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众所周知,湍流和涡旋都是自然界中的非线性现象,它们的直接数值模拟一直受到计算机速度和容量的限制。主要困难足湍流运动中包含了大大小小不同时间和空间尺度的涡旋运动。最大空间尺度可与平均运动的特征长度相比,而最小空间尺度取决于粘性耗散尺度,这大小尺度的比值随雷诺数的增大而迅速增大。为了模拟湍流,一方面计算区域的尺寸应大到足以包含最大的涡旋,另一方面计算网格的尺寸又要小到足以分辨最小的涡旋运动,因此网格数应较多。再加上计算模拟的时间长度应大于大涡旋的时间长度,而计算步长又要小于小涡旋的时间长度,因此计算步数应非常多,从而总的计算量非常大。国际上大都使用CRAY-Ⅰ或CRAY-Ⅱ这
It is well-known that both turbulence and vortex are nonlinear phenomena in nature. Their direct numerical simulation has been limited by the speed and capacity of the computer. The main difficulty turbulence movement contains large and small vortex movements of different time and space scales. The maximum spatial dimension can be compared with the characteristic length of the average motion, whereas the minimum spatial dimension depends on the viscous dissipation dimension, which increases rapidly with increasing Reynolds number. In order to simulate turbulence, on the one hand, the size of the calculation area should be large enough to contain the largest vortex. On the other hand, the size of the calculation grid should be small enough to distinguish the minimum vortex movement. Therefore, the number of grids should be more. In addition, the length of calculation simulation should be greater than the length of large vortex, and the calculation step is smaller than the length of small vortex. Therefore, the calculation steps should be very large, so the total calculation is very large. Most of the international use of CRAY-Ⅰ or CRAY-Ⅱ this