CFD Simulations of Combustion in Afterburner

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CFD simulations of combustion in Afterburner A Project Report Submitted in partial fulfilment of the requirements for the Degree of Master of Engineering in Faculty of Engineering by Hareesh.Bitla Aerospace Engineering INDIAN INSTITUTE OF SCIENCE BANGALORE – 560 012, INDIA July 2008

Transcript of CFD Simulations of Combustion in Afterburner

CFD simulations of combustion in AfterburnerA Project ReportSubmitted in partial fullment of therequirements for the Degree ofMaster of EngineeringinFaculty of EngineeringbyHareesh.BitlaAerospace EngineeringINDIAN INSTITUTE OF SCIENCEBANGALORE 560 012, INDIAJuly 2008iAcknowledgementsIt is my privilege and great pleasure to express my deep sense of gratitude to my guideProf.P.J.Paul sir, for his guidance and excellency in giving suggestions on the problemsi faced during my project work.I acknowledge the full support and encouragement extended by Prof. B. N. Raghunandan,Chairman of the Aerospace Engineering Department.I thank my mom and dad, who living lonely and taking the pain of my absence onlywaiting for my quick completion of my M.E, though i am not quick enough, now thechance for me to ask sorry from them.I thank all of my friends(shru,bindu,ashok,subbu,durga) who are there for me all the time,during my course work.I thank my labmates chetan bhai, abhishek, pradeep verma, for all the help they madeduring my working time in the lab. I specially want to thank Ravi sir, for allowing me tomake use of high-speed computer when i am hang up with my old and slow computer.Last but not least i sincerely believe in you, my God that you are behind my everyproceedings. Nothing much i can give you but a quote, that i am your devotee i love yougod so much.AbstractThis thesis is an eort to understand the functioning of an afterburner with both the coldand reacting hot uids. Geometry of afterburner is modeled in 60 degrees sector. After-burner are in use nowadays, most commonly in all the jet aircrafts, for better maneuveringcapabilities. Afterburners are devices used for thrust augmentation by dumping extra fueland burning the left-out oxygen in the exhaust of combustion chamber products.Extremely complicated compressible and turbulent ow phenomena happening in thewake of ameholder which are dicult to analyze and understand. The present workfocuses on understanding the ow phenomena in afterburner and behind the ameholder.The performance of afterburners and how the temperature elds varying in combustionprocesses are studied here. The aim is Evaluation of the preliminary design of afterburnerCFD simulations.3D steady compressible ow simulations are carried out to understand afterburner owsin greater detail than that can be gathered from control volume analysis. First a condenceover the application of the tool is obtained by performing simulations on a geometry withcold ow for which ow phenomenon is good.iiContentsAbstract ii1 INTRODUCTION 11.1 Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Operation of afterburner . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Afterburner and its components . . . . . . . . . . . . . . . . . . . . . . . . 42 Approach to the present report 62.1 Motivation for the current work . . . . . . . . . . . . . . . . . . . . . . . . 62.2 Objective of the current work . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 Organization of thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Literature review 83.1 Combustion Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2 Work by M.V.Ramana Reddy . . . . . . . . . . . . . . . . . . . . . . . . . 83.3 Work by Westbrook and Dryer . . . . . . . . . . . . . . . . . . . . . . . . . 93.4 Work by Ravichandran and Ganesan . . . . . . . . . . . . . . . . . . . . . 93.5 Work by Mattingley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Theory of combustion 114.1 Chemical reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.1.1 Well-stirred reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.2 Kollrack reaction mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 134.3 Blow out time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Flow features 155.1 Shear layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165.2 Flame stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175.3 Design requirement for vee-gutter ameholder . . . . . . . . . . . . . . . . 186 Aspects of modeling 196.1 Conservation equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.1.1 Continuity equation . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.1.2 Momentum equation . . . . . . . . . . . . . . . . . . . . . . . . . . 196.1.3 Energy equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20iiiCONTENTS iv6.1.4 Equation of state . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.2 Turbulence modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.2.1 k turbulence model . . . . . . . . . . . . . . . . . . . . . . . . . 206.2.2 Continuity equation . . . . . . . . . . . . . . . . . . . . . . . . . . . 216.2.3 Momentum equation . . . . . . . . . . . . . . . . . . . . . . . . . . 216.3 Combustion modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226.3.1 Eddy dissipation combustion model . . . . . . . . . . . . . . . . . . 227 Mesh generation 257.1 Splitting Of model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257.2 Unstructured Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267.3 Structured Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287.4 Hybrid mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307.5 Mesh Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Numerical methods 318.0.1 Discretisation of governing equations . . . . . . . . . . . . . . . . . 319 Problem denition 349.1 Afterburner description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349.1.1 Inlet conditions for combustor and afterburner . . . . . . . . . . . . 349.1.2 Blowout time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369.1.3 Afterburner performance . . . . . . . . . . . . . . . . . . . . . . . . 3810 CFD results 4210.1 Cold ow results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4210.2 Reacting ow results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4811 Conclusions 5911.1 Flameholder performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5911.2 Diuser performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5911.3 Temperature plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6011.4 Mass fraction Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60List of TablesvList of Figures1.1 Temperature-Entropy diagram for a jet engine with an afterburner . . . . . 21.2 Afterburner system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Dry and on conditions of an Afterburner . . . . . . . . . . . . . . . . . . . 45.1 Flow Pattern in the vicinity of V-gutter Flameholder . . . . . . . . . . . . 167.1 Front Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267.2 Middle Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277.3 Rear Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277.4 Middle Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289.1 Afterburner of K9 engine at test station . . . . . . . . . . . . . . . . . . . 