Korcan Kucukcoskun

Broadband Scattering of the Turbulence-Interaction Noise of a Stationary Airfoil: Experimental Validation of a Semi-Analytical Model

A novel semi-analytical model based on Amiets theory is proposed to predict the scattered acoustic field related to turbulence-interaction noise. The simulated scattered acoustic field is compared to the corresponding measurements of a stationary airfoil in a turbulent stream for validation purposes. The paper is composed of three main parts, where improvements and extensions of this semi-analytical model are presented. In the first part of the paper, a new formulation taking an intermediate level of geometrical near-field correction into account is derived. The second part provides an implementation of a strip method accounting for spanwise varying incoming flow conditions. The acoustic free-field response of the airfoil is computed using the geometrical near-field formulation with the strip method. In the third part, an innovative Boundary Element Method (BEM) approach is proposed in order to compute the scattered acoustic field of the airfoil by an obstacle. Finally, the scattered acoustic field resulting from the presence of a flat screen is computed by the semi-analytical method combined with the new BEM approach. A good agreement is obtained comparing with the measurements performed in an anechoic room.

Free and scattered acoustic field predictions of the broadband noise generated by a low-speed axial fan

Broadband noise generated by a low-speed industrial axial fan and its scattered field by a benchmark obstacle have been addressed. Amiets theory on turbulence-interaction noise has been extended in order to predict the acoustic response of a fan in its geometrical near-field. A segmentation technique has been applied for spanwise varying flow conditions. The improved model has been combined with boundary element method (BEM) for acoustic scattering. The validation of the broadband scattering technique has been performed through comparisons with an analytical model considering acoustic scattering from an infinite plate and with measurements of a low-speed axial fan operating nearby a flat scattering screen.

Effect of Inlet Distortions on Ducted Fan Noise

The paper presents an investigation of flow and noise produced by a generic ECS fan installed in a circular duct. A focus of the study is the evaluation of the effect of mean flow distortions and e ...

Noise Produced by a Tandem Diaphragm: Experimental and Numerical Investigations

The aeroacoustic installation effects on a ducted tandem diaphragm are investigated experimentally and numerically. Two different numerical approaches are applied to estimate the noise prediction: a scale-resolved approach and a stochastic approach. A Helmholtz solver is used to calculate the noise propogation inside the duct for both approaches. Comparison data is provided via acoustic, PIV and hotwire measurements.

Tonal and Broadband sound prediction of a locomotive cooling unit

The present work is dedicated to the understanding, modeling and eventually prediction of the noise generated by a laboratory-scale mock-up representative of a generic locomotive cooling unit. The geometry is relatively simple, but a difficulty in terms of modeling and simulation is the inclusion of the acoustic and aerodynamic installation effects taking place between a typical protection grid, a heat exchanger and a low-speed cooling fan combined in a parallelepipedic box setup. In our case the grid and heat exchanger, combined with a 90-degrees turning of the mean flow direction, are affecting the noise generated by the fan rotor through aerodynamic and acoustic installation effects. This study includes experimental and simulation work aimed at measuring and predicting such installation effects. On the experimental side, adding or removing components has permitted assessing the resulting changes quantified as delta-dB levels in the far-field. These far-field measurements reveal that the tonal component of the emitted spectrum, of relatively modest amplitude above the broadband noise, is the most strongly affected by the turning angle imposed by the mock-up geometry, but is not much altered by the presence of the grid and heat exchanger. The broadband component of the measured spectra shows some sensitivity to the presence of the grid and heat exchanger, presumably related to the alteration of the structure of the turbulence ingested by the fan, and due to acoustic absorption through the heat exchanger. On the simulation side, a first attempt is made to include the various components in a complete simulation chain. A semi-analytical approach is used to model the acoustic radiation, limited in this study to the contribution from the rotor blades subjected to turbulence interaction, consistently with the experimental observations. Some of the required input data include the incoming turbulence intensity and correlation length, provided in the present case by a RANS simulation of the mock-up. In this simulation, the heat exchanger is represented as a source term of the momentum equation, adjusted to yield the required pressure drop through this element. This model presents the advantage of simplicity, however comparisons between the predicted and measured turbulence intensities upstream of the rotor plane indicate that a more elaborated model would be necessary to correctly describe the alteration of turbulence through the narrow channels of such automotive heat exchanger. For the acoustic scattering part, the incident broadband acoustic field is scattered on the mock-up geometry using a specific numerical methodology based on a Boundary Element Method already validated by the present authors on simpler geometries. The heat exchanger is there represented by a lumped model characterized through transfer admittance matrix. The comparison between the measured and predicted acoustic fields indicate that a reasonable match is found as far as the spectral distribution of energy is concerned, however with overall levels that are substantially under-predicted. Likely explanations for the discrepancies stands in the fact that potentially important sources of noise have been neglected such as the rotor trailing-edge noise, stator noise or the noise associated to the complex vortical motion that develops between the shrouded rotor ring and the casing. More investigations will be required as well about the structure of the turbulence ingested by the rotor.

A Semi-Analytical Approach on the Turbulence Interaction Noise of A Low-Speed Axial Fan Including Broadband Scattering

This paper deals with the analytical and experimental modeling of the broadband noise generated by a low Mach number axial fan and scattered by an obstacle. The model proposed is a semi-analytical solution to predict the acoustic field of an industrial fan including installation effects. The model is based on Amiet’s theory on the turbulenceinteraction noise, which uses far and free-field assumptions, and is derived for uniform incoming flow properties impinging the leading edge of the blade. However, for most of the industrial applications and in the present case these assumptions become invalid. Therefore the theory has been extended in order to predict the acoustic response of the fan in the geometrical near-field. Segmentation has been applied to take the spanwise varying incoming flow conditions into account. This improved model has been combined with a Boundary Element Method (BEM) for acoustic scattering. The validation of the broadband scattering techniques has been performed through comparisons of results obtained by a semi-analytical model, the BEM model with a scattering screen, and the analytical model which contains the acoustic scattering from an infinite flat plate. The model is also applied to an industrial low-speed axial fan operating next to a flat scattering plate and the results are compared with the measurements performed in the anechoic chamber in both free and scattered-fields.

Experimental/Numerical Study of Ducted-Fan Noise: Effect of Duct Inlet Shape

The paper presents an investigation of flow and noise produced by the generic fan of an environmental control system installed in a circular duct, with a focus on the evaluation of the effect of me...

On the Scattering of Aerodynamic Noise by a Rigid Corner

The paper deals with the exact analytical solution for the scattering of point sources by a rigid corner, and various applications in aeroacoustics. The initial motivation is the assessment of fan noise scattering by corner-like surfaces such as the roof edge of a locomotive or of a building, as a typical installation effect. The exact expression of the Green’s function is first used to determine the sound field of point sources. Then the procedure is described for axial fans the axis of which is either parallel or perpendicular to one side of the incriminated corner, considering arrays of phased dipoles as equivalent source distributions. A good agreement is found in both configurations when comparing with numerical simulations performed with a commercial BEM software. In a last part the scattering of quadrupoles is addressed with special emphasis on the flap side-edge noise from high-lift devices. An asymptotic formulation of the Green’s function for a source close to the corner and a far-field observer is derived. The corresponding behaviour is believed to highlight underlying physics of high-frequency side-edge noise.