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    WUP logicals Gr 6 Grid location specification of ORIGIN command also see TR218 Grid manipulation with PINTO see TR218 Grid mesh matching of see GSET M Grid meshes copying of see GSET C Grid No Photon Help Grid No is the sequence number of the GRID element in the stack Typing in any valid number the total number of grid element will pop up the corresponding grid element and make it become the current element Only the attributes of the current GRID element can be modified GRID OFF Photon Help G rid OF f element range switches off the specified grid element s which will not appear in subsequent plots until switched on again See also GRID ON GRID ON Photon Help G rid ON element range switches on the specified grid element s which will appear in subsequent plots See also GRID OFF Grid origin displacement of see ZWADD GRID OUT Photon Help G rid OU t plane number subregion options plots an outline of the specified grid i e one with no interior detail See also GRIDS Grid planes transferring of see GSET T Grid points setting internal see GSET B Grid regions You use the REGEXT command to set default dimensions of grid regions See Encylopaedia entry for REGEXT Grid specification with PINTO see TR218 Grid systems in PINTO see TR218 Grid generation menu The grid generation and grid handling procedures of PHOENICS underwent major re development during 1991 2 The main new features were The possibility of specifying the geometry first and of subordinating the grid to it This facilitates the specification of boundary and internal features and allows the refinement of the grid in specific regions of the computational domain without disturbing the geometry A new grid generation menu facilitating the process of creating Cartesian cylindrical polar and body fitted curvilinear grids Grid planes in body fitted coordinates can be copied translated and rotated to generate new planes Transitions between two different section shapes eg square to circle can be readily generated A new generation of more powerful PIL commands the RSET and GSET suites that simplify the specification and handling of geometry and grids GRID Menu Mouse driven grid generation in GridMenu The VIEW facility for body fitted coordinates has been transformed into a mouse driven grid generation facility which allows the user to drop points and construct lines and frames using a mouse or the arrow keys when a mouse is not available Grids can be matched to frames without leaving the new system and the grid check facility previously available only through the GRDCHK command can be used to inspect the quality of the mesh Grid check uses a colour code to indicate the orthogonality of the grid at each point Settings effected in the VIEW environment are transferred automatically to the GridMenu session and recorded as PIL commands The MENSAV facilities will also record and replay VIEW sessions Grid specification commands for BFCs see GSET Group 6 GRIDDEFI Autoplot Help GRI

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  • standard model but with a smaller multiplying coefficient and the second of which allows the turbulence distortion ratio PK EP to exert an influence on the production rate of EP According to the authors the extra source term represents the energy transfer rate from large scale to small scale turbulence controlled by the production range time scale and the dissipation range timescale The net effect is to increase EP and thereby decrease KE when the mean strain is strong PK EP 1 and to decrease EP when the mean strain is weak PK EP Chen see Monson et al 1990 extended the model to perform low Reynolds number simulations of bounded flows by introducing the low Reynolds number KE EP extension of Lam and Bremhorst 1981 This extension is provided for in PHOENICS by allowing the CK modification to be used in combination with the Lam Bremhorst extension b Description of the model The CK modified KE EP model differs from the standard high Reynolds form of the KE EP model in that a the following model constants take different values PRT KE 0 75 PRT EP 1 15 C1E 1 15 C2E 1 9 2 1 and b an extra timescale KE PK is included in the EP equation via the following additional source term per unit volume S EP RHO F1 C3E PK 2 KE 2 2 where C3E 0 25 PK is the volumetric production rate of KE and F1 is the Lam Bremhorst 1981 damping function which tends to unity at high turbulence Reynolds numbers c Activation of the model The CK modification to the KE EP model is selected by TURMOD KECHEN which is equivalent TURMOD KEMODL plus the following PIL commands IENUTA 2 PRT KE 0 75 PRT EP 1 15 PATCH KECHEN PHASEM

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  • in aircraft Fire and smoke in a room Fire in an underground train Smoke movement in a multi storey building Smoke production 3 Steady Flames Secondary combustor for an incinerator After burner for an incinerator After burner for an incinerator Tyre incineration furnace Methane air combustion Free Turbulent diffusion flame Confined turbulent diffusion flame Turbulent Bunsen burner fourteen fluid model extract from a 1996 lecture on MFM Gas turbine combustor

