Supersonic jet mixing enhancement by delta-tabs

The results of a continuing investigation of the effect of vortex generators, in the form of small tabs at the nozzle exit, on the evolution of a jet are reported. Primarily, tabs of triangular shape are considered, and the effect is studied up to an equivalent jet Mach number of 1.8. By changing the orientation of the tab with respect to the nozzle exit plane, streamwise vortex pairs of opposite sign were generated. This resulted in either an outward election of jet core fluid into the ambient or an inward indentation of the mixing layer into the core of the jet. A triangular shaped tab with its apex leaning downstream, referred to as a delta tab, was found to be the most effective in influencing the jet evolution. Two delta tabs, spaced 180 degrees apart, completely bifurcated the jet. Four delta tabs increased jet mixing substantially, more than by various other methods tried previously; the mass flux at fourteen jet diameters downstream from the nozzle increased by about 50 percent over that for the no tab case. The tabs were found to be effective in jets with laminar or turbulent boundary layers as well as in jets with low or high core turbulence intensities

Effect of tabs on the evolution of an axisymmetric jet

The effect of vortex generators, in the form of small tabs at the nozzle exit, on the evolution of an axisymmetric jet was investigated experimentally over a jet Mach number range of 0.34 to 1.81. The effects of one, two, and four tabs were studied in comparison with the corresponding case without a tab. Each tab introduced an indentation in the shear layer, apparently through the action of streamwise vortices which appeared to be of the trailing vortex type originating from the tips of the tab rather that of the necklace vortex type originating from the base of the tab. The resultant effect of two tabs, placed at diametrically opposite locations, was to essentially bifurcate the jet. The influence of the tabs was essentially the same at subsonic and supersonic conditions indicating that compressibility has little to do with the effect

Acoustics-turbulence interaction

An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included

Evaluation and Performance Improvement of Antasari Intersection Banjarmasin City

The problem of signalized intersection is caused by the traffic volume continually increasing each year, automatically contributing high delay and frequent congestion and One indicator of traffic congestion at the roundabout is a decrease in vehicle speed [1]. Today's operated traffic lights have not yet capable of overcoming congestion which often occurs in the peak hours. The existing condition on intersection has not yet been able to accommodate the populous traffic volume; it can be seen from each of intersection foot while experiencing the vehicles daley. The imprecised existing condition on the Antasari intersection in Banjarmasin, is seen from the 4-phase control with the cycle time at 177 seconds, the degree of saturation is ≥ 0.85, and the delay is ≥ 60 seconds; making it categorized as the intersection with F-level of service (the worst). This research aims to analyse the existing condition of the Antasari intersection's performance, and to obtain some handling alternatives of Antasari intersection, with some approaches. To increase the performance of Banjarmasin's Antasari intersection, some handling alternatives are executed, such as: the control of Cycle Time, the control of phase direction (phase simulation), and the phase change by using KAJI program. Based on the field data, obtained the performance of Banjarmasin's Antasari intersection in existing condition: the cycle time is 177 seconds, degree of saturation is 2,879 or ≥ 0.85, delay is 963 seconds/pcu or ≥ 60 seconds/pcu, and the worst service level (F-level). In some intersection handling alternative results, there comes one alternative that is able to increase the intersection performance: through the phase simulation stages, with the phase adjustment of the north – south of KolonelSugiono streetamd the east – west of PangeranAntasari street, then the acquired results of the Service Level-C are: the delay value (D) is 23.33 seconds/pcu or ≤ 25 seconds/pcu, the degree of saturation (DS) is 0.671 or ≤ 0.85, and the cycle time (CT) is 67 seconds or ≤ 80 seconds

Noise from a Jet Discharging Into a Duct and Its Suppression

The present study addresses unwanted high intensity noise sometimes encountered in engine test facilities. A simplified model-scale experiment is conducted for a circular jet discharging into a cylindrical duct. For the given configuration the unwanted noise is found to be primarily due to the duct resonance modes excited by the jet. When the "preferred mode". frequency of the jet matches a duct resonant frequency there can be a locked-in "super resonance". accompanied by a high intensity tone. However, even in the absence of a locked-in resonance, high levels of unwanted noise may occur due to the duct modes excited simply by broadband disturbances of the jet. Various methods for suppression of the noise are explored. Tabs placed on the ends of the duct are found ineffective; so are longitudinal fins placed inside the duct. A rod inserted perpendicular to the flow at different axial locations is also found ineffective; however, when there is a super resonance it is effective in suppressing the tone. By far the best suppression is achieved by a wire-mesh screen placed at the downstream end of the duct; placing it on the upstream end also works, however, there is some penalty at high frequencies due to impingement noise. The screen not only eliminates any super resonance but also the duct mode spectral peaks in the absence of such resonance. Apparently it works by dampening the velocity fluctuations at the pressure node and thereby weakening the resonance condition, for the simplified configuration under consideration

