Aeroelastic Instability in Labyrinth Seals

1968 ◽  
Vol 90 (4) ◽  
pp. 369-374 ◽  
Author(s):  
F. Ehrich
Keyword(s):  
High Speed ◽  
Stability Boundary ◽  
Low Pressure ◽  
Labyrinth Seal ◽  
Stability Parameter ◽  
Pressure Perturbation ◽  
Labyrinth Seals ◽  
Stick Slip ◽  
Pivot Point ◽  
The Stability

Labyrinth seals and associated structural elements have been noted to sustain fatigue failure in high powered, high speed rotating machinery under circumstances that preclude blaming standing wave resonances or “stick-slip” excitation from rotor/stator rubs. Alford [2] has hypothesized that such failures may be caused by self-excited aeroelastic vibration of the seal. A model is defined in which a pressure perturbation in the seal internal volume between the high and low pressure teeth can cause an elastic rotation of the seal rotor or stator element about a virtual pivot point located on the high or low pressure side of the seal. This rotation, in turn, causes a nonuniform opening and closing of the high and low pressure clearances which can give rise to the hypothesized pressure perturbation. A stability parameter is then derived in terms of the high pressure and low pressure tooth clearances, the supply pressure to the seal, the seal width and height, and two parameters indicative of the elastic properties of the seal—its stiffness to radial motion and the location of its virtual pivot point. The stability criterion is applied to a pair of actual labyrinth seal rotors which differ from each other only slightly and are known, from actual practice, to straddle the stability boundary. That is, the larger diameter unit is known to be unstable and the smaller diameter unit known to be stable. On the basis of an instability incident simulated on component test, the stiffness used in evaluating the stability parameter is modified to be representative of the least stiff vibratory mode, and the stability parameter is shown to give reasonable indication of the stability problem in labyrinth seals.

A CFD Study on the Dynamic Coefficients of Labyrinth Seals

2012 ◽  
Author(s):  
Donghui Zhang ◽  
Chester Lee ◽  
Michael Cave
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Dynamic Coefficients ◽  
Rotating Impeller ◽  
Coupling Stiffness ◽  
Direct Stiffness ◽  
Compressor Efficiency

Labyrinth seals are widely used in gas compressors to reduce internal leakage and increase the compressor efficiency. Due to the eccentricity between the rotating impeller and the stationary part as *well as the shaft whirling motion, forces are generated when the leakage flow passing through the cavities and the seals. For a lot of applications with high speed and pressure, these forces can drive the system unstable. Thus, predicting the forces accurately become a very important for compressor rotordynamic designs. A lot of research and studies has been done to the seals itself, including bulk flow method, computational fluid dynamic (CFD) and test measurement. The seal and leakage flow interaction forces can be predicted relatively accurate. But very few research treat the seal and cavities as one component interacting with the leakage flow and produce the forces. This paper presents results of CFD investigations on the dynamic coefficients of one typical impeller eye seal and front cavity. The CFD results show that large forces are generated in the front cavity due to circumferential uniform pressure distribution, which caused by the downstream labyrinth seal. The forces generated in the front cavity are more than in the front seal. It was found that the inertia, damping, and stiffness are proportional to average pressure. The cross-coupling stiffness increases with speed with power of 2 while the direct stiffness increases with speed with power of about 1.7.

Deficiencies in Turbulence Modelling for the Prediction of the Stability Boundary in Highly Loaded Compressors

2019 ◽  
Author(s):  
Jose Moreno ◽  
John Dodds ◽  
Mehdi Vahdati ◽  
Sina Stapelfeldt
Keyword(s):  
High Speed ◽  
Stability Boundary ◽  
Turbulence Models ◽  
Stability Limit ◽  
Major Effect ◽  
Navier Stokes ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Multi Stage ◽  
The Stability

Abstract Reynolds-averaged Navier-Stokes (RANS) equations are employed for aerodynamic and aeroelastic modelling in axial compressors. Their solutions are highly dependent on the turbulence models for closure. The main objective of this work is to assess the widely used Spalart-Allmaras model’s suitability for compressor flows. For this purpose, an extensive investigation of the sources of uncertainties in a high-speed multi-stage compressor rig was carried out. The grid resolution near the casing end wall, which affects the tip leakage flow and casing boundary layer, was found to have a major effect on the stability limit prediction. Refinements in this region led to a stall margin loss prediction. It was found that this loss was exclusively due to the destruction term in the SA model.

