The separation point of the flow around a circular cylinder has been numerically and experimentally investigated in the regime of Reynolds number less than 280. The present results reveal that the long-existing discrepancy in the data concerning the time-averaged separation angles reported in the literature results mainly from the oscillating characteristics of the flow separation on the cylinder surface and the experimental methodologies rather than the commonly mentioned blockage-ratio effect. In the present experiment, the time-averaged separation angles are obtained by averaging the instantaneous images from a soap-film flow visualization instead of from the commonly used streakline images from finite time exposures. Excellent agreement has been achieved between the present experimental results and numerical simulations by the spectral element method. Particle-streak visualization in a towing tank has also been conducted to compare with that of the two-dimensional soap-film experiments. It reveals that the separation angle is insensitive to the three-dimensional effect. Variations of the time-averaged separation angles with Reynolds number can be represented by a four-term $\theta _{s}\hbox{--}{\it Re}^{-1/2}$ relationship in the range of $7\,{\le}\,{\it Re}\,{\le}\,200$. Moreover, if the data in the very low Reynolds number region are excluded, a simple linear $\theta_{s}\hbox{--}{\it Re}^{-1/2}$ relationship can be derived for $10\,{\le}\,{\it Re}\,{\le}\,200$. Since the dimensionless boundary layer thickness and the Strouhal–Reynolds number relationship for the circular cylinder are also known to be proportional to ${\it Re}^{-1/2}$, this linear relationship offers direct evidence that the flow characteristics of the boundary layer extend downstream along the cylinder surface to the separation point in this ${\it Re}$-range. The blockage effect on the separation angle has also been quantitatively analysed.

A planar 2-D liquid monopropellant microthruster fabricated from low temperature co-fired ceramic tapes and ignited by electrolysis is reported. The volume of the combustion chamber was 820 nL (0.82 mm³). Silver electrodes were screen printed and positioned on the top and bottom surfaces of the combustion chamber. A DC voltage potential applied across the electrodes was used to initiate decomposition of hydroxylammonium nitrate (HAN) based liquid monopropellants. A thrust output of 150 mN was obtained using a voltage input of 45 V. Measured ignition energies were as small as 1.9 J. Ignition delays, as short as a few hundred milliseconds, were found dependent on the type of HAN-based propellant and the voltage potential.