1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2013 SAE International All rights reserved. No part of this p
3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J2966_201309 SURFACE VEHICLE RECOMMENDED PRACTICE J2966 SEP2013 Issued 2013-09 Gu
5、idelines for Aerodynamic Assessment of Medium and Heavy Commercial Ground Vehicles Using Computational Fluid Dynamics RATIONALE This document is created to provide guidance for computational aerodynamic simulations of medium and heavy commercial ground vehicles. 1. SCOPE This document outlines gener
6、al requirements for the use of CFD methods for aerodynamic simulation of medium and heavy commercial ground vehicles weighing more than 10 000lbs. The document provides guidance for aerodynamic simulation with CFD methods to support current vehicle characterization, vehicle development, vehicle conc
7、ept development and vehicle component development. The guidelines presented in the document are related to Navier-Stokes and Lattice-Boltzmann based solvers. This document is only valid for the classes of CFD methods and applications mentioned. Other classes of methods and applications may or may no
8、t be appropriate to simulate the aerodynamics of medium and heavy commercial ground vehicle weighing more than 10 000lbs. 1.1 Purpose The purpose of this document is to standardize the use of Navier-Stokes and Lattice-Boltzmann CFD for aerodynamic simulation for medium and heavy commercial ground ve
9、hicles weighing more than 10,000lbs and to guide CFD users to utilize CFD tools effectively and efficiently. The recommendations are grouped under three main sections; CFD Model Setup, Solver Setup and Data Processing and Communication. The Model Setup Section aims to address issues related to model
10、 preparation and physical accuracy. It explains what physical properties need to be modeled and how they need to be configured. The Solver Setup Section deals with appropriate solver selection and different options in turbulence modeling, boundary layer representation and discretization. The last se
11、ction, Data Processing and Communication, gives guidance about how the CFD results need to be presented and interpreted. The section also contains recommendations on information collection and processing related to CFD simulations. 1.2 Document Use This document is structured to service both the nov
12、ice and the expert user. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2966 Issued SEP2013 Page 2 of 142. REFERENCES 2.1 Applicable Documents The following publications form a part of this spe
13、cification to the extent specified herein. Unless otherwise indicated, the latest issue of SAE publications shall apply. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA)
14、, www.sae.org. SAE R-177 Hucho, W-H., Aerodynamics of Road Vehicles, SAE International, ISBN: 978-0-7680-0029-0, 1988. SAE J1252 SAE Wind Tunnel Test Procedure for Trucks and Buses 2.2 Related Publications The following publications are provided for information purposes only and are not a required p
15、art of this SAE Technical Report. 2.2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. SAE 2009-01-1167 Holloway, S., Leylek, J., York, W., and Khalighi, B., “
16、Aerodynamics of a Pickup Truck: Combined CFD and Experimental Study,” SAE Int. J. Commer. Veh. 2(1):88-100, 2009, doi:10.4271/2009-01-1167. SAE 2006-01-3544 Bayraktar, I. and Bayraktar, T., “Guidelines for CFD Simulations of Ground Vehicle Aerodynamics,” SAE Technical Paper 2006-01-3544, 2006, doi:1
17、0.4271/2006-01-3544. SAE 2007-01-4295 Horrigan, K., Duncan, B., Sivakumar, P., Gupta, A., Wong, A., “Aerodynamic Simulations of a Class 8 Heavy Truck: Comparison to Wind Tunnel Results and Investigation of Blockage Influences,” SAE Technical Paper 2007-01-4295, 2007, doi:10.4271/2007-01-4295. SAE 20
18、10-01-0756 Duncan, B., Kandasamy, S., Sbeih, K., Lounsberry, T. et al., “Further CFD Studies for Detailed Tires using Aerodynamics Simulation with Rolling Road Conditions,” SAE Technical Paper 2010-01-0756, 2010, doi:10.4271/2010-01-0756. SAE 2012-01-0106 Sderblom, D., Elofsson, P., Hjelm, L., and L
19、ofdahl, L., “Experimental and Numerical Investigation of Wheel Housing Aerodynamics on Heavy Trucks,” SAE Technical Paper 2012-01-0106, 2012, doi:10.4271/2012-01-0106. SAE 2012-01-0107 Heinzelmann, B., Indinger, T., Adams, N., and Blanke, R., “Experimental and Numerical Investigation of the Under Ho
