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Author: Monica Christiansen
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ISBN:
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Languages : en
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Currently, the methods available for wind turbine noise prediction are either based on empirical data or require unrealistic computational costs. Although these methods are very valuable, a computationally efficient tool that is based on first principles is needed. The present research proposes a hybrid computational aeroacoustics approach for predicting turbulent-boundary-layer, trailing-edge (TBL-TE) noise. TBL-TE is of interest because it is a dominant source in the total broadband spectrum of wind turbine aerodynamic noise. The proposed method solves the Non-Linear Disturbance Equations (NLDE) for the unsteady flow field in the vicinity of the airfoil trailing edge. Then the noise at a location in far-field location is found by passing the NLDE solution to the aeroacoustics propagation code, PSU-WOPWOP. In this thesis, recent progress made with the development of the NLDE flow solver, TANDEM (Turbulence And Noise using the Disturbance Equation Method) is presented. Test cases are shown to validate the code. Finally, an assessment of the NLDE performance in wall bounded and trailing edge flows is discussed.
Author: Monica Christiansen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Currently, the methods available for wind turbine noise prediction are either based on empirical data or require unrealistic computational costs. Although these methods are very valuable, a computationally efficient tool that is based on first principles is needed. The present research proposes a hybrid computational aeroacoustics approach for predicting turbulent-boundary-layer, trailing-edge (TBL-TE) noise. TBL-TE is of interest because it is a dominant source in the total broadband spectrum of wind turbine aerodynamic noise. The proposed method solves the Non-Linear Disturbance Equations (NLDE) for the unsteady flow field in the vicinity of the airfoil trailing edge. Then the noise at a location in far-field location is found by passing the NLDE solution to the aeroacoustics propagation code, PSU-WOPWOP. In this thesis, recent progress made with the development of the NLDE flow solver, TANDEM (Turbulence And Noise using the Disturbance Equation Method) is presented. Test cases are shown to validate the code. Finally, an assessment of the NLDE performance in wall bounded and trailing edge flows is discussed.
Author: Abhishek Jain
Publisher:
ISBN:
Category :
Languages : en
Pages :
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AIRFOIL self-noise consists of five major sources. One of these identified sources is turbulent boundary layer -- trailing edge (TBL-TE) noise, which is an important source of rotor and wind turbine broadband noise, and the focus of this thesis. Trailing edge noise is the result of unsteady flow interacting with the trailing edge of an airfoil or other sharp edged flow surface. The presence of the sharp trailing edge scatters the sound generated by the turbulent eddies very efficiently, especially for sources in the immediate vicinity of the edge. There is a need for accurate and computationally efficient methods to calculate the turbulent boundary layer trailing-edge (TBL-TE) noise that are not reliant on empirical data. The majority of the current semi-empirical techniques are based on measurements from symmetric NACA airfoil sections (i.e. NACA 0012). These techniques are generally not coupled with CFD solvers to obtain turbulent boundary layer data that provides pertinent parameters used in the acoustic calculations. Some methods exist that incorporate CFD solutions like Large Eddy simulations (LES) into their noise prediction algorithms. But these are prohibitively expensive and impractical for routine use. The method described in this paper is a first principles approach that aims to predict the TBL-TE noise using computational aeroacoustic (CAA) techniques without resorting to empiricism.The prediction of trailing edge noise requires an accurate calculation of the boundary layer fluctuations in the vicinity of the trailing edge. Scales in the computational domain ranging from the small turbulent boundary layer scales to those of the long-range noise propagation need to be resolved. These data can be obtained using simulation techniques like Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES). However such simulations for complete helicopters or wind turbine rotors are impractical given today's computational resources. Also, DNS becomes unrealistic for the propagation of the acoustic signal to distant observers. The method described here overcomes these limitations by using a hybrid CAA approach coupled with a flow solver based on the non-linear disturbance equations (NLDE). The overall problem is separated into component problems with the NLDE equations applied over a relatively small noise generating region i.e. approximately the last 10% of the chord or less. This makes the solution more computationally efficient than LES for the full airfoil or rotor and enables the use of the most computationally efficient methods in the required regions. The proposed method is advantageous to helicopter and wind turbine manufacturers as it provides a tool for the prediction of rotor broadband noise at the design stage. This can also be used as a tool to reduce noise through the analysis of appropriate noise reduction devices.
Author:
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Category :
Languages : en
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Author:
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Category :
Languages : en
Pages : 18
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The potential benefits of using the Nonlinear Disturbance (NLD) equations, which govern flow variable fluctuations about an estimated mean, for the large-eddy simulation (LES) of wall bounded shear flows are investigated in this paper. In addition to verifying the suitability of the NLD equations for wall bounded flows, we build upon its advantages by introducing a new wall model that is easily and efficiently implemented within the NLD equation framework. The model implementation consists of defining a near wall region in which a modified linear set of equations are solved. The linear equation set allows disturbances to pass through and interact with the wall without altering the estimated mean. The streamwise and spanwise grid resolution of this near wall region can therefore be significantly relaxed while maintaining reasonable mean quantities such as skin friction. Comparisons of predicted turbulence intensity profiles and wall pressure spectra to experimental data for a fully developed turbulent flat plate boundary layer are used to verify the suitability of the NLD equations for wall bounded flows. Preliminary results of a turbulent channel flow simulation are also presented to assess the new wall model.
