Selecting the Dimensions of the Vaneless Diffuser of a Centrifugal Compressor Stage at the Primary Design Phase

2019 ◽  
pp. 43-57
Author(s):  
Y.B. Galerkin ◽  
A.F. Rekstin ◽  
O.A. Solovyeva
Keyword(s):  
Centrifugal Compressor ◽  
Design Method ◽  
Modeling Method ◽  
Design Flow ◽  
Optimal Size ◽  
Outer Diameter ◽  
Relative Width ◽  
Vaneless Diffuser ◽  
Radial Length ◽  
Vaneless Diffusers

The advances in the primary design method of centrifugal compressors of the Universal Modeling Method have led to the need to analyze and revise the recommendations for the optimal size and configuration selection of vaneless diffusers of centrifugal compressor stages. The results of CFD calculations of a family of vaneless diffusers with different relative width, radial length, velocity coefficients and flow angles at the inlet are used to develop new recommendations. The choice of the optimal width of the vaneless diffuser is based on ensuring a non-separable flow in it at the boundary of the surge. The optimal value of the relative radial length of the diffuser is in the range of 1.65–2.0. Considering the above, a formula for selecting the vaneless diffuser outer diameter is proposed depending on the design flow rate coefficient. The developed primary design method of vaneless diffusers is included in the software programs of the Universal Modeling Method and is used in design and research practice.

CFD-model of Vaneless Diffuser of Centrifugal Compressor

2021 ◽  
pp. 109-130
Author(s):  
О.А. Solovyeva ◽  
А.А. Drozdov ◽  
E.Yu. Popova ◽  
K.V. Soldatova
Keyword(s):  
Mathematical Model ◽  
Centrifugal Compressor ◽  
Dynamic Characteristics ◽  
Modeling Method ◽  
Relative Width ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Flow Parameters ◽  
Gas Dynamic ◽  
Vaneless Diffusers

The centrifugal compressor design involves the use of approximate engineering techniques based on mathematical modeling. One of such techniques is the universal modeling method, which proves to be practically applicable. Having generalized a series of CFD calculations, we used a mathematical model in the latest version of the compressor model to calculate flow parameters in vaneless diffusers. The diffuser model was identified based on the results of experimental studies of average-flow model stages carried out at SPbPU. The model is also used to calculate Clark low-flow centrifugal compressor stages with narrow diffusers with a relative width in the range of 0.5--2.0 %. For these stages, the developed mathematical model showed insufficient efficiency, since the dimensions of the diffusers go beyond the limits of its applicability. To solve this problem, we calculated a series of vaneless diffusers with a relative width in the range of 0.6--1.2 % in the ANSYS CFX software package. Relying on the results of CFD calculations, we plotted the gas dynamic characteristics of the loss coefficients and changes in the flow angle depending on the flow angle at the inlet to the vaneless diffuser. To process the calculated data, the method of regression analysis was applied, with the help of which a system of algebraic equations was developed that connects geometric, gas-dynamic parameters and similarity criteria. The obtained equations are included in a new mathematical model of the universal modeling method for calculating the flow parameters of vaneless diffusers. Comparison of the calculated gas-dynamic characteristics according to the new model with experimental data showed the average error of modeling the calculated (maximum) efficiency equal to 1.08 %

Primary Design of Vaneless Diffusers of Centrifugal Compressor Stages by the Universal Modeling Method

2021 ◽  
pp. 39-52
Author(s):  
O.A. Solovyeva ◽  
K.V. Soldatova ◽  
Y.B. Galerkin ◽  
A.F. Rekstin
Keyword(s):  
Continuous Flow ◽  
Design Method ◽  
Modeling Method ◽  
Inlet Section ◽  
Relative Width ◽  
Design Practice ◽  
Main Section ◽  
Flow Angle ◽  
Gas Dynamic ◽  
Vaneless Diffusers

Vaneless diffusers of industrial centrifugal compressors most often consist of a tapered inlet section and a parallel-walled main section. The study proposes to choose such a width of the main section, at which the flow in the diffuser remains unseparated at the surge limit. To implement the primary design method, an empirical formula was obtained to determine the minimum continuous flow angle depending on the relative width of the diffuser. The primary design of eighteen stages was completed, covering a practically important range of parameters. The corresponding gas-dynamic characteristics were calculated by the universal modeling method, the dimensions and angles of the flow were analyzed. The proposed primary design method is integrated into the universal modeling method and is used in design practice.

