Download or read book Jet Noise Prediction Based on Large Eddy Simulation written by and published by . This book was released on 1999 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Coupled Large Eddy Simulation synthetic Turbulence Method for Predicting Jet Noise written by Joshua Daniel Blake and published by . This book was released on 2020 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: The noise generated by jet engines represents a significant environmental concern that still needs to be addressed. Accurate and efficient numerical predictions are a key step towards reducing jet noise. The current standard in high-fidelity prediction of jet noise is large eddy simulation (LES), which resolves the large turbulent scales responsible for the low and medium frequency noise and models the smallest turbulent scales that correspond to the high frequency noise. While LES requires significant computational resources to produce an accurate solution, it fails to resolve the noise in the high frequency range, which cannot be simply ignored. To circumvent this, in this dissertation the Coupled LES-Synthetic Turbulent method (CLST) was developed to model the missing frequencies that relate to un-resolved sub-grid scale fluctuations in the flow. The CLST method combines the resolved, large-scale turbulent fluctuations from very large eddy simulations (VLES) with modeled, small-scale fluctuations from a synthetic turbulence model. The noise field is predicted using a formulation of the linearized Euler equations (LEE), where the acoustic waves are generated by source terms from the combined fluctuations of the VLES and the synthetic fields. This research investigates both a Fourier mode-based stochastic turbulence model and a synthetic eddy-based turbulence model in the CLST framework. The Fourier mode-based method is computationally less expensive than the synthetic eddy method but does not account for sweeping. Sweeping and straining of the synthetic fluctuations by large flow scales from VLES are accounted for in the synthetic eddy method. The two models are tested on a Mach 0.9 jet at a moderately-high Reynolds number and at a low Reynolds number. The CLST method is an efficient and viable alternative to high resolution LES or DNS because it can resolve the high frequency range in the acoustic noise spectrum at a reasonable expense.

Download or read book Nasa s Large Eddy Simulation Research for Jet Noise Applications written by James R. Debonis and published by BiblioGov. This book was released on 2013-06 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research into large-eddy simulation (LES) for application to jet noise is described. The LES efforts include in-house code development and application at NASA Glenn along with NASA Research Announcement sponsored work at Stanford University and Florida State University. Details of the computational methods used and sample results for jet flows are provided.

Download or read book Contributions to Jet Noise Prediction and Characterisation by Means of Hybrid Acoustic Analogy Techniques written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In Computational aeroacoustics, hybrid approaches first resolve the source and nearfield regions of the flow field by employing Reynolds Averaged Navier-Stokes (RANS) equations, Large Eddy Simulations (LES) or Direct Numerical Simulations (DNS). The source region data is used to form source terms, which are, in turn, applied to either empirical models or equations linearized around a mean flow. An acoustic analogy type of model is used to propagate the acoustics to the farfield regions. The aim of this research is two-fold: to introduce and test a hybrid acoustic analogy, based on a coupling between the Navier-Stokes equations, applied in the source region, and the Non-linear Euler (NLE) equations applied in the acoustic propagation region; and to test and validate a recently derived generalized acoustic analogy theory in the framework of jet noise with acoustic source information obtained from RANS or LES. In the first part, the coupling between the Navier-Stokes and the NLE equations is accomplished via a buffer region, which is used to interpolate and penalize the flow variables of interest from the source region. The penalized flow variables are then applied as source terms in the NLE equations, to calculate the acoustic propagation. The non-linear Euler equations, discretized using high-accurate dispersion-relation preserving schemes constitute a very efficient approach for jet noise predictions in complex environments, especially for supersonic and hypersonic jets, where nonlinearities may propagate over long distances. In the second part, a RANS- or LES-informed model, which is used to provide data for Goldstein's generalized acoustic analogy, is presented. The generalized acoustic analogy of Goldstein is considered, wherein the effects of non-parallelism are taken into account and an asymptotic expansion is utilized to simplify the adjoint Green function equations. The use of the adjoint Green's function leads to a simple model for jet

