Dynamic Modeling of Underplateform Damper used in Turbomachinery

The present work deals with the structural analysis of turbine blades and modeling of turbine blades. A common failure mode for turbine machines is high cycle of fatigue of compressor and turbine blades due to high dynamic stresses caused by blade vibration and resonance within the operation range of the machinery. In this work, proper damping system will be analyzed to reduce the vibrating blade. The main focus of the work is the modeling of under platform damper to evaluate the dynamic analysis of turbine-blade vibrations. The system is analyzed using Bond graph technique. Bond graph is one of the most convenient ways to represent a system from the physical aspect in foreground. It has advantage of putting together multi-energy domains of a system in a single representation in a unified manner. The bond graph model of dry friction damper is simulated on SYMBOLS-shakti software. In this work, the blades are modeled as Timoshenko beam. Blade Vibrations under different working conditions are being analyzed numerically. Keywords—Turbine blade vibrations, Friction dampers, Timoshenko Beam, Bond graph modeling. HE common failure mode of turbine blade is high cycle fatigue of compressor and turbine blade due to high resonances within the operation range of the machinery. Since the advent of steam and gas turbines and compressors, and their application in various industrial sectors, blade failures (the majority of which are caused vibration related fatigue stresses) have proven to be a major cause of breakdown; often resulting in a catastrophic damage. The continuing industrial trend in recent years is to generate more power/thrust per unit mass per unit cost of equipment. In particular, the building of larger steam and gas turbines, which operate with close tolerances at higher speeds has become commonplace. The reliability and service life of such equipment is of a great economic importance, so that improvements in design methods can be minimized failures. Blade vibration is also an important guide to preventative maintenance, scheduling, which can be a major contributor to increased reliability and service life. Dynamic loads, which generate blade vibration, can arise from various sources. Rotor imbalances, nonconcentric casings causing circumferential rotor clearance to vary and irregular intake geometry related pressure distribution within the air flow produce excitation forces at low integer engine orders.The stators located up and downstream of the rotor stage cause pressure fluctuations of higher integral orders. Vibrations asynchronous with rotor Dr. Vikas Rastogi is with the Sant Longowal Institute of engineering and Technology, Longowal, Sangrur, Punjab, India (phone: +91-1672-253306 fax: +91-1672-253123, e-mail: [email protected]). Vipan Kumar is a post graduate scholar with the Sant Longowal Institute of engineering and Technology, Longowal, Sangrur, Punjab, India (e-mail: [email protected]). Loveleen Kumar Bhagi is a research Scholar with the Sant Longowal Institute of engineering and Technology, Longowal, Sangrur, Punjab, India (email: [email protected]) speed are excited by rotating stall, compressor surging and unfavorable interaction blades and flow, which may cause self exciting flutter vibrations. The blades are very structural members, particularly in the case of a compressor. Significant number of their natural frequencies can be in the frequency range of nozzle excitation forces. Though blades can be “detuned” to avoid resonance at the machine steady operating speed, they will often experience several resonances during startup, shut down, and possibly overrun. A large number of failures and shut down can be explained by blade failure due to case by the vibration or flutter. In such cases, it may be possible to introduce damping either at the root, through slip at lower speeds, or through mechanical rubbing via shroud bands, base platform and/or lacing wires at higher speeds, where the root become interlocked. The several methods to reduce the dynamic stresses are namely (1) Decreasing the force of excitation. (2) Changing resonance frequency. (3) Increasing damping. Present paper investigates the proper damping system to reduce the blade vibration. Increasing damping is one of the feasible way as the other methods effects the design conditions. This is a motivation for use of friction damper under the platform of blades. These dampers not only reduce vibration of the turbine greatly, moreover, do not extract gas flow filled and stream flow filled. The proposed research will explore the optimum use of friction damper and its modeling. A very limited research has been carried out for friction damper modeling through bond graphs. Generally, blades are subjected to forced vibration by the variation of the flow of air. These stresses are produced by resonant vibrations, which significantly affect the life of turbo engine blades. A correct design of bladed disks required the capability to obtain the different resonant frequencies and the forced response of the turbine blade. The blade failures can be effectively reduced by employing dry friction/under-plateform damper. Dry friction damper dissipates energy in the form of heat due to the rubbing motion of the contacting surfaces resulting from the relative motion. Fig. 1 Location of Friction damper Vikas Rastogi, Vipan Kumar, Loveleen Kumar Bhagi Dynamic Modeling of Underplateform Damper used in Turbomachinery T dynamic stresses caused by blades vibration and