359.2 Afterburner model used with its dimensions . . . . . . . . . . . . . . . . . 3510.1 Density variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4310.2 Velocity variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4410.3 streamlines form chuteholes . . . . . . . . . . . . . . . . . . . . . . . . . . 4510.4 Streamlines from inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4610.5 Streamlines from inlet and its temperature variation . . . . . . . . . . . . . 4710.6 Temperature distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4810.7 Temperature distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4910.8 Temperature distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5010.9 Temperature distribution at X=.35 on ZX plane . . . . . . . . . . . . . . . 5110.10Temperature distribution at X=.45 on ZX plane . . . . . . . . . . . . . . . 5210.11Temperature distribution ZX plane . . . . . . . . . . . . . . . . . . . . . . 5310.12Temperature distribution ZX plane . . . . . . . . . . . . . . . . . . . . . . 5410.13Temperature distribution ZX plane . . . . . . . . . . . . . . . . . . . . . . 5510.14Temperature distribution ZX plane . . . . . . . . . . . . . . . . . . . . . . 5610.15Temperature distribution ZX plane . . . . . . . . . . . . . . . . . . . . . . 5710.16CO2 mass fraction variation variation . . . . . . . . . . . . . . . . . . . . . 58viChapter 1INTRODUCTION1.1 AfterburnersGas turbine engines for military ghter aircraft are often equipped with an afterburner forincreasing the thrust output of the engine. An afterburner is a duct in the engines exhaustsystem which acts as an auxiliary combustion chamber. The exhaust of a combustionchamber contains a large number of unused oxygen because of the high air-fuel ratiosnecessary to limit the gas stagnation temperature which the turbine blade is exposed.Thisexcess oxygen at the turbine exit makes it possible to burn additional fuel downstream andthereby to increase the nozzle exit temperature and jet velocity.Much higher afterburnertemperatures are allowed than those leaving combustor,because (a)there is no highlystressed rotating machinery downstream of the afterburner,and (b)operation is for shorterduration periods.Increase in eective thrust can be explained using T-s diagram for a jet engine withafterburner in g(1.1), which shows that afterburning is analogous to reheating in anopen-cycle stationary gas turbine. The energy release in afterburner at approximatelyconstant stagnation pressure shifts the nozzle expansion process to the right on the T-s diagram. As a result, nozzle enthalpy and temperature between T-s diagram constantpressure lines increase as the nozzle inlet stagnation temperature increases. This produceshigher jet velocities thus higher thrust.1CHAPTER 1. INTRODUCTION 2Figure 1.1: Temperature-Entropy diagram for a jet engine with an afterburner1.2 Operation of afterburnerAfterburner is an exhaust system that is tted to the exit of low pressure turbine in thegas turbine engine. The main components of afterburner are: diuser that reduces the owvelocity, screech liner to attenuate the transverse oscillations, fuel manifolds to provideproper fuel distribution and a ame stabilizer that provides the recirculation zone forame anchoring. Figure 1.2 shows the construction of afterburner. Afterburner receivesvitiated air from the exit of low pressure turbine (LPT) at a temperature range of 780K to 1065 K, and a pressure range of 55 KPa to 380 KPa from high altitude operationto sea level. The exit velocity of LPT is of the order 0.5 to 0.6 Mach. When one desiresto light up afterburner by admitting fuel into the core cavity, it is extremely dicult orimpossible to achieve a stable ame due to high incoming velocity. Hence, a diuser isemployed to reduce the velocity to the level of 0.3 Mach. A recirculation zone is created bya V-shaped blu body. Fuel is admitted through the manifold which is situated upstreamof central V-shaped- ame-stabilizer. The catalyst (platinum-rhodium) which is locatedin the ame stabilizer helps in igniting the mixture of hot air from LPT and the fuel thatis sprayed in the vaporized form through the manifold at a pressure of 700 kPa. In theCHAPTER 1. INTRODUCTION 3Figure 1.2: Afterburner systemexperimental test facility hot air is provided by a pre-heater ahead of afterburner. Atabout 450oC combustion is initiated. Then, all the other three manifolds are activated toachieve full afterburning at a fuel manifolds pressure of 2720 kPa. To simulate afterburnerentry conditions by the pre-heater, a fuel / air ratio in the range of 0.015 to 0.02 is needed.For full afterburning the overall fuel air ratio is in the range of 0.05 to 0.06.The transition from non-afterburning operation to afterburning operation is referred toas lighting the afterburner and is accomplished by energizing the igniters while introducingfuel into the afterburner through one of the fuel spray rings, referred to as the pilotring. The igniters initiate combustion of the fuel, the combustion being supported bythe unreacted air in the combustion products from the main combustion chamber. Theresulting ame is stabilized and held in place by one of the ameholder gutters, known asthe pilot gutter. Once this initial or pilot stage of afterburning is established, additionalfuel is supplied, usually sequentially, to each of the remaining or auxiliary spray ringsuntil all the spray rings are injecting fuel into the afterburner. The pilot ame ignites theadditional fuel and the ame expands from the pilot gutter to a series of auxiliary guttersto achieve full afterburning operation. Meanwhile, the variable area nozzle opens widerto provide additional ow area for discharging the hot gasses. The provision of fuel toCHAPTER 1. INTRODUCTION 4Figure 1.3: Dry and on conditions of an Afterburnerthe various spray rings, the opening of the variable area exhaust nozzle and the operationof the igniters is overseen and coordinated by an automatic control system operating inresponse to the position of a throttle lever set by the pilot of the aircraft. The timerequired for the above described lighting process is on the order of a few seconds. Thelightening process in afterburners is shown schematically in below gures.1.3 Afterburner and its componentsThe major requirement of the afterburner is to ensure adequate ame stability and com-pleteness of combustion within the specied length,while at the same time contributingminimum total pressure loss. Due to very high specic fuel consumption, afterburners areoperated only for short durations when necessary. During the major part of ight, whenthe afterburner is not under operation, the components of the afterburner namely diuser,ame stabilizer and fuel rings contribute a signicant amount of total pressure loss. Thisloss is still more when afterburner is under operation. As it depends on the ow machnumber and the ame holder blockage to keep the total pressure loss down to permissiblelevels. Further, in aircraft engines,length is of great importance. The design of afterburnershould be optimum so that for a given afterburner length,it oers the best combination ofafterburner characteristics such as high combustion eciency, low total pressure loss andCHAPTER 1. INTRODUCTION 5wide stability limits. To achieve these aims in the design and development of the