# Computational Investigations and Control of Shock Interference +
## 3 Model Validation
### Effect of Wall Cooling  
Shock-induced flow separation could result in several adverse effects on scramjet performance, including loss of aerodynamic and propulsive efficiency and onset of unstart. Due to these reasons, it is important to control or reduce the boundary-layer separation  
Figure 8: Isolator contours: (**a**) static pressure, (**b**) eddy viscosity ratio, (**c**) divergence of velocity, (**d**) axial velocity. and/or situate the pseudo-shock-train farther from the isolator entrance (which will be the inlet exit in a scramjet). As shown previously in Figure 8, a significant separation bubble is formed at the top and bottom walls along the centerline of the isolator. There is a theoretical basis that wall cooling could result in reducing the boundary-layer thickening and, therefore, could impact boundary-layer separation. To investigate this further, computational investigations were performed, and the results are presented in this section. All conditions were kept the same in this study as the model validation computations shown above, with the exception of the wall boundary condition, which was changed from adiabatic walls to isothermal walls at 150 K static temperature. Detailed flow features that are relevant to the understanding of shock-boundary-layer interaction are shown in Figure 9.  
These plots show the side wall and slices at multiple streamwise locations. The isothermal walls resulted in the pseudo-shock-train situating farther downstream the isolator than in the case with adiabatic walls. In addition, a higher eddy viscosity ratio was generated. The isothermal walls had a very positive effect on the flow separation observed in the case with the adiabatic walls. Corner flow separation is visible in both cases, but the separation bubble is significantly reduced, and there is no reverse flow present in this area with the isothermal walls. Furthermore, static temperature contours were also evaluated for both cases. The effect of the wall cooling in this contour is very clear. As shown in Figure 10, there is a high temperature region associated with the separation bubble in the case with adiabatic walls. As the Mach number of the flow decreases due to the pseudo-shock-train, much of the kinetic energy is transferred to thermal energy, resulting in the high temperature zone at the walls. With the isothermal walls with temperature fixed at 150 K, the boundary-layer growth is less dramatic, which reduces the size of the separation  
Figure 9: Isolator contours with isothermal walls: (**a**) static pressure, (**b**) eddy viscosity ratio, (**c**) divergence of velocity, (**d**) U-Velocity. bubble, allowing for the flow to maintain more speed than that with adiabatic walls. With this maintained flow speed, much kinetic energy is preserved, resulting in lower conversion into thermal energy. A deeper investigation into the physical effects of wall cooling is shown in Figure 11. From this figure, it can be observed that the divergence of velocity is lower in the initial portion of the pseudo-shock-train when the walls are cooled. The flow improvement caused by the isothermal wall cooling is illustrated in Figure 12, through the mass flux at the isolator exit. It is very clear that the mass flux distribution in the isolator cross-section is more uniform after the wall cooling has been implemented, particularly at the centerline. A more uniform profile can be observed with isothermal walls, compared to adiabatic walls. Mass flux is another good metric to observe for this study, as an increase in mass flux leaving the isolator can be attributed to decreased boundary-layer effects, which is a result of the wall cooling. Higher mass flux at the exit is desirable in this system to optimize performance. The static temperature at the exit is also shown in Figure 13. These results show that the wall region is much warmer with adiabatic walls, as expected. The core flow is also cooler in the case of isothermal wall cooling. These results show just how large the impact of the walls can be on the entire flowfield.