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    energy sources due to radiant energy transfer mechanical dissipation fluid compression and or expansion brings the enthalpy conservation equation into the same form as the mixture fraction equation Under these conditions if the system is adiabatic the enthalpy solution will be linearly related to the mixture fraction and so the user need only set STORE H1 in Group 7 of the Q1 file If thermal radiation is present and or there is heat exchange across the system boundaries then the user must solve for H1 i e SOLVE H1 SOLUTN H1 Y Y Y P P P Inlet Boundary Conditions The extended SCRS is applicable to two stream problems in which identification may be made of separate entry streams termed fuel and oxidiser There may be more than one entry port for each of these reactants but properties must be uniform and the same over each port for a given reactant The composition and temperature of the fuel and oxidiser streams are defined by way of the following commands SCRS FUIN FUEL OXID FP1 FP2 PROD1 PROD2 DILN TFU SCRS OXIN FUEL OXID FP1 FP2 PROD1 PROD2 DILN TOX where FUEL OXID FP1 FP2 PROD1 PROD2 and DILN denote the mass fractions of these species in their respective inlet streams and TFU and TOX are the absolute temperatures of the fuel and oxidiser streams The inlet conditions are specified using PATCHes with names beginning SCRS and with the characters F or O to indicate the fuel or oxidant stream These conditions may be applied at fixed pressure entrainment boundaries or at fixed mass inflow boundaries If the mass inflow is to be specified then the mass flux must be specified using a density calculated from the specified inlet composition temperature and velocity If the enthalpy H1 is solved then the inlet enthalpy must be calculated from the inlet composition and temperature The ESCRS does this automatically if the user sets the VALue for P1 equal to GRND1 and the VALue for H1 equal to GRND3 The following settings provide an example of such inlet boundary conditions for the fuel and oxidiser streams INLET SCRSF LOW 1 NX 2 2 1 1 1 NREGT VALUE SCRSF P1 GRND1 VALUE SCRSF W1 WINF VALUE SCRSF F 1 VALUE SCRSF CH4 YCH4IN VALUE SCRSF H1 GRND3 INLET SCRSO LOW 1 NX 4 4 1 1 1 NREGT VALUE SCRSO P1 GRND1 VALUE SCRSO W1 WINO VALUE SCRSO F 0 VALUE SCRSO CH4 YCH4IN VALUE SCRSO H1 GRND3 For BFC inlet PATCHes the user sets the VALue for P1 and the velocity resolutes equal to GRND3 as for example INLET SCRSF LOW 1 NX 2 2 1 1 1 NREGT VALUE SCRSF P1 GRND3 VALUE SCRSF V1 GRND3 VALUE SCRSF W1 GRND3 VALUE SCRSF F 1 VALUE SCRSF VCRT ZERO VALUE SCRSF WCRT WINF VALUE SCRSF CH4 YCH4IN VALUE SCRSF H1 GRND3 INLET SCRSO LOW 1 NX 4 4 1 1 1 NREGT VALUE SCRSO P1 GRND3 VALUE SCRSO V1 GRND3 VALUE SCRSO W1

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  • Combustion 2008
    solution for enthalpy can be abandoned and direct solution for temperature i e TEM1 can be recommended for all circumstances These developments involve replacing the MIXF i e mixture fraction variable by MIX1 MIX2 MIX3 etcetera which represent the mass fractions of material introduced by the first second third etcetera fuel supplying streams introducing the concept of the adiabatic flow temperature T1AD which is the temperature which would prevail if heat transfer to the solids surrounding the flowing gases were absent recognising that the solved for TEM1 variable which has no chemical reaction related sources represents the deviation of the actual temperature T1 from the adiabatic temperature thus T1 T1AD TEM1 and recognising that the enthalpy continues to have value as an auxiliary variable but only as stored not solved for The extreme scenarios distinguished In order to simplify the simulation process where possible it is useful to distinguish the following extreme scenarios Adiabatic mixed is burned one fuel bearing stream Adiabatic mixed is burned several fuel bearing streams Adiabatic mixed is burned several different fuel bearing streams Non adiabatic mixed is burned one fuel bearing stream Non adiabatic mixed is burned several fuel bearing streams Non adiabatic mixed is burned several different fuel bearing streams Adiabatic finite reaction rate one fuel bearing stream Adiabatic finite reaction rate several fuel bearing stream Adiabatic finite reaction rate several different fuel bearing stream These scenarios will be discussed individually one by one a Adiabatic mixed is burned one fuel bearing stream The solved for variable which is relevant to combustion is MIXF the mass fraction of material emanating from the fuel bearing in flow stream whatever its state of chemical aggregation Variables which it may be useful to store but not solve include the enthalpy H1 the temperature T1 the unburned fuel

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  • Turbulent mixing and chemical reaction; the multi-fluid approach
