Model tests on the asymmetry of airflow occurring in twin-intake systems at subsonic speeds

Abstract

In twin air-intake systems (i.e., a pair of intakes discharging into a common duct or chamber) in which the losses are affected by external boundary layers; asymmetry of flow between the two ducts occurs below a certain critical value of the flow coefficient (entry velocity + free-stream velocity). The effects of this asymmetry on intake efficiency, and more particularly on flow distribution at the compressor, may be important. If, as seems possible, the flow oscillates between the two sides, this may give rise to vibration of the aircraft. Wind-tunnel model tests have been made on a-pair of wing-root leading-edge intakes and on various arrangements of body-side submerged intakes. In all cases a region of flow asymmetry was observed. The appropriate flow coefficients are outside the main working range of the intakes, but are such as might be encountered in a dive, or on suddenly throttling back in level flight. The main factors determining the extent of the asymmetry are analysed briefly. A theory of intake loss is adapted to provide a method of predicting the critical flow coefficient.