Unsteady responses and correlation characteristics of propeller blades under turbulence excitation

Abstract

The turbulence ingestion force acting on the propeller is the primary source of noise and vibration for an underwater vehicle. This paper aims to quantitatively investigate the unsteady responses and blade-to-blade correlation characteristics of the rotating blades, which are two critical factors determining the consequent spectra of broadband unsteady forces. The ingested turbulence and unsteady loading of a 10-blade propeller downstream a turbulence-generating grid are numerically predicted based on Large Eddy Simulation. A theoretical approach of the correlation method is adopted to expound better the physical mechanism for the turbulence ingestion force. Through the partition of blade surface meshes in simulation, the extracted unsteady responses of separate blade strips reveal the broadband loadings varying with radii and blade sections. The distributions of flow field and fluctuating pressure demonstrate the cause of this spanwise discrepancy, as well as the relative contributions of different blade strips to the resultant unsteady loading. The correlation analysis on fluctuating velocity by the rotating sampling of simulated incoming turbulence shows the deviation of ingested flow from homogeneous isotropic turbulence. Additionally, the correlation analysis of unsteady forces distinguishes the sources of different broadband loadings. All of this in turn facilitates the modification of lift-curve slopes of blade strips and stretching factors in turbulence correlation tensors, ultimately improving the prediction accuracy of predominant broadband components by the correlation method. This work provides novel ideas for the mechanism study on turbulence ingestion force and beneficial references to the engineering design of noise-reduced propellers.