after-burner, adequate knowledge of the ow and combustion characteristics in the afterburneris of vital importance. Although most of the useful information about such complex owis still obtained by experimental methods, numerical simulation can be of great help tosupplement, support and even reduce the extent of experimental work.Eventhough theearlier works works mostly depend upon exorbitantly expensive experimental methodsand empirical correlations, the modern high-speed computers have changed the after-burner design approach because of the reduction in the number of experiments and quickand economical adaptability to dierent geometric congurations and input conditions.The majority of earlier numerical simulations have been two-dimensional axi-symmetric,considering only simple form of blu bodies.The main aim of present investigation is topredict the three-dimensional reacting ow elds in a practical afterburner system.Chapter 2Approach to the present report2.1 Motivation for the current workTraditionally combustion ow in the afterburner was calculated numerically and compu-tationally by two dimensional models, where the three dimensional eects in ow eldswere missing. The results obtained like total pressure loss, combustion eciency, massfraction contours in Ravichandran(10) may not resemble the actual ow. No people haveused the three dimensional model of afterburner to carry out combustion calculations init.Few studies like references[2],[3] have done three dimensional studies in afterburner nutnot done the combustion calculations, only cold ow analysis and swirl eects are stud-ied. There is no research paper concerning the combustion ow calculations in a full scalethree dimensional model numerically.So, here is an attempt to study reacting ow in afterburner using Eddy Dissipation modelfor combustion, and K- model for turbulence. The required afterburner design speci-cations are obtained from GTRE(Gas Turbine Research and Establishment ) company.This particular afterburner is tted in K9(KAVERI) engine which is currently using inLCA(Light Combat Aircraft).6CHAPTER 2. APPROACH TO THE PRESENT REPORT 72.2 Objective of the current workThe main objective of the proposed work is to improve the performance of afterburner onstudying the reacting mixing ow. For this CFD simulations for cold ow and reactingow have done. Methodology: To conduct CFD simulation in the afterburner geometry by making hybrid mesh for themodel using commercially available CFD software. The turbulence model used will be k model techniques. The combustion model used will be Eddy dissipation model techniques. The results obtained are analyzed and design iterations are suggested.2.3 Organization of thesisThis thesis is divided into multiple sections, beginning with an introduction to the oweld inside afterburner , the motivation behind this work and objectives of the Thesisin Chapter1 and Chapter 2. Literature review is carried in chapter 3. Flow featuresconcern with the geometry of the afterburner are discussed in chapter 4. Chapter 5discusses briey the turbulence theory and modeling and combustion theory and modelingrelated to afterburner. Chapter 6 deals with the types of mesh commonly used for CFDsimulations. Numerical methods suitable for dierent terms in Governing equations anddiscretization method are discussed in chapter 7. Problem denition, methodology andcomputational procedure adopted for performing the simulation are described in chapter8. Chapter 9 deals with results and discussion of simulation work carried out with k-turbulence model. Chapter 10 discusses conclusion of the present work carried out andchapter 11 gives the overview of present work and future scope.Chapter 3Literature review3.1 Combustion SimulationCombustion reaction mechanism of jetA fuel used in this report is single-step oxidationreaction, the corresponding input data is taken from Westbrook and Dryer(8). Numericalsimulation of combustion in afterburner is carried out by few people, due to the owcomplexity in afterburner- high temperature levels, high turbulence levels, presence ofameholder and propelling nozzle. M.V.Ramana reddy, T.R.Shembhakar and J.J.Issac,have done attempt to simulate the combustion in afterburner using computer code calledPHOENICS. But this study limited to two-dimensional ow eld only. Isothermal oweld studies in afterburner have carried out by Ganesan, Ravichandran(10). Aircraftengine design book by mattingly(1) also explains lot about afterburner ow eld system.In these no combustion process is considered. Only the ameholder eects and swirleects in afterburner are studied. But the present report deals with both combustionprocess and ameholder eects.3.2 Work by M.V.Ramana ReddyThe ow in the afterburner was assumed as steady, to-dimensional axi-symmetric andturbulent. Due to symmetry of the model computations were carried out in one half8CHAPTER 3. LITERATURE REVIEW 9of the afterburner. The grid employed was 18 cells in Y-direction and 64- cells in Z-direction. The V-gutter and nozzle were simulated by blocking the corresponding cellsin the computational domain by prescribing zero porosity for them. Computations werecarried out for both cold ow and ow with combust ion. The boundary conditionsare 830K static temperature, 3.2E5 Pa total pressure at the inlet. The wall is assumedadiabatic. And the simulations were carried out by solving conservation equations usingk turbulence model and spalddings eddy-breakup model.3.3 Work by Westbrook and DryerThe kinetic modeling of reaction mechanisms are studied thoroughly by these people.The 30 step kollarack reaction mechanism of jetA fuel also modeled kinetically by thesetwo people. But we used single-step oxidation reaction of jetA fuel described kineticallyby these people. All reaction mechanisms were dened by using Arrhenius kinetic rateequation. The values of pre-exponential factor and temperature index and activationenergy foe each independent reactions westbrook and dryer have predicted unique valuesafter conducting several experiments. These values are very useful in dening a chemicalreaction in a numerical simulation of combustion processes.3.4 Work by Ravichandran and GanesanThe cold ow eld in an afterburner system studied experimentally and numerically byRavichandran and Ganesan. Experimental setup is prepared by perspex material, andthe ow is studied in it. The v-gutter ameholder stabilization eects in an afterburnerstudied eectively. Numerically also the three dimensional steady state equations aresolved for dierent inlet swirl conditions and velocity vectors are presented in results. Forthis computational domain is discritized into 32 28 15 nodes in x, r, directions re-spectively and the intercode spacing is not uniform; especially very ne grid in directionfor radial V-gutter. The temperature of the ow eld is assumed to be 900K within oper-ating pressure 2.83atm. For various inlet swirl conditions the conservation equations areCHAPTER 3. LITERATURE REVIEW 10solved by SIMPLE procedure using tri-diagonal matrix algorithm. The nite dierencealgebraic equations are obtained by integration over control volumes for each variablesand diusive terms and the control volume boundaries. Under-relaxation factors are usedto promote the convergence.3.5 Work by MattingleyEngine design calculations were presented