# Computational Investigations and Control of Shock Interference +
## 4 Shock Interference in Modified Shock-Tube  
The IDRL configuration provided model validation in terms of comparison between measured and computed steady-state wall pressure values on the side-wall centerline and top-wall centerline. Such a comparison provided a significant insight into the ability of models utilized in computational code to capture key shock-physics metrics. However, the insight into the detailed temporal evolution of shock physics and the impact of wall cooling to control undesirable phenomena could not be obtained from the above case. In order to assess processes such as shock interference and the ability of wall cooling to mitigate the adverse effects of shock interference and shock-boundary-layer interactions under conditions at higher Mach numbers, a modified shock-tube was utilized. Since RANS only captures the mean flow characteristics, and a study of the temporal evolution of shock physics was desired, LES was utilized as it has the capability of resolving scales. Companion simulations with Unsteady-RANS (URANS) are also presented for comparison between URANS and LES methodologies in the context of their abilities to capture the transient shock physics.  
As mentioned earlier, a typical Sod's shock-tube consists of a one-dimensional inviscid flow in rectangular tube with closed ends containing two different fluids separated by a diaphragm in the middle of this shock-tube, where the fluid at the left side of this diaphragm (called the driver section) is typically at a higher pressure/density than the fluid at the right side of this diaphragm (called the driven section). Once the diaphragm breaks, a one-dimensional inviscid flow pattern including normal shock, compression waves, and expansion waves is established in the shock-tube. Sod's shock-tube problem does not account for viscous effects or inflow/outflow from either end of the tube. In this work, the Sod's shock-tube is modified so that shock-shock and shock-boundary-layer interactions that are likely to be observed in a scramjet isolator can be computationally investigated. This is accomplished by replacing the right and left walls with a high-speed velocity inlet and pressure outlet, respectively. This computational domain was 1 m long, with 0.03 m height and width. This configuration is longer and has a larger cross-section than the IDRL isolator utilized in the model validation study. It has a square cross-section versus the rectangular cross-section of the IDRL backpressured isolator. Initially, the driver and driven sections of the tube were set to 50 kPa and 5 kPa, respectively. The velocity inlet produced an incoming speed of 736.5 m/s or 3 Mach, with an outflow gauge and initial static pressure of 50 kPa, as well as a temperature of 150 K. A supersonic outflow boundary was specified so that the variables at the outlet were obtained using a 1 st order extrapolation. The walls were adiabatic, no-slip walls. For the isothermal wall case, the wall temperature was fixed at 200 K. The flow entering the shock-tube created a boundary layer and a pseudo-shock-train. A schematic of the modified shock-tube with square cross-section is shown below in Figure 15. The interference of high-speed flow entering from the right-side end of this shock-tube with square cross-section and a right-traveling shockwave generated due to the high-pressure region in the left-half of this duct can also result in Richtmyer-Meshkov-like instability. Any perturbation on that interface is susceptible to the shock acceleration and is expected to grow in amplitude.