Optimization of the Contact Geometry Between Turbine Blades and Underplatform Dampers With Respect to Friction Damping

2002 ◽  
Author(s):  
Lars Panning ◽  
Walter Sextro ◽  
Karl Popp
Keyword(s):  
Contact Area ◽  
Turbine Blades ◽  
Contact Geometry ◽  
Contact Forces ◽  
Real Contact Area ◽  
Friction Damping ◽  
Roughness Effects ◽  
Blade Vibration ◽  
Friction Forces ◽  
Damping Effect

The blades of rotating compressor or turbine disks are subjected to fluctuating fluid forces that cause blade vibrations. To avoid high resonance stresses, in many applications additional damping is introduced into the bladed disk assembly by means of friction damping devices such as underplatform dampers. These are mounted between adjacent turbine blades and pressed onto the platforms due to centrifugal forces to dissipate energy by the generated friction forces due to relative motions between the damper and the neighboring blades. In real turbomachinery applications, the rotating blades are subjected to spatial vibrations caused by a complex blade geometry and distributed excitation forces acting on the airfoil. Therefore, a spatial model is presented including an appropriate spatial contact model to predict the generalized contact forces acting between the damper and the blades accurately. Six degrees of freedom are considered for each contact between the damper and the respective neighboring blades. Roughness effects are considered that determine the real contact area with respect to the nominal contact area. Different spatial blade vibration modes are investigated with regard to the friction damping that is provided by the underplatform damper. To gain the maximum damping effect, the damper mass is optimized at different working conditions of the assembly like the excitation amplitudes and the engine order. Furthermore, the influence of the contact geometry upon the damping potential is investigated in detail including the damper as well as the blade platform geometry. In practice, different damper geometries are in operation. Studies will be presented that prove the capability of the developed model to compare the effectiveness of different damper and blade platform geometries. Asymmetric platform angles leading to different contact conditions at the left and right damper contact, respectively, are studied in detail to improve the damping effect.

Scale effects on the attachment pads and friction forces in syrphid flies (Diptera, Syrphidae)

2001 ◽  
Vol 204 (8) ◽  
pp. 1421-1431 ◽  
Author(s):  
S. Gorb ◽  
E. Gorb ◽  
V. Kastner
Keyword(s):  
Body Mass ◽  
Friction Force ◽  
Contact Area ◽  
Scale Effects ◽  
Real Contact Area ◽  
Resistance Force ◽  
Friction Forces ◽  
The Real ◽  
Frictional Properties ◽  
Real Contact

To test the role of constructional and dimensional factors in the generation of friction force by systems of setose attachment pads, six species of syrphid fly (Platycheirus angustatus, Sphaerophoria scripta, Episyrphus balteatus, Eristalis tenax, Myathropa florea and Volucella pellucens) were studied using light and scanning electron microscopy. Flies were selected according to their various body mass and attachment pad dimensions. Such variables as pad area, setal density, the area of a single setal tip and body mass were individually measured. A centrifugal force tester, equipped with a fibre-optic sensor, was used to measure the friction forces of the pads on a smooth horizontal surface made of polyvinylchloride. Friction force, which is the resistance force of the insect mass against the sum of centrifugal and tangential forces, was greater in heavier insects such as Er. tenax, M. florea and V. pellucens. Although lighter species generated lower frictional forces, the acceleration required to detach an insect was greater in smaller species. The area of attachment pads, setal tip area and setal density differed significantly in the species studied, and the dependence of these variables on body mass was significant. The frictional properties of the material of the setal tips were not dependent on the dimensions of the fly species. Similar results were obtained for the frictional properties of the pulvillus as a whole. Thus, the properties of the secretion and the mechanical properties of the material of the setal tips are approximately constant among the species studied. It is concluded that differences in friction force must be related mainly to variations in the real contact area generated by the pad on the smooth surface. The real contact area can be estimated as the summed area of the broadened setal tips of the pad in contact with the surface. The real contact area depends on such morphological variables as setal density and the area of a single setal tip. Although individual variables vary among flies with different dimensions, they usually compensate such that smaller setal tip area is partially compensated for by higher setal density.

