Discussion: “The Lomakin Effect in Annular Gas Seals Under Choked Flow Conditions” (Arghir, M., Defaye, C., and Frêne, F., 2007, ASME J. Eng. Gas Turbines Power, 129, pp. 1028–1034)

2007 ◽  
Vol 129 (4) ◽  
pp. 1143-1143 ◽  
Author(s):  
Dara Childs
Keyword(s):  
Gas Turbines ◽  
Flow Conditions ◽  
Choked Flow ◽  
Gas Seals

The Lomakin Effect in Annular Gas Seals Under Choked Flow Conditions

2006 ◽  
Author(s):  
Mihai Arghir ◽  
Cyril Defaye ◽  
Jean Freˆne
Keyword(s):  
Static Stability ◽  
Radial Force ◽  
Exit Section ◽  
Static Stiffness ◽  
Flow Conditions ◽  
Friction Forces ◽  
Choked Flow ◽  
Annular Seal ◽  
Quantitative Results ◽  
Gas Seals

The paper deals with the static stability of annular gas seals under choked flow conditions. For a centered straight annular seal choking can occur only in the exit section because the gas is constantly accelerated by friction forces. From the mathematical standpoint, the flow choking corresponds to a singularity that was never dealt with numerically. The present work introduces an original numerical treatment of this singularity that is validated by comparisons with the analytical solution for planar channel flow. An interesting observation stemming from these results is that the usual hypothesis of considering the flow as being isothermal is not correct anymore for a gas accelerated by a pressure gradient; the characteristics of the flow are the same but the quantitative results are different. The analysis of eccentric annular seals then shows that choked flow conditions produce a change in the static stiffness. For a subsonic exit section the Lomakin effect is represented by a centering radial force opposed to the rotor displacement. For a choked exit section the radial force stemming from an eccentricity perturbation has the same direction as the rotor displacement. The annular seal becomes then statically unstable. From the physical standpoint this behaviour is explained by the modification of the Lomakin effect that changes sign. The pressure and Mach number variations along the seal depict the influence of high compressible flow regimes on the Lomakin effect. This characteristic has never been depicted before.

The Lomakin Effect in Annular Gas Seals Under Choked Flow Conditions

2006 ◽  
Vol 129 (4) ◽  
pp. 1028-1034 ◽  
Author(s):  
Mihai Arghir ◽  
Cyril Defaye ◽  
Jean Frêne
Keyword(s):  
Static Stability ◽  
Radial Force ◽  
Exit Section ◽  
Static Stiffness ◽  
Flow Conditions ◽  
Friction Forces ◽  
Choked Flow ◽  
Annular Seal ◽  
Quantitative Results ◽  
Gas Seals

The paper deals with the static stability of annular gas seals under choked flow conditions. For a centered straight annular seal, choking can occur only in the exit section because the gas is constantly accelerated by friction forces. From the mathematical standpoint, the flow choking corresponds to a singularity that was never dealt with numerically. The present work introduces an original numerical treatment of this singularity that is validated by comparisons to the analytical solution for planar channel flow. An interesting observation stemming from these results is that the usual hypothesis of considering the flow as being isothermal is not correct anymore for a gas accelerated by a pressure gradient; the characteristics of the flow are the same but the quantitative results are different. The analysis of eccentric annular seals then shows that choked flow conditions produce a change in the static stiffness. For a subsonic exit section, the Lomakin effect is represented by a centering radial force opposed to the rotor displacement. For a choked exit section, the radial force stemming from an eccentricity perturbation has the same direction as the rotor displacement. The annular seal becomes then statically unstable. From the physical standpoint, this behavior is explained by the modification of the Lomakin effect, which changes sign. The pressure and Mach number variations along the seal depict the influence of high compressible flow regimes on the Lomakin effect. This characteristic has never been depicted before.

Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Static Stability ◽  
Operating Conditions ◽  
Eccentricity Ratio ◽  
Static Stiffness ◽  
Flow Conditions ◽  
Experiment Data ◽  
High Eccentricity ◽  
Stiffness Coefficients ◽  
Direct Stiffness ◽  
Gas Seals

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor–stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines. The paper deals with the leakage and static stability behavior of a fully partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360 deg mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces, and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-averaged Navier–Stokes solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7000 rpm, 11,000 rpm, and 15,000 rpm) including the nonrotating condition, three pressure ratios (0.17, 0.35, and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions; no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal (PDS) would be statically unstable.

Fanno Design of Blow-Off Lines in Heavy Duty Gas Turbine

2013 ◽  
Author(s):  
Marco Cioffi ◽  
Enrico Puppo ◽  
Andrea Silingardi
Keyword(s):  
Gas Turbines ◽  
Gas Flow ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Design Procedure ◽  
Flow Equation ◽  
Heavy Duty ◽  
Cross Sectional ◽  
Pipe Length ◽  
Choked Flow

In typical heavy duty gas turbines the multistage axial compressor is provided with anti-surge pipelines equipped with on-off valves (blow-off lines), to avoid dangerous flow instabilities during start-ups and shut-downs. Blow-off lines show some very peculiar phenomena and somewhat challenging fluid dynamics, which require a deeper regard. In this paper the blow-off lines in axial gas turbines are analyzed by adopting an adiabatic quasi-unidimensional model of the gas flow through a pipe with a constant cross-sectional area and involving geometrical singularities (Fanno flow). The determination of the Fanno limit, on the basis of the flow equation and the second principle of thermodynamics, shows the existence of a critical pipe length which is a function of the pipe parameters and the initial conditions: for a length greater than this maximum one, the model requires a mass-flow reduction. In addition, in the presence of a regulating valve, so-called multi-choked flow can arise. The semi-analytical model has been implemented and the results have been compared with a three-dimensional CFD analysis and cross-checked with available field data, showing a good agreement. The Fanno model has been applied for the analysis of some of the actual machines in the Ansaldo Energia fleet under different working conditions. The Fanno tool will be part of the design procedure of new machines. In addition it will define related experimental activities.

scholarly journals Fugitive Methane Emission Reduction Using Gas Turbines

1998 ◽  
Author(s):  
Todd Parker
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Cost Effective ◽  
Process Gas ◽  
Natural Gas Transmission ◽  
Air Intake ◽  
Lean Fuel ◽  
Gas Seals ◽  
Turbo Compressor ◽  
Many Sources

Natural gas transmission systems have many sources of fugitive methane emissions that have been difficult to eliminate. This paper discusses an option for dealing with one such source for operations using turbo-compressor units fitted with dry gas seals. Dry seals rely on a small leakage of process gas to maintain the differential pressure of the process against the atmosphere. The seal leakage ultimately results in waste gas that is emitted to the atmosphere through the primary vent. A simple, cost effective, emission disposal mechanism for this application is to vent the seal gas into the gas turbine’s air intake. Explosion hazards are not created by the resultant ultra-lean fuel/air mixture, and once this mixture reaches the combustion chamber, where sufficient fuel is added to create a flammable mixture, significant oxidation of the seal vent gas is realized. Background of the relevant processes is discussed as well as a review of field test data. Similar applications have been reported [1] for the more generalized purpose of Volatile Organic Compound (VOC) destruction using specialized gas turbine combustor designs. As described herein, existing production gas turbine combustors are quite effective at fugitive methane destruction without specialized combustor designs.

