## Abstract

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

large-scale 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 four-way 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 four-way coupling) among

droplets may be important. The LES with aerodynamic four-way coupling

reveals significant effects compared to two-way coupling for monodisperse

particles in a dense multiphase flow.

For single-phase JICF, the impact of nozzle shape on the large-scale 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 cross-sectional plane is found to be

single-peaked for these nozzles whereas circular and the nozzles with pointed orientation show double-peaked scalar distribution. It is the nozzles with a

single-peaked 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 single-phase flow in the limit of small

Stokes numbers.

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

large-scale 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 four-way 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 four-way coupling) among

droplets may be important. The LES with aerodynamic four-way coupling

reveals significant effects compared to two-way coupling for monodisperse

particles in a dense multiphase flow.

For single-phase JICF, the impact of nozzle shape on the large-scale 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 cross-sectional plane is found to be

single-peaked for these nozzles whereas circular and the nozzles with pointed orientation show double-peaked scalar distribution. It is the nozzles with a

single-peaked 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 single-phase flow in the limit of small

Stokes numbers.

Original language | English |
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Number of pages | 118 |
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ISBN (Electronic) | 13 978-91-628-6967-0 |

Publication status | Published - 2006 |

Externally published | Yes |