Spanwise structure of wall pressure on a cylinder in axial flow (original) (raw)
Related papers
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.
Wall pressure and coherent structures in a turbulent boundary layer on a cylinder in axial flow
Journal of Fluid Mechanics, 1995
Measurements of wall pressure and streamwise velocity fluctuations in a turbulent boundary layer on a cylinder in an axial air flow (&/a = 5.04, Re, = 2870) have been used to investigate the turbulent flow structures in the cylindrical boundary layer that contribute to the fluctuating pressure at the wall in an effort to deduce the effect of transverse curvature on the structure of boundary layer turbulence. Wall pressure was measured at a single location with a subminiature electret condenser microphone, and the velocity was measured throughout a large volume of the boundary layer with a hotwire probe. Auto-and cross-spectral densities, cross-correlations, and conditional sampling of the pressure and streamwise velocity indicate that two primary groups of flow disturbances contribute to the fluctuating pressure at the wall : (i) low-frequency large-scale structures with dynamical significance across the entire boundary layer that are consistent with a pair of large-scale spanwise-oriented counter-rotating vortices and (ii) higher frequency small-scale disturbances concentrated close to the wall that are associated with the burst-sweep cycle and are responsible for the short-duration large-amplitude wall pressure fluctuations. A bidirectional relationship was found to exist between both positive and negative pressure peaks and the temporal derivative of u near the wall. Because the frequency of the large-scale disturbance observed across the boundary layer is consistent with the bursting frequency deduced from the average time between bursts, the burst-sweep cycle appears to be linked to the outer motion. A stretching of the large-scale structures very near the wall, as suggested by space-time correlation convection velocity results, may provide the coupling mechanism. Since the high-frequency disturbance observed near the wall is consistent with the characteristic frequency deduced from the average duration of bursting events, the bursting process provides the two characteristic time scales responsible for the bimodal distribution of energy near the wall. Because many of the observed structural features of the cylindrical boundary layer are similar to those observed in flat-plate turbulent boundary layers, transverse curvature appears to have little effect on the fundamental turbulent structure of the boundary layer for the moderate transverse curvature ratio used in this investigation. From differences that exist between the turbulence intensity, skewness, and spectra of the streamwise velocity, however, it appears that transverse curvature may enhance (i.e. energize) the large-scale motion owing to the reduced constraint imposed on the flow by the smaller cylindrical wall.
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.
20th AIAA/CEAS Aeroacoustics Conference, 2014
The goal of this experimental study is to investigate wall pressure wavenumberfrequency spectra induced by a turbulent boundary layer in the presence of a mean pressure gradient. The mean pressure gradient is achieved by changing the ceiling height of a rectangular channel flow. Wall pressure spectra are measured for zero-, adverse-and favorable-pressure-gradient boundary layers by using a pinhole microphone combined to a high-frequency calibration of the sensor. A linear antenna based on a non-uniform distribution of remote microphones mounted on a rotating disk is also developed to obtain a direct measurement of both aerodynamic and acoustic components of wavenumber-frequency spectra. First results, comparisons and analyses are then discussed. Nomenclature
Pressure and shear stress measurements at the wall in a turbulent boundary layer on a cylinder
Physics of Fluids, 1997
The fluctuating wall shear stress, wall pressure, and streamwise velocity were measured simultaneously in a cylindrical boundary layer at a momentum thickness Reynolds number of Re ϭ2160 and a boundary layer thickness to cylinder radius ratio of ␦/aϭ5 using a hot wire wall shear stress probe mounted just upstream of a hearing aid microphone and a hot wire velocity probe. Variable Interval Time Averaging ͑VITA͒ event detection on streamwise velocity indicates that streamwise accelerations are associated with positive wall pressure peaks and sudden increases in wall shear stress. Likewise, positive pressure peak events are associated with streamwise accelerations and sudden increases in wall shear stress. VITA detection on wall shear stress reveals that increasing wall shear stress corresponds to streamwise accelerations and small-amplitude pressure rises, not distinct intense pressure peaks. Detection of strong adverse and favorable instantaneous pressure gradients indicates that a shear layer at y ϩ ϭ13 coincides with a positive peak in the wall pressure, suggesting that a positive wall pressure peak event is the key wall pressure signature associated with the burst cycle. Measurements of the cross-correlation indicate that the pressure-shear stress relationship is about two times weaker than the pressure-velocity relation and about ten times weaker than the shear stress-velocity relation. Thus, a strong relationship exists between wall pressure and streamwise velocity as well as between wall shear stress and streamwise velocity, but the relationship between wall shear stress and wall pressure is quite weak. Because of the similarity of the near-wall structure of all wall-bounded turbulent flows, regardless of transverse curvature, these conclusions should be applicable to planar boundary layers. © 1997 American Institute of Physics.
