  Following the recent observation that turbulent pipe flow can be
relaminarised by a relatively simple modification of the mean velocity profile,
we here carry out a quantitative experimental investigation of this phenomenon.
Our study confirms that a flat velocity profile leads to a collapse of
turbulence and in order to achieve the blunted profile shape, we employ a
moving pipe segment that is briefly and rapidly shifted in the streamwise
direction. The relaminarisation threshold and the minimum shift length and
speeds are determined as a function of Reynolds number. Although turbulence is
still active after the acceleration phase, the modulated profile possesses a
severely decreased lift-up potential as measured by transient growth. As shown,
this results in an exponential decay of fluctuations and the flow
relaminarises. While this method can be easily applied at low to moderate flow
speeds, the minimum streamwise length over which the acceleration needs to act
increases linearly with the Reynolds number.
