# Computational Investigations and Control of Shock Interference +
## 5 Conclusions  
Computational analysis presented in this work supports scientific understanding of shock interference and passive control of the adverse effects of shockwave boundary-layer interaction to prevent the onset of unsratt in a scramjet isolator for a backpressured isolator and a modified three-dimensional shock-tube. Model validation of the steady-state RANS calculations for the backpressured isolator was performed with experimental data. In addition, the modified shock-tube provided an opportunity to study the shock interference  
Figure 34: Static temperature and pressure distribution at t \(\approx\) 4.905 \(\times\) 10\({}^{-4}\) s with 300K Inflow. and shock-boundary-layer interaction effects that would occur in a scramjet isolator or a ram-accelerator when the high-speed flow from the inlet interacted with the shock produced due to the combustor pressure traveling and meeting in the isolator. An assessment of wall cooling effects on these phenomena is presented for both the backpressured isolator and the modified shock-tube. Wall cooling showed significant success in reducing the boundary-layer separation and the length and beginning of the pseudo-shock-train. In the case of the modified shock-tube, the static pressure comparison along the centerline of the tube demonstrated that the cooling of the walls only had minor effects on the shock-train; the effect was significant at the wall. It is well known that there are many differences between the underlying assumptions made in formulating URANS and LES methods. Both methodologies utilized a common structured mesh where the resolution (both spatial and time-step) was kept closer to the Kolmogorov scale to support large eddy simulation. In general, both URANS and LES results show shock-boundary-layer and shock-shock interference, and RANS with an appropriate mesh and turbulence closure model shows the ability to capture steady-state shock-structure, as shown in the model validation section. However, there are significant quantitative differences between the two methodologies in the form of differences in maximum pressure, temperature, and turbulence production. These differences include a higher temperature zone appearing near the wall, display of Richtmyer-Meshkov instability, and shock wrinkling due to interaction with small-scale turbulence, shown in LES results. Reporting has been scarce on the investigation of shock-shock interference and interaction with the boundary layer in high-speed internal flows, and therefore, it is difficult to perform a comparison of the results presented in this paper with other experimental or numerical studies. However, a few conclusions can be made based on the theoretical knowledge of turbulence and Richtmyer-Meshkov instability. It is well known that the prediction of boundary-layer development and thickness varies between RANS and LES, which clearly affects the formation of shocks inside the modified shock-tube. Similarly, vortex formation and roll-up near the walls are expected, but it is not captured by RANS methodology. LES is able to capture the vortex roll-up phenomena and displays a Richtmyer-Meshkov type instability, which can be expected under these conditions. Due to these reasons, LES is likely better suited to capture the shock physics in this case. This conclusion comes with a set of limitations. The LES approach gave a clear view of how shocks interact with the boundary layer, but its high computational cost limited broader parametric and sensitivity studies. While RANS is unable to capture the complex phenomena observed in the modified shock-tube, it is able to capture the time-averaged wall pressures in the isolator, where there is small shock interference. These results show that passive wall cooling could be a practical way to delay the onset of shock trains and reduce flow separation in scramjet isolators, helping to keep the engine stable under changing backpressure conditions. However, perfectly cooled walls have cost implications for practical aviation systems and are a slower process.