Acoustic characteristics of a ported shroud turbocompressor operating at design conditions

Abstract

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.

Acoustic and pressure characteristics of a ported shroud turbocompressor operating at near surge conditions

“…As mentioend before, the tonal features like Blade Pass Frequency (BPF), harmonics of BPF and the harmonics of rotor shaft speed ('buzz-saw' tones) are observed in the spectrum. The strength of the tonal features in the near impeller spectrum are relatively weaker for near surge operation as compared to the design operation [28]. It is interesting to note that the faint 'mid-tones' [28] that are present between the 'buzz-saw' tones in the near impeller spectrum for the design operation are not existent in the spectrum of the compressor operating near surge.…”

“…The strength of the tonal features in the near impeller spectrum are relatively weaker for near surge operation as compared to the design operation [28]. It is interesting to note that the faint 'mid-tones' [28] that are present between the 'buzz-saw' tones in the near impeller spectrum for the design operation are not existent in the spectrum of the compressor operating near surge. The broadband in the frequency range corresponding to characteristic 'whoosh' noise region is not seen in the spectrum of the near impeller probe as observed in the close-up sections presented in Figure 8 and Figure 9.…”

“…The fluid with high circumferential velocity is removed from the impeller passages and recirculated to the main flow via PS cavity. In contrast to the constant pull and push behaviour of the fluid along the impeller blades at the PS slot for design operation [28], a unidirectional radially outward flow is seen at the PS slot for the near surge operation as shown in Figure 13. The flow exits PS cavity in form of high speed jets corresponding to the structural struts.…”

Evolution of flow characteristics in a centrifugal compressor with an increase in operating speed

“…Details on the gas stand measurement are described in Sharma et al 11,36 . Schematic diagrams of the acoustic flow bench with the position of various sensors is shown in Fig.…”

“…Recent attempts to understand the relationship between flow and acoustic features of a PS compressor are made by decomposing the numerical flow field using proper orthogonal decomposition 11,12 and dynamic mode decomposition 13 Order (RO) tones or 'buzz-saw' tones 11,18 and Blade Pass Frequency (BPF) while broadband features include the so called 'whoosh' noise which is observed within the plane wave frequency range and Tip Clearance Noise (TCN) 18,19 seen beyond the plane wave frequency.…”