Study of complex strength characteristics of gas turbine odels fabricated by additive methods

Aeronautical and Space-Rocket Engineering

Strength and thermal conditions of flying vehicles


Аuthors

Alekseev V. V.*, Bobrov A. N., Kalugin K. S.**

Bauman Moscow State Technical University, MSTU, 5, bldg. 1, 2-nd Baumanskaya str., Moscow, 105005, Russia

*e-mail: Alekseevvadimiibmstu@gmail.com
**e-mail: Kalugin-09@mail.ru

Abstract

Recently, the studies related to the additive technologies application in various industries, including aviation and space-rocket mechanical engineering, are considered promising. An indisputable advantage of additive technologies is minimization, and, in some cases, complete elimination of the need for parts machining, which significantly reduces both the time consumption and the finished part cost.

There are several basic 3D-printing methods, differing in the source material and technology of the parts formation. Recently, the parts production by selective laser sintering of metal polymer compositions powders (SLM-printing) has become topical.

The SLM-printing technology consists in layer-by layer deposition and sintering of powder on a special substrate. However, application of the selective laser powders sintering method is associated with problems of the porosity formation and a decrease in the strength of the parts produced. Thus, the issue of practical application for parts of the space-rocket and aviation equipment, created by the 3D-printing, still remains open.

To substantiate the possibility of 3D-printing application in turbines production for laboratory test benches on compressed air, the strength calculation of the turbine from PLA-plastic printed on the 3D printer were performed. The tests were performed to confirm the calculations results.

When developing a turbine 3D-model the rotor wheel geometry was selected, based on the prototype, which was used in the turbine structure employed in the laboratory test bench installation at the BMSTU for the laboratory works for studying the energy characteristics of active turbines.

Besides the external loads, the gas turbines rotor wheels load-bearing capacity is affected by loading conditions, such as gas temperature. However, the gas turbines employed in laboratory work benches on the compressed air are operating, as a rule, at low operating temperature of 30-50°C. Thus, the temperature stresses may be neglected while strength calculations of the turbine disk.

A 3D-model of the turbine under test was built with the Autodesk Inventor program. A finite-element model containing about 4.15 million elements was built for the above said model. Its strength analysis was performed with the Autodesk Simulation Mechanical 2019 module. The mesh thickening was reduced to the base of one blade only, since the load distribution is symmetrical. It can be seen from the safety factor distribution fields that minimum safety factor corresponds to the root sections of the blades, and it is no less than 3.3.

While theoretical calculations the modified safety factor n1, accounting for the effect of the part material porosity (for the case of its manufacture by 3D­prototyping) through coefficient k, was 3.28.

For tests performing, an axial active supersonic gas turbine was manufactured from PLA-plastic according to the SLM-printing technology.

For tests performing, a test bench, consisting of an electric motor, a voltage regulator, a tachometer, a video camera, as well as a turbine under study was assembled.

The methodology of the experiment conducting is as follows: the turbine is fixed on the motor shaft by the keyed and glue joints. When the motor is connected to the mains (220 VAC), the shaft and the turbine begin rotating. The rotational speed is changed by a voltage regulator connected to the motor circuit, and can aquire values from 0 to 24000 rpm, which corresponds to the voltage range in the motor network from 0 to 220 V. The data on the motor rotational speed are read from the digital optical tachometer. The experiment is being shot by the video camera.

The strength calculations of the axial supersonic gas turbine fabricated from the PLA-plastic by the SLM-printing additive technology revealed that the safety factor in operation conditions of laboratory test benches with compressed air was higher than the maximum allowable one for the considered unit.

As a confirmation for calculations, the turbine rotational speed during the test reached 24,000 revolutions per minute, which is the maximum possible value for the engine used in the tests. With this, visible defects were not detected in the turbine itself.

On the assumption of the performed studies it was established that the turbine manufactured using additive technologies can be employed for the laboratory text benches operating on compressed air.

Keywords:

gas turbines, PLA-plastic, turbine strength, SLM-printing, strength test, 3D-prototyping, safety factor

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