A Method for the Calculation of Friction Damping in Blade Root Joints

2010 ◽  
Author(s):  
Stefano Zucca ◽  
Christian M. Firrone ◽  
Muzio Gola
Keyword(s):  
Dynamic Balance ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Contact Model ◽  
Friction Damping ◽  
Friction Forces ◽  
Blade Root ◽  
Modal Density ◽  
Numerical Solver ◽  
High Modal Density

In turbomachinery, the complete detuning of turbine blades in order to avoid high cycle fatigue damage due to resonant vibration is often unfeasible due to the high modal density of bladed disks. To obtain reliable predictions of resonant stress levels of turbine blades, accurate modelling of friction damping is mandatory. One of the most common sources of friction damping in turbine blades is the blade root, where energy is dissipated by friction due to microslip between the blade and the disk contact surfaces held in contact by the centrifugal force acting on the blade. In this paper a method is presented to compute the friction forces occurring at blade root joints and to evaluate their effect on the blade dynamics. The method is based on an upgraded version of the state-of-the-art contact model, currently used for the non-linear dynamic analysis of turbine blades. The upgraded contact model is implemented in a numerical solver based on the harmonic balance method able to compute the steady-state dynamic response of turbine blades. The proposed method allows solving the static and the dynamic balance equations of the blade and of the disk, without any preliminary static analysis to compute the static loads acting at the contact interfaces.

Asperity-Based Models of Micro-Scale Friction

2005 ◽  
Author(s):  
George G. Adams
Keyword(s):  
Contact Area ◽  
Tangential Force ◽  
Scale Dependence ◽  
Real Contact Area ◽  
Nonlinear Load ◽  
Friction Forces ◽  
Micro Scale ◽  
Load Dependence ◽  
Real Contact ◽  
Asperity Contacts

As surfaces become smoother and loading forces decrease in applications such as MEMS, NEMS, and magnetic recording devices, the size and number of the asperity contacts which comprise the real contact area continues to decrease. The tangential force which is measured between two sliding bodies is the combined result of friction forces which are present in a very large number of nano and micro scale asperity contacts. Recent experiments as well as modeling have shown considerable scale-dependence and nonlinear load-dependence of the friction force. These models will be reviewed and discussed.

An Analytical Thermodynamic Approach to Friction of Rubber on Ice

2012 ◽  
Vol 40 (2) ◽  
pp. 124-150
Author(s):  
Klaus Wiese ◽  
Thiemo M. Kessel ◽  
Reinhard Mundl ◽  
Burkhard Wies
Keyword(s):  
Coefficient Of Friction ◽  
Liquid Layer ◽  
Contact Area ◽  
Leading Edge ◽  
Viscous Friction ◽  
Analytical Approximation ◽  
Real Contact Area ◽  
Length Scales ◽  
Real Contact ◽  
Ice Surface

ABSTRACT The presented investigation is motivated by the need for performance improvement in winter tires, based on the idea of innovative “functional” surfaces. Current tread design features focus on macroscopic length scales. The potential of microscopic surface effects for friction on wintery roads has not been considered extensively yet. We limit our considerations to length scales for which rubber is rough, in contrast to a perfectly smooth ice surface. Therefore we assume that the only source of frictional forces is the viscosity of a sheared intermediate thin liquid layer of melted ice. Rubber hysteresis and adhesion effects are considered to be negligible. The height of the liquid layer is driven by an equilibrium between the heat built up by viscous friction, energy consumption for phase transition between ice and water, and heat flow into the cold underlying ice. In addition, the microscopic “squeeze-out” phenomena of melted water resulting from rubber asperities are also taken into consideration. The size and microscopic real contact area of these asperities are derived from roughness parameters of the free rubber surface using Greenwood-Williamson contact theory and compared with the measured real contact area. The derived one-dimensional differential equation for the height of an averaged liquid layer is solved for stationary sliding by a piecewise analytical approximation. The frictional shear forces are deduced and integrated over the whole macroscopic contact area to result in a global coefficient of friction. The boundary condition at the leading edge of the contact area is prescribed by the height of a “quasi-liquid layer,” which already exists on the “free” ice surface. It turns out that this approach meets the measured coefficient of friction in the laboratory. More precisely, the calculated dependencies of the friction coefficient on ice temperature, sliding speed, and contact pressure are confirmed by measurements of a simple rubber block sample on artificial ice in the laboratory.

