High resolution schemes for hyperbolic conservation laws

Review of computational studies on boiling and condensation

Human phonation does not always involve symmetric motions of the two vocal folds. Asymmetric motions can create slanted or oblique glottal angles. This study reports intraglottal pressure profiles for a Plexiglas model of the larynx with a glottis having a 10-degree divergence angle and either a symmetric orientation or an oblique angle of 15 degrees. For the oblique glottis, one side was divergent and the other convergent. The vocal fold surfaces had 14 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Results indicated that for either the symmetric or oblique case, the pressure profiles were different on the two sides of the glottis except for the symmetric geometry for a transglottal pressure of 3 cm H2O. For the symmetric case, flow separation created lower pressures on the side where the flow stayed attached to the wall, and the largest pressure differences between the two sides of the channel were 5%–6% of the transglottal pressure. For the oblique case, pressures were lower ...

Intraglottal pressure profiles for a symmetric and oblique glottis with a divergence angle of 10 degrees.

A numerical study of laminar incompressible flows in symmetric plane sudden expansions was carried out. Computations were performed for various Reynolds number and expansion ratios. The results revealed that the flow remains symmetric up to a certain Reynolds number depending on the expansion ratio, while asymmetries appear at higher Reynolds numbers. The computations indicated that the critical Reynolds number of the symmetry‐breaking bifurcation reduces when increasing the expansion ratio while the flow regains symmetry downstream of an initial channel length. The flow asymmetries were verified by comparing several discretization schemes up to fourth order of accuracy as well as various iterative solvers.

Bifurcation phenomena in incompressible sudden expansion flows

Principles of enhanced heat transfer: By R. L. Webb, Wiley, New York, 1994, ISBIN #0-471-57778-2 556 pp

A pressure-correction method is presented to solve incompressible viscous flows. The development of this method is aimed at dealing with unstructured grids, which are made of control volumes with arbitrary topology. To enhance the robustness of the method, all variables are collocated on the cell centers. The divergence theorem of Gauss is employed for discretization, and vector forms are used throughout the formulation. In this way the method is equally applicable to two- and three-dimensional problems. An overrelaxed approach is adopted for the approximation of the cross-diffusion flux to deal with “skew” grids. It can be seen that this approach is equivalent to some other approximations available in the literature. However, the present approach is more suitable for three-dimensional calculations without causing complication. This overrelaxed approach is also employed in the pressure-correction equation derived from the continuity constraint. Most prevailing methods simply ignore the cross-deri...

https://ir.nctu.edu.tw:443/bitstream/11536/12784/1/000234804400003.pdf

A pressure-correction method for incompressible flows using unstructured meshes

The flow in a valveless micropump is analyzed using both the CFD method and the lumped-system method. In the multidimensional simulation of the CFD model, the Navier–Stokes equations are solved using a finite volume method suitable for the use of unstructured grids. The moving membrane is modeled by imposing a reciprocating velocity boundary condition. It is seen that a good agreement with measurements can be obtained for various back pressures by adopting an appropriate membrane shape blending the parabolic and the trapezoidal profiles. The multidimensional predictions serve as benchmark solutions to the lumped-system analysis. In the latter analysis two correlations for the loss coefficients of the nozzle and the diffuser are employed. The results show that with a more accurate one of the two correlations, a better agreement with the multidimensional calculations is yielded. The performance of the pump can be evaluated by considering the pumping efficiency. The pumping efficiency can be approximately formulated in two different ways, depending on the average ratios of the outlet flow rate to the inlet flow rate in the pumping and supply stages. In the averaging process to determine the mean ratios, the transient region between the pumping stage and the supply stage is excluded. This leads to even closer agreement to the multidimensional calculations in the pumping efficiency. © 2008 Elsevier B.V. All rights reserved.

https://ir.nctu.edu.tw:443/bitstream/11536/8160/1/000260804500023.pdf

Evaluation of the performance of a valveless micropump by CFD and lumped-system analyses

https://ir.nctu.edu.tw:443/bitstream/11536/6524/1/000273358700027.pdf

Flux-blending schemes for interface capture in two-fluid flows

SUMMARY This paper is concerned with a number of upstream-weighted second- and third-order difference schemes. Also considered are the conventional upwind and central difference schemes for comparison. It commences with a general difference equation which unifies all the given first-, second- and third-order schemes. The various schemes are evaluated through the use of the general equation. The unboundedness and accuracy of the solutions by the difference schemes are assessed via various analyses: examination of the coefficients of the difference equation, Taylor series truncation error analysis, study of the upstream connection to numerical diffusion, single-cell analysis. Finally, the difference schemes are tested on one- and two-dimensional model problems. It is shown that the high-order schemes suffer less from the problem of numerical diffusion than the first-order upwind difference scheme. However, unboundedness cannot be avoided in the solutions by these schemes. Among them the linear upwind difference scheme presents the best compromise between numerical diffusion and solution unboundedness.

https://ir.nctu.edu.tw:443/bitstream/11536/3733/1/A1991FW62000003.pdf

A study of upstream-weighted high-order differencing for approximation to flow convection

https://ir.nctu.edu.tw:443/bitstream/11536/23770/1/000330814800073.pdf

Yeng-Yung Tsui

Papers

A pressure-correction method for incompressible flows using unstructured meshes

Evaluation of the performance of a valveless micropump by CFD and lumped-system analyses

Flux-blending schemes for interface capture in two-fluid flows

A study of upstream-weighted high-order differencing for approximation to flow convection

Phase change calculations for film boiling flows