    customary for geometric space makes possible the simulation of many turbulent single and multi phase flow phenomena for which conventional turbulence models fail especially those influenced by body forces or by chemical reaction This opportunity is exploited by the Multi Fluid Model MFM of turbulence which may be regarded as an extension and generalization of the PDF transport model of Dopazo O Brien Pope et al It is also the successor to and generaliser of numerous two fluid models of the kind which were already envisaged by Reynolds and Prandtl MFM uses a conventional finite volume method for computing the discretized PDFs which may be one two or multi dimensional The lecture explains the nature and practical utility of MFM Examples of its application are presented to both chemically inert and chemically reactive flow phenomena Contents of the lecture The task to be performed computing the PDF Efforts to avoid computing the PDF EBU the eddy break up model EDC the eddy dissipation concept 2FM the two fluid model Presuming the shape of the PDF Presuming that a few statistical properties will suffice Pioneering efforts to compute the PDFs The multi fluid model MFM approach to PDFs First steps towards

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  • any location consists of a population of fluids each having its own values of fuel air ratio free fuel mass fraction temperature and therefore smoke generation rate Their distributions will be shown in the next two figures Fig 3 3 mass fractions of three of the 20 distinct fluids postulated by the multi fluid model namely pure fuel vapour red pure air yellow and stoichiometric mixture blue Understandably the concentration of the pure fuel fluid diminishes that of the pure air fluid increases and that of the stoichiometric mixture fluid rises and falls with distance down the combustor The next sketch shows more profiles Fig 3 4 mass fractions of fluids 1 3 5 7 9 11 13 15 17 19 and 20 Evidently MFM s picture of the conditions in the combustor is more sophisticated than that of the single fluid model and it is qualitatively at least certainly more realistic Statistical properties of the fluid population can be easily deduced of which three now follow Fig 3 5 Root mean square fluctuations of mixture fraction The root mean square fluctuations are greatest at the left hand end where pure fuel meets pure air They diminish as the pure fuel disappears and fluids of intermediate fuel air ratio come into existence Fig 3 6 Mixture average temperature according to the single fluid and multi fluid models MFM blue curve shows a much lower population average temperature than the single fluid model for only near stoichiometric mixture material has the maximum temperature and there is not much of this in the population This observation explains why the smoke generation rate is so much lower for MFM Fig 3 7 Mixture average free fuel concentrations according to the single fluid and multi fluid models Interestingly there is more free fuel according to MFM and this would lead to an enlarged smoke generation rate were it not for the over whelming effect of the temperature dependence It is also noteworthy that MFM predicts that the finite free fuel region extends downstream beyond the point at which the population average mixture ratio is stoichiometric which accords with experimental observations Further insight into the way in which the fluid population changes with position in the combustor is provided by the following PDF print outs in which the figure on the left represents the PDF in histogram style while the figure on the right serves simply as a reminder of the random mixture concept which underlies MFM In the following list cell 5 is near the inlet to the combustor and cell 50 is adjacent to the outlet indicate which computational cell is in question out of the 50 which are provided for the whole combustor cell 5 cell 10 cell 15 cell 20 cell 30 cell 40 cell 50 It is interesting to observe that the shapes of these PDFs are rather un like those which are customarily presumed by those who seek to replace calculation by presumption Numerical data for the smoke production rate are contained in the following table which confirms that accounting for fluctuations predicts significantly less smoke production SFM stands for single fluid model and MFM for multi fluid model Run CONMIX SMOEXP NFLUIDS SFM rate MFM rate 1 5 0 7 0 20 6 09E4 3 32E4 3 5 The influence of the micro mixing constant Calculations have also been carried out for a range of values of the micro mixing constant CONMIX The numerical results are shown in the following table Run CONMIX SMOEXP NFLUIDS SFM rate MFM rate 2 1 0 7 0 20 6 09E4 8 59E5 1 5 0 7 0 20 6 09E4 3 32E4 3 10 0 7 0 20 6 09E4 4 91E4 4 100 0 7 0 20 6 09E4 5 56E4 Increasing the micro mixing constant CONMIX evidently increases smoke production This is understandable becaause it brings the mixture closer to the no fluctuations state postulated by the single fluid model The following pictures explain how this occurs by showing how the population