20、od Flow with Heat Transfer for a Scaled Tractor-Trailer,” SAE Technical Paper 2012-01-0107, 2012, doi:10.4271/2012-01-0107. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2966 Issued SEP2013 Pa
21、ge 3 of 142.2.2 AIAA Publications Available from AIAA, 1801 Alexander Bell Dr., Ste 500, Reston, VA 20191-4344, Tel: 800-693-2422 (inside USA and Canada) or 703-264-7551 (outside USA), www.aiaa.org. AIAA-G-077-1998 Guide for the Verification and Validation of Computational Fluid Dynamics Simulations
22、, ISBN: 978-1-56347-354-8. AIAA 2000-2306Spalart, P. R., “Trends in Turbulence Treatments“, June 2000. AIAA 98-3007 Poirier, D., et.al. “The CGNS System”, Fluid Dynamics Conference, 29th, Albuquerque, NM, June 15-18, 1998. AIAA 93-2906 Menter, F. R., “Zonal Two Equation k- Turbulence Models for Aero
23、dynamic Flows”, AIAA Paper 93-2906, 1993. 2.2.3 ASME Publications Available from ASME, Three Park Ave. New York, NY 10016-5990, Tel: 800-843-2763 (inside USA and Canada) or 973-882-1170 (outside USA), www.asme.org. ASME V however, it is recommended that all geometric details are preserved to achieve
24、 high accuracy in the prediction of underhood airflow resistance. For a fully detailed model, the number of facets will typically be greater than 6 million. 6. DATA PROCESSING AND COMMUNICATION CFD Simulations generate substantial amounts of data. Extracting the correct values using appropriate meth
25、ods and creating a standard to compare CFD results from multiple resources reduces user error and improves confidence in evaluation efforts. This section talks about how results can be presented and interpreted. It also contains recommendations on information collection and processing related to CFD
26、 simulations. 6.1 Aerodynamic simulations are dependent on an accurate representation of the test article geometry. Acceptable geometric sources include CAD/CAE files and scanned 3D model data. The geometric resolution of the model needs to be reported with the CFD results. Models for deformable par
27、ts and add-on devices that may influence vehicle aerodynamics need to be modeled in their intended design shape. 6.2 STEP and IGES are acceptable file formats to transfer CAD models between different sources when original CAD model is not available. 6.3 Vehicle geometric model should be exported to
28、the applicable CFD software package with highest accuracy possible. 6.4 Each report needs to include basic information about the simulation: 6.4.1 Vehicle make, model and year information along with a description of geometry of the test article. 6.4.2 Short description of the simulation. 6.4.3 Offic
29、ial name/title, date, version number and vendor information of the software product. 6.4.4 Type of the software code (such as Navier-Stokes or Lattice-Boltzmann) 6.4.5 Description of simulation procedure. 6.4.6 Aerodynamic data along with reference values for frontal area and velocity used for norma
30、lizing the force data. For example, if wind averaged drag coefficient needs to be calculated according to the guidelines in SAE J1252. 6.5 It is recommended to document the results in CGNS (as defined in AIAA 98-3007) compatible format where native file format is not readable. 6.6 Certain variables
31、are required to be reported with each simulation: 6.6.1 Averaged force coefficients (drag, yaw, side, etc.) per case with averaging information (such as number of iterations or simulation time for the averaging calculations). 6.6.2 Drag coefficient history plots showing variation of the value during
32、 the computational simulation. Initial fluctuations in the force coefficients at beginning of the iteration process may be omitted. 6.6.3 Contours, streamlines, vectors and iso-surfaces for velocity and pressure as required. It is recommended to use averaged values for creating plots for known unste
33、ady flow regions (such as vehicle wake and tractor-trailer gap). Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2966 Issued SEP2013 Page 11 of 146.6.4 Report pressure and force coefficient deve
34、lopment on vehicles longitudinal axis. Maximum pressure coefficient for the stagnation region should remain below 1.1. 6.6.5 Plot Y+ values on the model surface to confirm grid density and its applicability on the selected turbulence model and wall function. 6.6.6 Report maximum turbulence viscosity
