Aspi Rustom Wadia

Inner Workings of Aerodynamic Sweep

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single-stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level ofaft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/ boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the tip, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

Control of Tip-Clearance Flow in a Low Speed Axial Compressor Rotor With Plasma Actuation

This research investigates different dielectric barrier discharge (DBD) actuator configurations for affecting tip leakage flow and suppressing stall inception. Computational investigations were performed on a low speed rotor with a highly loaded tip region that was responsible for stall-onset. The actuator was mounted on the casing upstream of the rotor leading edge. Plasma injection had a significant impact on the predicted tip-gap flow and improved stall margin. The effect of changing the actuator forcing direction on stall margin was also studied. The reduction in stalling flow was closely correlated with a reduction in loading parameter that quantifies mechanisms responsible for end-wall blockage generation. The actuation reduced end-wall losses by increasing the static pressure of tip-gap flow emerging from blade suction-side. Lastly, an approximate speed scaling developed for the DBD force helped estimate force requirements for stall margin enhancement of transonic rotors.

Experimental Investigation of a Forward Swept Rotor in a Multistage Fan with Inlet Distortion

Previous studies 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 to multistage configurations. The experimental investigation compare two builds of an advanced 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 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 fans sensitivity with inlet distortion.