Experimental measurement of the influence of off-axis laser discharge on a projectile’s flow field
Creators: name: Pournadali Khamseh, Arastou
Publisher: name: No Publisher Supplied
Year: 2024

description: Trajectory control and maneuverability of aircraft at high speeds present significant challenges, primarily due to the need for substantial control authority. As the Mach number increases, conventional flight control methods become less effective because of the inherent inertia in mechanical actuators. During the time it takes for mechanical actuators to adjust the flight path, the vehicle can travel several times its own length at supersonic speeds. Plasma-based methods on the other hand can offer a solution for high-speed flow control, owing to their ability to rapidly induce changes in local fluid temperature and manipulate shock structures through energy deposition. This dissertation investigates the capability and effectiveness of the plasma-based flow control method, specifically Laser Energy Deposition (LED), for trajectory control in high-speed flows. The goal of this work is to quantify the ability of LED to achieve appreciable alteration of the aerodynamic loading about an ogive-cylinder. Experiments were performed within Rutgers University’s supersonic wind tunnel to measure the influenceof off-axis laser energy deposition on the flow field about an ogive cylinder at a freestream Mach number of 2.8. Perturbation of the flow field was accomplished using an infrared laser source, focused to a point ahead of the ogive cylinder. Stereoscopic particle image velocimetry (SPIV) measurements were performed to quantify the effects of energy deposition on the velocity field at discrete time delays following the generation of the spark. The primary effect of the discharge was toincrease the local temperature by creating a heated region, thereby altering the local Mach number. A lensing effect was observed as this region with a reduced local Mach number moved through the shock structure. Furthermore, the continued evolution of the heated area led to the formation of a vortex system and an induced jet. Moreover, SPIV measurements were conducted across a variety of LED test cases to quantify the impact of changes in energy deposition parameters on the perturbed flow field. These parameters included laser input energy, the laser’s operational mode (single or double-pulsed), and the location of the energy discharge. Results showed that the magnitude of the velocity changes was directly proportional to the laser input energy. Using a double-pulsed LED enabled stronger and more sustained changes in the velocity field. Altering the initial streamwise location of the discharge did not significantly impact the induced changes in thevelocity field. Surface pressure measurements were taken using a fast-responding, pressure-sensitive paint. These measurements enabled the observation of temporal changes in the surface pressure following the laser energy discharge. From these data, the induced side force was calculated to determine the strength and effectiveness of the laser dischargefor the trajectory control of such a projectile. Interactions between the heated region and the shock structure resulted in localized pressure reductions around the projectile’s nose. The energy discharge’s initial location had a direct effect on the magnitude of these pressure reductions. Results indicated that discharging energy closer to the ogive’s axis led to more pronounced changes in the pressure field, thereby generating a stronger side force. Moreover, using a double-pulsed LED resulted in a more substantial side force and more prolonged alterations in the pressure field over time.