Enhancement of Flow Diffusion in a Centrifugal Compressor Stage with Backward Curved Impeller by Shroud Extension – A Numerical Study

2014 ◽  
Vol 984-985 ◽  
pp. 1102-1107 ◽  
Author(s):  
Sivamani Seralathan ◽  
D.G. Roy Chowdhury ◽  
Anil Kumar Jaswal
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Numerical Study ◽  
Pressure Rise ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Side Walls

Efficient, compact centrifugal compressor with higher pressure ratios along with adequate surge margins necessitates developing non-conventional diffuser designs. A method of reducing shear losses on the stationary vaneless diffuser sidewalls is by rotating the side walls of vaneless diffuser. Forced rotating vaneless diffuser, a type in which the diffuser is integral with impeller and rotates at same speed, is obtained by extending the impeller disks beyond the blades. In this paper, the conventional stationary vaneless diffuser is redesigned to act as a ‘forced’ rotating vaneless diffuser. The effect of shroud extension is analyzed for the backward curved centrifugal impeller with shrouds extended by 40% with impeller exit diameter on flow diffusion and compared to an impeller with stationary vaneless diffuser. A higher static pressure rise by around 10% along with reduced losses is achieved by shroud extension configuration, RVD-ES. This indicates that the rate of diffusion is higher in the extended shroud configuration.

Performance Enhancement of the Centrifugal Compressor Stage With a Rotating Vaneless Diffuser: A Numerical Study

2014 ◽  
Author(s):  
Seralathan Sivamani ◽  
Roy Chowdhury Dibyakanti Ghosh
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Rise ◽  
Stagnation Pressure ◽  
Diameter Ratio ◽  
Design Flow ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Blade Tip

In order to reduce the energy losses associated due to diffusion in the centrifugal compressor stage, several radial diffuser designs have been tried and rotating vaneless diffuser is one among them. Forced rotating vaneless diffuser is formed by extending the impeller disks alone beyond the blade tip without affecting the blade tip geometry. Studies on completely replacing a stationary vaneless diffuser with rotating vaneless diffuser are not available in open domain yet. This paper reports the effect of rotating vaneless diffuser based on shroud extension concept on flow diffusion, performance and flow parameters in a centrifugal compressor stage at design and off-design flow conditions. A backward curved impeller with diffuser diameter ratio 1.40 is chosen for the present study. Rotating vaneless diffuser is formed by extending the impeller disks by 40% above the impeller exit diameter. The comparative studies are done with the same impeller having a stationary vaneless diffuser of equivalent diffuser diameter ratio in the downstream. Static pressure rise in RVD-ES configuration is higher compared to SVD and the energy coefficient improved by around 57.14% for RVD-ES over the entire flow range. The efficiency of RVD-ES and SVD are almost identical at Φ = 0.156. At design and other off-design flow coefficients, the efficiencies of RVD-ES are slightly lesser compared to SVD by 1.0 to 1.52%. The static pressure recovery coefficient of RVD-ES is higher than SVD. The stagnation pressure losses reduced drastically for RVD-ES. From the velocity vectors and contours of stagnation pressure distribution, it seen that additional energy is added to the fluid by the rotating walls of the vaneless diffuser. This results in increased kinetic energy of the fluid. Due to better diffusion process in RVD-ES, this results with a gain in increased static pressure rise with acceptable efficiency.

Analytical and Test Experiences Using a Rib Diffuser in a High Flow Centrifugal Compressor Stage

2001 ◽  
Author(s):  
James M. Sorokes ◽  
Jason A. Kopko
Keyword(s):  
Centrifugal Compressor ◽  
Quantitative Agreement ◽  
High Flow ◽  
Flow Coefficient ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Qualitative And Quantitative

The paper addresses the use of a rib style (partial height) vaned diffuser to improve the flowfield downstream of a high flow coefficient centrifugal impeller. Empirical and analytical (3-D CFD) results are presented for both the original vaneless diffuser and the replacement rib configuration. Comparisons are made between the CFD results and the data obtained through single stage rig (SSTR) testing. Comments are offered regarding the qualitative and quantitative agreement between the empirical and analytical results.

Investigation on Effect of Curvilinear Element Blades on Centrifugal Impeller Performance

2017 ◽  
Author(s):  
Kiyotaka Hiradate ◽  
Hiromi Kobayashi ◽  
Takahiro Nishioka
Keyword(s):  
Centrifugal Compressor ◽  
Performance Test ◽  
Design Guidelines ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
Numerical Calculations ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Compressor Impeller

This study experimentally and numerically investigates the effect of application of curvilinear element blades to fully-shrouded centrifugal compressor impeller on the performance of centrifugal compressor stage. Design suction flow coefficient of compressor stage investigated in this study is 0.125. The design guidelines for the curvilinear element blades which had been previously developed was applied to line element blades of a reference conventional impeller and a new centrifugal compressor impeller with curvilinear element blades was designed. Numerical calculations and performance tests of two centrifugal compressor stages with the conventional impeller and the new one were conducted to investigate the effectiveness of application of the curvilinear element blades and compare the inner flowfield in details. Despite 0.5% deterioration of the impeller efficiency, it was confirmed from the performance test results that the compressor stage with the new impeller achieved 1.7% higher stage efficiency at the design point than that with the conventional one. Moreover, it was confirmed that the compressor stage with the new impeller achieved almost the same off-design performance as that of the conventional stage. From results of the numerical calculations and the experiments, it is considered that this efficiency improvement of the new stage was achieved by suppression of the secondary flows in the impeller due to application of negative tangential lean. The suppression of the secondary flows in the impeller achieved uniformalized flow distribution at the impeller outlet and increased the static pressure recovery coefficient in the vaneless diffuser. As a result, it is thought that the total pressure loss was reduced downstream of the vaneless diffuser outlet in the new stage.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

