Forward Swept Rotor Studies in Multistage Fans With Inlet Distortion

Abstract

Previous experimental and analytical studies conducted to compare the performance of transonic swept rotors in single stage fans have demonstrated the potential of significant improvements in both efficiency and stall margin with forward swept blading. This paper extends the assessment of the payoff derived from forward sweep with respect to aerodynamic performance and stability to multistage configurations. The experimental investigation compares, on a back-to-back test basis, two builds of an advanced good efficiency, high pressure ratio, two-stage fan configuration tested alternately with a radial and a forward swept stage 1 blade. In the two-stage evaluations, the testing was extended to include the effect on inlet flow distortion. While the common second stage among the two builds prevented the overall fan from showing clean inlet performance and stability benefits with the forward swept rotor 1, this configuration did demonstrate superior front stage efficiency and tolerance to inlet distortion. Having obtained an already low distortion sensitivity with the radial rotor 1 configuration relative to current production military fan standards, the sensitivity to inlet distortion was halved with the forward swept rotor 1 configuration. In the case of the 180-degree one-per-rev distortion pattern, the two-stage configuration was evaluated both with and without inlet guide vanes (IGVs). The presence of the inlet guide vanes had a profound impact in lowering the two stage fan’s sensitivity with inlet distortion.

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“…Application of bowed stators to a high bypass ratio engine eleven-stage high-pressure compressor has resulted in substantial improvement in eciency, with no stability penalty. Mialn Banjac's et al [5] paper describes a methodology and a fully-tested and calibrated mathematical model for the treatment of endwall eects in axial compressor aerodynamic calculations.…”

Predicted and measured performance and stability of two variants of a military fan

“…Limited testing with the removable VIGVs found these to greatly reduce the For successful application of the technology in a multi-stage unit, increased surge margin was desirable from the front stage, particularly at part speeds. Forward-swept rotors were thus investigated [27,28], and the version 2 design, which is compared with version 1 in Fig. 1, was developed.…”