Numerical study of rotor unsteady forces and noise due to ingestion of grid-generated turbulence

Abstract

In many aeronautics and marine applications, the unsteady forces generated by propulsion rotors due to turbulence ingestion are a significant source of noise and create serious concerns. The understanding of rotor turbulence ingestion and the rotor noise generation mechanisms is vital to achieve an optimal design or apply noise control strategy. The current study is the first attempt to numerically investigate an underwater rotor ingesting grid-generated turbulence by large eddy simulation combined with the Ffowcs-Williams and Hawkings equation. The flow characteristics of two directly simulated turbulence grids with a mesh spacing of 4 and 6 in. are investigated and proved to be adequate for the rotor turbulence ingestion study. The simulated unsteady force spectra of the rotor show better agreement with the experimental results in terms of amplitudes and frequency ranges of the first haystack and broadband components compared to previous theoretical and numerical studies. The unsteady forces and noise of the rotor downstream of the 4-in. grid are slightly higher than those downstream of the 6-in. grid. A far-field noise prediction approach based on the time derivatives of the rotor axial and radial unsteady forces are investigated and validated. The far-field noise spectra and the rotor noise directivities predicted by the time derivative approach agree well with the Ffowcs-Williams and Hawkings equation in the main frequency range of underwater rotor noise. The noise directivities are found to be dominated by axial force related dipole sources.

Rotor aeroacoustic response to an axisymmetric turbulent boundary layer

“…Rotor ingestion of grid turbulence was also studied recently by Wu et al. (2023), who conducted LES of the Sevik (1974) experiment involving the Sevik rotor behind a turbulence grid. Two grids of different spacings and bar diameters were considered, and the computed rotor unsteady-thrust spectra were shown to predict the experimental results better in terms of both the broadband content and the spectral hump at the BPF than the theoretical model.…”

“…Several simulation techniques have been employed, including large-eddy simulation (LES) (e.g. Carolus, Schneider & Reese 2007;Wang, Wang & Wang 2015Wu et al 2023), hybrid methods combining Reynolds-averaged Navier-Stokes simulation with LES (e.g. Suzuki et al 2018Suzuki et al , 2019Arroyo et al 2019), and the lattice-Boltzmann method (e.g.…”

“…The turbulence-ingestion noise was found to be broadband with small peaks at the blade-passing frequency (BPF) and its harmonics, and significantly stronger than the rotor self-noise generated by blade trailing-edge vortex shedding. Rotor ingestion of grid turbulence was also studied recently by Wu et al (2023), who conducted LES of the Sevik (1974) experiment involving the Sevik rotor behind a turbulence grid. Two grids of different spacings and bar diameters were considered, and the computed rotor unsteady-thrust spectra were shown to predict the experimental results better in terms of both the broadband content and the spectral hump at the BPF than the theoretical model.…”

“…Carolus, Schneider & Reese 2007; Wang, Wang & Wang 2015, 2021; Wu et al. 2023), hybrid methods combining Reynolds-averaged Navier–Stokes simulation with LES (e.g. Suzuki et al.…”

Numerical Simulation of Grid-Generated Turbulence Interaction with a NACA0012 Airfoil

“…However, there is a lack of studies conducted which utilizes the grid-generated turbulence approach to examine the turbulence interaction with aerodynamic bodies immersed in the flow. More recently, Wu et al [43] reported one of the first successful attempts to investigated rotor-turbulence ingestion and noise generation from grid-generated turbulence using a solid grid setup.…”