Download or read book Development of Computational Aeroacoustics Code for Jet Noise and Flow Prediction written by National Aeronautics and Space Adm Nasa and published by . This book was released on 2018-09-27 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate prediction of jet fan and exhaust plume flow and noise generation and propagation is very important in developing advanced aircraft engines that will pass current and future noise regulations. In jet fan flows as well as exhaust plumes, two major sources of noise are present: large-scale, coherent instabilities and small-scale turbulent eddies. In previous work for the NASA Glenn Research Center, three strategies have been explored in an effort to computationally predict the noise radiation from supersonic jet exhaust plumes. In order from the least expensive computationally to the most expensive computationally, these are: 1) Linearized Euler equations (LEE). 2) Very Large Eddy Simulations (VLES). 3) Large Eddy Simulations (LES). The first method solves the linearized Euler equations (LEE). These equations are obtained by linearizing about a given mean flow and the neglecting viscous effects. In this way, the noise from large-scale instabilities can be found for a given mean flow. The linearized Euler equations are computationally inexpensive, and have produced good noise results for supersonic jets where the large-scale instability noise dominates, as well as for the tone noise from a jet engine blade row. However, these linear equations do not predict the absolute magnitude of the noise; instead, only the relative magnitude is predicted. Also, the predicted disturbances do not modify the mean flow, removing a physical mechanism by which the amplitude of the disturbance may be controlled. Recent research for isolated airfoils' indicates that this may not affect the solution greatly at low frequencies. The second method addresses some of the concerns raised by the LEE method. In this approach, called Very Large Eddy Simulation (VLES), the unsteady Reynolds averaged Navier-Stokes equations are solved directly using a high-accuracy computational aeroacoustics numerical scheme. With the addition of a two-equation turbulence model and the use of a relatively c...

Download or read book Large Eddy Simulation for Acoustics written by Claus Wagner and published by Cambridge University Press. This book was released on 2007-01-15 with total page 389 pages. Available in PDF, EPUB and Kindle. Book excerpt: Noise around airports, trains, and industries attracts environmental concern and regulation. Large-eddy simulation (LES) is used for noise-reduced design and acoustical research. This 2007 book, by 30 experts, presents the theoretical background of acoustics and LES, and details about numerical methods, e.g. discretization schemes, boundary conditions, and coupling aspects.

Download or read book Contributions to Jet Noise Prediction and Characterisation by Means of Hybrid Acoustic Analogy Techniques written by Vasileios Sassanis and published by . This book was released on 2018 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: In Computational aeroacoustics, hybrid approaches first resolve the source and nearfield regions of the flow field by employing Reynolds Averaged Navier-Stokes (RANS) equations, Large Eddy Simulations (LES) or Direct Numerical Simulations (DNS). The source region data is used to form source terms, which are, in turn, applied to either empirical models or equations linearized around a mean flow. An acoustic analogy type of model is used to propagate the acoustics to the farfield regions. The aim of this research is two-fold: to introduce and test a hybrid acoustic analogy, based on a coupling between the Navier-Stokes equations, applied in the source region, and the Non-linear Euler (NLE) equations applied in the acoustic propagation region; and to test and validate a recently derived generalized acoustic analogy theory in the framework of jet noise with acoustic source information obtained from RANS or LES. In the first part, the coupling between the Navier-Stokes and the NLE equations is accomplished via a buffer region, which is used to interpolate and penalize the flow variables of interest from the source region. The penalized flow variables are then applied as source terms in the NLE equations, to calculate the acoustic propagation. The non-linear Euler equations, discretized using high-accurate dispersion-relation preserving schemes constitute a very efficient approach for jet noise predictions in complex environments, especially for supersonic and hypersonic jets, where nonlinearities may propagate over long distances. In the second part, a RANS- or LES-informed model, which is used to provide data for Goldstein’s generalized acoustic analogy, is presented. The generalized acoustic analogy of Goldstein is considered, wherein the effects of non-parallelism are taken into account and an asymptotic expansion is utilized to simplify the adjoint Green function equations. The use of the adjoint Green’s function leads to a simple model for jet noise predictions for low frequencies and small observation angles, in the linear regime. Both approaches are extensively tested and validated against numerous benchmark problems and applications.

