Compressible vortex loops: effect of nozzle geometry

Vortex loops are fundamental building blocks of supersonic free jets. Isolating them allows for an easier study and better understanding of such flows. The present study looks at the behaviour of compressible vortex loops of different shapes, generated due to the diffraction of a shock wave from a shock tube with different exit nozzle geometries. These include a 15 mm diameter circular nozzle, two elliptical nozzles with minor to major axis ratios of 0.4 and 0.6, a 30 × 30 mm square nozzle, and finally two exotic nozzles resembling a pair of lips with minor to major axis ratios of 0.2 and 0.5. The experiments were performed for diaphragm pressure ratios of P4/P1=4, 8, and 12, with P4 and P1 being the pressures within the high pressure and low pressure compartments of the shock tube, respectively. High-speed schlieren photography as well as PIV measurements of both stream-wise and head-on flows have been conducted

Anodized aluminium pressure sensitive paint: effect of paint application technique

The porous surface of the Anodized Aluminium Pressure Sensitive Paint (AA-PSP) is what differentiates it from conventional sol–gel based PSPs, leading to a faster response time of the paint. The objective of the current study is to examine the effect of the paint application technique, i.e., whether the AA substrate is dipped or sprayed, on the pressure and temperature sensitivity. A more practical procedure for preparing the AA samples is also presented. Scanning Electron Microscope (SEM) images are acquired together with the calibration of the AA-PSP at various temperatures and pressures to determine the effectiveness of each application technique. The results revealed that the AA sample which was dipped in the PSP solution shows a higher pressure sensitivity than the sprayed one. The SEMs show that spraying leads to the covering up of the micropores created on the surface and undermining the benefit of anodization

Detonation driven shock wave interactions with perforated plates

The study of detonations and their interactions is vital for the understanding of the high-speed flow physics involved and the ultimate goal of controlling their detrimental effects. However, producing safe and repeatable detonations within the laboratory can be quite challenging, leading to the use of computational studies which ultimately require experimental data for their validation. The objective of this study is to examine the induced flow field from the interaction of a shock front and accompanying products of combustion, produced from the detonation taking place within a non-electrical tube lined with explosive material, with porous plates with varying porosities, 0.7–9.7%. State of the art high-speed schlieren photography alongside high-resolution pressure measurements is used to visualise the induced flow field and examine the attenuation effects which occur at different porosities. The detonation tube is placed at different distances from the plates' surface, 0–30 mm, and the pressure at the rear of the plate is recorded and compared. The results indicate that depending on the level of porosity and the Mach number of the precursor shock front secondary reflected and transmitted shock waves are formed through the coalescence of compression waves. With reduced porosity, the plates act almost as a solid surface, therefore the shock propagates faster along its surface

Application of pressure-sensitive paints to unsteady and high-speed flows

The Pressure-Sensitive Paint (PSP) technique allows the global pressure mapping of surfaces under aerodynamic conditions. The present study involves the application of Tris- Bathophenanthroline Ruthenium Perchlorate based PSP, developed in-house, to two different cases; a) the flow through a sonic nozzle, and b) the examination of the effect of dimples on glancing shock wave turbulent boundary layer interactions at transonic speeds

Study of detonation interactions inside a 2-D ejector using detonation transmission tubing

Study of detonation interactions inside a two-dimensional ejector using detonation transmission tubing was reported. The main objective of the ejector assembly in the study is to make the flow-field as close to 2-D as possible. Optical-grade Perspex sheets with a thickness of 10 mm were used on both sides of the nozzle to allow visualization of the flow. Wall pressure measurements were conducted at the locations. The NONEL tube was flush with the entrance of the nozzle. The signal to begin pressure measurements and image acquisition was obtained through a Kulite XT-190 transducer. The detonation was initiate by an electronic blasting machine, DynoStart 2, with a capacitance of 0.2μF and an output voltage of 2500 V. High-speed shadowgraphy was employed to visualize the flow. The results show that the effects of 3-D flow at the initial stage of the detonation affect the incident shock front and the reflected shock wave system at the nozzle entrance

A low-loss photonic silica nanofiber for higher-order modes

Optical nanofibers confine light to subwavelength scales, and are of interest for the design, integration, and interconnection of nanophotonic devices. Here we demonstrate high transmission (> 97%) of the first family of excited modes through a 350 nm radius fiber, by appropriate choice of the fiber and precise control of the taper geometry. We can design the nanofibers so that these modes propagate with most of their energy outside the waist region. We also present an optical setup for selectively launching these modes with less than 1% fundamental mode contamination. Our experimental results are in good agreement with simulations of the propagation. Multimode optical nanofibers expand the photonic toolbox, and may aid in the realization of a fully integrated nanoscale device for communication science, laser science or other sensing applications.Comment: 12 pages, 5 figures, movies available onlin