Accuracy of various fluid loading approximations for computing far field acoustic pressure from an infinite orthotropic cylinder

1983 ◽  
Vol 73 (S1) ◽  
pp. S71-S71
Author(s):  
Robert C. Haberman
Keyword(s):  
Acoustic Pressure ◽  
Far Field ◽  
Fluid Loading ◽  
Orthotropic Cylinder

scholarly journals Structural and Acoustic Responses of a Submerged Stiffened Conical Shell

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Meixia Chen ◽  
Cong Zhang ◽  
Xiangfan Tao ◽  
Naiqi Deng
Keyword(s):  
Conical Shell ◽  
Element Model ◽  
Analytical Models ◽  
Superposition Method ◽  
Far Field ◽  
Fluid Loading ◽  
Low Frequencies ◽  
Structural Responses ◽  
The Individual ◽  
Field Sound

This paper studies the vibrational behavior and far-field sound radiation of a submerged stiffened conical shell at low frequencies. The solution for the dynamic response of the conical shell is presented in the form of a power series. A smeared approach is used to model the ring stiffeners. Fluid loading is taken into account by dividing the conical shell into narrow strips which are considered to be local cylindrical shells. The far-field sound pressure is solved by the Element Radiation Superposition Method. Excitations in two directions are considered to simulate the loading on the surface of the conical shell. These excitations are applied along the generator and normal to the surface of the conical shell. The contributions from the individual circumferential modes on the structural responses of the conical shell are studied. The effects of the external fluid loading and stiffeners are discussed. The results from the analytical models are validated by numerical results from a fully coupled finite element/boundary element model.

scholarly journals A COMPARISON OF TRANSIENT INFINITE ELEMENTS AND TRANSIENT KIRCHHOFF INTEGRAL METHODS FOR FAR FIELD ACOUSTIC ANALYSIS

2013 ◽  
Vol 21 (02) ◽  
pp. 1350006 ◽  
Author(s):  
TIMOTHY F. WALSH ◽  
ANDREA JONES ◽  
MANOJ BHARDWAJ ◽  
CLARK DOHRMANN ◽  
GARTH REESE ◽  
...  
Keyword(s):  
Acoustic Pressure ◽  
Acoustic Analysis ◽  
System Stability ◽  
Far Field ◽  
Element Analysis ◽  
Infinite Element ◽  
Infinite Elements ◽  
Integral Methods ◽  
Element Approach ◽  
Kirchhoff Integral

Finite element analysis of transient acoustic phenomena on unbounded exterior domains is very common in engineering analysis. In these problems there is a common need to compute the acoustic pressure at points outside of the acoustic mesh, since meshing to points of interest is impractical in many scenarios. In aeroacoustic calculations, for example, the acoustic pressure may be required at tens or hundreds of meters from the structure. In these cases, a method is needed for post-processing the acoustic results to compute the response at far-field points. In this paper, we compare two methods for computing far-field acoustic pressures, one derived directly from the infinite element solution, and the other from the transient version of the Kirchhoff integral. We show that the infinite element approach alleviates the large storage requirements that are typical of Kirchhoff integral and related procedures, and also does not suffer from loss of accuracy that is an inherent part of computing numerical derivatives in the Kirchhoff integral. In order to further speed up and streamline the process of computing the acoustic response at points outside of the mesh, we also address the nonlinear iterative procedure needed for locating parametric coordinates within the host infinite element of far-field points, the parallelization of the overall process, linear solver requirements, and system stability considerations.

scholarly journals Direct numerical simulation of turbulent flow past a trailing edge and the associated noise generation

2008 ◽  
Vol 596 ◽  
pp. 353-385 ◽  
Author(s):  
RICHARD D. SANDBERG ◽  
NEIL D. SANDHAM
Keyword(s):  
Turbulent Flow ◽  
Surface Pressure ◽  
Pressure Difference ◽  
Acoustic Pressure ◽  
Three Dimensional ◽  
Far Field ◽  
Noise Generation ◽  
Reasonable Accuracy ◽  
Dimensional Theory ◽  
Trailing Edge

Direct numerical simulations (DNS) are conducted of turbulent flow passing an infinitely thin trailing edge. The objective is to investigate the turbulent flow field in the vicinity of the trailing edge and the associated broadband noise generation. To generate a turbulent boundary layer a short distance from the inflow boundary, high-amplitude lifted streaks and disturbances that can be associated with coherent outer-layer vortices are introduced at the inflow boundary. A rapid increase in skin friction and a decrease in boundary layer thickness and pressure fluctuations is observed at the trailing edge. It is demonstrated that the behaviour of the hydrodynamic field in the vicinity of the trailing edge can be predicted with reasonable accuracy using triple-deck theory if the eddy viscosity is accounted for. Point spectra of surface pressure difference are shown to vary considerably towards the trailing edge, with a significant reduction of amplitude occurring in the low-frequency range. The acoustic pressure obtained from the DNS is compared with predictions from two- and three-dimensional acoustic analogies and the classical trailing-edge theory of Amiet. For low frequencies, two-dimensional theory succeeds in predicting the acoustic pressure in the far field with reasonable accuracy due to a significant spanwise coherence of the surface pressure difference and predominantly two-dimensional sound radiation. For higher frequencies, however, the full three-dimensional theory is required for an accurate prediction of the acoustic far field. DNS data are used to test some of the key assumptions invoked by Amiet for the derivation of the classical trailing-edge theory. Even though most of the approximations are shown to be reasonable, they collectively lead to a deviation from the DNS results, in particular for higher frequencies. Moreover, because the three-dimensional acoustic analogy does not provide significantly improved results, it is suggested that some of the discrepancies can be attributed to the approach of evaluating the far-field sound using a Kirchhoff-type integration of the surface pressure difference.

Aerodynamic Far Field Noise in Idling Circular Sawblades

1984 ◽  
Vol 106 (3) ◽  
pp. 441-446 ◽  
Author(s):  
C. D. Mote ◽  
Wen Hua Zhu
Keyword(s):  
Sound Pressure ◽  
Acoustic Pressure ◽  
Dipole Source ◽  
Radial Coordinate ◽  
Far Field ◽  
Field Noise ◽  
Dipole Sources

The acoustic pressure radiated to the far field from dipole sources at the rim of a rotating circular sawblade is investigated theoretically and experimentally. Scattering from the sawblade surfaces and the presence of dipole source components in both the normal and radial coordinate directions explain the observed directivity and the dependence of the sound pressure upon sawblade rim velocity.

Influence of Design Parameters on the Unsteady Flow in a Centrifugal Fan

2007 ◽  
Author(s):  
M. Younsi ◽  
F. Bakir ◽  
S. Kouidri ◽  
R. Rey
Keyword(s):  
Unsteady Flow ◽  
Acoustic Pressure ◽  
Flow Behavior ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Design Parameters ◽  
Geometrical Parameters ◽  
Far Field ◽  
Centrifugal Fan ◽  
Wall Pressure Fluctuations

The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental study has been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these fans. The effects on the unsteady flow behavior related to irregular blade spacing, blade number and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using Computational Fluid Dynamics tools (CFD) based on Unsteady Reynolds Averaged Navier Stokes approach (URANS). The sliding mesh technique has been applied at the interfaces between the rotating and stationary zones in order to model the blades’ motion relative to the volute casing. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations (pressure and velocity fluctuations acquired upon the surfaces of the rotating blades) have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H). Using this model, the acoustic pressure has been computed at the fan exit duct. The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 [1] standard. In addition to this, pressure microphones have been flush-mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL) measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.

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