Abstract The control of co-flowing jets by varying lip thickness has been studied experimentally. Lip thickness is defined as the thickness of primary nozzle wall separating primary jet and secondary jet at the co-flowing nozzle exit. Co-flowing jets from a primary nozzle of diameter 10 mm (1.0 Dp) and a secondary duct with lip thickness (LT) 0.2 Dp, 1.0 Dp and 1.5 Dp at Mach numbers 0.6, 0.8 and 1.0 have been studied. Jet centreline total pressure decay, static pressure variation and jet mixing behaviour were analysed. The results show that the mixing of the co-flowing jet with substantial values of lip thickness is superior to the co-flowing jets with comparatively lower values of lip thickness. Co-flowing jets with lip thickness 1.0 Dp and 1.5 Dp experience a significantly higher mixing than the lip thickness 0.2 Dp jet, for all Mach numbers analyzed in the present study. Moreover, in the case of correctly expanded jets, the local static pressure is assumed to be equal to atmospheric pressure. This assumption becomes invalid for co-flowing jets with substantial lip thickness. The centerline static pressure varies sinusoidally above and below atmospheric pressure by a maximum of 11 %, which is due to wake dominance.

Co-Flowing Jet Control Using Lip Thickness Variation

Abstract Control of Mach 1.8 circular jet with slanted perforated tabs is studied experimentally. Two sets of perforated tabs were used for this study. The perforation angles were 0° and 30° with respect to axis of the nozzle. The blockage areas of the tabs were 5 %. The mixing enhancements caused by these tabs were studied in the presence of adverse and favorable pressure gradients, corresponding to nozzle pressure ratio (NPR) of 4, 5.74 and 8. For Mach number 1.8, jet NPR 4 corresponds to 30 % adverse pressure gradients and NPR 8 corresponds to 39.37 % favorable pressure gradients. The pressure decay characteristics and shadowgraph images of perforated tabs at different NPR were compared. There is 45 % and 65 % reduction in jet core length were observed for the 0° and 30° perforated tabs respectively in both pitot and shadowgraph experiments in comparison to uncontrolled jet.

Supersonic Jet Control by Tabs with Slanted Perforation

This article discusses the jet mixing effectiveness of rectangular tab with slots to distort the jet, thereby creating vortices of differing sizes to enhance the mixing. This article numerically investigates the effectiveness of slanted slotted/perforated rectangular tabs with the slot connecting the adjacent faces of the tab to control Mach 0.4 jet. To intensify the jet mixing process, two similar tabs with equal blockage ratio of 7% are placed at diametrically opposite locations of the convergent nozzle exit. The jet flow development in the axial and radial directions of the jet are investigated in detail. To measure the effectiveness of the slotted tabs, the results are compared with the free jet and with the jet operated with solid rectangular tab. The percentage reduction in the core length obtained is 84.1 and 74% for the jet employed with the slotted tab and the solid tab, respectively, when compared with the free jet. The results exhibit that the slotted tab distorts the jet in the near field to a greater extent when compared with the solid rectangular tab.

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Investigation of Jet Mixing Characteristics Using Slotted Rectangular Tabs

\n This paper presents the numerical simulation of Mach 1.5 supersonic jet with perforated tabs. The jet with straight perforation tab was compared with jets having slanted perforated tabs of different diameters. The perforation angles were kept as 0° and 10° with respect to the axis of the nozzle. The blockage areas of the tabs were 4.9 %, 4.9 % and 2.4 % for straight perforation, 10° slanted perforation (\n \n \n \n \n \n \n \n Φ\n \n \n \n  \n \n \n \n \n {{{\\Phi }}_{\\ }}\n \n  = 1.3 mm) and 10° slanted perforation (\n \n \n \n \n \n \n \n Φ\n \n \n \n  \n \n \n \n \n {{{\\Phi }}_{\\ }}\n \n  = 1.65 mm) respectively. The 3-D numerical simulations were carried out using the software. The mixing enhancements caused by these tabs were studied in the presence of adverse and favourable pressure gradients, corresponding to nozzle pressure ratio (NPR) of 3, 3.7 and 5. For Mach number 1.5 jet, NPR 3 corresponds to 18.92 % adverse pressure gradients and NPR 5 corresponds to 35.13 % favourable pressure gradients. The centerline Mach number of the jet with slanted perforations is found to decay at a faster rate than uncontrolled nozzle and jet with straight perforation tab. Mach number plots were obtained at both near-field and far field downstream locations. There is 25 % and 65 % reduction in jet core length were observed for the 0° and 10° perforated tabs respectively in comparison to uncontrolled jet.

