Minimization of the Local Rates of Entropy Production in the Design of Air-Cooled Gas Turbine Blades

1999 ◽  
Vol 121 (3) ◽  
pp. 466-475 ◽  
Author(s):  
G. Natalini ◽  
E. Sciubba
Keyword(s):  
Gas Turbine ◽  
Entropy Generation ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Equations Of Motion ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Entropy Generation Rate ◽  
Two Dimensional ◽  
Operational Conditions

The paper presents the results of a numerical configuration study made on a two dimensional model of an internally cooled gas turbine vane. The analysis applies to a two-dimensional cascade at medium Reynolds number, subsonic Mach number, and steady state. The full Navier-Stokes equations of motion for turbulent viscous flow, together with the appropriate energy equation, are solved via a standard finite-element code with a k-ε closure, to obtain complete velocity and temperature fields. These fields are then used to compute the entropy generation rates corresponding to the viscous (sv) and thermal (st) dissipation. The thermo-fluid dynamic efficiency of difference versions of the same base configuration is assessed comparing the global (or integral) entropy generation rate in the passage. The procedure is general, can be extended to different configurations and different operational conditions, and provides the designer with a rational and effective tool to assess the actual losses in the fixed and rotating turbomachinery cascades.

scholarly journals Entropy Generation in a 2-D Cascade at Different Angles of Attack: A Numerical Study

1997 ◽  
Author(s):  
Gianni Natalini ◽  
Enrico Sciubba
Keyword(s):  
Gas Turbine ◽  
Entropy Generation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Turbine Rotor ◽  
Loss Coefficient ◽  
Entropy Generation Rate ◽  
Two Dimensional ◽  
Design Point

This paper presents the results of an entropy generation calculation made on a representative gas turbine rotor blade; in particular, the numerical study has dealt with the different flowfields which are encountered when the angle of attack is varied in a two-dimensional cascade on axial, internally cooled gas turbine rotor. The analysis takes into consideration a two-dimensional cascade at medium Reynolds number (Rechord = 225000), sub-sonic Mach number (Main = 0.27), and steady state. The full Navier-Stokes equations of motion for a turbulent compressible viscous flow, together with the appropriate energy equation, are solved via a standard finite elements code with a k-ε closure, so that complete velocity- and temperature fields are obtained (including boundary-layer effects, via proper wall functions). These fields are then used to compute the entropy generation rates corresponding to the viscous- (Ṡv) and thermal (Ṡr) dissipation. Several configurations have been numerically tested, the reference one being at design conditions, and the remaining being obtained from it by varying the angle of attack α (defined as the angle, measured ccw, between the relative velocity vector W1 and the tangent to the blade chord at impingement point), to simulate volume flowrate variations. A commercial finite-element code (FIDAP, by FDI Inc.) has been modified to allow for the calculation of the local values of the entropy generation rates, the thermal- and viscous portions of which have been computed separately. The results at design point are shown to agree well with the available cascade performance data. The entropy generations rates are then used to compute the so-called entropy loss coefficient (a better name for which would be that of irreversibility coefficient, ζ, defined as:ζ=T0Δsh1s-h2iwhere T0 is the reference ambient temperature, Δs is the total local entropy generation rate (sum of the viscous- and thermal components), and h1i and h2i are the stagnation enthalpy upstream of the rotor and the ideal exit enthalpy respectively. The results are shown under the form of cp - and ζ graphs computed for different angles of attack α (from −4.4 to +7.6 degrees), and are representative of realistic situations which could arise in actual gas turbine rotors. The loss coefficient ζ is shown to attain a minimum value at design point. Integral values for the entropy generation rates are also computed, and total entropy losses are thus computed for the various configurations. Maps of the viscous- and thermal entropy generation rates are shown for each angle of attack, where of interest.

scholarly journals Oscillator Fin as a Novel Heat Transfer Augmentation Device for Gas Turbine Cooling Applications

