362
R. Naren Shankar et al.
From the figure, we can observe a sinusoidal wave pattern. From pressure value of
1, initially, it drops because of the expansion waves. Velocity of the flow is increasing
here because of decrement of pressure.
The expansion wave is reflected and converted into shock waves which leads to
increment of pressure. Again the shock waves are reflected back and are converted
into expansion wave leading to decrement of pressure. Because of this reflection
of expansion and shock waves the pressure value is oscillating sinusoidally. This
sinusoidal oscillation is termed as jet core that extends up to X/D p = 17.85. After
X/D p = 17.85 there is no oscillation in pressure which is referred to as characteristic
decay region. NPR 5 is a moderate under expanded level where the formation of Mach
disc is expected. But Mach disc is deteriorated to shock crossover by secondary jet
as can be observed in Fig. 3c. For separation distance 15 mm co-flowing jet (CFJ),
there are no oscillations whereas one single fall occurs. This is due to the formation
of Mach disc since it is not deteriorated by secondary jet because of finite separation
Fig. 3 Contrours for the 3 mm separation distance: a Total pressure contour, b Mach number
contour, c Numerical shadowgraph, d Turbulence KE
R. Naren Shankar et al.
From the figure, we can observe a sinusoidal wave pattern. From pressure value of
1, initially, it drops because of the expansion waves. Velocity of the flow is increasing
here because of decrement of pressure.
The expansion wave is reflected and converted into shock waves which leads to
increment of pressure. Again the shock waves are reflected back and are converted
into expansion wave leading to decrement of pressure. Because of this reflection
of expansion and shock waves the pressure value is oscillating sinusoidally. This
sinusoidal oscillation is termed as jet core that extends up to X/D p = 17.85. After
X/D p = 17.85 there is no oscillation in pressure which is referred to as characteristic
decay region. NPR 5 is a moderate under expanded level where the formation of Mach
disc is expected. But Mach disc is deteriorated to shock crossover by secondary jet
as can be observed in Fig. 3c. For separation distance 15 mm co-flowing jet (CFJ),
there are no oscillations whereas one single fall occurs. This is due to the formation
of Mach disc since it is not deteriorated by secondary jet because of finite separation
Fig. 3 Contrours for the 3 mm separation distance: a Total pressure contour, b Mach number
contour, c Numerical shadowgraph, d Turbulence KE