Download or read book Temporal Numerical Simulations of Turbulent Coanda Wall Jets written by Pietro Valsecchi and published by . This book was released on 2006 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: In a novel application of the temporal numerical simulation, an investigation ofturbulence modeling techniques is carried for the turbulent wall jet over aconvex surface (Coanda wall jet.) The simultaneous presence of multipleinstability mechanisms and the interaction with the turbulence dynamics at thesolid boundary produces a unique combination of different large turbulentcoherent structures that constitutes both a consistent challenge for numericalsimulations and an ideal test bed for turbulence models. The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jetrestricts the focus from the global turbulent Coanda wall jet to a smaller, localportion of the flow and offers a wide array of advantages to the present work. Inparticular, the size of the computational domain can be arbitrarily chosen inboth the spanwise and the streamwise directions. This allows to either suppressor enhance individual physical mechanisms and, consequently, to selectivelyreproduce different large coherent structures within the local flow. In the firstpart, temporal numerical simulations are employed to reproduce four differentflow scenarios of the local Coanda wall jet with a level of numerical resolutionthat, because of the reduced size of the computational domain, cannot be matchedby standard DNS of the entire physical flow (spatial DNS, or SDNS.)The TDNS of these four flow scenarios are then used in the second part for ana--posteriori analysis of different turbulence models in order to addresscommon shortcomings shown by Hybrid Turbulence Models (HTM). For each flowscenario, the turbulent flow field is deliberately decomposed in resolved andunresolved flows by the application of different filters in space correspondingto different grid resolution. The behavior of turbulence models can be reproducedfrom the resolved flow and compared to theturbulent stress tensor directlycalculated from the unresolved part of the flow field. Starting from the RANSlimit, turbulence models with different levels of complexity are studied. Successively, the performance of these models is analyzed at intermediatenumerical resolutions between RANS, LES, and DNS. Finally, an improvedformulation of the Flow Simulation Methodology (FSM) is proposed.
Download or read book Numerical Simulations of a Developing Turbulent Wall Jet Along a Thermally Active Surface written by Qingtian Wang and published by . This book was released on 1999 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulations of Wall Jets written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This document summarizes the three year investigation of transitional and turbulent wall jets using direct numerical simulation (DNS) and large eddy simulation (LES). Towards this end, a three-dimensional, incompressible Navier-Stokes code developed in our research group for DNS of boundary-layer transition was adapted to the wall jet geometry. The code is based on the spatial model and is fourth-order accurate. For the LES, a Smagorinsky based subgrid-scale turbulence model and explicit fourth-order accurate compact filtering were incorporated. As an initial condition, a base flow close to Glauert's similarity solution of the laminar wall jet was employed. This flow was forced by blowing and suction through a slot in the wall. Periodic forcing was used for investigating primary and secondary instabilities in transitional wall jets (Re=2OO) We discovered competing two-dimensional (2-D) and three-dimensional (3-D) instability mechanisms which can be influenced significantly by the type of forcing. 2-D large/amplitude forcing produces (2-D) large coherent structures which reduce wall shear but may lead to ejections of vortices from the wall and even to a detachment of the wall jet. Additional 3-D forcing weakens these coherent structures (especially in the near-wall region) and can thus prevent vortex ejections. In our LES of turbulent wall jets, rapid breakdown to turbulence was triggered by large/amplitude 3-D random forcing. Despite the purely 3-D forcing, 2-D coherent structures still emerge in the free shear layer-like outer region, an indication of the strong 2-D instability of the wall jet. A fully turbulent mean flow which compares well with experiments is obtained for higher Reynolds numbers (Re=2OOO).
Download or read book Numerical Simulation of Turbulent Jets with Rectangular Cross Section written by Robert V. Wilson and published by . This book was released on 1997 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three-dimensional turbulent jets with rectangular cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at low Reynolds numbers, whereas at the high Reynolds numbers filtered forms of the equations are solved along with a subgrid scale model to approximate effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Computations are performed for different inlet conditions which represent different types of jet forcing. The phenomenon of axis-switching is observed, and it is confirmed that this is based on self-induction of the vorticity field. Budgets of the mean streamwise velocity show that convection is balanced by gradients of the Reynolds stresses and the pressure.
