국내 최대 기계 및 로봇 연구정보

기술보고서

기술보고서 게시판 내용
타이틀	Experimental Study of Boundary Layer Transition With Elevated Freestream Turbulence on a Heated Flat Plate
저자	Ki-Hyeon Sohn and Eli Reshotko
Keyword	By-pass transition; Heat transfer; Flat plate
URL	http://gltrs.grc.nasa.gov/reports/1991/CR-187068.pdf
보고서번호	NASA CR-187068
발행년도	1991
출처	NASA Glenn Research Center
ABSTRACT	A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a lowspeed, closedloop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4% to 6%. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for Req < 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53% higher than Pr-2/3. A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a nearwall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the crosssectional shape of turbulent spots observed by others. Nonturbulent intervals were observed to possess large magnitudes of nearwall unsteadiness and turbulent intervals had peak values as much as 50% higher than were measured at fully turbulent stations. Nonturbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of TS waves for TI ?0.4%. However, for TI ?0.8% and 1.1%, TS waves are localized very near the wall and do not play a dominant role in the transition process.