Objectives of Laser‐Induced Energy Deposition for Active Flow Control

Abstract

A highly concentrated energy deposition has been proposed for a flow control concept in super-and hypersonic transportation. The plasma source can be implemented by laser-, microwave-or DC-discharge phenomena in the flow field upstream of a blunt body. In a wide range of Mach numbers the thermal modification of the gas condition mitigates the strength of the shock waves and improves the aerodynamic performance. This paper presents a discussion of the methodology and objectives of laser-induced energy deposition particularly with regard to the generation of laser-sustained plasma in supersonics. A steady-state argon plasma is maintained by an intensity field in the focal region of a continuous wave laser. The experimental results using drag, laser energy transmission and plasma radiation measurements determine the requirements for laser-sustained plasma and validate the control authority of this concept.

Wave Drag Reduction of Blunt Bodies Using Laser Sustained Energy Deposition In Argon Atmosphere

“…The threshold intensity I d f for laser sustained plasma is determined to be about 3.5 · 10 7 W/cm 2 for Mach 2.1 and about 5 · 10 7 W/cm 2 for Mach 2.7 at a beam waist diameter of 90 µm. 15 The increased threshold for maintenance at Mach 2.7 is due to an additional heat transfer by forced convection. Based on the static pressure measurements the body drag forces are calculated by the foreside surface integral of the normal pressure distribution.…”

“…This temperature difference might be caused by a forced motion of plasma core along the laser propagation axis (in direction of the radiation source) and by an increase of the maintained plasma core length. 15 Furthermore, at the moment of the spectrum snapshot the thermodynamic equilibrium is not valid for a maintained plasma in quiescent gas, according to the thermal equilibrium between the absorbed laser power and the losses of convection, conduction and radiation. Temperatures in the range between 15,000 to 20,000 K have been published for CO 2 laser sustained plasmas in slow streamed argon 8,10,13 at P L = 0.7 .…”

Joule heating flow control methods for high-speed flows

“…Sperber at al. 108 demonstrated this by achieving a drag reduction of approximately 60% at Mach 2.7. They suggest that the drag reduction occurs due to the low speed heated wake, which trails from the laser focal point, creating a recirculation region upstream of the body.…”

Forebody shock control devices for drag and aero-heating reduction: A comprehensive survey with a practical perspective

“…With further increase of deposition distance, drag and aeroheating reduction hold plateau patterns [239,240] while drag may even increase [241,278]. In addition, for a given deposition location, increasing both Mach and Reynolds values yields more drag reduction [241,278,283,285]. As the freestream Mach value increases beyond a given value, drag reduction degrades [241].…”