Download or read book Numerical Simulation of Turbulent Flows and Noise Generation written by Christophe Brun and published by Springer Science & Business Media. This book was released on 2009-03-07 with total page 344 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large Eddy Simulation (LES) is a high-fidelity approach to the numerical simulation of turbulent flows. Recent developments have shown LES to be able to predict aerodynamic noise generation and propagation as well as the turbulent flow, by means of either a hybrid or a direct approach. This book is based on the results of two French/German research groups working on LES simulations in complex geometries and noise generation in turbulent flows. The results provide insights into modern prediction approaches for turbulent flows and noise generation mechanisms as well as their use for novel noise reduction concepts.

Download or read book A Preliminary Study of Acoustic Prediction Technology Based on Detached Eddy Simulations for Supersonic Jets Impinging on Flat Plates written by Yuvraj Dewan and published by . This book was released on 2013 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: "An application of an existing industry tool to study supersonic jets impinging on flat plates is shown. This industry tool is the commercially available CFD package ANSYS FLUENT. The supersonic jet studied is perfectly expanded with a Mach number of 1.5, and it impinges on a flat surface 4 nozzle throat diameters from the jet exit. All turbulence modeling is done using a hybrid RANS/LES technique known as Delayed Detached Eddy Simulation (DDES). A transient solution is calculated using the pressure-based coupled solver formulation with the second-order bounded central-upwind spatial discretization and second-order implicit time marching scheme. Flow features like the stagnation bubble, wall jet and feedback mechanism were studied using countour plots. An examination was also done into the mean flow fields of the jet core. The acoustics of the case were studied using two different techniques, direct measurements and the use of a acoustics source surface method. Using limited computational power, reasonable agreement between simulation and experimental data was found for the flow-field and acoustics. Thus, it was demonstrated that ANSYS FLUENT can be used for this problem to provide good preliminary results in an industry setting with limited computational power"--Leaf vi.

