[PDF] Structure Preserving Numerical Simulation Of Compressible Flows eBook

Author : Nipun Kwatra
Publisher : Stanford University
Page : 117 pages
File Size : 26,49 MB
Release : 2011
Category :
ISBN :

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This thesis presents a semi-implicit method for simulating inviscid compressible flow and its extensions for strong implicit coupling of compressible flow with Lagrangian solids, and artificial transition of fluid from compressible flow to incompressible flow regime for graphics applications. First we present a novel semi-implicit method for alleviating the stringent CFL condition imposed by the sound speed in simulating inviscid compressible flow with shocks, contacts and rarefactions. The method splits the compressible flow flux into two parts -- an advection part and an acoustic part. The advection part is solved using an explicit scheme, while the acoustic part is solved using an implicit method allowing us to avoid the sound speed imposed CFL restriction. Our method leads to a standard Poisson equation similar to what one would solve for incompressible flow, but has an identity term more similar to a diffusion equation. In the limit as the sound speed goes to infinity, one obtains the Poisson equation for incompressible flow. This implicit pressure solve also lends itself nicely to solve for the pressure and coupling forces at a solid fluid interface. With this pressure solve as the foundation, we then develop a novel method to implicitly two-way couple Eulerian compressible flow to volumetric Lagrangian solids. The method works for both deformable and rigid solids and for arbitrary equations of state. Similar to previous fluid-structure interaction methods, we apply pressure forces to the solid and enforce a velocity boundary condition on the fluid in order to satisfy a no-slip constraint. Unlike previous methods, however, we apply these coupled interactions implicitly by adding the constraint to the pressure system and combining it with any implicit solid forces in order to obtain a strongly coupled system. Because our method handles the fluid-structure interactions implicitly, we avoid introducing any new time step restrictions and obtain stable results even for high density-to-mass ratios, where explicit methods struggle or fail. We exactly conserve momentum and kinetic energy (thermal fluid-structure interactions are not considered) at the fluid-structure interface, and hence naturally handle highly non-linear phenomenon such as shocks, contacts and rarefactions. The implicit pressure solve allows our method to be used for any sound speed efficiently. In particular as the sound speed goes to infinity, we obtain the standard Poisson equation for incompressible flow. This allows our method to work seamlessly and efficiently as the sound speed in the underlying flow field changes. Building on this feature of our method, we next develop a practical approach to integrating shock wave dynamics into traditional smoke simulations. Previous methods for doing this either simplified away the compressible component of the flow and were unable to capture shock fronts or used a prohibitively expensive explicit method that limits the time step of the simulation long after the relevant shock waves and rarefactions have left the domain. Instead, using our semi-implicit formulation allows us to take time steps on the order of fluid velocity. As we handle the acoustic fluid effects implicitly, we can artificially drive the sound speed c of the fluid to infinity without going unstable or driving the time step to zero. This permits the fluid to transition from compressible flow to the far more tractable incompressible flow regime once the interesting compressible flow phenomena (such as shocks) have left the domain of interest, and allows the use of state-of-the-art smoke simulation techniques.

Author : Eduard Feireisl
Publisher :
Page : 0 pages
File Size : 35,60 MB
Release : 2021
Category :
ISBN : 9783030737894

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This book is devoted to the numerical analysis of compressible fluids in the spirit of the celebrated Lax equivalence theorem. The text is aimed at graduate students in mathematics and fluid dynamics, researchers in applied mathematics, numerical analysis and scientific computing, and engineers and physicists. The book contains original theoretical material based on a new approach to generalized solutions (dissipative or measure-valued solutions). The concept of a weak-strong uniqueness principle in the class of generalized solutions is used to prove the convergence of various numerical methods. The problem of oscillatory solutions is solved by an original adaptation of the method of K-convergence. An effective method of computing the Young measures is presented. Theoretical results are illustrated by a series of numerical experiments. Applications of these concepts are to be expected in other problems of fluid mechanics and related fields.

Author : Mohamed M Hafez
Publisher : World Scientific
Page : 708 pages
File Size : 33,32 MB
Release : 2003-01-23
Category : Mathematics
ISBN : 9814486396

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This book consists of 37 articles dealing with simulation of incompressible flows and applications in many areas. It covers numerical methods and algorithm developments as well as applications in aeronautics and other areas. It represents the state of the art in the field.