average temperature rises with CONMIX Population average temperature distributions according to the single fluid and multi fluid models for CONMIX 1 0 5 0 10 0 100 0 Changes in other aspects of the solution are illustrated in the following series of pictures The smoke concentration distributions 1 0 5 0 10 0 100 0 The mass fractions of individual fluids 1 0 5 0 10 0 100 0 The root mean square fluctuations of mixture fraction 1 0 5 0 10 0 100 0 The population average free fuel mass fraction 1 0 5 0 10 0 100 0 3 6 The influence of the temperature dependence of the reaction Calculations have also been made with the base case values of CONMIX and NFLUIDS but with greater and smaller values of the temperature dependence constant SMOEXP The results are shown in the next table Run CONMIX SMOEXP NFLUIDS SFM rate MFM rate 5 5 0 1 0 20 1 95E3 1 65E3 6 5 0 3 0 20 1 19E3 7 76E4 1 5 0 7 0 20 6 09E4 3 32E4 7 5 0 10 0 20 4 17E4 2 16E4 Evidently increasing the temperature exponent makes the effect of fluctuations more pronounced The following pictures show the corresponding smoke distributions along the length of the combustor Mass fractions of smoke according to the single upper curve and twenty fluid lower curve models for the temperature exponent SMOEXP 1 0 3 0 7 0 10 0 3 7 The influence of the fluid population discretization CONMIX and SMOEXP have physical significances but as in all CFD calculations some purely numerical parameters may also influence the results In MFM calculations the most doubtful such parameter is NFLUIDS which measures the fineness of discretization of the fluid population Accordingly some calculations have been carried out to explore its effect with the result shown in the following table Run CONMIX SMOEXP NFLUIDS SFM rate MFM rate 8 5

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  • kind as governs concentration temperature kinetic energy of turbulence for by this time turbulence models were coming into prominence and other properties the home grown concept of upwind differencing which derived from the author s childhood experience of having lived near a pig sty and therefore known well how the direction of the wind influenced the strength of the influence of near neighbours and the naive concept that it should be possible to devise an iterative scheme which skipped cyclically from vorticity to stream function from stream function to velocity from velocity to turbulence quantitites from turbulence to effective viscosity from effective viscosity to vorticity transport and would indeed converge The computer programming and testing were carried out by Akshai Runchal and Micha Wolfshtein and the theory and results including the program were published as a book in Reference 10 1969 Although Runchal and Wolfshtein had been concerned only with non reacting flows the present author and WM Pun had been applying the same methodology to flows with chemical reaction This work was reported in a separate publication Reference 11 perhaps the very first 1968 publication in which CFD was applied to a recirculating flow exhibiting combustion Click here for results The computer program was included as a final chapter of Reference 10 Shortly afterwards it was used by British Coal Utilisation Research Association Morgan and Gibson 1977 as the basis of the first model of a coal fired furnace The size distribution of the particles was one of the features calculated Once again it is necessary to remark that the physical modelling was naive and that the mathematical method stream function vorticity ultimately proved not to be easily extensible to three dimensions However significant forward steps had been taken c The first but over looked 3D model The Imperial College team was slow in deciding which was the best way to handle three dimensional problems at first hoping that stream function vorticity methods could be generalised Reference 12 exemplifies this aspiration The best first step in the 3D direction was probably the SIVA SImultaneous Variable Adjustment procedure about which a publication Reference 13 eventually emerged This contained incidentally an application to combustion It was however the same paper which explained how the SIMPLE procedure hitherto used only for 3D boundary layers could also be used for re circulating flows and it was finally SIMPLE rather than SIVA which was then preferred However it is proper now to recognise that the first person to devise a method for and publish a paper 1972 on CFD applied to a 3D furnace was Ingo Zuber of Czechoslovakia Reference 14 His achievement is all the more praiseworthy because in the circumstances of the country and the times Zuber s access to Western scientific literature and his computer resources were both extremely limited d The 3D model which the world followed Much more notice was taken of the publication which recorded the techniques finally or at least for a long time adopted by the Imperial College group namely the 1974 publication of Patankar and Spalding Reference 15 This employed a cartesian or cylindrical