Using the Similarity Theory in the Design of Gas Turbine Engines

At present, in the promising development of gas turbine engines compared to at least the fourth generation products, there have been significant changes in the approaches to the design of engine. First of all, it is an increase in maximum values of temperature, gas pressure and circumferential flow speeds, an increase in power of the turbine stage, as well as improvement of the turbine manufacturing technology. All these factors lead to the fact that when designing the flow parts of the gas turbine, it is necessary at the fixed design flow rate of the working medium in the engine, i.e. at the fixed diameters, lengths of the nozzle and rotor blades forming the outline of the inter-blade channels, to increase the blade chords with the corresponding reduction of the number of blades in the row. The increase in turbine stage power associated with the increase in temperature, pressure (density), and circumferential velocity increases the bending stresses leading to the need to increase chords at a fixed blade length. Significant reduction of number of blades in stages, simplifies technology of blades manufacturing. A substantial increase in the maximum gas temperature, in the perspective of more than 2000 K, also leads to the need to increase the blade chords, due to the need to place cooling cavities in the blades. As a result, contradictions arise with the use of similarity theory in the design of stages of turbines of different purpose, as some of the main requirements of similarity are violated — geometric similarity of blade channels of the flow part and then the use of the generally accepted number Re by the chord of blades loses meaning. Therefore, it is necessary to carry out detailed investigations of all flow parameters in four stages of turbines with detection of influence of change of rotor blade chords at equal length of blades. And justify the effect of change of rotor blade chords on physical processes in flow parts of turbines in engines of various purpose.

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