Negative Stiffness in Gas Turbine Leaf Seals

2011 ◽  
Author(s):  
Ingo H. J. Jahn ◽  
Andrew K. Owen ◽  
Gervas Franceschini ◽  
David R. H. Gillespie
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Empirical Model ◽  
Negative Stiffness ◽  
Central Position ◽  
Mechanical Stiffness ◽  
Turbine Engine ◽  
Leaf Pack ◽  
Eccentric Rotor ◽  
Shaft Seals

The stiffness of contacting shaft seals such as brush seals and leaf seals is a required characteristic to accurately predict their performance and life in the gas turbine engine. This paper describes the results of a test campaign in which a series of eccentric rotor excursions are applied at low rotational speed and engine representative pressure differences to characterise the behaviour of a prototype leaf seal. A phenomenon that may best be described as negative seal stiffness is reported. Here, the displacement of the seal rotor to an eccentric position causes a resultant force, which, rather than trying to return the rotor to a central position, acts to amplify its displacement. These data were used to develop an empirical model of the seal behaviour. It was possible to model the negative stiffness phenomenon and show that it is caused by a combination of two effects: the inherent mechanical stiffness of the leaf pack, and the aerodynamic stiffness of the seal. The latter is caused by the pressure distribution and changes in the flow field through the leaf pack as a result of the displacement of the rotor.

Flow Field Simulations of a Gas Turbine Combustor

2002 ◽  
Vol 124 (3) ◽  
pp. 508-516 ◽  
Author(s):  
M. D. Barringer ◽  
O. T. Richard ◽  
J. P. Walter ◽  
S. M. Stitzel ◽  
K. A. Thole
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Large Scale ◽  
Guide Vane ◽  
Wall Region ◽  
Turbine Engine ◽  
Tunnel Section ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Combustor Liner

The flow field exiting the combustor in a gas turbine engine is quite complex considering the presence of large dilution jets and complicated cooling schemes for the combustor liner. For the most part, however, there has been a disconnect between the combustor and turbine when simulating the flow field that enters the nozzle guide vanes. To determine the effects of a representative combustor flow field on the nozzle guide vane, a large-scale wind tunnel section has been developed to simulate the flow conditions of a prototypical combustor. This paper presents experimental results of a combustor simulation with no downstream turbine section as a baseline for comparison to the case with a turbine vane. Results indicate that the dilution jets generate turbulence levels of 15–18% at the exit of the combustor with a length scale that closely matches that of the dilution hole diameter. The total pressure exiting the combustor in the near-wall region neither resembles a turbulent boundary layer nor is it completely uniform putting both of these commonly made assumptions into question.

Improved Understanding of Negative Stiffness in Filament Seals

2012 ◽  
Author(s):  
Gervas Franceschini ◽  
Ingo H. J. Jahn ◽  
Andrew K. Owen ◽  
Terry V. Jones ◽  
David R. H. Gillespie
Keyword(s):  
Experimental Testing ◽  
Negative Stiffness ◽  
Turbine Engines ◽  
Inertia Force ◽  
Central Position ◽  
Gas Turbine Engines ◽  
Leaf Pack ◽  
Seal Design ◽  
Geometric Configurations ◽  
D Model

Leaf seals have previously been proposed as an improved filament seal for gas turbine engines. Recently, a phenomenon known as negative stiffness has been reported from experimental testing. Good understanding of this phenomenon is required to ensure stable interaction between the seal and the rotor. In negative stiffness the displacement of the seal or rotor into an eccentric position causes a resultant force, which, rather than restoring the rotor to a central position, acts to amplify its displacement. The seal consists of a pack of thin planar leaves arranged around the rotor, with coverplates on either side of the leaf pack, offset from its surface. It is notable that negative stiffness only occurs when certain geometric configurations of the coverplates are employed. This paper gives insight into the fluid phenomena that contribute to the negative stiffness effect through the creation of a general 2-D model of the flow upstream of the leaf pack and between the leaves. These show that there is the capacity for the inertia force to be a significant contributor to the overall force acting on individual leaves depending on the coverplate configuration surrounding the leaf pack. The influence of a key parameter, coverplate height, is explored. Results from a test campaign with varying seal geometry are compared to the forces predicted by modeling to justify the proposed mechanisms for negative stiffness. The close agreement between the experimental and predicted data extends the previously published insight on negative stiffness to allow more general considerations for leaf seal design to be inferred.

