Numerical flow analysis of a centrifugal compressor with ported and without ported shroud

Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated. A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality of the ported shroud. In agreement with previous observations, it was found that the ported shroud reduces the flow disturbances in the blade passage for all operating conditions. However, the compressor efficiency for the off-design operation condition was found to be higher without the ported shroud, supporting the findings reported recently by an experimental investigation. The computational results are validated with experimental measurements in terms of the performance parameters and available Particle Image Velocimetry data. Copyright © 2014 SAE International

Acoustic characteristics of a ported shroud turbocompressor operating at design conditions

[EN] In this article, the acoustic characterisation of a turbocharger compressor with ported shroud design is carried out through the numerical simulation of the system operating under design conditions of maximum isentropic efficiency. While ported shroud compressors have been proposed as a way to control the flow near unstable conditions in order to obtain a more stable operation and enhance deep surge margin, it is often assumed that the behaviour under stable design conditions is characterised by a smooth, non-detached flow that matches an equivalent standard compressor. Furthermore, research is scarce regarding the acoustic effects of the ported shroud addition, especially under the design conditions. To analyse the flow field evolution and its relation with the noise generation, spectral signatures using statistical and scale-resolving turbulence modelling methods are obtained after successfully validating the performance and acoustic predictions of the numerical model with experimental measurements. Propagation of the frequency content through the ducts has been estimated with the aid of pressure decomposition methods to enhance the content coming from the compressor. Expected acoustic phenomena such as `buzz-saw¿ tones, blade passing peaks and broadband noise are correctly identified in the modelled spectrum. Analysis of the flow behaviour in the ported shroud shows rotating structures through the slot that may impact the acoustic and vibration response. Further inspection of the pressure field through modal decomposition confirms the influence of the ported shroud cavity in noise generation and propagation, especially at lower frequencies, suggesting that further research should be carried out on the impact these flow enhancement solutions have on the noise emission of the turbocharger.The project was sponsored and supported by BorgWarner Turbo Systems and the Regional Growth Fund (RGF Grant Award 01.09.07.01/1789C). The authors would like to thank BorgWarner Turbo Systems for permission to publish the results presented in this article. The support of the HPC group at the University of Huddersfield is gratefully acknowledged.Sharma, S.; Broatch, A.; Garcia Tiscar, J.; Allport, JM.; Nickson, AK. (2020). Acoustic characteristics of a ported shroud turbocompressor operating at design conditions. 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Numerical flow analysis in a centrifugal compressor near surge condition

This numerical study presents data relevant to the flow characteristics inside of a centrifugal compressor, at design and near-surge conditions. The main objectives were to characterize the flow structures and the associated instabilities near the stall point (prior to surge) and to contrast the obtained results against data acquired for a design operation condition. Generally, the operational range of compressors is limited at low mass flow rates by development of instabilities, e.g. stall and rotating stall. Such conditions lead to breakdown of the operability of the compressor, with flow reversal in the wheel passage. This results in large mass flow variations and pressure fluctuations within the compressor, lowering the compressor efficiency and pressure ratio. Large vibratory stresses are induced in the blade under such off-design operating conditions, affecting the blade life duration. Compressor stall and rotating stall are frequently regarded as "precursors" to the more damaging surge instability. The flow fields under design and off-design operating conditions are calculated using the Large Eddy Simulation (LES) approach. The complete geometry (360 degree) of the compressor is considered during analysis. It includes the ported shroud, the compressor wheel, the vaneless diffuser, the volute, and the exit pipe. The computationally expensive transient sliding mesh technique is used in order to capture the interaction between the wheel, the flow, and the stationary components of the compressor. The LES data are validated against available experimental measurements obtained under the same operating conditions (i.e. at design and off-design). The calculated frequency spectra when the compressor operated near-by the surge line indicated the presence of the rotating stall

Investigation of the surge phenomena in a centrifugal compressor using large eddy simulation

The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition. Copyright © 2013 by ASME