Transonic performance of an auxiliary airflow system for axisymmetric inlets

A large-scale model of an axisymmetric inlet with a centerbody auxiliary airflow system has been tested in the wind tunnel at transonic speeds. The auxiliary system allows additional airflow (other than in the main duct formed by the cowl and translating centerbody) to pass through the centerbody of the inlet and combine with the main duct airflow on its way to the engine face. The results of the tests are presented, and the inlet performance is compared to a closely related alternative inlet with a 'traveling' boundary-layer bleed system which precludes the use of a centerbody auxiliary airflow system. The comparison shows that the auxiliary airflow inlet can supply 7.7% more engine face airflow at Mach number 1.0 and is 26% shorter than the traveling bleed inlet. Even though maximum transonic airflow was not achieved at a comparable engine face mass-flow ratio of 0.580, a total-pressure distortion of 0.10 and a total-pressure recovery of 0.985 were achieved for the auxiliary airflow inlet while a recovery of only 0.965 was achieved for the traveling bleed inlet.