Downstream mixing gasdynamic lasers: a numerical solution

Thesis/Dissertation · Sun Dec 31 23:00:00 EST 1978

OSTI ID:5142565

Parthasarathy, K N

A numerical solution for downstream mixing gasdynamic laser flows is considered. In particular, the supersonic mixing flows of vibrationally excited N/sub 2/ with cold CO/sub 2/ and H/sub 2/O downstream of the nozzle exits is studied. The unsteady, two-dimensional Navier-Stokes equations, fully coupled with the appropriate finite-rate vibrational kinetic equations are solved by means of a time-dependent finite-difference numerical technique. The nozzles are very small, and the cavity pressures are low, leading to Reynolds numbers of the order of a thousand, based on h, the distance between the nozzles' centerlines. Due to low Reynolds numbers, only laminar mixing flows are studied. The profiles are fully mixed by a distance of 200 h from the nozzle exits. The optical quality of the medium is very good because of the small density gradients in the fully mixed flow field. The small-signal gains are a factor of two higher than for a conventional gasdynamic laser with the same reservoir conditions. The average small-signal gain shows a steady rise followed by a plateauing effect as the flow progresses downstream, indicating the good laser quality of the mixing flow field. Optimum results are obtained for laser gain with no velocity discontinuity between the mixing streams and with no catalyst (H/sub 2/O) present in the mixture. In the calculation for the 4000 K reservoir temperature, local small-signal gains as high as 13.5/m and average small-signal gain as high as 11.7/m are obtained. These appear to be the highest values noted in the literature for realistic viscous mixing flows and underscore the potential superiority of downstream mixing gasdynamic lasers over the conventional designs. The effect of the boundary layers issuing from the nozzles on the mixing phenomenon is also studied. The boundary-layer profiles are found to inhibit the mixing of the two streams and lower the small-signal gain.

• OSTI ID: 5142565
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420300* -- Engineering-- Lasers-- (-1989)
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
DIFFERENTIAL EQUATIONS
ELEMENTS
ENERGY LEVELS
ENERGY TRANSFER
EQUATIONS
EXCITED STATES
FLUID FLOW
GAS DYNAMIC LASERS
GAS LASERS
HYDROGEN COMPOUNDS
LASERS
MIXING
MULTIPHASE FLOW
NAVIER-STOKES EQUATIONS
NITROGEN
NONMETALS
NOZZLES
NUMERICAL SOLUTION
OXIDES
OXYGEN COMPOUNDS
PARTIAL DIFFERENTIAL EQUATIONS
VIBRATIONAL STATES
WATER