A Diffusion Factor Correlation for Centrifugal Impeller Stalling

1978 ◽  
Vol 100 (4) ◽  
pp. 592-601 ◽  
Author(s):  
C. Rodgers
Keyword(s):  
Centrifugal Compressor ◽  
High Loading ◽  
Centrifugal Impeller ◽  
Preliminary Design ◽  
Test Results ◽  
Diffusion Factor ◽  
Speed Range ◽  
Parallel Wall ◽  
Specific Speed ◽  
Vaneless Diffusers

Test results pertaining to the stalling characteristics of centrifugal compressor impellers with parallel wall vaneless diffusers are presented and studied to correlate the coincidence of stall with a limiting impeller diffusion capability. It is suggested that a modified diffusion factor, to include the effects of meridional curvature, provides improved stall correlation for a wide specific speed range of backswept impeller types. The possibility of applying this diffusion factor to high loading radially bladed impellers is discussed as dependent upon blockage and windage plus recirculation effects. Use of the diffusion factor limit in the preliminary design of most common turbomachinery types, incompressible and compressible, to assess impeller (or rotor) stall is conceivable.

A new methodology for preliminary design of centrifugal impellers with prewhirl

2019 ◽  
Vol 234 (3) ◽  
pp. 251-262 ◽  
Author(s):  
Xiaojian Li ◽  
Yijia Zhao ◽  
Zhengxian Liu ◽  
Hua Chen
Keyword(s):  
Centrifugal Compressor ◽  
Maximum Flow ◽  
High Flow ◽  
Centrifugal Impeller ◽  
Preliminary Design ◽  
Design Specification ◽  
Vaned Diffuser ◽  
Flow Capacity ◽  
Compressor Design ◽  
Aerodynamic Parameters

The overall trend of centrifugal compressor design is to strive for high aerodynamic performance and high flow capacity products. A new methodology is derived to implement a preliminary design for high flow capacity centrifugal impeller with and without prewhirl. First, several new non-dimensional equations connecting impeller geometric and aerodynamic parameters are derived for the maximum flow capacity. The effects of prewhirl on mass flow function, inlet diameter ratio and work coefficient are discussed, respectively. Then, based on these equations, a series of design diagrams are drawn to extract the universal rules in centrifugal impeller design with prewhirl. Some physical limits of design maps are also discussed. Finally, the throat area of impeller is discussed under prewhirl, and the matching principle between prewhirl impeller and vaned diffuser is derived and validated. The proposed method can be used to design a new centrifugal compressor, or to evaluate the design feasibility and the challenge of a given design specification.

Effect of Impeller Blade Loading on Compressor Stage Performance in a High Specific Speed Range

2011 ◽  
Vol 134 (4) ◽  
Author(s):  
Takanori Shibata ◽  
Manabu Yagi ◽  
Hideo Nishida ◽  
Hiromi Kobayashi ◽  
Masanori Tanaka
Keyword(s):  
Relative Velocity ◽  
Compressor Stage ◽  
Test Results ◽  
Blade Loading ◽  
Degree Of Reaction ◽  
Surge Margin ◽  
Speed Range ◽  
Specific Speed ◽  
Velocity Diffusion ◽  
Stage Efficiency

The authors previously found that compressor stage efficiency in a high specific speed range was significantly improved by employing an increased relative velocity diffusion ratio coupled with a high backsweep angle (Shibata et al., “Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction Optimizing Blade Loading of a 3D-Impeller,” ASME Paper No. GT2009-59588). In spite of such a high relative velocity diffusion ratio, the same surge margin as with a conventional design was able to be achieved by using a special front loading distribution with a lightly loaded inducer. In the present study, the blade loading distribution was further optimized in order to achieve a larger surge margin than previously. Four types of fully shrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the developed impeller achieved 3.8% higher stage efficiency and 11% larger surge margin than the conventional design without reducing the pressure coefficient and choke margin. It was concluded that aft loading coupled with a high degree of reaction was a very effective way to improve surge margin as well as stage efficiency. Stator matching was also investigated by changing the design incidence angle, which was shown to have a little influence on surge margin in the present test results.

