Abstract
The purposes of this study are to simulate compressible channel flows by a CFD commercial software (STAR-CD) and to compare the numerical results with those predicted by the conventional theory based on a quasi-one-dimensional assumption. We expect to obtain the real physical phenomena of channel flows encountered in practical applications. The physical models in the present study include the low-aspect-ratio channels (L/W=13), L-type and U-type channels with a converging effect on the cross sectional area, the high-aspect-ratio microchannels (L/W=1000) and U-type microchannels. Unlike the theory which shows a reduction in the average flow velocity by wall friction, the results reveal that the friction effect for low-aspect-ratio channels is negligible, the fluid is heated only near the wall and the temperature distribution is quite non-uniform across the cross section of channels. For the L-type and U-type channels, a high pressure region is formed at the entry in the outer region of the curved section and the flow velocity in the inner region is higher than that in the outer one. The behavior of flow after the curved section is reversed and the fluid temperature at the outer region is lower than the inner one. In addition, the simulation results also reveal that the fluid is accelerated in the curved section. The Mach number at the channel exit can reach a supersonic state if the pressure difference between the inlet and outlet is lower than that in a converging channel. It is also found that for high-aspect-ratio microchannels the numerical results are in good agreement with those according to the theoretical prediction. With an identical channel length, both the straight and the U-type microchannels have similar velocity and temperature fields. This fact indicates that, for high-aspect-ratio microchannels, one can simply utilize the theory based on a quasi-one-dimensional assumption to predict the phenomena of channel flows.