Labyrinth Air Seals Research Articles

3D CFD를 활용한 관통 래버린스 실의 회전체 동역학적 해석

Labyrinth seals are commonly used in various kinds of turbomachinery to reduce leakage flow. In the present 3D CFD analysis of see-through-type labyrinth air seal, the methodology of determining leakage and rotordynamic coefficients is suggested with the relative coordinate system for steady-state simulation. The leakage flow and rotordynamic forces predicted by using different solvers and turbulent models of FLUENT are compared with the results of the existing bulk-flow analysis code LABYSEAL.FOR and experiment. The present CFD result of direct stiffness(K) shows only improvement in prediction. The results of leakage and rotordynamic coefficients as well as computing time are sensitive against the used solver and turbulent model.

Distributed friction damping of travelling wave vibration in rods

A ring damper can be affixed to a rotating base structure such as a gear, an automotive brake rotor or a gas turbine's labyrinth air seal. Depending on the frequency range, wavenumber and level of preload, vibration of the base structure can be effectively and passively attenuated by friction that develops along the interface between it and the damper. The assembly is modelled as two rods that couple in longitudinal vibration through spatially distributed hysteretic friction, with each rod having periodic boundary conditions in a manner analogous to an unwrapped ring and disc. As is representative of rotating machinery applications, the system is driven by a travelling wave disturbance, and for that form of excitation, the base structure's and the damper's responses are determined without the need for computationally intensive simulation. The damper's performance can be optimized with respect to normal preload, and its effectiveness is insensitive to variations in preload or the excitation's magnitude when its natural frequency is substantially lower than the base structure's in the absence of contact.

Instability of an Axial Annular Flow-Induced Vibration of Thin Cylindrical Shells Having Freely Supported End

When thin cylindrical shells having freely supported end such as heat-shielding shells of after-burners, labyrinth air seals and annular structures in large diameter pipings are subjected to axial annular flow, an unstable vibration and a fatigue failure are apt to be occurred. In this paper, the unstable vibration of thin cylindrical shells is investigated cconsidering the fluid structure interaction between shells and fluid flowing through a narrow passage. The coupled equation of motion between shells and fluid is derived using Flügge's shell theory and Navier-Stokes equation. Especially, focusing on the higher circumferential vibrations, the unstable phenomenon of thin cylindrical shells is clarified by using root locus based on the complex eigenvalue analysis by using the mode functions obtained by the exact solution. The influence of shell-dimensions and so forth on the threshold of the instability of the coupled vibration of shells and flowing fluid are investigated and discussed.

627 Fluggeの殻理論による軸方向すきま流れを受ける固定-自由支持薄肉円筒殻の動的安定性(OS-4 流体関連振動,研究発表講演)

When thin cylindrical shells having freely supported end as labyrinth air seals and thermal shielding annular structures in large diameter piping are subjected to axial annular flows, an unstable vibration is apt to be occurred. The unstable vibration of thin cylindrical shells is investigated considering the fluid structure interaction between shells and flowing fluids. The coupled equation between shells and fluids is derived using the Flugge's shell theory and the Navier-Stokes equation. The unstable phenomenon is clarified by root locus based on the complex eigenvalue analysis. The influence of shell-dimensions on the threshold of the instability of the coupled vibration shells and flowing fluids is investigated. Especially, in this paper, the analysis is carried out by using two types of shell that have different length and water as a fluid.

726 軸方向すきま流れを受ける固定 : 自由支持薄肉円筒殻の振動安定性(連成振動系における流体励起不安定振動,OS-5 流体関連振動のメカニズムと計測制御(1))

When thin cylindrical shells having freely supported end as labyrinth air seals are subjected to axial leakage flows, an unstable vibration is apt to be occurred. The unstable vibration of thin cylindrical shells is analytically investigated considering the fluid structure interaction between shells and flowing fluids. The coupled equation between shells and fluids is derived using the Fliigge's shell theory and the Navier-Stokes equation. The unstable phenomenon is clarified by root locus based on the complex eigenvalue analysis. The influence of shell-dimensions on the threshold of the instability of the coupled vibration shells and flowing fluids is investigated.

Optimal Design of Split Ring Dampers for Gas Turbine Engines

Vibration analysis techniques used for labyrinth air seals are presented, along with a derivation of the methods used to calculate the dissipation capability of split ring dampers. After defining the problem in classical optimization format, the methods used to automate the process are presented, along with the results for a particular test case. For the case considered, the optimal designs were found to lie at or near the design space boundaries.

Aeroelastic Instability in FlOO Labyrinth Air Seals

Analysis of an aeroelastically unstable F100 labyrinth air seal has shown a stable design could be produced by tailoring the knife-edge lip clearance. An extensive engine experimental program confirmed that seals experienced high cycle fatigue (HCF) cracking resulting from clearance. Correlation has been demonstrated between analytically predicted instability and that observed during test engine operation. Experimental apparatus was developed to selectively augment or squelch the instability. These techniques improve definition of stability boundaries and provide a conservative means of substantiating stability margin with the revised configuration.

Nature, causes, and prevention of labyrinth air seal failures

This paper is devoted to the problems of labyrinth air seals where radially extending teeth are carried by rotating components. In view of the possibility of resonance, determination of the natural nodal frequencies of seal components and supporting structure by analysis, tests, or both is of vital importance in the design and development procedure. Construction of Campbell frequency diagrams is a basic requirement to assure adequate frequency mistuning margin against vibration and fatigue failures caused by rubs. Aerodynamic disturbing forces have also excited flexural vibration and fatigue failure of seals. A w/R stability criterion has proven effective in evaluating the hazard of aeroelastic vibration due to pressure drop across multi-tooth seals. Acoustic oscillations in the annular chamber into which the seal discharges have coupled with the corresponding natural nodal flexural vibration of seal components, which increases nodal flexural vibration of seal components, and increases the hazard of vibration and fatigue failure. Transient thermal instability may occur if the heat generated during rub causes the inner component to grow at a faster rate than outer. Seals must have compatible thermal expansions to maintain close clearances even when engine operating transients are rapid. The design and application of severed damper sleeves and ring to rotor components are effective in protecting air seals and the cylindrical walls of annular chambers aft of seals against flexural vibration and fatigue failures excited by aerodynamic disturbing forces. Since acoustically coupled oscillations persist over relatively long distances and thus involve additional components, severed damper sleeves have proven effective in protecting these thin-walled components excited by aerodynamic disturbing forces.