scholarly journals Slipping–rolling transitions of a body with two contact points

2021 ◽  
Author(s):  
Mate Antali ◽  
Gabor Stepan
Keyword(s):  
Rigid Body ◽  
Contact Point ◽  
Static Friction ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Friction Forces ◽  
Contact Points ◽  
Body Dynamics ◽  
Coulomb Model ◽  
Rigid Surfaces

AbstractIn this paper, the general kinematics and dynamics of a rigid body is analysed, which is in contact with two rigid surfaces in the presence of dry friction. Due to the rolling or slipping state at each contact point, four kinematic scenarios occur. In the two-point rolling case, the contact forces are undetermined; consequently, the condition of the static friction forces cannot be checked from the Coulomb model to decide whether two-point rolling is possible. However, this issue can be resolved within the scope of rigid body dynamics by analysing the nonsmooth vector field of the system at the possible transitions between slipping and rolling. Based on the concept of limit directions of codimension-2 discontinuities, a method is presented to determine the conditions when the two-point rolling is realizable without slipping.

scholarly journals Relationship between the real contact behavior and tribological characteristics of cotton fabric

Friction ◽  
2020 ◽  
Author(s):  
Rongxin Chen ◽  
Jiaxin Ye ◽  
Wei Zhang ◽  
Jiang Wei ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Contact Area ◽  
Dynamic Change ◽  
Tribological Characteristics ◽  
Real Contact Area ◽  
Cotton Fibers ◽  
Friction Behavior ◽  
Contact Behavior ◽  
The Real ◽  
Real Contact

Abstract The tribological characteristics of cotton fibers play an important role in engineering and materials science, and real contact behavior is a significant aspect in the friction behavior of cotton fibers. In this study, the tribological characteristics of cotton fibers and their relationship with the real contact behavior are investigated through reciprocating linear tribotesting and real contact analysis. Results show that the friction coefficient decreases with a general increase in load or velocity, and the load and velocity exhibit a co-influence on the friction coefficient. The dynamic change in the real contact area is recorded clearly during the experiments and corresponds to the fluctuations observed in the friction coefficient. Moreover, the friction coefficient is positively correlated with the real contact area based on a quantitative analysis of the evolution of friction behavior and the real contact area at different loads and velocities. This correlation is evident at low velocities and medium load.

scholarly journals Investigations on the Blade Vibration of a Radial Inflow Micro Gas Turbine Wheel

2007 ◽  
Vol 2007 ◽  
pp. 1-10 ◽  
Author(s):  
Shijie Guo
Keyword(s):  
Gas Turbine ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Turbine Blades ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Coupled Modes ◽  
Blade Vibration ◽  
Turbine Wheel ◽  
Micro Gas Turbine

This paper demonstrates the investigations on the blade vibration of a radial inflow micro gas turbine wheel. Firstly, the dependence of Young's modulus on temperature was measured since it is a major concern in structure analysis. It is demonstrated that Young's modulus depends on temperature greatly and the dependence should be considered in vibration analysis, but the temperature gradient from the leading edge to the trailing edge of a blade can be ignored by applying the mean temperature. Secondly, turbine blades suffer many excitations during operation, such as pressure fluctuations (unsteady aerodynamic forces), torque fluctuations, and so forth. Meanwhile, they have many kinds of vibration modes, typical ones being blade-hub (disk) coupled modes and blade-shaft (torsional, longitudinal) coupled modes. Model experiments and FEM analysis were conducted to study the coupled vibrations and to identify the modes which are more likely to be excited. The results show that torque fluctuations and uniform pressure fluctuations are more likely to excite resonance of blade-shaft (torsional, longitudinal) coupled modes. Impact excitations and propagating pressure fluctuations are more likely to excite blade-hub (disk) coupled modes.

