Gas Turbine Cascade Research Articles

A Reformulation of the Laminar Kinetic Energy Model to Enable Multi-mode Transition Predictions

AbstractThe paper describes the development of a novel transition/turbulence model based on the laminar kinetic energy concept. The model is intended as a base framework for data-driven improvements. Starting from a previously developed framework, mainly aimed at separated-flow transition predictions, suitable terms for model generalization are identified and reformulated for handling different transition modes, namely bypass and separated-flow modes. The ideology for the definition of new terms has its roots in mixing phenomenological and correlation-based arguments, ensuring generality and flexibility and allowing a variety of lines of action for improving model components via machine-learning approaches. The model calibration, carried out with reference to flat plate test cases subjected to different pressure gradients and freestream turbulence levels, is discussed in detail. Although the constructed model is calibrated on a group of classic flat plat cases, the validation campaign, mostly carried out on gas turbine cascades, demonstrates its ability to predict transitional flows with engineering accuracy. Finally, while the model is not specifically developed for natural transition predictions, satisfactory predictions are obtained in scenarios with low freestream turbulence for flat plate and airfoil flows.

Numerical analysis of catalyst particle deposition characteristics in a flue gas turbine with an improved particle motion and deposition model

To more accurately understand and predict the deposition behavior of catalyst particles in the flue gas turbine cascade, test and numerical combined study is performed in this paper. Based on the systematic analysis of the deposition process and physical mechanism of the catalyst particles, the traditional DRW model, critical velocity particle deposition model and removal model were corrected with the user defined function custom function and validated with the actual deposition morphology. On this basis, the effects of the particle Stokes number and flue gas parameters on the particle deposition characteristics of the flue gas turbine cascade were detailed investigated. The results show that the revised DRW model, critical velocity and removal model can more accurately predict the deposition location and deposition rate of particles in the turbine cascade. With the increase in the Stokes number of particles, the average particle impact rate on the blade surface gradually increased, while the average deposition rate showed a trend of first increasing and then decreasing. The average deposition rate of particles in the rotor blade surface is roughly twice as high as that in the stator surface. With the increase of the flue gas expansion ratio, the deposition rate of particles less than 3 μm gradually increases, while the deposition rate of particles greater than 3 μm tends to decrease. In addition, the change in the flue gas expansion ratio has no obvious effect on the particle deposition distribution in different size ranges.

Numerical study on aerodynamic performance and particle erosion characteristics of flue gas turbine

The 3-D numerical simulation method is coupled with erosion and particle rebound models based on the results of high temperature erosion tests to systematically study the gas-solid two-phase flow characteristics of a flue gas turbine for the first time. The aerodynamic loss characteristics of the flue gas-steam mixtures and particle erosion mechanism in the flue gas turbine cascade under design and non-design conditions are investigated. The results indicate that the mixing loss of cooling steam and gas, secondary flow loss, and separation loss significantly affect the entropy increment of the rotor cascade. The isentropic efficiency of the flue gas turbine under the design condition is 78.74%. The radial inflow of wheel cooling steam from the axial clearance has a radial impact and mixing effect on the mainstream flue gas, enhancing the generation and development of the secondary flow vortex in the rotor cascade. When the dimensionless cooling steam flow rate is reduced from 1 to 0.6, the isentropic efficiency of the flue gas turbine increases by approximately 0.9%. By contrast, when the dimensionless cooling steam flow rate increases from 1 to 2, the isentropic efficiency decreases by 0.42%. The erosion rate of the leading and trailing edges of the rotor is higher than those at other streamwise locations. The erosion of the rotor leading edge and the blade-tip trailing edge is caused by the high speed impact of particles above 10 ?m, while the erosion of the rotor root is caused by the grinding of 1-5 ?m particles carried by the secondary flow.