Finite-Element Analysis of Turbulent Flow in Annular Exhaust Diffusers of Gas Turbine Engines

1991 ◽  
Vol 113 (1) ◽  
pp. 104-110 ◽  
Author(s):  
E. A. Baskharone
Keyword(s):  
Finite Element ◽  
Flow Field ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Gas Turbine Engine ◽  
Element Formulation ◽  
Predictive Tool ◽  
Integration Algorithm ◽  
Element Discretization ◽  
Turbine Engine

A finite-element model of the turbulent flow field in the annular exhaust diffuser of a gas turbine engine is developed. The analysis is based on a modified version of the Petrov-Galerkin weighted residual method, coupled with a highly accurate biquadratic finite element of the Lagrangian type. The elemental weight functions in the finite-element formulation are so defined to ensure upwinding of the convection terms in the flow-governing equations while reverting to the conventional Galerkin’s definition for all other terms. This approach is equivalent to altering the integration algorithm as the convection terms in the element equations are derived, with the exception that the latter technique is tailored for low-order elements of the linear and bilinear types. Numerical results of the current analysis indicate that spurious pressure modes associated with this type of inertia-dominated flow are alleviated while the false numerical diffusion in the finite-element equations is simultaneously minimized. Turbulence of the flow field is modeled using the two-layer algebraic turbulence closure of Baldwin and Lomax, and the eddy viscosity calculations are performed at variably spaced points which are different from those in the finite-element discretization model. This enhances the accuracy in computing the wall shear stress and the inner/outer layer interface location. The computational model is verified using a set of experimental data at design and off-design operation modes of the exhaust diffuser in a commercial gas turbine engine. Assessment of the results in this case is favorable and, as such, provides evidence of the model capability as an accurate predictive tool in the diffuser detailed design phase.

Gas-Dynamics Design of Reversible Turbine for Marine Gas Turbine Engine

2017 ◽  
Author(s):  
Xiying Niu ◽  
Feng Lin ◽  
Weishun Li ◽  
Chen Liang ◽  
Shunwang Yu ◽  
...  
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Gas Dynamics ◽  
Gas Turbine Engine ◽  
Operating Conditions ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Turbine Engine ◽  
Power Turbine ◽  
Full Speed

Gas turbine engines are widely used as the marine main power system. However, they can’t reverse like diesel engine. If the reversal is realized, other ways must be adopted, for example, controllable pitch propeller (CPP) and reversible gearing. Although CPP has widespread use, the actuator installation inside the hub of the propeller lead to the decrease in efficiency, and it takes one minute to switch “full speed ahead” to “full speed astern”. In addition, some devices need to be added for the reversible gearing, and it takes five minutes to switch from “full speed ahead” “to “full speed astern”. Based on the gas turbine engine itself, a reversible gas turbine engine is proposed, which can rotate positively or reversely. Most important of all, reversible gas turbine engine can realize operating states of “full speed ahead”, “full speed astern“ and “stop propeller”. And, it just takes half of one minute to switch “full speed ahead” to “full speed astern”. Since reversible gas turbine engines have compensating advantages, and especially in recent years computational fluid dynamics (CFD) technology and turbine gas-dynamics design level develop rapidly, reversible gas turbine engines will be a good direction for ship astern. In this paper, the power turbine of a marine gas turbine engine was redesigned by three dimensional shape modification, and the flow field is analyzed using CFD, in order to redesign into a reverse turbine. The last stage vanes and blades of this power turbine were changed to double-layer structure. That is, the outer one is reversible turbine, while the inner is the ahead one. Note that their rotational directions are opposite. In order to realize switching between rotation ahead and rotation astern, switching devices were designed, which locate in the duct between the low pressure turbine and power turbine. Moreover, In order to reduce the blade windage loss caused by the reversible turbine during working ahead, baffle plates were used before and after the reversible rotor blades. This paper mainly studied how to increase the efficiency of the reversible turbine stage, the torque change under different operating conditions, rotational speed and rotational directions, and flow field under typical operating conditions. A perfect profile is expected to provide for reversible power turbine, and it can decrease the blade windage loss, and increase the efficiency of the whole gas turbine engine. Overall, the efficiency of the newly designed reversible turbine is up to 85.7%, and the output power is more than 10 MW, which can meet requirements of no less than 30% power of rated condition. Most importantly, the shaft is not over torque under all ahead and astern conditions. Detailed results about these are presented and discussed in the paper.

