Numerical Investigation of Negative Flow Characteristics in a Centrifugal Compressor with Vaned Diffuser and Internal Volute

2021 ◽  
Author(s):  
Bing Qiao ◽  
Yaping Ju ◽  
Chuhua Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Flow Separation ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Surface Flow ◽  
Flow Dynamics ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Compressor Aerodynamics

Abstract Negative flow from the outlet through the volute, diffuser, and impeller to the inlet of the centrifugal compressor can occur continuously as a result of system accidents. A physical comprehension of negative flow dynamics is crucial in evaluating the compressor characteristics under abnormal working conditions, and is also important in exploring the compressor aerodynamics over the entire flow range. However, limited research on the negative flow dynamics in centrifugal compressors, particularly with the consideration of vaned diffusers and volutes, can be found. This study aims to determine the compressor characteristics, including the negative flow rates of a centrifugal compressor, and to clarify the negative flow mechanism under the interaction of the volute, diffuser, and impeller. The last stage of a four-stage centrifugal compressor, including an internal volute, a vaned diffuser, and a closed impeller was simulated under both positive and negative flow conditions using a computational fluid dynamics (CFD) model. The results show that the pressure ratio-negative flow characteristic is almost matched with a parabolic curve. At negative flow rates, the backflow generated on the hub and shroud sides in the impeller expands upstream and causes flow separation in the diffuser. The negative flow enters the impeller at a large incidence angle and results in jet wall impingement on the pressure surface, flow spillage over the trailing edge, and flow separation near the suction surface. The impeller partially acts as a turbine impeller and performs negative work on the fluid. This work is of scientific significance to enrich the compressor aerodynamics in accident scenarios and of engineering value to improve the advanced design of compressor protection systems.

Effect of Vaned Diffuser on a Modified Turbocharger Centrifugal Compressor Performance

2014 ◽  
Vol 663 ◽  
pp. 347-353
Author(s):  
Layth H. Jawad ◽  
Shahrir Abdullah ◽  
Zulkifli R. ◽  
Wan Mohd Faizal Wan Mahmood
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Width Ratio ◽  
Outlet Section ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Minimum Width

A numerical study that was made in a three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an automotive turbo charger. In order to study the influence of vaned diffuser meridional outlet section with a different width ratio of the modified centrifugal compressor. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between the compressor impeller along the vaned diffuser. The aerodynamic characteristics were compared under different meridional width ratio. In addition, the velocity vectors in diffuser flow passages, and the secondary flow in cross-section near the outlet of diffuser were analysed in detail under different meridional width ratio. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken using commercial software so-called ANSYS CFX, to predict numerically the performance charachteristics. The results were generated from CFD and were analysed for better understanding of the fluid flow through centrifugal compressor stage and as a result of the minimum width ratio the flow in diffuser passage tends to be uniformity. Moreover, the backflow and vortex near the pressure surface disappear, and the vortex and detachment near the suction surface decrease. Conclusively, it was observed that the efficiency was increased and both the total pressure ratio and static pressure for minimum width ratio are increased.

Stability Improvement of a Turbocharger Centrifugal Compressor by a Nonaxisymmetric Vaned Diffuser

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Xinqian Zheng ◽  
Zhenzhong Sun ◽  
Tomoki Kawakubo ◽  
Hideaki Tamaki
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Centrifugal Compressor ◽  
Flow Separation ◽  
Static Pressure ◽  
Control Method ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Vaned Diffuser ◽  
Positive Effects

The nonuniformity of the flow field induced by a nonaxisymmetric volute significantly degrades the stability of a turbocharger centrifugal compressor. In this paper, a nonaxisymmetric vaned diffuser is investigated as a nonaxisymmetric flow control method using both three-dimensional computational fluid dynamics (CFD) and experiment. The numerical study first focuses on the relationship between the flow field and the static pressure distortion, and the steady CFD results indicate that the positive static pressure gradient in the rotating direction facilitates flow separation in the vaned diffuser and induces a nonuniform flow field. A nonaxisymmetric flow control method with variable stagger and solidity of the vaned diffuser is developed to suppress the flow separation, and the guideline of the method suggests narrowing flow passages where the flow separates or closing diffuser vanes upstream of flow separations. Steady CFD also presents the flow field of the investigated turbocharger centrifugal compressor with volute, and flow separation is found in the flow passages near the volute tongue. Under the guidance of the nonaxisymmetric flow control method, several nonaxisymmetric vaned diffusers are designed to make the flow field uniform, which are believed to be beneficial for compressor stability. Finally, an experiment is carried out to validate the positive effects of the nonaxisymmetric vaned diffuser for stability improvement. The test data show that Non-AxisVD (with a nonaxisymmetric vaned diffuser) extends the stable flow range (SFR) of the compressor by 26% compared with the AxisVD (with an axisymmetric vaned diffuser), at the cost of acceptable decreases in the maximum total pressure ratio and peak efficiency.

