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Computational Analysis of the Performance Characteristics of a Supercritical CO_{2} Centrifugal Compressor

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Real Gas Property Table

#### 2.2. Compressor Geometry and Mesh

#### 2.3. Numerical Methodology

## 3. Validation

## 4. Results and Discussion

#### 4.1. Effect of Tip Clearance

#### 4.2. Effect of Diffuser

#### 4.3. Flow Field Near the Impeller and Diffuser Interface

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Variation of thermodynamic properties near the critical point. (

**a**) Iso-baric specific heat near critical point. (

**b**) Variation of density near critical point.

**Figure 3.**Computational domains for different centrifugal compressor configurations. Inset figures represent the meridional geometry. (

**a**) Impeller alone. (

**b**) Impeller with vaneless diffuser. (

**c**) Impeller with vaned diffuser.

**Figure 5.**Comparison of present numerical results with the SNL experimental results [15] at inlet temperature of 309 K and pressure of 92 × 10${}^{5}$ Pa.

**Figure 6.**The y${}^{+}$ contour on hub and blade surface with K-$omega$ turbulence model. The blade trailing edge region is zoomed in the inset figure to show the maximum y${}^{+}$ value.

**Figure 7.**The isentropic compression efficiency and the total enthalpy at outlet for the impeller without and with tip clearance configurations. Solid lines indicate the total-static isentropic efficiency and the dashed lines shows the total enthalpy at the outlet.

**Figure 8.**Circumferential pressure contour at the trailing edge for mass flow rate of 4 kg/s. (

**a**) Impeller alone. (

**b**) Impeller with vaneless.

**Figure 9.**Blade pressure loading for impeller without tip clearance and with tip clearance at a mass flow rate of 4 kg/s.

**Figure 10.**Velocity vector plot on the meridional plane with mass flow rate averaged entropy at a mass flow rate of 4 kg/s. The flow at the outlet section is uniform in impeller without tip clearance configuration, while it becomes a wake flow in with tip clearance configuration. (

**a**) Impeller without tip clearance. (

**b**) Impeller with tip clearance.

**Figure 11.**Performance characteristics of various configurations. (

**a**) Comparison of isentropic compression efficiency of different configurations. The efficiency increases on the inclusion of the diffuser section in the impeller with the tip clearance configuration and attains a peak value near the design mass flow rate of 3.53 kg/s. (

**b**) Comparison of the total-static pressure ratio of different configurations. The pressure ratio for vaned diffuser decreases at a higher rate than the vaneless diffuser configuration which indicates the vaned diffuser becomes less efficient at mass flow rate more than 3.25 kg/s.

**Figure 12.**Relative Mach number contour plot at the span of 80% from hub to shroud at a mass flow rate of 3.2 kg/s. (

**a**) Impeller alone. (

**b**) Impeller with vaneless. (

**c**) Impeller with vaned.

**Figure 13.**Streamlines near leading edge of the main blade on the relative Mach number contour at a mass flow rate of 3.2 kg/s. (

**a**) Impeller alone. (

**b**) Impeller with vaneless diffuser. (

**c**) Impeller with vaned diffuser.

**Figure 14.**Volume near leading edge shows the regions where the pressure is lower than the inlet pressure at mass flow rate of 3.2 kg/s. (

**a**) Impeller alone. (

**b**) With vaneless diffuser. (

**c**) With vaned diffuser.

**Figure 15.**Volume shows the regions near trailing edge where the pressure is lower than the inlet pressure at a mass flow rate of 3.2 kg/s. (

**a**) Impeller alone. (

**b**) With vaneless diffuser. (

**c**) With vaned diffuser.

**Figure 17.**Pressure contour and velocity vector at span 50% span for impeller alone with vaned diffuser configuration. (

**a**) Impeller with vaned diffuser at mass flow rate of 1.4 kg/s. (

**b**) Impeller with vaned diffuser at mass flow rate of 3.8 kg/s.

**Figure 18.**Pressure contour at span 50% span of impeller with vaneless diffuser. (

**a**) Vaneless diffuser at mass flow rate of 1.4 kg/s. (

**b**) Vaneless diffuser at mass flow rate of 2.9 kg/s. (

**c**) Vaneless diffuser at mass flow rate of 4.5 kg/s

**Figure 19.**Velocity vectors near trailing edge of the main blade for vaneless configuration. (

**a**) Vaneless diffuser at mass flow rate of 1.4 kg/s. (

**b**) Vaneless diffuser at mass flow rate of 2.9 kg/s. (

**c**) Vaneless diffuser at mass flow rate of 4.5 kg/s.

Number of main blades | 6 | Blade thickness at impeller trailing edge | 0.762 mm |

Number of splitter blades | 6 | Blade height at impeller leading edge | 1.7 mm |

Impeller inlet radius at hub | 2.537585 mm | Blade angle of the impeller leading edge at hub | 17.88${}^{\circ}$ |

Impeller inlet radius at shroud | 9.372047 mm | Blade angle of the impeller leading edge at mean radius | 37.13${}^{\circ}$ |

Impeller exit radius | 18.68170 mm | Blade angle of the impeller leading edge at shroud | 50${}^{\circ}$ |

Full blade length | 25 mm | Blade angle of the impeller trailing edge | –50${}^{\circ}$ |

Splitter blade length | 12.5 mm | Angle between streamlines and shaft at impeller inlet | 0${}^{\circ}$ |

Axial length of the impeller | 15.9 mm | Angle between streamlines and shaft at impeller exit | 90${}^{\circ}$ |

Clearance gap at impeller tip | 0.254 mm | Blade thickness at impeller leading edge | 0.762 mm |

Number of vanes | 17 | Blade height at diffuser exit | 1.8 mm |

Diffuser inlet radius | 18.5 mm | Diffuser channel length | 10.6 mm |

Diffuser exit radius | 26.0 mm | Blade thickness at diffuser inlet | 0.0 mm |

Blade angle at diffuser inlet | 71.5 | Blade thickness at diffuser exit | 3.35 mm |

Blade height at diffuser inlet | 1.8 mm |

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**MDPI and ACS Style**

Raman, S.K.; Kim, H.D.
Computational Analysis of the Performance Characteristics of a Supercritical CO_{2} Centrifugal Compressor. *Computation* **2018**, *6*, 54.
https://doi.org/10.3390/computation6040054

**AMA Style**

Raman SK, Kim HD.
Computational Analysis of the Performance Characteristics of a Supercritical CO_{2} Centrifugal Compressor. *Computation*. 2018; 6(4):54.
https://doi.org/10.3390/computation6040054

**Chicago/Turabian Style**

Raman, Senthil Kumar, and Heuy Dong Kim.
2018. "Computational Analysis of the Performance Characteristics of a Supercritical CO_{2} Centrifugal Compressor" *Computation* 6, no. 4: 54.
https://doi.org/10.3390/computation6040054