Exploring Femtosecond Laser Plasma To Reduce Drag And Temperature Of Hypersonic Vehicle

The drag and temperature reduction of hypersonic vehicle has become an important research project in the field of aerospace, we explore femtosecond laser plasma to reduce drag and temperature of hypersonic vehicle, mainly focused on numerical simulation and theoretical analysis.Firstly, we analyze the evolution of plasma and shockwave induced b y femtosecond laser breakdown the air, and then investigate the mechanism of the drag and temperature reduction by femtosecond laser plasma by analyzing the interaction of plasma shockwave induced by injecting femtosecond laser energy ahead of the blunt body vehicle and bow shock over the head of the blunt-body vehicle in the flow field of 30 km apart from the surface of the earth at Mach number of 5. The plasma in high temperature and pressure is induced by femtosecond laser, then the plasma absorbs the laser energy and expands out of the focal domain, in this process the shockwave is formed, as the interaction of shockwave and the bow shock, the shape of bow shock is changed into weak oblique wave and reduces the pressure of the surface of blunt body, and achieves the reduction of drag and temperature of hypersonic vehicle.Then the Navier-Stokes equations are exploited to compute the drag and temperature reduction for different femtosecond laser energy, laser frequency, the focus position of laser point and Mach number of flow field. The present numerical experiment convinces us that with the laser energy increases the reduction ratio of the drag and temperature rise and the duration of the low-drag will lengthen, thus the required laser frequency will decrease in drag and temperature reduction of vehicle by femtosecond laser plasma. And when injecting femtosecond laser energy at L=100mm is 0.035 mJ, the femtosecond laser plasma can reduce the drag by 93%. When injecting femtosecond laser energy is 0.015 mJ at L=100mm, the femtosecond laser plasma can reduce the temperature by 80%. And when L/D is 2, the effect of drag and temperature reduction is the best. As the increase of Mach number, the temperature and drag reduction ratio will change according to increasing, reducing and platform.Lastly, a new energy injecting format that has three laser energy sources is put forward. According to the numerical simulation, this energy-deposition mode can reduce the drag and temperature of hypersonic vehicle much more obviously than the single laser energy injection mode, the injection mode of three laser energy points improves the optimum drag and temperature reduction ratio, save the laser energy, reduce the requirement of femtosecond laser and enhance the utilization rate of laser energy.