| 内容提要: |
To improve the measurement accuracy of sonic nozzle, the theoretical analysis and waviness profile measurement for the discharge coefficient of sonic nozzles were conducted. The theoretical discharge coefficient used a correlation model that accounts for both viscous effects due to the boundary layer along the nozzle wall (Cd,1), and the axisymmetric sonic line in the core region (Cd,2). Firstly, the inner surface coordinates of one sonic nozzle with nominal throat diameter of 7.45 mm were measured by CMM of NIM, including the throat diameter d and curvature radius Rc. The curve profile, roundness and waviness of the overall and local geometric contours are evaluated by using the data of CMM t and the perfect evaluation criteria about nozzle profile were proposed. Lastly, the Rc was used in calculating the theoretical discharge coefficients, Cd,th, while the d was used in calculating the experimental discharge coefficients, Cd,exp. The results showed the overall consistency between Cd,exp and Cd,th is better than 0.11% in the range of Reynolds number from 4.45×105 to 1.26×106. |