Figure 8 - uploaded by Sidharath Sharma
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Close-up view of the impeller, highlighting locations of the flow featuring transonic, sonic and supersonic speeds. Results show that main blade leading edges and both main and splitter blade trailing edges reach sonic conditions.
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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 o...
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... 6 indeed shows buzz-saw tones corresponding to each main blade. In order to test the aforementioned hypothesis, regions with Mach number 0:9 \ M \ 1:14 are shown in Figure 8. Transonic conditions can be clearly seen at the leading edges of the impeller main blades and at the trailing edges of both the main and splitter blades. ...
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Originally inspired by a classical modeling methodology in electrical engineering, the transfer matrix method (TMM) has proven to be an accurate and efficient way to model layered acoustic media. In the case of fluid, or effective fluid, media, the acoustic TMM elements are conventionally modeled as two-by-two matrices. In contrast, a six-by-six ma...
Citations
... Intensive experimental campaigns to investigate the surge phenomena on a specific circuit with a ported shroud have also been performed [108,109]. Finally, the ported shroud has been analyzed to understand its acoustic characteristics near a surge [110] and at design conditions [111]. ...
Centrifugal compressors are widely used in different fields. Their design requires high performance and a wide operating range, where, at lower mass flow rates, unstable flow dynamic phenomena occur, which are extremely harmful and, at the same time, complex to fully understand. This review paper presents the main research from the last 40 years on the subject of instability in centrifugal compressors, aiming to clarify the main (sometimes contradictory) causes, classifying them according to the component in which they are triggered or the interaction between them. Importance is given to works that develop criteria for the identification of the stability limit with simplified models. The main techniques used to extend the stability limit are also presented by distinguishing between passive and active fixed-flow control methods; moreover, the main works on variable geometry techniques are reported, showing the advantages and disadvantages of their use. Finally, an overview of the innovative applications of centrifugal compressors, such as fuel cells, is presented. The aim of this review is to highlight the continued interest in this field of study and provide the tools to understand the different unstable mechanisms and techniques used to extend the operating limit.
... Sharma et al. [54] A turbocharger compressor with ported shroud design ...
In the fields of environment and transportation, the aerodynamic noise emissions emitted from heavy-duty diesel engine turbocharger compressors are of great harm to the environment and human health, which needs to be addressed urgently. However, for the study of compressor aerodynamic noise, particularly at the full operating range, experimental or numerical simulation methods are costly or long-period, which do not match engineering requirements. To fill this gap, a method based on ensemble learning is proposed to predict aerodynamic noise. In this study, 10,773 datasets were collected to establish and normalize an aerodynamic noise dataset. Four ensemble learning algorithms (random forest, extreme gradient boosting, categorical boosting (CatBoost) and light gradient boosting machine) were applied to establish the mapping functions between the total sound pressure level (SPL) of the aerodynamic noise and the speed, mass flow rate, pressure ratio and frequency of the compressor. The results showed that, among the four models, the CatBoost model had the best prediction performance with a correlation coefficient and root mean square error of 0.984798 and 0.000628, respectively. In addition, the error between the predicted total SPL and the observed value was the smallest, at only 0.37%. Therefore, the method based on the CatBoost algorithm to predict aerodynamic noise is proposed. For different operating points of the compressor, the CatBoost model had high prediction accuracy. The noise contour cloud in the predicted MAP from the CatBoost model was better at characterizing the variation in the total SPL. The maximum and minimum total SPLs were 122.53 dB and 115.42 dB, respectively. To further interpret the model, an analysis conducted by applying the Shapley Additive Explanation algorithm showed that frequency significantly affected the SPL, while the speed, mass flow rate and pressure ratio had little effect on the SPL. Therefore, the proposed method based on the CatBoost algorithm could well predict aerodynamic noise emissions from a turbocharger compressor.
... The conducted research was aimed at determining the influence of the layer height change on the accuracy of the CAD model mapping using the FFF method. This method is very popular in the industry [14][15][16], and is more and more often used to produce parts for a specific purpose. Using this technology, the most popular thermoplastic material -polylactide -PLA, was used to balance the models of turbocharger rotors. ...
The methodology and measurement results of the machine part produced directly from the 3D-CAD numerical model are presented. Representative additive techniques based on polymer processing were used. The accuracy of replication of CAD numerical models was assessed in terms of both external surface analysis and part volume.
... Two techniques are used for the decomposition of the acoustic signals collected by an array of transducers, whether piezoelectric dynamic pressure transducers or microphones. The beamforming LCMV decomposition technique described in Ref. [24,26,29], and the Two Microphones Method (TMM) technique used in Ref. [25]. Although the TMM technique, due to its mathematical equation, is simpler to implement than the beamforming LCMV technique, Torregrosa et al. [24] states that the beamforming LCMV technique presents better results in the decomposition of acoustic waves. ...
