ICSV 14 Cairns • Australia 9-12 July , 2007 USING STATISTICAL METHODS TO PREDICT TURBULENCE INDUCED SOUND AND VIBRATION IN AEROSPACE AND AUTOMOTIVE APPLICATIONS (original) (raw)
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A model of wall pressure correlation for prediction of turbulence-induced vibration
Journal of Fluids and Structures, 2005
The vibration response of a structure excited by a turbulent boundary layer is investigated experimentally and numerically. First, the wall pressure in a high speed acoustic wind tunnel is characterized and the cross-spectral density is approximated using a Corcos model with frequency dependent correlation lengths and a modified Chase model. Both models agree quite well with the measured cross spectrum. Second, based on these turbulence models, the vibration response is predicted and compared to measurements. At lower frequencies both models perform well. In a higher frequency region, however, the vibration response is greatest for length scales that are much longer than the one given by the convection velocity of the turbulence, and in this frequency region only the modified Chase model works effectively. r
Flinovia - Flow Induced Noise and Vibration Issues and Aspects, 2014
For controlling the noise radiated from vibrating structures excited by turbulent boundary layer (TBL) it is relevant to develop numerical tools for understanding how the structure reacts to TBL excitation. Usually, the wall pressure fluctuations of the TBL are described through statistical quantities (i.e. space-frequency or wavenumber-frequency spectra) which depend on the TBL parameters. On the other hand, the vibro-acoustic models (i.e. Finite Elements, Boundary Elements, Transfer Matrix Methods, Analytical models, etc) evaluate deterministic transfer functions which characterise the response of the considered structures. The first part of this paper focuses on the coupling between the stochastic TBL and the deterministic vibro-acoustic models. Five techniques are presented. Numerical applications on an academic marine test case are proposed in order to discuss the calculation parameters and the interests / drawbacks of each technique. In the second part of the paper, the high frequency modelling with the Statistical Energy Analysis (SEA) method is considered. The focus is placed on the estimation of an important input of this method: the injected power by the TBL into the structure for each third octave band.
2 Vibrating Structures Excited by Random Pressure Fluctuations 2 . 1 Presentation of the Problem
2014
For controlling the noise radiated from vibrating structures excited by turbulent boundary layer (TBL) it is relevant to develop numerical tools for understanding how the structure reacts to TBL excitation. Usually, the wall pressure fluctuations of the TBL are described through statistical quantities (i.e. space-frequency or wavenumber-frequency spectra) which depend on the TBL parameters. On the other hand, the vibro-acoustic models (i.e. Finite Elements, Boundary Elements, Transfer Matrix Methods, Analytical models, etc.) evaluate deterministic transfer functions which characterise the response of the considered structures. The first part of this paper focuses on the coupling between the stochastic TBL and the deterministic vibro-acoustic models. Five techniques are presented. Numerical applications on an academic marine test case are proposed in order to discuss the calculation parameters and the interests/drawbacks of each technique. In the second part of the paper, the high fr...
Computation of Wall-Pressure Spectra from Steady Flow Data for Noise Prediction
AIAA journal, 2010
A method is proposed to calculate the trailing-edge broadband noise emitted from an airfoil, based on a steady Reynolds-averaged Navier-Stokes solution of the flowfield. For this purpose, the pressure spectrum on the airfoil surface near the trailing edge is calculated using a statistical model from the Reynolds-averaged Navier-Stokes mean velocity and turbulence data in the airfoil boundary layer. The obtained wall-pressure spectrum is used to compute the radiated sound by means of an aeroacoustic analogy, namely, Amiet's theory of airfoil sound. The statistical model for wall-pressure fluctuations is validated with two test cases from the literature, a boundary layer with an adverse pressure gradient, and a flat plate boundary layer without a pressure gradient. The influence of specific model assumptions is studied, such as the convection velocity of pressure-producing structures and the scale anisotropy of boundary-layer turbulence. Furthermore, the influence of the Reynolds-averaged Navier-Stokes simulation on the calculated spectra is investigated using three different turbulence models. The method is finally applied to the case of a Valeo controlled-diffusion airfoil placed in a jet wind tunnel in the anechoic facility of École Centrale de Lyon. Reynolds-averaged Navier-Stokes solutions for this test case are computed with different turbulence models, the wall-pressure spectrum near the trailing edge is calculated using the statistical model, and the radiated noise is computed with Amiet's theory. All intermediate results of the method are compared with experimental data.