2005 ◽  
Author(s):  
T. Ch. Siva Reddy ◽  
G. V. Ramana Murty ◽  
Prasad Mukkavilli ◽  
D. N. Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Pressure Recovery ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Pressure Recovery Coefficient

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

Flow Studies on a Centrifugal Compressor Stage With Low Solidity Diffuser Vanes

2002 ◽  
Author(s):  
Prasad Mukkavilli ◽  
G. Rama Raju ◽  
A. Dasgupta ◽  
G. V. Ramana Murty ◽  
K. V. Jagadeshwar Chary
Keyword(s):  
Centrifugal Compressor ◽  
Design Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Setting Angle ◽  
Set Up ◽  
Flow Improvement ◽  
Stagger Angle

Diffusers are found to play a significant role in the performance of centrifugal compressors. Extensive studies have been in progress in various research laboratories for improvement of performance with various types of diffusers. One such effort for study of performance of a centrifugal compressor stage with Low Solidity Diffuser (LSD) vanes is presented in this paper. The study was conducted at a tip mach number of 0.35. An exclusive test rig was set up for carrying out these flow studies. The LSD vane is formed using standard NACA profile with marginal modification at the trailing edge region. The study encompasses the variation of setting angle of the LSD vane and the vane solidity. The effect of solidity and the setting angle on overall stage performance is evaluated in terms of flow coefficient, head coefficient and efficiency normalised with respect to these parameters for the case of vaneless diffuser at design flow. Improvement in performance as well as static pressure recovery was observed with LSD as compared to vaneless diffuser configuration. It is concluded from these studies that there is an optimum solidity and stagger angle for the given stage with LSD vanes for the chosen configuration.

Experimental and Numerical Investigation of the Flow in a Vaneless Diffuser of a Centrifugal Compressor Stage. Part 1: Experimental Investigation

2005 ◽  
Vol 219 (10) ◽  
pp. 1053-1059 ◽  
Author(s):  
T Sato ◽  
J M Oh ◽  
A Engeda
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Boundary Layers ◽  
Centrifugal Compressor ◽  
High Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Very High

The flow in a radial vaneless diffuser downstream of a centrifugal compressor is highly complex, as the flow is turbulent, unsteady, viscous, and three-dimensional. Depending on the initial state of the end-wall boundary layers and the diffuser length, the flow may become fully developed or may separate from one of the walls. Therefore, to improve the diffuser performance, it is important to understand the flow field in the diffuser in detail. As the diffuser width is generally very small for most radial stages and an adverse pressure gradient exists, secondary flows are generated, making the flow fields more complicated. In addition, skewed boundary layers form on the wall surfaces. As flowrate is reduced, the flow field becomes more complicated and leads to rotating stall. This article presents detailed flow measurements in a vaneless diffuser of a centrifugal compressor stage with a very high flow coefficient radial impeller. Usually, centrifugal compressors with radial impellers are designed in the flow coefficient (ϕ) range ϕ = 0.01 - 0.16. Often, the need arises to design higher flow coefficient, ϕ, radial stages. Detailed measurements were carried out in the vaneless diffuser at seven radial positions downstream of a radial impeller designed for a very high flow coefficient of ϕ = 0.2. The experimental investigation was carried at four rotational speeds 13 000, 15 500, 18 000, and 20 500 r/min, but only the result of 20 500 r/min at near-design-point flowrate (5.11 kg/s) is reported in this article.

Multi-Blade Row Interactions in a Low Pressure Ratio Centrifugal Compressor Stage With a Vaned Diffuser

2011 ◽  
Author(s):  
Kishore Ramakrishnan ◽  
Simon K. Richards ◽  
Franc¸ois Moyroud ◽  
Vittorio Michelassi
Keyword(s):  
Centrifugal Compressor ◽  
Oil And Gas ◽  
Pressure Ratio ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Acoustic Interaction ◽  
Field Excitation

Previous experimental and CFD investigation of a GE Oil and Gas centrifugal compressor stage with a vaneless diffuser revealed a complex excitation mechanism caused by an aero-acoustic interaction between three blade rows. In stages with vaned diffusers, additional sources of aeromechanical excitation on the impeller can be expected. This unsteady CFD investigation is a follow-up from the previous vaneless diffuser study to identify any additional sources of excitation that arise in the presence of a vaned diffuser in preparation for aeromechanic tests to be conducted later. The study confirms that excitation from impeller-diffuser interaction generated acoustic modes can dominate the potential field excitation from the diffuser vanes. In addition, a significant aero-acoustic excitation to the impeller at a vane pass frequency corresponding to the sum of the vane counts in the two downstream vane rows is observed, and its origination is discussed. The latter excitation is different from that observed in the vaneless diffuser stage where the vane pass frequency observed by the impeller corresponds to the sum of the vane counts in the upstream and downstream vane rows.

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