*Corresponding Author

Abstract: - The present study is carried out with a motivation to investigate the axisymmetric supersonic jet

both experimentally and computationally. An open jet facility was utilized to carry out the experiments, and the

results were compared with computational simulations employing the K-omega SST turbulence model using

ANSYS software. It is important to note that, the computational validation has been done incorporating the

Rayleigh Pitot formula to match the centerline pressure for the uncontrolled jet, which has not been found in

supersonic core emphasized the role of VGs in enhancing mixing efficiency. The study also confirmed that

VGs significantly distort wave patterns within the supersonic core, crucial for improved jet mixing. This

research signifies the importance of VGs in augmenting the mixing of Mach 1.6 jets, offering the potential for

improved jet performance and reduced noise emissions in the aerospace industry.

Received: January 16, 2023. Revised: November 11, 2023. Accepted: December 8, 2023. Published: January 23, 2024.

improvement is particularly important in

diminishing the infrared plume and loud noise that

emanates from the hot exhaust gases of the jet, [1].

Control techniques are to be used to generate the

vortices in mixed proportion to achieve better

mixing, [4]. The control methods can be active or

passive. The Active control uses the external energy

to modify the jet flow characteristics. Whereas, the

passive control is achieved by the modifications in

the geometry of the nozzle.

geometry can be expressed using Equation 1, [5].

passive control techniques using the geometrical

modifications are very effective. For example, the

notched nozzles reduce the jet noise by enveloping

the sources of noise with low-speed turbulent flows

also responsible for the breakdown of the primary

jet which improves the mixing and reduces the

noise.

nozzle exit is another effective passive control

method. This thin metal strip, attached at the exit of

the nozzle, is known as a vortex generator (VG) or

tab. The types of vortices generated depend upon

the size and shape of the strip. Tab-like devices are

introduced in diametrically opposite positions at the

tabs on augmenting the supersonic jet mixing is

higher. The mixing enhancement is obtained along

with noise reduction by these devices. Essentially,

the centerline velocity is reduced due to the

improved mixing properties of these tabs, [13].

Moreover, the streamwise vortices are created due

to the tab-induced "indentation" in the shear layer,

[14]. Essentially, a "trailing vortex" at the tip of tabs

and a “necklace vortex” at the base of a tab are

fit and alignment within the settling chamber's

flange. The designed Nozzle can be found in Figure

1.

imported to ICEM CFD to develop a mesh. Meshing

is vital in CFD simulations as it divides the model

into smaller elements for accurate calculations. Part

names are assigned in the model and a blocking

technique is used to create an appropriate mesh

structure. In the current investigation, the

computational model has been discretized using a

node connection for a more seamless simulation.

The y+ value in the near-wall zone is maintained

within the range of 5 to 30. Additionally, the mesh

along the jet centerline is obtained by substituting

the corresponding values of Mach number and static

pressure, ahead of the shock, along the centerline in

the Reyleigh Pitot formula, as given by Equation 5,

[21].

shock. P1 is the freestream static pressure. M1 is the

incoming supersonic freestream Mach number.

cases are made dimensionless to obtain p/po. The

observation cannot be directly compared as the

supersonic core is wave-dominated and the pitot

probe essentially measures the pressure behind the

bow shock. Since the supersonic core is wave-

dominated, there is no way for the experimental

intrusive pressure measurement technique to

measure the actual total pressure experienced in the

supersonic core. Therefore, the Rayleigh Pitot

formula is utilized to convert the static centerline

pressure (computationally calculated) to the total

tested by comparing its results with experimental

Schlieren image and Numerical CFD particularly

focusing on the Mach disk formation at NPR 6. The

comparison between the Schlieren and the

numerical CFD data, as shown in Figure 6,

demonstrates that the numerical model is in line

with the experimental results, particularly regarding

shock core length.

The peak and trough of the centerline pressure

decay (Figure 7) show the region of the supersonic

core in the supersonic jet. The centerline pressure

along the Y axis is non-dimensionalized by the

settling chamber pressure and the axial length along

the X axis is non-dimensionalized by the exit

diameter of the axisymmetric jet. It is easy to

observe that, for the uncontrolled Mach 1.6 jet, the

supersonic core prevails around X/D=12, and after

that, there is a characteristics decay region.

method, demonstrates the fluid flow variations

based on density gradients. Strong expansion waves,

and shock cell length can be seen in Figure 8 and

Figure 9 revealing a significant presence of barrel

shock structures within the jet core.

Fig. 8: Schlieren image for the axisymmetric

uncontrolled jet at NPR 6