scholarly journals Effects of a Nonuniform Tip Clearance Profile on the Performance and Flow Field in a Centrifugal Compressor

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Yohan Jung ◽  
Minsuk Choi ◽  
Seonghwan Oh ◽  
Jehyun Baek
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Diffusion Processes ◽  
Leading Edge ◽  
Tip Clearance ◽  
Computational Results ◽  
Vaneless Diffuser ◽  
Trailing Edge ◽  
Flow Simulations ◽  
Compressor Performance

This paper presents a numerical investigation of the effects of a nonuniform tip clearance profile on the performance and flow field in a centrifugal compressor with a vaneless diffuser. This study focuses in particular on the magnitude and location of the wake. Six impellers with different tip clearance profiles were tested in the flow simulations. The accuracy of the numerical simulations was assessed by comparing the experimental data with the computational results for a system characterized by the original tip clearance. Although the performance improved for low tip clearances, a low tip clearance at the trailing edge improved the compressor performance more significantly than a low tip clearance at the leading edge. The flow field calculated for a system characterized by a low tip clearance at the trailing edge produced a more uniform velocity distribution both in the circumferential and in the axial directions at the impeller exit because the wake magnitude was reduced. As a consequence, this impeller provided a better potential for diffusion processes inside a vaneless diffuser.

Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage

2018 ◽  
Author(s):  
Masanao Kaneko ◽  
Hoshio Tsujita
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Transonic Centrifugal Compressor ◽  
Tip Leakage Flows

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.

Non-Uniform Two-Phase Flow of Supercritical Carbon Dioxide Centrifugal Compressor

2020 ◽  
Author(s):  
Wenrui Bao ◽  
Ce Yang ◽  
Li Fu ◽  
Changmao Yang ◽  
Lucheng Ji
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Static Pressure ◽  
Leading Edge ◽  
Phase Region ◽  
Tip Clearance ◽  
Two Phase ◽  
Supercritical Carbon

Abstract An asymmetric structure of volute in a supercritical carbon dioxide centrifugal compressor induces a non-uniform circumferential distribution of the upstream flow field, which inevitably affects the formation of a two-phase region of carbon dioxide in an impeller. In this work, unsteady simulations for centrifugal compressors were conducted. First, the influence of low static strip induced by low static pressure near volute tongue on the impeller flow field was presented. Then, the non-uniform flow field distribution in the impeller passages and flow characteristics of the passages at the impeller inlet were obtained. Finally, the two-phase regions in the impeller were presented. The results demonstrate that for a centrifugal compressor with volute, the two-phase region appears not only on the suction surface of the leading edge of the blade, but also in some impeller passages, on the pressure surface of the blade near the leading edge, and in the leading edge and mid-chord of tip clearance, under the design conditions. The low static pressure strip induced by the volute leads to a high-speed region in the impeller passages where the temperature and pressure of supercritical carbon dioxide fall below the critical point and carbon dioxide enters the two-phase region. Meanwhile, the static pressure on the blade surface is distorted under the influence of a high-speed region in the passages, resulting in the formation of a two-phase region at the tip clearance. The flow distortion of passages at the impeller inlet results in the appearance of two-phase regions on the both sides of leading edge of the blade. The dryness on the suction side of the blade leading edge and the leading edge of the tip clearance is lower, which indicated that the proportion of liquid-phase carbon dioxide is higher in these two-phase regions.

Application of a Multi-Block CFD Code to Investigate the Impact of Geometry Modeling on Centrifugal Compressor Flow Field Predictions

1996 ◽  
Author(s):  
Michael D. Hathaway ◽  
Jerry R. Wood
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Block Code ◽  
Tip Clearance ◽  
Trailing Edge ◽  
Flow Angle ◽  
Significant Difference ◽  
Single Block ◽  
The Impact ◽  
Actual Geometry

