1Department of Mechanical Engineering, PRRM Engineering College, Shabad–509 217, Jawaharlal Nehru Technological University, Hyderabad, India.
2Department of Mechanical Engineering, Vasavi College of Engineering, Osmania University, Hyderabad-500 031, India.
* Corresponding author.
A gas turbine rotor-blade assembly experiences a complex loading pattern, including varying temperatures as a result of start-up procedures. Hot section blades typically fail because of creep, oxidation, low-cycle fatigue (LCF) and high cycle fatigue (HCF). The turbine blades experience temperature excursion from ambient to the operating temperature during initial run-up. Although this time period is small (of the order of about 3 to 10 sec depending on the type of turbine), it is worthwhile to investigate the effect of the continually varying density and young's modulus (caused by such temperature changes) on the frequencies of turbine blades.
In the present paper Blades made out of two widely used materials, namely, Nimonic 86 and Inconel 738 are considered from ambient temperature (30°C) up to the expected operational temperature of about 900°C for the analyses to examine the influence of the varying temperatures on the blade during start up.
Blade stiffening effects and pressure loading on the blade are considered separately as well as combined together in the vibration analyses to obtain the natural frequencies and mode shapes of the blade from room temperature to the operational temperature for the two materials. A Comparative assessment is made about the vibration behaviour of these blades.
Finite element modeling, vibration, turbine blade, natural frequency, centrifugal loading, turbine start-up, pressure loading, operational temperature, rotational speed