19th AIAA/CEAS Aeroacoustics Conference, 2013
This paper concerns the direct measurement of wavenumber-frequency spectra beneath a two-dimensional Turbulent Boundary Layer. The main contribution of this work is the proposed setup that should help achieving a compromise between a small sensor diameter (to avoid spatial averaging) and small sensor spacing (to gain high spatial resolution). The effect of different pinhole sizes on quarter inch microphones is first studied using an acoustical coupler to perform relative calibrations. Single-point measurements of wall pressure fluctuations in a wind-tunnel confirm that a 0.5 mm pinhole quarter inch microphone correctly captures wall pressure statistics up to a frequency of 5 kHz. Under the assumption of stationnary pressure fields, it is then suggested how rotative Archimedean spirals mainly composed of pinhole microphones can provide a uniform coverage of pressure measurements on a disc, or high resolution measurements in selected directions. Using 57 of these pinhole pressure sensors, a probe microphone as a central sensor reference and 3 Knowles pressure sensor, one of the suggested designs of spiral-shaped rotative arrays was instrumented. Measurements have been performed at low Mach numbers (M < 0.1) in a closed-loop wind-tunnel, with the array flush mounted on a side of the wind tunnel. The TBL is characterized with velocity measurements, and 2D wavenumber spectra of the wall pressure fluctuations are obtained which reveal the convective peak at low frequencies.
Wall pressure fluctuations and radiated sound from turbulent boundary layer on an axisymmetric body
Acoustics Research Letters Online, 2000
An experimental investigation of the near-field pressure fluctuations on a hemisphere-nose of an axisymmetric body was conducted in three regions-laminar separation, turbulent shear layer, and developing turbulent boundary layer-at a Reynolds number(Re D) of 2.43×10 5 in an anechoic wind tunnel facility. A significant increase of energy level, especially at low frequencies, was noticed downstream of the laminar separation on the nose, and the positive events were observed in the turbulent shear layer region.
Flinovia - Flow Induced Noise and Vibration Issues and Aspects, 2014
The various methods to obtain 1-point and 2-point statistical properties of wall-pressure fluctuations from CFD are described and discussed. If only averaged flow quantities are available through Reynolds Averaged Navier Stokes computations, empirical models or sophisticated statistical modeling have to be used to estimate wall-pressure spectra and spatial correlations. While very useful at design stage, their applicability to complex flows or geometries seems quite limited. Considering the rapid growth of computational power, it seems clear that the main pathway for the near future is to rely on time-dependent flow simulations, typically Large Eddy Simulations, and to estimate the pressure statistics through a posteriori signal processing. It seems also possible, at the moment only for relatively high Mach number flows, to estimate not only the hydrodynamic part but also the tiny acoustic contribution. Examples of computations of this acoustic contribution to wall-pressure are given together with related experiments.
International Journal of Heat and Fluid Flow, 2001
The statistical properties of the¯uctuating wall-pressure ®eld are studied using a numerical database generated by large eddy simulation of incompressible turbulent¯ow in a plane channel Re s 640. Emphasis is given on the study of spectral features in the wavevector space and as a function of frequency, particularly in the region of low wavenumbers that are of major concern in submarine applications. A correction procedure is used to cancel the arti®cial pseudo-acoustic eect due to periodic boundary conditions. The in¯uence of superimposed perturbations on one wall of the channel is considered afterwards in comparison with the non-perturbed case. Ó