CFD codes capable of utilizing multi-block grids provide capability to analyze the complete geometry of centrifugal compressors including, among others, multiple splitter rows, tip clearance, blunt trailing edges, fillets, and slots between moving and stationary surfaces. Attendant with this increased capability is potentially increased grid setup time and more computational overhead — CPU time and memory requirements — with the resultant increase in “wall clock” time to obtain a solution. If the increase in “difficulty” of obtaining a solution significantly improves the solution from that obtained by modeling the features of the tip clearance flow or the typical bluntness of a centrifugal compressor’s trailing edge, then the additional burden is worthwhile. However, if the additional information obtained is of marginal use then modeling of certain features of the geometry may provide reasonable solutions for designers to make comparative choices when pursuing a new design. In this spirit a sequence of grids were generated to study the relative importance of modeling versus detailed gridding of the tip gap and blunt trailing edge regions of the NASA large low speed centrifugal compressor for which there is considerable detailed internal laser anemometry data available for comparison. The results indicate: 1) There is no significant difference in predicted tip clearance mass flow rate whether the tip gap is gridded or modeled. 2) Gridding rather than modeling the trailing edge results in better predictions of some flow details downstream of the impeller, but otherwise appears to offer no great benefits. 3) The pitchwise variation of absolute flow angle decreases rapidly up to 8% impeller radius ratio and much more slowly thereafter. Although some improvements in prediction of flow field details are realized as a result of analyzing the actual geometry there is no clear consensus that any of the grids investigated produced superior results in every case when compared to the measurements. However, if a multi-block code is available it should be used as it has the propensity for enabling better predictions than a single block code which requires modeling of certain geometry features. If a single block code must be used some guidance is offered for modeling those geometry features which can’t be directly gridded.

Mechanism of affecting the performance and internal flow field of an axial flow subsonic compressor with self-recirculation casing treatment

2020 ◽  
pp. 095441002094267
Author(s):  
Hao G Zhang ◽  
Fei Y Dong ◽  
Wei Wang ◽  
Wu L Chu ◽  
Song Yan
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Internal Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Stall Margin ◽  
Casing Treatment ◽  
Leakage Flows ◽  
Blade Tip ◽  
Compressor Performance

This investigation aims to understand the mechanisms of affecting the axial flow compressor performance and internal flow field with the application of self-recirculation casing treatment. Besides, the potentiality of further enhancing the compressor performance and stability by optimizing the geometric structure of self-recirculation casing treatment is discussed in detail. The results show that self-recirculation casing treatment generates about 7.06, 7.89% stall margin improvements in the experiment and full-annulus unsteady calculation, respectively. Moreover, the compressor total pressure and isentropic efficiency are improved among most of operating points, and the experimental and calculated compressor peak efficiencies are increased by 0.7% and 0.6%, respectively. The comparisons between baseline shroud and self-recirculation casing treatment show that the flow conditions of the compressor rotor inlet upstream are improved well with self-recirculation casing treatment, and the degree of the pressure enhancement in the blade top passage for self-recirculation casing treatment is higher than that for baseline. Further, self-recirculation casing treatment can restrain the leading edge-spilled flows made by the blade tip clearance leakage flows and weaken the blade tip passage blockage. Hence, the flow loss near the rotor top passage is reduced after the application of self-recirculation casing treatment. The rotor performance and stability for self-recirculation casing treatment are greater than those for baseline. The flow-field analyses also indicate that the adverse effects caused by the clearance leakage flows of the blades tip rear are greater than those made by the clearance leakage flows of the blades leading edge. When one injecting part of self-recirculation casing treatment is aligned with the inlet of one blade tip passage, the flow-field quality in the passage is not the best among all the passages between two adjacent injecting parts of self-recirculation casing treatment. Further, the flow-field analyses also indicate that the effect of the relative position between the blade and self-recirculation casing treatment on the flows in the self-recirculation casing treatment may be ignored during the optimization of the recirculating loop configuration.

Investigation of the instability mechanisms in a turbocharger centrifugal compressor with a vaneless diffuser by means of unsteady simulations

2016 ◽  
Vol 231 (11) ◽  
pp. 1558-1567 ◽  
Author(s):  
Xinqian Zheng ◽  
Anxiong Liu ◽  
Zhenzhong Sun
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Simulation Method ◽  
Great Accuracy ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Low Velocity

