Experimental and Computational Studies on Flow Characteristics of Single Expansion Nozzle

The present investigation aims to study the flow field characteristics of a single expansion nozzle (SEN). The flow field characteristics of conventional convergent-divergent (C-D) nozzle are also investigated for comparison. The experimental and computational studies were carried out for nozzle pressure ratios of 1.45, 1.55, 1.75, 2, 3, 4 and 5. The studies reveal that, for the single expansion nozzle the oblique shock moves towards the solid boundary with the increase of nozzle pressure ratio, which makes the flow to accelerate continuously in the majority of the divergent portion. The single expansion nozzle delivers the flow with higher Mach number than the C-D nozzle at the exit of the nozzle.

Investigation of the base flow of a generic space launcher with dual-bell nozzle

The typical afterbody flow of a space launcher is characterized by a strong interaction of the engine’s exhaust jet and the separated shear layer emerging from the main body. This interaction is further complicated by strong changes in the spatial and temporal behavior of the afterbody flow during the atmospheric ascent of a launcher. Theoretically, a dual-bell nozzle not only allows for a gain in payload compared to standard single-bell nozzles, but also it alters the wake flow topology due to the two nozzle modes. To predict the benefits as well as the additional risks, the afterbody flow of a generic space launcher model equipped with a cold-flow dual-bell nozzle is investigated in detail. The flow was analyzed for sub-, trans- and supersonic Mach numbers ranging from 0.3 to 2.9 for a variety of nozzle pressure ratios. Particle image velocimetry measurements and schlieren measurements with high repetition rate were performed to determine the dynamics of the separated shear layer, the nozzle jet and their interaction. It is shown that the reattachment length of the base flow decreases with increasing nozzle pressure ratio. Furthermore, the nozzle pressure ratio at which the dual-bell nozzle switches from sea-level mode to altitude mode is reduced by $$15\%$$ 15 % with high subsonic outer flow and by as much as $$65\%$$ 65 % for an outer flow at a Mach number of 1.6. Even for a constant nozzle pressure ratio, the nozzle flow topology depends on the Mach number of the outer flow.

Experimental Assessment of Corrugated Rectangular Actuators on Supersonic Jet Mixing

To improve the stealth capability of a military aircraft, the reduction in core length is essential to reduce the heat signature and the noise characteristics of the engine exhaust. The efficacy of rectangular vortex generators in achieving these objectives has been demonstrated by several researchers, owing to their simplicity. One way of producing the mixed-size vortices is by providing corrugations on the edge of the tab (actuator). Therefore, in the current study, two tabs of aspect ratio 1.5, mounted diametrically opposite to each other at the outlet of a Mach 1.73 circular nozzle, are examined at varying levels of expansions, ranging from overexpanded to underexpanded jet states. In addition, to generate the mixed-size vortices, three corrugation geometries, i.e., rectangular, triangular, and semicircular, are configured along the tab edges. Both quantitative and qualitative investigations are carried out by using the pitot probe to measure the stagnation pressures and by utilizing a shadowgraph technique to visualize the flow field. The corrugated tabs generated a significant mixing, and among them, the tabs with triangular corrugations are found to be most effective. A maximum reduction of about 99.7% in the supersonic core is obtained with triangular corrugated tabs at near-correct-expansion, corresponding to nozzle pressure ratio (NPR) 5. Interestingly, the semicircular corrugated tab significantly reduces the asymmetry near the nozzle exit plane. The shadowgraph images confirm the efficacy of different corrugated tabs in reducing the strength of the waves, prevalent in the supersonic core.

Mixing Characteristics and Enhancement of Sonic Elliptic Jets from a Twin Elliptic Orifice

The knowledge of jet mixing and its enhancement of elliptic jet are important in a propulsion system of aircraft, rocket, and missile’s system design for advancement of combustion via fuel-air mixture increment, lowering the jet noise and reduction of the plume infrared (IR) signature. The jet issuing from a twin elliptic orifice is non-uniform in shape that promotes the faster mixing and it influences by orifice exit conditions, so knowledge of absence of boundary layer and jet mixing characteristics is important. Hence, an experimental work helps to study the jet mixing for a twin elliptic orifice of aspect ratio two at nozzle pressure ratios of one, two, and three. The proximity between the orifices kept as one to 3mm in steps of one. The experimental readings were taken using pitot probe. The results revealed that jet mixing is faster and effective when the proximity between the orifices is closer to each other than the faraway distances at measured nozzle pressure ratios. Difference in orifice jet core exerted a noticeable influence at high proximity levels of nozzle pressure ratio of three and four for elliptic orifice.

Effect of Micro Jet Control on the Flow Filed of the Duct at Mach 1.5

This article reports the outcome of the windtunnel investigation on the role of micro jets as an active control on the wall pressure distribution. Four tiny jets of 1 mm diameter located at 90-degree intervals along a pcd of 1.3 are employed for the control. The Mach number considered for suddenly expanded flow through the nozzle is 1.5, and the microjets are expanded suddenly into a duct at the base with an area ratio of 3.24 times the CD nozzle exit area. The L/D ratio of the duct was reduced from 10 to 1 in steps of 1. The nozzle pressure ratio (NPR) was operated at 3 to 11 with and without control. The wall pressure distribution is observed in the suddenly expanded axi-symmetric duct. From the results, it has been found that the wall pressure distribution does not adversely influence the micro jet controller

Numerical Simulations of a CD Nozzle and the Influence of the Duct Length

A numerical method is used to observe the effect of microjets control on wall pressure spreading in sudden expansion two-dimensional planar duct. In order to find the microjet effectiveness 2-jets of 1 mm diameter orifice located precisely at 900 of intervals along a pitch-circle-distance (PCD) of 1.3 times the exit diameter of the nozzle in the base were employed to control actively. At the present study, the Mach number was used to calibrate the entry to duct was 2.2, and the area ratio of 2.56. The focus in this study and investigate the influence of length-to-diameter ratio (L/D) of a suddenly expanded duct and its effect on the development of the flow field. Hence, to achieve this, the duct length has been varied from 2 to 10. Nozzles are producing such Mach numbers the experiments were performed operating at nozzle pressure ratio (NPR) 3, 5, 7, 9, and 11. The convergent-divergent nozzle geometry has been studied using the K-ε standard wall function turbulence model and independently check with the ANSYS software.