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Computational Aeroacoustics in Low Mach Number Flows

2015-08-10
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Release : 2015-08-10
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Book Synopsis Computational Aeroacoustics in Low Mach Number Flows by : Pradera-Mallabiabarrena Ainara

Download or read book Computational Aeroacoustics in Low Mach Number Flows written by Pradera-Mallabiabarrena Ainara. This book was released on 2015-08-10. Available in PDF, EPUB and Kindle. Book excerpt: This work studies a flexible methodology to predict radiated noise. The main contributions of this work are focused on the way flow parameters are acquired in fluid dynamics simulations are synthesised, stored and later used to predict radiated noise, but also on the procedure considered in the radiation calculations. The methodology has been restricted to low Mach number flows where the noise generation is dominated by the interaction of the flow with a surface at least one of whose typical dimensions is short compared to the wavelength of intereset, known as a compact source. The radiation calculations may employ purely analytical methods or numerical methods, depending on the application. Finally, the requirements in data storage and transfer are significantly reduced by using this method. Besides, if the flow remains essentially the same, the Computational Fluid Dynamics simulation should not need to be repeated in case different acoustic scenarios should be studied.

Aeroacoustics of Low Mach Number Flows

2023-09-26 Technology & Engineering
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Release : 2023-09-26
Genre : Technology & Engineering
Kind : eBook
Book Rating : 587/5 ( reviews)

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Book Synopsis Aeroacoustics of Low Mach Number Flows by : Stewart Glegg

Download or read book Aeroacoustics of Low Mach Number Flows written by Stewart Glegg. This book was released on 2023-09-26. Available in PDF, EPUB and Kindle. Book excerpt: Aeroacoustics of Low Mach Number Flows: Fundamentals, Analysis and Measurement, Second Edition provides a detailed introduction to sound radiation from subsonic flow over moving surfaces. This phenomenon is the most widespread cause of flow noise in engineering systems, including fan noise, rotor noise, wind turbine noise, boundary layer noise, airframe noise and aircraft noise. This fully updated new edition includes additional problems, illustrations and summary materials to support readers. New content covers Rapid Distortion theory (RDT), boundary layer wall pressure fluctuations, and flow induced sound at surfaces. Themes addressing non-compressible flows have also been added, offering coverage of hydroacoustic as well as aeroacoustic applications. New support materials for this edition include course outlines, problem sets, sample MATLAB codes and experimental data to be found at www.aeroacoustics.net. - Addresses, in detail, sound from rotating blades, ducted fans, airframes, boundary layers, and more - Presents theory in such a way that it can be used in computational methods and calculating sound levels - Includes coverage of different experimental approaches to this subject

Computational Aeroacoustics

2012-12-06 Science
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Release : 2012-12-06
Genre : Science
Kind : eBook
Book Rating : 420/5 ( reviews)

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Book Synopsis Computational Aeroacoustics by : Jay C. Hardin

Download or read book Computational Aeroacoustics written by Jay C. Hardin. This book was released on 2012-12-06. Available in PDF, EPUB and Kindle. Book excerpt: 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).

Computational Aeroacoustics of Complex Flows at Low Mach Number

2010
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Release : 2010
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Book Synopsis Computational Aeroacoustics of Complex Flows at Low Mach Number by : Yaser Khalighi

Download or read book Computational Aeroacoustics of Complex Flows at Low Mach Number written by Yaser Khalighi. This book was released on 2010. Available in PDF, EPUB and Kindle. Book excerpt: Designing quiet mechanical systems requires an understanding of the physics of sound generation. Among various sources of noise, aerodynamic sound is the most difficult component to mitigate. In practical applications, aerodynamic sound is generated by complex flow phenomena such as turbulent wakes and boundary layers, separation, and interaction of turbulent flow with irregular solid bodies. In addition, sound waves experience multiple reflections from solid bodies before they propagate to an observer. Prediction of an acoustic field in such configurations requires a general aeroacoustic framework to operate in complex configurations. A general computational aeroacoustics method is developed to evaluate noise generated by low Mach number flow in complex configurations. This method is a hybrid approach which uses Lighthill's acoustic analogy in conjunction with source-data from an incompressible calculation. Flow-generated sound sources are computed by using either direct numerical simulation (DNS) or large eddy simulation (LES); scattering of sound waves are computed using a boundary element method (BEM). In this approach, commonly-made assumptions about the geometry of scattering objects or frequency content of sound are not present, thus it can be applied to a wider range of aeroacoustic problems, where sound is generated by interaction of complex flows with solid surfaces. This new computational technique is applied to a variety of aeroacoustic problems ranging from sound generated by laminar and turbulent vortex shedding from cylinders to realistic configurations such as noise emitted from a rear-view side mirror and a hydrofoil. The purpose of each test case, in addition to validation of the method, is to explore various physical and technical aspects of the problem of sound generation by unsteady flows. Through these test cases, it is demonstrated that the predicted sound field by this technique is accurate in the frequency range in which the sound sources are resolved by the computational mesh. It is also shown that in computation of sound, acoustic analogies are less sensitive to numerical errors than direct computations. Finally, a discussion on the efficacy of LES and the effect of sub-grid scale dynamics on predicted sound is presented.

