One-Dimensional Radial Flow Turbomachinery Performance Modeling

ONE-DIMENSIONAL RADIAL FLOW TURBOMACHINERY PERFORMANCE MODELING Robert J. Pelton Department of Mechanical Engineering Master of Science The Two-Element In Series (TEIS) and Two-Zone models have been used successfully for over twenty years to model test data for radial flow compressors and pumps. The models can also be used to predict the performance of new machines provided that the model inputs can be accurately specified. Unfortunately, use of the TEIS and Two-Zone models as a predictive tool has been limited because an accurate and broadly applicable method of predicting the modeling parameters, ηa, ηb, χ and δ2p does not exist. Empirical models have been developed to predict the TEIS and Two-Zone modeling parameters based on a large database of centrifugal pump and compressor test results. These test data were provided by ConceptsNREC and have been collected over the past 40 years. The database consists of a wide range of machines including some that were designed and tested by ConceptsNREC and others from the open literature. Only cases with a vaneless diffuser or volute have been included in the analysis to avoid any possible impeller-diffuser interactions. From the database, models for all of the TEIS and Two-Zone parameters have been derived using basic regression techniques. Three different models are proposed for each of the two TEIS modeling parameters, ηa and ηb. One model for pumps, another for compressors, and a combined model applicable for all machines is given. For the Twozone parameters, χ and δ2p, a single set of models was developed to represent the design point performance and another showing how χ and δ2p vary off-design. The combined models for ηa and ηb are 30% and 70% more accurate than the current state-of-the-art models, respectively. The new models account for the variance in χ and δ2p at off-design flow conditions and further refine the accuracy of the overall prediction by correctly modeling the loss mechanisms in the impeller passage. Validation work has shown that the set of models that predict ηa, ηb, χ and δ2p can be solved to consistently produce sensible results and yield a reasonable “blind” prediction of the performance of a wide range of radial compressors and pumps. These models constitute the first broadly applicable method for predicting the required TEIS and TwoZone variables and are sufficiently accurate to provide initial performance estimates of new impeller designs.