by mattingley in Aircraft Engine Design book.It also describes the afterburner performance and ameholder performance on knowing thedesired input data. AEDSys Software is developed by him which has totally 8 sections, IN-LET, COMPRESSOR, TURBINE, NOZZLE, EQL, COMBUSTION, MAIN BURNER,AFTERBURNER. each of this section calculates the ow eld properties in that particu-lar zone of engine. We used COMBUSTION, AFTERBURNER sections. COMBUSTIONsection solves kollarack reaction mechanism of jetA fuel and gives blowout time time andmole fractions of product species on solving WSR equations. AFTRBURNER sectioncalculates the afterburner performance points at dierent stations of afterburner. Mat-tingleys work on AEDSys supports many of the calculations required while evaluatingthe afterburner components performance.Chapter 4Theory of combustionThe system of partial dierential equations describing the adiabatic, one dimensional,ideal-gas phase chemical reaction without axial molecular or turbulent diusion is givenbynit + Unix = fi(nk, T) i, k = 1...NS (4.1)wherefi = 1(ij ij)(RjRj) j = 1...JJ (4.2)In equation 4.2 Rj and Rj are modied arrhenius expressions for forward and backwardrates for jthreaction.Rj = kj

(nk) kj(4.3)Rj = kj

(nk) kj(4.4)In above equations ni is the mass-specic mole number of the ithspecies(i=1..NS), T isthe temperature; is the mixture mass density; kj, kj are the stoichiometric coecientsof species reactants and products respectively. kj and kj are the forward and reverserate constants. JJ is the total number of independent chemical reactions.11CHAPTER 4. THEORY OF COMBUSTION 124.1 Chemical reactorsThe interplay of mixing and chemical and chemical processes that enable ameholding, ina wake region can be better understood by using chemical engineering or chemical reactortheory.4.1.1 Well-stirred reactorThe Well-stirred reactor is an idealization of ow systems in which ow stream is recir-culated in some way to promote gross-mixing of products, reactants, and reaction inter-mediates. The physical reactor is being modeled is usually referred to as a back-mixedor jet-stirred reactor. in terms of turbulent mixing theory, the WSR assumption impliesthat the gross recirculating ow velocity is so great, and the turbulent diusion acrossstreamlines so rapid, that every entering uid particle has instantaneous access to everyother uid particle. This assumption does not require that mass or energy transfer causedby molecular diusion will necessarily will occur between the uid particles.For ows that are time-steady, and for which the axial gradient term in equation4.1 canbe approximated by the nite dierence formulaUdnidx unix so that equation(4.1) becomesUAni ` niAx = fi(ni, T)i, k = 1...NS (4.5)where ` ni refers the upstream or entry value of ni into the control volume of volume V =Ax and A u = m. with this notation WSR equations become mV (ni ` ni) = fi(ni, T)i, k = 1...NS (4.6)This WSR chemical reactor will be applied to ameholder wake to calculate blowout time.The chemical reactions involved in this wake region are described by 30 step kollrackreaction mechanism and these are solved by AEDSys software.CHAPTER 4. THEORY OF COMBUSTION 134.2 Kollrack reaction mechanismIn 1976 Reiner kollrack devised a 30-step reaction mechanism for modeling combustion ofjet fuel, including production of NOx. The rst two reactions are physico-elementaryreactions,but are global reactions,devised to represent very great number of complexand largely unknown steps in the pyrolysis of the jet fuel molecules to smaller fragments.C12H23 + O2 5C2H4 + C2H3 + O2 (4.7)C12H23 + OH 6C2H4 + O (4.8)C2H4 + H C2H3 + H2 (4.9)H + H H2 (4.10)O + O O2 (4.11)H + OH H2O (4.12)H + O2 OH + O (4.13)O + H2 OH + H (4.14)CO + OH CO2 + H (4.15)H + H2O OH + OH (4.16)CH3 + O2 CH2O + OH (4.17)HO2 M + H + O2 + M (4.18)HO2 + H OH + OH (4.19)CH2O + OH H2O + HCO (4.20)O + H2O OH + OH (4.21)N2 + O NO + N (4.22)CHAPTER 4. THEORY OF COMBUSTION 14N + O2 NO + O (4.23)N + OH NO + H (4.24)HCO + O2 HO2 + CO (4.25)HCO + OH H2O + CO (4.26)C2H4 + OH C2H3 + H2O (4.27)CH2O + HO2 HCO + OH + OH (4.28)C2H2 + HO2 HCO + CH2O (4.29)C2H3 + O2 C2H2 + HO2 (4.30)NO + HO2 NO2 + OH (4.31)C2H4 + HO2 CH3 + HCO + OH (4.32)H2 + CH3 CH4 + H (4.33)C2H2 + OH CH3 + CO (4.34)CH3 + O CH2O + H (4.35)4.3 Blow out timeWhich is required parameter in case of designing the ame holders. It denes the time atwhich the maximum rate of reaction occurs and the corresponding combustion eciency if at all perturbed from its value the ame will blow-o.To calculate the blow out time the region behind the ame holder is modeled as the Well-stirred reactor(WSR). The combustion process is assumed as 30 step reaction mechanismand the corresponding WSR equations are solved using AEDSys software.Chapter 5Flow featuresThe mechanism of ame holding in the afterburner appears to be same as in the mainburner, but there is a subtle dierence between two. In the main burner primary zonethee recirculation bubble is fueled from the inside and is conned by the combustor domeand liner walls so that the primary zone combustion is forced to take place within theconnes of recirculation bubble. Consequently, there is no discernable ame front, andspatially homogeneous combustion occurs within the micro-mixed reaction zone. In theafterburner, however, the recirculation zone is fueled from the outside, so that discrete,standing turbulent ame front is established in the shear driven mixing layer at the outeredge of recirculation bubble. The chemical reactions responsible for ame holding occurin a very small micro mixed reaction zone immediately behind the upstream-propagatingame front. by the time the burning gases, which are disentrained in to the recirculationbubble, ow back up stream to be re-entrained in the mixing layer, combustion is nearlycomplete. There is negligible chemical reaction within hot recirculation zone, as it iscomposed of almost burnt products. The hot recirculated gases that are mixed in withinexternal ow merely help to stabilize the axial location of the standing turbulent amefront.15CHAPTER 5. FLOW FEATURES 16Figure 5.1: Flow Pattern in the vicinity of V-gutter Flameholder5.1 Shear layersThe afterburner utilizes turbulent shear layers for both ameholding and ame spread. Tounderstand this method of mixing, consider two uniform, parallel owing streams of gasowing continuously over a splitter plate. Immediately downstream of the splitter plate,the axial velocities are U1 and U2. For clarity, it is initially assumed that the pressuresand densities of both streams are equal and constant, and that boundary layers on thesplitter plate and duct walls can be ignored.If the to velocities dier, for example U1 > U2, a shear layer is generated at the interfacebetween two streams, in which momentum is transported laterally from faster to the slowerstream. Not only are vorticity and momentum transported laterally but also thermal andmechanical energy, and mass(molecules) may be transported laterally as well. If the twostreams have dierent molecular identities, the shear layer is also a mixing layer. Byanalogy with the denition of boundary layer thickness m in the gure(5.1) is dened asCHAPTER 5. FLOW FEATURES 17the region within which the mole fractions of mixant gases dier by 1 percent or morefrom their respective values in the unmixed