Download or read book Numerical Simulation of Turbulent Jets with Rectangular Cross section written by Robert V. Wilson and published by . This book was released on 1997 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Direct Numerical Simulations and Modeling of Jets in Crossflow written by Suman Muppidi and published by . This book was released on 2006 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulations of Multiphase Turbulent Jets written by Thomas Gabriel Almeida and published by . This book was released on 2004 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation and Spectral Modal Analysis of Nonlinear Dynamics and Acoustics in Turbulent Jets written by Akhil Nekkanti and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent jets are canonical flows that occur when fluid emerges from an orifice into the surrounding environment, such as the jet from aircraft engines. As the fluid emerges from the nozzle, it forms an unstable shear layer that grows very rapidly, forming large-scale coherent structures, which are the main sources of aft-angle jet noise. The mechanism behind the generation of jet noise is still not fully understood. Further insights into characteristics of coherent structures can aid our understanding of turbulence, and in modeling and controlling various mechanisms. The development of techniques for the education of coherent structures is another objective of this work.The main foci of this work are: (i) performing high-fidelity numerical simulations of turbulent jets and extracting physical insights from coherent flow structures, and (ii) developing techniques that extract these flow structures from the large dataset generated by these simulations. In recent years, spectral proper orthogonal decomposition (SPOD) has emerged as a major tool for extracting coherent structures. In the first part, we extend SPOD for low-rank reconstruction, denoising, prewhitenening, frequency-time analysis, and gappy-data reconstruction. Two approaches for flow-field reconstruction are proposed, a frequency-domain approach, and a time-domain approach. A SPOD-based denoising strategy is also presented, which achieves significant noise reduction while facilitating drastic data compression. A convolution-based strategy is proposed for frequency-time analysis that characterizes the intermittency of spatially coherent flow structures. When applied to the turbulent jet data, SPOD-based frequency-time analysis reveals that the intermittent occurrence of large-scale coherent structures is directly associated with high-energy events. Lastly, a new algorithm, gappy-SPOD, is developed that leverages the space-time correlation of SPOD modes to estimate missing data. Even for highly chaotic flows with up to 20% missing data, our method facilitates that structures associated with different time scales are well-estimated in the missing regions. For the cases considered here, it outperforms established techniques such as gappy-POD and Kriging. In the second part, we investigate the nonlinear dynamics and controllability of coherent structures by actuating them. Large-eddy simulations (LES) of two unforced and four forced jets at Re = 50,000 and M_j = 0.4 were performed. The two unforced jets include an initially laminar and a turbulent jet. All four forced jets are turbulent and are forced at the azimuthal wavenumbers m=0, m=±1, m=±2, and m=±6. The unforced and forced jets were validated with companion experiments. Compared to the turbulent jet, the initially laminar jet develops later but at a faster rate, which is a result of the vortex pairing in the shear layer. The emphasis of the analysis is on characterizing the vortex pairing and the associated nonlinear energy transfer. Here, for the first time, we evaluate the spectral energy budget based on the leading modes of the SPOD. Our analysis reveals that energy flows from the fundamental to its subharmonic, resulting in the growth of the subharmonic. These results provide evidence for a previously suggested parametric resonance mechanism. In the forced jets, we examine the effect of forcing using a recently proposed method, bispectral mode decomposition (BMD), which extracts flow structures associated with nonlinear triadic interactions. We use BMD to construct a cascade of triads and find that the most dominant triads arise due to fundamental self-interaction and second-harmonic-fundamental difference interaction. Furthermore, our analysis of the far-field in the unforced and m=0-forced jets sheds light on the crucial role of difference-interactions in the generation of jet noise.
Download or read book 43rd AIAA Aerospace Sciences Meeting Exhibit written by and published by . This book was released on 2005 with total page 664 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Modeling of a Turbulent Plane Jet Impingement on a Solid Wall written by Chwen-Yuan Guo and published by . This book was released on 1982 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Direct numerical simulations of turbulence written by Kile Siebert Watson and published by . This book was released on 1994 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Study of Turbulence and Scalar Mixing in a Wall jet Using Direct Numerical Simulation written by and published by . This book was released on 2006 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Investigation of Coherent Structures in a Turbulent Coanda Wall Jet written by A. Gross and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings of the 5th International Conference on Jets Wakes and Separated Flows ICJWSF2015 written by Antonio Segalini and published by Springer. This book was released on 2016-07-18 with total page 603 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume collects various contributions from the 5th International Conference on Jets, Wakes and Separated Flows (ICJWSF2015) that took place in Stockholm during June 2015. Researchers from all around the world presented their latest results concerning fundamental and applied aspects of fluid dynamics. With its general character, the conference embraced many aspects of fluid dynamics, such as shear flows, multiphase flows and vortex flows, for instance. The structure of the present book reflects the variety of topics treated within the conference i.e. Jets, Wakes, Separated flows, Vehicle aerodynamics, Wall-bounded and confined flows, Noise, Turbomachinery flows, Multiphase and reacting flows, Vortex dynamics, Energy-related flows and a section dedicated to Numerical analyses.
Download or read book Numerical Simulation of Turbulent Shock Induced Separated Flows written by Afaque Shams and published by LAP Lambert Academic Publishing. This book was released on 2011-03 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shock-induced flow separation and its subsequent reattachment are encountered in many configurations, such as supersonic inlets or rocket nozzles. These phenomena involve complex interactions of boundary layers with compression or expansion waves and exhibit a low-frequency unsteady behaviour which still requires a clear explanation. This study aims at better identifying the physical mechanisms which drive the global structure of these flows and suggesting improved numerical tools in order to predict these more accurately. The appearance of free and restricted separations in supersonic separated jets is more particularly investigated. Various hypotheses are tested to explain the evolution of the associated unsteady asymmetric wall pressure field in function of the nozzle pressure ratio. New numerical strategies are proposed and lead to identify more accurately the appearance of free and restricted separations and the time-varying morphology of the flow during the transition process. Possible origins of side-load activities are extensively investigated by performing the azimuthal expansion of wall pressure field.
Download or read book A Theory for Turbulent Curved Wall Jets written by Joint Institute for Aeronautics and Acoustics. Joint Institute for Aeronautics and Acoustics and published by . This book was released on 1986 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book AIAA Journal written by American Institute of Aeronautics and Astronautics and published by . This book was released on 2006 with total page 1380 pages. Available in PDF, EPUB and Kindle. Book excerpt:
