Generation and distribution of turbulence-induced forces on a propeller

Abstract

Inflow turbulence is the primary source of propeller unsteady forces, especially for broadband components. In this work, the inflow turbulence and unsteady force on a 10-blade propeller are numerically studied on the basis of large eddy simulation to provide insights into the generation mechanism of this type of excitation. We use turbulence grid and Fourier synthesis method to produce incoming turbulence with spatial flow structure and temporal fluctuation in simulation. The predicted thrust spectrum from this numerical method achieves better measurement consistency than that obtained from theoretical calculation. The turbulence spectra and velocity distribution reveal intrinsic broadband characteristics and spatial inhomogeneity of grid-induced inflow. The transient velocity field and time-dependent thrusts on adjacent blades are cross contrasted to illuminate the generation process of broadband humps in the unsteady force spectra. Additionally, the broadband unsteady forces are simultaneously decomposed into four frequency bands to reveal the corresponding excitation sources for various spectral components and into nine radial blade strips to explore the contribution rates of fluctuating loading at various radial positions. The research is beneficial for comprehensive understanding on turbulence-induced exciting force and practical engineering design of noise-reduced propellers.