LOW-REYNOLDS-NUMBER INSTABILITY OF THE LAMINAR FLOW BETWEEN WAVY WALLS
Instability of a viscous incompressible flow in a channel with wavy walls is investigated theoretically, numerically and experimentally. Linear stability analysis shows that appropriately chosen wall waviness leads to flow destabilization at surprisingly low Reynolds numbers. The unstable mode of disturbances forms a vortex array, which travels downstream. The remarkable feature is that the most destabilizing waviness does not introduce any additional flow resistance. The outcome of the stability analysis are consistent with the result of direct numerical simulation obtained using CFD finite volume package FLUENT (Ansys Inc.). Preliminary experimental data gained for a channel with appropriately corrugated wall seem to confirm these predictions.
Destabilization of a laminar flow in a rectangular channel by transversely-oriented wall corrugation
Linear stability of the flow through the transversely corrugated channel with flat sidewalls is investigated numerically. Two variants of the wall corrugation are considered: symmetric sinusoidal waviness of the top and bottom walls and onesided corrugation, i.e., one of the walls remains flat. Spectrally accurate Galerkin method formulated in a transformed domain is used for the solution of the main flow and linear stability equations. Unstable normal modes have been identified and their parametric variation has been determined. The results show that for sufficiently large aspect ratios, the influence of the sidewalls is weak and the stability properties resemble those of the spanwise-periodic channel (investigated recently by the first author). It means that an appropriately designed transversal corrugation may be regarded as a promising method for passive enhancement of mixing in laminar regime.
The power of negativity : selected writings on the dialectic in Hegel and Marx
Part 1 The Philosophic Moment of Marxist-Humanism Part 2 Studies in Hegalian and Marxian Dialectics, 1956-63 Part 3 Theory and Practice at a Turning Point, 1964-71 Part 4 After Philosophy and Revolution: Hegel's Absolutes and Marx's Humanism, 1972-81 Part 5 The Changed World and the Need for Philosophic New Beginnings, 1982-87