35、 ratio with an iso-surface plot. In general, turbulence viscosity ratio (TVR) values may be above 1000, but they need to remain below 1000 in the free stream region. 6.6.7 Check and report maximum velocity in the computational domain. In general, the maximum velocity needs to be below 150 m/s in mos
36、t cases. 7. NOTES 7.1 Marginal Indicia A change bar (l) located in the left margin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a
37、 complete revision of the document, including technical revisions. Change bars and (R) are not used in original publications, nor in documents that contain editorial changes only. PREPARED BY THE SAE TRUCK AND BUS AERODYNAMICS AND FUEL ECONOMY COMMITTEE Copyright SAE International Provided by IHS un
38、der license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2966 Issued SEP2013 Page 12 of 14APPENDIX A ATTACHMENT A Grid Convergence Index (GCI) Calculation Procedure Celik, B., 2008 1. Define a representative grid size h. For three-dimensional calcul
39、ations: =g34691g1840g3533(g1848g3036)g3015g3036g2880g2869g3473g2869/g2871where N is the total number of volume elements, and g1848g3036is the element volume. 2. Create three different sets of grids and calculate drag coefficients for each of them using same solver and model settings. It is recommend
40、ed that the grid refinement factor r=hg2913g2925g2931g2928g2929g2915hg2916g2919g2924g2915 to be larger than 1.3. For representative grid sizes h1(fine grid), h2(coarse grid), and h3(coarsest grid), define refinement factor r: g1870g2870g2869=g2870g2869 and g1870g2871g2870=g2871g2870 where g2869g2870
41、g2871. 3. Calculate apparent order p from: g1868=1g1864g1866(g1870g2870g2869)g3627g1864g1866g3627g2013g2871g2870g2013g2870g2869g3415 g3627 +g1869(g1868)g3627 g1869(g1868) =g1864g1866g4678g1870g2870g2869g3043g1871g1870g2871g2870g3043g1871g4679 using a numerical iterative process. In above equations:
42、g1871=1g1871g1859g1866(g2013g2871g2870g2013g2870g2869) g2013g2871g2870=g1829g1856g2871g1829g1856g2870and g2013g2870g2869=g1829g1856g2870g1829g1856g2869where g1829g1856g3038represents the drag coefficient calculated for the respected grid. 4. Calculate extrapolated drag coefficient: g1829g1856g3032g3
43、051g3047g2870g2869=g3435g1870g2870g2869g3043g1829g1856g2869g1829g1856g2870g3439g3435g1870g2870g2869g30431g34395. Calculate approximate relative error: g1857g3028g2870g2869= g3628g1829g1856g2869g1829g1856g2870g1829g1856g2869g3628 Extrapolated relative error: g1857g3032g3051g3047g2870g2869=g4708g1829g
44、1856g3032g3051g3047g2870g2869g1829g1856g2869g1829g1856g3032g3051g3047g2870g2869g4708 Grid Convergence Index for fine grid: g1833g1829g1835g3033g3036g3041g3032g2870g2869=1.25 g1857g3028g2870g2869g1870g2870g2869g30431Copyright SAE International Provided by IHS under license with SAENot for ResaleNo re
45、production or networking permitted without license from IHS-,-,-SAE J2966 Issued SEP2013 Page 13 of 14ATTACHMENT B Iteration Error Estimation (IEE) Calculation Procedure x 1. Calculate iteration error using: g2013g3036g3047g3032g3045,g3036g3041=g3557g3435g1829g1856g3036g3041g2878g2869g1829g1856g3036
46、g3041g3439g2019g3036where n is the iteration number, and g2019g3036is the principal eigenvalue of the solution matrix of the linear system that could be calculated from: g2019g3036=g3557g3630g1829g1856g3036g3041g2878g2869g1829g1856g3036g3041g3630g3630g1829g1856g3036g3041g1829g1856g3036g3041g2879g286
47、9g3630The uncertainty g2012g3036g3047g3032g3045in iteration convergence can be estimated as: g2012g3036g3047g3032g3045=g3557g3630g2013g3036g3047g3032g3045,g3036g3041g3630g2019g3028g3049g30321where is any appropriate form, e.g., g1838g2998norm. g2019g3028g3049g3032represents an average value of g2019
48、g3036over reasonable number of iterations. If g2019g3028g3049g30321.0 , the resulting iteration error would not be a representative number. It is recommended to apply |g2019| 2 limiter to stay conservative when calculating g2019g3028g3049g3032. It is also recommended to have at least one order of magnitude smaller iteration error than the Grid Convergence Index (GCI) for each calculation. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,
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