Suboptimal control for drag reduction in turbulent pipe flow

Abstract

A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables partial derivativep/partial derivativetheta\(w) and partial derivativeupsilon(theta)/partial derivativer\(w) are applied with two actuations phi(theta) and phi(r). To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at Re-tau = 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 and partial derivativeupsilon(theta)/partial derivativer\(w) and phi(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. (C) 2002 Published by The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.