scholarly journals An Air Jet Distortion Generation System

2014 ◽  
Vol 2014 ◽  
pp. 1-17
Author(s):  
M. Sivapragasam ◽  
S. Ramamurthy ◽  
M. D. Deshpande ◽  
P. White
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Total Pressure ◽  
Gas Turbine Engine ◽  
Test Facility ◽  
Generation System ◽  
Turbine Engine ◽  
Air Jet ◽  
Engine Testing ◽  
Distortion Parameters

An air jet distortion generation system is developed to simulate the distorted flow field ahead of gas turbine engines in ground test facility. The flow field of a system of four jets arranged circumferentially and issuing into a confined counterflow was studied experimentally and numerically. The total pressure distortion parameters were evaluated at the Aerodynamic Interface Plane (AIP) for several values of mass flow ratios. Since the total pressure loss distribution at theAIPis characteristically “V” shaped, the number of jets was increased to obtain total pressure distributions as required for gas turbine engine testing. With this understanding, a methodology has been developed to generate a target total pressure distortion pattern at theAIP. Turbulent flow computations are used to iteratively progress towards the target distribution. This methodology was demonstrated for a distortion flow pattern typical of use in gas turbine engine testing using twenty jets, which is a smaller number than reported in the literature. The procedure converges with a root-mean-square error of 3.836% and is able to reproduce the target pattern and other distortion parameters.

Flow Field Computations of Combustor-Turbine Interactions Relevant to a Gas Turbine Engine

2004 ◽  
Vol 126 (1) ◽  
pp. 122-129 ◽  
Author(s):  
Sarah Stitzel ◽  
Karen A. Thole
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbine ◽  
High Performance ◽  
Computational Study ◽  
Pressure Profile ◽  
Turbine Engines ◽  
Turbine Engine ◽  
Stator Vane ◽  
Secondary Flow Field

The current demands for high-performance gas turbine engines can be reached by raising combustion temperatures to increase power output. High combustion temperatures create a harsh environment that leads to the consideration of the durability of the combustor and turbine sections. This paper presents a computational study of a flow field that is representative of what occurs in a combustor and how that flow field convects through the first downstream stator vane. The results of this study indicate that the development of the secondary flow field in the turbine is highly dependent on the incoming total pressure profile. The endwall heat transfer is also found to depend strongly on the secondary flow field.

Flow Field Computations of Combustor-Turbine Interactions Relevant to a Gas Turbine Engine

2003 ◽  
Author(s):  
Sarah Stitzel ◽  
Karen A. Thole
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbine ◽  
High Performance ◽  
Computational Study ◽  
Pressure Profile ◽  
Turbine Engines ◽  
Turbine Engine ◽  
Stator Vane ◽  
Secondary Flow Field

The current demands for high performance gas turbine engines can be reached by raising combustion temperatures to increase power output. High combustion temperatures create a harsh environment that leads to the consideration of the durability of the combustor and turbine sections. This paper presents a computational study of a flow field that is representative of what occurs in a combustor and how that flow field convects through the first downstream stator vane. The results of this study indicate the development of the secondary flow field in the turbine is highly dependent on the incoming total pressure profile. The endwall heat transfer is found to also depend strongly on the secondary flow field.

Flow Field Simulations of a Gas Turbine Combustor

2001 ◽  
Author(s):  
M. D. Barringer ◽  
O. T. Richard ◽  
J. P. Walter ◽  
S. M. Stitzel ◽  
K. A. Thole
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Large Scale ◽  
Guide Vane ◽  
Wall Region ◽  
Turbine Engine ◽  
Tunnel Section ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Combustor Liner

The flow field exiting the combustor in a gas turbine engine is quite complex considering the presence of large dilution jets and complicated cooling schemes for the combustor liner. For the most part, however, there has been a disconnect between the combustor and turbine when simulating the flow field that enters the nozzle guide vanes. To determine the effects of a representative combustor flow field on the nozzle guide vane, a large-scale wind tunnel section has been developed to simulate the flow conditions of a prototypical combustor. This paper presents experimental results of a combustor simulation with no downstream turbine section as a baseline for comparison to the case with a turbine vane. Results indicate that the dilution jets generate turbulence levels of 15–18% at the exit of the combustor with a length scale that closely matches that of the dilution hole diameter. The total pressure exiting the combustor in the near wall region neither resembles a turbulent boundary layer nor is it completely uniform putting both of these commonly made assumptions into question.

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