Ejector performance at high temperatures and pressures

Attention has recently been given to the use of thrust augmenting ejectors in the wings of V/STOL aircraft. Laboratory experiments using low temperature and pressure primary air have measured high-performance levels with well-designed ejectors. The present experiments were motivated by aircraft designers' questions regarding the effects of realistic temperatures and pressures on ejector performance. The simplest geometry was used: a convergent nozzle issuing into an axisymmetric duct that entrained from and exhausted to ambient conditions. The length of the ejector was varied from 12 to 0.75 diam. Primary temperatures and pressures spanned the intervals 60 to 1000°F and 10 to 80 psig. In support of existing theory, the mass entrainment performance usually decreased with increasing primary pressure although an aeroacoustic interaction reversed the trend over small intervals. Increasing the primary temperature decreased the performance of long ejectors but had little effect on the performance of short ejectors. The results are interpreted in terms of measurements of the pressure along the wall of the mixing duct and total pressure and temperature profiles acquired at the exhaust plane of the ejector.