Vent Gas Collection From Gas Compressor Dry Gas Seals

2004 ◽  
Author(s):  
Ari Suomilammi
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Experience ◽  
Methane Emissions ◽  
Emissions Reduction ◽  
Transmission Pipeline ◽  
Reduce Emissions ◽  
Gas Seals ◽  
National Programs ◽  
Year 2000

Gasum is an importer of natural gas and is operating and maintaining the Finnish transmission pipeline in which the pressure is maintained with three compressor stations. Gasum’s compressor stations are unmanned and remotely controlled from the central control room. Some of the compressor units are equipped with dry gas seals. The otherwise satisfactory operation of dry gas seals has the disadvantage of methane emissions. Reduction of methane emissions has been stated as a target by international auspices of the Kyoto Protocol or through national programs seeking to reduce emissions. The application described in this paper to collect vent gases from the dry gas seals was installed into four of the compressor units during 2001. The compressors are centrifugal compressors: two of them are Nuovo Pignone PCL603 with PGT10DLE (10 MW) gas turbine and two are Demag DeLaval 2B-18/18 with Siemens Tornado gas turbines (6,5 MW). It is normal for dry gas seals to have a small leakage of gas through the seals due to the function principle and required cooling of the seals. This gas emitted from the seals is normally about of 5...10nm3/h per one compressor unit during operation and during the stand-still the leakage is almost zero. In the year 2000 the total amount of emitted gas in Gasum’s units was about 50.000 nm3 per four compressor units. The target was to find an efficient method to collect the dry gas seal vent gas and utilize it. The solution must be simple and its investment costs must be feasible. Injection of the vent gases to the gas turbine inlet air flow was selected as a solution among some alternatives. The operating experience so far has been several thousands of operating hours without any malfunctions. The amount of collected gas by this system has been in the range of 80.000 nm3 per annum. The total cost of the system for four compressor units was about 85.000€. The intention of this paper is not to describe any scientific approach to the issue but to present a practical solution with operating experience.

Numerical Study on Choked Flow of CO2 Refrigerant in Helical Capillary Tube

2018 ◽  
Vol 26 (03) ◽  
pp. 1850027 ◽  
Author(s):  
Pravin Jadhav ◽  
Neeraj Agrawal
Keyword(s):  
Fluid Dynamics ◽  
Present Model ◽  
Capillary Tube ◽  
Numerical Study ◽  
Fundamental Principle ◽  
Tube Diameter ◽  
Published Data ◽  
Flow Conditions ◽  
Pressure Drops ◽  
Choked Flow

This paper presents a numerical study on an adiabatic helical capillary tube employing homogenous and choked flow conditions of a CO2 transcritical system. The theoretical model is based on the fundamental principle of fluid dynamics and thermodynamics. The result of the present model validates with the previously published data. The influence of operating and geometric parameters on the performance of the capillary tube has been evaluated. Flow characterizations of choked and unchoked flow conditions are determined. As the evaporator pressure drops, from unchoked condition to choked state, the percentage change in mass flow rate is minimal. A simulation graph is developed which has been helpful for the design of the helical capillary tube. The choked flow condition in a capillary tube is avoided by either increasing tube diameter of the fixed length tube or decreasing the length of the fixed tube diameter.

Effects of Variational Particle Restitution Characteristics on Turbomachinery Erosion

1993 ◽  
Author(s):  
Awatef Hamed ◽  
Timothy P. Kuhn
Keyword(s):  
Gas Turbines ◽  
Laser Doppler Velocimetry ◽  
Particle Trajectory ◽  
Particle Dynamics ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Sampling Techniques ◽  
Flow Conditions ◽  
Mean Values ◽  
Particle Velocities

This paper presents the results of an investigation to determine the effects of variational particle rebounding models on surface impacts and blade erosion patterns in gas turbines. The variance in the particle velocities after the surface impacts are modeled based on the experimental measurements using Laser Doppler Velocimetry (LDV) under varying flow conditions. The probabilistic particle trajectory computations simulate the experimental variance in the particle restitution characteristics using cumulative distribution functions and random sampling techniques. The results are presented for the particle dynamics through a gas turbine flow field and are compared to those obtained with deterministic rebound models based on experimental mean values.

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