1998 ◽  
Author(s):  
Oguz Uzol ◽  
Cengiz Camci
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Gas Turbine ◽  
Turbulent Kinetic Energy ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Internal Cooling ◽  
Pin Fin ◽  
Heat Transfer Augmentation

A new concept for enhanced turbulent transport of heat in internal coolant passages of gas turbine blades is introduced. The new heat transfer augmentation component called “oscillator fin” is based on an unsteady flow system using the interaction of multiple unsteady jets and wakes generated downstream of a fluidic oscillator. Incompressible, unsteady and two dimensional solutions of Reynolds Averaged Navier-Stokes equations are obtained both for an oscillator fin and for an equivalent cylindrical pin fin and the results are compared. Preliminary results show that a significant increase in the turbulent kinetic energy level occur in the wake region of the oscillator fin with respect to the cylinder with similar level of aerodynamic penalty. The new concept does not require additional components or power to sustain its oscillations and its manufacturing is as easy as a conventional pin fin. The present study makes use of an unsteady numerical simulation of mass, momentum, turbulent kinetic energy and dissipation rate conservation equations for flow visualization downstream of the new oscillator fin and an equivalent cylinder. Relative enhancements of turbulent kinetic energy and comparisons of the total pressure field from transient simulations qualitatively suggest that the oscillator fin has excellent potential in enhancing local heat transfer in internal cooling passages without significant aerodynamic penalty.

scholarly journals Entropy Generation Rates in Two-Dimensional Rayleigh–Taylor Turbulence Mixing

Entropy ◽  
2018 ◽  
Vol 20 (10) ◽  
pp. 738 ◽  
Author(s):  
Xinyu Yang ◽  
Haijiang He ◽  
Jun Xu ◽  
Yikun Wei ◽  
Hua Zhang
Keyword(s):  
Time Evolution ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Two Dimensional ◽  
Spatial Averaging ◽  
Mixing Process ◽  
Thermal Entropy ◽  
Large Gradient ◽  
Turbulence Mixing

Entropy generation rates in two-dimensional Rayleigh–Taylor (RT) turbulence mixing are investigated by numerical calculation. We mainly focus on the behavior of thermal entropy generation and viscous entropy generation of global quantities with time evolution in Rayleigh–Taylor turbulence mixing. Our results mainly indicate that, with time evolution, the intense viscous entropy generation rate s u and the intense thermal entropy generation rate S θ occur in the large gradient of velocity and interfaces between hot and cold fluids in the RT mixing process. Furthermore, it is also noted that the mixed changing gradient of two quantities from the center of the region to both sides decrease as time evolves, and that the viscous entropy generation rate ⟨ S u ⟩ V and thermal entropy generation rate ⟨ S θ ⟩ V constantly increase with time evolution; the thermal entropy generation rate ⟨ S θ ⟩ V with time evolution always dominates in the entropy generation of the RT mixing region. It is further found that a “smooth” function ⟨ S u ⟩ V ∼ t 1 / 2 and a linear function ⟨ S θ ⟩ V ∼ t are achieved in the spatial averaging entropy generation of RT mixing process, respectively.

Choice of the Pseudo-Optimal Configuration of a Cooled Gas-Turbine Blade Based on a Constrained Minimization of the Global Entropy Production Rate

1996 ◽  
Author(s):  
Gianni Natalini ◽  
Enrico Sciubba
Keyword(s):  
Gas Turbine ◽  
Turbine Blade ◽  
Entropy Generation ◽  
Optimization Procedure ◽  
Optimal Configuration ◽  
Generation Rate ◽  
Maximum Temperature ◽  
Entropy Generation Rate ◽  
Gas Turbine Blade ◽  
Blade Profile