Aeroacoustic Computation of Tones Generated from Low Mach Number Cavity Flows, Using a Preconditioned Method

2016
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Release : 2016
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Book Synopsis Aeroacoustic Computation of Tones Generated from Low Mach Number Cavity Flows, Using a Preconditioned Method by : Brent Paul

Download or read book Aeroacoustic Computation of Tones Generated from Low Mach Number Cavity Flows, Using a Preconditioned Method written by Brent Paul. This book was released on 2016. Available in PDF, EPUB and Kindle. Book excerpt: The hydrodynamically generated noise produced from flow over cavities includes both broadband and tones. The frequency content and amplitude of the resulting noise is a function of the cavity geometry and the approaching boundary layer. The cavity length to depth ratio (L/D) is an important parameter that governs the characteristics of cavity noise generated. While both of the noise components are important this work will focus on the production of cavity tones. Cavity tones typically have higher sound pressure levels and can propagate over longer distances than the broadband noise.The enhancements to the numerical code shown in this work result in the first non-hybrid tool for the prediction of low speed cavity noise. At moderate subsonic Mach numbers the direct calculation of cavity tones has been performed by numerous researchers using highly accurate spatial and time discretization. However, most researchers that are trying to predict the noise from low Mach number flows take a hybrid approach where the fluid dynamics of the simulation are solved with a computational fluid dynamics (CFD) solver and the acoustics are solved separately. The other solver is often based on Lighthills Acoustic Analogy or an asympototic method such as the Expansion about Incompressible Flow (EIF). This work calculates the conservative Navier-Stokes variables to directly predict the cavity tones.The numerical solver CHOPA (Compressible, High-Order Parallel Acoustics) is extended in this work for the accurate and fast calculation of low Mach number cavity flows. A time-derivative preconditioner equalizes the acoustic wave and turbulence convective speeds to allow for a more efficient time step and shorter calculation times. Because the preconditioner destroys the time accuracy of the solution a dual-time step approach is used for the time integration. Other modifications to the code are required to facilitate the proper implementation of the preconditioner: Matrix-based artificial dissipation, buffer zone, and extrapolation boundary condition. An extension by Buelow of Choi-Merkles viscous preconditioner is selected for this work.There are several different numerical validations performed on the preconditioned Navier-Stokes solver to ensure high quality solutions. First, the combination buffer zone/extrapolation boundary condition is tested by simulating the propagation of a Gaussian pressure pulse. Then the preconditioner is tested with several different analyses. The convection of a uniform velocity flow field with a random perturbation imposed on the flow field tests if the preconditioned solution is independent of the flow Mach number. Then a time accurate Gaussian pressure pulse tests the ability of the preconditioner to solve a time dependent solution. Lastly, a laminar boundary layer flow is calculated and compared to an exact solution showing that the preconditioner is effective for viscous flows. The prediction of cavity tones from a deep (L/D = 0.78) and shallow (L/D = 2.35) cavity is simulated for comparison against the experimental measurements of Block. The Mach number of the simulations varied from 0.05 to 0.4. The cavity tone frequencies have an acceptable comparison against the measurements for the deep cavity. However, the shallow cavity tones were almost independent of the flow speed, which may be an indication that standing waves in the cavity could be responsible for the tones for this geometry. The other cavity simulations replicated the experiment by Stallings et al.for L/D = 5.42 and L/D = 6.25 for a Mach number of 0.2. The time-averaged wall pressure fluctuations were compared to measurements. While the predicted wall pressures did not match the experiment the discrepancy is because of the existence of a wake mode in the numerical results. This is a two-dimensional phenomenon where a large vortex is generated in the cavity and then violently ejected from the cavity, significantly increasing drag. While not matching the experiment the results behave as expected for a cavity resonating in a wake mode.

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