Test Technique for the Measurement of Intake Drag of Air-Breathing Vehicles

Abstract

KNOWLEDGE of intake drag is important in estimating the performance of the aerospace vehicle. The contribution to the intake drag is mainly due to the external and internal flow through the intake and termed as external and internal drag. External drag is mainly composed of drag due to cowl, diverter, and spillage of flow (pre-entry drag), while the internal drag is due to the wall skin friction and pressure distribution on the walls of the duct. Various components of the drag associated with a typical intake of an air-breathing vehicle are shown in Fig. 1. It is possible to estimate the internal drag in the absence of any flow separation while the estimation of external drag is difficult particularly when the intake is operating in subcritical condition. At this operating condition of intake, experimental method is the only source to determine the intake drag. Hitherto, drag due to intake alone is measured having the intake specially mounted to the forebody of the fuselage and front portion of intake forming a metric part with a balance.Available test techniques demand a special balance and suitable modifications to the intake module [1]. This is cumbersome and involves more time and additional cost towards design, fabrication and calibration of new balance. As an alternative, a test technique developed and patented for the direct measurement of after body drag in the base flow wind tunnel [2–4] is used to demonstrate the usefulness of this technique for the measurement of intake drag in a limited Mach number range. An important feature of this test technique (Fig. 2) is that it facilitates simultaneous measurements of total pressure recovery profiles of the duct flow as well as intake drag for the different mass flow conditions.