Numerical Study on Sonic Underexpanded Co-flowing Jet …
363
distance. Total pressure contour, Mach number contour, Numerical shadowgraph,
and turbulence contour for 3 mm separation distance is shown in Fig. 3.
From the pressure contour, we can see that less influenced wake region is occurring
because of less value of the separation distance. Potential core has been elongated
because of the presence of the surrounding flow. Surrounding jet prevents the central
jet to interact with the atmosphere reducing mixing. From the Mach contour, localised
supersonic reason is visible. The localised supersonic reason demises in magnitude.
Even though the flow is sonic under expanded the inlet pressure gives raise to localised
supersonic regions that occur along the X-axis. There are six supersonic regions
visible. Numerical shadowgraph shows the occurrence of expansion waves and shock
waves reflection. The shocks from primary and secondary jets interact together in the
near field. Weak potential core is found as shock waves are crossing the potential core
of the inner jet. Shear layer between the jets is very insignificant, i.e. not dominant.
Whereas the outer shear layer becomes dominant. Figure 4, shows the contours for
the 15 mm separation distance. Potential core length has been reduced because of
the interaction between secondary jet and primary jet. In the Mach number contour
localised supersonic region is visible. In density gradient contour we can see that for
15 mm separation distance potential core has been reduced. Because of the reduced
potential core less number of Mach discs has been formed in that. We can also see
shear layer with high turbulence in wake region. Figure 5 shows the total pressure
contours at various X/D p locations for the 3 and 15 mm lip thickness. From the figure,
it is clearly evident that the wake region is very high for increased lip thickness.
Because of this, the core length of the 15 mm lip configuration is reduced compared
to the reduced lip of 3 mm configuration. Thus, it is concluded that wake dominance
plays a vital role in reducing the core.
4 Conclusion
Numerical simulation was carried out to study the effect of separation distance in
co-flowing jet. From the results of the total pressure plot, the core length of 15 mm lip
configuration is reduced very much because of wake dominance due to the separation
distance. The total pressure is increasing and decreasing because of expansion and
shock waves for 3 mm separation distance and for the 15 mm separation distance
only pressure drop is seen. From the contours of Mach number and density gradient
it is observed that for the 15 mm separation distance Mach discs are seen and for the
3 mm separation distance, shock crossover is observed. The results of the numerical
simulation are also validated with the experimental results. The interaction of shock
waves in primary and secondary jets was observed in the numerical shadowgraph.
Hence it is concluded that the separation distance plays a vital role in reducing the
core.
363
distance. Total pressure contour, Mach number contour, Numerical shadowgraph,
and turbulence contour for 3 mm separation distance is shown in Fig. 3.
From the pressure contour, we can see that less influenced wake region is occurring
because of less value of the separation distance. Potential core has been elongated
because of the presence of the surrounding flow. Surrounding jet prevents the central
jet to interact with the atmosphere reducing mixing. From the Mach contour, localised
supersonic reason is visible. The localised supersonic reason demises in magnitude.
Even though the flow is sonic under expanded the inlet pressure gives raise to localised
supersonic regions that occur along the X-axis. There are six supersonic regions
visible. Numerical shadowgraph shows the occurrence of expansion waves and shock
waves reflection. The shocks from primary and secondary jets interact together in the
near field. Weak potential core is found as shock waves are crossing the potential core
of the inner jet. Shear layer between the jets is very insignificant, i.e. not dominant.
Whereas the outer shear layer becomes dominant. Figure 4, shows the contours for
the 15 mm separation distance. Potential core length has been reduced because of
the interaction between secondary jet and primary jet. In the Mach number contour
localised supersonic region is visible. In density gradient contour we can see that for
15 mm separation distance potential core has been reduced. Because of the reduced
potential core less number of Mach discs has been formed in that. We can also see
shear layer with high turbulence in wake region. Figure 5 shows the total pressure
contours at various X/D p locations for the 3 and 15 mm lip thickness. From the figure,
it is clearly evident that the wake region is very high for increased lip thickness.
Because of this, the core length of the 15 mm lip configuration is reduced compared
to the reduced lip of 3 mm configuration. Thus, it is concluded that wake dominance
plays a vital role in reducing the core.
4 Conclusion
Numerical simulation was carried out to study the effect of separation distance in
co-flowing jet. From the results of the total pressure plot, the core length of 15 mm lip
configuration is reduced very much because of wake dominance due to the separation
distance. The total pressure is increasing and decreasing because of expansion and
shock waves for 3 mm separation distance and for the 15 mm separation distance
only pressure drop is seen. From the contours of Mach number and density gradient
it is observed that for the 15 mm separation distance Mach discs are seen and for the
3 mm separation distance, shock crossover is observed. The results of the numerical
simulation are also validated with the experimental results. The interaction of shock
waves in primary and secondary jets was observed in the numerical shadowgraph.
Hence it is concluded that the separation distance plays a vital role in reducing the
core.