Centrifugal compressor study in mini-jet engine

• Main Author: Guo, Shuai.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Aeronautical engineering::Aircraft motors and engines
• Online Access: http://hdl.handle.net/10356/54696
• Institution: Nanyang Technological University

Mini-turbojet engines, with their advantages of small size and less weight, are widely used in the unmanned area vehicles. One of the most significant parts – the mini centrifugal compressor is investigated in this study. In order to optimize the pressure ratio and efficiency of a mini centrifugal compressor, the design of experiments (DOE) technique and computational fluid dynamics (CFD) are used in this study. A numerical model is built using Axcent® software to study the compressor performance. The grid independence and near wall mesh sensitivity studies are conducted using Spalart-Allmaras (S-A) turbulence model with the pbCFD® solver. The appropriate model is recommended with 214,389 grid nodes, and the y+ value is between 20~100. The experiments of the SR-30 mini turbojet engine are conducted at 4 different rotating speeds: 50,000 RPM; 60,000 RPM; 70,000 RPM and 80,000 RPM. All the data are collected under steady state. The validation of simulation results with the experimental data shows less than 4% difference on the pressure ratio. Based on the numerical method, the compressor performance map of the SR-30 mini turbojet engine is given. Together with the flow distribution at the impeller inlet, the compressor surge and choke studies are conducted to predict the operating range. The first design investigates three compressor parameters from geometrical analysis. Both the first-order and the second-order regression model are used to optimize the original compressor. The first design shows 4.54% increase in isentropic efficiency and 15.85% increase in pressure ratio. The second design is conducted separately of impeller and diffuser. The screen analysis is used to select six parameters for impeller and four parameters for diffuser. Both the Pareto front solutions and the weighted metric method are used to find out the optimal solutions from the compressors. The second design shows 5.63% increase in efficiency and 21.89% increase in pressure ratio. The third design is a totally new design from a meanline analysis software – Compal. Based on the size limitation for the mini-jet engine, the third design is generated with 10.5 mm hub radius impeller and 10 blades diffuser under two commercial optimization softwares, TurboOpt II and IOSO. The third design shows 2.99 in pressure ratio (12.8% increase than the original one) and 77.77 % in isentropic efficiency (10.9% increase than the original one). After all the designs are finished, we are fabricating the optimized compressors and testing the new engine. The testing is on-going and the results will be shown in the future work.