The problem of determining the optimal configuration of a cooled gas-turbine blade is approached by an entropy minimization technique proposed in previous works by the same authors. The present paper describes the application of the same line of thought to a more complex (and realistic) pseudo-optimization procedure, in which the objective function is again the global entropy generation rate, but two integral constraints are added to the original formulation: the maximum blade temperature (weak constraint) and the overall enthalpy drop of the working fluid in the blade passage (strong constraint). The discontinuous optimization procedure is presented here in an application which resembles a trial-and-error technique, but can be rigorously and formally described and implemented [12]. As a “zero configuration”, a realistic 2-D geometry is considered, and the thermo-fluiddynamic field around it is computed via a standard finite-element code. Then, the entropy generation rates in the blade/fluid system are calculated, and the value of the overall enthalpy drop of the gas as well as the value and location of the maximum blade temperature are recorded. Keeping all other parameters fixed (in particular, maintaining the same cooling air flowrate), the geometry of the blade is slightly “perturbed”, by introducing arbitrary modifications in the blade profile, the number and location of cooling holes, etc. Again, the velocity and temperature fields are computed, and inlet conditions are tuned so that the overall enthalpy drop remains approximately constant and the blade maximum temperature does not exceed a certain assigned value. An “optimal” configuration is found, which is affected by the minimal entropy generation rate, while abiding to the imposed constraints. The procedure is demonstrated on a realistic blade profile, and is shown to produce a better performing cascade, at least in this 2-D simulation. The extension to 3-D problems is — in principle — straightforward (but see Section 3 for further comments).

Numerical Analysis of the Effects of Non-Uniform Surface Roughness on Compressor Stage Performance

2010 ◽  
Author(s):  
Mirko Morini ◽  
Michele Pinelli ◽  
Pier Ruggero Spina ◽  
Mauro Venturini
Keyword(s):  
Surface Roughness ◽  
Gas Turbine ◽  
Traditional Approach ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Compressor Stage ◽  
Turbine Performance ◽  
Performance Map ◽  
Overall Performance ◽  
Stage Performance

Gas turbine performance degradation over time is mainly due to the deterioration of compressor and turbine blades, which, in turn, causes a modification of the compressor and turbine performance maps. Since detailed information about the actual modification of the compressor and turbine performance maps is usually unavailable, component performance can be modeled and investigated (i) by scaling the overall performance map, or (ii) by using stage-by-stage models of the compressor and turbine and by scaling each single stage performance map to account for each stage deterioration, or (iii) by performing 3D numerical simulations, which allow to both highlight the fluid-dynamic phenomena occurring in the faulty component and grasp the effect on the overall performance of the component. In this paper, the authors address the most common and experienced source of loss for a gas turbine, i.e. compressor fouling. With respect to the traditional approach, which mainly aims at the identification of the overall effects of fouling, authors investigate a micro-scale representation of compressor fouling (e.g. blade surface deterioration and flow deviation). This allows (i) a more detailed investigation of the fouling effects (e.g. mechanism, location along blade height, etc.), (ii) a more extensive analysis of the causes of performance deterioration and (iii) the assessment of the effect of fouling on stage performance coefficients and on stage performance maps. The effects of a non-uniform surface roughness on both rotor and stator blades of an axial compressor stage are investigated by using a commercial CFD code. The NASA Stage 37 test case was used as the baseline geometry. The numerical model already validated against experimental data available in literature was used for the simulations. Different non-uniform combinations of surface roughness levels on rotor and stator blades were imposed. This makes it possible to highlight how the localization of fouling on compressor blades affects compressor performance, both at an overall and at a fluid-dynamic level.

Gas Turbine Temperature Prediction Using Unsteady CFD and Realistic Non-Uniform 2D Combustor Exit Properties

2008 ◽  
Author(s):  
Fre´de´ric N. Felten ◽  
Semir Kapetanovic ◽  
D. Graham Holmes ◽  
Michael Ostrowski
Keyword(s):  
Boundary Conditions ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Computational Cost ◽  
Computational Domain ◽  
Two Dimensional ◽  
Gas Temperature ◽  
Sliding Mesh ◽  
Flow Gradients ◽  
The Impact

Typical Computational Fluid Dynamics (CFD) studies performed on High Pressure Turbines (HPT) do not include the combustor domain in their analyses. Boundary conditions from the combustor exit have to be prescribed at the inlet of the computational domain for the first HPT nozzle. It is desirable to include the effect of combustor non-uniformities and flow gradients in order to enhance the accuracy of the aerodynamics and heat transfer predictions on the nozzle guide vanes and downstream turbine blades. The present work is the continuation of steady and quasi-unsteady studies performed previously by the authors. A fully unsteady nonlinear approach, also referred to as sliding mesh, is now used to investigate a first HPT stage and the impact of realistic non-uniformities and flow gradients found along the exit plane of a gas turbine combustor. Two Turbine Inlet Boundary Conditions (TIBC) are investigated. Simulations using a two-dimensional TIBC dependant on both the radial and circumferential directions are performed and compared to baseline analyses, where the previous two-dimensional TIBC is circumferentially averaged in order to generate inlet boundary conditions dependant only on the radial direction. The two elements included in the present work, combustor pitchwise non-uniformities and full unsteady blade row interactions are shown to: (1) alter the gas temperature profile predictions up to ±5%; (2) modify the surface temperature predictions by ±8% near the trailing edge of the vane suction side; (3) increase the overall pressure losses by roughly 1%, and (4) modified the ingestion behavior of the purge cavity flow. In addition, keeping in mind the tradeoff between improved predictions and computational cost, the use of an unsteady sliding mesh formulation, instead of a quasiunsteady frozen gust, reveals the importance of the two-way unsteady coupling between adjacent blade rows for temperature and pressure predictions.

scholarly journals Investigating of Turbine Blades Geometrical Change Effects on Dynamic Performance of IGT-25 Gas Turbine

2019 ◽  
Author(s):  
Nima Zamani Meymian ◽  
Hossein Rabiei
Keyword(s):  
Gas Turbine ◽  
Mass Flow ◽  
Gas Flow ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Turbine Blades ◽  
Gas Generator ◽  
Air Compressor ◽  
Power Turbine ◽  
Geometrical Change

In the paper, the effect of gas generator turbine blades’ geometrical change has been studied on the overall performance of a twin-shaft 25MW gas turbine with industrial application, under dynamic conditions. Geometrical changes include change of thickness and height of gas generator turbine blades which in turn would result in the change in the mass flow rate of passing hot gas, as well as isentropic efficiency in each stage of the turbine. Gas turbine modeling in the paper is zero-dimensional and takes place with consideration of dynamic effects of volume on air compressor components, combustion chamber, gas generator turbine, power turbine, fuel system, as well as effects of heat transfer dynamics between blades, gas path, and effects of operators on inlet guide vanes, fuel valves, and air compressor discharge valve. In the mathematical model of each of the components, steady-state characteristics curves have been used, extracted from 3-Dimensional computational fluid dynamics (CFD). To do so, characteristic curves of the first and second stages of the four-stage turbine have been updated through 3-D fluid dynamic analysis so that the effect of geometrical changes in turbine blades would be applied. Results from effects of these changes on characteristics of transient gas flow including output power of gas generator turbine and power turbine, inlet and outlet temperatures of turbine stages, as well as air and fuel mass flow rates have been provided from the start-ups until reaching the nominal load would be achieved.

Cooling Improvement of Gas Turbine Rotary Blades

2020 ◽  
Author(s):  
Faezeh Rasimarzabadi ◽  
Ramin Kamalimoghadam ◽  
Mahmoud Najafi ◽  
MohammadReza Mohammadi ◽  
Nasrin Sahranavard Fard
Keyword(s):  
Gas Turbine ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Tangential Velocity ◽  
Navier Stokes ◽  
Rotating Shaft ◽  
Navier Stokes Equations ◽  
Calculation Results ◽  
Cooling Air

Abstract A new method is presented to improve cooling of the turbine blades by using active extraction from the compressor outlet to supply more cooling air with more energy. The cool air is extracted from the end of compressor through a set of peripheral holes to the air transferring channels on the disc edge or torque tube using the tangential velocity vector of the rotating shaft which results in increasing the amount and energy of the cooling air. In fact a forward angle of inlet holes for the channels is used to help the pressurized air overcome the air centrifugal force and to accelerate the flow going into the torque tube. To investigate the effect of new idea, both the original and proposed models are analyzed using 3D CFD simulation on a selected physical domain of a gas turbine. The compressible rotating Navier-Stokes equations are used for numerical simulation of two geometries. The governing equations, mesh treatment, boundary conditions and numerical setup are described. The calculation results are compared to those of the original turbine shaft to show the heat transfer improvement by enhancing the cooling flow rate and fluid energy.

Conjugate Heat Transfer Simulation and Entropy Generation Analysis of Gas Turbine Blades

2021 ◽  
Author(s):  
Yaping Ju ◽  
Yi Feng ◽  
Chuhua Zhang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Entropy Generation ◽  
Conjugate Heat Transfer ◽  
Turbine Blades ◽  
Measurement Data ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Gas Turbine Blades ◽  
Internally Cooled

Abstract Reynolds averaged Navier-Stokes model-based conjugate heat transfer method is popularly used in simulations and designs of internally cooled gas turbine blades. One of the important factors influencing its prediction accuracy is the choice of turbulence models for different fluid regions because the blade passage flow and internal cooling have considerably different flow features. However, most studies adopted the same turbulence models in passage flow and internal cooling. Another important issue is the comprehensive evaluation of the losses caused by flow and heat transfer for both fluid and solid regions. In this study, a RANS-based CHT solver for subsonic/transonic flows was developed based on OpenFOAM and validated and used to explore suitable RANS turbulence model combinations for internally cooled gas turbine blades. Entropy generation, able to weigh the losses caused by flow friction and heat transfer, was used in the analyses of two internally cooled vanes to reveal the loss mechanisms. Findings indicate that the combination of the k-? SST-?-Re? transition model for passage flow and the standard k-e model for internal cooling agreed best with measurement data. The relative error of vane dimensionless temperature was less than 3%. The variations of entropy generation with different internal cooling inlet velocities and temperatures indicate that reducing entropy generation was contradictory with enhancing heat transfer performance. This study, providing a reliable computing tool and a comprehensive performance parameter, has an important application value for the design of internally cooled gas turbine blades.

An Improved Proper Orthogonal Decomposition Technique for the Solution of a 2-D Rotor Blade Inverse Design Problem Using the Entropy Generation Rate as the Objective Function

2007 ◽  
Author(s):  
G. Panzini ◽  
E. Sciubba ◽  
A. Zoli-Porroni
Keyword(s):  
Objective Function ◽  
Proper Orthogonal Decomposition ◽  
Entropy Generation ◽  
Design Problem ◽  
Fluid Dynamic ◽  
Orthogonal Decomposition ◽  
Inverse Design ◽  
Entropy Generation Rate ◽  
Cfd Simulations ◽  
Proper Orthogonal

This paper discusses the optimization of a 2D rotor profile attained via a novel inverse-design approach that uses the entropy generation rate as the objective function. A fundamental methodological novelty of the proposed procedure is that it does not require the generation of the fluid-dynamic fields at each iteration step of the optimisation, because the objective function is computed by a functional extrapolation based on the Proper Orthogonal Decomposition (POD) method. With this new method, the (often excessively taxing) computational cost for repeated numerical CFD simulations of incrementally different geometries is substantially decreased by reducing much of it to easy-to-perform matrix-multiplications: CFD simulations are used only to calculate the basis of the POD interpolation and to validate (i.e., extend) the results. As the accuracy of a POD expansion critically depends on the allowable number of CFD simulations, our methodology is still rather computationally intensive: but, as successfully demonstrated in the paper for an airfoil profile design problem, the idea that, given a certain number of necessary initial CFD simulations, additional full simulations are performed only in the “right direction” indicated by the gradient of the objective function in the solution space leads to a successful strategy, and substantially decreases the computational intensity of the solution. This “economy” with respect to other classical “optimization” methods is basically due to the reduction of the complete CFD simulations needed for the generation of the fluid-dynamic fields on which the objective function is calculated.

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