Definition of sub-classes in sinusoidal pulsatile air flow at onset of transition to turbulence in view of velocity and frictional field analyses

The definition of the sub-classes in sinusoidal pulsatile pipe flow at the onset of transition to turbulence is given through the analyses of the velocity and the frictional field measurements conducted. For this reason, a systematic experimental study was carried out and the validation of the results was compared with those available in the literature. The time averaged and the oscillating components of the local velocities, (U) over bar (ta)(r) and vertical bar(U) over bar (os,1)vertical bar (r) are measured throughout the pipe cross-section and compared with the theoretical background. A variety of friction factors are also evaluated and the correlations in terms of the functional relationship between dimensionless parameters of lambda(sL)/lambda(u,ta)= f ( root omega'/root Re-ta(3/4)) are proposed. Therefore the limit between quasi steady and intermediate region, and the limit between intermediate and inertia dominant region in the pulsatile pipe flow are found to be at the magnitudes of root omega'/root Re-ta(3/4) = 0.145 and root omega'/root Re-ta(3/4) = 1.5, respectively. Laminar pulsatile flows even at onset of transition can be classified as quasi-steady and inertia dominant sub-classes for root omega' < 5.44 and root omega' > 27.22, respectively. According to the presented experimental study, the intermediate region can also be divided into two subclasses for root omega' <= 8.61 and root omega' > 8.61 as a result of the velocity and the frictional fields. Furthermore, the relationships among time averaged pressure drop, time averaged mean velocity and time averaged friction factor are investigated and the critical limit of root omega' = 8.61 is found. A new parameter, normalized pressure drop, Delta P* is proposed and a common relationship between Delta P* and Re-ta,Re-crit root omega' is derived as Delta P* = f (Re-ta,Re-crit root omega') with a mean deviation of +/- 25%. (C) 2014 Elsevier Ltd. All rights reserved.