Fangyuan Lou

The Effect of Gas Models on Compressor Efficiency Including Uncertainty

Since isentropic efficiency is widely used in evaluating the performance of compressors, it is essential to accurately calculate this parameter from experimental measurements. Quantifying realistic bounds of uncertainty in experimental measurements are necessary to make meaningful comparisons to computational fluid dynamics simulations. This paper explores how the gas model utilized for air can impact not only the efficiency calculated in an experiment, but also the uncertainty associated with that calculation. In this paper, three different gas models are utilized: the perfect gas model, the ideal gas model, and the real gas model. A commonly employed assumption in calculating compressor efficiency is the perfect gas assumption, in which the specific heat, is treated as a constant and is independent of temperature and pressure. Results show significant differences in both calculated efficiency and the resulting uncertainty in efficiency between the perfect gas model and the real gas model. The calculated compressor efficiency from the perfect gas model is overestimated, while the resulting uncertainties from the perfect gas model are underestimated. The ideal gas model agrees well with the real gas model, however. Including the effect of uncertainty in gas properties results in very large uncertainties in isentropic efficiency, on the order of ten points, for low pressure ratio machines.

The Development of a High Speed Centrifugal Compressor Research Facility

To improve the understanding of high performance centrifugal compressors found in modern aircraft, the aerodynamics through these machines need to be experimentally studied. To accurately capture the complex flow phenomena through these devices, research facilities which can accurately simulate these flows are necessary. These facilities must have the capability to generate the speeds and pressure ratios found in modern centrifugal compressors to match the Mach number and Reynolds number found in actual engine operating environments. This paper describes the development of such a facility at Purdue University in cooperation with Rolls-Royce. This facility utilizes a Rolls-Royce compressor used on helicopter turboshaft engines. The steady-state performance of this compressor is quantified and described. The facility provides the capabilities to develop an increased understanding of the complex flow structures found in modern high performance compressors.

Development of a Research Facility to Study the Flow Field in an APU-Style Inlet

For the many applications of gas turbine engines installed with APU-style inlets such as unmanned aerial vehicles, auxiliary power units, and helicopters, the inlet swirl distortion created from these complicated inlet systems has become a major performance and operability concern. To improve the design of the APU-style inlet systems, better understanding of the flow field and the mechanism for swirl development is necessary. This paper describes the development of a research facility at Purdue University, in cooperation with Honeywell, that provides relevant flow rates through an APU-style inlet such that detailed measurements can be taken in the flow field. A subcritical air ejector is used to continuously flow the inlet at desired corrected mass flow rates. A PID control method is used to maintain the stable operation of the flow system. The steady performance of this system is quantified, and the method used to improve the operation steadiness is described. The facility provides stable operation of the inlet over a wide range of corrected mass flow rate from 1.0 lbm/s to 5.5 lbm/s, which matches the Reynolds number and Mach number in the real engine operating environments and enables further research in resolving the detailed flow field and understanding of the swirl development inside the APU-style inlet.

Interpreting Aerodynamics of a Transonic Impeller from Static Pressure Measurements

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.

Calculating High Speed Centrifugal Compressor Performance from Averaged Measurements

Abstract To improve the understanding of high performance centrifugal compressors found in modern aircraft engines, the aerodynamics through these machines must be experimentally studied. To accurately capture the complex flow phenomena through these devices, research facilities that can accurately simulate these flows are necessary. One such facility has been recently developed, and it is used in this paper to explore the effects of averaging total pressure and total temperature measurements to calculate compressor performance. Different averaging techniques (including area averaging, mass averaging, and work averaging) have been applied to the data. Results show that there is a negligible difference in both the calculated total pressure ratio and efficiency for the different techniques employed. However, the uncertainty in the performance parameters calculated with the different averaging techniques is significantly different, with area averaging providing the least uncertainty.