streams.The corresponding growth rate of the shear layer for streams of dierent densities givenby equationx = C_ 1 r1 + s.5r__1 + s.52__1 (1 s.5)(1 + s.5)1 + 1.29(1+r)(1r)_ (5.1)whereC = .25 to .45s= 2rho1r = U2U1Another parameter used generally is mean convective velocity dened byUc = U1 + s.5U21 + s.5 (5.2)5.2 Flame stabilizationTwo general types of ame stabilizing devices are used generally blu body ameholdervee-gutters and piloted burners, where a small piloting heat source is used to ignite themain fuel ow.In our present model vee-gutter ameholder is employed. The vee-gutter ameholdershave the advantage of low ow blockage and low total pressure loss. They are simple andlightweight and have a good development history. The wake of a vee-gutter ameholderis divided into two regions: a recirculation zone or bubble and a shear-driven mixinglayer, as shown in gure(5.1). The recirculation zone is characterized by a strong reverseow and very low chemical reaction rates. As combustion is essentially complete in therecirculation zone, the temperature is nearly equal to adiabatic ame temperature corre-sponding to the fuel-air ratio of the approaching stream. The mixing layer is characterizedby very strong shear, steep temperature gradients, and vigorous chemical reaction in themicro mixed region behind the ame front, which is propagating upstream against themean velocity within the mixing layer. Following the termination of the mixing layer byCHAPTER 5. FLOW FEATURES 18disentrainment of the recirculating gases, the ame front continues to propagate outwardtowards the walls.The design goal is to select parameters that will cause the ame region to stand at alocation between xm, the mixing transition point dened by equations(5.1) and (5.2), andx = L2, where L is length of recirculation bubble. At about x = L2 the mixing layer beginsto break down as a result of disentrainment of gases from mixing layer into the recir-culation bubble. This is an interesting balancing act because the ame front must notpermitted to propagate so freely upstream that it ashes back to the spray bars, normust it be allowed to blow-o downstream because the mixing layer and recirculationzone are not long enough.To nd the values of parameters that will provide the needed range for ame stabiliza-tion, the mixing zone will be modeled as a single micromixed well -stirred reactor(WSR)of lateral thickness equal to the average shear layer thickness m and of axial length equalto one-half of the recirculation bubble. The mean residence time or stay time in the WSRcan be estimated byts = m m =m(L2)mUc= L2Uc(5.3)where Uc is the convective velocity within the mixing layer, dened by equation 4.2.5.3 Design requirement for vee-gutter ameholderThe requirement for the ame front to stabilize is therefore that residence time or staytime ts of the gases owing through the mixing layer must be greater than, or equal to,the WSR residence time at blowout tBO which is explained in section4.3 .because the ts > tBO in the mixing layer is required, the design requirement for amestabilization can be stated asts = L2Uc= LU1+s.5U21+s.5> tBO (5.4)Chapter 6Aspects of modelingThe mathematical models used for simulating the combustion of JetA fuel in afterburneris fully compressible, transient Reynolds Averaged Navier-Stokes equations and spatiallyltered fully compressible, transient Navier Stokes equations. commercial uid dynamics(CFD) code, CFX-11 supplied by ANSYS inc., was used to perform simulations.6.1 Conservation equations6.1.1 Continuity equationujxj= 0 (6.1)6.1.2 Momentum equation(uiuj)xj= peffxi+ (2()Sijxj+ SMi (6.2)where t = Ck2

;Cmu = 0.0845; Sij = 12(uixj+ ujxi) ; The source term in the momentumequation SMx=0 SMy = 0; SMz = - g;19CHAPTER 6. ASPECTS OF MODELING 206.1.3 Energy equationHeffujxj=(( + t) Txj)xj((D + Dt)hmymxj)xj+ SE (6.3)where Heff = E + peff; t = tcpPrt; Prt=0.9; SE is the net volumetric heat releasedue to radiation and combustion.6.1.4 Equation of stateTo close this system of equations, two relations must be introduced. Firstly there is theequation of state, which for a perfect gas ism = pWRT(6.4)where R is the universal gas constant, R= 8314 J kg1 K1.Secondly there is constitutive equation ,h = CpT (6.5)in which Cp is the constant pressure specic heat of air. Cp is the weak function oftemperature.6.2 Turbulence modeling6.2.1 k turbulence modelThe k is a two equation turbulence model. This model is widely used because it of-fers good compromise between numerical eort and computational accuracy. This modeluses the gradient diusion hypothesis to relate the Reynolds stresses to mean velocitygradients and the turbulent viscosity. The turbulent viscosity is modeled as product ofturbulent velocity and turbulent length scale. In k model, the turbulence velocity scaleCHAPTER 6. ASPECTS OF MODELING 21is computed from the turbulent kinetic energy, which is provided from the solution of itstransport equation. The turbulent length scale is estimated from two properties of theturbulence eld, usually the turbulent kinetic energy and its dissipation rate. The dissi-pation rate of the turbulent kinetic energy is provided from the solution of its transportequation. In k model, k is the turbulence kinetic energy and is dened as the varianceof the uctuations in velocity. It has dimensions of (L2T2). is the turbulence eddydissipation (the rate at which the velocity uctuations dissipate ), and has dimensions of per unit time (L2T3). The k model introduces two new variables k and into thesystem of equations. The continuity and momentum equations will be then equation isthen6.2.2 Continuity equationujxj= 0 (6.6)6.2.3 Momentum equation(uiuj)xj= peffxi+ (2( + t)Sijxj+ SMi (6.7)where t = Ck2

;Cmu = 0.0845; t is the viscosity accounting for turbulence.The value of k and come directly from the dierential transport equations of turbulentkinetic energy and turbulence dissipation rate :kujxj=(k( + t) kxj)xj+ Pk (6.8)ujxj=(

( + t) xj)xj+ C1

kPkC2

2k (6.9)where k =

= 1.39; C1 = 1.42 - (1 01+3 ; = Sk

; S=_2SijSij; 0 = 4.38; = 0.012;since the ow is considered compressible, the equation of state is also solved which isCHAPTER 6. ASPECTS OF MODELING 22given byP = RT (6.10)6.3 Combustion modeling6.3.1 Eddy dissipation combustion modelIn this model, the detailed combustion mechanism of JetA fuel developed by Kollrack(1976) is used. This mechanism involves 30 elementary reactions among 21 species:C12H23,C2H4,C2H3,CH4, H2O, CO2, H2, CO, O2, N2, O, H, OH, HO2, H2O2, CH3,CH2O, CH2O, HCO, N, NO. The EDC model is used to introduce turbulencechemistryinteractions. The model is based on a general reactor concept for the calculation of theaverage net species production rates in turbulent reactive ows. Combustion takes placein the regions of the turbulent eld where the highest molecular uxes occur. Those re-gions are associated with the smallest turbulence structures, the so-called ne-structures.Through a step-wise description of the turbulence energy cascade process from large toprogressively smaller eddies, an expression for the mass fraction of the ne-structuresand for the characteristic time scale for mass exchange between the ne-structures andthe bulk uid is derived, dependent upon the turbulence quantities and the viscosity: = 9.67 34_k = 0.41_

