Cold gas dual-bell tests in high-altitude simulation chamber

An experimental investigation has been carried out to study dual-bell transition behavior in different set ups inside a high-altitude test facility. Cold gas tests were carried\ud out under two different operating conditions namely (i) test\ud nozzle operating in self-evacuation mode and, (ii) test nozzle operating with an additional ejector nozzle (pre-evacuated condition). Although forward transition nozzle pressure ratio does not show any change in its value irrespective of the type of test facility and test set up, the re-transition nozzle pressure ratio shows a significant increase (7–8%) in its value when tested in the high-altitude facility. The latter is caused due to\ud plume blowback effect which dominates during shut down\ud transients in such facilities. Driven by the high atmospheric pressure, the jet exhaust is pushed backwards into the altitude chamber causing the re-transition to occur earlier than that observed in sea-level tests. Further the reduced mass flow rates for nozzle operation in different test set ups in a high altitude test facility also reduces the magnitude of side-load peaks during the dual-bell transitions