A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ∂ p/∂χ-w and ∂υo/∂w are applied with two actuations ∅o and ∅r. To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at Reτ = 150 are performed. When the control law is applied, a 13-23% drag reduction is achieved. The most effective drag reduction is made at the pair of ∂υo/∂r-w and ∅r. An impenetrable virtual wall is observed by the controlled wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant.
Bibliographical noteFunding Information:
This work was supported by a grant from the National Research Laboratory of the Ministry of Science and Technology, Korea. The first author acknowledges the support of KOSEF and NSFC (Grant No. 10072032 and 19732005). She also thanks the support of the Faculty of Mechanical Engineering of Tsinghua University.
All Science Journal Classification (ASJC) codes
- Mechanical Engineering
- Physics and Astronomy(all)
- Fluid Flow and Transfer Processes