Validation of Conjugate Heat Transfer Predictions on Labyrinth Seals and Novel Designs for Improved Component Lifetime

2011 ◽  
Author(s):  
Dominik Born ◽  
Kurt Heiniger ◽  
Giorgio Zanazzi ◽  
Thomas Mokulys ◽  
Patrick Grossmann ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steam Turbine ◽  
Conjugate Heat Transfer ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Transfer Coefficients ◽  
Labyrinth Seals ◽  
Heat Transfer Coefficients ◽  
Low Pressure Turbine ◽  
Single Flow

Cyclic lifetime assessment of steam turbine components has become increasingly important for several reasons. In the last years and decades the nominal steam temperatures and pressures were further increased to improve cycle efficiency. In addition, the market constantly demands increased flexibility and reliability for given lifetime exploiting the limits of the existing materials. A number of components in a steam turbine are critical in the focus of lifetime predictions such as the rotor and front stage blades, the inner casing and the area of labyrinth seals connected to the life steam. For this reason, it becomes extremely important to rely on accurate predictions of local temperatures and heat-transfer-coefficients of components in the steam path. The content of this paper aims on the validation of the numerical tools based on CHT (conjugate heat transfer) approach against experimental data of a labyrinth seal regarding discharge coefficients and measured heat transfer coefficients. Furthermore, a real steam turbine application has been optimized in design and operation to improve lifetime. The improved prediction of temperature and heat transfer allowed novel designs of labyrinth seals of a single flow high-pressure turbine and a combined intermediate and low-pressure turbine, which helped to strongly increase the component lifetime of a steam turbine rotor by more than 100%.

Calculation of Disk Temperatures in Gas Turbine Rotor-Stator Cavities Using Conjugate Heat Transfer

2010 ◽  
Author(s):  
Aneesh Sridhar Vadvadgi ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Conjugate Heat Transfer ◽  
Computational Cost ◽  
Disk Surface ◽  
Turbine Rotor ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients ◽  
Variable Surface

The present study deals with the numerical modeling of the turbulent flow in a rotor-stator cavity with or without imposed through flow with heat transfer. The commercial finite volume based solver, ANSYS/FLUENT is used to numerically simulate the problem. A conjugate heat transfer approach is used. The study specifically deals with the calculation of the heat transfer coefficients and the temperatures at the disk surfaces. Results are compared with data where available. Conventional approaches which use boundary conditions such as constant wall temperature or constant heat flux in order to calculate the heat transfer coefficients which later are used to calculate disk temperatures can introduce significant errors in the results. The conjugate heat transfer approach can resolve this to a good extent. It includes the effect of variable surface temperature on heat transfer coefficients. Further it is easier to specify more realistic boundary conditions in a conjugate approach since solid and the flow heat transfer problems are solved simultaneously. However this approach incurs a higher computational cost. In this study, the configuration chosen is a simple rotor and stator system with a stationary and heated stator and a rotor. The aspect ratio is kept small (around 0.1). The flow and heat transfer characteristics are obtained for a rotational Reynolds number of around 106. The simulation is performed using the Reynolds Stress Model (RSM). The computational model is first validated against experimental data available in the literature. Studies have been carried out to calculate the disk temperatures using conventional non-conjugate and full conjugate approaches. It has been found that the difference between the disk temperatures for conjugate and non-conjugate computations is 5 K for the low temperature and 30 K for the high temperature boundary conditions. These represent differences of 1% and 2% from the respective stator surface temperatures. Even at low temperatures, the Nusselt numbers at the disk surface show a difference of 5% between the conjugate and non-conjugate computations, and far higher at higher temperatures.

Numerical Investigation of the Heat Transfer and Flow Phenomena in an IP Steam Turbine in Warm-Keeping Operation With Hot Air

2017 ◽  
Author(s):  
Dennis Toebben ◽  
Piotr Łuczyński ◽  
Mathias Diefenthal ◽  
Manfred Wirsum ◽  
Stefan Reitschmidt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Steam Turbine ◽  
Flow Structure ◽  
Conjugate Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hot Air ◽  
Start Up ◽  
Flow Phenomena

