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

与换热器翅片排等间距的矩形截面钝体垂直于来流处时，会产生非定常、非均匀的横流，该非定常流区为非定常蜂窝状结构。本研究由风洞实验和有限差分法数值模拟两部分组成。首先，在风洞中同时测量翼排周围的压力和尾迹的速度分布，可以评估由于缝隙中形成的偏流的不稳定而出现的两种或两种以上流型的瞬时阻力和升力，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有很好的对应关系。结果表明，偏置流动是亚稳态的，可以在间隙中间歇性地切换，间隙和尾迹流的不均匀是显著的…更多的是在间隙比S/H的临界值以下的范围内。我们还发现，对于B/H=3，5的长方形圆柱，尾流速度的均匀性在临界间隙处最好。接下来，我们开发了计算矩形柱体绕流的计算机程序，以更好地了解钝体的流体力学和热力学的详细特性。采用有限体积法，在雷诺数为(1，4，7)×10~3的贴体曲线坐标系下，计算了具有不同B/H比的矩形截面钝体的绕流和热场，并成功地模拟了一些有趣的流动和热现象，当B/H比约为2.5和6时，流型发生了临界变化，即完全分离流动、交替再附流和静止再附流。Nusselt数分布很好地对应于绕物体的流动运动，如涡形区的大小和沿侧壁向下游散落的涡流的概念。计算结果与实测值吻合较好，计算结果清楚地反映了钝体形状对气动和热力特性的影响。结果还揭示了尾迹与分离气泡之间的相互作用。此外，还用标准k-epsilon湍流模型计算了矩形物体的湍流流动。然而，k-epsilon湍流模型的计算结果与非定常现象的实验结果存在一定的差异。在六篇论文中，我们报道了一排鳍的最佳横截面形状和布置的实验和数值模拟结果。较少

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