Experimental study of flow and mass transfer characteristics over a blunt-faced flat plate in pulsating flow

Abstract

Laboratory measurements were made of flow and mass transfer over a blunt flat plate of finite thickness, which is placed in a pulsating free stream, $U_{infinite} = U_{o}(1 + A_{o} cos2 \pi f_{p}t)$. Low turbulence-intensity wind tunnel experiments were conducted for small and moderate Reynolds numbers, $560 \leq Re_{H} \leq 8000$. The majority of experiments were carried out in the ranges of $f_{p} = 20.0 - 80.0 Hz$ and $A_{o} \leq 0.15$. Flow properties were measured by I-type hot-wire and split-film probes. Mass transfer rates were measured by employing the naphthalene sublimation technique. The present results for non-pulsation flows ($A_{o} = 0.0$) were shown to be consistent with the published data. For pulsating approach flows, plots were constructed to illustrate the distributions of the wall static pressure, the longitudinal mean velocity and turbulent intensity, and the Sherwood number, Sh, as a function of the stream-wise distance $x^{*}$ measured from the leading-edge separation line. As either of $A_{o}$ or $f_{p}$ increases, the time-mean reattachment length reduces significantly, which means the height and length of separation bubble reduces simultaneously; the position where $C_{p}$ is recovered moves upstream, and the minimum value of $C_{p}$ gradually decreases; the reverse flow is more intensified; there is a great augmentation of longitudinal component of turbulent energy. In the zone of separation bubble, the effect of pulsation on Sh is conspicuous. Sh decreases monotonically from a value at the separation point to the minimum value near the secondary separation point where Sh becomes minimum, and Sh increases appreciably with increasing $x^{*}$, after passing the secondary separation point to the maximum value at the reattachment point and then decreases monotoincally afterward. The secondary separation point and the position where Sh has maximum moves further upstream as either of $A_{o}$ or $f_{p}$ increases. At large $Re_{H}$, the rela...