Hybrid particle/finite-volume PDF methods for three-dimensional time-dependent flows in complex geometries.

摘要

Modeling of complex turbulent reacting flows is of great importance in efforts to reduce the fuel consumption and pollutant emissions of many practical devices. The transported PDF method offers the salient advantage that the chemical reaction and other one-point processes (e.g., radiative emission) can be represented exactly without modeling assumptions. To date the PDF method has been mostly applied to statistically stationary axisymmetric jet flames and other canonical flow configurations.; This research has broadened the accessibility of PDF methods so that they can be brought to bear in complex engineering flows of practical interest, which usually require three-dimensional time-dependent simulations for complicated (unstructured and/or deforming) meshes. For these flows, it is desirable to integrate the particle-based solution schemes into existing grid-based research and engineering computational fluid dynamics (CFD) codes with a hybrid particle/finite-volume PDF method. Key issues for further application of hybrid PDF methods to engineering flows include particle algorithms, particle/FV consistency and efficient algorithms for complex chemistry. In this thesis, an efficient, robust and accurate hybrid particle/FV method has been developed to tackle these three issues.; The developed consistent and computationally efficient hybrid particle/FV PDF methods have been used to simulate a homogeneous-charge compression-ignition engine. A sensitivity study on effects of variations in engine operating conditions has shown that the simulation results are reasonably close to the experimental measurements and correctly capture the trends. The effects of variations in global equivalence ratio, wall temperature, swirl level, degree of mixture inhomogeneity, and a top-ring-land crevice have been investigated to examine the influence of turbulence/chemistry interactions on autoignition timing and emissions. This work demonstrates that the combination of consistent hybrid particle/finite-volume algorithms, detailed chemical kinetics, and chemistry acceleration strategies make PDF methods practicable for three-dimensional time-dependent modeling of practical combustion devices.