A series of numerical experiments were performed in which energy was deposited ahead of a cone traveling at supersonic/hypersonic speeds. The angle of attack was zero, and the cone half-angles ranged from 15 to 45 deg. The Mach numbers simulated were 2, 4, 6, and 8. The energy was deposited instantaneously along a finite length of the cone axis, ahead of the cone's bow shock, causing a cylindrical shock wave to push air outward from the line of deposition. The shock wave would sweep the air out from in front of the cone, leaving behind a low-density column/tube of air, through which the cone (vehicle) propagated with significantly reduced drag. The greatest drag reduction observed was 96%. (One-hundred percent drag reduction would result in the complete elimination of drag forces on the cone.) The propulsive gain was consistently positive, meaning that the energy saved as a result of drag reduction was consistently greater than the amount of energy "invested" (i.e., deposited ahead of the vehicle). The highest ratio of energy saved/energy invested was approximately 6500% (a 65-fold "return" on the invested energy). We explored this phenomenon with a high-order-accurate multidomain weighted essentially nonoscillatory finite difference algorithm, using interpolation at subdomain boundaries. This drag-reduction/shock-mitigation technique can be applied locally or globally to reduce the overall drag on a vehicle.
Lines of energy are deposited ahead of supersonic and hypersonic vehicles in order to create a low-density channel, through which a vehicle can travel with dramatically reduced drag. Temperature and pressure are both also reduced on the front surfaces of the vehicle, while density and pressure are increased at the vehicle base. When applied off-center, this technique can be used to control the vehicle, employing the entire body as the control surface and eliminating the need for actuators. Results for drag-reduction, temperature-reduction, and control forces are presented here.Hypersonic and supersonic vehicles/missiles generate shock waves, which are accompanied by a host of technical challenges. These include increased drag, sonic boom, and destructively high temperatures and pressures on their airframe and components. "Suddenly heating" an extended path of air, ahead of the shock wave and along the vehicle's velocity vector, results in rapid expansion of the heated air. This creates a long, hot, low-density core, into which the vehicle's shock wave expands, followed by the vehicle itself (Figure 1c). This deposition is occurs in pulsed fashion, being repeated when each core has been traversed and the ambient air is once again encountered by the vehicle. Strategically heating extended regions of gas ahead of the vehicle can therefore mitigate the shock wave, as well as its deleterious effects. Also, since the vehicle will preferentially fly along the low-density channel, (e.g. be partially steered by it), adjusting the direction/position of the hot core formation can be utilized as a method of control (Figure 2). FIGURE 1: Display of the maximum drag reduction (percentage) resulting from the low density cores for each of the supersonic flows computed. Bigger cores result in lower drag.
The work presented in this paper explores the possibilities of increasing specific impulse of ALP by generating the ablative plasma in a strong magnetic field. A magnetic field of 4.5 Tesla was used to direct a laser (1064 nm YAG, 200-450 mJ/pulse) generated plasma in order to create a virtual nozzle and increase specific impulse. The work demonstrated that the magnetic field normal to the target surface serves to contain high pressure, high temperature plasma plume ejected from the surface. A pendulum was used to measure the thrust with and without magnetic field. It has been shown that for the conditions used in this experiment, magnetic field increased the thrust by a factor of 2.
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