Abstract
Relative to the surge and stall compliance governed by civil aviation airworthiness regulation of FAR/CCAR33.65, the engine needs to have adequate stability margin throughout its operating envelope. That requires engine compression components to have sufficient surge margin. Inlet distortion is one of the main factors affecting compression components’ surge margin and engine operability. According to the civil aero engine operation scenario, the most likely cause for total pressure distortion formed by the uneven flow field at the exit of the inlet is crosswind condition. In order to quantify the inlet distortion characteristics and understand the distortion attenuation for each compression component of a high bypass ratio turbofan engine, whole engine inlet distortion test was conducted. Three distortion conditions were simulated by different grids, and the distortion characteristics in terms of distortion index was measured by total pressure rake in the test. The test results showed that for high bypass ratio turbofan engine, the inlet distortion is mainly distributed in the area of outer 60% height of fan blade and does not enter the engine inner flowpath. However initial distortion exists in the clean inlet condition at the outlet of both the outer and inner flowpath since the engine structure is not completely circumferentially symmetric. After passing through the flowpath, the degree of distortion will be reduced. At a maximum IDCmax = 6.5% in the inlet, it is reduced to no more than 1% at both outlets of outer flowpath and booster (excluding the initial distortion due to the initial inhomogeneity). The smaller inlet distortion will produce smaller instability effect to the downstream components. At the higher speed/mass flow condition, the amount of distortion attenuation through the flowpath is larger.