The technology of internal combustion engines has improved to meeting international regulations, applying turbocharging as an effective method. However, the works under extreme conditions requires strict maintenance plans, since when it fails, it completely deteriorates the functioning of the turbocharged engine. In this work, two procedures are used to characterize some operating failures. Faulted blades are introduced in the compressor to simulate typical failures observed in automotive turbochargers. Four centrifugal compressors mounted with perfect and defected blades are used to compare changes during three failures steps, using experimental vibration and acoustic analyses. The vibratory response of the compressor is obtained by analyzing the vibration signals measured on the turbochargers. Furthermore, sound pressure measurements are performed to evaluate the noise radiation based on an acoustic wave decomposition technique. The experimental results rendered for the vibratory response and noise generation from the turbocharger compressor permit the characterization of automotive turbocompressor operating failures.
... Intensive experimental campaigns to investigate surge phenomena, on a specific circuit, have been also undertaken both without [20,21] and with ported shroud [22,23]. Moreover, the ported shroud has been analyzed to understand its acoustic characteristics near surge [24] and at design conditions [25]. ...
The design features of a centrifugal compressor must guarantee high performance and a wide operating range. The ported shroud was developed specifically to extend the operating limit. It is a passive flow control device based on a cavity for flow recirculation to avoid blade passage blocking in near surge conditions. A CFD simulation campaign using a simplified model identified the differences in the performance of the centrifugal compressor with ported shroud, compared to the baseline case. The use of a stability criterion to determine the limit mass flow rate, developed in a previous study by the authors, highlighted and quantified the extension of the surge margin in the case with ported shroud for different rotational speeds. An increase in the surge margin of 11% was detected at design speed, but with a lower trend at higher speeds. An in-depth flow analysis showed the main physical mechanisms in the compressor that occur for different operating conditions: at near surge conditions the cavity recirculates the low momentum flow located in the inducer region; it re-energizes the mainstream decreasing the circumferential velocity component; an improvement of up to 7% of the pressure ratio was obtained. Instead, at best efficiency conditions the flow recirculation worsens the performance by reducing the flow incidence at the rotor leading edge. Finally, using unsteady simulations with a complete 3D model and with the application of the stability criterion it was possible to confirm that the ported shroud can effectively extend the operating range.
... The feature extraction methods of coherent flow structure have been proposed in the literature. One of the widely used fluid machinery approaches [20,21] is the proper orthogonal decomposition (POD) method, which can help visualize large-scale high-energy flow structures in the flow field. Sharma et al. [22] applied the POD technique to investigate the localization of the energetic noise sources in an impeller. ...
This study numerically investigates the beneficial effects of positive pre-swirl on the
aerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates. Four positions of VIGV are considered, including 0◦, 30◦, 45◦, and 60◦ angles. The latter three positions of VIGV induce positive pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings.
... The curve representing the operating characteristics of the machine with the polymer disc obtained for a speed of 80,000 rpm ( Figure 7) has a concave shape-as in the previous cases, while the curve obtained for the aluminium disc has changed in nature and took a slightly convex shape. This shape demonstrates that the nature of the operation of the turbocharger compressor is typical [43]. Nevertheless, at this speed, the parameters achieved by both discs are similar. ...
This paper describes a novel method for the experimental validation of numerically optimised turbomachinery components. In the field of additive manufacturing, numerical models still need to be improved, especially with the experimental data. The paper presents the operational characteristics of a compressor wheel, measured during experimental research. The validation process included conducting a computational flow analysis and experimental tests of two compressor wheels: The aluminium wheel and the 3D printed wheel (made of a polymer material). The chosen manufacturing technology and the results obtained made it possible to determine the speed range in which the operation of the tested machine is stable. In addition, dynamic destructive tests were performed on the polymer disc and their results were compared with the results of the strength analysis. The tests were carried out at high rotational speeds (up to 120,000 rpm). The results of the research described above have proven the utility of this technology in the research and development of high-speed turbomachines operating at speeds up to 90,000 rpm. The research results obtained show that the technology used is suitable for multi-variant optimization of the tested machine part. This work has also contributed to the further development of numerical models.
... The former is a series of noise peaks occur at blade passing frequency (BPF) and its harmonics, while the latter covers a wide frequency range that researchers are interested in [13][14][15][16][17][18][19]. Furthermore, "buzz-saw" tones are also important acoustic phenomena in a turbocharger compressor, which was introduced in the numerical and experimental work o Sharma et al [20][21][22]. It is worthwhile to point out that characteristics of compressor aerodynamic noise vary with the compressor working condition, which makes compressor noise more complex. ...
