Study of similarities for fluid-dynamic noise

Based on the principles of acoustic similarity, the main similar relationships of fluid-dynamic noise are studied by analyzing its basic theory and excitation mechanism, especially the necessary amendment while the Reynolds numbers of a model and a real one are not equal. The results show that it is feasible to calculate the acoustic properties of a real object from the outcome of model test, while the moving states of fluid on surfaces of model and real one are not essentially distinctive, although their fluid-dynamically acoustic similarity is not exact. Then an appropriate correction according to the difference between their Reynolds numbers is needed. As an example, the results of model test of ship propellers were analyzed and calculated to show the main characteristics of scale effect. The amendments when the measuring distances do not meet the similar relations and the influences of propeller leaves' vibration are discussed as well.