scholarly journals Estimation of real contact area during sliding friction from interface temperature

AIP Advances ◽  
2016 ◽  
Vol 6 (6) ◽  
pp. 065227
Author(s):  
Sung Keun Chey ◽  
Pengyi Tian ◽  
Yu Tian
Keyword(s):  
Contact Area ◽  
Sliding Friction ◽  
Real Contact Area ◽  
Interface Temperature ◽  
Real Contact

Experimental Investigation on the Rubbing Process of Labyrinth Seals Considering the Material Combination

2020 ◽  
Author(s):  
Lisa Hühn ◽  
Oliver Munz ◽  
Corina Schwitzke ◽  
Hans-Jörg Bauer
Keyword(s):  
Turbine Blades ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Contact Forces ◽  
Experimental Investigations ◽  
Process Data ◽  
Labyrinth Seals ◽  
Material Combination ◽  
Higher Temperature ◽  
And Control

Abstract Labyrinth seals are used to prevent and control the mass flow rate between rotating components. Due to thermally and mechanically induced expansions during operation and transient flight maneuvers, a contact, the so-called rubbing process, between rotor and stator cannot be excluded. A large amount of rubbing process data concerning numerical and experimental investigations is available in public literature as well as at the Institute of Thermal Turbomachinery (ITS). The investigations were carried out for different operating conditions, material combinations, and component geometries. In combination with the experiments presented in this paper, the effects of the different variables on load due to rubbing are compared, and discussed with the focus lying on the material combination. The influence of the material on the loads can be identified as detailed as never before. For example, the contact forces in the current experiments are higher due to a higher temperature resistance of Young’s modulus. The analysis will also be based on the rubbing of turbine blades. Design guidelines are derived for labyrinth seals with improved properties regarding tolerance of rub events. Based on the knowledge obtained, guidelines for designing reliable labyrinth seals for future engines are discussed.

As-Built Geometry and Surface Finish Effects on Fatigue and Tensile Properties of Laser Fused Titanium 6Al-4V

2017 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Emily Henry ◽  
Casey Holycross ◽  
Jeff Brown
Keyword(s):  
Tensile Properties ◽  
Surface Finish ◽  
Fatigue Behavior ◽  
Turbine Blades ◽  
Material Behavior ◽  
Small Scale ◽  
Internal Cooling ◽  
Roughness Effects ◽  
Form And Function ◽  
And Function

The as-built material behavior of additive manufactured (AM) Titanium (Ti) 6Al-4V is investigated in this study. A solution heat treated, aged, stress relieved, and hot isostatic pressed Laser Powder Bed Fusion (LPBF) AM process was used to manufacture the specimens of interest. The motivation behind this work is based on the ever-growing desire of aerospace system designers to use AM to fabricate components with novel geometries. Specifically, there is keen interest in AM components with complex internal cooling configurations such as turbine blades, nozzle vanes, and heat exchangers that can improve small scale propulsion performance. Though it is feasible to three-dimensionally print parts that meet the Fit portion of a part characteristic description and identification, the Form and Function portions have proven to be more difficult to conquer. This study addresses both the Form and Function characteristics of the LPBF AM process via the investigation of geometry variation and surface roughness effects pertaining to mechanical properties and fatigue behavior of Ti 6Al-4V. Results show that geometry variation may be the cause of increased vibration fatigue life uncertainty. Also, both fatigue and tensile properties show profound discrepancies associated with surface finish. As-built surface finish specimens have lower fatigue and ductility performance, but the results are more consistent than polished data.

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