Sammanfattning
The objective of this thesis is to numerically simulate a fluid jet injected into a crossflow of the same or another fluid, respectively. Such flows are encountered in many engineering applications in which cooling or mixing plays an important role, e.g. gas turbine combustors. The jet in crossflow (JICF) is used both for cooling and for injecting liquid fuel into the air stream prior to combustion. The numerical simulations regard three space dimensions and track also the flow dynamics by integrating the governing equations in time. The spatial and the temporal resolution are such that the largescale flow structures are resolved. Such an approach is referred to as large eddy simulations (LES). The motion of the fuel droplets is treated by Lagrangian particle tracking (LPT) with the stochastic parcel method, along with submodels for evaporation, collision, breakup, and a novel submodel for aerodynamic fourway coupling: The particle drag is corrected depending on relative positions of the particles. Mixture fraction and temperature transport equations are solved to enable the modeling of droplet evaporation and the mixing of the gaseous fuel with ambient air.
In the simulations of multiphase JICF, several computed results are shown to be inconsistent with the underlying assumptions of the LPT approach: The magnitude of the Weber numbers indicates that droplets are not spherical in large portions of the flow field in wide ranges of parameters which are relevant for gas turbine operation. The magnitude of the droplet spacing suggests that aerodynamic interaction (indirect fourway coupling) among droplets may be important. The LES with aerodynamic fourway coupling reveals significant effects compared to twoway coupling for monodisperse particles in a dense multiphase flow.
For singlephase JICF, the impact of nozzle shape on the largescale coherent structures and the mixing is studied. Effects of circular, square, and elliptic nozzles and their orientation are considered. It is demonstrated that square and elliptic nozzles with blunt orientation raise turbulence levels significantly. The scalar distribution in a crosssectional plane is found to be singlepeaked for these nozzles whereas circular and the nozzles with pointed orientation show doublepeaked scalar distribution. It is the nozzles with a singlepeaked distribution which are the better mixers.
The differences and similarities of single and multiphase JICF are compared, and it is demonstrated that the flow field solution for multiphase flow approaches the flow field solution of singlephase flow in the limit of small Stokes numbers.
In the simulations of multiphase JICF, several computed results are shown to be inconsistent with the underlying assumptions of the LPT approach: The magnitude of the Weber numbers indicates that droplets are not spherical in large portions of the flow field in wide ranges of parameters which are relevant for gas turbine operation. The magnitude of the droplet spacing suggests that aerodynamic interaction (indirect fourway coupling) among droplets may be important. The LES with aerodynamic fourway coupling reveals significant effects compared to twoway coupling for monodisperse particles in a dense multiphase flow.
For singlephase JICF, the impact of nozzle shape on the largescale coherent structures and the mixing is studied. Effects of circular, square, and elliptic nozzles and their orientation are considered. It is demonstrated that square and elliptic nozzles with blunt orientation raise turbulence levels significantly. The scalar distribution in a crosssectional plane is found to be singlepeaked for these nozzles whereas circular and the nozzles with pointed orientation show doublepeaked scalar distribution. It is the nozzles with a singlepeaked distribution which are the better mixers.
The differences and similarities of single and multiphase JICF are compared, and it is demonstrated that the flow field solution for multiphase flow approaches the flow field solution of singlephase flow in the limit of small Stokes numbers.
Originalspråk  engelska 

Kvalifikation  Doktor 
Tilldelande institution 

Handledare 

Tilldelningsdatum  2006 nov 28 
Förlag  
Tryckta ISBN  9789162869670 
Status  Published  2006 
Bibliografisk information
Defence detailsDate: 20061128
Time: 10:15
Place: Room M:E, Mbuilding, Ole Römers väg 1, Lund Institute of Technology
External reviewer(s)
Name: Sommerfeld, Martin
Title: Prof. Dr.Ing. habil.
Affiliation: MartinLutherUniversity HalleWittenberg, Germany

Ämnesklassifikation (UKÄ)
 Strömningsmekanik och akustik