On the Influence of the Diffuser Inlet Shape on the Performance of a Centrifugal Compressor Stage

1983 ◽  
Author(s):  
K. Bammert ◽  
M. Jansen ◽  
M. Rautenberg
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Field Measurements ◽  
Single Stage ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Essential Components

Results from an experimental study of the influence of the diffuser inlet shape on the performance of the diffuser and the whole compressor stage are presented. The investigations were carried out using a single stage centrifugal compressor. Three different vaned diffusers were tested. From detailed flow field measurements the influence of the diffuser inlet shape on the performance of the essential components of the compressor stage, i.e. the impeller, the diffuser, and the collecting chamber was analyzed. It is shown that the reaction of the vaned diffuser on the efficiency of the impeller is only weak but the losses in the collecting chamber are considerably affected by the used diffuser types.

CFD Analysis of Unsteady Flow Interactions in a Centrifugal Compressor Stage

2000 ◽  
Author(s):  
A. Koumoutsos ◽  
A. Tourlidakis ◽  
R. L. Elder
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Fourier Transforms ◽  
Flow Analysis ◽  
Design Flow ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage

This paper describes the unsteady flow analysis in a centrifugal compressor stage using a three dimensional CFD algorithm. The flow unsteadiness arising from the interaction between the impeller and the diffuser has been analysed using an algorithm suitable for equal or multiple number of rotor and diffuser blades. The multi-block, structured grid CFD code TASCflow was used as a basis and algorithm development was undertaken to provide the required capability of modelling the unsteady interactions of the impeller and the diffuser. The centrifugal compressor stage studied consists of an impeller with splitters and a vaned diffuser. The results presented are for off-design flow conditions where some experimental results were available for comparison. The results obtained for the steady-state model show a good agreement with the measurements. In general the unsteady flow field obtained show a reasonable agreement with experimental data and demonstrates significant differences when compared to the steady state results especially in terms of the velocity field. A detailed analysis of the unsteady flow field is carried out using Fourier transforms of velocity and pressure at various locations of the flow field and the level of unsteadiness is determined as distributed to various frequencies. The unsteadiness in the impeller passage is much less than in the diffuser where a strong coupling is predicted in the vaneless space.

An Investigation of the Stability Enhancement of a Centrifugal Compressor Stage Using a Porous Throat Diffuser

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Lee Galloway ◽  
Stephen Spence ◽  
Sung In Kim ◽  
Daniel Rusch ◽  
Klemens Vogel ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Stall Inception ◽  
Centrifugal Compressor Stage ◽  
Operating Range ◽  
Stable Operating ◽  
The Stability ◽  
Circumferential Pressure

The stable operating range of a centrifugal compressor stage of an engine turbocharger is limited at low mass flow rates by aerodynamic instabilities which can lead to the onset of rotating stall or surge. There have been many techniques employed to increase the stable operating range of centrifugal compressor stages. The literature demonstrates that there are various possibilities for adding special treatments to the nominal diffuser vane geometry, or including injection or bleed flows to modify the diffuser flow field in order to influence diffuser stability. One such treatment is the porous throat diffuser (PTD). Although the benefits of this technique have been proven in the existing literature, a comprehensive understanding of how this technique operates is not yet available. This paper uses experimental measurements from a high pressure ratio (PR) compressor stage to acquire a sound understanding of the flow features within the vaned diffuser which affect the stability of the overall compression system and investigate the stabilizing mechanism of the porous throat diffuser. The nonuniform circumferential pressure imposed by the asymmetric volute is experimentally and numerically examined to understand if this provides a preferential location for stall inception in the diffuser. The following hypothesis is confirmed: linking of the diffuser throats via the side cavity equalizes the diffuser throat pressure, thus creating a more homogeneous circumferential pressure distribution, which delays stall inception to lower flow rates. The results of the porous throat diffuser configuration are compared to a standard vaned diffuser compressor stage in terms of overall compressor performance parameters, circumferential pressure nonuniformity at various locations through the compressor stage and diffuser subcomponent analysis. The diffuser inlet region was found to be the element most influenced by the porous throat diffuser, and the stability limit is mainly governed by this element.

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.

Surge Inception in a Transonic Centrifugal Compressor Stage

2011 ◽  
Author(s):  
Isabelle Tre´binjac ◽  
Nicolas Bulot ◽  
Xavier Ottavy ◽  
Nicolas Buffaz
Keyword(s):  
Centrifugal Compressor ◽  
Short Wavelength ◽  
Stokes Equations ◽  
Pressure Sensors ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Choked Flow ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. Unsteady 3D simulations were performed with the code elsA that solves the turbulent averaged Navier-Stokes equations, at three operating points: choked flow, peak efficiency and near surge. Unsteady pressure measurements up to 150 kHz were carried out in the entry zone of the vaned diffuser (in the vaneless space and in the semi-vaneless space) when the compressor came into surge. These static pressure sensors were mounted on the shroud enwall. The paper focuses on the vaneless and semi-vaneless space where the surge originates. A detailed analysis of the flow pattern coming from the unsteady computations from choked flow towards surge led to identify the physical mechanisms involved in the surge inception. It is shown that, when approaching surge, the flow is destabilized by a severe modification of the shock system in the vaned diffuser inlet. The first perturbation is acquired from the transducer located just upstream of the shock foot (i.e. on the vane suction side surface), indicating a movement of the shock towards the vaneless space. This perturbation travels upstream and leads to the strongest short-wavelength perturbation acquired from the transducer located just upstream of the vane leading edge. This strongest short-wavelength perturbation which level may reach almost four times the mean exit pressure value triggers the full scale instability.