The stable-flow range of a compressor is predominantly limited by surge and stall. In this paper, an unsteady simulation method was employed to investigate the instability mechanisms of a high-speed turbocharger centrifugal compressor with a vaneless diffuser. In comparison with the variation in the pressure obtained by dynamic experiments on the same compressor, unsteady simulations show a great accuracy in representing the stall behaviour. The predicted frequency of the rotating stall is 22.5% of the rotor frequency, which agrees with to the value for the high-frequency short-term rotating stall obtained experimentally. By investigating the instability of the flow field, it is found that the unstable flow of the turbocharger compressor at high rotational speeds is caused by the tip clearance leakage flow and the ‘backflow vortices’ originating from the interaction of the incoming flow and the backflow in the tip region of the passages. The asymmetric volute helps to induce the occurrence of stall in certain impeller passages because it generates an asymmetric flow field. The high-pressure low-velocity area from the 180° circumferential position to the 270° circumferential position is dominant and strengthens the backflow at the trailing edge of the impeller, finally triggering the stall.

Prediction of Centrifugal Compressor Performance From Choke Through Stall With a Physical Throttle

2015 ◽  
Author(s):  
Xiaocheng Zhu ◽  
Kai Jia ◽  
Zhaohui Du
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Internal Flow ◽  
Ambient Conditions ◽  
Vaneless Diffuser ◽  
Flow Physics ◽  
Flow Simulations ◽  
Performance Curves ◽  
Compressor Performance

Numerical simulation results of the internal flow field of a centrifugal compressor with vaneless diffuser are presented by solving three-dimensional Reynolds averaged compressible NS equations using CFD software CFX. A physical throttle added at the downstream of the volute has been successful in stabilizing the flow at all flow rates. Ambient conditions are held fixed at both the inlet and exit of the domain. Numerical results of an investigation in which the predicted aerodynamic performance of the centrifugal compressor with vaneless diffuser is compared with the measured experimental data over the entire design speedline from choke through stall are presented. Performance curves of different components are also presented. A physical throttle approach for the prediction of the unsteady flow physics that lead to stall is proposed and a series of unsteady-flow simulations are used to illustrate the instability flow physics in the impeller, the vaneless diffuser and the volute.

Application of a Multi-Block CFD Code to Investigate the Impact of Geometry Modeling on Centrifugal Compressor Flow Field Predictions

1997 ◽  
Vol 119 (4) ◽  
pp. 820-830
Author(s):  
M. D. Hathaway ◽  
J. R. Wood
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Block Code ◽  
Tip Clearance ◽  
Trailing Edge ◽  
Flow Angle ◽  
Significant Difference ◽  
Single Block ◽  
The Impact ◽  
Actual Geometry

CFD codes capable of utilizing multi-block grids provide the capability to analyze the complete geometry of centrifugal compressors including, among others, multiple splitter rows, tip clearance, blunt trailing edges, fillets, and slots between moving and stationary surfaces. Attendant with this increased capability is potentially increased grid setup time and more computational overhead—CPU time and memory requirements—with the resultant increase in “wall clock” time to obtain a solution. If the increase in “difficulty” of obtaining a solution significantly improves the solution from that obtained by modeling the features of the tip clearance flow or the typical bluntness of a centrifugal compressor’s trailing edge, then the additional burden is worthwhile. However, if the additional information obtained is of marginal use, then modeling of certain features of the geometry may provide reasonable solutions for designers to make comparative choices when pursuing a new design. In this spirit a sequence of grids were generated to study the relative importance of modeling versus detailed gridding of the tip gap and blunt trailing edge regions of the NASA large low-speed centrifugal compressor for which there is considerable detailed internal laser anemometry data available for comparison. The results indicate: (1) There is no significant difference in predicted tip clearance mass flow rate whether the tip gap is gridded or modeled. (2) Gridding rather than modeling the trailing edge results in better predictions of some flow details downstream of the impeller, but otherwise appears to offer no great benefits. (3) The pitchwise variation of absolute flow angle decreases rapidly up to 8 percent impeller radius ratio and much more slowly thereafter. Although some improvements in prediction of flow field details are realized as a result of analyzing the actual geometry there is no clear consensus that any of the grids investigated produced superior results in every case when compared to the measurements. However, if a multi-block code is available, it should be used, as it has the propensity for enabling better predictions than a single block code, which requires modeling of certain geometry features. If a single block code must be used, some guidance is offered for modeling those geometry features that cannot be directly gridded.

