Confined and Unsteady Flows

A nonlinear harmonic balance technique for the analysis of aerodynamic asymmetry of unsteady flows in turbomachinery is presented. The present method uses a mixed time-domain/frequency-domain approach that allows one to compute the unsteady aerodynamic response of turbomachinery blades to self-excited vibrations. Traditionally, researchers have investigated the unsteady response of a blade row with the assumption that all the blades in the row are identical. With this assumption the entire wheel can be modeled using complex periodic boundary conditions and a computational grid spanning a single blade passage. In this study, the steady/unsteady aerodynamic asymmetry is modeled using multiple passages. Specifically, the method has been applied to aerodynamically asymmetric flutter problems for a rotor with a symmetry group of 2. The effect of geometric asymmetries on the unsteady aerodynamic response of a blade row is illustrated. For the cases investigated in this paper, the change in the diagonal terms (blade on itself) dominated the change in stability. Very little mode coupling effect caused by the off-diagonal terms was found.

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On nonlocal fractal laminar steady and unsteady flows

Acta Mechanica ◽

10.1007/s00707-020-02929-8 ◽

2021 ◽

Vol 232 (4) ◽

pp. 1413-1424

Author(s):

Rami Ahmad El-Nabulsi

Keyword(s):

Unsteady Flows ◽

Steady And Unsteady Flows

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Uncertain Transport in Unsteady Flows

2020 IEEE Visualization Conference (VIS) ◽

10.1109/vis47514.2020.00010 ◽

2020 ◽

Author(s):

Tobias Rapp ◽

Carsten Dachsbacher

Keyword(s):

Unsteady Flows

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The Effects of Periodicity Assumptions in Porous Media Modelling

Transport in Porous Media ◽

10.1007/s11242-021-01587-1 ◽

2021 ◽

Author(s):

T. O. M. Forslund ◽

I. A. S. Larsson ◽

J. G. I. Hellström ◽

T. S. Lundström

Keyword(s):

Fluid Flow ◽

Lattice Boltzmann ◽

Single Unit ◽

Unsteady Flows ◽

Unit Cell ◽

Porous Bed ◽

Bed Porosity ◽

Macroscopic Properties ◽

Boltzmann Method ◽

Method Model

AbstractThe effects of periodicity assumptions on the macroscopic properties of packed porous beds are evaluated using a cascaded Lattice-Boltzmann method model. The porous bed is modelled as cubic and staggered packings of mono-radii circular obstructions where the bed porosity is varied by altering the circle radii. The results for the macroscopic properties are validated using previously published results. For unsteady flows, it is found that one unit cell is not enough to represent all structures of the fluid flow which substantially impacts the permeability and dispersive properties of the porous bed. In the steady region, a single unit cell is shown to accurately represent the fluid flow across all cases studied

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