Solid Tab Research Articles

Investigation of Jet Mixing Characteristics Using Slotted Rectangular Tabs

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.

Study of Slanted Perforated Jets

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.

Numerical Investigation of the Air Tabs Technique in Jet Flow

It is well known that the solid tab technique is effective in enhancing mixing in jet flow, but its protrusion nature will also incur thrust loss. Previous experimental results on the so-called air tab technique have revealed that the air tab can achieve a level of mixing enhancement similar to the solid tab, although it will not introduce any thrust loss. The present numerical investigation aims to study, in detail, the evolution and generation of the streamwise vortices by the air tab under both subsonic and supersonic conditions. For the air tab case, the injected air stream will be bent and twisted by the greater momentum of the primary jet and bifurcate subsequently into two streams. Each stream corresponds to one half of the counter-rotating streamwise vortices pair. The two sources that are responsible for the generation of the streamwise vortices in the solid tab can also be found in the air tab case.

Effect of Tabs on Rectangular Jet Plume Development

The near-field mixing performance of a rectangular jet with and without solid tabs introduced at the nozzle lip was studied under supersonic (underexpanded) operating conditions. The effects of tab shape, tab location, and tab number were investigated. Flow visualization of the jet plume was accomplished via Schlieren imaging, and the velocity and turbulence fields quantified via laser Doppler anemometry measurements. Laser Doppler anemometry data were gathered along the jet centerline and on cruciform transverse and spanwise traverse lines downstream of the nozzle exit. Tab shape has only a minor effect, however tab location and number are sensitive parameters for jet plume development. Tabs located on the nozzle wide edge can lead to jet bifurcation, whereas tabs located on the narrow edge cause increased mixing primarily in the major axis direction. A nozzle with four tabs located on its wide edges was the most effective for overall enhancement of jet mixing.

Mixing Enhancement in Subsonic Jet Flow Using the Air-Tab Technique

M IXING enhancement in jet flow has long been the topic of extensive research due to its important applications in aircraft propulsion and combustion. It also has military importance when mixing enhancement is used to suppress the infrared red signature for the fighter jet exhausts. Many passive or active approaches or techniques to enhance jet mixing have been developed and explored, and some of these techniques had also been reviewed and summarized by Gutmark and Grinstein [1]. In passive control strategies, the tabs or vortex generators in particular are simple but effective techniques in flow control. Bradbury and Khadem [2] were the pioneers to study the effect of solid tabs on jet flow. They found that the nozzle boundary-layer thickness, turbulence level, and convergent ratio did not have very strong influence on the jet development. On the other hand, to insert small rectangular tabs into the jet flow on the nozzle perimeter would induce some profound effects on the jet development. Since then, many researchers have been working on this technique. Notable examples include Samimy et al. [3], Reeder and Samimy [4], Zaman et al. [5], Yu and Koh [6], Paoli et al. [7] and many others. Zaman [8] conducted a systematic test on a series of nozzles with various shapes or orifices and found that the spreading of most asymmetric jets was not much different from that of a round jet, but the biggest increase in jet spreading was observed with the tabs. However, the penalty of introducing the tabs is also found to be significant. The thrust lost due to the tabs varies from 4.1 to 23.7%when theflowblockage (proportional to the facing area of tabs) increases from 1.1 to 14.1%. Tominimize the thrust lost caused by tabs but yet maintain its effectiveness in mixing enhancement is important to practical applications. Researchers have been searching for new techniques with better effects on mixing but minimum penalty on thrust. This Note presents results using the socalled air-tab technique. The air-tab technique is achieved by injecting a small amount of air (less than 1% of the volume flow rate of the primary jet) into the plume of the primary jet at choked speed and at certain attacking angles (45 and 90 deg with respect to the primary jet direction). The air-tab technique shows minimum or no impact on thrust, but it would be able to provide significant effect as the solid tab on the mixing enhancement. A similar idea had been used in air and fuel mixing: for example, the experiments conducted byMilanovic and Zaman [9,10]. The description of the experimental setup is presented subsequently. It will be followed by the results and discussion. The Note ends with brief concluding remarks.

Active flow control of jet mixing using steady and pulsed fluid tabs

Flow control techniques for increasing the rate of jet mixing in axisymmetric nozzle flows have been investigated. A combination of water tunnel and high-speed airflow facilities is used to assess the near-field jet behaviour. Solid tabs, steady fluid tabs (i.e. discrete radially discharged control jets located close to the core jet exit), and pulsed fluid tabs are compared. The effect of fluid tab velocity amplitude, pulse rate, and pulse phase are studied using open-loop control. The measurements indicate that fluid tabs generate a similar streamwise vortex formation process (and hence display increased mixing) as previously observed in solid-tabbed nozzle flows. In incompressible testing the mixing effectiveness with a pair of pulsed fluid tabs 180° out-of-phase was as good as a twin solid tab nozzle for a control jet flowrate of only 0.5 per cent of the primary (core) jet flow. In preliminary high-speed testing similar benefits of fluid tabs over solid tabs were observed. Further study of pulsed fluid tabs is recommended; they have the attractive performance benefit that they can be easily switched off when not needed and offer increased flexibility as the basis of an optimized active control jet mixing device.

Effect of Tab Parameters on Near-Field Jet Plume Development

A full understanding of jet mixing behavior is essential in the aircraft design process, particularly when propulsion system integration issues are considered (for example, jet afterbody interactions, jet plume characterization, and jet noise reduction). The present work is motivated by an interest in unconventional jet exhaust nozzle design, specifically tabbed nozzles. The near-field mixing performance arising from a simple axisymetric jet shear layer and three-dimensional perturbed jet shear layers created via a range of solid tab designs introduced at the nozzle exit plane has been studied under subsonic and supersonic operating conditions. The effects of velocity ratio, tab shape, tab number, and tab orientation angle are investigated. Flow visualization of the tab effects is accomplished via laser-induced fluorescence in low-speed flow and schlieren imaging under supersonic conditions. The mean and rms axial velocity as well as pitot pressure and total temperature profiles have been measured along the jet centerline and on orthogonal cruciform radial traverse lines downstream of the nozzle exit. The performance of the solid tab in causing bifurcation of the jet was found to follow the same trend under both subsonic and supersonic conditions, indicating that the dominant features of the streamwise vorticity introduced by the tabs are essentially independent of the Mach number. The experimental results revealed that the decay of the jet core velocity was only weakly dependent on velocity ratio (over the range studied here), tab orientation angle, and tab shape. The mixing of the jet was, however, a strong function of the tab projected area, tab width, and tab number. The optimum tab number was found to be 2.