(6.11)These quantities are subsequently used in the reactor modeling of the ne structures. Itis concluded that the model provides a link between the small-scale turbulence structures(or ne structures), where reactions take place, and the grid-scale turbulence structuresthat can be described by turbulence models like the RNG k, which is used in this work.A detailed analysis of the turbulence energy cascade model that was used to derive theexpressions Equations and can be found in Ertesvag and Magnussen (2000).When the EDC model is to be integrated in a CFD code like FLOWSIM every singleCHAPTER 6. ASPECTS OF MODELING 23computational cell is considered to be composed of a reactive space, namely the ne-structures and the surrounding uid that is inert. The reactive space is modeled as aPerfectly Stirred Reactor (PSR) exchanging mass and energy with the surrounding inertuid. Thus, the solution of a PSR problem in every single cell involving the system ofnon-linear algebraic equations consisting of the mass and energy balances is required. Tomake the simulations more robust, temporal derivatives are added in the balances and theset of non-linear algebraic equations is transformed into an initial value problem wherethe ODE set of mass and energy balances (equations(6.6) and (6.7)) is integrated form aknown initial state to steady-state.dymdt = (ymym)(1 ) + mMm m = 1, 2....NS (6.12)dhdt =

ymhmymhm(1 ) + qrad (6.13)The superscript asterisk refers to quantities in the ne structures. If there is no superscriptaveraged quantities over the cell are meant. In Eq(6.13) the net radiative heat transferrate qrad from the ne-structures to the surrounding uid is neglected.In this work, the implicit Euler method is used for time marching when solving the setof ODEs. As only the steady-state solution is needed, relatively large time steps canbe taken, thus reducing the required number of iterations and the required CPU time.Solution of the system of Eqs(6.12) and (6.13) provides values for the variables in thene structures (T, ym,.... m=1, . . ., NS) and for the net species production rates .min the ne-structures. Eventually, the average net species production rates, Rm, that aresubstituted in the species transport equations (Eq(6.12)), which are integrated over eachcontrol volume, are calculated from:Rm = (1 )(ymym) (6.14)Thus, the eect of turbulence on the source terms, RmMm, of the species transportequations (Eq(6.14)) is taken into account through the determination of the mass fractionCHAPTER 6. ASPECTS OF MODELING 24and of the characteristic time scale of the ne structures.Chapter 7Mesh generationThe partial dierential equations that govern uid ow and heat transfer are not usuallyamenable to analytical solutions, except for very simple cases. Therefore, in order toanalyze uid ows, ow domains are split into smaller subdomains (made up of geometricprimitives like hexahedrons and tetrahedrons in 3D and quadrilaterals and triangles in2D). The governing equations are then discritized and solved inside each of these sub-domains. Typically, one of three methods is used to solve the approximate version ofthe system of equations: nite volumes, nite elements, or nite dierences. In a CFDanalysis, the number of cells in the mesh should be taken suciently large, such that anadequate resolution is obtained for the representation of the geometry of the ow domainand the expected ow phenomena in this domain. The accuracy of numerical solutionis partly determined by the nature of the mesh used to represent the physical domain.In CFD, numerical error are dependent on quality of mesh and becomes visible in owsolution. Dierent types of mesh generation techniques are discussed below.7.1 Splitting Of modelMesh generation is carried out in Ansys IcemCfd software. Two types of meshes can becreated for a model one is structured mesh, other is unstructured mesh. Present model25CHAPTER 7. MESH GENERATION 26Figure 7.1: Front Partis divided into three parts to proceed with mesh generation(Front part, middle part,rear part). Middle part is done with unstructured mesh. This part consists of V-gutterassembly and chute holes. Making a structured mesh to this geometries is a complexprocedure so for that reason unstructured mesh has been created to this part. Front andrear parts are done with structured mesh.The details of unstructured and structured meshes are explained briey in the followingsections.7.2 Unstructured MeshAn unstructured mesh is characterized by irregular connectivity is not readily expressedas a two or three dimensional array in computer memory. This allows for any possibleelement that a solver might be able to use. Compared to structured meshes, the storagerequirements for an unstructured mesh can be substantially larger since the neighbor-hood connectivity must be explicitly stored. The most popular family of algorithms forunstructured grid generation are those based upon Delaunay triangulation, but othermethods, such as quadtree or octree approaches are also used. Given a set of points in aCHAPTER 7. MESH GENERATION 27Figure 7.2: Middle PartFigure 7.3: Rear PartCHAPTER 7. MESH GENERATION 28Figure 7.4: Middle Partplane, a Delaunay triangulation of these points is the set of triangles such that no pointis inside the circumcircle of a triangle. The triangulation is unique if no three points areon the same line and no four points are on the same circle. The octree approach is basedon spatial subdivision algorithm in which cells are recursively subdivided until requiredresolution is obtained. In RANS calculation, unstructured mesh is preferred in the regionwhere convective uxes are dominant. Part of the model with unstructured mesh is shownin g2.1.7.3 Structured MeshStructured mesh generation is popular and successful method of discretising domain.The method is based on direct mapping from physical domain to computational domain.Boundary points prescribed within physical domain are used to interpolate points withincomputational domain. The major advantage of structured mesh generation is that theimplicit mapping inherently stores the mesh connectivity and hence maintaining low mem-ory overheads. In RANS calculation, structured mesh is preferred in the regions whereviscous stresses are dominant. A structured mesh is characterized by regular connectivityCHAPTER 7. MESH GENERATION 29that can be expressed as a two or three dimensional array. This restricts the elementchoices to quadrilaterals in 2D or hexahedra in 3D. Structured mesh is obtained usingtwo types of algorithms namely Algebraic grid generation algorithms and Numerical gridgeneration algorithm. In Algebraic grid generation algorithms, coordinates of nodes iscalculated using some functions. In Numerical grid generation algorithms, coordinates ofnodes is calculated by solving partial dierential equations. Blocking had done for thefollowing shown parts of the model to create structure mesh. The mesh statistics followsasRare part mesh - 2lakh elements, 3lakh nodesFront part mesh - 3 lakh elements, 4 lakh nodesCHAPTER 7. MESH GENERATION 307.4 Hybrid meshA hybrid mesh is a mesh that contains structured portions and unstructured portions.Hybrid mesh is similar to unstructured mesh in that they use identical method of datastorage. The only dierence is that, the hybrid meshes are constructed using more thenone cell topology. The