| Objective: | Develop techniques for integrating directed energy apertures on transonic and supersonic aircraft.
| Description: | The integration of lasers on both tactical and strategic air platforms is usually accomplished through the use of some form of turret. This protrusion out into the air stream affords a wide angle view for the laser system, but is usually accompanied by undesirable turret vibration (jitter) as well as distortions in the local density field (aero-optic distortion). Both of these effects are connected with the strong unsteady three-dimensional separated flow surrounding and behind the turret, and both effects contribute to beam distortion, and ultimate loss of energy on target (or information to a receiver). The canonical “hemisphere atop a cylinder” style of turret, which is a logical starting point for a low-speed (subsonic) type of turret, has very little classical aerodynamic history behind it, even though it is comprised of the union of two very basic shapes (the half sphere and the cylinder). This is due to the fact that it is not a streamlined nor aerodynamic shape, and only came into use with the advent of lasers. The relative void in low-speed aerodynamic turret work has begun to be filled over the past decade with a number of low-speed hemisphere cylinder studies conducted and published. These works involve the use of flow control, in an effort to minimize the effects of unsteady separation, and hopefully in the process, to minimize jitter and wavefront distortion. The situation in turret integration for transonic and supersonic flight applications is considerably more sparse, and there is an obvious need for novel approaches for design in this portion of the flight envelope. Mitigating the potential effects of shock formation (with the resulting unsteady separation and very strong oscillating gradients) is a primary concern. Part of the challenge of turret design is that as the eye is rotated or elevated, the shape presented to the flow direction changes. While it is possible to adapt the flow control to a particular elevation and azimuth look angle, this makes for a very complicated optimization problem. Successful turrets cannot be optimized only for a single position of operation.
| | PHASE I: Identify design parameters to be optimized for a high-speed turret (Mach 0.7 to Mach 1.5). Develop a process for design, optimization, analysis, and test of a high-speed turret, including flow control, and produce design.
| | PHASE II: Refine design from Phase I, and validate procedure with wind tunnel testing, measuring both jitter and beam degradation due to aero-optics. Optimize flow control. Estimate benefit in both aero-optical and jitter characteristics from wind tunnel data.
| | PHASE III
| | DUAL USE COMMERCIALIZATION:
Military Application: Conduct large-scale testing of concept in wind tunnel test and/or flight test.
Commercial Application: Secure laser communication systems.
| References: | 1. Smith, B.R., “Application of LES Methods to Military Aircraft Flow Problems,” AIAA-2010-343.
2. Arunajatesan, S. and Sinha, N., “Analysis of Line of Sight Effects in Distortions of Laser Beams Propagating Through a Turbulent Turret Flow Field,” AIAA-2005-1081.
| | Keywords: | directed energy, transonic, supersonic, turret, aperture, laser |