The small-gap equations for the stability of Couette flow with respect to non-axisymmetric disturbances are derived. The eigenvalue problem is solved by a direct numerical procedure. It is found that there is a critical value of Ω2/Ω1(Ω1, Ω2 and R1, R2 are the angular velocities and radii of the inner and outer cylinders respectively) of approximately −0·78, above which the critical disturbance is axisymmetric and below which it is non-axisymmetric. In particular for R1/R2 = 0·95, Ω2/Ω1 = −1, the wave-number in the azimuthal direction of the critical disturbance is m = 4. This result is confirmed when the full linear disturbance equations are considered, i.e. the small-gap approximation is not made.

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Computational Fluid Dynamics (CFD) was employed for investigating Solar Chimney Power Plants (SCPP). The effect of the geometric dimensions on the fluid dynamics and heat transfer was investigated. The thermal efficiency of the collector was found to improve with increasing scale, due to an increase of the heat transfer coefficient. The spread in relevant Reynolds numbers for the collector and chimney was four orders of magnitude from the smallest to the largest scale. Parametric studies were also performed to determine the effect of the distance of the collector from the ground on the power output. An optimum distance was determined for two different scales.

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