dimensional computations of internal flow in synthetic jet cavity are carried out to
understand the effect of cavity flow and compared with the experimental data. High-order compact difference
scheme is used to resolve weak induced flow of the synthetic jet. Though this simulation, the three-dimensional
longitudinal vortices due to the flow in the cavity is captured, which may be important for flow control using
synthetic jet.
(2) Okada, K.; Fujii, K. and Miyaji, K., "COMPUTATIONAL STUDY OF THE SEPARATED FLOW STRUCTURE INDUCED BY THE SYNTHETIC JET ON A BACKWARD-FACING STEP'', The 10th International Conference on Fluid Control, Measurements, and Visualization', (2009).
Abstract
In order to clarify the mechanis m of the synthetic jet on the massively separated flow appearin g at the
backward-facing step, flow-fields with/without the synthetic jet are numerically simulated. Implicit large eddy
simu lation using high-order and high-resolution compact difference scheme is applied. A flo w field without a
synthetic jet, flo w fields with the synthetic jet at non-dimensional frequencies of the wall oscillation, F+h =0.2 and
F+h =2.0, are co mputed, where no-dimensional frequency of F+h is normalized with the height of backward-facing
step and free stream velocity. A lthough previous studies show that each F+h is good conditions, the present
computation shows that length of the separation region only at F+h =0.2 beco me 25 percent shorter than that without
synthetic jet. It seems that F+h =0.2 is near shear layer instability frequency without the synthetic jet. Strong
two-dimensional vortices induced fro m the synthetic jet interact with the shear layer, wh ich results in the increase of
the Reynolds stress. At F+h =2.0, length of the separation region is almost same as that without synthetic jet. M ixing
is not enhanced in the shear layer because Reynolds stress does not increase. Weak and short periodic vortices
induced fro m the synthetic jet do not interacts with the shear layer very much.
(3) Okada, K.; Fujii, K. and Miyaji, K., "Computational Study of Frequency and Amplitude Effects on Separation Flow Control With the Synthetic Jet", 'ASME 2009 International Mechanical Engineering Congress & Exposition', (2009).
Abstract
In order to investigate the frequency and amplitude effects of the synthetic jet on the flow field, numerical simulation is
carried out. Even though the final objective of this study is to understand mechanism of separation control for various
objects, streamline and bluff bodies, the configuration of backward-facing step is chosen as the first step because of the
simplicity. Three-dimensional Navier-Stokes equations are solved. Implicit large eddy simulation using high-order
compact difference scheme is applied. The present analysis is addressed on the frequency characteristics of the synthetic jet
for understanding frequency characteristics and flow-filed. Three cases are selected, No-control, F+h =0.2 and F+h =2.0,
where non-dimensional frequency F+h is normalized with the height of backward-facing step and the free stream velocity.
The present computation shows that at F+h =0.2, separation length is 20 percent shorter than the No-control case. Strong
two-dimensional vortices generated from the synthetic jet interact with the shear layer, which results in the increase of the
Reynolds stress in the shear layer region. These vortices are deformed into three-dimensional structures, which make
Reynolds stress stronger in the recirculation region. At F+h =2.0, size of the separation length is almost same as the No-
control case because the mixing between the synthetic jet and the shear layer is not enhanced. Weak and short periodic
vortices induced from the synthetic jet do not interacts with the shear layer very much and diffuse in the recirculation region.
(4) Okada, K.; Fujii, K., Oyama, A., Nonomura, T., Asada, K. and Miyaji, K., "Computational Study of the Synthetic Jet on Separated Flow over a Backward-Facing Step", 'ASME 2010 International Mechanical Engineering Congress & Exposition', (2010).
Abstract
Frequency effects of the synthetic jet on the flow field over a backward facing step are investigated using numerical
analysis. Three-dimensional Navier-Stokes equations are solved. Implicit large-eddy simulation using high-order compact
difference scheme is conducted. The present analysis is addressed on the frequency characteristics of the synthetic jet
for understanding frequency characteristics and flow filed. Three cases are analyzed; the case computing flow over
backward facing step without control, the case computing flow with synthetic jet control at F+h =0.2, and the case computing
flow with synthetic jet control at F+h =2.0, where non-dimensional frequency F+h is normalized with the height of
backward-facing step and the freestream velocity. The present computation shows that separation length in the case of the flow
controlled at F+h =0.2 is 20 percent shorter than the case without control. Strong two-dimensional vortices generated
from the synthetic jet interact with the shear layer, which results in the increase of the Reynolds stress in the shear layer region.
These vortices are deformed into three-dimensional structures, which make Reynolds stress stronger in the recirculation region.
Size of the separation length in the case of the flow controlled at F+h =2.0 is almost the same as the case without control
because the mixing between the synthetic jet and the shear layer is not enhanced. Weak and short periodic vortices induced from
the synthetic jet do not interacts with the shear layer very much and diffuse in the recirculation region.