Dynamic Evaluation of a Three Point Mount Baseplate for a Motor Driven, Centrifugal Compressor Package

2003 ◽  
Author(s):  
Joseph S. Kubany ◽  
Joseph A. Tecza ◽  
Per Gustafsson
Keyword(s):  
Centrifugal Compressor ◽  
Mode Shapes ◽  
Test Results ◽  
Variable Speed ◽  
Element Analysis ◽  
Harmonic Response ◽  
Surrounding Structure ◽  
Speed Range ◽  
Floating Platforms ◽  
Variable Speed Motor

Maintaining acceptable alignment can be an issue for rotating machinery on off-shore floating platforms. Distortion arising from motion within the platform can change the alignment of the production machinery if that machinery is mounted rigidly to the platform. One way to eliminate the effects of such distortion is to attach the machinery on its own baseplate, which is connected to the platform using a three point mounting system. Anti-Vibration Mounts (AVMs) are used at each support location, and these devices are effective in isolating the baseplate and its machinery from the surrounding structure. The package discussed in this paper consists of a centrifugal compressor, a gear, and a 6.3 MW (8500 hp) variable speed motor (1000–1890 RPM) mounted on a baseplate. The equipment train has vibratory modes that could not be moved from the operating speed range. Some of these mode shapes show coupled motion between the motor and the baseplate. Test results were compared to the detailed Harmonic Response Finite Element Analysis (FEA) of the coupled structure, which predicts both baseplate resonance and motor rotor response amplitudes. Both analysis and testing demonstrate that these modes do not have a significant effect on package operation.

Effect of Impeller-Extended Shrouds on Centrifugal Compressor Performance as a Function of Specific Speed

1983 ◽  
Vol 105 (3) ◽  
pp. 457-465 ◽  
Author(s):  
L. Sapiro
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Centrifugal Compressors ◽  
Gas Compression ◽  
Blade Tip ◽  
Compressor Performance ◽  
The Subject ◽  
Specific Speed ◽  
Vaneless Diffusers ◽  
Outside Diameter

Centrifugal compressors for gas compression applications usually employ low-pressure ratio, backward-swept impellers with vaneless diffusers. To increase the compressor flow range and speed, impeller blades are occasionally trimmed, resulting in an extended shroud configuration. The effect of extended front and back impeller shrouds on the performance of centrifugal compressors with vaneless diffusers, and the variation of this effect as a function of specific speed, is thus of concern and is the subject of this paper. An investigation was carried out on two backward-swept shrouded impellers of common blade tip and inducer hub diameters, but different inducer tip diameters (corresponding to low and high specific speeds), with the front and back shrouds extending 20 percent above the blade’s outside diameter.

Effects of Blade Number on the Efficiency of Centrifugal Compressor Impellers

2000 ◽  
Author(s):  
Colin Rodgers
Keyword(s):  
Centrifugal Compressor ◽  
Dynamic Models ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Momentum Exchange ◽  
One Dimensional ◽  
Blade Number ◽  
Study Results ◽  
Speed Range ◽  
Specific Speed

The results of a study directed towards identifying optimum blade numbers for aviation and turbocharger type centrifugal compressor impellers is presented. The study focused upon a simplified one dimensional frictional model supported by impeller test data over a wide specific speed range, plus limited correlation with computational fluid dynamic models. The study results indicated that optimum blade numbers were a function of specific speed, blade backsweep angle, and DeLaval number. With a backsweep angle of 45 degrees and DeLaval number of unity the optimum blade numbers were ≈ 30 and ≈ 15 at low and high specific speeds respectively. It was shown that efficiency decreased with low blade number primarily due to low momentum exchange i.e., low slip factor. In order to condense the analysis only the impeller component of the compressor stage was studied, wherein the geometry and operating conditions were characterized in terms of five parameters, with particular emphasis on specific speed.

Effect of Impeller Blade Loading on Compressor Stage Performance in a High Specific Speed Range

2010 ◽  
Author(s):  
Takanori Shibata ◽  
Manabu Yagi ◽  
Hideo Nishida ◽  
Hiromi Kobayashi ◽  
Masanori Tanaka
Keyword(s):  
Relative Velocity ◽  
Compressor Stage ◽  
Test Results ◽  
Blade Loading ◽  
Conventional Design ◽  
Surge Margin ◽  
Speed Range ◽  
Specific Speed ◽  
Velocity Diffusion ◽  
Stage Efficiency

The authors previously found that compressor stage efficiency in a high specific speed range was significantly improved by employing an increased relative velocity diffusion ratio coupled with a high backsweep angle. In spite of such a high relative velocity diffusion ratio, the same surge margin as with a conventional design could be achieved by using a special front loading distribution with a lightly loaded inducer. In the present study, the blade loading distribution was further optimized in order to achieve a larger surge margin than previously. Four types of fully shrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the developed impeller achieved 3.8% higher stage efficiency and 11% larger surge margin than the conventional design without reducing the pressure coefficient and choke margin. It was concluded that aft loading coupled with a high degree of reaction was a very effective way to improve surge margin as well as stage efficiency. Stator matching was also investigated by changing the design incidence angle which was shown to have little influence on surge margin in the present test results.

