We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you!
Presentation is loading. Please wait.
Published byKorbin Greenslade
Modified over 2 years ago
10-1 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Chapter 10 Transient Flow Modeling Introductory FLUENT Training Sharif University of Technology Lecturer: Ehsan Saadati
Transient Flow Modeling 10-2 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Motivation Nearly all flows in nature are transient! – Steady-state assumption is possible if we: Ignore transient fluctuations Employ ensemble/time-averaging to remove unsteadiness (this is what is done in modeling turbulence) In CFD, steady-state methods are preferred – Lower computational cost – Easier to postprocess and analyze Many applications require resolution of transient flow: – Aerodynamics (aircraft, land vehicles,etc.) – vortex shedding – Rotating Machinery – rotor/stator interaction, stall, surge – Multiphase Flows – free surfaces, bubble dynamics – Deforming Domains – in-cylinder combustion, store separation – transient Heat Transfer – transient heating and cooling – Many more.
Transient Flow Modeling 10-3 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Origins of Transient Flow Naturally occurring transients – transient flow due to growth of instabilities within the fluid or a non-equilibrium initial fluid state – Examples: natural convection flows, turbulent eddies of all scales, fluid waves (gravity waves, shock waves) Forced transients – Time-dependent boundary conditions, source terms drive the transient flow field – Examples: pulsing flow in a nozzle, rotor-stator interaction in a turbine stage Kelvin-Helmholtz Cloud InstabilityBuoyant Box Falling Into a Pool of Water
Transient Flow Modeling 10-4 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Transient CFD Analysis Simulate a transient flow field over a specified time period – Solution may approach: Steady-state solution – Flow variables stop changing with time Time-periodic solution – Flow veriables fluctuate with repeating pattern – Your goal may also be simply to analyze the flow over a prescribed time interval. Free surface flows Moving shock waves Etc. Extract quantities of interest – Natural frequencies (e.g. Strouhal Number) – Time-averaged and/or RMS values – Time-related parameters (e.g. time required to cool a hot solid, residence time of a pollutant) – Spectral data – fast Fourier transform (FFT)
Transient Flow Modeling 10-5 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Transient Flow Modeling Workflow Enable the transient solver. Set up physical models and boundary conditions as usual. – Transient boundary conditions are possible – you can use either a UDF or profile to accomplish this. Prescribe initial conditions – Best to use a physically realistic initial condition, such as a steady solution. Assign solver settings and configure solution monitors. Configure animations and data output/sampling options Select time step and max iterations per time step Prescribe the number of time steps. Run the calculations (Iterate)
Transient Flow Modeling 10-6 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Enabling the Transient Solver To enable the transient solver, select the Transient button on the General problem setup form: Before performing iterations, you will need to set some additional controls. – Solver settings – Animations – Data export / Autosave options
Transient Flow Modeling 10-7 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Selecting the Transient Time Step Size Time step size, t, is set in the Run Calculation form. – t must be small enough to resolve time-dependent features; make sure the convergence is reached within the number of Max Iterations per Time Step – The order or magnitude of an appropriate time step size can be estimated as: – Time step size estimate can also be chosen so that the transient characteristics of the flow can be resolved (e.g. flow within a known period of fluctuations) To iterate without advancing in time, specify zero time steps. This will instruct the solver to converge the current time step only. The PISO scheme may aid in accelerating convergence for many transient flows (set in the Solution Methods form).
Transient Flow Modeling 10-8 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Transient Flow Modeling Options Adaptive Time Stepping – Automatically adjusts time-step size based on local truncation error analysis – Customization possible via UDF Time-averaged statistics – Particularly useful for LES turbulence calculations For the density-based solver, the Courant number defines: – The global time step size for density-based explicit solver. – The pseudo time step size for density- based implicit solver Real time step size must still be defined in the Iterate panel
Transient Flow Modeling 10-9 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Transient Flow Modeling – Animations You must set up any animations BEFORE performing iterations. – Animation frames are written/stored on-the-fly during calculations.
Transient Flow Modeling ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Creating Animations – Alternate Method Another method in FLUENT is available which makes use of the Execute Commands feature. Text commands or macros can be defined which are executed by the solver at prescribed iteration or time step intervals. This approach is very useful in creating high-quality animations of CFD results. – A command is defined which generates an animation frame (contour plot, vector plot, etc.) and then writes that frame to a hard copy file. – Third-party software can then be used to link the hard copy files into an animation file (AVI, MPG, GIF, etc.)
Transient Flow Modeling ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Performing Iterations The most common time advancement scheme is the iterative scheme. – The solver converges the current time step and then advances time. – Time is advanced when Max Iterations/Time Step is reached or convergence criteria are satisfied. – Time steps are converged sequentially until the Number of Time Steps is reached. Solution initialization defines the initial condition and it must be realistic. – Sets both the initial mass of fluid in the domain and the initial state of the flow field. Non-iterative Time Advancement (NITA) is available for faster computation time.
