Aerospace Technic and Technology

One of the promising, yet relatively underexplored, approaches to turbine component cooling is the application of the Ranque vortex effect in turbine cooling systems, enabling temperature-based separation of the cooling flow. The Ranque effect is observed in swirling fluid flows; therefore, within the context of gas turbines, the most logical location for its application in separating the flow by total temperature is the pre-swirl system (PSS), whose primary function is to impart circumferential motion to the flow. The subject of this study is the mechanisms governing the process of total temperature separation of a rotating flow in a centrifugal force field, as well as their application to the improvement of the PSS in the turbine of a small-scale gas turbine engine. The objective of the work is to reduce the temperature of the cooling air supplied to the turbine rotor blades (RB) by improving the design of the PSS through the utilization of the Ranque effect. The research tasks include identifying the PSS configuration that achieves the greatest reduction in the cooling air temperature supplied to the RB, using optimization-oriented CFD simulations of the swirling flow within the PSS flow passage. Results. From the perspective of temperature separation, the findings demonstrate the inefficiency of the jet-type cooling air supply to the PSS flow passage in the baseline engine design. This inefficiency is caused by the presence of intense secondary vortices in the flow passage of the PSS, which hinder flow separation by total temperature and promote mixing, thereby leading to temperature equalization. This study proposes supplying compressed air tangentially at angles different from those in the baseline design into the annular duct of the direct-injection type PSS, at the outlet of which the airflow is physically divided into two streams: a relatively cold stream and a relatively hot stream. The cold stream is directed to the inlet of the RB cooling system, while the hot stream is directed radially outward to seal axial gaps between the nozzle guide vanes and the turbine wheel. The calculation results demonstrated that even minor design modifications to the baseline PSS of the investigated engine allow a reduction of the cooling air temperature supplied to the RB by 2.1 K. Optimizing the tangential air supply to the PSS can provide a reduction in the total temperature of the coolant by 4 K, which, according to stress analysis, increases the service life of the turbine rotor blade by 9%. Conclusions. The conducted study confirmed the feasibility of applying the Ranque effect in cooling air supply systems for turbine rotor blades to reduce coolant temperature. Implementation of the energy separation concept in PSSs of engines larger than the one investigated in this study will eliminate design constraints that limit flow separation by total temperature, thereby yielding a more pronounced positive effect from the use of the Ranque effect in turbine blade cooling systems. Scientific novelty. For the first time, the application of the Ranque vortex effect in the design of the PSS for cooling air supply to turbine rotor blades has been proposed. This solution enables either a reduction in cooling air temperature or a decrease in its consumption without compromising RB durability, thereby enhancing the service life or efficiency of gas turbine operation.

turbine; cooling system; pre-swirl system; Ranque effect; total temperature separation; turbine blade

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