Numerical Study of Flow Field Similarity Problem for High Speed Water Entry of Navigating Body in Different Test Environments

The high speed entry problem of navigating body involves complex phenomena such as high speed impact, transient evolution of flow field, and fluid-solid coupling, etc. It is common and necessary to study the high speed entry problem of navigating body by using scaled-down test, and the similarity theory is the most important theoretical basis for the design and result prediction of scaled-down test. In the actual test, it is often impossible to meet all parameters obeying the similarity relationship, thus causing distortions in some parameters of the test conditions, and these distortions will affect the accuracy of the test results prediction. In this paper, we analyze the similar aberrations of the vertical entry water field and ballistic trajectory under three different test environments, such as atmospheric pressure, reduced pressure and hypergravity, based on the quantitative analysis theory and the numerical simulation of Fluent simulation platform. This paper analyzes the characteristics of the change of the cavity and trajectory of the prototype navigable body with vertical water entry, then compares them with the normal compression ratio, the reduced compression ratio and the supergravity scaling ratio respectively, and finds that the change of the cavity flow field cannot be accurately simulated under the normal compression ratio due to the atmospheric pressure distortion, and the predicted value of the overall size of the cavity is smaller than that of the prototype, and the surface closure time is greatly advanced. Compared with the prediction results of vertical and inclined water inflow, the theoretical compression reduction ratio can significantly improve the prediction ability, but the closure time of the water inflow is delayed, because the cavitation number is incompatible with the atmospheric density coefficient. Since the main fluid parameters are in accordance with the similarity relationship, the prototype cavitation morphology can be accurately predicted under the hypergravity scale. The displacement velocity trajectory at the initial stage of vertical water entry can be well predicted under the three environments.