Nowadays, steam turbines in conventional power plants deal with an increasing number of startups due to the high share of fluctuating power input of renewable generation. Thus, the development of new methods for flexibility improvements, such as reduction of the start-up time and its costs, have become more and more important. At the same time, fast start-up and flexible steam turbine operation increase the lifetime consumption and reduce the inspection intervals. One possible option to prevent these negative impacts of a flexible operation is to keep the steam turbine warm during a shut down and a startup. In order to do so, General Electric has developed a concept for warm-keeping respectively pre-warming of a high-pressure (HP) / intermediate-pressure (IP) steam turbine with hot air: After a certain cool-down phase, air is passed through the turbine while the turbine is rotated by the turning engine. The flow and the rotational direction can be inverted to optimize the warming operation. In order to fulfill the requirements of high flexibility in combination with reduced costs and thermal stresses during the start-up, a detailed investigation of the dominant heat transfer effects and the corresponding flow structure is necessary: Complex numerical approaches, such as Conjugate Heat Transfer (CHT), can provide this corresponding information and help to understand the physical impact of the flow phenomena. The aim of the present work is thus to understand the predominant heat transport phenomena in warm-keeping operation and to gain detailed heat transfer coefficients within the flow channel for blade, vane and shrouds. A multitude of steady-state simulations were performed to investigate the different warm-keeping operation points. Data from literature was recomputed in good agreement to qualitatively validate the numerical model in windage operation. Furthermore, the steady-state simulations were compared with transient Computational Fluid Dynamics (CFD) simulations to verify that the flow in warming operation can be simulated with a steady-state case. The transient calculations confirm the steady-state results. A variation of the mass flow rate and the rotational speed was conducted to calculate a characteristic map of heat transfer coefficients. The Conjugate Heat Transfer simulations provide an insight into the flow structure and offer a comparison with the flow phenomena in conventional operation. In addition, the impact of the flow phenomena on the local heat transfer was investigated.

Conjugate Heat Transfer in a Rotor-Stator System With Through-Flow

2002 ◽  
Author(s):  
Reby Roy ◽  
B. V. S. S. S. Prasad ◽  
S. Srinivasa Murthy
Keyword(s):  
Heat Transfer ◽  
Boundary Layer Thickness ◽  
Conjugate Heat Transfer ◽  
Rotating Disk ◽  
Thermal Boundary Layer Thickness ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Commercial Code ◽  
Through Flow

The conjugate heat transfer in a stationary cylindrical cavity with a rotating disk and fluid through-flow is analysed at various rotational speeds ranging from 10000 to 50000 rpm by using a finite volume commercial code. The numerical model and code are validated for a problem, which involves rotation and fluid through-flow. A reduction of the thermal boundary layer thickness and increase in the heat transfer coefficients are observed with increase in the rotational speed. Marked differences are noticed between the Nusselt numbers obtained from the conjugate and constant temperature analyses.

Heat Transfer in Stepped Labyrinth Seals

1988 ◽  
Vol 110 (1) ◽  
pp. 63-69 ◽  
Author(s):  
S. Wittig ◽  
K. Jacobsen ◽  
U. Schelling ◽  
S. Kim
Keyword(s):  
Heat Transfer ◽  
Wall Friction ◽  
Leakage Flow ◽  
Test Rig ◽  
Transfer Coefficients ◽  
Labyrinth Seals ◽  
Finite Element Program ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Element Program

Leakage flow and heat transfer of scaled-up stepped labyrinth seals were investigated experimentally and numerically. The experiments were conducted in a test rig under steady conditions. For different geometries and pressure ratios a finite element program was used to determine the temperature distribution and subsequently the heat transfer coefficients. In verifying the experimental results, the flow field of the seals was calculated numerically by a finite difference program. Heat transfer coefficients were derived utilizing the well-known analogies between heat transfer and wall friction.

Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an IP Steam Turbine Blading During Startup

2020 ◽  
Author(s):  
Dieter Bohn ◽  
Christian Betcher ◽  
Karsten Kusterer ◽  
Kristof Weidtmann
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Steam Turbine ◽  
Heat Transport ◽  
Convective Heat ◽  
Thermal Design ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Mechanisms

Abstract As a result of an ever-increasing share of volatile renewable energies on the world wide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-Conjugate-Heat-Transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market. The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection and radiation during a startup of an IP steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT-simulations the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and time-saving way. The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds’ number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds’ number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approx. 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.

