Zinc oxide (ZnO) is an adaptable material that has distinctive properties, such as high-sensitivity, large specific area, non-toxicity, good compatibility and a high isoelectric point, which favours it to be considered with a few exceptions. It is the most desirable group of nanostructure as far as both structure and properties. The unique and tuneable properties of nanostructured ZnO shows excellent stability in chemically as well as thermally stable n-type semiconducting material with wide applications such as in luminescent material, supercapacitors, battery, solar cells, photocatalysis, biosensors, biomedical and biological applications in the form of bulk crystal, thin film and pellets. The nanosized materials exhibit higher dissolution rates as well as higher solubility when compared to the bulk materials. This review significantly focused on the current improvement in ZnO-based nanomaterials/composites/doped materials for the application in the field of energy storage and conversion devices and biological applications. Special deliberation has been paid on supercapacitors, Li-ion batteries, dye-sensitized solar cells, photocatalysis, biosensors, biomedical and biological applications. Finally, the benefits of ZnO-based materials for the utilizations in the field of energy and biological sciences are moreover consistently analysed.

https://iopscience.iop.org/article/10.1088/1361-6528/ab268a/pdf

A review on ZnO nanostructured materials: energy, environmental and biological applications.

Supersonic mixing in airbreathing propulsion systems for hypersonic flights

Experimental investigation on drag and heat flux reduction in supersonic/hypersonic flows: A survey

Using a nanoparticle-based planar laser-scattering technique and supersonic particle image velocimetry, we investigated the effects of micro-ramp control on incident shockwave and boundary-layer interaction (SWBLI) in a low-noise supersonic wind-tunnel with Mach number 27 and Reynolds number Rθ = 5845 High spatiotemporal resolution wake structures downstream of the micro-ramps were detected, while a complex evolution process containing a streamwise counter-rotating vortex pair and large-scale hairpin-like vortices with Strouhal number Stδ of about 05–065 was revealed The large-scale structures could survive while passing through the SWBLI region Reflected shockwaves are clearly seen to be distorted accompanied by high-frequency fluctuations Micro-ramp applications have a distinct influence on flow patterns of the SWBLI field that vary depending on spanwise locations Both the shock foot and separation line exhibit undulations corresponding with modifications of the velocity distribution of the inco

Experimental investigation of the micro-ramp based shock wave and turbulent boundary layer interaction control

Influence of jet-to-crossflow pressure ratio on nonreacting and reacting processes in a scramjet combustor with backward-facing steps

Due to influence of compressibility, shock wave, instabilities, and turbulence on supersonic flows, current flow visualization and imaging techniques encounter some problems in high spatiotemporal resolution and high signal-to-noise ratio (SNR) measurements. Therefore, nanoparticle based planar laser scattering method (NPLS) is developed here. The nanoparticles are used as tracer, and pulse planar laser is used as light source in NPLS; by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is realized. The flow-following ability of nanoparticles in supersonic flows is studied according to multiphase flow theory and calibrating experiment of oblique shock wave. The laser scattering characteristics of nanoparticles are analyzed with light scattering theory. The results of theoretical and experimental studies show that the dynamic behavior and light scattering characteristics of nanoparticles highly enhance the spatiotemporal resolution and SNR of NPLS, with which the flow field involving shock wave, expansion, Mach disk, boundary layer, sliding-line, and mixing layer can be imaged clearly at high spatiotemporal resolution.

Supersonic flow imaging via nanoparticles

Due to the influence of shock wave and turbulence, supersonic density field exhibits strongly inhomogeneous and unsteady characteristics. Applying traditional density field measurement techniques to supersonic flows yields three problems: low spatiotemporal resolution, limitation of measuring 3D density field, and low signal to noise ratio (SNR). A new method based on Nano-based Planar Laser Scattering (NPLS) technique is proposed in this paper to measure supersonic density field. This method measures planar transient density field in 3D supersonic flow by calibrating the relationship between density and concentration of tracer particles, which would display the density fluctuation due to the influence of shock waves and vortexes. The application of this new method to density field measurement of supersonic optical bow cap is introduced in this paper, and the results reveal shock wave, turbulent boundary layer in the flow with the spatial resolution of 93.2 μm/pixel. By analyzing the results at interval of 5 μs, temporal evolution of density field can be observed.

Study of density field measurement based on NPLS technique in supersonic flow

Flow in a flat-plate zero-pressure-gradient boundary layer at Mach 3 was visualized via nanoparticle-based planar laser scattering (NPLS). Coherent structures such as an individual hairpin vortex and hairpin packet were identified in the streamwise-wall-normal plane on the basis of the now accepted hairpin model. Λ-shaped vortices were found in a staggered pattern in the streamwise-spanwise plane, which indicated H-type transition in the present experiments. This is the direct evidence (in the form of flow visualization) of such coherent structures in a supersonic boundary layer. A series of NPLS images taken in streamwise-spanwise planes at different heights is presented, and the three-dimensional structures of the supersonic boundary layer agree well with the hairpin model.

/pdf/visualization-of-coherent-structures-in-a-supersonic-flat-xp3t0af9nq.pdf

Visualization of coherent structures in a supersonic flat-plate boundary layer

Flow visualization of supersonic mixing layer has been studied based on the high spatiotemporal resolution Nano-based Planar Laser Scattering (NPLS) method in SML-1 wind tunnel. The corresponding images distinctly reproduced the flow structure of laminar, transitional and turbulent region, with which the fractal measurement can be implemented. Two methods of measuring fractal dimension were introduced and compared. The fractal dimension of the transitional region and the fully developing turbulence region of supersonic mixing layer were measured based on the box-counting method. In the transitional region, the fractal dimension will increase with turbulent intensity. In the fully developing turbulent region, the fractal dimension will not vary apparently for different flow structures, which embodies the self-similarity of supersonic turbulence.

The fractal measurement of experimental images of supersonic turbulent mixing layer

The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized via NPLS, and the transient fine structures were identifiable in NPLS images, which were used to analyze the effects of flow control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer, delaying mixing layer transition; and the 3D tapes can enhance the 3D characteristic of the mixing layer, advancing mixing layer transition. 3D structures of the mixing layer were visualized, and the H-type Λ vortexes were found with 3D tapes control.

LiFeng Tian

Papers

Supersonic flow imaging via nanoparticles

Study of density field measurement based on NPLS technique in supersonic flow

Visualization of coherent structures in a supersonic flat-plate boundary layer

The fractal measurement of experimental images of supersonic turbulent mixing layer

A flow control study of a supersonic mixing layer via NPLS