Tip-Shroud Labyrinth Seal Effect on the Flutter Stability of Turbine Rotor Blades

2019 ◽  
Author(s):  
Roque Corral ◽  
Michele Greco ◽  
Almudena Vega
Keyword(s):  
Rotor Blade ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Stability Prediction ◽  
Labyrinth Seals ◽  
Turbine Rotor Blade ◽  
The Stability ◽  
Shrouded Rotor ◽  
Tip Shroud

Abstract The effect of the tip-shroud seal on the flutter onset of a shrouded turbine rotor blade, representative of a modern gas turbine, is numerically tested and the contribution to the work-per-cycle of the aerofoil and the tip-shroud are clearly identified. The numerical simulations are conducted using a linearised frequency domain solver. The flutter stability of the shrouded rotor blade is evaluated for an edgewise mode and compared with the standard industrial approach of not including the tip-shroud cavity. It turns out that including the tip shroud significantly changes the stability prediction of the rotor blade. This is due to the fact that the amplitude of the unsteady pressure created in the inter-fin cavity, due to the motion of the airfoil, is much greater than that of the airfoil. It is concluded that the combined effect of the seal and its platform tends to stabilise the rotor blade for all the examined nodal diameters and reduced frequencies. Finally, the numerical results are shown to be consistent with those obtained using an analytical simplified model to account for the effect of the labyrinth seals.

Dynamic Stability of a Motorized High Speed Machine Tool Spindle Supported on Bearings

2014 ◽  
Vol 612 ◽  
pp. 29-34
Author(s):  
Jakeer Hussain Shaik ◽  
J. Srinivas
Keyword(s):  
Machine Tool ◽  
Frequency Response ◽  
High Speed ◽  
Stability Boundary ◽  
Second Phase ◽  
Element Formulation ◽  
Machining Parameters ◽  
Response Functions ◽  
Frequency Response Functions ◽  
The Stability

Dynamic behaviour of spindle system influences chatter stability of machine tool considerably. Self-excited vibrations of the tool results in unstable cutting process which leads to the chatter on the work surface and it reduces the productivity. In this paper, a system of coupled spindle bearing system is employed by considering the angular contact ball bearing forces on stability of machining. Using Timoshenko beam element formulation, the spindle unit is analyzed by including the gyroscopic and centrifugal terms. Frequency response functions at the tool-tip are obtained from the dynamic spindle model. In the second phase, solid model of the system is developed and its dynamic response is obtained from three dimensional finite element analysis. The works on analysis of the stability of milling processes focus on calculating the stability boundary of the machining parameters based on the dynamic models characterizing the milling processes. The stability lobe diagrams are generated from frequency response functions (FRF’s) lead to an stability limit prediction for the system at high speed ranges.

Development of a Novel In-Situ-Generated Foamed Gel as Temporary Plugging Agent Used for Well Workover: Affecting Factors and Working Performance

SPE Journal ◽  
2019 ◽  
Vol 24 (04) ◽  
pp. 1757-1776 ◽  
Author(s):  
Hu Jia ◽  
Xin-Yu Yang ◽  
Jin-Zhou Zhao
Keyword(s):  
High Speed ◽  
Gas Permeability ◽  
Crosslinking Agent ◽  
Low Pressure ◽  
Fluid Loss ◽  
Coefficient Function ◽  
Foaming Agent ◽  
Working Performance ◽  
The Stability

