Computational Fluid Dynamics (CFD): Smart Use of Advanced Modelling - PowerPoint PPT Presentation

Computational Fluid Dynamics (CFD): Smart Use of Advanced Modelling Tools Dr Anna M. Karpinska Portela Senior Process Scientist - Asset Performance Optimisation Birmingham, 28 Jan. 2020

What is CFD? ▪ “If we know what is happening within the vessel, then we are able to predict the behaviour of the vessel as a reactor. Though fine in principle, the attendant complexities make it impractical to use this approach.”– Octave Levenspiel (1972) ▪ “Computational fluid dynamics (CFD) changes this picture. Using CFD, we can compute three dimensional velocity fields and follow interactions of reactants and products through a tank. We can use this information to optimize tank geometry and operation.“ – Randal W. Samstag (2015) ▪ CFD is a powerful numerical modelling tool, which allows for flow visualisation with detailed characterisation of the special phenomena under varying process conditions. 2

CFD for Wastewater – Art and Science ▪ Since over two decades – application of CFD extended to civil and environmental engineering ▪ Recent developments in multiphase flow – steady increase of the use of CFD in wastewater engineering ▪ To date, CFD has been primarily used for evaluation of hydraulic problems at wastewater and sludge treatment streams level ▪ More advanced application of CFD is increasingly studied- simulation of the integrated flow field and physical, chemical and/or biological processes for optimized process design and plant operation 3

CFD for Wastewater – Opportunities ▪ Analysis of the multiphase flow behaviour ▪ Prediction of the impact of wide range of operating conditions on the local-scale phenomena: ▪ Flow field + interfacial mass transfer + chemical reactions ▪ High-precision technique for evaluation of the engineering systems, which are expensive and difficult to reproduce in lab- and pilot-scales ▪ Robust tool for: ▪ Unit process design ▪ Troubleshooting ▪ Optimisation (“tune for benefit”) ▪ Enhanced process performance ▪ Energy-optimised operation ▪ Elimination of “Build, Test & Correct” and “The Rule of Thumb” approaches 4

CFD for Wastewater- Examples Headworks Flow splitters PSTs Samstag and Wicklein, 2015 ASPs Lagoons Karpinska and Bridgeman, 2017 5

Current and Future Added Value of CFD ▪ Flow Field and few Internal Processes- well established, but require some care and effort for quality solution ▪ Many Internal Processes are emerging and requiring significant care and effort in the CFD Model Wicklein et. al, 2016 6

Future Added Value of CFD ▪ Use of CFD to build knowledge (input, output, backmixing, recirculation) for improved simpler models (Compartmental Models -CM) Alvarado et al., 2012 7

Challenges to be addressed? ▪ No guidance document with regard to “Good Modelling Practice” (GMP) covering state -of- the-art, knowledge gaps and future needs ▪ Lack of educational support and targeted training ▪ Users rely on either self-training or very limited training courses provided by CFD manufacturers (lacking problem specifics as water/wastewater treatment is hardly their core business) ▪ Frequent CFD software misuse by inexperienced users ▪ Incorrect problem statement ▪ Poor model choice ▪ Wrong setup assumptions ▪ Misinterpretation of the results ▪ Reduced confidence in outcomes of CFD analysis (decreased usage of the software) ▪ Lack of handbook dedicated to CFD applied to wastewater practice 8

Challenges – CFD for ASP ▪ Complete CFD simulation of ASP is challenging ▪ No unequivocal CFD modelling guideline for ASPs ▪ Biologically active liquid- gas- solids system ▪ Complex hydrodynamics (interactions between the phases) ▪ Biochemical conversion rates ▪ High mesh resolution required for solution accuracy Karpinska and Bridgeman, 2017 ▪ Massive computational costs (RAM & CPU) and long simulation run times ▪ Data collection for calibration and validation- time consuming and resource expensive (ADV, ADCP, LDV, tracer testing, spatial profiling) ▪ Overall cost of CFD analysis is high, yet cheaper than capital costs of a new asset ! Rehman et al., 2014 9

Common ASP Modelling Pitfalls ▪ Model oversimplification - use of the most computationally inexpensive modelling scenario ▪ Steady-state analysis & turbulence modelled with standard k-epsilon model ▪ Neutral density (clean water set as a working fluid, no solids transport) ▪ Fixed bubble size (rigid spheres)- neglecting Bubble Size Distribution (no coalescence and breakup) ▪ Coarse mesh ▪ Lack of calibration ▪ Errors in the results and validation Overestimation of the turbulent interactions (wrong initial assumption & inappropriate model) 10 Karpinska and Bridgeman, 2017

Who are we? Working Group on Computational Fluid Dynamics (CFD) for Unit Processes Management Team (MT): ▪ Julien Laurent, Engees Strasbourg, France - Chair ▪ Randal Samstag † , Civil and Sanitary Engineer, USA - Secretary ▪ Jim Wicks, The Fluid Group, UK – Vice-Chair ▪ Ingmar Nopens, Ghent University, Belgium ▪ Ed Wicklein, Carollo Engineers, USA ▪ Anna Karpinska Portela, Southern Water, UK ▪ Alonso Griborio, Hazen and Sawyer, USA ▪ Steve Saunders, Ibis Group, USA ▪ Olivier Potier, Université de Lorraine, France https://iwa-connect.org/ ▪ Damien Batstone, University of Queensland, Australia ▪ Nelson Marques, Blue Cape, Portugal ▪ Usman Rehman, AM-TEAM, Belgium 11

IWA Working Group for CFD – Current Activities ▪ Papers/Books ▪ Papers available on ▪ GMP for CFD in wastewater engineering ▪ State-of-the-art on CFD modelling of the unit processes ▪ A protocol for the use of CFD as a supportive tool for wastewater treatment plant modelling ▪ IWA Scientific and Technical Report- GMP CFD for Wastewater - book in preparation (expected July 2020) ▪ Dissemination ▪ Platform presentations in conferences (IWA events, IWA/WEF WRRFMod Seminars, WEFTEC, Watermatex, Water&IT, ..) ▪ Workshops and Webinars to promote GMP for CFD ▪ WaterWiki, IWA-Connect, LinkedIn https://www.wrrmod2020.org/ https://iwa-network.org/all-events/ https://weftec.org/ 12

Good CFD Modelling Practice – 4 Steps ▪ Define Problem ▪ Gather Data ▪ Solve Problem ▪ Show Results Wicklein et al., 2016 13

Complete Flow of a CFD Modelling Process for Quality Output ▪ Dimensions ▪ Model selection for problem ▪ Geometry & meshing ▪ Boundary Conditions ▪ Physics ▪ Solution Methods ▪ Convergence Wicklein et al., 2016. 14

Dedicated CFD GMP Book – available soon! ▪ Dedicated chapters covering ▪ Fundamentals ▪ Multiphase modelling ▪ Individual unit treatment processes ▪ State-of-the-art ▪ GMP – with case study ▪ Knowledge gaps ▪ Research needs ▪ Future trends 15

Thank you for your attention! anna.karpinska-portela@southernwater.co.uk Rehman et al., 2017 16