polar grid the SIMPLE algorithm in which the equations for velocity components and other variables are solved sequentially rather than simultaneously temperature and pressure dependent density and viscosity the k epsilon turbulence model the six flux radiation model and a kinetically controlled global chemical reaction This method was widely disseminated by the authors and their colleagues at Imperial College and it was extensively adopted by others during the following years 1 3 The first experimental research To bring to a close this review of the more remote past the PhD thesis of Amr Serag Eldin Reference 16 will be mentioned His work at Imperial College between 1973 and 1976 was probably the first ever carried out specifically for testing whether a CFD code was capable of predicting the performance of a steady flow combustor of gas turbine type The thesis was exemplary in its thoroughness and honesty Of especial interest in view of subsequent experiences are the following extracts from Amr s preface I first tested the model for cold flow and obtained favourable results I then tested it for hot flows and otained generally disappointing results Hence I adopted a more sophisticated combustion model which takes into account the effect of concentration fluctuations The agreement improved markedly but was still disappointing in the primary zone Again this was attributed to the combustion model which overlooks the effect of chemical kinetics Right at the start therefore of the researches devoted to testing the validity of CFD based prediction procedures for combustion questions arose about how the influences of concentration fluctuations and chemical kinetics and especially the interactions between them were to be introduced into the model These questions have remained incompletely resolved until the present day The improved models referred to which took account of fluctuations but not adequately of chemical kinetics were those of References 17 and 18 1971 namely the eddy break up and presumed pdf methods In somewhat modified forms they are still regrettably in widespread use 1 4 Concluding remarks about the early years The foregoing review reveals that by the mid 1970s CFD for combustion had become a reality Adequate means had been discovered and published for solving the relevant equations and only more computer power would be needed to enable large and geometrically complex problems to be solved Moreover models of turbulence chemistry and radiation had been devised which though far from perfect were enabling predictions to be made on occasion of a quality justifying hope that steadily conducted research would soon make them very good Although it was to the gas turbine that most attention was given because of the financial support which could be then obtained from the aerospace industry attention also began to be paid to the reciprocating engine to power station furnaces and to fire hazards Thus the present author has found among his papers a 1969 proposal made at a meeting of the Institution of Mechanical Engineers in London Reference 19 for the application of CFD to the Diesel engine and Patankar and he presented a paper concerned with applications to furnaces in 1972 Reference 20 Readers of the remainder of the present paper may well conclude that the optimism of those early years has proved to be sadly falsified by subsequent achievements Click here for a historical summary made in 1995 2 The present The use of commercial computer codes The numerical methods The physical models The widening of the field of application The overall degree of success 2 1 The use of commercial computer codes It could be reasonably argued that it was the needs of the combustion engineers in the aero space industry which brought the CFD software business into existence the reason being that the complexity of the combustion process left expensive experimentation as the only alternative Certainly some of the first computer codes sold by CHAM to UK and US gas turbine manufacturers were specifically for combustor simulation for the desigers of the other gas turbine components ie the compressor and the turbine already possessed computer based methods which they judged perhaps unwisely to be satisfactory Several of those combustor codes are still in existence and use having of course also been significantly further developed by their users and at least one of them entered the public domain by way of the US Army enabling competing CFD code vendors to start business which they did with alacrity Maintaining and refining a special purpose computer code is an expensive and arduous business which few organizations can afford It has therefore proved more cost effective to create and maintain a few general purpose computer codes which can be applied to special purpose problems This strategy was first exemplified by CHAM s PHOENICS code released in 1981 and Creare s FLUENT code released in 1983 Both were capable of simulating either reacting or non reacting flows Every few years since then in one country