EI-NO-- NTNU Trondheim Norges teknisk-naturvitenskapelige universitet DqktorIngenioravhandling 1997:29 1 0 2 2 Institutt for mekanikk, termo- og fluiddynamikk Trondheim MTF-rapport 1997:149 (D) moners TA am Computational analysis of the flow field downstream of flow conditioners Asbjern Erdal February 1997 Thesis for the dr. ing. degree Department of Applied Mechanics, Thermodynamics and Fluid Dynamics Norwegian University of Science and Technology Page 2 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Abstract A flow conditioner (FC) is a device installed upstream of a flow meter in order to remove swirl and to correct a distorted flow profile generated by inappropriate installation conditions. Using an FC can reduce installation effects in flow measurements. Numerous attempts have been made to isolate metering stations from piping-induced disturbances, and many different FCs have been designed. Some have proved capable of meeting the flow quality requirements in the metering standards, but doubts have remained about the factors dictating their performance. The design methods used earlier, such as screen theory, cannot give a fundamental understanding of how an FC works. This thesis shows, however, that computational fluid dynamic (CFD) techniques can be a valuable tool to examine several parameters which may affect the performance of an FC. It is, among other things, shown that the flow pattern through a complex geometry, like a 19-hole plate FC, can be simulated with good accuracy by a k-s turbulence model. The calculations illuminate how variation in pressure drop, overall porosity, grading of porosity across the cross-section and the number of holes affect the performance of FCs. These questions have been studied experimentally by researchers for a long time. Now an understanding of the important mechanisms behind efficient FCs emerges from the predictions. The research is documented in 6 papers which step by step study various aspects of the topic. Page 4 Preface This thesis consists of six papers and an introduction which gives a survey of the matter. The work has been carried out in the period 1992 - 1996. The thesis is based on research performed at K-Lab after my hospitation at The Norwegian Institute of Technology from 1992 to 1993. During this period I have been motivated and inspired by many people both at Statoil, The Norwegian Institute of Technology and Institute for Energy Technology. First of all I will express my deepest and sheerest thanks to my former supervisor in Statoil, Dr. Jan Bosio. His involvement during initiation of this work and inspiration during preparation has been highly appreciated. I wish to thank my academic supervisors Professor Helge I. Andersson and Professor Per-Age Krogstad for their valuable support and advice during this work. I also want to thank my co-authors Dag Lindholm, Dag Thomassen, Lars Even Torbergsen, Stein Rimestad, Anne Synnave Sivertsen and Morten Langsholt for many fruitful discussions. I wish to thank my employer Statoil, represented by my supervisor Dr. Svein Birger Thaule and chief engineer Dr. Karl Sjaen, who have given me the opportunity and resources to prepare this Dr. ing. thesis. Finally, and most important, I will thank my wife Magny and our four children for all patience and support throughout these years. Without this help it would have been difficult to complete the thesis in due time. Page 5 Page 6 Contents Abstract.............................................................................................................................. 3 Preface............................................................................................................................... 5 Contents ............................................................................................................................. 7 List of papers..................................................................................................................... 8 Introduction ....................................................................................................................... 9 Orifice plate meters...................................................................................................... 11 Installation effects in orifice meters........................................................................... 13 Flow conditioners developed before 1987 ................................................................. 18 Modem flow conditioners ........................................................................................... 20 Flow conditioners and international metering standards ........................................... 27 CFD codes and upstream effects................................................................................ 29 The Phoenics CFD code ............................................................................................. 31 Progress in the papers in this thesis................................................................................. 32 Paper I.......................................................................................................................... 34 Paper II......................................................................................................................... 36 Paper III.......................................................................................................................... 37 Paper IV....................................................................................................................... 38 Paper V......................................................................................................................... 39 Paper VI.......................................................................................................................... 41 Conclusions ..........................................................................................................................42 References ............................................................................................................................44 Page 7 List of papers This thesis is based on the following papers, referred to in the text by Roman numerals : I : Erdal, A, Lindholm, D and Thomassen, D, Development of a flow conditioner, North Sea Flow Measurement Workshop, Peebles, Scotland, October 1994. II : Erdal, A, Torbergsen, L E, Rimestad, S and Krogstad, P A, Evaluation of a CFD-model for simulation of simplified flow conditioners, Fluid Flow Measurement 3rd International Symposium, San Antonio, USA, 1995. m: Erdal, A, Sivertsen, A S, Langsholt, M and Andersson, H I, Three-dimensional computation of turbulent flow through a flow conditioner, Proceedings of the 8th International conference on Flow Measurement, Flomeko '96, Beijing, China, pp 718-723, 1996. IV: Erdal, A. and Andersson, H I, Numerical aspects of flow computation through orifices, Accepted for publication in Flow Measurement and Instrumentation. V : Erdal, A, Torbergsen, L E, Andersson, HI and Krogstad, P A, Flow development of two simplified and one K-Lab/Laws flow conditioners - experiments and calculations, Accepted for the 1997 ASME Fluids Engineering Division Summer Meeting, Symposium on Devices for Flow Measurement and Analysis. Paper number FEDSM 97-3216. VI: Erdal, A, A numerical investigation of different parameters that affect the performance of flow conditioners, Submitted to How Measurement and Instrumentation. Page 8 Introduction Technological innovations are essential for maintaining the competitiveness for the gas companies. In this context, metering technology represents a key area of expertise for gas companies which buy and sell huge volumes each day. Achieving the highest possible reliability in flow measurements has great economic importance. Neither side in a transaction should be penalised for measuring errors. Figure 1 shows the Norwegian transport system for natural gas to continental Europe. Norway exported 30 billion standard cubic metres through these pipelines in 1995, and plans to export 60 billion standard cubic metres in 2000. An uncertainty of 0.5 to one per cent in the measured volume passing through the sales metering stations represents an annual value of about USD 35-70 million from 2000. Control of uncertainty in the metering stations, and particularly of the parameters that have a negative impact on measurement accuracy, is clearly of primary importance; ref. Bosio and Erdal [Bosio 1996a]. The most commonly used method for metering large gas flows is based on the orifice meter. A significant amount of research has been done in recent years to evaluate the adequacy of specifications for orifice meter installations. To eliminate the effect of poor installation conditions, flow conditioners (PCs) have been recommended upstream of the orifice meter. Substantial efforts have been devoted to developing PCs with good performance. A thorough understanding of the flow field through an PC is critical to any work on optimising the design of these devices. The flow can be studied both experimentally and by computer simulations. This thesis will analyse the flow structure downstream of perforated plate PCs with the aid of computational fluid dynamic (CFD) techniques. With this approach, it is possible to introduce wide-ranging parameters and evaluate their effects using computer methods. Validation experiments for selected cases can demonstrate the method's credibility.