Joachim Golliard

Achieving accurate and efficient prediction of HVAC diaphragm noise at realistic Reynolds and Mach numbers

Despite the aeroacoustic expertise reached nowadays in air and ground transportation, energy sector or domestic appliances, reaching a decibel accuracy of an acoustic prediction for industrial cases is still challenging. Strong investments are made nowadays by oil and gas companies to determine and reduce the sound produced by °ow inside industrial ducts, such as pipelines or gazoduct. Heating, Ventilating and Air Conditioning noise reduction in a car has become a strong condition of comfort for passengers and then a concern for car manufacturers.

Whistling of short corrugated pipes: Experimental investigation of the source locations

The goal of this study is to investigate the issue of the aeroacoustic source location within corrugated pipes. For this purpose, a configuration with a short pipe and well defined boundary conditions is chosen. These investigations have been carried out focusing on the first two whistling modes. This allows for a precise knowledge of the distribution of the acoustic velocity and pressure within the pipe. The methodological investigation of the source locations has been carried out by using straight pipe segments to replace the corrugated section near the acoustic velocity nodes and near the acoustic velocity antinodes. The sections of the corrugated pipe near the acoustic velocity antinodes has been identified as the main location of the sound sources.

Improved jet noise modeling using a new acoustic time scale

To calculate the noise emanating from a turbulent flow (such as a jet flow) using Lighthills analogy, knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and length-scales and convection velocities are needed. However, if we are using a RANS calculation then we obtain only steady characteristics of the flow and it is then necessary to model the unsteady behaviour in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor (or equivalently the spectral density), less attention has been given to underlying physics that dictate the proper choice of timescale. In early studies various authors tended to assume that the acoustic timescale was proportional to the turbulent dissipation rate but later studies have revealed that a frequency dependent relationship gives better results. In this paper we recognise that there are several time dependent processes occurring within a turbulent flow and propose a new way of defining an acoustic timescale. An isothermal single-flow M0.75 jet has been chosen for the present study and essential fluid dynamic information and turbulent parameters have been obtained using a modified k-e method. The jet noise prediction at 90 deg is found using Lighthills analogy and directivity is estimated using an asymptotic solution of Lilleys formulation. Predictions reveal good agreement between the noise predictions and observations. Furthermore, the new time-scale has an inherent frequency dependency that arises naturally from the underlying physics thus avoiding supplementary mathematical enhancements to the model.

Direct measurements of acoustic damping and sound amplification in corrugated pipes with flow

The flow-induced pulsations in corrugated pipes result from a feedback loop between an acoustic resonator and the noise amplification at each shear layer in the axisymmetric cavities forming the corrugations. The quality factor of the resonator is determined by the reflection coefficients at the ends of the corrugated pipe and by the damping in the pipe. In this work, the damping of acoustic waves in a set of smooth and corrugated pipes is measured by a direct method. For these measurements, the tested pipes are placed between two measuring pipes equipped with flush-mounted pressure transducers to allow reconstruction of the acoustic waves with the two-microphone method. Loudspeakers are used to generate acoustic waves, and anechoic terminations allow near reflection-free conditions. The tests are done in air without flow and with flow velocities up to 60 m/s. The results for the corrugated pipes allow to investigate the influence of the corrugations on the damping. Two cases are considered: Without flow, the visco-thermal damping is increased for the corrugated pipe compared to a smooth pipe of same diameter. When there is a flow in the pipe, the damping results depend strongly on the flow velocity. At certain frequencies which depend on the flow velocity, the damping increases or decreases. The regions of increase or decrease are shown to be at constant ranges of Strouhal numbers. The decrease of the damping can in some cases be such that acoustic waves are amplified through the corrugated pipe. This corresponds to the acoustic source behavior of the shear layers. The measured amplification is compared to the computed source term due to the axisymmetric cavities.

Experimental investigation of the source locations for whistling short corrugated pipes

The goal of this study is to investigate the issue of the aeroacoustic source location within corrugated pipes. A configuration with a short pipe and well defined boundary conditions has been chosen, in order to have a precise knowledge of the distribution of the acoustic velocity and pressure within the pipe. The source locations have been investigated methodologically by using straight pipe segments to replace the corrugated section near the acoustic velocity nodes or near the acoustic velocity antinodes. The main locations of the sound sources have been identified to be the sections of the corrugated pipe near the acoustic velocity antinodes. Copyright ©2010 by ASME.

Aeroacoustics of a wall perforation in the pure grazing flow regime: effect of the perforation geometry

Acoustical dampers are used in order to avoid the noise propagation. Well known examples are the aero-engine liners, the IC-engine exhaust muffers, and the liners in combustion chambers. These devices comprise wall perforations, responsible for their sound absorbing features. Understanding the effect of the flow on the acoustic properties of a perforation is essential for the design of acoustic dampers. In the present work the effect of grazing flow on the impedance of slit shaped wall perforations is experimentally investigated by means of a multi-microphone impedance tube. Measurements are carried out for perforations with different geometries. The focus of the experiments is on the Strouhal number dependence of the acoustic impedance. An analytical model of the aeroacoustic behaviour of a two-dimensional wall perforation subject to grazing flow is proposed. These theoretical results are used to qualitatively explain the effect of the perforation geometry on its acoustic absorption properties.

Linear sound amplification and absorption in a corrugated pipe

Linear sound propagation in an axisymmetric corrugated pipe with shear flow is studied numerically and experimentally. The acoustic and hydrodynamic perturbations are described by the linearized Euler equations (LEEs) in a parallel shear flow. Wave propagation and scattering are computed by means of a multimodal method where the disturbances are expressed as a linear combination of acoustic modes and hydrodynamic modes. The Floquet-Bloch approach is used to calculate the wavenumber in the periodic system. Both sound amplification and absorption, depending on the Strouhal number, are well predicted compared to experiments, which means that the flow-acoustic coupling in the system is effectively described by the present model. It is also shown that the corrugated pipe can amplify the sound even if the shear layer over the cavities is stable everywhere.

Numerical study of flow-induced pulsations in pipe systems with closed branches

In this work, a numerical technique based on two-dimensional incompressible computations and vortex sound theory is applied to investigate the flow-acoustic interaction in T-joints, which can lead to resonances in piping systems with closed side branches. The impact of aspects such as the flow direction and edge geometry is analyzed. In spite of the fact that the CFD simulations have a low-Reynolds number, the numerical results are consistent with experimental observations available in the literature, which confirms that the method can be useful for engineering applications, as it provides physically meaningful information at a low computational cost.