High thermal efficiency of a gas turbine is dependent on high turbine entry temperature, which is limited by the turbine blade and vane materials. Continuous cooling of these components allows their environmental operating temperature to exceed the material’s creeping temperature without affecting the blade and vane integrity. Heat conduction from the turbine blades to the turbine disc requires the discs to be cooled and thus prevent thermal fatigue and uncontrolled expansion and contraction rates.

Most of the blade cooling methods improve the cooling either with enhancement of heat transfer surfaces by changing the blade channel geometries or increase heat transfer coefficients by changing the flow properties. This encounters the gas turbine manufacturers to high cost for any change of blade design. Since large number of gas turbine engines are working throughout the world with traditional cooling systems, modification of cooling system of gas turbine fleet by low cost can be explainable for users and so can help global energy saving. In some well-known heavy duty gas turbine engines, the air is led from the compressor exit through the radial holes on the hollow shaft rotor. Due to the structure of these inlet holes, only static pressure force drives the air inside the rotor toward the air cooling channels around the turbine wheel where it is led through radial holes to the root of the rotary blades.

In this paper, a new method is presented for cooling improvement of the turbine blades supplying more cooling air with more energy by active extraction from the compressor. The cool air is extracted from the compressor through inlet holes to the air transferring channels on the disc edge or hollow shaft using tangential velocity of the rotating shaft which results in increasing the amount and energy of the cooling air. In fact a forward angle of the channels is used to help the pressurized air overcome the air centrifugal force and accelerates the inward flow through the center hollow shaft. High rotational movement of the shaft can have a positive effect on adding pressure and mass flow rate of the bleed air into the internal cooling air channels of the turbine blades. It keep fixed the blade geometry and make some simple changes in extraction cooling air holes which dramatically reduce the manufacturing complexity comparing to the other cooling methods. Thus increasing turbine performance as well as extending the blade life can be possible by low cost modifications. It is analyzed using CFD simulation on a simplified model of a gas turbine. The numerical method is utilized for discretization of the rotating Navier-Stokes equations and numerical simulation of different new geometries of the holes into the gas turbine shaft. The governing equations, mesh treatment, boundary conditions and numerical setup are described. The captured results are compared to those of original turbine shaft to show the heat transfer improvement by enhancing the cool flow rate and fluid energy and the most efficient inlet holes geometry is select.


Cooling Improvement of Gas Turbine Rotary Blades

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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