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

[EN] 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 (UAVs), auxiliary power units (APUs), 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.The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: The project is sponsored and supported by BorgWarner Turbo Systems and the Regional Growth Fund (RGF Grant Award 01.09.07.01/1789C).Sharma, S.; Garcia Tiscar, J.; Allport, JM.; Barrans, S.; Nickson, AK. (2020). Effects of ported shroud casing treatment on the acoustic and flow behaviour of a centrifugal compressor. International Journal of Engine Research. 21(6):998-1011. https://doi.org/10.1177/1468087419880431S998101121

Enhancing the surge margin of a Centrifugal Compressor with different Blade Tip Geometry

The reliability operation for small fuel cells and hybrid fuel cell with gas turbine requires centrifugal compressor surge prevention. This study concerns a high speed centrifugal compressor stage with different blade tip geometries. The investigations were performed with unsteady three-dimensional, compressible flow simulations. A novel parameterization method has been developed to alter the tip geometry of an impeller blade. Different tip geometries are investigated includes flat tip blade, main blade winglet, main and splitter blade winglet and finally pressure side grooved tip. The performance and internal flow results are presented at surge, design and near choke points. The conclusion is that the tip geometry has a significant effect on the compressor performance and the operation stability at lower flow rates. The pressure ratio and surge margin for the blades with winglet have been improved, and decreased for the grooved tip geometry. More uniform flow at impeller outlet with winglet blade. The use of winglet tip displaces the tip leakage vortex away from the blade and weakening the impingement effect. The winglet tip reduces the aerodynamic losses by unloading the tip section, reducing the leakage flow rate and turning the leakage flow in a more stream wise direction

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

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

[EN] 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.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The project was sponsored and supported by the BorgWarner Turbo Systems and the Regional Growth Fund (RGF Grant Award 01.09.07.01/1789C).Sharma, S.; Garcia Tiscar, J.; Allport, JM.; Barrans, S.; Nickson, AK. (2021). Evolution of flow characteristics in a centrifugal compressor with an increase in operating speed. International Journal of Engine Research. 22(5):1592-1604. https://doi.org/10.1177/1468087420916606S1592160422

Parametric study of casing treatment for turbine blade in aero engine application

Tato diplomová práce otevírá otázku možnosti zlepšení vlastností kompresoru za pomoci numerické simulace proudění. Hlavním cílem je zvýšení operačního rozsahu na jednom stupni axiálního kompresoru s využitím zařízení pro pasivní kontrolu proudu umístěných ve skříni kompresoru. Prvně bylo prověřeno chování víru ve štěrbině mezi lopatkou a skříní následně celkové charakteristiky původního rotoru. Při snižování hmotnostního průtoku simulace odhalila zvýšený vliv koncového výru na hlavní proud. Navíc byl největší koncový vír v režimu blízkém odtrhávání proudění. Z tohoto důvodu byly pro kontrolu koncového víru navrženy čtyři verze drážkování implementováním sinusové úpravy geometrie. Tři ze čtyř testovaných verzí ukázaly možnost výrazného zvýšení rozsahu stabilního proudění. Nicméně prodlužení operačního rozsahu mělo za následek snížení celkové účinnosti. Na konec této práce jsou navrženy doporučení pro další výzkum.This present thesis addresses the question whether it is possible to obtain compressor’s performance increase with the aid of flow numerical simulations. The main objective is to extend the stable operating range of an axial single stage compressor by using passive flow control devices located on the compressor shroud. Firstly, it is examined the rotor’s tip leakage flow and after that, the overall performance without control. When reducing the mass flow rate, the simulation reveals an increased influence of tip vortex on the main flow. Additionally, large tip vortex is observed close to stall condition. Therefore, four different casing treatments are designed by implementing sinusoidal reshaping to control the tip vortex. Three out off four tested configurations showed ability to extend significantly the stall margin region. However, an increase in the operability had a penalty for the efficiency. On the end of the presented work recommendations are proposed for future research.

The impact of housing features relative location on a turbocharger compressor flow

This work presents an investigation on a flow phenomenon marked by in-plane velocity non-uniformity associated with a ported shroud turbocharger compressor observed upstream of the compressor inlet at lower operating speeds. The effect of structural struts in the ported shroud (PS) cavity and the location of the volute tongue on velocity non-uniformity is studied in this paper by numerically modelling the complete compressor stage using a (Un)steady Reynolds Averaged Navier-Stokes (RANS & URANS) approach. The results show that the amplitude of in-plane velocity non-uniformity is reduced by removing the struts from the PS cavity. Furthermore, the change in location of the volute tongue is shown to either substantially diminish or enhance the amplitude of velocity non-uniformity based on the relative position of the volute tongue and the struts. The study concludes that the velocity non-uniformity is dependent on the coupled effect of volute tongue and the strut position in the PS cavity

Noise of Turbocharger Compressors

International audienceNoise produced by turbocharger compressors is becoming a major concern of turbocharging industry. But confusion exists regarding the sources of the noise. This paper discusses this noise from an aerodynamicist's point of view. Blade passing frequency noise and flow instability related noise are in particularly examined. Focus is on how these two noises are generated and how they may be controlled at source level. The aerodynamic causes of the noises are described and identified, and measures to reduce them at compressor design stage are proposed

Vaned recess anti-stall for axial-flow fans and compressors

The study of anti-stall techniques for fans and compressors has never been more significant, since the potential applications were recognised in gas turbines, tunnel ventilation (jet fans) and industrial process where fans/compressors would benefit from the devices. This thesis will discuss the techniques achieving competitiveness by modifying the conventional casing design of the fan and compressor, which is referred to as casing treatments, taking into account the change of maximum efficiency and flow range. An experimental investigation to examine the influence of the vaned recess casing treatment on stall margin, operating efficiency and flow field of a low speed axial flow fan with aerospace type blade loading is presented. Different geometrical designs of the vaned passages were examined and more than 65% of stall margin improvements and over twice pressure rise with insignificant peak efficiency change were obtained. Experiments to examine the effect of casing treatments on the flow field were carried out using the same fan rig with a tip clearance of 1.2% of the blade height. A high frequency data acquisition system including both hardware and software was developed and the 3-D flow measurements with a slanted hot-wire were undertaken. The first detailed results of flow measurements associated with the vaned recess casing treatment are presented, including both time-averaged and ensemble-averaged measurement results. The flow features in both the solid casing and treated casing builds are captured and comparison between the builds presented. The results revealed that the stall margin improvement due to the casing treatment was not achieved by reducing the incidence nor by increasing the total pressure in the tip region. It appeared that the combined functions of elimination of the whirling flow, the removal of the randomness of the inlet flow and modification of the tip clearance flow are salient features associated with the mechanism of the treatment. The steady flow field of the test fan with various tip clearances has also been simulated in the rotating frame with computational fluid dynamics (CFD) to investigate the clearance effect on the end-wall flow development and to elucidate the behaviour of the tip leakage flow, and hopefully shed more light onto the flow phenomena involved