A Study on the Secondary Flow Loss Reduction in a Gas Turbine Cascade by Combining Optimized Fence and Inclined Blades

A Study on the Secondary Flow Loss Reduction in a Gas Turbine Cascade by Combining Optimized Fence and Inclined Blades

Field inversion for data-augmented RANS modelling in turbomachinery flows

Turbulence modelling in turbomachinery flows remains a challenge, especially when transition and separation phenomena occur. Recently, several research efforts have been devoted to the improvement of closure models for Reynolds-averaged Navier-Stokes (RANS) equations by means of machine learning approaches which make it possible to extract the knowledge hidden inside the available high-fidelity data (from experiments or from scale-resolving simulations). In this work the use of the field inversion approach is investigated for the augmentation of the Spalart–Allmaras RANS model applied to the flow in low pressure gas turbine cascades. As a first step, the field inversion method is applied to the T106c cascade at two different values of Reynolds number (80000-250000): An adjoint-based gradient method is employed in order to minimise the prediction error on the wall isentropic Mach number distribution. The data obtained by the correction field are then analysed by means of an Artificial Neural Network (ANN) which makes it possible to generalise the correction by finding correlations which depend on physical variables. A study on the definition of the input variables and on the architecture of the ANN is performed. Different kind of corrections are evaluated and a particularly robust correction factor is obtained by limiting the range of the correction in the spirit of intermittency models. Finally, the ANN is introduced in an augmented version of the Spalart–Allmaras model which is tested on the T106c cascade (for values of the Reynolds number not considered during the training) and for the T2 cascade. The prediction ability of the method is investigated by comparing the numerical predictions with the available experimental data not only in terms of wall isentropic Mach number distribution (which was used as goal function during the field inversion) but also in terms of mass-averaged exit angle and kinetic losses.

Secondary Flow Loss Reduction by Endwall Contouring in Gas Turbine Cascade Using Optimization Technique

Secondary Flow Loss Reduction by Endwall Contouring in Gas Turbine Cascade Using Optimization Technique

Numerical Simulation of the Inlet/Outlet Pressure Ratio Effect on the Heat Transfer Coefficient in an Air Turbine Cascade

Based on the state-of-the art methods of gas turbine cascade heat transfer assessment, a theoretical model of the two-dimensional air turbine cascade is proposed, wherein gas flows past the turbine blade profile. The velocity, temperature, and pressure fields, as well as the heat transfer distribution along the pressure and suction surfaces, the leading and trailing edges of the turbine blade were computed via FLUENT software at different pressure ratios. This permitted of studying the heat transfer evolution at different pressure ratios in the same position and at the same pressure ratio in different positions.

Unstructured Shock-Fitting Calculations of the Transonic Flow in a Gas Turbine Cascade

Unstructured Shock-Fitting Calculations of the Transonic Flow in a Gas Turbine Cascade

Novel algorithm using Active Metamodel Learning and Importance Sampling: Application to multiple failure regions of low probability

Calculation of tail probabilities is of fundamental importance in several domains, such as in risk assessment. One major challenge consists in the computation of low-failure probability in cases characterized by multiple-failure regions, especially when an unbiased estimation of the error is required. Methods developed in literature rely mostly on the construction of an adaptive surrogate, tackling some problems such as the metamodel building criterion and the global computational cost, at the price of a generally biased estimation of the failure probability. In this paper, we propose a novel algorithm suitable for low-failure probability and multiple-failure regions, permitting to both building an accurate metamodel and to provide a statistically consistent error. Indeed, an importance sampling technique is used, which is quasi-optimal since permits, by exploiting the knowledge of the metamodel, to provide two unbiased estimators of the failure probability. Additionally, a gaussian mixture-based importance sampling technique is proposed, permitting to drastically reduce the computational cost when estimating some reference values, or the failure probability directly from the metamodel.Several numerical examples are carried out, showing the very good performances of the proposed method with respect to the state-of-the-art in terms of accuracy and computational cost. A physical test-case, focused on the numerical simulation of non-ideal gas turbine cascades, is also investigated to illustrate the capabilities of the method on an industrial case.

