关键词: 堵塞技术;推力;发动机;高空试验;拉瓦尔喷管

Abstract: Choking technique is an available way to reduce altitude test cost and respond insufficient capacity of the pumping equipments. Under the conditions of various exhaust ambient pressure， four group experiments of a turbofan engine with Laval nozzle were performed to identify the effect of choking on engine thrust. The maximum difference of test total thrust in these experiments was up to 6.2%. In order to find the reason of thrust difference and promote the accuracy of estimating engine thrust obtained in altitude test under choking condition， relative theory and calculation analysis were studied， then the estimation method of changes caused by mean influence factors was developed. The results revealed that the main influence factors of test total thrust included engine speed，correction method and flow behavior in nozzle expansion section. According to estimation method presented， the total thrust changes caused by these factors were evaluated. The maximum difference decreased to 0.8% after eliminating these changes. At the same engine speed， the referred total thrust increased with the raise of the exhaust ambient pressure and the maximum difference was 3.3%.

Key words: Choking technique;Thrust;Engine;Altitude test;Laval nozzle