Advanced Spray and Combustion Modelling

Abstract

Abstract Advanced Spray and Combustion Modelling Ahmed Abed Al-Kadhem Majhool, 2011 Doctor of Philosophy, The University of ManchesterThe first attempt at modelling a fully Eulerian model for poly-disperse nature of the spray flowwithout using droplet size classes was proposed by Beck and Watkins [2003a]. The parametersused to describe the distribution of droplet sizes are the moments of the droplet size distributionfunction. Transport equations for only some moments of the spray distribution function arederived and solved through classical Eulerian schemes. The velocities to be used in the twotransport equations are obtained by defining moment-average quantities and constructing furthertransport equations for the relevant moment-average velocities. The continuous distribution ofdroplets is approximated using an analytically integrable function to use as a number distributionwas sought such that the volume distribution it produced was a reasonable approximation to aRosin-Rammler distribution. The new form of the continuous function was later revised by Yueand Watkins [2004], who implemented the Gamma distribution whose parameters were obtainedfrom the transport equations for second, third and fourth moments. This permits the form ofthe two parameter number size distribution to be totally calculated and to all predictions ofchanges to the distribution in space and time. Hydrodynamics submodels were implementedin Jones [2009] with higher order of numerical tools. The model is implemented in a new codebased on current numerical methods detailed in Ferziger and Peri ́ [2002], so as to make use of chigh resolution differencing schemes for the transportation of the moments and enable improvedresolution of the solution by using an unstructured grid topology.The thesis presents work across three different subjects of investigations into the modelling ofspray development and its interaction with non-reactive and reactive flow. The first part ofthis research is aimed to create a new and robust family of convective scheme to capture theinterface between the dispersed and the carrier phases without the need to build up the interfaceboundary. The selection of Weighted Average Flux (WAF) scheme is due to this scheme beingdesigned to deal with random flux scheme which is second-order accurate in space and time. Theconvective flux in each cell face utilizes the WAF scheme blended with Switching Technique forAdvection and Capturing of Surfaces (STACS) scheme for high resolution flux limiters. Howeverin the next step, the high resolution scheme is blended with the scheme to provide the sharpnessand boundedness of the interface by using switching strategy. The proposed scheme is tested on capturing the spray edges in modelling hollow cone type sprays without need to reconstructtwo-phase interface. A test comparison between TVD scheme and WAF scheme using the sameflux limiter on convective flow on hollow cone spray is presented. Results show that the WAFscheme gives better prediction than the TVD scheme. The only way to check the accuracy of thepresented models are evaluations according to physical droplets behaviour and its interactionwith air. In the second part, due to the effect of evaporation the temperature profile in thereleased fuel vapour has been proposed. The underlying equation utilizes transported vapourmass fraction. It can be used along with the solution of heat transfer inside a sphere. Afterapplying boundary conditions, the equation can provide a solution of existing conditions atliquid-gas interface undergoing evaporation and it is put in a form similar to well-known one-third rule equation. The resulting equation is quadratic type that gives an accurate prediction forthe thermo-physical properties due to the non-linear relation between measured properties andtemperature. Comparisons are made with one-third rule where both equations are implementedin simulating hollow cone spray under evaporation conditions. The results show the

Date of Award	1 Aug 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Arthur Watkins (Supervisor)