Conjugate Heat Transfer CFD Predictions of the Surface Averaged Impingement Heat Transfer Coefficients for Impingement Cooling With Backside Cross-Flow

2013 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Reyad A. A. Abdul Hussain ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Cross Flow ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Square Array ◽  
Velocity Turbulence

A 10 row impingement heat transfer configuration with a single sided exit at the end of the impingement gap was modelled using conjugate heat transfer CFD. The predictions were compared with experimental results for an electrically heated, 6.35mm thick, metal wall of nimonic-75, which was impingement cooled. The geometry investigated was a square array of inline impingement 10 × 10 holes with X/D of 4.66 and Z/D of 3.06, where D = 3.27mm. The use of metal walls enabled the local surface averaged heat transfer coefficient h, to be estimated from an imbedded thermocouple that logged the rate of cooling when the heating was removed. Conjugate heat transfer analysis provided local h values, which were surface averaged for comparison with the measured h. The CFD results also provided velocity, turbulence and Nusselt number distributions on the target and impingement jet surfaces. The aerodynamics data enabled the pressure loss of the system to be predicted, which compared well with experimental measurements. The predicted surface distributions of Nusselt number were similar to the surface turbulence kinetic energy distributions, which demonstrated the importance of turbulence in convective heat transfer. Surface averaged heat transfer coefficients were predicted and are in good agreement with the measurements for five coolant mass flow rates. The predicted and measured results for surface averaged h were similar to measurements of other investigators for similar impingement geometries.

Thermal Modeling of an Intermediate Pressure Steam Turbine by Means of Conjugate Heat Transfer—Simulation and Validation

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Dominik Born ◽  
Peter Stein ◽  
Gabriel Marinescu ◽  
Stefan Koch ◽  
Daniel Schumacher
Keyword(s):  
Heat Transfer ◽  
Steam Turbine ◽  
Conjugate Heat Transfer ◽  
Thermal Stresses ◽  
Numerical Models ◽  
Thermal Modeling ◽  
Transfer Coefficients ◽  
Intermediate Pressure ◽  
Pressure Steam ◽  
Product Costs

Today's power market asks for highly efficient turbines which can operate at a maximum flexibility, achieving a high lifetime and all of this on competitive product costs. In order to increase the plant cycle efficiency, during the past years, nominal steam temperatures and pressures have been continuously increased. To fulfill the lifetime requirements and still achieve the product cost requirements, accurate mechanical integrity based assessments on cyclic lifetime became more and more important. For this reason, precise boundary conditions in terms of local temperatures as well as heat transfer coefficients are essential. In order to gain such information and understand the flow physics behind them, more and more complex thermal modeling approaches are necessary, like computational fluid dynamics (CFD) or even conjugate heat transfer (CHT). A proper application of calculation rules and methods is crucial regarding the determination of thermal stresses, thermal expansion, lifetime, or creep. The aim is to exploit during turbine developments the limits of the designs with the selected materials. A huge effort especially in validation and understanding of those methodologies was done with detailed numerical investigations associated to extensive measurement studies at onsite turbines in operation. This paper focuses on the validation of numerical models based on CHT calculations against experimental data of a large intermediate pressure steam turbine module regarding the temperature distribution at the inner and outer casing for nominal load as well as transient shut-down.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Effect of Tip Gap and Squealer Geometry on Detailed Heat Transfer Measurements Over a High Pressure Turbine Rotor Blade Tip

2004 ◽  
Vol 126 (2) ◽  
pp. 221-228 ◽  
Author(s):  
Hasan Nasir ◽  
Srinath V. Ekkad ◽  
David M. Kontrovitz ◽  
Ronald S. Bunker ◽  
Chander Prakash
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Transfer Coefficients ◽  
Blow Down ◽  
Turbine Rotor Blade ◽  
Heat Transfer Coefficients ◽  
Gap Height

The present study explores the effects of gap height and tip geometry on heat transfer distribution over the tip surface of a HPT first-stage rotor blade. The pressure ratio (inlet total pressure to exit static pressure for the cascade) used was 1.2, and the experiments were run in a blow-down test rig with a four-blade linear cascade. A transient liquid crystal technique was used to obtain the tip heat transfer distributions. Pressure measurements were made on the blade surface and on the shroud for different tip geometries and tip gaps to characterize the leakage flow and understand the heat transfer distributions. Two different tip gap-to-blade span ratios of 1% and 2.6% are investigated for a plane tip, and a deep squealer with depth-to-blade span ratio of 0.0416. For a shallow squealer with depth-to-blade span ratio of 0.0104, only 1% gap-to-span ratio is considered. The presence of the squealer alters the tip gap flow field significantly and produces lower overall heat transfer coefficients. The effects of different partial squealer arrangements are also investigated for the shallow squealer depth. These simulate partial burning off of the squealer in real turbine blades. Results show that some partial burning of squealers may be beneficial in terms of overall reduction in heat transfer coefficients over the tip surface.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with to the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

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