advantage is that cells of dierent topology can placed in owregion where they are most suited. Hybrid mesh consists of pyramidal elements. Theseelements are created when we merge unstructured and structured meshes. Structured andunstructured meshes which are created for the model parts are merged nally across theinterfaces to create hybrid mesh for the entire model as shown in gure.7.5 Mesh StatisticsStructured meshFor Front partNumber of elements - 44271Number of nodes - 38857For Rear PartNumber of elements - 53811Number of nodes - 47479Unstructured mesh(middle part)Number of elements - 547518Number of nodes - 92616Hybrid meshNumber of elements - 653876Number of nodes - 179276This particular Hybrid mesh is imported to Ansys Cfx Softare to solve the ow eldin the model.Chapter 8Numerical methodsThe mathematical models discussed in chapter 6 dene the general equations for whichwe wish to nd the solution. In general it is not possible to derive analytical solutions tothese equations, so other methods must be found. Numerical methods are generally usedin these circumstances. the fundamental numerical method used in this work is:The geometry is discritized into many small volumes (mesh or grid); The conservationequations are integrated over the discritized volumes;The modied conservation equations are approximated by nite dierence equations ; andThe nite dierence equation are solved using an iterative solver.As the CFX-10 commercial CFD code was used to simulate the uid ows, only a briefoutline of the numerical models used will be presented here, adapted from user manualof the code. For a more complete derivation of these equations the reader is referred toVersteeg and Malalasekara (4), Ferziger and Peric (2), Patankar(3) or Fletcher (11).8.0.1 Discretisation of governing equationsThis approach involves discretizing the spatial domain into nite control volumes usinga mesh. The governing equations are integrated over each control volume, such that therelevant quantity (mass, momentum, energy, etc.) is conserved in a discrete sense for eachcontrol volume.The gure below shows a typical mesh with unit depth (so that it is two-dimensional),31CHAPTER 8. NUMERICAL METHODS 32on which one surface of the nite volume is represented by the shaded area.It is clear that each node is surrounded by a set of surfaces which comprise the nitevolume. All the solution variables and uid properties are stored at the element nodes.Consider the mean form of the conservation equations for mass, momentum and a passivescalar, expressed in Cartesian coordinatesujxj= 0 (8.1)(uiuj)xj= peffxi+ (2( + t)Sij)xj+ SMi (8.2)Heffujxj=_( + t) Txj_xj_(D + Dt)hmymxj_xj+ SE (8.3)These equations are integrated over a control volume, and Gauss divergence theorem isapplied to convert some volume integrals to surface integrals. For control volumes thatdo not deform in time, the time derivatives can be moved outside of the volume integralsand the equations become:_SUjdnj = 0 (8.4)_SUjUidnj = _SPdnj +_Smueff_Uixj+ Ujxi_dnj +_VSUjdV (8.5)_SUjHeffdnj =_Seffdnj (8.6)where V and S respectively denote volume and surface regions of integration, and dnj isthe dierential Cartesian component of the outward normal surface vector. The surfaceintegrals are the integrations of the uxes and the volume integrals represent source oraccumulation terms. Changes to these equations due to control volume deformation arepresented belowThe rst step in solving these continuous equations numerically is to approximatethem using discrete functions. Now consider an isolated mesh element such as the oneshown below. The surface uxes must be discretely represented at the integration pointsto complete the conversion of the continuous equation into their discrete form. TheCHAPTER 8. NUMERICAL METHODS 33integration points, ipn, are located at the center of each surface segment in a 3D elementsurrounding the nite volume. The discrete form of the integral equations are written asip(Ujnj)ip = 0 (8.7)ip(Pni)ip + ip(eff(Uixj+ Ujxi)nj)ip + SUiV = ip mip(Ui)1p (8.8)ip mip1p = ip(effxjnj + SV (8.9)where V is the control volume, the subscript ip denotes an integration point, the sum-mation is over all the integration points of the nite volume, nj is the discrete outwardsurface vector,t is the time step. Note that the First Order Backward Euler schemehas been assumed in this equation, although a second order scheme is also available asdiscussed below. The discrete mass ow through a surface of the nite volume is denotedby m ip and is given by: m = (Ujnj)ip (8.10)High resolution schemeThe High Resolution Scheme computes locally to be as close to 1 as possible withoutviolating boundedness principles. The recipe for is based on that of Barth and Jesperson.The high resolution scheme is therefore both accurate (reducing to rst order near dis-continuities and in the free stream where the solution has little variation) and bounded.Note that for vector quantities, such as velocity, beta is independently calculated for eachvector componentChapter 9Problem denition9.1 Afterburner descriptionThe geometry considered for modeling is Afterburner system of K9 engine. It is consistingof liner, vee-gutter ameholder, spay bars for fuel injection, and nozzle. The geometryand its details are shown in below gures.9.1.1 Inlet conditions for combustor and afterburnerSince the inlet of the afterburner receives exhaust gases from main combustion chamber,the mass fractions of species gases left out in the exhaust mixture has to be calculated.For this NASA glenns computer program has used. The performance points for mainburner are shown in below tables.FuelFlow(Kgs ) AirFlow(Kgs ) Pressure(KPa) Temp(K) Fuel AirRatio0.984 46.35 212.0 1046 0.0212Bypass ow conditions for main burner listed as:BypassFlow(Kg/s) Pressure(KPa) Temp(K)9.1 220.3 458.234CHAPTER 9. PROBLEM DEFINITION 35Figure 9.1: Afterburner of K9 engine at test stationFigure 9.2: Afterburner model used with its dimensionsCHAPTER 9. PROBLEM DEFINITION 36The above ow conditions were setup in the NASA glenns computer program and theexhaust of main burner gass species concentration is calculated. These values will bethe core ow inlet conditions for afterburner. Main burner exhaust gas mixtures speciesconcentration listed in below table:Mass fractionsC2 0.15886CO2 0.06363H2O 0.02478N2 0.75273To allow the dierent mass ow through the nozzle during combustion process, the areaof the nozzle exit diameter can be altered. And the values suitable for cold ow andreacting ow of nozzle diameter listed as:Coldflow(meters) Hotflow(meters)0.548 0.0249.1.2 Blowout timeOnce the meshed model has imported to CFX ow solver, the corresponding core inlet,bypass ow, fuel mass ow conditions will be given and the ow is solved. Now consideringthe ow eld behind the vee-gutter ameholder, the wake behind it forms a recirculationregion. This region is now modeled as well-stirred chemical reactor in AEDSys KINETXsoftware. The length and area of this bubble are measured from ow simulations, thesewill be the input values for KINETX software. The data entry values are listed in belowtable.A(cm2) L(cm) Type mA mf52 3.5 WSR 1 0.02KINETX software solves the 30 step Kollarack combustion reaction mechanism of jet fuelin this recirculation region and gives blowout time, residence time, mole fractions,massfractions