Flow Control scaling

1
Flow Control scaling

• Yoshi Kubota

2
Outline

• What is the flow control?
• Introduction of the flow control
• Objectives
• Reynolds stress
• Production, reduction of the Reynolds shear
  stress
• Effect of flow control
• Summary

3
Why we should do flow control?

• Drag reduction
• Thrust producing
• Fluid noise reduction
• etc.

4
What is flow control?
1 Gad-el-Hak, M. Modern developments in flow
control, Appl. Mech. Rev., 49 (1996) 365-379.
5
Objectives

• What is the concept of flow control?
• What is the effect of flow control?
• Relation of scale, Reynolds stress with flow
  control

6
Reynolds stress
continue equation
Reynolds decomposition
Reynolds stress tensor
7
Production and diffusion of Reynolds shear stress
in near-wall

• Low pressure region correspond the core of
  streamwise vortex
• High pressure region generate by streamwise
  vortex work
• Reynolds shear stress product by vortex work
• Reduction of wall friction drag, production of
  Reynolds stress and TKE can control by streamwise
  vortex.

2 Kasagi, N., Sumitani, Y., Suzuki, Y. and
Iida, O. Kinematics of the quasi-coherent
vortical structure in near-wall turbulence, Int.
J. Heat Fluid Flow, 16 (1995) 2-10.
8
Conceptual diagram of energy flow

• Conceptual diagram of energy flow between the
  near-wall vortices and the large-scale
  outer-layer structures
• Streamwise vortex product near wall and transport
  to outer low speed region by large scale vortex

5 Iwamoto, K., Kasagi, N. and Suzuki, Y.
Dynamical Roles of Large-Scale Structures in
Turbulent Channel Flow, Proc. Computational
Mechanics, WCCM VI in conjunction with APCOM'04,
Sept. 5-10, 2004, Beijing, China (2004) MS022-174.
9
Reynolds number effect by stream wise vortex scale

• Many of turbulent flow has very small length and
  time scale streamwise vortex.

3 N.Kasagi, Y.Suzuki and K.Fukagata. Turbulent
Flow control Pality, 182 (2003) 20-26
10
Effect of flow control by DNS

• Reynolds shear stress in channel flow at Re 650
  with damping in the near-wall layer
• Effect of flow control is clearly at inside of
  controlled area
• Also, effect is clearly at outside of controlled
  area

5 Iwamoto, K., Kasagi, N. and Suzuki, Y.
Dynamical Roles of Large-Scale Structures in
Turbulent Channel Flow, Proc. Computational
Mechanics, WCCM VI in conjunction with APCOM'04,
Sept. 5-10, 2004, Beijing, China (2004) MS022-174.
11
Example result of flow control

• Cross-sectional view of instantaneous streamwise
  velocity in channel flow
• Structure size is uncontrolled lt controlled in
  outer region.
• Flow control is effective in outer region.
• Reynolds shear stress reduce at outer region

4 N.Kasagi. Feedback Control of Turbulent Wall
Shear Flow, Nagare 25 (2006) 13-22
12
Summary

• Show the concept and effect of flow control
• Show the relation between Reynolds stress with
  flow control