Re=2.5×10³～2.7×10⁵における二次元音速ノズルの臨界圧力比と流出係数 : 特に, スロート幅の影響

抄録

We present the characteristics of the critical pressure and discharge coefficient on the twod-imensional sonic nozzles at a low Reynolds number. The geometric shape of the nozzle is based on the ISO 9300 sonic-Venturi nozzle. The two-dimensional sonic nozzles of five different width were used in order to get low Reynolds numbers. The static pressure distribution along the wall of the nozzle and the behavior of the shock wave in the nozzle are shown. The discharge coefficients were obtained by the two critical sonic nozzles method to prove the mechanism of the reduction of the critical pressure ratio at a low Reynolds number. When the throat width was 2.5mm, the boundary layer near the throat was separated and, consequently, the recovery of pressure by the diffuser was not sufficient. The recovery of pressure was not improved with increasing the upstream pressure. The discharge coefficient of the 2.5-mm-wide nozzle was substantially decreased by the separation of the boundary layer, and the 20-mm-wide nozzle also decreased due to the formation of the corner vortex at the entrance of the two-dimensional nozzle. The discharge coefficient on the sonic nozzle is governed by two parameter ; α and β. At the three-dimensional sonic nozzle, a depends on the velocity profile at the throat and β is affected by the thickness of the boundary layer. On the contrary, at the two-dimensional sonic nozzle, the value of a changes markedly with changing throat width, but the value of β is constant since β is not affected by the throat width.