scholarly journals Simulation of Flow in Turbopump Vaneless and Vaned Diffusers with Fluid Injection

2000 ◽  
Vol 6 (1) ◽  
pp. 57-65
Author(s):  
Ali Ogut ◽  
Diego Garcia Pastor
Keyword(s):  
Flow Separation ◽  
Flow Region ◽  
Design Flow ◽  
Low Flow ◽  
Fluid Injection ◽  
Bottom Surface ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Wide Range

In future space missions by NASA there will be a need for “Space Transfer Vehicles” to perform varying orbital transfers and descents. This requires engines capable of producing different levels of thrust. To accomplish this, the turbopumps employed in these engines should efficiently provide a wide range of flow outputs. However, current fuel and oxidizer turbopumps with vaned diffusers do not perform efficiently at off-design (low) flow rates mainly due to flow separation in the vaned diffuser.This paper evaluates the effectiveness of boundary layer control by fluid injection (blowing) for suppressing or eliminating the flow separation in a vaned diffuser. A 3-D flow model including vaneless and vaned diffusers of a liquid hydrogen (LH2) turbopump is studied using the CFD code FIDAP. The paper presents the results of the model at design and offdesign flow conditions.The model results showed that flow separation occurs at the top or suction surface of the vaneless diffuser and at the bottom or pressure surface of the vaned diffuser at off-design flow rates. When fluid injection was applied through the bottom surface of the vaned diffuser, the separated flow region was reduced almost entirely, resulting in an increase in pressure recovery of up to 21% with varying fluid injection rates. Results also showed that there is an optimum injection rate which is most effective in reducing or eliminating the region of flow separation.

scholarly journals Analysis of the Unsteady Flow Field in a Centrifugal Compressor from Peak Efficiency to Near Stall with Full-Annulus Simulations

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Yannick Bousquet ◽  
Xavier Carbonneau ◽  
Guillaume Dufour ◽  
Nicolas Binder ◽  
Isabelle Trebinjac
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Suction Side ◽  
Operating Point ◽  
Peak Efficiency ◽  
Vaned Diffuser

This study concerns a 2.5 pressure ratio centrifugal compressor stage consisting of a splittered unshrouded impeller and a vaned diffuser. The aim of this paper is to investigate the modifications of the flow structure when the operating point moves from peak efficiency to near stall. The investigations are based on the results of unsteady three-dimensional simulations, in a calculation domain comprising all the blade. A detailed analysis is given in the impeller inducer and in the vaned diffuser entry region through time-averaged and unsteady flow field. In the impeller inducer, this study demonstrates that the mass flow reduction from peak efficiency to near stall leads to intensification of the secondary flow effects. The low momentum fluid accumulated near the shroud interacts with the main flow through a shear layer zone. At near stall condition, the interface between the two flow structures becomes unstable leading to vortices development. In the diffuser entry region, by reducing the mass flow, the high incidence angle from the impeller exit induces a separation on the diffuser vane suction side. At near stall operating point, vorticity from the separation is shed into vortex cores which are periodically formed and convected downstream along the suction side.

