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The spatially developing compressible plane mixing layer with a convective Mach number of 0.7 is investigated by direct numerical simulation. A pair of equal and opposite oblique instability waves is introduced to perturb the mixing layer at the inlet. The full evolution process of instability, including formation of $ \mrm{\Lambda} $-vortices and hairpin vortices, breakdown of large structures and establishment of self-similar turbulence, is presented clearly in the simulation. In the transition process, the flow fields are populated sequentially by $ \mrm{\Lambda} $-vortices, hairpin vortices and ‘flower’ structures. This is the first direct evidence showing the dominance of these structures in the spatially developing mixing layer. Hairpin vortices are found to play an important role in the breakdown of the flow. The legs of hairpin vortices first evolve into sheaths with intense vorticity then break up into small slender vortices. The later flower structures are produced by the instability of the heads of the hairpin vortices. They prevail for a long distance in the mixing layer until the flow starts to settle down into its self-similar state. The preponderance of slender inclined streamwise vortices is observed in the transversal middle zone of the transition region after the breakup of the hairpin legs. This predominance of streamwise vortices also persists in the self-similar turbulent region, though the vortices there are found to be relatively very weak. The evolution of both the mean streamwise velocity profile and the Reynolds stresses is found to have close connection to the behaviour of the large vortex structures. High growth rates of the momentum and vorticity thicknesses are observed in the transition region of the flow. The growth rates in the self-similar turbulence region decay to a value that agrees well with previous experimental and numerical studies. Shocklets occur in the simulation, and their formation mechanisms are elaborated and categorized. This is the first three-dimensional simulation that captures shocklets at this low convective Mach number.

This work aims at constructing efficient high-order hybrid schemes to resolve both smooth and discontinuous regions of flow fields. To this end, a new kind of smoothness indicator, referred to as global smoothness indicators in this article, is designed first. The new smoothness indicators contain only simple difference operators and, therefore, are computationally very inexpensive. A family of high-order hybrid schemes is constructed based on the new smoothness indicators. In this kind of hybrid scheme, classic weighted essentially non-oscillatory (WENO) schemes with work as a sub-scheme for capturing the discontinuities, while the corresponding linear optimal schemes of the WENO work as another sub-scheme for resolving the smooth region. It is shown theoretically that the convergence rates of the hybrid schemes always can reach the optimal order as the mesh is refined past a limit resolution. The robustness, high efficiency and high resolution of the hybrid schemes are demonstrated through several repre...

The SnO2 thin film CO gas sensors have been fabricated on silicon nanostructured surface made using a femtosecond pulsed laser irradiation. The measurement shows a significant response to the CO gas at room temperature. While a SnO2 sensor fabricated on a flat surface shows no response when CO gas exists at room temperature. The high area/volume ratio and sharp structures of the nanospikes enhance the sensitivity of SnO2 at room temperature.

Species conservation equations for SF6+, SF6-, and electrons have been solved by the method of MacCormack with a Shuman filter and by the flux corrected transport (FCT) method. A detailed comparison of numerical results with analytical solutions to species conservation equations shows that in order to achieve the same accuracy the grid size required by both methods is the same. Compared with the FCT method, the algorithms of MacCormack's method with Shuman filter are the simpler and computational costs are lower.