Effect of Impeller Extended Shrouds on Centrifugal Compressor Performance as a Function of Specific Speed

1982 ◽  
Author(s):  
L. Sapiro
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Centrifugal Compressors ◽  
Gas Compression ◽  
Blade Tip ◽  
Compressor Performance ◽  
The Subject ◽  
Specific Speed ◽  
Vaneless Diffusers ◽  
Outside Diameter

Centrifugal compressors for gas compression applications usually employ low-pressure ratio, backward-swept impellers with vaneless diffusers. To increase the compressor flow range and speed, impeller blades are occasionally trimmed, resulting in an extended shroud configuration. The effect of extended front and back impeller shrouds on the performance of centrifugal compressors with vaneless diffusers, and the variation of this effect as a function of specific speed, is thus of concern and is the subject of this paper. An investigation was carried out on two backward-swept shrouded impellers of common blade tip and inducer hub diameters, but different inducer tip diameters (corresponding to low and high specific speeds), with the front and back shrouds extending 20 percent above the blade’s outside diameter.

High Specific Speed, High Inducer Tip Mach Number, Centrifugal Compressor

2003 ◽  
Author(s):  
C. Rodgers
Keyword(s):  
Mach Number ◽  
Centrifugal Compressor ◽  
Transonic Flow ◽  
High Efficiency ◽  
Flow Fields ◽  
Test Results ◽  
Positive Slope ◽  
Stall Margin ◽  
Recovery Characteristic ◽  
Specific Speed

The demand for more efficient turbocharger and aviation centrifugal compressors operating at higher pressure ratios and specific speeds with extended flow ranges is focusing research efforts on the inducer and diffuser transonic flow fields. At pressure ratios above 5.0 and specific speeds of unity inducer tip relative Mach numbers exceeding 1.4 can be encountered, precipitating both increased shock losses and diminished stall margin. The results of compressor rig testing on a research 6.8 inch tip (173mm) diameter single stage centrifugal compressor operating with inducer tip relative Mach number up to 1.5 are presented. The test results reveal high efficiency combined with extended flow range. This was achieved through improved impeller stability with shroud bleed, thereby permitting the diffuser to operate stably on its positive slope recovery characteristic.

Effect of the Exit System on the Performance of a Low Specific Speed Industrial Centrifugal Compressor Stage

2003 ◽  
Author(s):  
Jean-Luc Di Liberti
Keyword(s):  
Centrifugal Compressor ◽  
High Frequency ◽  
Rotating Stall ◽  
Cfd Analysis ◽  
Compressor Stage ◽  
Test Results ◽  
Centrifugal Compressor Stage ◽  
Surge Margin ◽  
Low Specific Speed ◽  
Specific Speed

A low specific speed stage was tested with two different size volutes and a return vane system. The stage was instrumented with pressure probes at various locations, including the inlet and discharge flanges, diffuser inlet, diffuser exit, and return vane inlet. Cobra probes were positioned at the diffuser inlet and the return vane inlet for the return vane configuration to measure the flow angles. High frequency transducers were installed in the diffuser. This paper presents the test results showing the effect of two different volute sizes and of the return vane system on surge margin, rotating stall onset, and overall rotor and stage performance. Rotating stall criteria are reviewed, since this stage was previously tested with a different diffuser pinch. The performance is compared with some CFD analysis.

A CFD Study on a Base and a Flow-Trimmed Low Specific Speed Centrifugal Compressor

2010 ◽  
Author(s):  
Donghui Zhang ◽  
Jean-Luc Di Liberti ◽  
Michael Cave
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Test Results ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Compressor Efficiency

A numerical study on a baseline and a 25% trimmed compressor is presented in this paper. The CFD results are compared with the test results and good agreements are reached. Both CFD and test results show that flow trimming reduces the compressor efficiency and flow range. For compressors with specific speed lower than 0.038, flow trimming is not recommended.

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