Investigation of Jet Mixing Characteristics Using Slotted Rectangular Tabs (original) (raw)
Related papers
Characteristics of Sonic Jets with Tabs
Shock Waves, 2006
The results of an experimental investigation on the effect of a vortex generator in the form of a mechanical tab placed at the nozzle exit on the evolution of jet and its decay are reported in this paper. Jets from a sonic nozzle with and without tabs operated at nozzle pressure ratios from 2 to 7 were studied. Tabs with two combinations of length-to-width ratio were investigated by keeping the blockage area constant. The tabs offered a blockage of 10.18% of the nozzle exit area. The centerline pitot pressure decay shows that for the tabbed jet a maximum core reduction of about 75% can be achieved at a nozzle pressure ratio (NPR) 7 compared to an uncontrolled jet. The shadowgraph pictures show that the tabs drastically weaken the shock structure in the jet core and disperse the supersonic zone of the flow making them occupy a greater zone of the flow field compared to the plain nozzle. This causes the waves to become weaker and the jet to spread faster. The tabs are found to shed counter-rotating vortices all along the edges, resulting in enhanced mixing. Isobaric contours reveal that the streamwise vortices cause an inward indentation of the entrained mass into the jet core and an outward ejection of core flow. To understand the distortion introduced by tabs on the jet crosssection and its growth leading to bifurcation of the jet, a surface coating visualization method was developed and employed. Communicated by K. P. J. Reddy.
Effect of tab length on supersonic jet mixing
Physics of Fluids
An experimental investigation has been carried out to assess the efficiency of rectangular tabs of 5% blockage with three different aspect ratios of 1, 1.5, and 2, in promoting the mixing of a Mach 1.73 axisymmetric free jet, in the presence of adverse and favorable pressure gradient, by varying the operating nozzle pressure ratio (NPR) from 4 to 8, in steps of 1, covering all the three levels of expansion, namely, the over-, correct-, and underexpaned states at the nozzle exit. For NPR 4, the Mach 1.73 jet is overexpanded with an adverse pressure gradient of about 23%. At NPR 5, the nozzle is almost correctly expanded with an adverse pressure gradient of only about 3%. At NPRs 6, 7, and 8, the nozzle is underexpanded with favorable pressure gradients of 16%, 35%, and 55%, respectively. It is found that as high as about 88% reduction in the core length is achieved by the tab with an aspect ratio of 1.5 at NPR 7. However, the reduction caused by tabs with aspect ratios of 1 and 2 is ...
Parametric study of jet mixing enhancement by vortex generators, tabs, and deflector plates
1996
ABSTRACT This paper provides a comparison of three passive mixing enhancement techniques employed on an axisymmetric jet. In the first part of this paper, blockage, velocity, and average vorticity data are presented for delta tabs and half delta-wing vortex generators. It is determined that the blockage associated with a half delta-wing vortex generator (h/D= 0.2, angle of attack= 30, and sweep angle= 60) is approximately 1/3 of the blockage of a delta tab of equivalent projected frontal area blockage (2% of jet exit area).
The Effects of Scalloping Width and Position on Jet Mixing of Lobed Nozzles
Journal of Aerospace Technology and Management, 2015
AbstrAct: A series of geometric models of lobed nozzles with a central plug was created by different scalloping positions and widths. The shapes of lower and upper edges, cutting depth were kept unchanged. In this study, by the use of numerical simulation, the effects of scalloped width and position on the performance of jet mixing in the pumping condition were analyzed. The results indicated that, as the position of scalloped lower edge kept constant, the radial position of the accelerated mixing region of sidewalls did not change. The accelerated mixing region is enlarged as scalloped width increased, while the growth rate of enlarged region is less than the growth rate of scalloping width. When the scalloped region with the same width moved outward in the radial direction, the mixing rate of the region of the lobe outer edges increased. However, the distance for complete mixing of the primary stream in the core region was increased. It was also found that inward moving of scalloped lower edge enhanced the effect of strengthening streamwise vortices but induced more pressure loss.
Study of Slanted Perforated Jets
Int. J. Turbo Jet-Engines, 2013
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 per foration geometry tabs in controlling high speed jets to enhance the mixing of jet with the ambient air, to sup press 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 per forated tab the main jet interacts with the slanted perfo rated 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 down stream 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.
Effect of cross wire tab orientation on twin jet mixing characteristics
Experimental Thermal and Fluid Science, 2018
The effect of the relative azimuthal orientation of the cross wires, placed at the exit of two identical converging-diverging nozzles, on the flow field of the twin jet is studied experimentally. The nozzle is designed for Mach number of 1.8, with the inter-nozzle spacing of 1.5 and 2.25 times the nozzle exit diameter. Pitot pressure surveys are conducted along the centerline and the cross-stream direction of the twin jet. Cross wire is shown to be successful in reducing the core length and enhancing the mixing characteristics at all the NPRs studied. The combinations of the horizontal and vertical orientation of the cross wire are found to significantly influence the development of the jet flow field for twin jets. Wires, both mounted vertically, are found to be superior in enhancing the mixing characteristics and reducing the core length. The shadowgraph images reveal that the wire bifurcates the jet and displaces the fluid away from the centerline. Strong shocks are formed near the cross wire, but the pressure losses and enhanced mixing of the jet fluid result in smaller supersonic core length with less number of shock-cells.
Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing
Actuators
This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the...
INCAS BULLETIN
Jet mixing becomes necessary for its wide range of applications from household appliances to modern high technology rockets. Various researchers have studied the enhancement of jet mixing and concluded that the most effective jet mixing is due to the engagement of a vortex generator at the exit plane of the nozzle, thereby creating vortices of different sizes to enhance the mixing. To intensify the jet mixing, two similar innovative vortex generators with a total blockage ratio of 3.5% are placed diametrically opposite locations of the convergent nozzle. The Aspect Ratio of the convergent nozzle is 1. A numerical investigation is carried out to assess the effectiveness of the vortex generator for Mach numbers of 0.4, 0.5, 0.6, 0.7 and 0.8. The centerline Pitot pressure decay was calculated and found to exhibit the core length reduction due to the introduction of the Vortex generator. To measure the effectiveness of the jet mixing using vortex generators, the results are compared wit...
Control of Subsonic and Sonic Jets with Limiting Tabs
International Journal of Turbo & Jet-Engines, 2017
Aerodynamic mixing of subsonic and sonic jets with limiting tabs, with and without corrugations, has been studied experimentally. Limiting tab located at the nozzle exit and at a downstream distance of 0.5D has been considered in this study. Mixing caused by the tab at nozzle exit is found to be better that of tab at 0.5D, for both plain and corrugated geometries. Also, both tabs caused better mixing for underexpanded sonic jets than the correctly expanded sonic jet and subsonic jets. At nozzle pressure ratio 3 the plain tab at the nozzle exit reduced the core by about 56 % and the corrugated tab by about 51 %. But when the plain tab is placed at 0.5D the jet mixing is retarded. However, the corrugated tab at 0.5D enhances the mixing, though not up to the level of the same tab at 0D, at all Mach numbers except 0.6. The maximum reduction of core caused by shifted corrugated tab is 14 % for Mach 0.8 jet.