Авіаційно-космічна техніка та технологія (Aug 2020)
INFLUENCE OF CREEP OF MATERIAL OF A HIGH PRESSURE NOZZLEVANES ON THEIR OPERABILITY
Abstract
The creation of aircraft gas turbine engines that meet modern requirements for the resource, especially its hot part, requires not only more advanced design methods but also an analysis of operability and damageability during the resource to find reserves aimed at improving reliability. One of the most complex and heat-stressed components of a modern gas turbine engine is the nozzle vanes of a high-pressure turbine, directly perceiving the high temperature of the gas at the exit of the combustion chamber and having an advanced convection-film cooling system. The service life nozzle vanes of modern aviation gas turbine engines can be tens of thousands of hours. At the same time, the maximum operating mode can reach only a few hundred hours. It is believed that damage to nozzle vanes on an engine occurs mainly in hot climatic zones. Nevertheless, as the analysis of computational studies for modern aviation gas turbine engines shows, such statements are erroneous. The direct consequence of the action of elevated temperatures and high thermal stresses is the creep of the material. A computational study of the effect of creep of the material of the nozzle vanes of a high-pressure turbine under various operating conditions of the engine on their operability was carried. It is shown that with increasing flight altitude the working temperature of the nozzle vane begins to increase, and creep processes are accelerated for all climatic zones of operation. Since with increasing flight altitude, the temperature difference for different climatic zones gradually decreases, at high altitudes, where the temperature in different climatic zones differs slightly, stress relaxation processes proceed identically. In this case, with an increase in temperature, creep processes proceed faster, and the stress level to which stress relaxation occurs becomes lower. Thus, with increasing flight altitude, damage in cold conditions approaches that under normal and hot conditions, and at high altitudes, it can even be higher. The regularities of the influence of climatic conditions and flight altitude on the strength of the nozzle vanes of high-pressure turbines and their operability are established, based on which the need to take into account the operating time of the engine in various climatic conditions when determining the service life of nozzle vanes is shown.
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