V.M.Khailov, V.S.Baykov, Y.M.Kiselev

Central Institute of Aviation Motors, Moscow

V.M.Mal’kov

Institute of Theoretical and Applied Mechanics, Novosibirsk

Combination of low pressure, low molecular weight, high temperature, as well as other known features of the CW chemical lasers’ gas flows make many troubles for designers of pressure recovery systems (PRS). This situation reflects in all parts of the PRS: supersonic diffusers, coolers, and ejecting systems.

The main processes in diffusers and ejectors are considered briefly in this article. Design procedure of PRS gas-dynamic channel is described. Question about optimization of traditional scheme ejectors and possibility of using of compact high-pressure ejectors, so called differential, are considered. Choose of gas-dynamic channel geometry, number of ejector stages, PRS working parameters depends on parameters of gas flow of laser for which this PRS is designed.

The same time, the real systems’ technical requirements (gabarits, weight, operation time, efficiency, and others) limit PRS dimensions, number of stages, ejecting gas flow rates, etc. Therefore the design process includes annualizing and selection of some different alternative approaches. Two alternatives are defined with ejecting gas sources. They are high-pressure gas generator (GG) and turbo-compressor (TC) technologies. These approaches are discussed both for CW DF-chemical laser (DFCL) and chemical oxygen iodine laser (COIL) applications.

The GG technology. Among main advantages of the gas generators are their efficiency, technical flexibility, minimal gabarits, weight, and start-up time. Various types of the GG are considered as well as various propellant, fuel and oxidizer components.

An objective for optimization of the ejector (and lasers) work parameters usually is a maximal value of an ejection factor (a ratio between the laser and ejector gas flow rates). A big difference between low molecular weights (m) of the DFCL gas media and (m) higher values of the GG combustion products is one of the most serious problem for the DFCL ejection factor growth. A similar critical parameter for the ejection factor of the COIL PRS is a low-pressure value of the laser gas media. All these features lead to reduction of the ejection factors. Meanwhile high temperature of the GG combustion products requests an additional cooling of the PRS.

Some water added as a component to ejecting gases produced by the GG improves this technology. A reduction of the ejecting gas temperature in this case may be compensated with some reduction of the molecular weight m of the final ejecting mixture. However, this way opens some promising technological opportunity to build the ejector channels without active cooling systems. Modern materials carry work temperatures on the level of 1300-1400 K. It allows saving of high pressure and Mach number values inside the ejector.

The TC technology becomes rival for large-scale and long operation time lasers. Use of air breathing machines for the ejecting gas generation is, probably, an effective way to provide big flow rates for a long time. Since the lasers are very unique devices, while turbo-compressors are widespread in various technologies, their selection of the existing aviation motors looks quite reasonable. In spite of some apparent problems as big gabarits and weight of such TC, this approach may be considered as an attractive engineering (and economical) solution for some discussed applications.

There may be two different technical schemes. One of them assumes the air bleeding from the motor’s compressors (TC), while another one use the total exhaust flow from the aviation motor. The first approach provides a high air pressure (@ 20 atm), however, the flow rate does not exceed 10% of such motor’s summary exhaust. Meanwhile in the second case, the gas stagnation pressure is on the 2-3 atm level only, however, the total flow rate reaches more than a hundred kilogram per second.

The modern aviation motors with afterburners provide high temperature mixtures, which may be diluted by some water as well as in the GG.

Some real technical solutions of PRS for DF-laser and COIL are considered.

Comparative analysis of mass-dimensional performances of PRS realized on the base of GG and aviation technologies is made. Diagram of qualitative dependence of whole system weight from quantity of tests, on which it is designed, is given. Evidently, that weight of PRS based on aviation technology is less then weight of PRS based on GG technology when the quantity of system tests is large.