Experimental study on interaction between the internal solitary wave and a hydrofoil based on the spectral proper orthogonal decomposition

Abstract

Internal solitary waves (ISWs) are a well-known phenomenon of water motion in the ocean, and their strong shear flow has a non-negligible harm to underwater marine engineering structures. To clarify the variation law of flow field and force during the interaction between ISW and common marine engineering structures-hydrofoils, in this paper, the spectral proper orthogonal decomposition (SPOD) method is introduced into the ISW problem for the first time. The advantage of this method is that it can display the flow field information in the frequency domain, and we obtained the flow field structure in the frequency domain during the whole flow process and mode 1 at the primary frequency with this method. We also obtained the time evolution flow field and force data through the particle image velocimetry technology and force sensor. The results show that the characteristics of flow field described by time domain and frequency domain show good consistency. According to the analyses results, we divide the flow process into low-frequency steady state and high-frequency disturbance. Most notably, we use the SPOD method to find that the sub-peak threshold of the flow frequency is surprisingly consistent with the sub-peak threshold of the force frequency. The main modes and frequency information of the flow field obtained by the SPOD method can provide valuable guidance for hydrofoil structures to avoid and predict ISW hazards in actual marine engineering operations.