This paper presents the experimental results on the flow characteristics of a suddenly expanded flow from subsonic and sonic nozzles. The present study employs passive control in the form of a rib to investigate the base pressure for the enlarged duct. The nozzle pressure ratio (NPR) was varied from 1 to 7. The length to diameter ratio of the enlarged duct was varied from 0.5D to 6D. The aspect ratio of the rib was varied from 0.45 to 1.25. The experimental results showed that the base pressure was strongly influenced by the aspect ratio of the rib at a given L/D ratio. For L/D = 0.5, NPR 3 was found to be critical as seen from the increasing trend in base pressure with NPR. The present study explicitly reveals that, the base pressure in a suddenly expanded axi-symmetric duct can be controlled by employing a rib of appropriate aspect ratio as a passive control device.
This investigation aims to present the jet mixing characteristics and thrust variations of the subsonic jet employed with plain triangular tab and semi-circular corrugated tab by numerical simulation. A triangular tab with semi-circular corrugations is used in this regard at the exit plane of a convergent nozzle, to study the behavior of the jet and its structure. The near jet flow field is studied for different Mach numbers of 0.6, 0.8 and 1, and the comparisons were done for the jet employed with plain triangular tab. To validate the numerical results, experimental validation is carried out for 0.6 Mach jet. The thrust and the potential core length of any jet depend mainly on the percentage of blockage ratio. Since the relationship between the thrust and blockage ratio is such that, the blockage ratio increases, the thrust and the potential core length decreases and vice-versa. The blockage ratio is kept 8.27 % for both the corrugated and plain triangular tabs. From the results, it is found that the Potential core length of the free jet is cut down to 66 % by the jet employed with plain triangular tab, whereas it is 64.5 % for the corrugated tab enabled jet. It is also concluded that the corrugated tab enhances the thrust by 4.43 % for the same blockage ratio and increases potential core length by 3.33 % when compared with the plain triangular tab. This increase in thrust is there by an added advantage of this investigation.
Purpose The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the locations of the semi-circular corrugations are varied along the leaned sides of the triangular tabs. Design/methodology/approach The tabs are fixed at the exit of the nozzle facing each other 180° apart. To quantify the jet mixing effectiveness of the semi-circular corrugated tabs, Pitot pressure measurements were carried out for the cases of over-expansion, marginally over-expansion and under-expansion levels of Mach 1.6 jet, along the jet centerline and the jet spread, along and normal to the tab axis. Findings The results exhibit that the semi-circular corrugated Tab A augments the jet mixing when compared to Tabs B and C. This impact in jet mixing is strongly due to the small-scale vortices shed from the tabs and the mixed effect of the corrugation locations and expansion ratio. The maximum percentage reduction in core length is about 73.6 per cent for the jet with semi-circular corrugated Tab A at NPR 5, whereas it is 71.4 and 67.1 per cent for Tabs B and C, respectively. Practical implications The reduction in core length of the jet with minimum thrust loss is obtained by controlling the jet used with semi-circular corrugated triangular tabs of equal blockage ratio 5.12 per cent with respect to the nozzle exit diameter. Originality/value The locations of the semi-circular corrugations varied systematically at the equally leaned sides of the triangular tab ensure the novelty of this study.
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