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Research Papers: Gas Turbines: Turbomachinery

Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors

[+] Author and Article Information
Taher Halawa

Mechanical Engineering Department,
University of British Columbia,
Vancouver, BC V6T 1Z4, Canada
e-mail: taherhalawa@alumni.ubc.ca

Mohamed S. Gadala

Mechanical Engineering Department,
University of British Columbia,
Vancouver, BC V6T 1Z4, Canada
e-mail: gadala@mech.ubc.ca

Mohamed Alqaradawi

Mechanical and Industrial
Engineering Department,
Qatar University,
Al Tarfa, Doha 2713, Qatar
e-mail: myq@qu.edu.qa

Osama Badr

Mechanical Engineering Department,
British University in Egypt,
Al-Shorouk City 11837, Egypt
e-mail: osama.badr@Bue.edu.eg

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 15, 2014; final manuscript received November 1, 2014; published online December 23, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(7), 072604 (Jul 01, 2015) (10 pages) Paper No: GTP-14-1513; doi: 10.1115/1.4029169 History: Received August 15, 2014; Revised November 01, 2014; Online December 23, 2014

Numerical investigation of the optimization of the stall control efficiency for a high speed centrifugal compressor using air injection is presented. External air was injected close to the diffuser entrance at the shroud surface of the vaneless region. Injection was applied with mass flow rates of 0.7%, 1%, and 1.5% of the design inlet mass flow rate with six different angles of 0 deg, 10 deg, 20 deg, 30 deg, 40 deg, and 180 deg measured from the positive tangential direction at the vaneless region. Detailed comparisons were made between the case without using air injection and the different air injection cases by comparing velocity, pressure, and force fluctuations with time. Results showed that as the injection mass flow rate increases, the number of diffuser passages with reversed flow decreases for all cases of injection except for the case of reverse tangent injection. Results indicated that using angle of injection of 30 deg minimized the stall area and provided the least force fluctuations with no reversed flow compared to other injection angles. Finally, it was found that injecting air with mass flow rate of 1.5% of the inlet mass flow rate at an angle of 30 deg resulted in shifting of stall onset to a mass flow rate corresponding to 3.8 kg/s instead of 4 kg/s for a compressor without using air injection control.

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References

Figures

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Fig. 1

Cross section of the NASA CC3 centrifugal compressor [22]

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Fig. 8

Pressure contours at 95% of span during stall

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Fig. 9

Velocity vectors through the tip clearance (at region 1 indicated in Fig. 8)

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Fig. 10

Velocity vectors through the tip clearance (at region 2 indicated in Fig. 8)

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Fig. 11

Velocity vectors through the tip clearance (at region 3 indicated in Fig. 8)

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Fig. 12

Description of (a) the injection locations and (b) the injection angle

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Fig. 13

The number of diffuser passages with reversed flow for various angles of injection and injection mass flow rates

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Fig. 14

Flow path lines colored by Mach number value for various angles of injection at the minimum and maximum injection mass flow rate used

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Fig. 15

Variation of the force acting on blades in the axial direction with time for the best injection cases and for the case without using injection

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Fig. 16

Variation of the force acting on blades in X-direction with time for the best injection cases and for the case without using injection

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Fig. 17

Variation of the force acting on blades in Y-direction with time for the best injection cases and for the case without using injection

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Fig. 2

The CFD numerical model of the NASA CC3 compressor

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Fig. 3

Mesh independency test (pressure variation at the midspan with the axial direction z). (a) For three different mesh cases and for the calculated extrapolation curve and (b) for the fine mesh case clarified with error bars.

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Fig. 4

Mesh accuracy verification: (a) temporal accuracy and (b) convergence history

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Fig. 5

Mesh configuration for the impeller and diffuser

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Fig. 6

Pressure map (comparison between numerical model results and experiments [22])

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Fig. 7

Validation for the pressure and velocity profiles: (a) pressure ratio variation at the impeller shroud with the percent meridonal chord (numerical results versus measurements [22]) and (b) velocity ratio variation from hub to tip at radius ratio of 1.05 inside the vaneless region (numerical results versus measurements [31])

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Fig. 18

The angle of injection α at the radial-axial plane

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Fig. 19

Pressure variation at points in the vaneless region with time at Θ = 30 deg for α = 10 deg, 15 deg, and 20 deg

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