A4 Conference proceedings

Comparison of Moment-Based Methods for Representing Droplet Size Distributions in Supersonic Nucleating Flows of Steam


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Publication Details
Authors: Afzalifar Ali, Turunen-Saaresti Teemu, Grönman Aki
Publication year: 2016
Language: English
Title of parent publication: International Symposium on Transport Phenomena and Dynamics of Rotating Machinery ISROMAC 2016
Start page: 1
End page: 14
JUFO-Level of this publication: 0
Open Access: Open Access publication

Abstract
This article investigates the effectiveness of two moment-based methods along with a monodispersed model (Mono) in representing the droplet size distribution and characteristics of steam flows with spontaneous condensation in supersonic nozzles. The moment-based methods are a conventional method of moments (MOM) along with its enhanced version using Gaussian quadrature, namely the quadrature method of moments (QMOM). The predictions of the droplet size distribution by these models are evaluated against the full spectrum resolved by an Eulerian-Lagrangian (E-L) method which tracks the evolution of the liquid phase in a Lagrangian frame of reference. On the other hand, an Eulerian reference frame is chosen to cast all the equations governing the phase transition and fluid motion for the MOM, QMOM and Mono. This choice of reference frame is essential especially to draw a meaningful comparison regarding complex flows in wet-steam turbines. The reason is that the most important advantage of the moment-based methods is that the moment-transport equations can be conveniently solved in an Eulerian frame avoiding burdensome challenges in working with a Lagrangian framework for complicated flows. The non-realizability problem and associated restrictions on temporal and spatial discretization schemes are discussed. The main focus is on the accuracy of the QMOM and MOM in representing the water droplet size distribution. The comparisons between models are made for two supersonic low-pressure nozzle experiments reported in the literature. Results show that the QMOM, particularly inside the nucleation zone, predicts moments closer to those of the E-L method. Therefore, for the test case in which the nucleation is significant over a large proportion of the domain, the QMOM clearly provides results in better agreements with the E-L method in comparison with the MOM.

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Last updated on 2017-27-03 at 11:33