Effect of double splitter blades position in a centrifugal compressor impeller

2018 ◽  
Vol 233 (6) ◽  
pp. 689-701
Author(s):  
Adil Malik ◽  
Qun Zheng
Keyword(s):  
Performance Improvement ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Surface Flow ◽  
Flow Conditions ◽  
Suction Surface ◽  
Pressure Surface ◽  
Compressor Impeller ◽  
Novel Design ◽  
Total Pressure Ratio

This paper reveals a novel design of centrifugal compressor impeller with multisplitter blades for performance improvement. In order to investigate the effects of the location of the splitter between two main blades, two sample impellers were designed, keeping all flow conditions and impeller definitions same as the experimentally validated impeller: (1) with big splitter close to suction surface of main blade and smaller splitter close to pressure surface; (2) with small splitter close to suction surface of main blade and big splitter close to pressure surface. Flow field in both the impellers is analyzed and compared with the original experimentally validated impeller. Total pressure ratio is increased with improved efficiency in multisplitter blade impellers with the addition of pair of big and small splitters blades. It was identified that small splitter close to the suction surface of the main blade and big splitter close to the pressure surface has more uniform flow, reduced separation, and better efficiency than the placement of big splitter close to the suction surface.

Effect of Circumferential Static Pressure Non-Uniformity Caused by a Volute on Flow in High Pressure Ratio Centrifugal Compressor With Vaneless and Vaned Diffuser

2013 ◽  
Author(s):  
Hideaki Tamaki ◽  
Masaru Unno ◽  
Xinqian Zheng ◽  
Yangjun Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Gas Turbines ◽  
Static Pressure ◽  
Incidence Angle ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Operating Range ◽  
Surge Line

Centrifugal compressors are deemed to have a wide operating range. Recirculation devices, which comprise a bleed slot, an upstream slot and an annular cavity connecting them, are often used particularly compressors for turbochargers. They remove low energy fluid at the inducer and improve the incidence angle of the impeller leading edge, i.e. the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. The impeller of a centrifugal compressor is often housed in a volute. Since the geometry of the volute is not axisymmetric, the impeller might be surrounded by an asymmetric flow field, hence there is the potential to enlarge the compressor operating range and improve efficiency using a recirculation device with an asymmetrically-distributed bleed slot, referred to here as a non-axisymmetric recirculation device. The authors [1] applied non-axisymmetric recirculation devices to a compressor with a vaneless diffuser. The results showed the effectiveness of a non-axisymmetric recirculation device with a bleed slot partially channeled in the circumferential direction. They also showed that the surge line of the compressor characteristics, which is the line connecting the operational points of the smallest flow rates on all peripheral Mach numbers, was significantly affected by the change in the circumferential position of the bleed slot relative to the volute tongue. The tested compressor was originally designed to feature a vaned diffuser [2]. Enhancing the compressor operating range is the key for marine use turbochargers, integrally geared compressors, multistage compressors and gas turbines as well as automotive turbochargers. These compressors normally use vaned diffusers. In this study the authors tried to apply non-axisymmetric recirculation devices developed in their previous study [1] to compressors with a vaned diffuser. Moreover different circumferential positions of the bleed slot relative to the volute tongue were tested as well as the vanelss diffuser case. The change in the surge line of the compressor characteristics was much smaller compared to the compressor with the vaneless diffuser. The circumferential static pressure distributions in the compressors in combination with vaneless and vaned diffusers were measured to determine the above reason as well as conducting unsteady calculations with a simplified outlet boundary condition. These measurements and calculations showed that the impeller with the vaned diffuser was surrounded by a less distorted static pressure field than that with the vaneless diffuser. These results implied that the vaned diffuser depresses the spread of the circumferential static pressure non-uniformity effect caused by a volute to the impeller.

scholarly journals Investigation of Suction Flow Control on Centrifugal Compressor with Vaned Diffuser

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 583
Author(s):  
Suleyman Emre Ak ◽  
Sertac Cadirci
Keyword(s):  
Flow Control ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Performance Improvements ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses ◽  
Suction Flow

In this study, the effect of suction flow control on a centrifugal compressor at operation and stall flow rates was investigated using computational fluid dynamics (CFD). The compressor geometry was reconstructed from available open source profile data and the CFD analyses have been performed on this geometry using the appropriate mesh. To validate the CFD results, the compressor performance line was acquired and compared with the experimental results obtained at the design rotational speed. Then, suction flow control was employed at various suction slot positions with different suction flow rates to improve the performance of the compressor at operation and stall flow rates. As a result of the suction flow control trials, 0.85% increase in pressure ratio and 0.8% increase in adiabatic efficiency were achieved while the compressor was running at operation flow rate. The performance improvements corresponding to the stall flow rate of the compressor were 2.5% increase in pressure ratio and 2% increase in adiabatic efficiency.