or another further general purpose codes with similar capabilities have made their appearance As a consequence almost all industrial companies using CFD techniques for designing and improving their equipment or processes nowadays buy or lease software from one of the CFD software vendors 2 2 The numerical methods The numerical methods which are most commonly employed differ little in essence from those of Reference 15 The major novelties are body fitted coordinate grids are often employed unstructured grids ie those in which cells may be arbitrarily arranged and addressed are preferred in some codes avoided by others some codes employ fine grid embedding techniques which can bring the benefits sought from unstructured grids without their disadvantages there is a tendency to use more simultaneous and less sequential solution procedures a few codes can exploit parallel computer architectures by use of domain decomposition multi grid solution procedures are employed so as to accelerate convergence the six flux radiation model is replaced by one or other of the more accurate but more expensive discrete transfer Reference 21 or discrete ordinates Reference 22 methods The consequence of these developments coupled with the immense increase in the power of computer hardware is that it is now possible for CFD models to be set up which fit the geometrical complexities of the equipment very well yet still provide accurate numerical solutions in an acceptable time Whether the numerically accurate solutions provide realistic predictions of how the combustors will actually behave is of course quite another matter for realism depends on the physical models which are employed and on the correctness of the material properties which are supplied to them This will be discussed in the next section 2 3 The physical models The advances on the numerical side of modelling have not unfortunately been matched by corresponding successes on the physical side Nevertheless there have been several developments of which the outcomes most in evidence currently are chemical kinetics models of great complexity both for hydrocarbon combustion and for the reactions giving rise to oxides of nitrogen detailed improvements of turbulence models of the k epsilon type modifications of the eddy break up model for predicting the influence of the turbulence energy and scale on the time average reaction rates Reference 23 1976 modifications of the presumed pdf approach for the representation of the effects of concentration fluctuations on the rates of production of particular chemical species for example NOX and smoke Reference 24 1980 methods of avoiding the arbitrariness of the presumed pdf approach by computing the pdfs ie probability density functions from more rigorously based pdf transport methods Reference 25 1982 Much valuable work has been done but in the present author s opinion reservations must be expressed about each of the items mentioned as follows There is still no agreement about which reduced chemistry model represents the best compromise in respect of realism and computational economy The improvements recommended by various authors differ with the result that none have been generally accepted The eddy break up model requires not to be improved but replaced for it represents as does the flamelet model a turbulent reacting mixture as the mingling of just two distinct fluids and two is too small a number to do justice to reality The presumptions about pdf shape lack general validity and are used more because one must use something than for plausible reasons The pdf transport method although admirable in intention has been held back by its reliance on the computationally expensive Monte Carlo method for which reason it is little used in engineering practice 2 4 The widening of the field of application Despite the shortcomings just alluded to the use of CFD for combustion sumulation has become widely accepted as being a valuable aid to the designers and operators of equipment and to those who are concerned with its environmental and safety impacts A short list of active application areas now follows but without references because a balanced list would be too large land and aircraft gas turbines gasoline engines diesel engines power station furnaces whether fired by gas oil coal peat or wood open hearth blast re heating and other furnaces of the iron and steel industry incinerators domestic and other space heating appliances fire spread and explosions in factories off shore oil platforms and other hazard prone plants guns and missiles At least in this respect ie the widening of the field the optimism of the early 1970s has been vindicated 2 5 The overall degree of success The success of the CFD for combustion campaign could be called complete if nowadays all designs of combustion related equipment were near finalized by the use of CFD predictions and experimental verification were called for only at the end to ensure that the predictions had been near enough correct This is NOT the situation at the present