Download or read book On the Use of Linearized Euler Equations in the Prediction of Jet Noise written by R. R. Mankbadi and published by . This book was released on 1995 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Jet Noise Physics and Modeling Using First Principles Simulations written by and published by . This book was released on 2003 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Very Large Eddy Simulations of Jet Noise written by R. R. Mankbadi and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Large Eddy Simulation of Airfoil Self noise written by Joseph George Kocheemoolayil and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Sustaining the continued growth of aviation is critically dependent on managing its noise emission. Developing tools to predict airframe noise from first principles is a pacing item in this regard. Within this context, noise generated by flow past airfoils constitutes an important canonical problem that is also relevant to a wide variety of other applications such as wind turbine noise, cooling fan noise, turbofan noise, propeller noise and helicopter blade noise. The noise generated by a turbulent flow that encounters the trailing edge of an airfoil is the fundamental component of all these problems. Over the past 15 years, significant strides have been made towards using large eddy simulations (LES) for predicting airfoil noise from first-principles. However, they have largely been restricted to canonical configurations at low Reynolds numbers. Perhaps the restriction to low Reynolds numbers is the most serious limitation since majority of the experiments target full-scale Reynolds numbers making one-to-one comparisons impossible. This thesis focuses on extending the scope of LES based predictions to full-scale Reynolds numbers and non-canonical configurations such as the near-stall and post-stall regimes which have received very limited attention owing to their complexity. Wall-modeled large eddy simulations (WMLES) that combine LES with a model for unresolved near-wall turbulence are used to predict airfoil noise at high Reynolds numbers. The Benchmark Problems for Airframe Noise Computations (BANC) workshop is held every year as part of the AIAA/CEAS Aeroacoustics conference. Category 1 of the workshop targets airfoil trailing edge noise prediction at high Reynolds numbers relevant to engineering applications. No first-principles based approach free of empiricism and tunable coefficients has had success in this category to date. Independently validated far-field noise measurements are available for four configurations in the category. Our simulations predict trailing edge noise accurately for all four configurations. Detailed comparisons are made with dedicated experiments. Insensitivity of the simulation results to important aleatory and epistemic uncertainties is established. Resolution requirements for making accurate noise predictions using WMLES are identified through a systematic grid-refinement study. Developing the capability to predict airfoil noise for near-stall and post-stall configurations is necessary to investigate their suspected responsibility for a phenomenon known as Other Amplitude Modulation (OAM) of wind turbine noise. Predicting the flow past a wind turbine airfoil in the post-stall regime is a formidable challenge in itself. In particular, there is a school of thought that large scale three-dimensionality and extreme sensitivity to the experimental facility are inevitable and preclude the possibility of a fair comparison between simulations and measurements in this regime. However, in agreement with a recent theoretical study our simulation results indicate that the lower lift due to large scale three-dimensionality can be reproduced even in span-periodic simulations if the domain size is sufficiently large. The large span simulation predicts the pressure distribution around the airfoil with unprecedented accuracy. Successful prediction of pressure fluctuations on the airfoil surface beneath the suction side boundary layer is demonstrated in the near-stall and post-stall regimes. Previously unavailable two-point statistics of surface pressure fluctuations are documented.

Download or read book Turbulent Statistics from Time Resolved Piv Measurements of a Jet Using Empirical Mode Decomposition written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-05-22 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important. Dahl, Milo D. Glenn Research Center PARTICLE IMAGE VELOCIMETRY; LARGE EDDY SIMULATION; TURBULENCE; JET AIRCRAFT NOISE; AEROACOUSTICS; NOISE PREDICTION (AIRCRAFT); MATHEMATICAL MODELS; SUBSONIC FLOW

Download or read book Direct and Large Eddy Simulation V written by Rainer Friedrich and published by Springer Science & Business Media. This book was released on 2004-04-30 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fifth ERCOFfAC workshop 'Direct and Large-Eddy Simulation-5' (DLES-5) was held at the Munich University of Technology, August 27-29, 2003. It is part of a series of workshops that originated at the University of Surrey in 1994 with the intention to provide a forum for presentation and dis cussion of recent developments in the field of direct and large-eddy simula tion. Over the years the DLES-series has grown into a major international venue focussed on all aspects of DNS and LES, but also on hybrid methods like RANSILES coupling and detached-eddy simulation designed to provide reliable answers to technical flow problems at reasonable computational cost. DLES-5 was attended by 111 delegates from 15 countries. Its three-day pro gramme covered ten invited lectures and 63 original contributions partially pre sented in parallel sessions. The workshop was financially supported by the fol lowing companies, institutions and organizations: ANSYS Germany GmbH, AUDI AG, BMW Group, ERCOFfAC, FORTVER (Bavarian Research Asso ciation on Combustion), JM BURGERS CENTRE for Fluid Dynamics. Their help is gratefully acknowledged. The present Proceedings contain the written versions of nine invited lectures and fifty-nine selected and reviewed contributions which are organized in four parts: 1 Issues in LES modelling and numerics 2 Laminar-turbulent transition 3 Turbulent flows involving complex physical phenomena 4 Turbulent flows in complex geometries and in technical applications.

Download or read book An Approximate Jet Noise Prediction Method Based on Reynolds averaged Navier Stokes Computational Fluid Dynamics Simulation written by Craig Allen Hunter and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Trailing Edge Noise Prediction Using Large Eddy Simulation and Acoustic Analogy written by Eric Manoha and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: