Calculations of Cooled Turbine Efficiency

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
J. H. Horlock ◽  
Leonardo Torbidoni
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Coolant Flow ◽  
The Other ◽  
Turbine Stage ◽  
Isentropic Expansion ◽  
Turbine Efficiency ◽  
Flow Through ◽  
Definition Of ◽  
Industrial Gas Turbine

The efficiency of a cooled turbine stage has been discussed in the literature. All proposed definitions compare the actual power output with an ideal output, which has to be determined; but usually, one of two definitions has been used by turbine designers. In the first, the so-called Hartsel efficiency, the mainstream gas flow, and the various coolant flows to rotor and stator are assumed to expand separately and isentropically to the backpressure. In the second, it is assumed that these flows mix at constant (mainstream) gas pressure before expanding isentropically (sometimes, the rotor coolant flow is ignored in this definition). More recently, it has been suggested that a thermodynamically sounder definition is one in which the gas and coolant flows mix reversibly and adiabatically before isentropic expansion to the backpressure. In the current paper, these three efficiencies are compared, for a typical stage—the first cooled stage of a multistage industrial gas turbine. It is shown that all the efficiencies fall more or less linearly with increase of the fractional (total) coolant flow. It is also shown that the new definition of efficiency gives values considerably lower than the other two efficiencies, which are more widely used at present. Finally, the various irreversibilities associated with the flow through a cooled turbine are calculated. Although all these irreversibilities increase with the fractional coolant flow, it is shown that the “thermal” irreversibility associated with film cooling is higher than the other irreversibilities at large fractional coolant flow.

Calculations of Cooled Turbine Efficiency

2006 ◽  
Author(s):  
J. H. Horlock ◽  
Leonardo Torbidoni
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Back Pressure ◽  
Coolant Flow ◽  
The Other ◽  
Turbine Stage ◽  
Turbine Efficiency ◽  
Flow Through ◽  
Definition Of ◽  
Industrial Gas Turbine

The efficiency of a cooled turbine stage has been discussed in the literature. All proposed definitions compare the actual power output with an ideal output, which has to be determined; but usually one of two definitions has been used by turbine designers. In the first, the so-called Hartsel efficiency, the mainstream gas flow and the various coolant flows to rotor and stator are assumed to expand separately and isentropically to the back pressure. In the second it is assumed that these flows mix at constant (mainstream) gas pressure before expanding isentropically (sometimes the rotor coolant flow is ignored in this definition). More recently it has been suggested that a thermodynamically sounder definition is one in which the gas and coolant flows mix reversibly and adiabatically before isentropic expansion to the back pressure. In the current paper these three efficiencies are compared, for a typical stage — the first cooled stage of a multistage industrial gas turbine. It is shown that all the efficiencies fall more or less linearly with increase of the fractional (total) coolant flow. It is also shown that the new definition of efficiency gives values considerably lower than the other two efficiencies, which are more widely used at present. Finally, the various irreversibilities associated with the flow through a cooled turbine are calculated. Although all these irreversibilities increase with the fractional coolant flow, it is shown that the “thermal” irreversibility associated with film cooling is higher than the other irreversibilities at large fractional coolant flow.

Film Cooling of Turbine Blade Surface With Extended Exit Holes

2014 ◽  
Author(s):  
Fariborz Forghan ◽  
Omid Askari ◽  
Uichiro Narusawa ◽  
Hameed Metghalchi
Keyword(s):  
High Temperature ◽  
Turbine Blade ◽  
Film Cooling ◽  
Gas Flow ◽  
Three Dimensional ◽  
Suction Side ◽  
Ideal Gas ◽  
Coolant Flow ◽  
Blade Surface ◽  
Flow Through

The main goal of gas turbine design is the effective use of energy. Usually, the efficient high temperature first and second stage turbine blade surface is cooled by jet of coolant flow from extended exit holes (EEH). Against the prevailing hot gas flow, the flow through EEH must be designed to form a film of cool air over the blade. Computational analyses are performed to examine the cooling effectiveness of flow from EEH over the suction side of a blade by solving conservation equations (mass, momentum and energy) and the ideal gas equation of state for the three-dimensional, turbulent, compressible flow. A diverging flow through EEH is typically choked at its throat, resulting in a supersonic flow, a shock and then a subsonic flow downstream. The location of the shock relative to the high-temperature gas flow over the blade determines the temperature distribution along the blade surface; which is analyzed in detail when the coolant flow rate is varied.

Numerical Study on Flow and Heat Transfer of a Cooled First Stage Vane of a Gas Turbine

2016 ◽  
Author(s):  
Lv Ye ◽  
Zhao Liu ◽  
Xiangyu Wang ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Numerical Study ◽  
Coolant Flow ◽  
The Other ◽  
Edge Region ◽  
Flow Rates ◽  
Flow And Heat Transfer ◽  
Film Cooling Holes

This paper presents a numerical simulation of composite cooling on a first stage vane of a gas turbine, in which gas by fixed composition mixture is adopted. To investigate the flow and heat transfer characteristics, two internal chambers which contain multiple arrays of impingement holes are arranged in the vane, several arrays of pin-fins are arranged in the trailing edge region, and a few arrays of film cooling holes are arranged on the vane surfaces to form the cooling film. The coolant enters through the shroud inlet, and then divided into two parts. One part is transferred into the chamber in the leading edge region, and then after impinging on the target surfaces, it proceeds further to go through the film cooling holes distributed on the vane surface, while the other part enters into the second chamber immediately and then exits to the mainstream in two ways to effectively cool the other sections of the vane. In this study, five different coolant flow rates and six different inlet pressure ratios were investigated. All the cases were performed with the same domain grids and same boundary conditions. It can be concluded that for the internal surfaces, the heat transfer coefficient changes gradually with the coolant flow rate and the inlet total pressure ratio, while for the external surfaces, the average cooling effectiveness increases with the increase of coolant mass flow rates while decreases with the increase of the inlet stagnation pressure ratios within the study range.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Marc Fraas ◽  
Tobias Glasenapp ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Gas Flow ◽  
Density Ratio ◽  
Coolant Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Film Cooling Holes

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

A Numerical Modelling of Stator-Rotor Interaction in a Turbine Stage With Oscillating Blades

2002 ◽  
Author(s):  
V. I. Gnesin ◽  
L. V. Kolodyazhnaya ◽  
R. Rzadkowski
Keyword(s):  
Gas Flow ◽  
Mutual Influence ◽  
Structural Equations ◽  
Rotor Blades ◽  
Turbine Stage ◽  
Aerodynamic Forces ◽  
Time Step ◽  
Outer Flow ◽  
Flow Through ◽  
Flow Nonuniformity

In real flows nonstationary phenomena connected with the circumferential non-uniformity of the main flow and those caused by oscillations of blades are observed only jointly. An understanding of the physics of the mutual interaction between gas flow and oscillating blades, and the development of predictive capabilities is essential for improved overall efficiency, durability and reliability. In the study presented the algorithm proposed involves the coupled solution of 3D unsteady flow through a turbine stage and dynamic problem for rotor blades motion by action of aerodynamic forces without separating of outer and inner flow fluctuations. The partially integrated method involves the solution of the fluid and structural equations separately, but information is exchanged at each time step, so that solution from one domain is used as boundary condition for the other domain. 3D transonic gas flow through the mutually moving stator and rotor blades with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of Godunov-Kolgan. The structure analysis uses the modal approach and 3D finite element model of a blade. The blade moving is assumed to be constituted as a linear combination of the first natural modes of blade oscillations with the modal coefficients depending on time. There has been performed the calculation for the last stage of the steam turbine. The numerical results for unsteady aerodynamic forces due to stator-rotor interaction are compared with results obtained with taking into account the blades oscillations. It has investigated the mutual influence of both outer flow nonuniformity and blades oscillations. It has shown that amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to rotor moving past one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow nonuniformity downstream from the blade row. Moreover, the spectrum involves the harmonics which are not multiple to the rotation frequency.

