摘要

The interactive influences of oscillation frequency and velocity amplitude ratio on onset of transition in pulsatile pipe flow are investigated experimentally in the ranges of time-averaged and oscillating Reynolds numbers of 1019 +/- 35 <= Re(ta <=)4817 +/- 164 and 107 4 <= Re-os <= 4261 +/- 145 with velocity ampli-tude ratio of 0.05 0.0017 <= A(1) < 0.96 +/- 0.03 for 227 runs. Oscillation frequency is in the range of 0.1 Hz <= f <= 14 Hz corresponding to Womersley number range of 2.72 <= roY root omega'(') <= 32.21 covering quasi steady, intermediate and beginning of inertia dominant regimes of pulsatile laminar flow. The onset of transition in laminar pulsatile pipe flow can be retarded up to Re-ta,(crit)= 4817 at root omega'= 3.85 in the covered experimental range. No more effect of A(1) on Re-ta.Crit is seen for root omega' > 8.61 although there is a considerable effect of A(1) on Re-os crit. The effect of root omega' on Re-ta,(crit) and Re-os (crit) is not observed for A(1) < 0.30. The interactive influences of root omega' and Al are also investigated on Re-ta (crit) as functions of Re-ta (crit) = Re-ta,Re-crit (A(1) root omega') and Re-ta,Re-crit = Re-ta,Re-crit (root omega'/A(1)). The interactive influences of root omega' and A(1) are not seen on Re-ta,Re-crit for root omega' > 8.61. This shows that the time-periodicity (root omega',A(1)) does not affect significantly the onset of transition at the beginning of inertia dominant region of pulsatile laminar flow (omega' > 8.61) when compared with their interactive effects in the quasi-steady and intermediate regions (root omega' < 8.61). For flow classification of pulsatile flow at the onset of transition, a new non-dimensional interactive oscillation number, l(os) = root omega'/A(1) is proposed. According to this non-dimensional number, the pulsatile flow at the onset of transition can be subclassified such as quasi-steady for l(os) < 5, intermediate for 5 <= l(os) <= 30 and inertia dominant regions of pulsatile pipe flows for L-os > 30 considering the effects of both root omega' and A(1) on contrary to the classifications available in the literature.

  • 出版日期2017-3