FLOW AND MASS-TRANSFER MEASUREMENTS FOR A FLAT-PLATE OF FINITE THICKNESS IN PULSATING FLOW

Laboratory measurements were made of flow and mass transfer over a blu nt flat plate of finite thickness, which is placed in a pulsating free stream, U-infinity = U-0(1 + A(0) cos 2 pi f(p)t). Low turbulence-int ensity wind tunnel experiments were conducted for small and moderate R eynolds numbers, 770 less than or equal to Re-H less than or equal to 8000. Pulsation was generated by means of an acoustic speaker. The maj ority of experiments were carried out in the ranges of f(p) = 20.0-80. 0 Hz and A(0) less than or equal to 0.15. Flow properties were measure d by I-type and split-film probes. Mass transfer rates were measured b y employing the naphthalene sublimation technique. The present results for non-pulsation flows (A(0) = 0.0) were shown to be consistent with the published data. For pulsating approach flows, results are provide d for 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-e dge separation point. As A(0) or f(p) increases, the time-mean reattac hment length is reduced significantly. This implies that the height an d length of the separation bubble shrink simultaneously; the position where C-p is recovered moves upstream, and the minimum value of C-p de creases; the reverse flow is intensified; and a substantial augmentati on of turbulent energy is discernible. In the separation bubble, the e ffect of pulsation on Sh is conspicuous. Sit decreases monotonically f rom the separation point to the minimum value near the secondary separ ation point, and Sh increases appreciably with increasing x, after pa ssing the secondary separation point to the maximum value at the reatt achment point: and afterward, Sh decreases. The secondary separation p oint and the position where Sit has a maximum move further upstream, a s A(0) or f(p) increases. At large Re-H, the relative influence of pul sation on Sh weakens. (C) 1998 Elsevier Science Ltd. All rights reserv ed.