NUMERICAL NEAR-STALL PERFORMANCE PREDICTION FOR A LOW SPEED SINGLE STAGE COMPRESSOR
Michael G.E. Shuey · OhioLink ETD Center (Ohio Library and Information Network) · 2005
Computational Fluid Dynamics is used to model turbomachinery compressor performance throughout the entire operating range.While it can be very accurate for peak performance calculations, it often is inaccurate around near-stall.CFD tends to predict too large of a peak pressure rise.A few reasons are proposed and explored during the course of this thesis: 1) The complexities of tip modeling 2) Stator loss and blockage on the compressor 3) Multibladerow effects 4) Unsteady effects.All analyses tested on the compressor rotor used by Masahiro Inoue.A multi-block grid was used to adequately model the clearance gap.A standard Wilcox k-ω turbulence model was used.Steady single blade row and multi-bladerow analysis were done.An unsteady single bladerow analysis was also made.The implementation of a Low Speed Pre-conditioner and Matrix Dissipation were also studied to see their benefits on the convergence and performance prediction of this rotor.The results were plotted on a compressor speedline of total pressure rise coefficient vs. exit corrected flow.This allowed for comparisons between the tested cases.These results were compared with published experimental results.Steady state results were close to experimental data at design point, but over-predicted the pressure rise as the compressor was throttled toward stall.Adding the stator loss from the multi-bladerow analysis was a significant improvement to this accuracy, as the stator was shown to have large separation, but still over-predicted the pressure rise.It was determined that there was little or no multi-bladerow interaction.Unsteady analysis of the rotor alone resulted in little additional loss before stall, but greatly improved accuracy for flow coefficients lower than the peak pressure rise where unsteady effects are prevalent.The numerical analysis required to achieve accuracy in compressor modeling depends on the area of the speedline.Near design point, steady state, rotor-alone analysis may be sufficient.As the compressor nears stall, it is important to take into consideration turbulence effects and all rotors and stators.For flow coefficients lower than the peak pressure rise of the compressor speedline, unsteady analysis is required to achieve accurate results.