A novel design methodology for enhanced compressor performance based on a dynamic stability metric

Abstract

(cont.) compressor design optimization framework allows a versatile definition of the objective function such that any combination of pressure ratio, efficiency and dynamic stability can be prescribed at various operating speeds. The compressor design optimization framework uses an effective blade-to-blade CFD method (fast blade performance prediction method) to predict the blade row performance which is used to evaluate the compressor performance and dynamic stability. The fast blade performance prediction method is estimated to be 100 times faster than a direct numerical simulation and it is shown that the accuracy is within 2% of the direct numerical simulation results. Design Optimization of a Generic Three Stage Compressor. Two different design philosophies commonly used in compressor design practice are adopted. The first design philosophy is aimed at improving efficiency and the second is targeted to improve operability over the entire compressor operating range. The compressor design optimization for enhanced efficiency demonstrates that improvements in efficiency are due to an optimal matching of the compressor stages. The results show an average efficiency improvement of 1% throughout the operating envelope. At maximum climb conditions an efficiency enhancement of 2.7% is achieved. Furthermore, optimizing for efficiency does not deteriorate stability but yields an average improvement in surge margin of 2.6 points. The compressor design optimization based on ...

This thesis introduces a new way to quantify the stability of compression systems. Unlike surge margin, the new metric is directly related to the damping of the natural oscillations of the compression system that lead to rotating stall and surge. Furthermore, the new metric captures the shape of the compressor characteristic such that it accounts for the sensitivity of compressor stability to changes in operating line conditions. This metric is used as a primary design variable in a compressor optimization design framework with the goal to enhance compressor performance and operability. The novel design methodology is applied to a generic three stage axial compressor. The baseline three-stage compressor design is optimized to demonstrate the potential performance and operability improvements. More specifically, the work presented in this thesis addresses the following objectives: Development of a New Stability Metric Based on Dynamic Considerations. The simulation results indicate that there is no correlation between surge margin and damping of the compression system and that the changes in damping ratio along the operating line much more fundamentally represent the dynamic behavior and stability margin of the compression system. From this a new dynamic stability metric is developed which is comprised of two parts: (1), the dynamic behavior of the compression system at operating conditions is captured by quantifying the growth rate of the perturbations in the flow field, and (2) the shape of the compressor characteristic is accounted for to quantify the deterioration in compressor dynamic stability with changes in working condition. Implementation of the New Stability Metric in a Compressor Design Optimization Framework. The new