**3.1 Impact of divergent angles**

In this work, analysis has been carried out at a standard back pressure of 90 kPa with different divergent angles, i.e., 0, 0.5, 1 and 1.5° are considered. The basic purpose of considering the different divergent angles is to analyze the movement of the combustion phenomena inside the isolator. For each divergent angle with a standard adverse pressure gradient of 90 kPa, the contour lines of static temperature, mass density, Mach number and static pressure are measured. From **Figures 3**–**7**, it is observed that with an increase in the divergent angle the location of the shock train will be moved near to the leading edge of the domain. At a divergent angle of 1.5°, as the flow gets separated the strong expansion wave is generated leading to negative pressure drop at the inception of the Mach wave train. When compared to the divergent angles of 1 and 1.5° in the scramjet isolator, the divergent angle of 0° with constant isolator area supports better back pressure. This is because with an increase in the divergence angle, the shock train generated inside the isolator converts the Mach shock wave into normal shock wave initially and again converts into oblique shock wave. The drawbacks of the normal shock wave generated inside the isolator due to an increase in the divergent angle leads to boundary layer separation on the either sides of the wall of the domain, resulting in the decrease of the intensity of the initial shock wave train. **Figure 3** represents the Mach number and static pressure distribution along the axis of the isolator with different divergent angles. From **Figures 3**–**7** it is noted that variation in divergence angle leads to stronger shock wave train resulting in rapid pressure losses. The

#### **Figure 6.**

*Static pressure distribution at constant back pressure with variable divergence angles.*

**Figure 4.**

**Figure 5.**

**8**

*Density distribution at constant back pressure with variable divergence angles.*

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

*Mach distribution at constant back pressure with variable divergence angles.*
