The authors of the paper have developed and successfully tested a method for optimizing the impingement starter of a gas turbine engine (GTE), considering its joint operation with the auxiliary power unit (APU). As a result, a way to increase the efficiency of the existing launch system during the modernization of the turbofan engine was found. Hereinafter, start efficiency is a reduction in engine starting time and its possibility under all operating conditions.

When designing and modernizing a gas turbine engine, the main attention is usually paid to its main components: compressor, combustion chamber, turbine, etc. Huge efforts are spent to improve the properties of these components, as evidenced by the huge number of publications. However, there are several “secondary” elements in the gas turbine engine. One of them is the launch system and the turbo starter included in it, which is a small turbine driven by compressed air from the APU. It is used to spin the engine rotor at startup. Even though this element is small compare to the engine and only works for a short time, the operation of a gas turbine engine is impossible without it. This system must provide the ability to start the engine in a short time (for military aircraft in a very short time) at any operating conditions.

The presented work appeared while verifying the possibility of using existing turbo starter for a modernized engine using modern APU while fulfilling all existing operational limitations. To solve it, a methodology was developed for determining the possibility of joint operation of the starter turbine and the APU, as well as the parameters of the air system there. The essence of the methodology is that a characteristic of the form: flow parameter is the function of the pressure drop across the turbine is determined for an air turbine of a turbo starter based on CFD modeling in the NUMECA program The calculated characteristic of the turbine was obtained taking into account the correction factors found during verification, and is in good agreement with the experimental data.

The obtained characteristic was combined with the characteristic of the APU in the same coordinates for different flight conditions. The intersection points of the characteristics of the turbine and the APU corresponded to the operating points of the launch system. Non-intersection of the characteristics of the APU and the turbine signals the impossibility of the launch system operation at this mode. At the found work points, the main parameters of the launch system were determined using CFD modeling. In particular, the torque values ​​on the output shaft were checked. If it exceeded the limit value under the conditions of structural strength, work in this mode was considered as impossible. The torque value was also used to calculate the engine start time.

Based on the developed methodology for determining the possibility of joint operation of the launch system, an optimization algorithm for the turbo starter turbine was developed and implemented.

Based on the developed tools, the possibility of using existing turbo starters to launch the modernized engine was analyzed. It was found that the considered variants for air turbo starters do not meet the requirements: the first variant provides torque above the permissible, and the second one has a long start time. Using the developed algorithms, the shape of the flow path of the first turbo starter variant was optimized, which made it possible to find such an option for its modernization that with minimal changes in the design provides the permissible value of the torque on the shaft with  an acceptable start time in at operating modes.


Optimization of an Air Turbo Starter Considering its Joint Work With an Auxiliary Power Unit

Division / Sponsor:
International Gas Turbine Institute (IGTI)

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

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