scholarly journals Comparison of Two Diffusers in a Transonic Centrifugal Compressor

2003 ◽  
Vol 9 (4) ◽  
pp. 279-284 ◽  
Author(s):  
Koji Nakagawa ◽  
Hiroshi Hayami ◽  
Yuichi Keimi
Keyword(s):  
Numerical Simulation ◽  
Centrifugal Compressor ◽  
Flow Separation ◽  
Pressure Ratio ◽  
Maximum Pressure ◽  
Vaned Diffuser ◽  
Transonic Centrifugal Compressor ◽  
Flow Mechanisms ◽  
Series Of Experiments ◽  
Low Solidity Cascade Diffuser

Flow mechanisms suppressing the flow separation in two diffusers, a low-solidity cascade diffuser and a vaned diffuser with additional small vanes near the inlet, were compared mainly by numerical simulation. As the superiority of the low-solidity cascade diffuser was expected, a series of experiments was conducted using a transonic centrifugal compressor with a maximum pressure ratio of 7. The performance of the compressor with the vaned diffuser was comparable to that of the low-solidity cascade diffuser only between the surge point and the design flowrate at a pressure ratio of 3.5. The maximum flowrate of the vaned diffuser was lower than that of the low-solidity cascade diffuser. At higher rotational speeds, the pressure ratio at the surge point, the efficiency, and the flow range of the low-solidity cascade diffuser exceded those of a vaned diffuser at a pressure ratio of 3.5.

scholarly journals Study of the flow characteristics in multi-row vaned diffusers of a centrifugal compressor stage

2018 ◽  
Vol 10 (9) ◽  
pp. 168781401879960 ◽  
Author(s):  
Yanjie Zhao ◽  
Jingyin Li
Keyword(s):  
Pressure Gradient ◽  
Centrifugal Compressor ◽  
Flow Separation ◽  
Total Pressure ◽  
Flow Characteristics ◽  
Present Calculation ◽  
Compressor Stage ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage

The vaned diffuser has a significant impact on the performance and operating range of a centrifugal compressor stage, and multi-row vaned diffusers are applied to improve the compressor characteristics in this article. In order to validate the effectiveness of the present calculation method, the calculation results of the centrifugal compressor with the conventional diffuser have been verified by the experimental data. The simulation results reveal that, compared with the original model at design point, the isentropic efficiency increases by 2.8% and 4.1%, and the total pressure ratio increases by 1.9% and 3.4%, for the compressor stage with the two-row vaned diffuser and the three-row vaned diffuser, respectively. The models with multi-row vaned diffusers also give higher static pressure recovery coefficient and lower total pressure loss coefficient. A pressure gradient formed on vane suction surface near vane leading edge develops the flow separation in the conventional diffuser. The pressure gradient thus causes the secondary flow from hub to shroud on vane suction surface, aggravating the separation in the rear part of the conventional diffuser. The analysis of flow characteristics in diffuser passages also shows that using multi-row vaned diffusers can alleviate flow separation appearing in the diffuser passages.

Compressible Flowfield Characteristics of Butterfly Valves

1989 ◽  
Vol 111 (4) ◽  
pp. 400-407 ◽  
Author(s):  
M. J. Morris ◽  
J. C. Dutton
Keyword(s):  
Flow Separation ◽  
Pressure Ratio ◽  
Disk Surface ◽  
Surface Flow ◽  
Operating Conditions ◽  
Local Geometry ◽  
Operating Pressure ◽  
Butterfly Valve ◽  
Pressure Distributions ◽  
Flow Separation And Reattachment

The results of an experimental investigation into the flowfield characteristics of butterfly valves under compressible flow operating conditions are reported. The experimental results include Schlieren and surface flow visualizations and flowfield static pressure distributions. Two valve disk shapes have been studied in a planar, two-dimensional test section: a generic biconvex circular arc profile and the midplane cross-section of a prototype butterfly valve. The valve disk angle and operating pressure ratio have also been varied in these experiments. The results demonstrate that under certain conditions of operation the butterfly valve flowfield can be extremely complex with oblique shock waves, expansion fans, and regions of flow separation and reattachment. In addition, the sensitivity of the valve disk surface pressure distributions to the local geometry near the leading and trailing edges and the relation of the aerodynamic torque to flow separation and reattachment on the disk are shown.

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