Journal of the Acoustical Society of America, 2021
When performing measurements with wall-installed microphone array, the turbulent boundary layer (TBL) that develops over the measuring system can induce pressure fluctuations that are much greater than those of acoustic sources. It then becomes necessary to process the data to extract each component of the measured field. For this purpose, it is proposed in this paper to decompose the measured spectral matrix into the sum of matrices associated with the acoustic and aerodynamic contributions. This decomposition exploits the statistical properties of each pressure field. On the one hand, assuming that the acoustic contribution is highly correlated over the sensors, the rank of the corresponding cross-spectral matrix is limited to a finite number. On the other hand, the correlation structure of the aerodynamic noise matrix is constrained to resemble a Corcos-like model, with physical parameters estimated within the separation procedure. This separation problem is solved by a Bayesian inference approach, which takes into account the uncertainties on each component of the model. The performance of the method is first evaluated on wind tunnel measurements and then on a particularly noisy industrial measurement setup: microphones flush mounted on the fuselage of a large aircraft.
XXIII Congreso de Métodos Numéricos y sus Aplicaciones (ENIEF) (La Plata, noviembre 2017), 2017
The application of computer fluid dynamics to the estimation of a stochastic wind loading model for vibration analysis of flexible buildings is studied in this paper. Large-Eddy-Simulation with random turbulence field as inflow boundary condition is used for estimating along the wind forces, across the wind forces and torsional moments along the height of the building. The stochastic turbulence of the inlet flow is modeled using techniques proposed in the literature and variations suggested by the authors, and along the wind and along the wind forces and torsional moments applied along the building height are estimated with sampled random processes resulting from the CFD analyses. The application of this numerical technique during the design stage of a concrete-wall 36storey building with a parallelogram-shape plan is described. This structure is prone to high floor accelerations due to wind loading, compromising occupant comfort. The construction of random loading models for this building considering time and space correlation of forces and torsional moments is discussed and the use of the random loading to the design process of supplemental damping devices for the building is described.
Boundary pressure induced by a turbulent flow acting on a structure is an important vibration source that generates broad-band noise inside cars. The classical way to identify the exciting pressure is the measurement of boundary layer pressure in order to characterize correlation length to be used in a Corcos-like model for boundary pressure cross spectrum. This is a complicated and time consuming experimental procedure, that needs a dedicated set-up. Here, an indirect measurement of the wall pressure fluctuation is proposed. The principle is based on a method, called RIFF, which was developed in the last years in case of mechanical or acoustic excitations. This method is based on the measurement of the vibration field of the structure. The advantage of this method is that the force distribution applied to the structure is reconstructed locally and thus does not depend on the conditions located at the boundaries of the window of measurement. In this paper, the possibility of reconstructing by RIFF the boundary pressure field produced by obstacles placed in flow is investigated.
On the sensitivity of sound power radiated by aircraft panels to turbulent boundary layer parameters
Journal of Sound and Vibration, 2012
The objective of the present study is to investigate and quantify how sensitive the response of an aircraft panel is to the change of the turbulent flow parameters. Several empirical models currently exist that provide the turbulent boundary layer wall pressure cross spectrum. These wall pressure cross spectrum models are usually dependent on four parameters: the reference power spectrum, the flow convective velocity, and the coherence lengths in streamwise and spanwise directions. All the proposed models provide different predictions for the wall pressure cross spectrum. Also, real flow conditions over aircraft do not conform to the ideal behavior of the turbulent boundary layer pressure predicted by the models. In this context, the questions that this work aims to explore are ''What is the impact of different wall pressure estimates in the radiated sound power?'' and ''What is the effect of the range of possible flow conditions on the radiated sound power?''. For that objective, data from flight tests and estimates provided by the empirical models are used to predict radiated sound power, and the results are compared. A sensitivity analysis is performed and the relative contribution of each boundary layer parameter to the radiated sound power is obtained.
Separation of the acoustic and aerodynamic wall pressure fluctuations
HAL (Le Centre pour la Communication Scientifique Directe), 2020
Wall pressure measurements may results from two contributions: one coming from the acoustic sources and another induced by the turbulent boundary layer (TBL) pressure. An accurate separation of these two contributions may be required for two purposes: first, the extraction of the acoustic part is necessary for the quantification and the localization of the acoustic sources and second, the extraction of the TBL part is needed for the characterization of the vibro-acoustic excitation of the wall. In this paper, a post-processing method is proposed to perform this separation through a decomposition of the measured crossspectral matrix using the statistical properties of the two contributions, especially their different spatial correlation structures. The approach is assessed on parietal pressure measurements acquired in a wind-tunnel with controlled sources and flow.