Turbulent Pulsating Convective Flow in the Quasi-Steady and Low-Frequency Regimes

Abstract

The instantaneous and time-averaged dynamics of turbulent pulsating convective pipe flow is investigated experimentally over Strouhal number, St=3.3×10−4−0.12 that falls in the quasi-steady and low-frequency regimes, pulsation amplitude, βb=0.05−0.2, and bulk Reynolds numbers, Reb=7528−10,920. The analytical expressions for pulsation amplitudes of centerline velocity, bulk velocity, and Nusselt number are derived. The time series of oscillating components of centerline velocity (Uc˜), cross-sectionally averaged bulk velocity (Ub˜), and Nusselt number (Nu˜) depicts that the phase differences between Uc˜, and Ub˜, and between Ub˜, and Nu˜ increase with St nonmonotonically with near zero phase difference at St→0. The time-averaged pulsating Nusselt number Nu¯ is invariant of St for St > 0.01. Nu¯ depends marginally on βb. The relative mean Nusselt number, Nur=Nu¯/Nus<1 for Reb≥8885 and Nur>1 for Reb = 7528. The general observations from this study is that, in the quasi-steady and low-frequency regimes, turbulent pulsating flows leads to marginal changes in the time-averaged Nusselt number Nu¯ compared to the time-averaged Nusselt number Nus in steady flow condition at any Reb.