EXPERIMENTAL INVESTIGATION OF TYPICAL CONSTANT-AND VARIABLE-AREA EXHAUST NOZZLES AND EFFECTS ON AXIAL-FLOW TURBOJET-ENGINE PERFORMANCE

摘要

Several turbojet engines with both constant and variable-area noz¬zles have been investigated in the NACA Lewis altitude wind tunnel over a wide range of flight conditions with and without afterburning cycles (burning of additional fuel in the tail pipe). The pertinent data from these many studies have been collected and analyzed to extend full-scale nozzle performance to higher exhaust-nozzle pressure ratios and to investigate the effects of constant- and variable-area nozzles on turbojet-engine operation. Velocity coefficients from 0.94 to 0.99 and flow coefficients from 0.95 to 0.99 were obtained for the conical noz¬zles with exhaust-nozzle pressure ratios up to 3.6. For a variable-area nozzle that was almost planar in both the open and closed positions, a constant velocity coefficient of about 0.98 above the critical pressure ratio was obtained.nEngine performance of several turbojet engines with both constant-area and variable-area nozzles was investigated over a range of thrusts. The time rate of thrust change of a turbojet engine could be materially improved by use of a variable-area as compared with a constant-area exhaust nozzle;at 45,000 feet, a 25-percent thrust change with a variable-area nozzle required only 7 percent of the time required with a constant-area nozzle. The specific fuel consumption obtainable at a given thrust was about the same for both types of exhaust nozzle.