Active involvement of students in co-curriculum (sports) versus generic skills

The active involvement of students in sports activities is viewed from different levels of achievement beginning with the national representation of the residential colleges, faculties, and universities in prestigious sporting events at international levels. The skills that are developed through extra-curricular activities are generic skills. The involvement of students in co-curricular activities can help to shape their generic skills, thus leading to self-promotion in the workplace. Therefore, the purpose of this research was to examine the enhancement of generic skills among engineering and technical students of UTHM who are actively involved in co-curricular activities (sports). This study will focus on identifying the factors of involvement, the level of application among students, and the perceptions of the students through their active involvement in extra-curricular activities (sports). A survey was conducted using a quantitative approach. A general questionnaire, which was designed to fulfil the objectives and to answer the research questions for this study, was distributed to 213 engineering and technical student athletes of UTHM who are actively involved in co-curricular activities (sports). It was found that the engineering and technical student athletes of UTHM agreed that their active involvement in extra-curricular activities (sports) was due to interpersonal, intrapersonal and structural factors. The results showed that out of seven generic skills, three constructs of generic skills, namely communication, teamwork and management, demonstrate a high level of application through active involvement in extra-curricular activities (sports). These findings may also help the university to focus on the development of generic skills in engineering and technical students through co-curricular activities (sports) in addition to producing athletes who are able to create a name for the university at national or international level

Dispersion of Love waves in a stochastic layer

We consider the problem of propagation of Love waves in an elastic layer of uniform thickness overlying a half-space. The layer is assumed to have elastic properties which vary randomly with position. The mean field in the layer is obtained using the smoothing method. Some interesting cases are described graphically

Isolation and Characterization of Phage Specific to E. Coli O157:H7

. Phage therapy is not new because it has been practiced since the early 1900s to cure diseases such as shigellosis, typhus and dysentery that caused by bacteria. However, when antibiotics were discovered in 1941, this antibacterial therapy was quickly abandoned by most western scientists. Antibiotic treatment is usually prescribed to treat pathogenic bacteria E. coliO157:H7. However, since 1950s, the widespread resistance to antibiotics has raised public concern on development of alternatives to antibiotics. As a result of this resistance, there becomes a need for an alternative treatment to work synergistically with antibiotic to deal with bacterial infections. This has led to a new approach by the use of bacteriophage which is phage therapy. Once again, this treatment has received attention as an alternative method against bacterial infection. Phage therapy is the treatment on pathogenic bacterial infections by using bacteriophage which capable of invading bacterial cells and disrupting bacterial metabolism before lysing it. Phages are extremely host-specific and the natural enemies of bacteria. It soon becomes clear that there are huge numbers of bacteriophages existed and waiting to be isolated. Phage specific to E. coliO157:H7 was successfully isolated from sewage treatment sample. The appearance of plaques on lawn of E. coliO157:H7 plate indicates phage capabilities to infect and lyses the host cells. The isolated phage was further characterized based on its morphology, genomic profile, physicochemical attributes, and host specificity to assess their potentials to be developed as phage therapy against E. coliO157:H7

Background Oriented Schlieren Applied to Study Shock Spacing in a Screeching Circular Jet

Background oriented schlieren (BOS) is a recent development of the schlieren and shadowgraph methods. The BOS technique has the ability to provide visualizations of the density gradient in both the axial and radial directions. The resultant magnitude of the density gradients allows for comparison with shadowgraph images. This paper first compares data obtained by the BOS and shadowgraph techniques at identical conditions in a free jet. The patterns and spacing of the shock trains obtained by the two techniques are found to be consistent with one another. This provides confidence in the shock spacing measurement by the BOS technique. Due to its simpler setup, BOS is then applied to investigate the shock spacing associated with the screech phenomenon, especially during stage jumps. Screech frequencies from a 37.6 mm convergent nozzle, as a function of jet Mach number (M(sub j)), are shown to exhibit various stages. As many as eight stages are identified with the present nozzle over the range 1.0 < M(sub j) <1.7. BOS images are acquired at various screech conditions and the shock spacing is examined as a function of M(sub j)

Sharing your assets? A holistic review of the sharing economy

Even though academics and practitioners extensively apply the notion of the sharing economy (SE), the conceptualization and the literature construction remained disjointed and dispersed due to the lack of a rigorous attempt to understand the core concept of the SE. This concept is multidimensional, which makes its investigation essential for practitioners and academics. Based on a 15-year data set collected from the Web of Science database, our paper seeks to provide a pervasive science plot of the intellectual structure of the SE field. A bibliometric review method was used by studying documents published from 2005 to 2020, using the VOSviewer, Bibexcel, SPSS, and GunnMap2 software. Providing an overview of articles, authors, the most influential journals, and themes of research, we contribute to the literature on the SE by identifying and proposing six research groups in MDS analysis, six research clusters in HCA analysis, and future study directions. Eventually, the research acknowledges the theoretical contribution, the limits of the present study, and recommends further study directions