Author : Nipun Kwatra
Publisher :
Page : pages
File Size : 31,33 MB
Release : 2011
Category :
ISBN :

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This thesis presents a semi-implicit method for simulating inviscid compressible flow and its extensions for strong implicit coupling of compressible flow with Lagrangian solids, and artificial transition of fluid from compressible flow to incompressible flow regime for graphics applications. First we present a novel semi-implicit method for alleviating the stringent CFL condition imposed by the sound speed in simulating inviscid compressible flow with shocks, contacts and rarefactions. The method splits the compressible flow flux into two parts -- an advection part and an acoustic part. The advection part is solved using an explicit scheme, while the acoustic part is solved using an implicit method allowing us to avoid the sound speed imposed CFL restriction. Our method leads to a standard Poisson equation similar to what one would solve for incompressible flow, but has an identity term more similar to a diffusion equation. In the limit as the sound speed goes to infinity, one obtains the Poisson equation for incompressible flow. This implicit pressure solve also lends itself nicely to solve for the pressure and coupling forces at a solid fluid interface. With this pressure solve as the foundation, we then develop a novel method to implicitly two-way couple Eulerian compressible flow to volumetric Lagrangian solids. The method works for both deformable and rigid solids and for arbitrary equations of state. Similar to previous fluid-structure interaction methods, we apply pressure forces to the solid and enforce a velocity boundary condition on the fluid in order to satisfy a no-slip constraint. Unlike previous methods, however, we apply these coupled interactions implicitly by adding the constraint to the pressure system and combining it with any implicit solid forces in order to obtain a strongly coupled system. Because our method handles the fluid-structure interactions implicitly, we avoid introducing any new time step restrictions and obtain stable results even for high density-to-mass ratios, where explicit methods struggle or fail. We exactly conserve momentum and kinetic energy (thermal fluid-structure interactions are not considered) at the fluid-structure interface, and hence naturally handle highly non-linear phenomenon such as shocks, contacts and rarefactions. The implicit pressure solve allows our method to be used for any sound speed efficiently. In particular as the sound speed goes to infinity, we obtain the standard Poisson equation for incompressible flow. This allows our method to work seamlessly and efficiently as the sound speed in the underlying flow field changes. Building on this feature of our method, we next develop a practical approach to integrating shock wave dynamics into traditional smoke simulations. Previous methods for doing this either simplified away the compressible component of the flow and were unable to capture shock fronts or used a prohibitively expensive explicit method that limits the time step of the simulation long after the relevant shock waves and rarefactions have left the domain. Instead, using our semi-implicit formulation allows us to take time steps on the order of fluid velocity. As we handle the acoustic fluid effects implicitly, we can artificially drive the sound speed c of the fluid to infinity without going unstable or driving the time step to zero. This permits the fluid to transition from compressible flow to the far more tractable incompressible flow regime once the interesting compressible flow phenomena (such as shocks) have left the domain of interest, and allows the use of state-of-the-art smoke simulation techniques.

Author : Ben Chacon
Publisher :
Page : pages
File Size : 23,28 MB
Release : 2013
Category :
ISBN : 9781303791697

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The fundamental equations for compressible flow are solved using a velocity - pressure - vorticity formulation producing a solution that satisfies continuity and vorticity definitions up to machine accuracy. Chapter 1 reviews many algorithms used to solve this problem. Unlike those methods, no pressure - velocity relation or artificial compressibility is assumed in the present formulation, so the equations for kinematics, pressure and momentum are decoupled independent building blocks in the iterative process. As a consequence, the resulting modular algorithm can be used directly for compressible or incompressible flows, contrasting with other current techniques. Moreover the present formulation also applies to two-dimensional and three-dimensional, structured and unstructured grids without any changes, even though only the two-dimensional version was implemented. In Chapter 2, the original formulation is described. A functional minimization technique is used to discretize the kinematics equations, mimicking continuous methods used in the field of functional analysis and providing a common framework to understand, model and implement the solution algorithm. Suitable preconditioning and radial interpolation techniques are employed to balance precision and computational speed. The Poisson equation for pressure is solved similarly by minimizing a suitable functional. The momentum equations are then solved using a finite volume approach adding a controlled amount of artificial viscosity according to mesh size and Reynolds number, resulting in a stable calculation. The vorticity is then obtained as the curl of the velocity. Temperature is similarly computed from the energy equation in an outer loop. Suitable adjustments to pressure and temperature enable the ideal gas equation to fit both the compressible and incompressible paradigmsSubsequent chapters deal with validation, applying the computer efficient implementation of the algorithm to a variety of well documented aerodynamic benchmark problems. Examples include compressible and incompressible flow, steady and unsteady problems and flow over cylinders and airfoils over a variety of Reynolds and subsonic Mach numbers.