Global visualization and quantification of compressible vortex loops

The physics of compressible vortex loops generated due to the rolling up of the shear layer upon the diffraction of a shock wave from a shock tube is far from being understood, especially when shock-vortex interactions are involved. This is mainly due to the lack of global quantitative data available which characterizes the flow. The present study involves the usage of the PIV technique to characterize the velocity and vorticity of compressible vortex loops formed at incident shock Mach numbers ofM=1.54 and1.66. Another perk of the PIV technique over purely qualitative methods, which has been demonstrated in the current study, is that at the same time the results also provide a clear image of the various flow features. Techniques such as schlieren and shadowgraph rely on density gradients present in the flow and fail to capture regions of the flow influenced by the primary flow structure which would have relatively lower pressure and density. Various vortex loops, namely, square, elliptic and circular, were generated using different shape adaptors fitted to the end of the shock tube. The formation of a coaxial vortex loop with opposite circulation along with the generation of a third stronger vortex loop ahead of the primary with same circulation direction are of the interesting findings of the current study

Mixing in Circular and Non-circular Jets in Crossflow

Coherent structures and mixing in the flow field of a jet in crossflow have been studied using computational (large eddy simulation) and experimental (particle image velocimetry and laser-induced fluorescence) techniques. The mean scalar fields and turbulence statistics as determined by both are compared for circular, elliptic, and square nozzles. For the latter configurations, effects of orientation are considered. The computations reveal that the distribution of a passive scalar in a cross-sectional plane can be single- or double-peaked, depending on the nozzle shape and orientation. A proper orthogonal decomposition of the transverse velocity indicates that coherent structures may be responsible for this phenomenon. Nozzles which have a single-peaked distribution have stronger modes in transverse direction. The global mixing performance is superior for these nozzle types. This is the case for the blunt square nozzle and for the elliptic nozzle with high aspect ratio. It is further demonstrated that the flow field contains large regions in which a passive scalar is transported up the mean gradient (counter-gradient transport) which implies failure of the gradient diffusion hypothesis

Statistical analysis of the velocity field in a mechanical precessing jet flow

An experimental investigation of a precessing jet issuing from a mechanically rotating nozzle directed at an angle of α=45° relative to the axis of rotation is reported. Both conventional and conditional statistics of the velocity field of the jet were measured using a combined hot-wire and cold-wire (to identify any reverse flow) probe. Three distinct values (≈0.005, 0.01, and 0.02) of the precession Strouhal number Stp (≡ rotation frequency × nozzle diameter / jet exit bulk velocity) were used to assess the effect of varying Stp. The measurements reveal that the Strouhal number in general has significant influence on the entire mixing field generated by a precessing jet. The occurrence of precession at all the Strouhal numbers of investigation produces a central recirculation zone at x ≤ 7d, where x is a distance measured from the rotating nozzle exit. A critical Strouhal number, i.e., Stp,cr ≈0.008 for the present case, is identified: at Stp ≥ Stp,cr the core jet converges to the axis of rotation while at Stp ≥ Stp,cr it does not. The characteristics of the turbulent flow in the near and intermediate regions are quite different and depend upon the magnitude of Stp. The near-field region, x/d ≤ 10-15, is dominated by a regime of global precession of the entire jet. As a result, the large-scale entrainment of the ambient fluid is substantially enhanced while the fine-scale turbulent mixing is suppressed. Under the supercritical regime (i.e., Stp ≥ Stp,cr), the jet in the far field resembles some features of the nonprecessing counterpart. Nevertheless, significant differences still retain in the statistical properties. © 2005 American Institute of Physics.J. Mi and G. J. Natha

Phase 3, Randomized, 20-Month Study of the Efficacy and Safety of Bimatoprost Implant in Patients with Open-Angle Glaucoma and Ocular Hypertension (ARTEMIS 2)

Objective- To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of 10 and 15 µg bimatoprost implant in patients with open-angle glaucoma (OAG) or ocular hypertension (OHT). Methods- This randomized, 20-month, multicenter, masked, parallel-group, phase 3 trial enrolled 528 patients with OAG or OHT and an open iridocorneal angle inferiorly in the study eye. Study eyes were administered 10 or 15 µg bimatoprost implant on day 1, week 16, and week 32, or twice-daily topical timolol maleate 0.5%. Primary endpoints were IOP and IOP change from baseline through week 12. Safety measures included treatment-emergent adverse events (TEAEs) and corneal endothelial cell density (CECD). Results- Both 10 and 15 µg bimatoprost implant met the primary endpoint of noninferiority to timolol in IOP lowering through 12 weeks. Mean IOP reductions from baseline ranged from 6.2–7.4, 6.5–7.8, and 6.1–6.7 mmHg through week 12 in the 10 µg implant, 15 µg implant, and timolol groups, respectively. IOP lowering was similar after the second and third implant administrations. Probabilities of requiring no IOP-lowering treatment for 1 year after the third administration were 77.5% (10 µg implant) and 79.0% (15 µg implant). The most common TEAE was conjunctival hyperemia, typically temporally associated with the administration procedure. Corneal TEAEs of interest (primarily corneal endothelial cell loss, corneal edema, and corneal touch) were more frequent with the 15 than the 10 µg implant and generally were reported after repeated administrations. Loss in mean CECD from baseline to month 20 was ~ 5% in 10 µg implant-treated eyes and ~ 1% in topical timolol-treated eyes. Visual field progression (change in the mean deviation from baseline) was reduced in the 10 µg implant group compared with the timolol group. Conclusions- The results corroborated the previous phase 3 study of the bimatoprost implant. The bimatoprost implant met the primary endpoint and effectively lowered IOP. The majority of patients required no additional treatment for 12 months after the third administration. The benefit-risk assessment favored the 10 over the 15 µg implant. Studies evaluating other administration regimens with reduced risk of corneal events are ongoing. The bimatoprost implant has the potential to improve adherence and reduce treatment burden in glaucoma

How Chevrons Decrease Broadband Jet Noise in Cruise.

Broadband shock noise is reduced because chevrons increase the shear-layer thickness between the flight stream and the jet. It is shown experimentally and with results of a theory of Michalke that this is directly related to a reduction of the axial variation of the pressure amplitudes in the mean flow field of the jet. Since broadband shock noise is the result of an interaction between the turbulence in a jet and the axial variation of the mean flow field the chevrons yield a reduced noise emission. The effects of chevrons on the sound emission from nozzles operating at underexpanded conditions are demonstrated with experimental results. In a cruise condition with a flight Mach number 0.85, the chevron nozzle yields a lower broadband shock noise. It is shown experimentally as well as with the theory of Michalke that chevrons reduce the shock cell spacing, which explains the higher frequencies for broadband shock noise