Studies on Jet noise are usually conducted on "Transient" and "steady" Jets. Transient Jet refers to the staring processes on Jet formation (e. g. initial shock wave and starting vortex ring). The quasi-steady Jet forms after these Transient phenomena. In the present study, the common facilities for studing the noise sources in the Transient and steady Jet are reviewed. In the next step design of a reflected shock tube is presented. This facility makes it possible to study the noise sources in both Transient and steady Jets. The results of experimental aeroacoustic studies on a hot supersonic Jet with the facility are presented an analyzed for the next step. The Mach number of the generated Jet is 1. 4 with a total temperature of 950 K. Comparison of the results of the designed reflected shock tube with those of common facilities shows the advantages of reflected shock tube for experimental aeroacoustic studies on Transient and steady hot Jets.

This paper investigates the influence of a weak-Jet on the development of a turbulent axisymmetric strong Jet. A parametric study is carried out to evaluate simultaneously the effect to the Jets-spacing (S/D=3 and S/D=7. 5) and their velocity ratios in range 0≤ λ ≤ 1. The mixing phenomenon is studied numerically by the finite volume method using the 3D-RANS second-order model, which gives a good agreement with the available data. Three distinct regions of this type of Jets interaction are evidenced. This study confirms that the Jets spacing affects strongly the converging region and has a minor effect on the combining region. It is found that the weak Jet attracts the strong Jet and the combining region extends from 30D to 40D where the self-similarity of a single Jet is obtained. The Jet width decreases when velocity ratio and Jets spacing augment. In the combining region, in comparison with the free Jet, it is found that the addition of a weak-Jet increases the decay rate of the centerline velocity.

This manuscript bridges the fields of Jet propulsion, synthetic Jets and thermoacoustic engines. We introduce the case that synthetic Jets in air can be considered a consistent approach for propulsion systems. To date, studies on synthetic Jet propulsion have been scattered and rather subsidiary. Furthermore, investigating the perspective of propulsion can provide new insights into the field of synthetic Jets and the physics of propulsion. In this work, synthetic Jet propulsion in air is demonstrated and studied for acoustic and thermoacoustic cases. We developed synthetic Jet systems and characterized the resulting propulsion regarding several relevant parameters such as geometric factors and the frequency and power of acoustic Jets electromechanically and thermally produced. We demonstrated the 10. 4-mN and 2. 7-mN thrust in the acoustic and thermoacoustic modes, respectively, using compact tabletop assemblies. The physical mechanism of the Jets has been modeled, simulated, verified with Schlieren imaging and laid in the perspective of adherent literature. Similarities and differences regarding traditional Jet propulsion systems are discussed. Synthetic Jet propulsion in air using a thermal cycle is experimentally demonstrated for the first time.

In this paper a CFD investigation on the interaction between an offset Jet and an oblique wall Jet using twodimensional steady RANS equations is performed. This combination is denoted WOJ (Wall Offset Jets). Several turbulence models such as the standard k-ω , SST k-ω , standard k-ε , RNG k-ε and realizable k-ε models are tested in the present study. A parametric study is performed to highlight the wall inclination effect on the WOJ flow maximum velocity decay as well as the shear layers spreading. Comparison between combined wall and offset Jet (WOJ) and single offset Jet (SOJ) flows is also established. Results show that increasing the wall inclination improves the combined wall and offset Jets flow spreading. Furthermore, the outer shear layers spreading, is better than the inner shear layers one. Comparing to the combined wall and offset Jet flow (WOJ), a better spreading is found in the case of single offset Jet flow (SOJ).

Background: Previous literatures have shown a Transient ischemic attack (TIA) mimic rate of 9-31%. We aimed to ascertain the proportion of stroke mimics amongst suspected TIA patients.Methods: A prospective observational study was performed in Ghaem Hospital, Mashhad, Iran during 2012-2013. Consecutive TIA patients were identified in a stroke center.The initial diagnosis of TIA was made by the resident of neurology and final diagnosis of true TIA versus TIA mimics was made after 3 months follow-up by stroke subspecialist.Results: A total of 310 patients were assessed during a 3-month period of which 182 (58.7%) subjects were male and 128 (41.3%) were female. Ten percent of the patients was categorized as a TIA mimic. The presence of hypertension, aphasia, duration of symptoms, and increased age was the strongest predictor of a true TIA. Migraine was the most common etiology of stroke mimic in our study.Conclusion: It seems that many signs and symptoms have low diagnostic usefulness for discrimination of true TIA from non-cerebrovascular events and predictive usefulness of any sign or symptom should be interpreted by a stroke neurologist.