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Improvement of cavitation mass transfer modeling based on local flow properties

Abolfazl Asnaghi ( Institutionen för mekanik och maritima vetenskaper, Marin teknik) ; Andreas Feymark ; Rickard Bensow ( Institutionen för mekanik och maritima vetenskaper, Marin teknik)
International Journal of Multiphase Flow (0301-9322). Vol. 93 (2017), p. 142–157.
[Artikel, refereegranskad vetenskaplig]

This paper presents and studies the effect of two modifications to improve cavitation mass transfer source term modeling for transport equation based models by considering local flow properties. The first improvement is by creating an analogy between the phase change time scale and turbulence time scale, and have the model to automatically adjust mass transfer rate based on the flow. This will alleviate the manual calibration of model parameter that is often necessary in presently used models. The second modification introduces an influence of shear stress on the liquid rupture in flows relevant for hydromachinery. This relates to that the pressure threshold, which represents the criteria of when phase change occurs, is normally taken as the value relevant for a fluid at rest, but is in reality affected by the flow conditions. To demonstrate the effect of the model modifications, the three-dimensional, fully turbulent, cavitating flow around the Delft Twist11 foil is simulated. The suggested modifications are implemented in and evaluated using the Sauer mass transfer model, with simulations performed with an incompressible implicit LES flow model. The pressure distribution across different sections of the foil, lift force, and cavitation behavior, such as generation, separation, and collapse processes, are studied and compared with the experimental data. The comparison shows the capability of the presented model to improve the prediction of the complex physics of the cavitation around the Twist11 foil, compared with using only the original Sauer mass transfer model.

Nyckelord: Cavitation; Simulation; Mass transfer model; Turbulent; LES

Highlights • Two new modifications are proposed to improve the cavitation mass transfer models in the transport equation framework. • The first modification is built on an analogy between phase change relaxation time and the velocity strain rate to adjust the mass transfer rate. • In the second modification, the viscous stress tensor is considered in the calculation of pressure threshold. • Unsteady LES simulation of cavitation is performed for Delft Twist11 case by employing the proposed modifications.

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Denna post skapades 2017-06-14.
CPL Pubid: 249852