Study on Secondary Flow Loss Reduction in Gas Turbine Cascade by Optimization method

Study on Secondary Flow Loss Reduction in Gas Turbine Cascade by Optimization method

Reduction method for secondary flow loss in a gas turbine cascade

Reduction method for secondary flow loss in a gas turbine cascade

Numerical investigation of flow unsteadiness and heat transfer on suction surface of rotating airfoils within a gas turbine cascade

The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper. The calculation is performed using ν2¯−f model with the numerical results of pressure fluctuation and heat transfer performance over 4 sample points being analyzed and compared with existing experimental data. It shows that the static pressure change has significant impact on heat transfer performance of the fore suction surface, especially in the active region of the shock waves formed from the trailing edge of upstream nuzzles. While, for the rear suction surface, the flow turbulence contributes more to the heat transfer change over the surface, due to the reduced pressure oscillation through this region. Phase shifted phenomenon across the surface can be observed for both pressure and heat transfer parameters, which should be a result of turbulence migration and wake passing across the airfoil.

Turbine vane film cooling: Heat transfer evaluation using high-order discontinuous Galerkin RANS computations

A high-order accurate CFD solver, based on the Discontinuous Galerkin (DG) finite element method, is here employed to compute the heat transfer, with and without film coolant injection, around a turbine vane extensively tested in a wind tunnel. The numerical solution makes also use of a high-order polynomial representation of the airfoil curved boundary in order to minimize the numerical sources of error, leaving possibly only those related to the physical model adopted. The objective of the work is therefore twofold: on the one hand to provide a detailed investigation, often beyond the reach of the experiments, of the complex flow field arising in a film-cooled gas turbine cascade, on the other hand to ascertain the limits of the Reynolds-averaged Navier-Stokes (RANS) approach and its associated turbulence model when using high-order accurate methods. The DG formulation is briefly reviewed, as well as the experimental apparatus and the measuring technique, and then the code is applied to the computation of various test cases characterized by different reference Reynolds and Mach numbers. Two-dimensional results (up to seventh-order accurate) obtained both with the high- and low-Reynolds version of the k-ω model employed are presented. Reasonably good agreement between experimental and numerical results is obtained, even though the outcomes are far from being completely satisfactory especially for flow regimes in the low Reynolds number range. This is due to the lack of suitable modeling of the laminar-turbulent transition process taking place around the blade leading edge. Such a complex phenomenon is out of reach of the modeling capabilities of the high-Re k-ω model, while can be roughly mimicked by the low-Re version of the model, which is able to provide a delayed onset of the turbulence quantities along the blade surface.Third-order accurate computation of the three-dimensional turbine vane are also presented in this work and compared with available measurements to investigate the relevant fluid flow phenomena occurring and to discuss significant issues related to an accurate prediction of the turbine wall heat transfer.

Improving a conjugate-heat-transfer immersed-boundary method

Purpose– The purpose of this paper is to provide the current state of the art in the development of a computer code combining an immersed boundary method with a conjugate heat transfer (CHT) approach, including some new findings. In particular, various treatments of the fluid-solid-interface conditions are compared in order to determine the most accurate one. Most importantly, the method is capable of computing a challenging three dimensional compressible turbulent flow past an air cooled turbine vane.Design/methodology/approach– The unsteady Reynolds-averaged Navier–Stokes (URANS) equations are solved within the fluid domain, whereas the heat conduction equation is solved within the solid one, using the same spatial discretization and time-marching scheme. At the interface boundary, the temperatures and heat fluxes within the fluid and the solid are set to be equal using three different approximations.Findings– This work provides an accurate and efficient code for solving three dimensional CHT problems, such as the flow through an air cooled gas turbine cascade, using a coupled immersed boundary (IB) CHT methodology. A one-to-one comparison of three different interface-condition approximations has shown that the two multidimensional ones are slightly superior to the early treatment based on a single direction and that the one based on a least square reconstruction of the solution near the IB minimizes the oscillations caused by the Cartesian grid. This last reconstruction is then used to compute a compressible turbulent flow of industrial interest, namely, that through an air cooled gas turbine cascade. Another interesting finding is that the very promising approach based on wall functions does not combine favourably with the interface conditions for the temperature and the heat flux. Therefore, current and future work aims at developing and testing appropriate temperature wall functions, in order to further improve the accuracy – for a given grid – or the efficiency – for a given accuracy – of the proposed methodology.Originality/value– An accurate and efficient IB CHT method, using a state of the art URANS parallel solver, has been developed and tested. In particular, a detailed study has elucidated the influence of different interface treatments of the fluid-solid boundary upon the accuracy of the computations. Last but not least, the method has been applied with success to solve the well-known CHT problem of compressible turbulent flow past the C3X turbine guide vane.

