The surge limit of compressors is one key parameter in the design process of modern turbocharger compressors for automotive applications. Since the compressor is operated close to the surge limit, the determination of the exact position of the surge limit is of high importance. Numerical methods like steady-state simulations are state-of-the-art methods for predicting the performance of turbocharger compressors in an industrial environment. Transient, time-resolved numerical simulations of a complete compressor model are too time consuming and numerically expansive and thus no option during the design process in an industrial environment. In contrast to the prediction of the performance, the determination of the surge limit with any numerical method with high accuracy is still an unsolved challenge. Various recent publications and several numerical and experimental investigations of the authors undertaken at Hochschule RheinMain and TU Darmstadt confirmed exactly this. 
This paper presents a new methodology, based on the analysis of transient experimental signals, to determine the surge limit of a turbocharger compressor with high accuracy. This is achieved through a fourier analysis of the unsteady compressor outlet pressure signal for transient surge runs. Within the scope of the transient surge run, the transition between stable and surge operation can be seen clearly in the time-resolved signals as well as in the frequency analysis. This surge limit will then be used as a validation of the numerically determined surge limit. The numerical surge limit is determined from steady-state simulations. In this case, the last converged operating point is defined as the surge limit. Hence, it is more of a convergence limit than a surge limit. 
Finally, the validation results will be discussed critically and some ideas on how to efficiently indicate surge in steady-state or transient simulations will be proposed. This will be an outlook on the second part of the paper. Since the authors suggest, that possible indicators can only be detected in unsteady simulations, the further investigations of the project will be focused on a reduced numerical model. This reduced model will enable an efficient transient simulation, which is necessary for the application in an industrial design process. The basics of the latter will be presented in detail by Paul et&nbsp;al. in the second part of the paper. This part will outline the simplifications made with the reduced model and investigate the limits of a reduced model with regard to decisive flow phenomena.

On the Challenge of Determining the Surge Limit of Turbocharger Compressors: Part 1 – Experimental and Numerical Analysis of the Operating Limits

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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