Study on Aerodynamic Redesign of a High Pressure Ratio Centrifugal Compressor

2010 ◽  
Author(s):  
Chaolei Zhang ◽  
Qinghua Deng ◽  
Zhenping Feng
Keyword(s):  
Centrifugal Compressor ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Aerodynamic Performance ◽  
Compressor Stage ◽  
Operation Condition ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Optimum Configuration ◽  
Operation Conditions

This paper describes the aerodynamic redesign and optimization of a typical single stage centrifugal compressor, in which the total pressure ratio was improved from the original 4.0 to final 5.0 with the restrictions of keeping the impeller tip diameter, the design rotational speed and the design mass flow rate unchanged. Firstly the backsweep angle and the outlet blade height of the impeller were adjusted and the vaned diffuser was redesigned. Then a sensitivity analysis of the aerodynamic performance correlated to the primary redesign centrifugal compressor stage with respect to the chosen redesign variables was conducted, according to the parameterized results of the impeller and the vaned diffuser. Secondly the impeller and the vaned diffuser were optimized respectively under the stage environment at the design operation condition to improve the stage isentropic efficiency by using a global optimization method which coupled Evolutionary Algorithm (EA) and Artificial Neural Network (ANN), provided by the commercial software NUMECA DESIGN-3D. Subsequently the detailed performance maps of the centrifugal compressor stage corresponding to the primary redesign configuration and the optimum configuration were presented by Computational Fluid Dynamics (CFD) simulation. Finally the flow fields correlated to the centrifugal compressor configurations before and after optimization at the design operation condition were also compared and analyzed in detail. As a result the design target was achieved after the primary redesign, as a 2.7% gain in stage efficiency and a 3.6% increase in stage pressure ratio were obtained when compared with the primary redesign configuration after optimization. Moreover, the aerodynamic performance of the optimum configuration at the off-design operation conditions was also improved.

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.

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.

scholarly journals Effect of the Unsteadiness on the Diffuser Flow in a Transonic Centrifugal Compressor Stage

2009 ◽  
Vol 2009 ◽  
pp. 1-11 ◽  
Author(s):  
N. Bulot ◽  
I. Trébinjac
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Centrifugal Compressor ◽  
Wake Flow ◽  
Pressure Waves ◽  
Pressure Side ◽  
Compressor Stage ◽  
Impeller Blade ◽  
Centrifugal Compressor Stage ◽  
Diffuser Flow

The study is focused on the analysis of the flow structure within the vaned diffuser of a transonic high-pressure centrifugal compressor stage. The analyzed time-dependent flow field comes from unsteady computations of the stage using a 3D Navier-Stokes code with a phase-lagged technique, at an operating point close to the design point. A good comparison with available experimental data allowed the use of CFD for investigating the details of the flow in order to assess the effect of the unsteadiness in the diffuser flow development. Applying various data processing techniques, it is shown that the unsteadiness is due to the jet and wake flow structure emerging from the radial impeller and to the pressure waves brought about by the interaction between the vane bow shock wave and the impeller blade. The interaction between the pressure waves and the vane pressure side boundary layer leads to a pulsating behavior of separated bubbles within the diffuser. The pressure waves are similar in shape and strength whatever the blade height. The observed change in the flow field from hub to tip is due to migration of the low momentum fluid contained in the wake toward the pressure side/hub corner.

scholarly journals Experimental Investigation of Unsteady Flow Phenomena in a Centrifugal Compressor Vaned Diffuser of Variable Geometry

1999 ◽  
Vol 121 (4) ◽  
pp. 763-771 ◽  
Author(s):  
F. Justen ◽  
K. U. Ziegler ◽  
H. E. Gallus
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Fluctuations ◽  
Suction Side ◽  
Front Wall ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Impeller Outlet ◽  
Flow Phenomena ◽  
Radial Gap

The behavior of vaned radial diffusers is generally considered to be due to the flow phenomena in the vaneless and the semi-vaned space in the diffuser inlet region. Even considering unsteady aspects, the adjacent diffuser channel is regarded as less important. The flat wedge vaned diffuser of the centrifugal compressor stage investigated allows an independent continuous adjustment of the diffuser vane angle and the radial gap between impeller outlet and diffuser vane inlet, so that information about the importance of these geometric parameters can be obtained. The time-dependent pressure distribution on the diffuser front wall and on the suction and pressure surfaces of the diffuser vanes reveal that in the semi-vaned space mainly the region near the vane suction side is influenced by the unsteady impeller-diffuser interaction. Downstream in the diffuser channel the unsteadiness does not decay. Here, pressure fluctuations are appearing that are distinctly higher than the pressure fluctuations in the vaneless space. An estimation of the influence of the unsteadiness on the operating performance of the centrifugal compressor stage is made by measurements at choke and surge limit for different diffuser geometries.

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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