Introduction To Computational Fluid Dynamics. Presented by Marc Laing CFD Team Manager

Transcription

1 Introduction To Computational Fluid Dynamics Presented by Marc Laing CFD Team Manager Slide 1

2 50 years research in fluid and thermodynamics Flow meter calibration and development testing State-of-the-art flow test facilities: Oil, gas and water Multiphase (including high pressure) Erosion (gas, liquid and sand) Elevated Pressure and Temperature Heavy oil Wet gas NEL is a world leading authority on thermo-fluids and holds the UK s primary flow measurement standard Slide 2

3 NEL s CFD Expertise Over 25 years CFD support to the oil & gas sector (downhole, subsea, topside) Growing specialised CFD Team CFD consultancy (design, optimisation and troubleshooting) CFD validation in our flow laboratory (combined modelling & testing) NEL lead on specialised oil & gas applications: Erosion Multiphase Flow measurement Thermal analysis Hydraulic modelling Slide 3

4 What is CFD? Three Stages to CFD: Computational Fluid Dynamics (CFD) is a powerful modelling tool used to predict the detailed threedimensional behaviour of liquid, gas and air flows in a wide range of industrial applications. Define Geometry Mesh Solution Slide 4

5 Geometry Creation How is the 3 Dimensional geometry created? Geometry can be provided straight from CAD, often this can work well, but in some cases can be more time consuming than building from scratch General Assembly & Isometric drawings can be used to define 3D geometry Slide 5

6 How To Create A Mesh In order to create an acceptable mesh the following need to be considered: Identify areas of interest in the flow e.g. The sharp edge of an orifice plate Ensure aspect ratio and skewness are with acceptable limits Ensure cell growth is acceptable and does not grow sharply in areas of particular interest Slide 6

7 Solver Settings In order to solve any simulation it is necessary to supply all of the relevant boundary conditions and this is done in the solver. At NEL we use ANSYS Fluent as our solver. Examples of setting that might be applied are: Turbulence model Inlets and outlets (Flow rates, pressure driven flow etc) Heat input/sinks Operating pressure Material properties Slide 7

8 Example Of Hybrid Mesh Tetrahedral Cells (unstructured) Boundary Layer Mesh Hexahedral Cells (structured) Slide 8

9 Where Can CFD Be Used In Oil & Gas To quantify installation effects on flow meters To predict temperature changes (for example thermal cooldown) To quantify mis-measurement (for example a non concentric orifice plate) Prediction of erosion To show compliance with a standard Skid design Flare meter correction Gas dispersion HVAC Vortex Induced Vibration (VIV) To predict multiphase flow regimes To predict wet gas flow regimes Separation Slide 9

10 Other Industries Where CFD Can Be Used Nuclear Renewables Marine Aviation Environmental Military Construction Slide 10

11 Example 1 Eccentric Orifice Plate Slide 11

12 Model Geometry Flow Slide 12

13 CFD Model vs Reality Movement of Orifice Plate Slide 13

14 Velocity Streamlines As Installed Case Wall Attachment Recirculating Flow Slide 14

15 Installation - Ideal vs As Installed Ideal Installation As Installed Wall Attachment Slide 15

16 Example 2 Flare Gas Installation Effects Slide 16

17 Typical Issues With Flare Gas Metering Systems Large turndown ratio required due to extreme variations in flow rate e.g. blowdown conditions Typically only Ultrasonic Flow Meters can deal with the required turndown ratio Normally single path USM s are used which are extremely sensitive to non ideal flow profiles Generally there is no location on the pipeline where the meter can be installed as per the manufacturers recommendations Slide 17

18 Project Scope NEL were contacted to provide a correction factor that could be programmed into the flow computer of an Ultrasonic Flow Meter installed in a flare gas line. CFD was undertaken for the following lines: HP Flare LP Flare Analysis was conducted over a range of different flowrates in order to calculate a correction factor that was representative of the operating range. Slide 18

19 Meter Location Meter Location Slide 19

20 Flow Path Slide 20

21 Example Of Mesh Slide 21

22 Ideal Installation vs As Installed Ideal Installation As Installed Slide 22

23 Velocity Streamlines Slide 23

24 Ideal Profile vs As Installed Slide 24

25 How Is This Applied To The Meter The USM can be corrected by supplying Velocity Distribution Factors (VDFs) which can be calculated from the results of the CFD analysis. The more VDFs supplied the greater the accuracy (generally for flare gas 5 points is sufficient) This enables the meter to be corrected on the fly and therefore no further processing is required. The advantage of this method is that the meter does not have to be removed and the process does not need to be shut down. Ensures flaring consent is not breached. Slide 25

26 Erosion Modelling Slide 26

27 Why Is Erosion A Concern? Many wells are now located deeper and higher pressure, therefore system integrity is of critical importance. Many geographical areas e.g. Egypt, Trinidad etc have relatively large sand production rates Shale gas production is increasing rapidly and sand production is a serious concern Company reputation environmental discharge must be avoided at all cost Loss of revenue Unexpected shutdowns are costly and to be avoided Slide 27

28 Subsea XMT Erosion Choke Valve Erosion Hot Spot Erosion Hot Spot Slide 28

29 Choke Valve Erosion Slide 29

30 Choke Valve Streamlines Slide 30

31 Advantages of Undertaking Erosion Prediction After undertaking an erosion assessment using CFD the operator can be confident of: Safe operation Life expectation of equipment Valve performance System integrity i.e. No discharge to the environment Slide 31

32 Summary CFD is a very powerful predictive technique which can be used to understand how complex systems perform. CFD can be used to model situations that could not be tested such as deep water high pressure wells. CFD can be interrogated much more easily than physical testing as you are not limited by instrumentation. CFD is very effective for predicting trends or changes, such as incorreclty installed flow meters. Slide 32

33 Question? Please feel free to send me a question if you are interested to know more: Marc.Laing@tuv-sud.co.uk Thanks for taking the time to watch this webinar. Slide 33