Effect of different parameters on the boundary layer transition position of sonic nozzle

Abstract

For sonic nozzles, the discharge coefficient (Cd) is an essential parameter of flow characteristics, which is mainly affected by geometric structure and the development of boundary layer. And, the transition process of boundary layer for sonic nozzle is affected by many factors, including Reynolds number, macro structure, meso-micro surface structure, turbulence intensity, wall heat transfer and so on. Therefore, in order to analyze the influences of these factors on the transition position of boundary layer, the Cd and geometric dimension (throat diameter, d, average roughness, Ra, maximum roughness, Rz, and waviness, wa) of three sonic nozzles with throat diameter of 1.919 mm, 3.808 mm, and 7.453 mm were experimental investigated and measured. Furthermore, a series of CFD simulations through the k-w SST transition model for axisymmetric sonic nozzles were established to research the variation law of boundary layer transition position and Cd when Reynolds numbers ranges from 4.6 × 104 to 4.7 × 107 and different parameters, such as meso-micro surface structure (Ra, Rz and wa) and turbulence intensity (Tu). The validity of the simulation model was confirmed by the experimental data of National Institute of Metrology of China (NIM). Finally, the relationships between the transition position of boundary layer and different parameters were obtained.