Harinath SP, Vinayaka N
Abstract: Rotary blade design is an important research area due to its criticality in applications in turbo machinery like steam turbine, aero or land based gas engines. A small mistuning gives rise to stress development through mode localization under high speed rotating conditions. Various elements like shrouds, lacing wire and tie-bolts are used as blade interconnecting elements. In the present work lacing wire is used as blade interconnecting element and the research deals with comparative case studies of frequency evaluation for without lacing and with lacing blade configurations of a HP Gas Turbine rotor. The lacing wire adds required stiffness to obtain greater structural performance as it is more aerodynamic and feasible when compared to without lacing wires free standing blades. The HP blade length of turbine is optimized based on the stress and the frequency checks. The positioning of lacing wire at 3/4th along the blade height of HP turbine blades and wire cross section considered is circular are considered for this research work. A Design of Experiments (DOE) is carried out to optimize the dimensional parameter of the lacing wire. Assuming root of turbine blade is 100 % under fixity condition, the study involves critical parametric evaluations involved in achieving mechanical integrity in airfoil design and blade platform design. Mechanical Integrity involves frequency margin checks, stress checks, analysis of Campbell diagram, checks for gross yield stress and so on, for design and off-design conditions for a given stage efficiency of 83 % in an ideal HP turbine of a gas turbine engine.
Keywords: Gas engines, lacing wire, HP Gas Turbine rotor, DOE, mechanical integrity, frequency margin, Campbell diagram