Interpreting Aerodynamics of a Transonic Impeller from Static Pressure Measurements

Fangyuan Lou,John Charles Fabian,Nicole Leanne Key

doi:10.1155/2018/7281691

Fangyuan Lou, John Charles Fabian + Show 1 more

Open Access

https://doi.org/10.1155/2018/7281691

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Abstract

This paper investigates the aerodynamics of a transonic impeller using static pressure measurements. The impeller is a high-speed, high-pressure-ratio wheel used in small gas turbine engines. The experiment was conducted on the single stage centrifugal compressor facility in the compressor research laboratory at Purdue University. Data were acquired from choke to near-surge at four different corrected speeds (Nc) from 80% to 100% design speed, which covers both subsonic and supersonic inlet conditions. Details of the impeller flow field are discussed using data acquired from both steady and time-resolved static pressure measurements along the impeller shroud. The flow field is compared at different loading conditions, from subsonic to supersonic inlet conditions. The impeller performance was strongly dependent on the inducer, where the majority of relative diffusion occurs. The inducer diffuses flow more efficiently for inlet tip relative Mach numbers close to unity, and the performance diminishes at other Mach numbers. Shock waves emerging upstream of the impeller leading edge were observed from 90% to 100% corrected speed, and they move towards the impeller trailing edge as the inlet tip relative Mach number increases. There is no shock wave present in the inducer at 80% corrected speed. However, a high-loss region near the inducer throat was observed at 80% corrected speed resulting in a lower impeller efficiency at subsonic inlet conditions.

Highlights

High-pressure-ratio centrifugal compressors have been widely used in turbochargers and turboshaft engines because of their compact size, high efficiency, and wide operating range
The impeller exit total pressure is derived from the measured total temperature at the deswirl exit, the inlet mass flow rate, and the areaaveraged static pressure measured at the impeller trailing edge using the continuity and the turbomachinery Euler equation [14]
Compressor exit pressure is measured using the 100 psid modules with uncertainty less than 0.05% of full scale. This renders an uncertainty in the total pressure ratio less than 0.2% from 80% to 100% corrected speed

Summary

Introduction

High-pressure-ratio centrifugal compressors have been widely used in turbochargers and turboshaft engines because of their compact size, high efficiency, and wide operating range. Results showed that the first flow instability occurred near the shroud in the inducer due to the interference of shock waves with the tip leakage vortex. The relative Mach number at the impeller leading edge tip was about 1.3, the same as the case studied by Krain et al [4, 5], and the results showed similar flow patterns as well. The low-velocity regions were first observed near the shroud/suction-side area in the inducer due to the interaction between the shock wave and the tip leakage flow. This interaction enhances the total pressure loss in the inducer. Flow in transonic impellers is more complex due to the presence of shock waves; reversed flow near the shroud in the inducer may occur due to the presence of shock waves; the tip leakage flow plays a more important role both within the impeller and at the exit of impeller; flow instabilities may start further upstream at the throat of inducer due to the interaction of shock waves and tip leakage flow

Scope of the Paper

Facility and Instrumentation

Results and Discussions

Conclusions