Transient Flow Modeling ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Convergence Behavior Residual plots for transient simulations are not always indicative of a converged solution. A residual plot for a simple transient calculation is shown here. You should select the time step size such that the residuals reduce by around three orders of magnitude within one time step. – This will ensure accurate resolution of transient behavior.
Transient Flow Modeling ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Tips for Success in Transient Flow Modeling Use PISO scheme for Pressure-Velocity Coupling – this scheme provides faster convergence for transient flows than the standard SIMPLE approach. Select the time step size so that the solution converges nominally three orders of magnitude for each time step (of course, convergence behavior is problem-specific). Select the number of iterations per time step to be around 20 – it is better to reduce the time step size than to do too many iterations per time step. Remember that accurate initial conditions are just as important as boundary conditions for transient problems – initial condition should always be physically realistic! Configure any animations you wish to see before running the calculations.
WS6-1 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Introduction to CFX Workshop 6 Electronics Cooling.
1 Ι © Dassault Systèmes Ι Confidential Information Ι SolidWorks Flow Simulation Instructor Guide.
Javier Junquera Molecular dynamics in different ensembles.
Javier Junquera Advanced Computing Starting-up: How to setup the initial conditions for a Molecular Dynamic Simulation.
Deep Dive Into Autoguiding. Contents Introduction Brief on Basics Guide Technical Blurb PHD Guiding Software PHD Advanced Settings EQMod Pulse Guiding.
Mark Sherman Danilo Centazzo. 2 Introduction to FEMAP Agenda Day 1 Introduction Install, Setup and Customize FEMAP The User interface and the On-Line.
Copyright 2011 John Wiley & Sons, Inc Business Data Communications and Networking 11th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons, Inc.
6-Hour Hands-On Introduction to LabVIEW. Course Goals Become comfortable with the LabVIEW environment and data flow execution Ability to use LabVIEW to.
1 The Arena modeling system is a flexible and powerful tool that allows analysts to create animated simulation models that accurately represent virtually.
Simulation with Arena, 5th ed.Chapter 4 – Modeling Basic Operations and InputsSlide 1 of 68 Modeling Basic Operations and Inputs Chapter 4 Last revision.
Computing Higher - SD Process – Topic 2 St Andrew’s High School Unit 2 Software Development Process.
2 Welcome To Defect Management Training Objective: The objective of this course is to learn about standards that emphasize a best practice approach for.
CHAM June 2009 Gateways to PHOENICS: SHELLFLO. Lecture to Heat Transfer Society, June 24, 2009 Advanced Stream Analysis: Predicting the Flow in Shell-and-Tube.
G5BAIM Artificial Intelligence Methods Graham Kendall Simulated Annealing.
1 Benefits Transfer and Meta Analysis Professor Anil Markandya Department of Economics and International Development University of Bath
Profile Fitting for Analysis of XRPD Data using HighScore Plus v3 Scott A Speakman, Ph.D. Center for Materials Science and Engineering at MIT
Debugging ACL Scripts. Basic Debugging Steps If the script failed, check the log. The log will tell you on what command the script failed. If knowing.
Chapter 17: Recovery System Failure Classification Storage Structure Recovery and Atomicity Log-Based Recovery Shadow Paging Recovery With Concurrent Transactions.
Introduction to Sentaurus TCAD David Pennicard – University of Glasgow.
Computational Heat Transfer and Fluid Flow Oct 17-21, 2007 Xian, China CFD: Progress and Prospects by Brian Spalding, of CHAM, Ltd A lecture at the Asian.
Dynamos in Accretion Disks: A general review and some moderately biased comments Chicago - October 2003.
Basic principles of numerical radiation hydrodynamics and the RALEF code M. M. Basko ELI, Prague 10 July 2014 Keldysh Institute of Applied Mathematics,
Sampling Design & Procedure. Population The aggregate of the all the elements, sharing some common set of characteristics that comprises the universe.
Copyright: Silberschatz, Korth and Sudarshan 1 Chapter 23: Advanced Data Types and New Applications.
Data Assimilation Training Course, Reading, 5-14 May 2010 Observation Operators in Variational Data Assimilation David Tan, Room 1001
Quality Tools and Techniques in the School and Classroom.
DC-API: Unified API for Desktop Grid Systems Gábor Gombás MTA SZTAKI.
EE-M /6: IS L3&4 1/32 v2.0 Lectures 3&4: Linear Machine Learning Algorithms Dr Martin Brown Room: E1k Telephone:
PHOENICS User Meetings 2008 PRELUDE PRELUDE New PHOENICS pre-processor Why does PHOENICS need a new pre- processor? In the first years of PHOENICS, data.
Uncertain models and modelling uncertainty Marian Scott Dept of Statistics, University of Glasgow EMS workshop, Nottingham, April 2004.
© 2016 SlidePlayer.com Inc. All rights reserved.