Investigation of Damping Potential of Strip Damper on a Real Turbine Blade

Abstract

This paper investigates the damping potential of strip dampers on a real turbine bladed disk. A 3D numerical friction contact model is used to compute the contact forces by means of the Alternate Frequency Time domain method. The Jacobian matrix required during the iterative solution is computed in parallel with the contact forces, by a quasi-analytical method. A finite element model of the strip dampers, that allows for an accurate description of their dynamic properties, is included in the steady-state forced response analysis of the bladed disk. Cyclic symmetry boundary conditions and the multiharmonic balance method are applied in the formulation of the equations of motion in the frequency domain. The nonlinear forced response analysis is performed with two different types of boundary conditions on the strip: (a) free-free and (b) elastic, and their influence is analyzed. The effect of the strip mass, thickness and the excitation levels on the forced response curve is investigated in detail.

Modeling and Testing Friction Flexible Dampers: Challenges and Peculiarities

“…Dry friction can be incorporated into the blade design, in the form of shrouds, lacing wires or zigzag pins. Alternatively, external devices such as solid dampers (available in several designs, cylindrical, curved flat, wedge damper, etc), thinstrip dampers [3,4] or ring dampers [5,6] of the different sources of damping in turbo engines was performed in [2]. It was shown that the values of Q (amplitude factor, inverse of the loss factor η) may vary as follows: 3000 to 10,000 for material damping, 50 to 140 for root damping, 180 to 2500 for shroud damping, and 15 to 250 for platform damping (external dry friction dampers).…”

“…The design of the strips, not only for sealing but also for damping purpose, represents a topic of recent interest for the turbine designers, as very few studies can be found in literature [3,4].…”

Forced Response Prediction of Turbine Blades with Flexible Dampers: The Impact of Engineering Modelling Choices

“…Most of the proposed calculation methodologies for bulk UPDs use simplifying assumptions, such as neglecting the damper inertia or flexibility [11,19,25]. However, these assumptions, perfectly adequate for solid UPDs, cannot be applied to model strip dampers, as they are highly flexible and consequently their flexible vibrational modes need to be taken into account in the modelling process through FE modelling [17].…”

“…In this way the strips act both as friction dampers and as an additional constraint affecting the blade natural frequencies. The design of the strips, not only for sealing, but also for damping purpose, represents a topic of recent interest for the turbine designers, as very few studies can be found in literature [4,17].…”

“…Alternatively, external devices such as solid dampers (available in several designs, namely cylindrical, curved flat, wedge damper, etc. [10][11][12][13][14][15][16] or thin-strip dampers [17] can be added to minimize the resonant blade response. These external dry friction dampers are extensively used in turbine designs because they are easy to manufacture, install and substitute, relatively inexpensive and can withstand high temperatures.…”