scholarly journals СНИЖЕНИЕ ВИБРОНАПРЯЖЕННОСТИ ПОПАРНО БАНДАЖИРОВАННЫХ РАБОЧИХ ЛОПАТОК ТУРБИНЫ

2020 ◽  
pp. 52-58
Author(s):  
Юрий Петрович Кухтин ◽  
Руслан Юрьевич Шакало
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Turbine Engine ◽  
Exciting Forces ◽  
Working Blades

To reduce the vibration stresses arising in the working blades of turbines during resonant excitations caused by the frequency of passage of the blades of the nozzle apparatus, it is necessary to control the level of aerodynamic exciting forces. One of the ways to reduce dynamic stresses in rotor blades under operating conditions close to resonant, in addition to structural damping, maybe to reduce external exciting forces. To weaken the intensity of the exciting forces, it is possible to use a nozzle apparatus with multi-step gratings, as well as with non-radially mounted blades of the nozzle apparatus.This article presents the results of numerical calculations of exciting aerodynamic forces, as well as the results of experimental measurements of stresses arising in pairwise bandaged working blades with a frequency zCA ⋅ fn, where fn – is the rotor speed, zCA – is the number of nozzle blades. The object of research was the high-pressure turbine stage of a gas turbine engine. Two variants of a turbine stage were investigated: with the initial geometry of the nozzle apparatus having the same geometric neck area in each interscapular channel and with the geometry of the nozzle apparatus obtained by alternating two types of sectors with a reduced and initial throat area.The presented results are obtained on the basis of numerical simulation of a viscous unsteady gas flow in a transonic turbine stage using the SUnFlow home code, which implements a numerical solution of the Reynolds-averaged Navier-Stokes equations. Discontinuity of a torrent running on rotor blades is aggravated with heat drops between an ardent flow core and cold jets from film cooling of a blade and escapes on clock surfaces. Therefore, at simulation have been allowed all blowngs cooling air and drain on junctions of shelves the impeller.As a result of the replacement of the nozzle apparatus with a constant passage area by a nozzle apparatus with a variable area, a decrease in aerodynamic driving force by 12.5 % was obtained. The experimentally measured stresses arising in a pairwise bandaged blade under the action of this force decreased on average by 26 %.

AERODYNAMICS AND HEAT TRANSFER INSIDE A GAS TURBINE MID-PASSAGE GAP

2021 ◽  
pp. 1-13
Author(s):  
Faisal Shaikh ◽  
Budimir Rosic
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Heat Load ◽  
Turbine Blades ◽  
Turbine Stage ◽  
Gas Turbine Blades ◽  
Cooling Flows ◽  
Turbine Efficiency ◽  
Gap Flow

Abstract Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the midpassage gap. The midpassage gap reduces turbine efficiency and causes additional heat load into the vane platform, as well as changing the distribution of endwall heat transfer and film cooling. This paper presents a low-order analytical analysis to quantify the effects of the midpassage gap on aerodynamics and heat transfer, verified against an experimental campaign and CFD. Using this model, the effects of the gap can be quantified, for a generic turbine stage, based only on geometric features and the passage static pressure field. It is found that at present there are significant losses and a large proportion of heat load caused by the gap, but that with modified design this could be reduced to negligible levels. Cooling flows into the gap to prevent ingression are investigated analytically and with CFD. Recommendations are given for targets that turbine designers should work toward in reducing the adverse effects of the midpassage gap. A method to estimate the effect of gap flow is presented, so that for any machine the significance of the gap may be assessed.

