We show that an embarked intense femtosecond laser can substantially reduce the drag experienced by a supersonic object.

Transitional Shockwave/Boundary Layer Interactions (SBLI) is studied experimentally. Experiments are conducted on a hollow-cylinder flare model in the R2Ch blowdown facility at a Mach number of 5 for three different Reynolds numbers in the transitional regime. Unsteady wall pressure measurements are conducted along with mean and unsteady heat flux measurements and high-speed Schlieren imaging. The images are then processed using Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) to extract relevant information. Two main phenomena are identified and documented: the oblique modes traveling in the shear layer above the recirculation region and the streaks appearing in the reattachment region. New results illustrating the multiple physical origins of the streaks, either linked with globally unstable modes and convectively unstable mechanisms, are discussed.

The goal of this study is to demonstrate experimentally the "Laser Spike" concept in a supersonic flow. The "Laser Spike" uses a thin filament of plasma created by a femtosecond laser. This plasma filament formed by the TeraWatt laser pulse acts as a linear energy deposition upstream of the shock wave created by a blunt body. It has been found that the laser energy deposition induces a significant transient reduction of the drag. This reduction has been quantified using a drag balance. These experiments have been simulated numerically by modeling the plasma filament as a source term in the energy equation. It is shown that the plasma filament created by the ultra-short laser pulse forms a low-density heated core that interacts with the detached bow shock. This interaction produces an inflating recirculating bubble and leads to a transient reduction of the drag. These findings demonstrate the interest of ultrashort laser for flow control. Drag reduction, flow control and trajectory control are among the possible applications of the "laser spike" concept. Sonic boom alleviation could also be improved with this device.