Progress in pipe and channel flow turbulence, 1961–2011

Although much progress has been made in pipe and channel flow turbulence over the past 50 years since the Turbulence Colloquium Marseille 1961 (TCM 1961), these simple wall-bounded turbulent flows have continuously baffled us, refusing to reveal their true and complete nature. In a broader sense, almost everything we thought we knew about wall-bounded turbulent flows, including the scaling laws that appear in textbooks, has been the subject of further scrutiny. An overview of the progress that has been made since TCM 1961 is presented, followed by discussions on unresolved issues that would require further investigations.