Award Date

12-1-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

William Culbreth

Second Committee Member

Brendan O'Toole

Third Committee Member

Darrell Pepper

Fourth Committee Member

Evangelos Yfantis

Fifth Committee Member

Sahjendra Singh

Number of Pages

128

Abstract

Inviscid flow theory governs the bulk motion of a gas at some distance away from the walls (i.e. outside the boundary layer). That is to say, there are no viscous forces in the bulk flow, which is modeled using the Euler equations. The Euler equations are simply the Navier-Stokes equations with zero viscosity terms. An ideal inviscid fluid, when brought into contact with a surface or wall, would naturally slip right past it since the fluid has no viscosity. In real life, however, a thin boundary layer forms between the wall or surface and the bulk flow. Shock wave boundary layer theory governs this flow. That boundary layer naturally starts as laminar, but grows in thickness over the length of the boundary until it either separates (due to an adverse pressure gradient) or becomes turbulent. Generally, a turbulent boundary layer is thicker (or reaches further into the bulk flow) than a laminar boundary layer. The flow is regime is even more complicated when moving supersonically, where shocks and boundary layer interact to cause even greater turbulence and unsteadiness.

For most engineering applications involving supersonic flow, a turbulence and unsteadiness is undesirable. However, for the application of presented herein it was postulated that the turbulence and unsteadiness would help mitigate the propagation of a blast/shock wave traveling in an expanding duct or laser beam tube. It was also postulated that small wall obstructions in the flow could enhance those effects to the point of mitigating the impulsive forces of the blast/shock wave on a thin laser focusing optic. Three questions were asked and answered:

1. Will the blast/shock wave generated from fusion burn propagate from the target chamber to the final optic? Yes, it will.

2. If the blast/shock wave does propagate to the final optic, is it strong enough to damage the final optic? Yes, it does.

3. If the advancing blast/shock wave is strong enough to damage to final optic, what types of mitigation strategies can be deployed to lessen or eliminate the impacts of the blast/shock wave on the final optic? Yes, they can.

By purposely tripping the boundary layer using small wall obstructions in a short section of beam tube, the turbulent boundary layer may grow in thickness to point where it reaches far enough into the bulk flow to cause the bulk to flow to lose it's parallel streamlined looking profile. The turbulent boundary layer may also reach far enough into the bulk flow that it "sees" the turbulent boundary layer from the opposite side of the wall, thus really knocking the bulk flow out of its streamlined pattern. Upon exiting the short section of beam tube, this turbulent and unsteady flow is not directly in-line with an opening to a longer beam tube section, and therefore does not supersonically jet across but enters the longer section of diverging beam tube subsonically and naturally slows.

Keywords

Boundary layer; Inviscid flow; Laminar boundary layer; Shock waves; Sound pressure; Thermal boundary layer; Viscosity

Disciplines

Aerodynamics and Fluid Mechanics | Fluid Dynamics | Mechanical Engineering

Language

English


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