Discharge coefficient of a chemical laser nozzle

Abstract

The throat half-width (h*) of a two-dimensional chemical laser nozzle can be as small as 0.005 cm. At moderate or low plenum pressures the Reynolds number is small, and the thickness of the laminar boundary layer at the throat is substanital. For the oxidizer nozzles, in particular, a knowledge of the throat displacement thickness (delta*)* is important for several reasons. Determination of plenum conditions, especially the fraction of undissociated fluorine, depends on the discharge coefficient (C/sub D/) defined for a two-dimensional nozzle as C/sub D/ = 1 -(delta*)*/h*. A second reason for establishing (delta*)* is to replace the zero-value assumption often used to initiate the boundary-layer calculation for the divergent part of the nozzle with a more realistic value for (delta*)*. In contrast to stagnation-point flow, the pressure gradient parameter (..beta..) does not have a unique value at the throat, and consequently it is also important to establish ..beta..* for this calculation. (An asterisk denotes throat conditions.) Cold flow tests, where there is little or no wall heat transfer, have shown the dependence of C/sub D/ on Reynolds number Re. As expected these tests show (delta*)* ..cap alpha.. (Re)/sup -1/2/, and C/sub D/ is substantially below unity at Reynolds numbersmore » of importance for chemical lasers. For the oxidizer nozzles, however, the wall is water cooled while the core flow is hot (1200K), and wall heat transfer substantially changes (delta*)* from its cold flow value. The determination of (delta*)* and ..beta..* are explored. Based on the results of this analysis, a new test procedure is suggested that would establish ''effective'' values for these parameters.« less