Taguchi Based Regression Analysis of End-Wall Film Cooling in a Gas Turbine Cascade with Single Row of Holes

AbstractNumerical investigations were conducted on a turbine cascade, with end-wall cooling by a single row of cylindrical holes, inclined at 30°. The mainstream fluid was hot air and the coolant was CO

Simulation of the Transitional Flow in a Low Pressure Gas Turbine Cascade With a High-Order Discontinuous Galerkin Method

In the last decade, discontinuous Galerkin (DG) methods have been the subject of extensive research efforts because of their excellent performance in the high-order accurate discretization of advection-diffusion problems on general unstructured grids, and are nowadays finding use in several different applications. In this paper, the potential offered by a high-order accurate DG space discretization method with implicit time integration for the solution of the Reynolds-averaged Navier–Stokes equations coupled with the k-ω turbulence model is investigated in the numerical simulation of the turbulent flow through the well-known T106A turbine cascade. The numerical results demonstrate that, by exploiting high order accurate DG schemes, it is possible to compute accurate simulations of this flow on very coarse grids, with both the high-Reynolds and low-Reynolds number versions of the k-ω turbulence model.

Numercial Simulation on Three-Dimensional Unsteady Flow in a Supercharged Boiler Gas Turbine

To the unsteady characteristic of three-dimensional flow in the gas turbine blade cascades, based on sliding mesh and a standard turbulent flow model, Fluent software was employed to solve the Reynolds averaged N-S equation. The numberical result of unsteady flow field is obtained in gas turbine cascade for supercharged marine boiler. This paper shows the axial distribution of Ma in the position of β=0 in a calculational period time, and the effect of trails to flow field characteristics. The result can provide guidelines for aerodynamic optimization design of gas turbine stage cascade.

Steady CFD Analysis on Gas Turbine Stage Cascade Based on Mixing Plane Model

Based on a standard dual-equation turbulent flow model and coupled explicit solver,a wall function method was employed to closure the Reynolds averaged N-S equation .The mixing plane method was adopted to tranfer parameters between rotor and stator cascades. A approximate linear law is obtained in gas turbine cascade for supercharged marine boiler,which governs the variation of some parameters at the outlet of the turbine stage cascade along the blade height direction,such as pressure,velocity,as well as temperature and Ma.The results can provide guidelines for aerodynamic optimization design of the gas turbine stage cascade and the scientific management of this kind of set.

810 乱れ条件下における高負荷ガスタービン翼列の損失に関する研究(GS-5 回転機械)

810 乱れ条件下における高負荷ガスタービン翼列の損失に関する研究(GS-5 回転機械)

Impact of Different Film-Cooling Modes at Trailing Edge on the Aerodynamic Performance of Heavy Duty Gas Turbine Cascade

In this paper, the trailing edge film cooling flow field of a heavy duty gas turbine cascade has been studied by central difference scheme and multi-block grid technique. The research is based on the three-dimensional N-S equation solver. By way of analysis of the temperature field, the distribution of profile pressure, and the distribution of film-cooling adiabatic effectiveness in the region of trailing edge with different cool air injection mass and different angles, it is found that the impact on the film-cooling adiabatic effectiveness is slightly by changing the injection mass. The distribution of profile pressure dropped intensely at the pressure side near the injection holes line with the large mass cooling air. The cooling effect is good in the region of trailing edge while the injection air is along the direction of stream.