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Amirhasan Jafari-MasterThesis.pdf (2.22 MB)

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Investigation of a Cavity Simulating the Clearance Gap at the Grooved Tips of Axial High Pressure Turbines

Jafari, Amirhasan
http://rave.ohiolink.edu/etdc/view?acc_num=csu1432651730

Abstract Details

, Master of Science in Mechanical Engineering, Cleveland State University, Washkewicz College of Engineering.
Modern gas turbines operate at high overall pressure ratio and high gas temperature. The presence of tip clearance flows together with the high gas temperature will result in high aerodynamic losses and high heat transfer and can be detrimental to the blade tip. This work simulates the flow and heat transfer through the clearance gap for base line flat tip and cavity tip geometries with a stationary and moving shroud. Various parameters were investigated to assess the possibility of minimizing tip heat flux and aerodynamic losses. Those parameters include: 1) Cavity depth-to-width ratio, 2) Clearance-to-width ratio, 3) Different shroud speeds. The Computational Fluid Dynamics (CFD) code ANSYS Fluent was used to perform the calculations. Turbulence was modeled using Spalart-Allmaras (SA) model which was available in Fluent and the Reynolds number investigated is 15,000 which is based on inlet velocity and cavity height. Areas of high heat transfer rate were identified on the blade tip and the change of gas leakage for different tip treatments were examined. Also, the effect of tip injection on tip desensitization was assessed for four different jet blowing ratios (0.5, 1.0, 2.0, and 3.0), three different jet angles (30°, 90°, and 150°), and three different jet locations (Camber Line (CL), Pressure Side (PS), and Suction Side (SS)). It is shown that injecting air to the tip gap region always reduces the aerodynamic loss across the tip due to leakage flow. Higher blowing ratios are more effective in reducing the mass flow rate through the tip gap. One of the finding of the present study shows that blowing ratio has the highest effect on the flow in the region compared to the other two parameters examined (jet angle and jet location). The present study shows that a jet at lower blowing ratios such as M=0.5 and M=1.0 reduces heat flux to the surface by reducing the heat transfer coefficient. However, at higher velocities such as M=2.0 and M=3.0 cause more disturbance in the jet downstream and increase the heat transfer rates and are detrimental for the blade. It is shown that blowing air at a shallow angle like 30° reduces the heat transfer coefficient values more effectively in comparison with a more steeper angle like 90°. Blowing in the opposite direction of the mainstream flow does not improve the heat transfer coefficient significantly. Finally, it was found out that jets at pressure side are more effective in reducing heat transfer values of the cavity wall in comparison with central and suction side jets.
Mounir Ibrahim, PhD (Committee Chair)
Asuquo Ebiana, PhD (Committee Member)
Vikram Shyam, PhD (Committee Member)
Mechanical Engineering

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Citations

  • Jafari, A. (2015). Investigation of a Cavity Simulating the Clearance Gap at the Grooved Tips of Axial High Pressure Turbines [Master's thesis, Cleveland State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=csu1432651730

    APA Style (7th edition)

  • Jafari, Amirhasan. Investigation of a Cavity Simulating the Clearance Gap at the Grooved Tips of Axial High Pressure Turbines. 2015. Cleveland State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=csu1432651730.

    MLA Style (8th edition)

  • Jafari, Amirhasan. "Investigation of a Cavity Simulating the Clearance Gap at the Grooved Tips of Axial High Pressure Turbines." Master's thesis, Cleveland State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1432651730

    Chicago Manual of Style (17th edition)

csu1432651730
266
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This open access ETD is published by Cleveland State University and OhioLINK.