Numerical Prediction Of Aerodynamic Noise Research Articles

Numerical Prediction of Aerodynamic Noise for a Propeller-wing Configuration and an Investigation of Pitch Effect

Driven by the sustainable and eco-friendly vision of aviation, Distributed Electric Propulsion (DEP) technology has received much attention for its high aerodynamic efficiency. Simultaneously, lower noise emissions from DEP configurations are desired and therefore it is important to investigate the aerodynamic noise features, which include but are not limited to the noise generation mechanism and the effect of propeller-propeller/wing interactions. This paper focuses on a numerical approach, which is suitable for industrial practice, for predicting the aerodynamic noise of propeller-wing configurations. A generic DEP configuration is employed, consisting of a Mejzlik 2-blade propeller installed on the leading edge of a NACA0018 airfoil. A hybrid method of computational aeroacoustics has been performed in the present simulations, where aeroacoustics in the near field is solved by coarse-grid compressible large-eddy simulations and then the acoustic far field is calculated by the Ffowcs-Williams Hawkings analogy. The influence of grid resolution is studied based on Pope's criterion M and satisfactory results are achieved at a moderate mesh count as compared to the experimental measurements. Further simulations are conducted to investigate the effect of propeller pitch on the aerodynamic performance, noise generation and propeller-wing interactions.

Step-by-Step Numerical Prediction of Aerodynamic Noise Generated by High Speed Trains

In this paper, the unsteady flow around a high-speed train is numerically simulated by detached eddy simulation method (DES), and the far-field noise is predicted using the Ffowcs Williams-Hawkings (FW-H) acoustic model. The reliability of the numerical calculation is verified by wind tunnel experiments. The superposition relationship between the far-field radiated noise of the local aerodynamic noise sources of the high-speed train and the whole noise source is analyzed. Since the aerodynamic noise of high-speed trains is derived from its different components, a stepwise calculation method is proposed to predict the aerodynamic noise of high-speed trains. The results show that the local noise sources of high-speed trains and the whole noise source conform to the principle of sound source energy superposition. Using the head, middle and tail cars of the high-speed train as noise sources, different numerical models are established to obtain the far-field radiated noise of each aerodynamic noise source. The far-field total noise of high-speed trains is predicted using sound source superposition. A step-by-step calculation of each local aerodynamic noise source is used to obtain the superimposed value of the far-field noise. This is consistent with the far-field noise of the whole train model’s aerodynamic noise. The averaged sound pressure level of the far-field longitudinal noise measurement points differs by 1.92 dBA. The step-by-step numerical prediction method of aerodynamic noise of high-speed trains can provide a reference for the numerical prediction of aerodynamic noise generated by long marshalling high-speed trains.

Numerical prediction of aerodynamic noise from impeller blowers of straw threshing machines

An impeller blower is one of the major aerodynamic noise sources in straw threshing machines. To reduce its aerodynamic noise, it is essential to understand the mechanism of gas-material-coupled unsteady flow causing aerodynamic noise. However, it is difficult to clarify the mechanism through measurement. Therefore, the following topics are studied in this article. First, a full-field transient numerical simulation of the gas and solid particulates’ unsteady flow inside the impeller blower was carried out using a dense discrete phase model and a large eddy simulation turbulence model. Second, based on the Ffowcs Williams–Hawkins equation, the aerodynamic noise of the impeller blower of the straw threshing machines was numerically calculated. Finally, the numerical results were verified by aerodynamic noise test. The results indicate that (1) sound pressure level at the inlet of the impeller blower is the highest, mainly at 100 Hz, which is the fundamental frequency of the rotating impeller, while the sound pressure level at the fourth harmonic frequency of 400 Hz is the main source of the outlet. The total sound pressure level at the inlet is greater than that at the outlet. It is concluded that the dipole source of the rotating impeller is the main noise source, which was generated by the interaction of blade with the air and material as the impeller rotated. Also, acoustic attenuation, acoustic resonance, and impact noise of material and machinery play important roles in aerodynamic noise distribution. (2) The test and simulation results show good agreement, so the numerical model of aerodynamic noise is reliable. This study will provide a reference for the structural and acoustic optimization design of impeller blowers and their integration into threshing machines.

Numerical Prediction of Aerodynamic Noise Generated from an Aircraft in Low Mach Number Flight

AbstractThe paper describes numerical prediction of aerodynamic noise generated from an Aircraft. Simulation of turbulent flow is done solving the incompressible Navier‐Stokes equation, where turbulence is modeled applying the orthogonal subgrid scale (OSGS) method with dynamical subscales. Because of comparison, the same simulation is done using the LES (Large Eddy simulation). It is shown how simulation of turbulent flow affects the prediction of acoustic sources calculated using Lighthill's analogy. Translation from the time to frequency domain is done through DFT (Direct Fourier Transform), which gives smaller usage of memory. Acoustic sources are used in the inhomogeneous Helmholtz equation to simulate pressure wave propagation in the domain. It is shown that OSGS with dynamical subscales gives better representation of the spectrum. Overall, better prediction of energy transfer across large and small eddies will give better allocation and presentation of acoustics sources. These sources will change wave propagation of the pressure in the acoustic field. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical prediction of aerodynamic noise generated from missile for low Mach number flows

Numerical prediction of aerodynamic noise generated from missile for low Mach number flows

Direct Numerical Prediction of Aerodynamic Noise Emitted from a Generic Automobile Rear-View Mirror

Direct Numerical Prediction of Aerodynamic Noise Emitted from a Generic Automobile Rear-View Mirror

Numerical Prediction of Aerodynamic Noise Radiated from Propeller Fan

Numerical Prediction of Aerodynamic Noise Radiated from Propeller Fan

Numerical prediction of aerodynamic noise radiated from a cross-flow fan

The surface pressure fluctuations of blades, vortex wall, and the rear wall of a cross-flow fan are commonly considered as the aerodynamic noise sources of an air conditioning unit. In order to predict the noise, these pressure fluctuations were at first obtained by solving the 2D unsteady Reynolds-averaged Navier-Stokes (RANS) equations using a computational fluid dynamics software. It was validated by the fan performance experiments that the prediction of static pressure in the channel agreed well with the test data. It means the results of the pressure fluctuations obtained from the numerical simulation are correct. Then, the Ffowcs Williams-Hawkings (FW-H) equation was used to predict the far-field noise caused by these sources. The errors of the prediction of the sound-pressure levels of the blade passing frequency (BPF) and total noise are within 4 and 3 dB, respectively, comparing with the corresponding measured data. It is shown from the numerical prediction that only the surface pressure fluctuations of the rear wall and the vortex wall are main sources, and that the method of numerical prediction of aerodynamic noise radiated from a cross-flow fan is successful.

On Numerical Prediction of Aerodynamic Noise of Turbulent Flow

On Numerical Prediction of Aerodynamic Noise of Turbulent Flow