etc.,. And the values of these are listed below in table.CHAPTER 9. PROBLEM DEFINITION 37FlowElementType WSR @Blowout(WSR)EquivalenceRatio 0.3109 0.3109ResidenceTime(sec) 4.474E 3 6.244E 4Area(cm2) 52.00 52.00Length(cm) 3.50 0.00V olume(cm3) 182.00 0.00SpaceV elocity(m/s) 7823.00 294.50Flowrate(Kg/sec) 1.02 1.02Enthalpy(kJ/Kg) 2412.00 2412.00Combustionefficiency 0.0347 43.28Temperature(K) 1045.00 0.00CHAPTER 9. PROBLEM DEFINITION 38Species MoleNumbers MoleFractions MassFractionsC12H23 1.162E 04 1.196E 04 1.945E 02C2H2 1.795E 07 1.847E 07 4.673E 06C2H3 7.992E 07 8.226E 07 2.162E 05C2H4 4.894E 06 5.037E 06 1.373E 04CH2O 1.714E 12 1.765E 12 5.147E 11CH3 4.872E 12 5.015E 12 7.326E 11CH4 1.000E 20 1.029E 20 1.604E 19CO 2.522E 12 2.596E 12 7.063E 11CO2 4.106E 02 4.226E 02 1.81HCO 4.146E 12 4.268E 12 1.203E 10H 3.576E 12 3.681E 12 3.605E 12H2 8.633E 14 8.917E 14 1.746E 13H2O 3.906E 02 4.020E 02 0.704HO2 1.795E 07 1.847E 07 5.923E 06N 1.156E 20 1.190E 20 1.620E 19NO 1.721E 20 1.771E 20 5.163E 19NO2 1.000E 20 1.029E 20 4.601E 19N2 0.750 0.772 21.0O 4.277E 12 4.402E 12 6.843E 11OH 1.073E 10 1.104E 10 1.824E 09O2 0.141 .0145 4.519.1.3 Afterburner performanceFrom experiments done, the inlet pressure and temperature conditions are known. Indata entry the required input is given as listed below in table:Angle R Ga1 Ga2 PTa1 PTa2 TTa1 TTa2 GFs35 0.96 46.611 9.76 211.7 222.2 1046 463 2.224CHAPTER 9. PROBLEM DEFINITION 39whereGa1 - core mass ow(kg/s)Ga2 - Bypass mass ow (kg/s)Gfs - Fuel mass ow (kg/s)PTa1 - Total pressure of core ow(KPa)PTa2 - Total pressure of bypass ow (KPa)TTa1 - Total temperature of core ow (K)TTa2 - Total temperature of bypass ow (K)Input to AFTRBRN to compute diuser performance Diuser performance canbe obtained by giving following input data.Totalpressure(kPa) 211.70TotalTemperature(K) 1046.0Machnumber 0.5Mixturegasflow(Kg/sec) 23.00Outerradius(cm) 40.000Innerradius(cm) 37.477Height(cm) 5.0467Pressure(kPa) 179.75V elocity(m/sec) 310.2Area(m2) 8.2525The above values have given in AEDSys AFTRBRN software and the diuser performanceis obtained. The results are listed below in table:DiuserCHAPTER 9. PROBLEM DEFINITION 40 m(Kg/sec) 23.00 1.336Pt(kPa) 208.7Tt(K) 1046Pressure(kPa) 206.90Mach 0.1137V elocity(m/sec) 58.42Area(m2) 34.91Area(m2) 6.756I(N) 1.0656Diuser PerformanceDiffuserEfficiency 0.9006Pressurerecoverycoefficient 0.8503Totalpressureratio 0.9858Totalpressurelosscoefficient 9.3797E 02Totalpressureloss 6.3031E 02Flame HoldersBlowout time which is obtained from KINETX is given as input to get the ameholderperformance. The listed below tables are having ameholder performance values: m(Kg/sec) 24.10 1.300Pt(kPa) 208.6Tt(K) 2000Pressure(kPa) 206.70Mach 0.1196V elocity(m/sec) 80.14Area(m2) 34.91Area(m2) 7.075I(N) 1.3716CHAPTER 9. PROBLEM DEFINITION 41Flameholder performanceDragCoefficient(CD) 0.5751Totalpressurelosscoefficient 0.9696Totalpressureratio 0.9917Flame holders Dimensions required15vee gutterwidth(cm) 0.6667Channelheight(cm) 6.667Afterburnerlength(cm) 23.55Chapter 10CFD resultsSingle step reaction of jetA fuel combustion has simulated using Eddy dissipation com-bustion model and k turbulence model in afterburner using ANSYS CFX ow solver.10.1 Cold ow results42CHAPTER 10. CFD RESULTS 43Figure 10.1: Density variationCHAPTER 10. CFD RESULTS 44Figure 10.2: Velocity variationCHAPTER 10. CFD RESULTS 45Figure 10.3: streamlines form chuteholesCHAPTER 10. CFD RESULTS 46Figure 10.4: Streamlines from inletCHAPTER 10. CFD RESULTS 47Figure 10.5: Streamlines from inlet and its temperature variationCHAPTER 10. CFD RESULTS 48Figure 10.6: Temperature distribution10.2 Reacting ow resultsCHAPTER 10. CFD RESULTS 49Figure 10.7: Temperature distributionCHAPTER 10. CFD RESULTS 50Figure 10.8: Temperature distributionCHAPTER 10. CFD RESULTS 51Figure 10.9: Temperature distribution at X=.35 on ZX planeCHAPTER 10. CFD RESULTS 52Figure 10.10: Temperature distribution at X=.45 on ZX planeCHAPTER 10. CFD RESULTS 53Figure 10.11: Temperature distribution ZX planeCHAPTER 10. CFD RESULTS 54Figure 10.12: Temperature distribution ZX planeCHAPTER 10. CFD RESULTS 55Figure 10.13: Temperature distribution ZX planeCHAPTER 10. CFD RESULTS 56Figure 10.14: Temperature distribution ZX planeCHAPTER 10. CFD RESULTS 57Figure 10.15: Temperature distribution ZX planeCHAPTER 10. CFD RESULTS 58Figure 10.16: CO2 mass fraction variation variationChapter 11Conclusions11.1 Flameholder performanceWake behind the V-gutter ameholder-that is the recirculation region, is modeled as well-stirred reactor, and the ow inside this reactor is solved in AEDSys KINETX software.The result from which showing that residence time is greater than the blowout time, whichis the condition ame stabilization. So the performance of V-gutter ameholder is goodenough.11.2 Diuser performanceAfter giving input conditions for afterburner in AEDSys AFTRBRN software, the diuserperformance values are obtained. The mach number at the exit of diuser is 0.17, whichis the signicant thing required for GTRE company. SO following the diuser dimensionsmight help them to improve the performance of afterburner.59CHAPTER 11. CONCLUSIONS 6011.3 Temperature plotsThe temperature distributions behind the ameholder showing the temperature regionsalong the edge of the recirculation bubble. Telling that the combustion process is occuringin the micro-mixing shear layer by entraining unburnt products into it and disentrainingburnt products into recirculation region.From temperature distribution along planed we can note that tha maximum attainedtemperature was 1230K, which is approximately nearer to the adiabatic ame temperatureof the mixture combustion.Near liner region in the plots always showing the lesser teperatures this is due to theattached ow observed which is comming out of chute holes. The liner can bare highertemperatures by its material, so changing the chute hole design will probably help to mixthe bypass ow with core ow and higher temperature near the liner.11.4 Mass fraction PlotsThe mass fraction variation of jetA fuel curve along the length of afterburner showing thecomplete combustion of fuel by not leaving any of the fuel left in mixture.Bibliography[1] Aircraft engine design, Jack D.Mattingly, William H.Heiser, Daniel H.Daley, 2003[2] Computational Methods for Fluid Dynamics, J.H.Ferziger and M.Peric[3] Numerical Heat Transfer and Fluid Flow, Suhas V.Patankar[4] An Introduction to Computational Fluid Dynamics, H.K. Versteeg and W.Malalasekara, Longman Group, 1995[5] M. Zellat, Th. Rolland, and F. Poplow, Three-Dimensional Modeling of Combustionand Soot Formation in an Indirect Injection Diesel Engine, SAE Paper 900254(1990).[6] J. B. Maxwell, Data Book on Hydrocarbons (D. Van Nostrand Company, Inc.,Princeton, New Jersey, 1958).[7] Technical Data on Fuel (J. W. Rose and J. R. Cooper, John Wiley and Sons, NewYork, 1977).[8] C. K. Westbrook and F. L. Dryer, Chemical Kinetic Modeling of HydrocarbonCombustion, Prog. Energy Combust. Sci. 2984 10,l-57 (1984).[9] CFD simulations of steam cracking furnaces using detailed combustion mechanisms,G.D. Stefanidis, B. Merci, G.J. Heynderickx,., G.B. Marin Computers and ChemicalEngineering,2006,30:635-649[10] Numerical Simulation of Combusion in afterburner61BIBLIOGRAPHY 62[11] C.A.J. Fletcher - Computational Techniques for Fluid Dynamics99