CFD Studies on the Performance of a Centrifugal Compressor With Single Wall Rotating Vaneless Diffusers at the Wall Extension Ratios of 1.1 and 1.15

2017 ◽  
Author(s):  
Srinivasa Rao Konakala ◽  
Mukka Govardhan
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
Static Pressure ◽  
Substantial Improvement ◽  
Significant Loss ◽  
Vaneless Diffuser ◽  
Shear Forces ◽  
Overall Performance ◽  
Vaneless Diffusers ◽  
And Performance

Efficiency of the centrifugal compressor is affected by non-uniform flow at the exit of the impeller and the losses in the diffuser. This causes a significant loss of total pressure and drop in the performance of a centrifugal compressor. By rotating some portion of stationary vaneless diffuser walls with the speed of the impeller, the shear forces between the flow and diffuser walls are greatly reduced. Thereby improvement in the operating range and performance is achieved. This paper presents CFD studies on the effect of different single wall rotations i.e. hub rotation and shroud rotation of the vaneless diffusers on the overall performance at 10% and 15% extension of impeller walls. It is observed that the performance characteristics of compressors with all RVD models offer higher static pressure recovery and also higher rate of diffusion compared to the base compressor with SVD. It is clear that as extended radius increases from 10% to 15%, substantial improvement of efficiency and reduction of losses are observed for both type of models. Out of two single wall rotation models, SRVD model is able to better mix the jet-wake type of impeller exit flows and minimizes the losses therein and improve the performance of the centrifugal compressor.

Off-Design Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1995 ◽  
Vol 117 (4) ◽  
pp. 602-608 ◽  
Author(s):  
A. Pinarbasi ◽  
M. W. Johnson
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Secondary Flows ◽  
Design Flow ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Flow Rates ◽  
Study Results

Detailed measurements have been taken of the three-dimensional velocity field within the vaneless diffuser of a backswept low speed centrifugal compressor using hot-wire anemometry. A 16 percent below and an 11 percent above design flow rate were used in the present study. Results at both flow rates show how the blade wake mixes out more rapidly than the passage wake. Strong secondary flows inherited from the impeller at the higher flow rate delay the mixing out of the circumferential velocity variations, but at both flow rates these circumferential variations are negligible at the last measurement station. The measured tangential/radial flow angle is used to recommend optimum values for the vaneless space and vane angle for design of a vaned diffuser.

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.

scholarly journals Study on Two Types of Stall Patterns in a Centrifugal Compressor with a Wide Vaneless Diffuser

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1251
Author(s):  
Qian Zhang ◽  
Liang Zhang ◽  
Qiuhong Huo ◽  
Lei Zhang
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Propagation Speed ◽  
Radius Ratio ◽  
Vaneless Diffuser ◽  
Vaneless Diffusers ◽  
Stall Cells ◽  
The Stability ◽  
The One

Two types of stall patterns in the centrifugal compressor with a wide vaneless diffuser were numerically studied in this paper. We carried out kinds of three-dimensional numerical simulations of the instability process in wide vaneless diffusers with different radius ratios. The results show that there are two kinds of stall patterns in wide vaneless diffusers with different radius ratios. For a short diffuser with a radius ratio of 1.5, the speed of the propagation of stalled cells is relatively high, and the propagation speed and frequency of stall cells do not change with the decrease in the flow rate. For a long diffuser with a radius ratio of 1.8, the propagation velocity of stall cells is smaller to the one in the short diffuser, and increases with the decrease in flow rate. For wide vaneless diffusers with different radius ratios, the main factor causing stall is the outlet reflux. Reducing the radius ratio of the wide vaneless diffuser has an important influence on the stability of the centrifugal compressor.

scholarly journals Mathematical model of centrifugal compressor vaneless diffuser based on CFD calculations

2020 ◽  
Vol 178 ◽  
pp. 01014
Author(s):  
Olga Solovyeva ◽  
Aleksandr Drozdov
Keyword(s):  
Mathematical Model ◽  
Centrifugal Compressor ◽  
Similarity Criteria ◽  
Relative Width ◽  
Inlet Flow ◽  
Flow Angle ◽  
Gas Dynamic ◽  
Modelling Method ◽  
Vaneless Diffusers ◽  
The Mathematical Model

The approximate engineering techniques based on mathematical modelling are used in centrifugal compressor design. One of such methods is the well-proven Universal Modelling Method, developed in the scientific and research laboratory “Gas dynamics of turbo machines”, SPbPU. In the modern version of the compressor model, vaneless diffusers mathematical model was applied based on a generalization of the CFD calculations. The mathematical model can be used for vaneless diffusers with a relative width in the range of 1.4 – 10.0%, with a radial length up to 2.0, in the range of inlet flow angles 10 to 90 degrees, the inlet velocity coefficient in the range of 0.39 – 0.82, Reynolds number varying from 87 500 to 1 030 000. The model was also used for calculating low-flow-rate model stages with narrow diffusers with diffusers’ relative width in the range of 0.5 – 2.0%. The mathematical model showed lesser accuracy. To widen the model applicability, new series of CFD-calculations were executed. A series of vaneless diffusers was designed with relative width in the range of 0.6 – 1.2%, The gas-dynamic characteristics of loss coefficients and outlet flow angle versus inlet flow angle of diffuser were calculated. Regression analysis was used to process the calculated data. System of algebraic equations linking geometric, gas-dynamic parameters and similarity criteria was developed. The obtained equations are included in a new mathematical model of the Universal Modelling Method.

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