scholarly journals CFD-researches of centrifugal compressor stage vane diffusers

2021 ◽  
Author(s):  
Aleksey Borovkov ◽  
Yuri Galerkin ◽  
Evgeniy Petukhov ◽  
Aleksandr Drozdov ◽  
Vladimir Yadikin ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Incidence Angle ◽  
Suction Side ◽  
Complex Nature ◽  
Compressor Stage ◽  
Deviation Angle ◽  
Recovery Coefficient ◽  
Centrifugal Compressor Stage ◽  
Flow Deviation ◽  
Separation Zones

Abstract The paper presents result of CFD simulations of a series of centrifugal compressor stage vane diffusers in the Ansys CFX. Objects of research are vane diffusers with external relative diameter (relative to the diameter of the impeller) equal to 1.5, vane inlet angle of 20 degrees, relative vane heights of 0.025, 0.034, 0.045, 0.06, 0.08, vane profile curvature angles of 10, 15, 20 degrees. The characteristics of polytrophic efficiency, loss coefficient, recovery coefficient, ratio of inlet and outlet velocities, flow deviation angle versus incidence angle are set. The analysis of the flow structure in the vane diffuser channels is presented. Unlike with a straight vane cascade, the deviation angle in the circular rows of vane diffusers tends to increase with increasing row density. This may be due to the complex nature of the interaction of the active part of the flow with separation zones. In rows with almost straight vanes at a lower density, the separation zone on the pressure side decreases, and even shifts to the very end of the suction side.

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.

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.

Analysis of the flow in a transonic centrifugal compressor stage from choke to surge

2011 ◽  
Vol 225 (7) ◽  
pp. 919-929 ◽  
Author(s):  
I Trébinjac ◽  
N Bulot ◽  
N Buffaz
Keyword(s):  
Centrifugal Compressor ◽  
Suction Side ◽  
Bow Shock ◽  
Wake Flow ◽  
Pressure Waves ◽  
Pressure Side ◽  
Compressor Stage ◽  
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 three-dimensional 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. Numerical results were validated with experimental data coming from laser Doppler anemometry and unsteady pressure measurements. This article focuses on the change in flow structures when the operating point moves from choke to surge. The main changes in the impeller consist in an enlargement of the wake (of the jet-wake flow structure) and an increase in the exit time-averaged flow angle. Consequently, in the diffuser passage, the main flow trajectory moves towards the vane pressure side, and the boundary layer separation transfers from pressure side to suction side. The interaction between the vane bow shock wave and the impeller blade leads to pressure waves α+, which propagate in the diffuser passage. These pressure waves generate alternately opposite and favourable pressure gradients, which drive the boundary layers to periodic separation. From choke to surge, the intensity of the pressure waves α+ increases. The interaction also leads to subsonic pockets Г, which are torn out from the vane-leading edge bow shock and swept along the vane suction side. The induced change in the shock shape and location combined with the severe hub/suction side corner separation are thought to be at the origin of the surge inception.

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

1998 ◽  
Author(s):  
Friedrich Justen ◽  
Kai U. Ziegler ◽  
Heinz E. Gallus
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Fluctuations ◽  
Suction Side ◽  
Front Wall ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Pressure Surface ◽  
Flow Phenomena ◽  
Radial Gap

The behaviour 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 investigated centrifugal compressor stage 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 suction and pressure surface 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 which 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.

Analysis of Diffusers With Different Number of Vanes in a Centrifugal Compressor Stage

2001 ◽  
Author(s):  
N. He ◽  
A. Tourlidakis
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Rise ◽  
Leading Edge ◽  
Operating Conditions ◽  
Dominant Factor ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage

In this paper, a computational analysis of a high-speed centrifugal compressor stage for turbocharger applications is presented. Emphasis is focused on the effect of different number of diffuser vanes, and for this reason four different designs of the vaned diffuser are analysed. The first three of the diffusers consist of 11, 22 and 33 vanes, respectively, with their leading edge at a radius of 1.075 times the radius of the impeller tip. The fourth one consists of 22 vanes with its leading edge at 1.15 times the radius of the impeller tip. All the above vane designs are of double circular arc shape. A steady CFD analysis is carried out using the Reynolds-Averaged Navier-Stokes solver TASCflow at design and off-design operating conditions. An averaging approach is used at the interface between the impeller and the diffuser. A detailed comparison between the predicted and the available experimental data is performed in terms of pressure rise and efficiency characteristics, and very good agreement is accomplished. In addition, detailed flow distributions are compared and critically analysed. One of the most important conclusions is that while maintaining the overall throat area and the location of the leading and trailing edges of the diffuser, as the number of diffuser vanes increases, the pressure recovery coefficient at the semi-vaneless space at surge condition was found to reduce, the wake pattern becomes more pronounced and the velocity distribution at vaneless and semi-vaneless space becomes more distorted when passing the same mass flow rate and therefore the diffuser has a narrower flow range. On the other hand, it was found that the diffuser outlet to throat area ratio is not the dominant factor to influence the flow range when the number of vanes changes.

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.

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