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INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...

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3. Numerical Methods<br />

In the numerical simulation, the governing equations are discretized and solved by<br />

computer programs where appropriate numerical algorithms are required. An ideal<br />

numerical algorithm should<br />

• be linearly stable for all cases of interest;<br />

• ensure the positivity property when appropriate;<br />

• be reasonably accurate;<br />

• be computationally efficient.<br />

There are several numerical methods available for the fluid mechanics. The methods<br />

ranging from the most discrete (or particulate) in nature to the most continuous (or<br />

global) include:<br />

• particle methods<br />

• characteristic methods<br />

• Lagrangian finite difference/finite volume method<br />

• Eulerian finite difference/finite volume method<br />

• finite element methods<br />

• spectral methods<br />

Each method has advantages and disadvantages, consequently has the preferable applications.<br />

Usually, it is difficult or inefficient for a stand-alone method to simulate<br />

a complex system. Hybrid method, which is like a bootstrapping process, combines<br />

the advantages of the multiple methods and minimizes their disadvantages. The disadvantage<br />

of hybrid method is that the consistency problem is more serious. Special<br />

strategies are needed to keep consistency between the multiple methods.<br />

In this chapter the numerical methods employed to solve the single droplet evaporation<br />

and drying equations, QMOM and DQMOM transport equations are explained.<br />

In this work, the DDM computations performed by Humza [68] are used to validate the<br />

DQMOM results for water spray in air in two-dimensional, axisymmetric configuration.<br />

Hence, the numerical details of the DDM simulations can be referred to Humza [68].

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