Summary Foams can be used as well-killing fluid for workover operation in low-pressure oil and/or gas wells. However, foams usually come from gas injection under high pressure or high-speed stirring, which is complicated, expensive, and hazardous. In addition, the foam's stability is still limited by the current method of adding viscous polymer or the single crosslinking between the polymer and single crosslinking agent. This paper explores a simple and safe in-situ generating procedure under surface conditions by virtue of the coefficient function of the CO2-gas-producing chemicals (GPCs) and the foaming agent. The foam stability is enhanced through the double crosslinking with the application of chromium acetate III (Cr3+) and polyethyleneimine (PEI), which guarantees its stability in the wellbore. This systematic study consists of optimization of different foaming agents, gel bases, and the effect of the GPC compositions (carbonate and acid) and their quantity, a macroscopic comparison of the stability and rheological properties of the double crosslinking and the common single crosslinking systems, with further investigation of their stability differences through microscopic research, and a coreflooding experiment to evaluate working performance. Within 4 days, the density of this novel foamed gel varies from 0.711 to 0.910 g/cm3 at 35°C, satisfying the present operation requirements for density and stability. This is because of the function of the GPCs and foaming agent, which means that finer foams can be obtained to achieve target low density. Meanwhile, on the basis of the double crosslinking, a more compact gel structure is formed; thus the stability can be effectively improved. Results also demonstrated that this foamed gel shows a favorable performance of low fluid loss and temporary plugging, and the gas-permeability-recovery rate is up to 93.90%, which proves the gel to be effective for formation-damage control. This study suggests that the novel in-situ-generated foamed gel has the potential to achieve favorable well-workover performance in low-pressure and low-temperature reservoirs.

Rotordynamic Impact of Swirl Brakes on Labyrinth Seals With Smooth or Honeycomb Stators

1997 ◽  
Author(s):  
K. Kwanka
Keyword(s):  
Stability Limit ◽  
Labyrinth Seal ◽  
Flexible Rotor ◽  
Labyrinth Seals ◽  
Identification Procedure ◽  
Continuous Growth ◽  
Rotating Speed ◽  
Dynamic Coefficients ◽  
Flow Through ◽  
The Stability

The flow through labyrinth seals of turbomachinery generates forces which can cause self-excited vibrations of the rotor above the stability limit. The stability limit is reached at a specific rotating speed or power. The continuous growth in of power density and rotating speed necessitates an exact prediction of the stability limit of turbomachinery. Usually the seal forces are described with dynamic coefficients. A new, easy-to-handle identification procedure uses the stability behavior of a flexible rotor to determine the dynamic coefficients. Systematic measurements with a great number of labyrinth seal geometries lead to reasonable results and demonstrate the accuracy and sensitivity of the procedure. A comparison of the various methods used to minimize the excitation indicates which seal is more stable and will thus improve the dynamic behavior of the rotor.

Rotordynamic Characterization of Labyrinth Seals in Steam Turbines: Effects of Thermal and Mechanical Loads

2018 ◽  
Author(s):  
Filippo Cangioli ◽  
Steven Chatterton ◽  
Paolo Pennacchi ◽  
Leonardo Nettis ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Flow Model ◽  
High Pressures ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Critical Conditions ◽  
Accurate Estimation ◽  
Transfer Model ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
The Stability

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities. Consequently, a more accurate estimation of the dynamic behavior of the machine has become mandatory as well as the stability assessment. Steam turbines are subjected to high temperatures, high pressures and centrifugal forces that could change the nominal geometry, especially the clearance profile in correspondence of the sealing components, occasionally generating a convergent or divergent annulus. In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth. By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different inlet pre-swirl ratios, as well as the stability of the seal are investigated in this paper. The model can be extremely useful for the dynamic characterisation of a wide class of labyrinth seals considering the effect of the surrounding environment on the rotordynamic coefficient prediction.

