Impact of simple surge-enhancing inlet geometries on the acoustic behavior of a turbocompressor

Self Cite

Developments in materials, manufacturing and computing methods have catalysed the generation of efficient compressor designs with higher specific power outputs. Centrifugal compressors have become pervasive in environments demanding a combination of higher power with smaller sizes such as unmanned aerial vehicles, micro gas turbines and turbochargers. These compressors are expected to perform optimally in a range of operational speeds and mass flow states with low acoustic emissions. The impact of operating speed on the flow and acoustic characteristics of a ported shroud compressor has been explored in this work. The operation of the open and blocked configurations of the compressor at the design and near surge points each of a lower and a higher speedline was numerically and experimentally investigated. Comparing the results, the model was shown to predict the operation of the compressor for both configurations at the investigated operating points satisfactorily in terms of both performance and dominant acoustic features. With an increase in the velocity and the Mach number due to increased operational speed, changes in the flow behaviour in the inducer and diffuser were observed. An increase in operational speed was shown to generally increase the overall acoustic emission of the compressor for both configurations. The number of distinct tones in the acoustic output and their magnitude were also seen to be a function of operating speed.

“…Straight ducts were used to uncouple issues due to the PS from those caused by more realistic inlet geometries such as elbows 30 and tapered ducts. 31…”

Section: Methodsmentioning

confidence: 99%

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

Sharma

García-Tíscar

Allport

et al. 2020

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“…In any case, straight ducts are used to uncouple issues due to the PS from those caused by more realistic inlet geometries such as elbows 25 and tapered ducts. 26…”

Section: Methodsmentioning

confidence: 99%

Effects of ported shroud casing treatment on the acoustic and flow behaviour of a centrifugal compressor

Sharma

García-Tíscar

Allport

et al. 2019

Self Cite

Centrifugal turbomachines of smaller sizes operating at higher speeds have become pervasive due to the increased specific power and reliability achieved by improvements in manufacturing, materials and computational methods. The presence of these small turbomachines, specifically compressors, in helicopters, unmanned aerial vehicles, auxiliary power units, turbochargers and micro gas turbines necessitates superior aerodynamic performance over a broad operational range, which is widely achieved by ported shroud casing designs. In addition to aerodynamic performance, acoustic emissions have become a critical aspect of design for these small centrifugal compressors due to high operational speeds. Furthermore, the literature on the acoustic effects of the casing treatment is rather limited. Therefore, the impact of ported shroud casing treatment on the acoustic and flow features of the compressor operating at the design and near-surge conditions have been quantified by numerically modelling the open and blocked configuration of the compressors. Upon comparing with experimental results, the numerical spectra are shown to capture the differences between the two configurations at the investigated operating points with reasonable accuracy. Although the casing treatment is generally seen to decrease the overall acoustic emission of the compressor at both operating conditions, increased propagation of tonal content in the direction upstream to the impeller is observed, particularly for design operation. Broadband characteristics in the lower and medium frequency regions usually associated with near-surge operation including ‘whoosh’ noise are observed to be alleviated by the ported shroud casing treatment.

“…1 In the compressor, active noise, including whoosh noise, is generated at a broad range of frequencies. 2,3 Also, the geometry of the elements directly upstream or at the inlet of the compressor affects its active noise characteristics, as shown by Broatch et al 4 or Sharma et al 5 In the turbine, sound and noise are actively generated at high frequencies and are associated with the rotation of the rotor blades, including rotating shock waves at high turbine expansion ratios. Passive acoustic properties influence the low-frequency engine pulsations and are affected by the geometry of the turbine and its operating conditions.…”

Section: Introductionmentioning

confidence: 99%

Radial turbine sound and noise characterisation with acoustic transfer matrices by means of fast one-dimensional models

Torregrosa

García-Cuevas

Inhestern

et al. 2019

Estimating correctly the turbine acoustics can be valuable during the engine design stage; in fact, it can lead to a more optimised design of the silencer and aftertreatment, as well as to better prediction of the scavenging effects. However, obtaining the sound and noise emissions of radial turbocharger turbines with low computational costs can be challenging. To consider these effects in a time-efficient manner, the acoustic response of single-entry radial turbines can be characterised by means of acoustic transfer matrices that change with the operating conditions. Exploiting the different time-scales of the acoustic phenomena and the change in the operating point of the turbine, lookup tables of acoustic transfer matrices can be computed. Then, the obtained characterisation can be used in mean-value engine models. This article presents a method for generating these lookup tables by means of fast one-dimensional simulations of thoroughly validated fidelity, in terms of both acoustics and extrapolation capabilities. Due to the inherent behaviour of radial turbines, the number of computations needed to fill the lookup tables is relatively small, so the method can be used as a simple preprocessing phase before mean-value simulation campaigns.