The finite element method in low speed aerodynamics

The finite element procedure is shown to be of significant impact in design of the 'computational wind tunnel' for low speed aerodynamics. The uniformity of the mathematical differential equation description, for viscous and/or inviscid, multi-dimensional subsonic flows about practical aerodynamic system configurations, is utilized to establish the general form of the finite element algorithm. Numerical results for inviscid flow analysis, as well as viscous boundary layer, parabolic, and full Navier Stokes flow descriptions verify the capabilities and overall versatility of the fundamental algorithm for aerodynamics. The proven mathematical basis, coupled with the distinct user-orientation features of the computer program embodiment, indicate near-term evolution of a highly useful analytical design tool to support computational configuration studies in low speed aerodynamics

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is a combined activity of Case Western Reserve University, Ohio Aerospace Institute (OAI) and NASA Lewis. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1991 are described

ハン カイホウガタ プロペラファン ノ クウリョク セイノウ ト ナイブ リュウドウ ニカンスル ケンキュウ

博士（工学）佐賀大

Aeroacoustic diffraction and dissipation by a short propeller cowl in subsonic flight

This report develops and applies an aeroacoustic diffraction theory for a duct, or cowl, placed around modelled sources of propeller noise. The regime of flight speed is high subsonic. The modelled cowl's inner wall contains a liner with axially variable properties. Its exterior is rigid. The analysis replaces both sides with an unsteady lifting surface coupled to a dynamic thickness problem. The resulting pair of aeroacoustic governing equations for a lined 'ring wing' is valid both for a passive and for an active liner. Their numerical solution yields the effective dipole and monopole distributions of the shrouding system and thereby determines the cowl-diffracted component of the total radiated field. The sample calculations here include a preliminary parametric search for that liner layout which maximizes the cowl's shielding effectiveness. The main conclusion of the study is that a short cowl, passively lined, should provide moderate reductions in propeller noise

Acoustic Source Characterization of Marine Propulsors

Marine propulsors represent one of the most important contributors among anthropogenic sounds radiated into water. Blade based propulsors, e.g., propellers, generate tones at the blade passing frequency and its harmonics, especially in cavitating conditions. In addition to hydrodynamic noise, pressure fluctuations cause vibrations in ship hull leading to mechanical noise. For noise prediction purposes, it is highly beneficial to characterize the noise sources as simplified, complex valued arrays having information on source positions, source strengths and phases. In this paper, procedure to characterize marine propulsors as acoustic sources with inverse method is introduced. First, the numerical model with complete hydro-acoustic sources is investigated. Second, a source model composed of sensible number and distribution of elementary (“equivalent”) compact sources is specified. Then selected responses are used as input in source characterization with inverse method. Finally, the model with equivalent sources is solved and the results are validated by comparison against the results from the complete simulation model. The introduced acoustic source characterization procedure of marine propulsors is applicable also for the responses determined experimentally, e.g., in a cavitation tunnel when the pressure transducer array is determined appropriately

Boundary integral methods for acoustic scattering and radiation

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A source-extraction based coupling method for computational aeroacoustics

This thesis involves the computation of aerodynamically generated sound using a source-extraction based coupling approach. In the present coupling method, the unsteady aerodynamic calculation and the calculation of sound propagation are separated artificially. A set of acoustic perturbation equations is derived by decomposing all flow variables into their dominant part and their fluctuating part, and neglecting some small-magnitude terms, and further simplified into a set of isentropic perturbation equations. Accompanying the derivation of the acoustic perturbation equations, a new extracting formulation for the acoustic source terms contained in the unsteady flow field is proposed. The acoustic source terms required in solving the acoustic perturbation equations are computed numerically from the time-dependent solutions of the unsteady flow field. In the simulation of the unsteady flow, the unsteady Reynolds-Averaged-Navier-Stokes equations (RANS) based cell-centred finite volume method is mainly used. A large eddy simulation (LES) technique is also employed in the investigation of one application case. A powerful and efficient high order dispersion-relation-preserving (DRP) finite difference scheme with fully staggered-grid variable arrangements is implemented in the solution of the acoustic perturbation equations. The performance of a set of radiation boundary conditions is examined for various background flows. A suitable and efficient coupling procedure, in conjunction with the source-extraction formulation, is designed between the cell-centred finite volume based CFD solver and the fully-staggered finite difference based acoustic solver. A range of acoustic model problems are investigated with the purpose of assessing the feasibility and accuracy of the source-extraction formulation associated with the coupling procedure. These model problems include wave propagation, reflection, interaction, and scattering, of acoustic pulse with/without background mean flow. The accuracy of computational results from these model problems is very encouraging when reasonable computational mesh sizes and time steps are used in both the CFD solver and the acoustic solver. Several applications of the source-extraction based coupling method to some more complex cases have also been examined. These cases are: 1) generation and propagation of sound by a series of vortices impinging on a finite thin flat plate; 2) generation and propagation of sound from a subsonic flow past a finite thin flat plate with a small angle of attack; 3) generation and near field radiation of aerodynamic sound from an low speed, laminar flow over a two-dimensional automobile door cavity; 4) flow-induced noise from an open cavity turbulent flow. These application calculations have demonstrated preliminarily the capability and potential of the new source extraction formulation for solving more realistic aeroacoustic problems

Introduction to experimental aeroacoustics, Lecture 1

This introductory lecture gives an overview of the challenges and pitfalls of wind tunnel experiments in aeroacoustics. Most concepts introduced here will be developed in following lecture

Wind tunnel wall interference (January 1980 - May 1988): A selected, annotated bibliography

This selected bibliography lists 423 entries on the subject of wall interference during testing in wind tunnels. It is the third in a series of bibliographies on the subject. The first, NASA TM-87639, August 1986, is concerned with the reduction of wall interference by the use of adaptive walls. The second, NASA TP-89066, December 1986, is on wall interference in V/STOL and high lift testing. This, the third in the series, covers the wall interference literature published during the period January 1980 through May 1988, generally excluding those topics covered in the first two parts