Numerical Simulation of Supersonic Jet Control by Tabs with Slanted Perforation

Numerical analysis of subsonic jets with and without tabs (vortex generators with exit area blockage of 4.84%) has been done in the present research paper. Two tabs has been fixed at nozzle exit diametrically opposite. ANSYS CFX software was used for analysis purpose and to understand the flow characteristics at four different Mach numbers 0.4, 0.6, 0.8 and 1.0. The main objective of the present study is to analyze the effect of innovative vortex generators in the form of solid tabs with triangular fins on either side offset to each other on the performance characteristics. Due to counter rotating streamwise vortices, there is large engulfment of masses from ambient air into the core jet, resulting in the reduction of potential core length.

Numerical Study on the Effect of Innovative Vortex Generators in the Mixing Enhancement of Subsonic Jets

Abstract This paper presents the numerical simulation of the subsonic jets controlled by slanted perforated tabs and its performance of mixing efficiency is compared with the jet controlled by solid tab and free jet. The objective of this paper is to study the performance of slanted perforation geometry tabs in controlling high speed jets to enhance the mixing of jet with the ambient air, to suppress the noise level and to minimize the thrust loss. In this paper the simulations have been carried out using the commercial meshing and analysis software. Due to the effect of tabs the potential core decay occurs and velocity reduces drastically because of enhanced mixing produced by the tabs. From the results it is found that in slanted perforated tab the main jet interacts with the slanted perforated jet which causes in effective mixing, instability in jets and lower thrust loss when compared with the free jet. The decay of the potential core and velocity reduction is computed by simulation for 0.4 Mach number. Velocity plots are obtained at both near field and far field downstream locations to study the jet distortion with slanted perforated tabs and solid tabs. The results obtained for perforated tabs for 0.4 Mach number are also compared with various other Mach numbers. They have also been validated with experimental results which show good agreement with the computational results.

Study of Slanted Perforated Jets

The purpose of this paper is to experimentally analyze the effect of wing shape of various insects of different species in a flapping micro aerial vehicle (MAV).,Six different wings are fabricated for the MAV configuration, which is restricted to the size of 15 cm length and width; all wings have different surface area and constant span length of 6 cm. The force is being measured with the help of a force-sensing resistor (FSR), and the coefficients of lift were calculated and compared.,This study shows that the wing “Tipula sp” has better value of lift than other insect wings, except for the negative angle of attacks. The wing “Aeshna multicolor” gives the better values of lift in negative angles of attack.,This paper lays the foundation for the development of flapping MAVs with the insect wings. This type of wing can be used for spying purpose in the military zone and also can be used to survey remote and dangerous places where humans cannot enter.,This paper covers all basic insect wing configurations of different species with exact mimics of the veins. As the experimental investigation was carried for different angle of attacks, velocities and flapping frequencies, this paper can be used as reference for future flapping wing MAV developers.

Experimental investigation on lift generation of flapping MAV with insect wings of various species

Jet from convergent nozzle under correctly expanded condition was controlled by two tabs kept opposite to each other with straight perforation and slanted perforation at different angles of 10°, 20° and 30°. This jet was compared with uncontrolled jet and jet with solid tab. It was found that jet with tab of slanted perforation 30° was having a lesser potential core as compared to jet with solid Tab. Further it was found that the effectiveness of the tab with slanted perforation increased with increasing slanted perforation angle. The streamwise vortices introduced by the slanted perforation in tabs were inclined towards the centreline of the jet and thereby causing the disturbance in potential core region of the primary jet and resulting in faster decay of the jet.

R. Asad Ahmed

Papers

Study of Slanted Perforated Jets

Experimental investigation on lift generation of flapping MAV with insect wings of various species

Effect of Slanted Perforation in Tabs for Subsonic and Transonic Jets

Lift enhancement technique using roller belt arrangement for moving surface over a composite wing structure considering fluid-material interaction

One-way fluid-material interaction study on a plunging UAV wing