Rotordynamic Characterization of a Staggered Labyrinth Seal: Experimental Test Data and Comparison With Predictions

2018 ◽  
Author(s):  
Filippo Cangioli ◽  
Giuseppe Vannini ◽  
Paolo Pennacchi ◽  
Lorenzo Ciuchicchi ◽  
Leonardo Nettis ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Flow Model ◽  
Labyrinth Seal ◽  
Accurate Estimation ◽  
Stability Assessment ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Working Principle ◽  
The Stability

As well known, the stability assessment of turbomachines is strongly related to internal sealing components. For instance, labyrinth seals are widely used in compressors, steam and gas turbines and pumps to control the clearance leakage between rotating and stationary parts, owing to their simplicity, reliability and tolerance to large thermal and pressure variations. Labyrinth seals working principle consists in reducing the leakage by imposing tortuous passages to the fluid that are effective on dissipating the kinetic energy of the fluid from high-pressure regions to low-pressure regions. Conversely, labyrinth seals could lead to dynamics issues. Therefore, an accurate estimation of their dynamic behavior is very important. In this paper, the experimental results of a long-staggered labyrinth seal will be presented. The results in terms of rotordynamic coefficients and leakage will be discussed as well as the critical assessment of the experimental measurements. Eventually, the experimental data are compared to numerical results obtained with the new bulk-flow model (BFM) introduced in this paper.

Improving the Stability of Labyrinth Gas Seals

1997 ◽  
Vol 123 (2) ◽  
pp. 383-387 ◽  
Author(s):  
K. Kwanka
Keyword(s):  
Stability Limit ◽  
Labyrinth Seal ◽  
Flexible Rotor ◽  
Labyrinth Seals ◽  
Continuous Growth ◽  
Rotating Speed ◽  
Dynamic Coefficients ◽  
Flow Through ◽  
Gas Seals ◽  
The Stability

The flow through labyrinth seals of turbomachinery generates forces which can cause self-excited vibrations of the rotor above the stability limit. The stability limit is reached at a specific rotating speed or power. The continuous growth of power density and rotating speed necessitates an exact prediction of the stability limit of turbomachinery. Usually the seal forces are described with dynamic coefficients. A new, easy-to-handle identification procedure uses the stability behavior of a flexible rotor to determine the dynamic coefficients. Systematic measurements with a great number of labyrinth seal geometries lead to reasonable results and demonstrate the accuracy and sensitivity of the procedure. A comparison of the various methods used to minimize the excitation indicates which seal is more stable and will thus improve the dynamic behavior of the rotor.

Wear Prediction of Strip Seals Through Conductance

2004 ◽  
Author(s):  
Farshad Ghasripoor ◽  
Norman A. Turnquist ◽  
Mark Kowalczyk ◽  
Bernard Couture
Keyword(s):  
Thermal Conductivity ◽  
High Speed ◽  
Wear Behavior ◽  
Close Correlation ◽  
Labyrinth Seal ◽  
The Body ◽  
Minor Effect ◽  
Labyrinth Seals ◽  
Steam Leakage ◽  
A Minor

Labyrinth seal assemblies are often used to reduce gas and/or steam leakage in turbines. Caulked-in continuous strip seals are one of the common forms of seals employed on both the rotating and stationary components of turbines. Labyrinth seals perform best when minimum clearances are achieved during the steady state operation of the turbine. However, the design of the turbine and its operation during transient periods of start-up, shut-down and hot re-start often result in interference between the seal components. In the case of the strip seals, this leads primarily to wear of the strip, which in effect adds to leakage. The aim of this paper is to show that strip tip heating and melting during the rub is the main mechanism of wear in the strip. Hence thermal conductivity through the strip and into the body mass in which it is caulked is the primary controlling factor in seal wear. This paper will discuss the use of thermal conductivity and geometry of the strip in predicting wear during high speed rubs against a proprietary material. A close correlation between calculated and experimental strip seal wear data with a number of seal alloys will be demonstrated. Test data will indicate that material properties such as tensile strength and hardness have a minor effect on the wear behavior of continuous seal elements during high-speed rubs.

Sign in / Sign up

Export Citation Format

Share Document