【摘要】 我們很早就知道流體在圓管中作層流運動時,泊西里(Poiseulle)的流速分佈只是在距進口處相當長的一段距離處才能實現。如管子進口是圓滑的,則在進口處斷面上的流速是均匀分佈的,此後流速分佈即逐漸轉變直至抛物線形的流速分佈完全形成爲止。由進口處至完全轉化成抛物線形流速分佈所需的距離曾先後經鮑辛尼斯克(Boussinesq)和錫拉(Schiller)進行過研究,他們求得了計算此轉化長度的公式。但是對於在二平行平板間的層流運動,其轉化長度的計算尚無公式可資利用。爲此本文應用錫拉理論對此進行了計算,求得了此轉化長度的公式爲L=0.0259bR,式中,L爲轉化長度,R爲雷諾數,b爲二平板間的距離之半。更多还原

【Abstract】 It has long been realised that for laminar flow through a circuclar pipe, the Poiseulle’s velocity distribution exits only at a sufficient distance downstream from the entrance to the pipe. For a well-rounded entrance, the velocily distribution at the entrance is approximately uniform, it then varies gradually with the distance from the entrance until the parabolic distribution is fully developed. The distance from the entrance required for practically complete transition has been calculated by Boussiuesq and olso by Schiller, and formulas for calculating tle transition length have been proposed. For laminar flow between parallel plates, however, no information for the length of transition appears to be available. An attempt is thus made, in this paper, to calculate this lenqth by applying Schiller’s theory; and the result obtained is given by L=0.0259bR in which L is the transition length, b is half the distance between the plates and R is the Reynolds number.更多还原