Measurement of Nonsteady Forces in Three Turbine Stage Geometries Using the Hydraulic Analogy

1978 ◽  
Vol 100 (4) ◽  
pp. 525-532 ◽  
Author(s):  
N. F. Rieger ◽  
A. L. Wicks
Keyword(s):  
Free Surface ◽  
Gas Flow ◽  
Two Dimensional ◽  
Turbine Stage ◽  
Summary Table ◽  
Rotating Blade ◽  
Blade Row ◽  
Gasdynamic Flow ◽  
Flow Through ◽  
Hydraulic Analogy

Experimental results for the nonsteady forces and nonsteady torques acting at the e.g. of an instrumented moving turbine blade have been obtained. Three different turbine stage geometries have been tested in this manner. The data described was obtained using a rotating model turbine stage consisting of a row of stationary inlet nozzles and a rotating blade row. The hydraulic analogy was used to stimulate the two-dimensional gasdynamic flow through the three stage geometries in turn. The free-surface horizontal flow of water across the rotating water table then represents the gas flow through the stage. Results for the nonsteady forces and torques in the tangential, axial, and torsional directions are presented as dimensionless force ratios or dimensionless torque ratios in each instance. Charts of results are presented for various stage pressure ratios, for practical ranges of stage velocity ratios. Typical results and observed trends are discussed in detail, and a summary table of observed nonsteady excitation values is presented.

Estimating the Loss Associated With Film Cooling for a Turbine Stage

2010 ◽  
Author(s):  
Chia Hui Lim ◽  
Graham Pullan ◽  
John Northall
Keyword(s):  
Film Cooling ◽  
Control Volume ◽  
Flow Direction ◽  
Three Dimensional ◽  
Turbine Stage ◽  
Flow Properties ◽  
Pragmatic Approach ◽  
Turbine Efficiency ◽  
Mainstream Flow ◽  
The Impact

A methodology is presented to allow designers to estimate the penalty for turbine efficiency associated with film cooling. The approach is based on the control volume analysis of Hartsel and the entropy-based formulations of Young and Wilcock. The present work extends these techniques to include flow ejected at compound angles and uses three-dimensional CFD to provide the mainstream flow properties. The method allows the loss contribution from each hole to be identified separately. The proposed method is applied to an aeroengine high-pressure turbine stage. It is found that, if the efficiency definition includes all irreversibilities, the penalty associated with film cooling would be 8.0%. However, if the pragmatic approach is adopted whereby the unavoidable entropy generated due to the equilibration of coolant and mainstream static temperatures is ignored, the efficiency penalty is 0.7%. Finally, a series of case studies is used to quantify the impact of changes to the local mainstream flow direction and coolant ejection angle on the predicted turbine efficiency. It is shown, quantitatively, that reducing the angle between the directions of the coolant and mainstream flows offers the greatest potential for the designer to improve film cooled turbine efficiency.

3D Unsteady Forces of the Transonic Flow Through a Turbine Stage With Vibrating Blades

2002 ◽  
Author(s):  
Romuald Rza˛dkowski ◽  
Vitaly Gnesin
Keyword(s):  
Transonic Flow ◽  
Gas Flow ◽  
Element Model ◽  
Ideal Gas ◽  
Rotor Blades ◽  
Turbine Stage ◽  
Unsteady Forces ◽  
Outer Flow ◽  
Natural Modes ◽  
Flow Through

Numerical calculations of the 3D transonic flow of an ideal gas through turbomachinery blade rows moving relatively one to another with taking into account the blades oscillations is presented. The approach is based on the solution of the coupled aerodynamic-structure problem for the 3D flow through the turbine stage in which fluid and dynamic equations are integrated simultaneously in time, thus providing the correct formulation of a coupled problem, as the blades oscillations and loads, acting on the blades, are a part of solution. An ideal gas flow through the mutually moving stator and rotor blades with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of Godunov-Kolgan and moving hybrid H-H grid. The structure analysis uses the modal approach and 3D finite element model of a blade. The blade motion is assumed to be constituted as a linear combination of the first natural modes of blade oscillations with the modal coefficients depending on time. The algorithm proposed allows to calculate turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account the blade oscillations by action of unsteady loads caused both outer flow nonuniformity and blades motion. There has been performed the calculation for the stage of the turbine with rotor blades of 0.765 m. The numerical results for unsteady aerodynamic forces due to stator-rotor interaction are compared with results obtained with taking into account the blades oscillations.

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