... Meanwhile, the variation of pressure fluctuations decreases from P1 to P5, which indicates that the blade surface roughness mainly affects the pressure fluctuation near leading edge. This is similar to the compressor flow observed in Fig. 11.The relationship between compressor pressure fluctuation and noise has been discussed in the references [17,21], which state that the high pressure fluctuation induces high compressor noise in most cases. Thus, it is speculated that a compressor with high roughness value has a high noise level, especially and in this research. ...
A numerical study was conducted to investigate the effects of blade surface roughness on compressor performance and tonal noise emission. The equivalent sand-grain roughness model was used to account for blade surface roughness, and a hybrid method that combines computational fluid dynamics and boundary element method was used to predict compressor performance and tonal noise. The numerical approach was validated against experimental data for a baseline compressor. Nine different cases with different blade surface roughness were studied in this paper, the global performance was analyzed under compressor design speed, and the tonal noise level was predicted under the design condition. The results indicate that compressor total-to-total pressure ratio and isentropic efficiency were gradually decreased with the increasing blade surface roughness. Besides, the blade total pressure loss coefficient and the efficiency loss coefficient were also increased. It was found that the reverse flow at the leading edge of compressor rotor blades reduced blade loading. The pressure fluctuation at the leading edge showed that the peak of pressure fluctuations increased as the blade surface roughness was increased. The sound pressure level at blade-passing frequency shows a significant change with variation in blade surface roughness, which results in an increased total noise level. Furthermore, it was shown that the blade surface roughness had nearly no influence on acoustic directivity, but the sound pressure level increased with the increase in roughness, especially at blade-passing frequency.
... The flow characteristics predicted by the numerical model were validated using the PIV flow measurements at a plane upstream to the impeller and a reasonable correlation between numerical and measured acoustic spectra [9] was observed. Reduced order modelling of flow variables using Dynamic Mode Decomposition (DMD) [11,5] and Proper Orthogonal Decomposition (POD) [12,13] are being actively used to investigate the flow mechanisms. Semlitsch and Mihăescu [11] and Sundström et al. [9] analysed the flow instabilities associated with the compressor operating at lower mass flow rates while Sharma et al. [12,13] explored links between high-energy flow and acoustic features using mode decomposition. ...
... Reduced order modelling of flow variables using Dynamic Mode Decomposition (DMD) [11,5] and Proper Orthogonal Decomposition (POD) [12,13] are being actively used to investigate the flow mechanisms. Semlitsch and Mihăescu [11] and Sundström et al. [9] analysed the flow instabilities associated with the compressor operating at lower mass flow rates while Sharma et al. [12,13] explored links between high-energy flow and acoustic features using mode decomposition. ...
... Tonal features, including the 'mid-tones' that are seen in between the two rotating order (RO) tones, are heavily accentuated in the numerical spectra as compared to the measured spectra. Furthermore, broadband elevation in the diffuser spectra, which is expected to be caused by the interaction of diffuser outlet flow with the volute tongue [12,29], is also not observed in the corresponding numerical spectra. Overall trend and dominant features like BPF and RO tones are reasonably captured in the numerical spectra of inducer and diffuser probes. ...
Developments in computing infrastructure and methods over the last decade have enhanced the potential of numerical methods to reasonably predict the aerodynamic noise. The generation and propagation of the flow induced noise are aerodynamic phenomena. Although the fluid flow dynamics and the resultant acoustics are both governed by mass and momentum conservation equations, former is of convective and/or diffusive nature while the latter is propagative showing insignificant attenuation due to viscosity except for small viscothermal losses. Aeroacoustic modelling of systems with intricate geometries and complex flow is still not mature due to challenges in the accurate tractable representation of turbulent viscous flows. Therefore, state-of-the-art for computing flow-induced noise in small centrifugal compressors is reviewed and critical evaluation of various parameters in the numerical model is undertaken in this work. The impact of various turbulence formulations along with corresponding spatial and temporal resolutions on performance and acoustic predictions are quantified. The performance predictions are observed to be within 1.5% of the measured values irrespective of turbulence and timestep parameters. The noise generated by the impeller is observed to be reasonably correlated with the measurements and the absolute values of the sound pressure levels along with decay rates predicted by LES and SBES formulations are better than the similar predictions from DES and URANS formulations. The impact of timestep size is observed and is determinant of the frequency up to which spectra can be appropriately resolved. Furthermore, results emphasise the importance of high spatial resolution for scale resolving turbulence formulations to yield better results and the information can be used to select appropriate numerical configuration considering time and accuracy trade-offs.
... The acoustic performance of radial turbochargers can be divided into passive and active categories. 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. ...
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.
