Flow resistance characteristics of pulsating laminar flow in rectangular channels

Experimental investigations on the resistance characteristics of pulsating laminar flow in different sizes rectangular channels are performed at ambient temperature and pressure. The influence of the pulsating period was checked for 6 < T < 600 s; the relative amplitude of Re ranged from 0.05 to 0.92. Both the experiments and the theory show that, the ratio Cf signified the time average pulsating frictional resistance coefficient to that of steady flow equals one for the same Reynolds number in part of the laminar region which the time average Re, the pulsating frequency and the relative amplitude of Re are as small as possible. And in this laminar region, the aspect ratio of rectangular channel has no significant effect on the ratio Cf. However, as the time average Re and the relative amplitude of Re increase, the flow regime becomes no longer laminar even though the real time pulsating Re is less than the transition Reynolds number. Two reasons leading to the phenomenon: (1) the acceleration decreases the transition Re, (2) and the maximum of pulsating Re exceeds the transition Reynolds number. The results of pulsating flow experiments on four kinds of different sizes rectangular channels are consistent.