Transition From Laminar to Turbulent Flow Measured with Magnetic Resonance Flow Imaging

During the transition from laminar to turbulent flow in a pipe, the velocity distribution changes from being purely unidirectional to one that has an average component in the flow direction superimposed with fluctuating unsteady motions. We imaged velocity profiles of pure fluids and fiber suspensions during this transition using magnetic resonance flow imaging. To probe fluid motion at different time scales we varied the interval between velocity encoding pulses. At a given flow rate, the maxima in signal intensity in the obtained velocity profiles were higher when short time scales were probed than when long times were applied. The relation between imaging timescale and signal intensity is discussed in terms of loss of coherence in the motion of the fluid. Differences in velocity and signal intensity at different time scales for pure fluid and fiber suspensions are discussed.