Demands on the high by-pass ratio of modern civil engine, an increasing radial offset between the booster and the high pressure compressor highlights the importance of S-shaped gooseneck. A desirable balance between the length and the radial offset by optimizing inner-wall and outer-wall for gooseneck will save the length of low pressure rotor and improve the situation to deliver the flow through it.
This paper presented a geometric modeling method which adopted polynomial curves to construct inner-wall and section area distribution for goosenecks. With the given boundary dimensions of gooseneck, the location of inflection point served as a variable to control the inner-wall curve, and the peak value and its location served as the other two variables to control the area distribution curve. A series of 3-D models were built from the baseline gooseneck model in order to analyze the relationships between the geometric parameters and the aerodynamic performance.
The 3-D numerical simulation results indicated that the peak value of area distribution has the most important effects on the total pressure loss of gooseneck. An appropriate peak value of area distribution could be obtained by changing the normalized Mach number at peak point to weaken the flow separation near the outer-wall and after the struts. Inner-walls with large curvature near the entrance of gooseneck, and area distributions with an appropriate peak location, would improve the streamline of outer-wall and restrain the flow separation. Subsequently, the relationships between the geometric control variables and the total pressure loss were established.
Moreover, taking the constructional blocking effects of struts into account, a series of simplified 2-D flow paths were modeled and the relationships were reestablished. The 2-D results indicated that the simplified model could also reveal the flow field near the inner-wall address the correct peak value. But the optimum peak location and the inner-wall inflection point were not consistent with the 3-D results due to the geometric changes on the outer-wall. The equivalent method will be further improved in the future research.