time for any of the fields of application and as the years go by its attainability has appeared less rather than more probable As computers have increased in power and mathematical methods improved in efficiency it has become less and less justifiable to blame the discrepancies between predictions and measurements on the coarseness of the grid or the inability to procure complete convergence The deficiencies of the underlying physical models have become as a consequence increasingly obvious Deficiencies of this kind are much harder to remove than are those of the numerical kind Computer scientists abound who can improve hardware and software and mathematicians who can devise more efficient algorithms are also not rare An advance in science however which is what CFD for combustion now requires depends on rare combinations of circumstance namely someone must have the bright idea and sufficient leisure and energy to develop it until he or she is reasonably confident that it represents a worth while advance that person must then communicate it to others who can pass it on possibly with augmentation but at least without attenuation the idea then has somehow to survive the self preserving tendencies of the current conventional wisdom to which if it is indeed of value it must to some extent be opposed in due course the idea has to reach someone who has the intellectual power to appreciate its value and a resource distribution capability to enabling it to be tried out In what particular sector of combustion science are bright ideas most needed In the view of the present author it is that concerned with turbulence chemistry interactions This opinion will be further developed in part 3 3 of the present paper 3 The future The use of Internet based services The reduced use of body fitted coordinates The models of turbulence and chemistry 3 1 The use of Internet based services The future of CFD for combustion will be influenced by general developments in the way CFD will be used It is thefore worth turning for a moment from the particular to the general In the view of the present author the most significant change that will come about will be through the use of the Internet The reason is that there exist three deterrents to the wider use of computer simulation techniques especially by small and medium sized enterprises these are the cost of the software the cost of hardware of sufficient power to run many fine grid simulations and the scarcity and expense of personnel capable of using them However techniques are already available and are being continuously improved for enabling an engineer with a flow simulation problem to have it solved by setting up the geometry of the apparatus with the aid of a computer aided design package on his or her personal computer transmitting this via Internet to a remote CFD service centre supplying such additional information about inflows outflows what is to be predicted and how much he or she is prepared to pay as complete the specification of the problem in question after some time return to his her PC and there find and explore a graphically displayed simulation of the flow in question receive such additional information as has been requested about particular features of the simulation for example combustion efficiency or production rate of NOX advice concerning the probable error bounds what was the cost of the service down load the whole or part of the files embodying the simulation for further study In order to illustrate the CAD to CFD part of this a 1997 example will be shown during delivery of the lecture wherein a domestic gas burner was simulated This particular calculation was as it happens not performed remotely but it could have been The change that seems likely to come into being has been characterised as like that in society when bucket and well technology was replaced by piped water When low cost and quality assured computations are available to all on tap and on payment according to use terms it seems likely that many combustion engineers will choose that way of working 3 2 The reduced use of body fitted coordinates The user of the remote computing service will not care on what computational grid his or her combustor simulation has been conducted so he will be able to concentrate his attention only on the physical results However that freedom from worry lies a few years in the future therefore until then the CFD code user will still need to concern himself with what grid to use in order to fit his geometry It is widely believed that the only way to represent curved wall combustors and such small but important features as fuel nozzles and air injection holes is to use unstructured body fitted coordinate grids However since the creation of such grids is often troublesome and expensive it seems probable that better ways will be sought and found Indeed one such better way has been found quite recently It has been published on CHAM s website Reference 26 and it seems probable that unless

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