Author: W. Schroeder
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
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Book Description
The paper presents a large-eddy simulation of the flow over a sharp trailing edge. To minimize the computational effort inflow conditions for fully turbulent compressible boundary layers are developed. The LES findings show good agreement with other numerical and experimental data. For the prediction of the trailing-edge noise, acoustic perturbation equations are derived, which are excited by sources determined from results of a compressible flow simulation. Results of acoustic fields are presented for a model problem.
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Category : Aeronautics
Languages : en
Pages : 944
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Book Description
Author: Jay C. Hardin
Publisher: Springer Science & Business Media
ISBN: 1461383420
Category : Science
Languages : en
Pages : 525
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Book Description
Computational aeroacoustics is rapidly emerging as an essential element in the study of aerodynamic sound. As with all emerging technologies, it is paramount that we assess the various opportuni ties and establish achievable goals for this new technology. Essential to this process is the identification and prioritization of fundamental aeroacoustics problems which are amenable to direct numerical siIn ulation. Questions, ranging from the role numerical methods play in the classical theoretical approaches to aeroacoustics, to the correct specification of well-posed numerical problems, need to be answered. These issues provided the impetus for the Workshop on Computa tional Aeroacoustics sponsored by ICASE and the Acoustics Division of NASA LaRC on April 6-9, 1992. The participants of the Work shop were leading aeroacousticians, computational fluid dynamicists and applied mathematicians. The Workshop started with the open ing remarks by M. Y. Hussaini and the welcome address by Kristin Hessenius who introduced the keynote speaker, Sir James Lighthill. The keynote address set the stage for the Workshop. It was both an authoritative and up-to-date discussion of the state-of-the-art in aeroacoustics. The presentations at the Workshop were divided into five sessions - i) Classical Theoretical Approaches (William Zorumski, Chairman), ii) Mathematical Aspects of Acoustics (Rodolfo Rosales, Chairman), iii) Validation Methodology (Allan Pierce, Chairman), iv) Direct Numerical Simulation (Michael Myers, Chairman), and v) Unsteady Compressible Flow Computa tional Methods (Douglas Dwoyer, Chairman).
Author: John David Anderson
Publisher: AIAA
ISBN: 9781563474590
Category : Science
Languages : en
Pages : 710
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Book Description
This book is a self-contained text for those students and readers interested in learning hypersonic flow and high-temperature gas dynamics. It assumes no prior familiarity with either subject on the part of the reader. If you have never studied hypersonic and/or high-temperature gas dynamics before, and if you have never worked extensively in the area, then this book is for you. On the other hand, if you have worked and/or are working in these areas, and you want a cohesive presentation of the fundamentals, a development of important theory and techniques, a discussion of the salient results with emphasis on the physical aspects, and a presentation of modern thinking in these areas, then this book is also for you. In other words, this book is designed for two roles: 1) as an effective classroom text that can be used with ease by the instructor, and understood with ease by the student; and 2) as a viable, professional working tool for engineers, scientists, and managers who have any contact in their jobs with hypersonic and/or high-temperature flow.
Author: Ernst Heinrich Hirschel
Publisher: Springer Science & Business Media
ISBN: 3540265198
Category : Technology & Engineering
Languages : en
Pages : 419
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Book Description
The last two decades have brought two important developments for aeroth- modynamics. One is that airbreathing hypersonic flight became the topic of technology programmes and extended system studies. The other is the emergence and maturing of the discrete numerical methods of aerodyn- ics/aerothermodynamics complementary to the ground-simulation facilities, with the parallel enormous growth of computer power. Airbreathing hypersonic flight vehicles are, in contrast to aeroassisted re-entry vehicles, drag sensitive. They have, further, highly integrated lift and propulsion systems. This means that viscous eflFects, like boundary-layer development, laminar-turbulent transition, to a certain degree also strong interaction phenomena, are much more important for such vehicles than for re-entry vehicles. This holds also for the thermal state of the surface and thermal surface effects, concerning viscous and thermo-chemical phenomena (more important for re-entry vehicles) at and near the wall. The discrete numerical methods of aerodynamics/aerothermodynamics permit now - what was twenty years ago not imaginable - the simulation of high speed flows past real flight vehicle configurations with thermo-chemical and viscous effects, the description of the latter being still handicapped by in sufficient flow-physics models. The benefits of numerical simulation for flight vehicle design are enormous: much improved aerodynamic shape definition and optimization, provision of accurate and reliable aerodynamic data, and highly accurate determination of thermal and mechanical loads. Truly mul- disciplinary design and optimization methods regarding the layout of thermal protection systems, all kinds of aero-servoelasticity problems of the airframe, et cetera, begin now to emerge.
Author: Wayne Johnson
Publisher: Cambridge University Press
ISBN: 1107355281
Category : Technology & Engineering
Languages : en
Pages : 949
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Book Description
A rotorcraft is a class of aircraft that uses large-diameter rotating wings to accomplish efficient vertical take-off and landing. The class encompasses helicopters of numerous configurations (single main rotor and tail rotor, tandem rotors, coaxial rotors), tilting proprotor aircraft, compound helicopters, and many other innovative configuration concepts. Aeromechanics covers much of what the rotorcraft engineer needs: performance, loads, vibration, stability, flight dynamics, and noise. These topics include many of the key performance attributes and the often-encountered problems in rotorcraft designs. This comprehensive book presents, in depth, what engineers need to know about modelling rotorcraft aeromechanics. The focus is on analysis, and calculated results are presented to illustrate analysis characteristics and rotor behaviour. The first third of the book is an introduction to rotorcraft aerodynamics, blade motion, and performance. The remainder of the book covers advanced topics in rotary wing aerodynamics and dynamics.
