WP1 - Propellers’ parameters were selected, and propellers are being designed and manufactured at Mejzlik
- Aeroacoustic analyses were conducted under both static (no inflow) and forward flow conditions, with varying inflow velocities between 9 to 14 m/s, and a constant propeller rotation of 5000 rpm. Two identical 5-bladed propellers with a diameter of = 9” and Pitch to Diameter ratio / = 1 were mounted on a NACA 0018 wing. The results highlighted the significant impact of relative phase to minimize the propeller noise, particularly at the first Blade-Passing Frequency (BPF) for all directivity angles. Experimental results revealed that:
- Phase synchronization effectively reduces the sound pressure level in the low-frequency band, especially at the first blade-passing frequency.
- A relative phase difference of 90° between the propellers resulted in distinct acoustic characteristics, characterized by reduced BPF amplitudes across all directivity angles.
- The tip-to-tip separation distance between the rotors had no significant impact on noise reduction. This highlighted the dominant influence of relative phase and forward flow conditions in determining noise levels.
WP2 - Developed and validated the method to numerically compute the near-field and far-field acoustic characteristics of propellers.
- The capability and use of a new acoustic model, called “sponge layer”, are assessed for achieving robust non-reflective boundary conditions.
- Machine Learning (ML) and Radon-Cumulative-Distributed Transform (RCDT) with Proper Orthogonal Decomposition (POD) based techniques are investigated to compute Reduced Order Models (ROM) of DEP propeller aerodynamics and acoustics.
- Established the potential and limitations of the ROM in reproducing aerodynamic and acoustic outputs.
- The effects of flow and geometric conditions on DEP noise were discussed based on the numerical results, concerning the advance ratio, propeller pitch, and the leading-edge installation effects.
- Study several cases to analyse the effects of multi-propeller interactions on DEP noise.
WP 3 - Noise shielding and suppression technologies development
- Investigative efforts encompass a range of techniques including acoustic shielding, implementation of porous materials, and control of the propeller phase.
- five main suppression technologies have been investigated experimentally: acoustic shielding of the propeller, porous material interaction with the turbulence interaction noise, trailing edge serrations, phase synchronization of propellers.
- CFD simulations using Lattice Boltzmann Method (LBM) implemented in ProLB software were performed to assess porous treatment efficiency for noise reduction.
- A TMM solver for curved structure has been implemented in AlphaCell and validated against literature work.
- The far field noise analysis shows that porous treatment of the leading edge helps reducing the noise at low frequency but incurs a greater penalty at high frequency.
WP4 - Project Management control and dissemination & outreach.