Improvement in the stability of a turbocharger centrifugal compressor by tip leakage control

2016 ◽  
Vol 231 (5) ◽  
pp. 700-714 ◽  
Author(s):  
Saeed Mirzaee ◽  
Xinqian Zheng ◽  
Yun Lin
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Dominant Factor ◽  
Tip Leakage Flow ◽  
Jet Injection ◽  
Tip Leakage ◽  
Air Jet ◽  
Stable Flow

The occurrence of surge or stall in a centrifugal compressor and the role of the tip clearance flow in the instability in the centrifugal compressor are investigated in this study. A computational method is used to study the flow field in the centrifugal compressor in order to gain a better understanding of the surge or stall mechanism. It is found that, near surge or stall conditions, the tip leakage flow at the leading edge deflects more upstream; as the deflection increases, a more severe spillage occurs which finally leads to instability of the compressor. A ring air jet injection is used to eliminate the instabilities and to extend the stable flow range of the compressor. Using an air jet injection, the stable flow range of the compressor was successfully increased with minimal decrease in the efficiency of the compressor. The effects of different injection parameters such as the mass flow, the yaw angle, the injection angle, the slot width and the slot distance on the compressor flow field are studied, and an optimum design for the air jet injection is developed. Further investigation of the compressor with the optimum injection configuration shows that, near surge or stall conditions, the tip leakage at the leading edge is still under control, manifesting a much smaller spillage than does the Dresser–Rand Datum compressor without an air injection. The dominant factor for the instability of the compressor with an injection is found to be the leading-edge separation rather than the tip leakage.

Effects of Diffuser Vane Geometries on Compressor Performance and Noise Characteristics in a Centrifugal Compressor

2013 ◽  
Author(s):  
Yohei Morita ◽  
Nobumichi Fujisawa ◽  
Takashi Goto ◽  
Yutaka Ohta
Keyword(s):  
Centrifugal Compressor ◽  
Noise Level ◽  
Leading Edge ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Numerical Techniques ◽  
Vaned Diffuser ◽  
Noise Characteristics ◽  
Edge Vortex ◽  
Compressor Performance

The effects of the diffuser vane geometries on the compressor performance and noise characteristics of a centrifugal compressor equipped with vaned diffusers were investigated by experiments and numerical techniques. Because we were focusing attention on the geometries of the diffuser vane’s leading edge, diffuser vanes with various leading edge geometries were installed in a vaned diffuser. A tapered diffuser vane with the tapered portion near the leading edge of the diffuser’s hub-side could remarkably reduce both the discrete frequency noise level and broadband noise level. In particular, a hub-side tapered diffuser vane with a taper on only the hub-side could suppress the development of the leading edge vortex (LEV) near the shroud side of the diffuser vane and effectively enhanced the compressor performance.

Effects of Non-Axisymmetric Volute on Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

2020 ◽  
Author(s):  
Zitian Niu ◽  
Zhenzhong Sun ◽  
Baotong Wang ◽  
Xinqian Zheng
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Stability Boundary ◽  
Rotating Stall ◽  
Evolution Process ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Centrifugal Compressors ◽  
Specific Location

Abstract Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources to induce the non-axisymmetric flow in a centrifugal compressor, which has an important effect on the performance of compressors. However, the influence of volute on rotating stall is not clear. Therefore, the effects of volute on rotating stall by experimental and numerical simulation have been explored in this paper. It’s shown that one rotating stall cell generates in a specific location and disappears in another specific location of the vaneless diffuser as a result of the distorted flow field caused by the volute. Also, the cells cannot stably rotate in a whole circle. The frequency related to rotating stall captured in the experiment is 43.9% of the impeller passing frequency (IPF), while it is 44.7% of IPF captured by three-dimensional unsteady numerical simulation, which proves the accuracy of the numerical method in this study. The numerical simulation further reveals that the stall cell initialized in a specific location can be split into several cells during the evolution process. The reason for this is that the blockage in the vaneless diffuser induced by rotating stall is weakened by the mainstream from the impeller exit to make one initialized cell disperse into several ones. The volute has an important influence on the generation and evolution process of the rotating stall cells of compressors. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that rotating stall can be weakened or suppressed, which is helpful to widen the operating range of centrifugal compressors.

Sign in / Sign up

Export Citation Format

Share Document