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.

Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Isabelle Trébinjac ◽  
Pascale Kulisa ◽  
Nicolas Bulot ◽  
Nicolas Rochuon
Keyword(s):  
Shock Wave ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Wake Flow ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
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. The characteristic curves of the compressor stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the compressor stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted toward the unsteady results. The model, in particular, enhances the prediction of the choked mass flow.

Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

2008 ◽  
Author(s):  
Isabelle Tre´binjac ◽  
Pascale Kulisa ◽  
Nicolas Bulot ◽  
Nicolas Rochuon
Keyword(s):  
Shock Wave ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Wake Flow ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
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. The characteristic curves of the compressor stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the compressor stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.

Investigation of Unsteady Impeller-Diffuser Interaction in a Transonic Centrifugal Compressor Stage

2010 ◽  
Author(s):  
Yangwei Liu ◽  
Baojie Liu ◽  
Lipeng Lu
Keyword(s):  
Centrifugal Compressor ◽  
Flow Direction ◽  
Equation System ◽  
Compressor Stage ◽  
Spatial Correlations ◽  
Tip Leakage Flow ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor ◽  
Steady Simulation

In this paper, unsteady impeller-diffuser interaction in a transonic centrifugal compressor stage, which is composed of an impeller with splitter blade and a vaned diffuser, was studied numerically. The unsteady interaction has a significant impact on the time-averaged flow, which are presented by the so-called deterministic correlations in the average-passage equation system (APES) proposed by Adamczyk. Both steady and unsteady simulations were carried out at the design and off-design conditions. Results from the steady and unsteady simulations were compared to highlight the importance of the unsteady interactions and to help assess the shortcomings of simple mixing-plane methods. The comparisons indicate that the unsteady interactions should be considered in the simulations since the differences between the time averaged unsteady results and steady simulation results are significant especially at off-design conditions. Then the interactions between impeller and diffuser were studied in detail to advance the understanding of the flow physics involved. The results show that the impeller/diffuser interaction can affect a range of 30% impeller chord from impeller trailing edge on impeller performance, while whole chord length on diffuser performance. The potential effects of the diffuser cause an unsteady pressure disturbance at the impeller exit, leading to the unsteadiness of impeller load, tip leakage flow and losses. While the unsteadiness of impeller exit flow cause period varieties of inlet flow conditions for the diffuser and have large impacts on diffuser performance. Based on the unsteady results, deterministic correlations in the APES framework were computed and analyzed in order to reveal some shortcomings of present deterministic correlations models and to make some contributions to the modeling development. The distribution characteristics of deterministic correlations were studied. The study indicates that the deterministic correlations in the impeller and diffuser have the similar magnitudes, and that the correlations in the passages have large gradients in circumferential direction and decrease rapidly in flow direction especially in the vaneless space. The deterministic correlations at the impeller/diffuser interface were compared with their spatial correlations using the framework of the deterministic decomposition. The comparisons show that the spatial correlations have some discrepancies with the total deterministic correlations at the impeller/diffuser interface.

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.

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.

scholarly journals Influence of blade geometry on secondary flow development in a transonic centrifugal compressor

2018 ◽  
Vol 2 ◽  
pp. I1RSJ3 ◽  
Author(s):  
Moritz Mosdzien ◽  
Martin Enneking ◽  
Alexander Hehn ◽  
Daniel Grates ◽  
Peter Jeschke
Keyword(s):  
Secondary Flow ◽  
Centrifugal Compressor ◽  
Large Scale ◽  
Optimization Methods ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Impeller Blade ◽  
Flow Development ◽  
Transonic Centrifugal Compressor ◽  
Increasing Demand

Due to the increasing demand for higher efficiencies of centrifugal compressors, numerical optimization methods are becoming more and more relevant in the design process. To identify the beneficial features of a numerical optimized compressor design, this paper analyses the influence of arbitrary blade surfaces on the loss generation in a transonic centrifugal compressor. The paper therefore focuses on an analysis of the secondary flow development within the impeller blade passages. To do this, steady simulations were performed on both a baseline and an optimized blade design. Two distinct design features of the optimized compressor stage were identified, which lead to a more homogenous impeller exit flow and thus to an increase in total-to-static efficiency of 1.76% points: the positive lean in the near-tip region and the positive blade curvature in the rear part of the optimized impeller. Furthermore, through extensive experimental investigations conducted on a large scale test rig it has been possible to prove the particular impeller outflow characteristics of the baseline compressor stage.

1D and 3D-Design Strategies for Pressure Slope Optimization of High-Flow Transonic Centrifugal Compressor Impellers

2018 ◽  
Author(s):  
A. Hildebrandt ◽  
T. Ceyrowsky
Keyword(s):  
Centrifugal Compressor ◽  
High Flow ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Angle Distribution ◽  
Compressor Stage ◽  
Impeller Blade ◽  
Design Point ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor

The present paper deals with the numerical and theoretical investigations of the effect of geometrical dimensions and 1D-design parameters on the impeller pressure slope of a transonic centrifugal compressor stage for industrial process application. A database being generated during the multi-objective and multi-point design process of a high flow coefficient impeller, comprising 545 CFD (Computational Fluid Dynamics) designs is investigated in off-design and design conditions by means of RANS (Reynolds Averaged Navier Stokes) simulation of an impeller with vaneless diffuser. For high flow coefficients of 0.16 < phi < 0.18, the CFD-setup has been validated against measurement data regarding stage and impeller performance taken from MAN test rig experimental data for a centrifugal compressor stage of similar flow coefficient. The paper aims at answering the question how classical design parameter, such as the impeller blade angle distribution, impeller suction diameter and camber line length affect the local and total relative diffusion and pressure slope towards impeller stall operation. A second order analysis of the CFD database is performed by cross-correlating the CFD data with results from impeller two-zone 1D modelling and a rapid loading calculation process by Stanitz and Prian. The statistical covariance of first order 1D-analysis parameters such as the mixing loss of the impeller secondary flow, the slip factor, impeller flow incidence is analyzed, thereby showing strong correlation with the design and off-design point efficiency and pressure slope. Finally, guide lines are derived in order to achieve either optimized design point efficiency or maximum negative pressure slope characteristics towards impeller stall operation.

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.

Numerical Investigation of the Unsteady Flow Inside a Centrifugal Compressor Stage With Pipe Diffuser

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Daniel R. Grates ◽  
Peter Jeschke ◽  
Reinhard Niehuis
Keyword(s):  
Experimental Data ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Measurement Techniques ◽  
Navier Stokes ◽  
Compressor Stage ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor ◽  
Computational Fluid Dynamics Cfd ◽  
The Subject

The subject of this paper is the investigation of unsteady flow inside a transonic centrifugal compressor stage with a pipe-diffuser by utilizing unsteady 3D Reynolds-averaged Navier–Stokes simulations (unsteady 3D URANS). The computational fluid dynamics (CFD) results obtained are compared with detailed experimental data gathered using various steady and unsteady measurement techniques. The basic phenomena and mechanisms of the complex and highly unsteady flow inside the compressor with a pipe-diffuser are presented and analyzed in detail.

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.

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