Studies on the optimum Shapes of Cross-Section and Arrangement of Fin Rows of a Heat Exchanger

一排均匀分布的矩形截面海崖体垂直于来流放置，如换热器的翅片排，在排上产生非定常和非均匀的流动，该流动包括具有非定常胞元结构的分离流区。本研究包括风洞实验和有限差分法数值模拟。首先，在风洞中同时测量了鳍排周围的压力和尾流的速度分布，从而可以评估由间隙中形成的偏流的非定常性而出现的两种或多种流型的每种模式中的瞬时阻力和升力，并且在偏流中，我们发现压力分布和升力和阻力与尾流速度分布的良好对应。结果表明，间隙中的偏流是亚稳态的，可以间歇性地切换，间隙和尾流的非均匀性是显著的 关于我们 在低于临界值的差距比S/H的范围内。我们还发现，对于细长矩形柱体，在临界间隙处，尾迹速度的均匀性最好，B/H=3，5 × 10 ~（-1）列。其次，我们开发了计算矩形柱绕流的计算机代码，以更好地了解海崖体的流体动力学和热动力学的详细特性。用有限体积法在贴体曲线坐标系下计算了雷诺数为（1，4，7）× 10 ~ 3时，不同B/H比和翼型分离的矩形截面海崖体绕流和热场，成功地模拟了一些有趣的流动和热现象，得到了临界流态，当B/H比约为2.5和6时，即出现完全分离流、交替再附着流和静止再附着流。它还澄清，努塞尔数分布以及对应于一个运动的身体周围的流动，如涡流形成区域的大小和概念的涡流脱落下游的侧壁。计算结果与实测结果吻合较好，并清楚地显示了海崖体形状对气动和热力特性的影响。结果还揭示了尾流与分离泡之间的相互作用。此外，还用标准k-ε湍流模型计算了矩形体周围的湍流流动。然而，对于非定常现象，k-ε模型、湍流模型和实验结果之间存在一些差异。我们在六篇论文中报道了肋排最佳横截面形状和布置的实验和数值模拟结果。少

A row of uniformly spaced bluff bodies with a rectangular cross-section placed perpendicularly to an approaching flow like the fin rows of a heat exchanger produces unsteady and non-uniform flow across the row, which consists In separated flow region with an unsteady cell structure. The present study consists of experiments In a wind tunnel and numerical simulations of flow by a finite difference method. Firstly, a simultaneous measurements of pressures around the circumference of a fin row and velocity distribution of a wake In a wind tunnel allow the evaluation of instantaneous drag and lift forces In each mode of two and more flow patterns which appear by unsteadiness of a biased flow formed In the gaps, and In the biased flow, we find good correspondence of pressure distributions and lift and drag forces to wake velocity profiles. It Is concluded that the biased flow is metastable and can switch Intermittently In gaps, and that the nonuniformity of gap and wake flows is significant … More in the range of the gap ratio S/H below a critical value. We find also that the uniformity of a wake velocity Is the best at the critical gap for elongated rectangular cylinders, B/H=3, 5 In rows. Next, we have developed the computer-code for computation of flows around rectangular cylinders, to gain a better Insight into the detailed characteristics of the fluld- and thermo-dynamics of bluff bodies. By a finite volume method, both laninar flow and thermal fields around bluff bodies with a rectangular cross section of various B/H ratios and an aerofoil seption haie been computed on body-fitted curvilinear coordinates at a Reynolds number of(1, 4, 7)x1O^3, and we can successfully simulate some Interesting flow and thermal phenomena whereby a flow pattern critically, changes when the B/H ratio Is about 2.5 and 6 ; that Is, a fully separated flow, an alternately reattached one and a stationarily reattached one. It is also clarified that Nusselt number distribution well corresponds with a motion of flow about the body, such as the size of a vortex-formation region and a notion of vortices shed downstream over the side walls. The present computational code Is certified to be suitable as the computed results show a good agreement with the measured results, and the computed results clearly show the effects of a shape of the bluff body on aero- and thermo-dynamic characteristics. The results reveal an interactions between a wake and separation bubbles, also. Furthermore, turbulent flows around rectangular bodies also have been computed by a standard k-epsilon turbulence model. There are, however, some discrepancies between the results from the k-epsilon, turbulence model and experiments for unsteady phenomena. We have reported the results of experiments and numerical simulations on the optimum shapes of cross-section and arrangement of a row of fins, In six papers. Less